Human Habitation Beyond Earth

1. Introduction

Most of the stations are believed to be permanent by default, which makes them important in the explorative plans for the growing space. Attention is currently given to the establishment of a base in some of the extra-terrestrial planets like Mars. Factors or conditions inside the base are expected to be the same as those found in a space station for it to sustain human life. Notable differences across the two stations revolves around the fact that the base station would be forced to adopt either the planet or the moon environment it is posted on. It would equally be used in any of the environments to its own advantage especially in terms of the natural resources. Notably, establishing a robust base either on moon or another planet can be such an ambitious task. A well manned base which is established on the moon can be said as being attainable due to the moon’s closeness to the planet Earth. The proximity makes it easier to access and temperatures on the moon are almost same to the one realized on Earth.

Compared to the Moon, establishing a base on such a planet like Mars can be a bit complicated and might take relatively a long time. However, an insulated base established on the moon with the help of solar energy, and oxygen and water extracted from the local materials using chemical processes is believed to be self-sustaining in the distant future. Proposals have been surfaced regarding the interplanetary habitations, which is likely to be one of the long-standing answers towards accommodation of growing population on planet Earth. At the same time, it can objectively be declared that significant expansions of the extra-terrestrial bases might help in developing means of handling the harsh environments, which can be an indicator for effective management of the functioning land areas found in other planets. Notably, there are still imminent complications associated to human inhabitant in the space stations. A major complication includes the supply of power to such complicated residential.

The extra-terrestrial bases or the space stations are regarded as spacecrafts that have the capacity of allowing the crewmembers to survive, for relatively long lasting periods through which the spacecraft keeps moving around the planets (Sharkh et al. 2014). Notably, the spacecrafts are used as significant bases for the researchers to introduce space science as well as examination. Most of the space bases, if not all, are driven by solar energy with the help of solar panels. The energy is essentially dispersed via the space station divisions. The figure below provides a demonstration of the key parts of an extra-terrestrial base.

The components found in a space stations varies widely depending on its mission and purpose, for instance, scientific space stations carries research equipment while military space stations are designed to accommodate weapons. However, all space stations have core components used in operations and maintenance of mission that include equipment and monitoring goals as well as supporting human crew, if any. As such, the following lists core in a space stations.

The electrical system of the extra-terrestrial base is believed to operate in the same mode as the microgrid. It involves integration of different modules, which are not limited to the solar boards needed for energy production. In addition, shuttles linked to extra-terrestrial base would benefit from the source of power. The goal of the study includes evaluation of the design of PECs, which have the capacity of being subjected to most of the hostile environments. Most of them cover such conditions like extreme temperatures and radiations among others via their application, which is done alongside the power supply utilities found in a space station.

Research problem

There are several pioneer companies and organizations looking at establishing extra-terrestrial bases, for example, on Mars. These bases would need to have some kind of power supply, in order to operate equipment. The Microgrids concept is relevant to “islanded” or isolated energy systems and would possibly be a suitable mode of operation for such extreme energy systems. Electrical power provide in space must be manipulated with the help of power electronics, which are designed to endure such a hostile conditions. This project will therefore investigate the appropriate design of the PECs meant for Microgrids to be used in space, based on the prevailing power electronic components said to have been approved for use across the space.

Project Objectives

To explore electrical power in space and how it is manipulated by PECs

To investigate the design of PECs for the space Microgrids

To determine the control and modes of conversion of the electric power in space

To study, analyse and suggest the best efficient way regarding power conversion, costs and efficiency

2. Literature Review

Sunlight has largely been regarded as the most essential source of energy for most of the spaceships. Notably, technologies are believed to have been developed to effectively transform the solar energy into useful electrical power. With the help of process referred to as photovoltaic, it is possible that thousands of the solar cells have the capacity of converting the solar energy into electric power. Only four set of the arrays would produce around 84-120 kilowatts of the electric power. The arrays would even generate or produce more electric power than what would be needed by the station. Only 60% of the power produced would be utilized in charging the batteries. The installed batteries would facilitate power to the entire station at times when there is no sunlight. Nickel-hydrogen batteries are essentially used in storing electrical energy as they are designed to discharge around 3800 cycles with a lifespan of at least 6.5 years.

It is worth noting that NASA is trying hard enough to replace these batteries with lithium-ion batteries. The latter is believed to 3 times powerful, lightweight and they are very small in comparison with the nickel-hydrogen batteries. The lithium ion batteries have exceptional lifecycle because they can be charged as well as discharged severally. As pointed out by Majeau-Bettez et al. (2011), one lithium battery would effectively replace two nickel hydrogen batteries of the equal capacity. Target missions like Venus and Titan missions need advanced battery systems which would operate in temperatures ranging from -1000C to 5000C with a 10 years lifespan. The electrical power system for the space station is essentially made of the orbital replacement units (ORU). The latter has the hardware components which are replaceable with the help of spacewalk and robotics. The ORU gives room for power generation, storage and distribution for the necessary space station.

Developed to assist the astronauts at the time of site exploration on the Martian and the lunar surfaces, the Service Exploration Vehicles (SEV) are essentially built for the purposes of accommodating the two astronauts and but in case of an emergency, it can accommodate up to four individuals. Notably, the vehicles has a maximum speed of approximately 10km/hr with the wheels designed to pivot the 3600. This makes it possible to navigate in any direction. Normally, pressurized cabin would allow the astronauts to survive for at least 14 days. In addition, the vehicles are equipped with essential robotic manipulators for the purposes of picking objects that would aid observations. Recently, the DC-DC converters have gained increased attention across the power electronics field. Several studies have been conducted that include the control approaches, applications and the topologies (Gha, 19). Tarisciotti et al. (2018) utilized the active clamp bridge topology in examining the isolated ABAC DC-DC converters for the modern aerospace. The researchers went ahead comparing the entire topology with Dual Active Bridge topology (DAB). Some of the comparative parameters include efficiency, control requirements and the output waveforms. The weight to volume ratio for the mentioned topologies was essentially analysed. The research indicated that the ABAC topology is better compared to the DAB converters.

Nevertheless, Tarisciotti et al. (2017) went ahead evaluating the isolated bidirectional DC-DC topologies attached to the HVDC aerospace microgrids. Researchers conducted a trade-off evaluation of the topologies with the help of an interface of the 270V DC network as well as the 28V DC network. The findings further confirmed that most of the ABAC converters sound promising for the applications. Further studies touched on the DC-DC converters which are used in the aerospace Microgrids [Gha 19]. Furthermore, a study by Gao et al. (2019) on the droop impact of control systems like the loop dynamics, gains, comparative stability and sources, utilized in the droop control of the DC voltage supply across the microgrids. The findings proposed the whole idea of global droop gains as it appears in the determinant of stability behaviour inclined to the parallel sources attached to DC systems.

Tehrani et al. (2018) went ahead proposing a black box model associated to the converters especially for the constant power loadings. The latter has been linked to the stability of the DC microgrids. The authors drew comparison of stability analysis based on the detailed model of the converters and load approximation of the constant power. Sensitivity analysis of the parasitic elements associated to the load converter was also performed. They noted that black box model led to results, which correspond to the significant averaged analytical model, would account for actual values associated to the parasitic elements. Moreover, a study by Ghanbari et al. (2019) utilized the state space modelling as well as the reachability analysis in studying transient behaviour across the uncertainties of the PV current before determining the efficiency of droop control linked to aerospace DC converters.

Several studies have given attention to the power switches especially on the boost converter input (Cor 16; Comea et al., 2016; Garrigos et al., 2019) researched on bidirectional power flow in the switched capacity cell of the hybrid DC-DC converters. The simulation results and the 2 kW converter prototype drew reference to the good dynamic performance and the reference waveform. Garrigos et al. (2019) linked the interleaved DC-DC converter to larger and medium power fuel cell in which the design led to non-isolated as well as high DC voltage gain. The circuit design, experimental validation, and simulation made use of 24V/100V, 500W prototype. The study hypothesised that the prototype would perform accordingly in both the simulation as well as the experiment.

2.1 Background History

Prominence of a large, stable, crewed Earth satellite was acknowledged early in the history of rocket flying. At the end of the 1930s, an emergent wave of new scientists started to design and evaluate the concept of new designed satellites and space stations. At a similar time, sequences of papers emphasizing the importance of extra-terrestrial basis power supply concept for space assignments. Subsequently the researches have encompassed various articles on the power electronic devices, and set-up of space stations and particular space vehicles (Jamil et al. 2009). These vary in terms of quality and preciseness from completely science fiction to comprehensive engineering calculations. Some of them merits reflection on establishment extra-terrestrial basis and ways in which people would live and conduct daily routines accordingly.

Many of the purposes that could be done by a space station or extra-terrestrial basis could likewise be achieved by Earth satellites, which are neither outsized, stable, nor staffed. The exclusive function of the space station and extra-terrestrial basis is its implementation as a base for massive space vehicles, science laboratory, and home to crews of astronauts and cosmonauts live. The Earth is not a totally suitable base, owning to the presence of the atmosphere, which presents a serious re-entry problem, and, in greater part, to the strong gravitational field at the surface of the Earth. Contemporary rockets and the bigger ones that will be built when progress is finalized on proclaimed engines of millions of tons of horsepower are trying to send very considerable payloads onto space journeys (Lim et al. 2017). Nevertheless, these will still do not meet the expectation of more cutting-edge space assignments. One limited answer is to fashion ever superior chemical power supply or large boosters of higher-performing by means of nuclear thrust. Yet, the achievements of the mission will constantly be restricted by the propulsion of the biggest booster system obtainable at any given moment (Behera and Parida 2014). Space assignments including crewed voyages to the adjacent planets would have to look forward to new generations of rocket advancement. The space station and extra-terrestrial basis propose an alternate solution (Deroy et al. 2019).

This technique of action would include more than a few steps. Separate deliveries of fuel, guidance gears, mechanical material, pieces, tools, workers, and foods would be shipped from the Earth to the space basis, having the dimension of each delivery restricted by the performance of obtainable fuels. The build-up of pieces of machinery may continue as much as needed, and the achievable total is, then, basically limitless. Long-range spaceships would be manufactured and set out on the basis. For specific missions, the spaceship may come back to the base and uses it recurrently. This is one of the advantages of establishment of space basis along with others such as the discovery of new human habitats, development of new agricultural techniques and more importantly colonization of humans on other planets than Earth. Other than being, a staging centre for apparatus, the space basis would also be a transmission point for people. Teams envisioned for distanced space expeditions could experience an introductory period of adjustment to the space atmosphere on board of the station in advance to departure. The basis may also be implemented for isolation. Returning spaceship and staffs may probably carry illnesses or other forms of pollution, and must not be allowed to come back straight to Earth prior to careful examination.

Numerous suggestions for planning and erecting a space station and extra-terrestrial basis have been discussed and evaluated in the past. The more convincing analyses demonstrate that a min orbital load ability is essential before a basis may be built. In addition to this threshold, a randomly big station may be constructed (Miller et al. 2018). Moreover, there are other remaining complications to be solved in launching a space basis including the specifics of fabrication, the establishment for suitable power supply, and evaluation of such aspects distressing staffs as air, nourishment, water, emissions, gravity, and impacts of foreign elements. To tackle the power supplying issue, the microgrids concept as an isolated energy system is presented by different companies. Electrical power design in space must be handled by power electronics designed to endure such a hostile environment, which may include radiation and extreme temperatures (Imhof et al. 2017). Therefore, the aim of this article is to examine the design of PECs for the space microgrids on the basis of currently approved components.

2.2 Power Electronics

Power electronics constitutes the fusion of the power production, control structures, analogue electronics, and the semiconductor appliances (Barbieri 2019). It should be noted that electric power might not be practical until the transformation is done to attain the required shape such as the heat, light or even sound among others. For the purposes of regulating these shapes, a more operative way would adjust the energy, which is a process that leads towards the study of power electronics. The attention emanates from the prior study of the commercial thermistors and the silicon regulated rectifying devices that appeared in the late 1950s. Prior to this, the ultimate control of the electrical energy used to be achieved with the help of thyratrons as well as the mercury arc devices believed to function based on the rule of the physical facts in vapours and gases.

In order to attain significant drive of the power electronics, it is evident that devices would be fabricated to essentially function like a switch. The power electronic appliances may not be beneficial if they work alone in the real world situation. This means that there is need to integrate them into a functional circuit together with other supporting parts. The supporting parts would essentially work as decision makers as they direct the PE buttons for the purposes of attaining a desirable output (Rashid 2017). The diagram below gives a picture of the PE scheme.

The control unit receives the output response or signal from the receivers and links it with the basic codes before delivering the feedback to the significant firing circuit. The FC produces pulses in a way that would regulate nor control the PE switches, hence referred to as a pulse producing circuit (Valchev and Van den Bossche, 2018).

2.3 Power Electronics Converters

Power electronics are designed to process and control the flow of electrical energy (power, voltage, and current) to the load by component need and not oversupplying. Power electronics converters applications include electrical machine motion control, active power filter, switched mode power supplies, vehicular technology and renewable energy (Qahouq and University of Alabama 2016). Power converters are used to modify form whereby voltage and electrical currents are used to transmit information; in power electronics, the converters carry power. Some uses of power electronics converters are the use of DC-DC converters in such devices computers, personal computers, televisions, and mobile phones.

Some of the small devices included in the role include the energy collecting as well as implantable appliances and the larger ones may not be limited to the power transmissions and the power generators (Zhong 2017). The PECs make the significant use of the electronic elements mounted on semiconductor switches as they function in a diverse frequency level that range from 50-100 MHz. The efficient support is directed to varied uses in which the PECs take advantage of the dissimilar traits not limited to the soft and hard switches and the current-fed and voltage-fed switches (Sharkh et al. 2014). Power transformation takes four categories including the DC-AC conversion and the AC-DC conversion, which is more application in many cases.

Cases of renewable sources as well as motor energy would require the DC-AC converter to facilitate variable or constant AC voltage output (Zhang et al. 2018). Most of the battery derived machines need the DC-DC transformers for the purposes of arranging for the needful DC voltage required for diverse loads. The DC-DC converters can as well be implemented for the purposes of maximizing energy collection from the renewable energy sources like the wind power and the solar cells. The AC-AC converters can be used for the purposes of altering either the frequency or voltage of the AC source. The key application of the PECs in space would dominantly consider the DC-DC transformers across the microgrid units (Zhang et al. 2018).

Notably, a microgrid would be regarded as a small-scale power network which works with the rest of power networks. The main role of the microgrids is to disperse, circulate, distribute, implant, and regionalize the energy generation. Small scale or the local power station would have the storage utilities and the power production units, which would define the margins and deliberate the microgrid. In space stations, the microgrids would work independently (Domingues-Olavama et al. 2017). With the help of PECs and the energy generators, energy is converted and stored at microgrid centres.

2.3.1 Power Electronics Converters in Space

Moreover, aerospace power systems have a significant consumption of DC power. However, AC power is considerably a “driver” for creating more electric technology (MET). This has amplified the practice of power electronic converters to regulate and operate power in the associated systems. Furthermore, power system engineers are continually under pressure as they are assigned with improving highly adaptive answers that conform to today’s functioning environments including space stations (Domingues-Olavarría et al. 2017). Consequently, high-power density devices are causing a high amount of attention from universal engineers who encounter broad space restrictions in function areas including mobile telecoms substructure, industrial mechanization, transportation, implanted computing gear, and microgrids power supplying (Barros et al. 2019). The condensed package and exceptional thermal functioning increase designers’ self-assurance regarding the long-term dependability of these modules, even in the most challenging industrial usages. Fabricating power systems has turned into an increasingly challenging area, as clients are more and more appealed to applications that are plainly designed and provide high functioning while staying economical.

2.3.2 Power Electronic Converter Designs Concepts based on Space Application

Non-isolated/Isolated

Non-isolated transformers are usually preferred in uses that electrical isolation is not an obligation, as they are smaller and expensive, and more effective and dependable. However, in space application purposes, an isolated power electronics converter is necessary due to a functioning environment (Feng et al. 2017). Figure 2.A demonstrates an overall layout of non-isolated power electronics transformers wherein the circuit does not include magnetic or electric quarantine. In contrast, isolated power transformers usually practice either convertor or attached inductor for multiple subjects like voltage level changing, attaining multiple outputs, granting galvanic separation and earth loop avoidance. An earth loop is shaped when there is more than one electro-conductive pathway among the “ground” terminals and two or more parts of the apparatus. The electro-conductive loop-shaped is a huge loop projection that collects meddling currents simply. Notably, the loop is bigger, there will be more meddling. For instance, the building’s steel structure is used as the ground, and then the loop can be as big as the entire construction (De Silva et al. 2019). The resistance in the earth connections alters the meddling currents into voltage oscillations in the earth system. This marks the system earth unbalanced and leading to instability and inaccurateness in signals.

Figure 2.B portrays an overall design of the isolated power electronics transformers wherein a convertor is engaged to arrange for electrical isolation. The AC converter in those transformers requisite an AC voltage or a square/quasi-square wave voltage at the prime side for accurate set-up and saturation prevention. A converter can be implemented in buck type transformers to permit voltage step-up characteristics. The step-up mode feature can be implemented for different purposes containing DC-to-DC converters (Wang and Blaabjerg 2018). Frequently, especially within the space station environment, where an extra battery may not be accessible when offered voltage is not fit for the system being provided. For instance, the engines implemented in a space shuttle propulsion system necessitate much higher voltages than could be provided by a battery unaided. Even though arrays of batteries were implemented, the additional mass and space occupies would be too much to be useful. The solution to this issue is to practice fewer batteries and to enhance the accessible DC voltage to the essential level by means of a boost transformer (De Silva et al. 2019). An additional difficulty with batteries, big or tiny, is that their yield voltage differs as the accessible load is exhausted and eventually the battery voltage turns out to be too low to muscle the circuit being charged. Though, if this low yield level can be increased back fit for a convenient level over again, by implementing a boost transformer, the service life of the battery can be prolonged which is an essential issue within the space station. A step-up converter is one of the modest kinds of switch-mode transformers. As the designation implies, it receives an entering voltage and enhances or escalate it. It is generally composed of an inductor, a semiconductor bottom, a diode, and a capacitor. On the other hand, the step-down transformer reduces the output voltage which is also useful in microgrid units in space.

Moreover, a straightforward way to attain manifold outputs in a single transformer is to implement manifold windings convertors or attached inductors. Furthermore, engaging transformers in the circuit permits electrical isolation that delivers galvanic quarantine among the input and output units of a power electronic element (Feng et al. 2017). Once two or more electrical appliances part a mutual ground in a power structure, the current from the feedback path of a device can disturb the process of other appliances, which can be dodged by employing converters(Haj, Mohandas, & Robbins, 1989).

There are several types of converters that include, under isolated converters; Forward, Flyback, Half bridge, Full Bridge, and; Push pull, and Boost, Buck, and Buck Boost categorised under non-isolated but selecting DC-DC converters depends on:

Input voltage

Output voltage

Safety

costs

2.3.3 Power electronics in Microgrids

The role of power electronics in microgrids and their importance at the centre of microgrids, power electronics are taking the paramount place as indicated by Wang et al. (2012). This comes in the light of the growing use of the Distributed Energy Resources as far as the electrical power system is put into consideration. Wang et al. (2012) alluded to the fact that the microgrid paradigm essentially interconnects the multiple customers to the DER units. Based on the research conducted by Wang et al. (2012) indicated that the Grid forming unit has a fundamental function in terms of regulating the system voltage, as well as frequency while balancing the load demands and generation of power. The grid forming units are essentially changed for the purposes of operating as a current source. Two approaches of GFU can be implemented for this control need and this first includes the static transfer switch which allows the DER to either operate in the current- and the voltage- controlled mode. The modes need to correspond to the grid connected or islanded operations.

Molinas (2008) also indicated that Grid Feeding Units have the capacity of adjusting the provided reactive and active powers, which need to follow the necessary power dispatch requirements. The Grid Feeding Units can take advantage of the direct power control, the current control and AC voltage control. The final control mechanism provided by power electronics, as noted by Wang et al. (2012), include grid supporting units which are normally controlled for the purposes of extracting maximum active power from the known primary energy source, as well as provision of the ancillary services for the purposes of enhancing power quality improvement. A small PV system, for instance, can be served along the functions of the power quality conditioner. Apart from microgrid control, power electronics play another fundamental role of power management. The power electronics are essentially dominated by the electronically coupled DER. This makes the microgrid to be more interactive, distributed and more intelligent. For proper power management, a hierarchical control system is engaged in restoration of the frequency and voltage deviations perform energy management task and power balancing. The importance of power electronics in their respective application cannot be ignored. Massoud et al. (2016) highlighted the fact that the skyrocketed development in terms of the power electronic converters and the semiconductor devices are essentially gaining attention in such applications like renewable energy sources, drive systems, and importantly High Voltage DC transmission and Flexible AC Transmission Systems,

The significant control of the power converters is said to play a fundamental role in terms of meeting the necessary requirements, as well as the essential standards associated to relevant application. The most notable example includes the grid integration of the renewable energy sources, in which the quality linked to the injected power is important when establishing the control mechanism. Across the drive system applications, both the high dynamic performance and robustness are part of the demanding factors. Power electronics is taking a significant place in the electric vehicles, solid-state transformers and energy storage systems (Massoud et al. 2016). Control of the power converters appears in main areas such as the DC-AC converters which appear in the HVDC systems, FACTS devices, grid integration and power quality enhancement. The DC-DC converters are dominant in the DC-DC transformers and electric vehicles. The AC-AC converters are applicable to the solid state transformer and drive systems. The high voltage gain power converters play focal role across the photovoltaic power generation because of the low output voltage of the arrays, as well as safety concerns.

2.4 Current Source Inverter (CSI) & Voltage Source Inverter (VSI)

Power electronics transformers can be categorized as either voltage or current source inverter converters depending on input electrical system, as is depicted in Figure 3. The majority of the power electronics transformers are provided with voltage sources but others function with current sources (Teixeira and Bevan 2017). In voltage-supplied transformers, a capacitor is coupled in parallel with the power supply, therefore, the input voltage cannot alter promptly and in current-supplied transformers is coupled in series with the power supply, therefore, and the input current cannot alter rapidly (Ahmed et al. 2017). Because of the physic law stating that 2 voltage sources by dissimilar magnitude cannot be coupled in parallel, the charge of voltage-supplied transformer is similar to a current source and regularly an inductor filter is coupled in series with the charge. Similarly, since 2 current sources with dissimilar scale cannot be coupled in series, the charge of current-supplied transformer is similar to a voltage source and frequently a capacitor filter is coupled in parallel with the charge.

High-power schedulable DC power supply, although it has many necessary features required for space station application, however, the atmosphere wherein high-power sources are installed regularly exposes them to harsh circumstances (Teixeira and Bevan 2017). Permanence, therefore, is an essential factor to reflect on when designing suitable power source. This in order necessitates engineers to evaluate the effect of a power source’s structure, and to assess regular voltage-supplied converter power supplies with the uncommon current-supplied convertor, as this choice has a great impact on the sturdiness and steadfastness of the electrical device. A current-supplied power converter is applied less frequently than voltage-supplied converters mainly due to cost and the more perplexing boxing required (Ahmed et al. 2017). Eventually, nevertheless, the safeguard offered by the current-supplied structure can diminish functioning and maintenance costs in the long term and is the best fit for the circumstances met in usual examining and development surroundings. This makes them a proper choice for space stations or extra-terrestrial environments.

Within power transformers with inverter bridge, the exchanging devices per section of a voltage supply source are not permitted to switch on simultaneously, the turning outlines must contain a dead-time. Alternatively, the off and on turning handles of every leg of the current source must not switch off at the same time. Contrasting voltage-supplied and current- supplied transformers, impedance source designed transformers are invulnerable to both dead-time and open-circuits (Ahmed et al. 2017). As mentioned above, current-supplied transformers are very widespread for renewable energy uses including solar cells since its input inductors can deliver a nonstop input current, normally with low fluctuations that in turn leads to reduction in the negative influence of high-ripple current on high current-low voltage sources. On the other hand, the inadequacy of an input inductor in voltage-supplied transformers lead to extensive fluctuated current at the input; though, since these transformers don’t have any “right half-plane” (RHP), they have quicker active response compared to current-supplied transformers with input inductors (Sharkh et al., 2014).

2.4.1 Hard Switching & Soft Switching

Power electronics transformers commonly work with semiconductor switching apparatus and energy-storing modules. Taking a simple power transformers shifted at high frequencies, the conversion between switching positions can be accompanied by voltage oscillation and short duration electrical transients on the semiconductors. The categories of power electronics transformers are switched manually and are able to generate electromagnetic intrusion (EMI) discharges as a consequence of high voltage and current fluctuation in a short period of time that can extend through the circuit from the inlet to the outlet (Lee et al. 2018). Furthermore, a huge share of power waste is because of switching power waste in hard switching converter which capable of considerably reducing the effectiveness of the power transformer. To decrease or remove the above-mentioned problems in hard switching transformers, diverse switching methods like “zero current switching” (ZCS) and “zero voltage switching” (ZVS) topologies have been presented.

The switching techniques are recognized as soft-switching methods as they decrease the switching tension as such do not generate noteworthy EMI in switching procedure, and likewise, the power waste happened because of high-frequency swapping is insignificant with these approaches (Lee et al. 2018). The option of choosing soft-switching methods rely on the precise features of the power electronics circuit, for instance, converting frequency, prerequisite package and magnitude, nature of switching equipment implemented, and system regulation complications. While, soft-switched transformers are more useful compared to hard-switched transformers, but because of the significant development in the expansion and advancement of the novel “wide bandgap” (WPG) semiconductor shifters with rapid switching competency and little conduction loss, hard-switched transformers are occasionally favoured to decrease system intricacy and expense. However, this cannot yet substitute soft-switched converters for high precisions and critical space applications.

2.4.2 Conversion: Power Converters Categories

The core subject of power electronics transformers is to modify a power condition to satisfy the particular obligations of diverse applications. To gain this aim, the systems should be capable of consistently changing one mode power to another mode by delivering current and voltage of diverse frequency and magnitude (Dibaji et al. 2019). Figure 3 demonstrates 4 dissimilar power transformations between direct and alternating current mode of electrical power. AC/DC transformers transform the AC to direct current. While DC/AC transformers or inverters function in the opposite direction of rectifiers and transforms DC to an alternating current of wanted degree and frequency. DC-DC transformers or choppers transform a constant direct current with a specific magnitude to another DC at altered voltage intensity (Turriate et al. 2019).

2.4.3 DC-DC Converters for Power System Space-Adapted Design

DC-DC converters are manufactured to meet with high-efficacy output in a wide-ranging range of aerospace uses including general daily consumptions, portable devices, battery feeders, LCD boards and lighting devices, POS outlets, and etc. Moreover, DC-DC converters are generally categorized into two classes (Dibaji et al. 2019). First, converters that alter one DC voltage into another throughout yield voltage, which is apart from the load. Secondly, converters with DC-DC separation walls that electrically split two circuits.

According to the nature of their structure, un-tuned DC-DC transformers can provide equal to 70% to 90% power productivity, while tuned ones deliver up to 85% efficiency. Due to the high productivity that DC-DC transformers provide, they have endured as one of the most active pieces in the whole power electronics range (Dai et al. 2018). There are 2 main drivers supporting the DC-DC transformers market to develop: First, large-scale implementation in current computing and satellite pieces of machinery. Second, plentiful possibilities for power system engineers to test and invent in the field of circuit fabrication and converter construction and topology, which allows them to design particular converter modules that go along with system-level necessities including space stations.

The rising rate of DC-DC transformers incorporation in computing and satellite pieces of machinery validates the advantage of the power system design, in addition to the improved adoption of these units. DC-DC transformers are obliging in manufacturing smaller and less complex printed circuit board (PCB) - owning to the tractability they provide to designers with regard to testing and customization (Rajeevan, 2019). Furthermore, DC-DC transformer-based smaller PCB units permit original equipment manufacturers (OEMs) to improve the space-usages where they must use by addition of attractive characteristics within a small form factor (SFF) (Turriate et al. 2019). Considering the mentioned factors, it can be understood why DC-DC transformers are grown into the module for high-efficiency output in harsh and space-critical extra-terrestrial uses.

2.4.4 Space-Adapted Power Electronics Converters -Features and Companies

There are several companies that offer radiation-hardened converters, voltage controllers or associated power ICs for implementation in-space uses. These transformers may be either isolated or non-isolated but are usually are equipped with voltage step-down feature. These transformers, which are normally fabricated by means of hybrid or PCB-based structure, are mainly presented by power supply producers. One the other hand, semiconductor producers with radiation-hard features also fabricate non-isolated converters and shifting regulators constructed like either monolithic ICs or multi-chip components (Icaza et al. 2019). They likewise manufacture associated chips including linear controllers, block functions for fashioning DC/DC transformers and shifting regulators.

2.5 Radiation-Hardened Space Power Electronics

One of the dynamic companies in the field is of space-adapted power electronics is BAE systems. BAE Systems manufactures and fabricates a vast range of radiation-hardened space gears, from standard modules and solo board computers to full system loads (Seyedi et al. 2019). Following years of manufacturing power supply gear for inner use, the company lately presented “point-of-load converters” in its flag product collection. Functioning from 3V to 6V inlet, these gears are ranked for outlet currents up to 22A, when placed parallel, while providing total dose protection to 100 krad.

Moreover, CISSOID is another space gear manufacture that has delivered an innovation approach. On the subject of the radiation hardness of power electronic components, the corporation notices that the most customary malfunction mechanism in components that are exposed to radiation is latching up. A latch-up is a form of short-circuiting that can happen in a unified circuit due to positive or negative voltage short electrical transients on an inlet or outlet head of electronic chips. CISSOID gears are essentially resistant to latch-up. Consequently, these electronic components display exceptional functioning alongside radiation.

Furthermore, Intersil Co. manufactures a vast array of radiation-hardened and single event impacts space degree compatible electrical components for space usage and strict environment uses (Peng et al. 2018). Intersil's radiation-hardened electronic products attain the severe voltage accuracy obligatory for microprocessors, field-programmable gate arrays and micro regulators space-adopted, application-specific integrated circuits, and severe environment uses. The manufactory’s approaches allow regulation precision over inlet voltage, converter shifting noise, and load transformation and have demonstrated highly consistent performance within blended radiation rates and other severe environmental conditions (Rudolf et l., 2017).

2.6 Temperature-Adapted Space Products Power Electronics

Besides radiation-hardened electronic equipment, there are other aspects that need to be met in order to label a product space-adapted. API Technologies fabricates and produces a vast range of space-adapted, radiation-hardened power electronic converters. Products within this category offer rad-hard gears with permanence over the wide temperature range. API Technologies’ radiation-hardened power transformers and controller components are fabricated for harsh environmental circumstances and radiation (Soelkner 2016). API Technologies majors in decreasing size, mass, and power intake for critical space structures where severe restraints are of extreme significance. The API space-designed gears can endure radiation up to 300 krad. In addition, using impenetrable packaging and they can operate in the temperature range of -55° to +125°C. Moreover, CISSOID is also a manufacturer of high-temperature semiconductor products, providing standard electronic components and specific solutions for power conversion devices in intense temperature and extreme environmental conditions. CISSOID produces highly dependable electronics functioning from -55°C to +225°C.

2.6.1 Space-Adapted Power Distribution Modules

Moreover, “Cobham's Power Technologies offer high end-to-end efficiency from the satellite bus (22 to 100 V) down to the point of load. The PDMs are a two-stage solution that leverages resonant mode control, zero voltage/zero-current switching, chip on board manufacturing, planar magnetics, proprietary FETs, controllers and drivers to provide greater than 50 W of power at 83%+ end-to-end efficiency to an FPGA or ASIC”(Patel, 2004). These components are also rad-hard to tolerate radiation up to 50krad and single-event latch-up resistance up to 80 MeV.cm2/mg. Cobham's Power Technologies manufacture a series of isolated point-of load-modules (iPOLs) and input regulator modules (IRM) that cooperatively form a power conversion mechanism. Power Distribution Module is a low-voltage (5 to 30V) electric converter fabricated to receive from the single power supply and disperse that power to several circuits.

2.6.2 High Reliable and High-Performance Power Electronics

3D Plus is a producer of innovative high-density 3D microelectronic components designed to meet the need for high consistency, high functioning, and tiny scale's electronics. The organization produces a wide range of radiation-tolerant products containing POL transformers (Lee et al. 2018). Rad hard through design, the corporation’s space adapted point-of-load DC/DC transformers deliver a single and modifiable outlet voltage with exceptional efficacy and exceptional dynamic enactment essential for fast and DC/DC transformers for Space low-voltage electronic components including field-programmable gate arrays (Emadi 2017).

In addition, Peregrine Semiconductor also has a comprehensive collection of highly reliable solutions for space uses containing buttons and point-of-load DC/DC transformers. Peregrine’s converters are confirmed to be resistant to single-event latch-up and ionizing radiation-induced noises - making it perfectly adapted for space purposes. Peregrine’s power electronic products are recognized for high yielding and productivity. The leading power electronics company produces DC/DC converters featured with radiation-patient point-of-load mechanisms (Dai et al. 2018). By providing excellent performance, reduced size and mass, these power electronic components can substitute multi-chip elements in space-qualified purposes. The arrangement of small scale, a high degree of integration and effectiveness decreases whole system mass and accompanying expenditures (Teixeira and Bevan, 2017). Peregrine’s transformers are fabricated to function through a wide bus rail and deliver a yield voltage supplying side range of circuits while carrying continuous yield currently. The transformers likewise accomplish high peak efficacy of +93% by means of monolithic design.

2.7 Power Electronics and Management

A balanced portfolio is being worked by the Planetary Science Division of NASA while using the available budget. This is achievable with the help of the decadal survey, which is believed to attract the scientific discoveries associated to the solar system. The balanced suite of the missions indicate the need for the low volume or less mass PEs as well as management components and systems which can operate in an environment for further missions. Notably, advances in terms of electrical power technologies would be needed for electrical systems and components for future platforms and spacecrafts. This would address the mass, capacity, efficiency, size, the program, reliability requirements and durability among others.

The In-Space Electric Propulsion, the Radioisotope Power Systems (RPS) and Advanced Modular Power Systems (AMPS) are some of the programs of interest that would benefit the technological area and its advancements. The programs such as the Power Processing Units, the Hall Thrusters and the Mars Sample Return would call for advancement in the control systems and components (Zhao et al. 2016). Further parameters observed in the advancement include the speed, system robustness, efficiency and energy density need to work within the necessary thermal range and a range of the thermal cycles. Novel methods needed in minimization of the weight of PPUs might also be of interest. Further advancements might be inclined towards the packaging process, the power electronic devices and cabling with power ranging to a few watts for the minimum missions while large missions would take up to 20 kilowatts (Li and Han 2016). Nevertheless, the Science Mission Directorate would further require a more intelligent and a fault or error tolerant Power Management and Distribution systems for the need to managing the power system when engaging deep space missions.

2.7.1 Energy Storage

Power is needed in space for lighting, communication, life support, experiments, and propulsion. Power in a space is crucial for running and maintaining operations as well as functions Designing a reliable system is challenging, losing power on an International Space Station, everything on board could perish. Choosing a reliable power flow technique is priority to ensure the entire system is balanced in terms of power generation and power consumption. Constraints such as thermal overloads, frequency and voltage fluctuations are to be avoided (Wang et al. 2016). Due to near constant availability and intensity of sunlight and ray in space, solar panel to generation power is optimal taking both production and maintenance cost. International Space stations use solar cells to generate power. However, in order to generate enough energy to power the equipment and systems, large number of cells are arranged in series. This method of converting sunlight to electricity is called photovoltaic. During power generation, transmission, distribution, a lot of heat is generated because of resistance that can damage spacecraft equipment. In order to dissipate the heat from the spacecraft into space, radiators are used. Thermal control systems also ensure the temperatures are within the required range uses heaters and louvers, thermal switches, and heat pipes to transfer heat the heat from the sources towards the radiators and away from instruments (Wang et al. 2016).

It is worth noting that a space station is not always in direct sunlight. For instance, during an eclipse, the solar panels do not generate power that is essential in functionality and orbiting of the space station. In this case, power supply for the equipment relies fundamentally on stored electric power through rechargeable batteries. Batteries usage and choice depends on discharge rate, temperature, and life span. Nickel-Hydrogen batteries are used at the International Space Station, they are designed to last 6.5 years, in a 30-year life mission, and the batteries will be replaced multiple times. Since 2017, the electric power storage units are now being replaced by the Lithium-ion batteries which are small, lightweight, which saves room and weight and three times more efficient than the Nickel-Hydrogen batteries. Importantly, the batteries used have to withstand the extreme and widely varying temperatures from one extreme of very hot to very cold, space environments and must be packed such that risk is played at minimum such that in case of an accidental like explosion, the astronauts are not injured. NASA’s main concern is safety of both the equipment and human life, for human-carrying space stations. The lithium-ion are the most powerful available batteries on the market but the downside is a risk called thermal runaway, this is when defects or mishandling causes the battery to overheat and explode. On the International Space Station, NASA has found a way to pack the batteries in a way that in case a thermal runaway takes place, this would not lead to a total tragedy. The batteries are charged during the sunlight part of the orbit.

The future missions would need advanced primary as well as secondary battery systems with the capacity of functioning at temperatures ranging from -1000 C for most of the Titan missions, to around 400-5000C for most of the Venus missions. Apparently, only a span of -2300C to around +1200C would be needed for the Lunar Quest. The 2011 PSD Relevant Technology Document and Outer Planet Assessment Group have attracted attention on high energy density systems, which would be needed by either the planetary exploration or the Enceladus missions. Besides, the electrochemical battery with high energy density would offer more than 50000 charge or discharge cycles with an operating life of 10 years. This would serve the 20 year life for the geosynchronous spacecraft (GEO) and the low-earth orbiting spacecraft. Advanced battery storage capabilities would address the necessary energy requirements for the missions alongside the radiation tolerance characteristics. Magnetic energy or mechanical storage devices are used as loading levelling or energy storage technologies might also be of interest (Bose 2017). The technologies have the capacity of minimizing the mass and the size of the power systems to be encountered in future.

2.7.2 Other sources of energy in space

Spaceflights are known for presenting challenges when it comes to collection and storage of electrical power. Some of the spacecraft components call for large amounts of the electrical power. However, most of the satellites in the earth orbit are essentially powered with the help of the solar arrays. With the help of the photovoltaic technology, solar is becoming one of the most significant sources of energy. On the other hand, probes known for travelling for long distances would require the radioisotope thermoelectric generators (RTGs). The devices have pellets of the radioactive material, commonly Plutonium, which is known for production of heat. The heat can be converted to electric power with the help of thermocouples. Therefore, nuclear is another important sources. Fuel cells and batteries are also other sources. Fuel cells would combine two chemical components for purposes of producing eat and electricity. Common types include the hydrogen-oxygen fuel cells.

3. The Design Process

3.1 Problem Statement

DC-DC converters have faced a problem of difficulty in achieving a high step-up voltage transformation ratio. It has been a big challenge to achieve high voltage gains of 10–20 for converter circuits for aerospace applications (Harada, Ninomiya, & Gu, 1992). The use of general non-isolated boost chopper circuits has faced the challenge because of the parasitic resistance (Harada, Ninomiya, & Gu, 1992). Though magnetic coupling used in many designs achieve the required high transformation ratio, this results in non-negligible power dissipation (Hayashi, Matsugaki, & Ninomiya, 2018). There is a need for a design that will address these problems and result in higher efficiencies.

Objective

To design DC-DC power electronics converter circuit with the following specifications:-

Input voltage (Vin) = 70-80V

Output voltage (Vout) = 700-800V

Load current (IL) = 50A

Capacitors

Transformers

4 Diodes

4 Mosfets powered by separate PWM

Extracted from Tarisciotti et al. (2017)

3.2 Topologies

3.2.1 Cycloconverter

A cycloconverter is a frequency changer; it can charge AC power at a certain frequency to AC power to a different frequency. With a cycloconverter power, transfer takes place in two directions (bidirectional). Smooth operations are only achieved if the frequencies are not the same as half of the frequencies input values (Ronanki and Williamson, 2017). The two types of cycloconverters are

Step up cycloconverter: uses natural commutation and produces a higher frequency than the input frequency.

Step down cycloconverter: uses forced commutation and outputs a lower frequency than the input frequency.

Cycloconverters are also classified as:

Single phase to single phase: two back to back connected full wave converters, when one is in operation, the other one is disabled and no current will flow.

Three phases to single phase: similar to single phase to single phase, the supply is three phase and the output is single phase (Xu et al., 2016).

Three-phase to three-phase: main applications in three phase induction and synchronous machines. By changing the motor supply frequency, the motor speed is adjusted.

3.2.2 Synchro converter

This type of converter converts 3-phase voltage and frequency from constant value a varying DC voltage and then further reconverts it to AC with varying voltage and frequency. In control systems the converter provides voltage to torque using an amplifier and servomotor. Mainly used in applications which require high accuracy, large torques such as autopilot systems. They are also used in in underwater detection systems, communication and navigation systems (Ronanki and Williamson, 2017). Synchros have no mechanical stops, a constant speed and independent of the load, long life expectancy and a very low failure rate.

Four basic synchro converter types are:

Control transmitter

Control receiver

Control transformer: works as transducer and error detector

Control differential

3.2.3 Voltage source PWM inverter:

Pulse width Modulation (PWM) is used in inverters to achieve a steady output voltage irrespective of the load. The PWM inverters also have additional circuits for voltage control and protection. The efficiency of the inverter is determined by the quality of its waveform. Main function of the voltage source PWM inverter is to convert AC to DC. The voltage converter is used in many different system interconnecting modes and can drive any motor type.

3.2.4 Multilevel-PWM

Most important advantage of the Multilevel PWM is cost reduction; the inverter uses low power components while delivering high power output.

3.2.5 Matrix converters

Pure energy conversion devices, which does store energy, by using bidirectional controlled switch, it achieves automatic AC to AC power conversion. This can be used as an alternative to double sided Pulse Width Modulation rectifier. Matrix converters are described by sinusoidal waveforms that display the switching frequencies, input and output (Zapata et al. 2018). A controllable power factor input is achievable with bidirectional switches. Due to the lack of bilateral switches, which operate at high frequencies, the output to input voltage ratio is limited.

There are 3 approaches of Matrix converter control that include :

Pulse width modulation

Space vector modulation

Venturi-analysis function of transfer

3.3 Modulation strategies

There are numerous methods, which can be used in power electronics converters; this includes Pulse Density Modulation (PDM), Hysteresis Modulation, and Pulse Width Modulation (PWM).

3.3.1 Pulse Width Modulation (PWM)

PWM is used for controlling different analogue devices for example encoding purposes in Telecommunications, controlling speed of motors, voltage regulation, used in audio and video amplifiers and for controlling the heat generated in computer motherboards. PWM controls analog circuits using microprocessor’s digital outputs. In this method, the conversion from digital to analog is not necessary, noise effects are kept low by keeping the signal digital. In PWM method the energy is spread by a series of pulses not as continuously changing signal. Its advantages are providing accuracy and quick response time, initial costs is very low, helps motors generate very high torque even when running at low speeds and helps prevents burning of LEDs whilst maintaining brightness of LEDs. Due to PWM high frequency, switching losses are significantly high and it induces radio Frequency Interference.

3.3.2 Hysteresis modulation

This is the easiest of the three modulation strategies to implement in practice. It is simple, robust and independent of load parameter changes. The deficiencies with the hysteresis are (i) the spread of harmonic spectrum caused by the variable switching frequency, (ii) if DC link middle point and system neutral are not connected the results is an increased current error and (iii) poor output current (quality) shows that hysteresis modulation has to be combined with other methods like looping feedback so as to enhance the output current quality. Because of these drawbacks, it is better to use other modulation strategies for microgrids.

3.3.3 Pulse density modulation

(PDM) is not often used, used in converters for induction heating at high frequency (150 kHz).

4. Project Design

4.1 Design parameters and specifications

The specification for this project has been highlighted under section 4.1.1. The additional parameters include the following

Rated output power-10kW for IBCI, ABAC and DAB

Sampling time – 10µs

Switching frequency – 100kHz

Power Transfer Inductance – 7.56µH

Magnetizing Inductance - 50µH

Clamp capacitance – 2.5µF

Output filter capacitance - 20µF

4.2 The need of the design and assumptions

The design gives a clear picture of the anticipated system. This provides a clear map of the areas which are assigned significant specifications and parameters. The design is also important in the sense that it bolsters the ideation process while trying to model the project. A number of assumptions were considered in developing the design. First, all the parameters are reasoned within the desirable range that would not result in the inefficiencies or failure in terms of performance of some of the components. Secondly, it is assumed that all the components can be accessed from the outlets for the purposes of running the design process.

4.3 Selection of Topology

For space applications a comparison of the two converters ABAC and DAB was carried out. The comparison was considering efficiency, volume and weight for detailed applications of a DC-DC converter. Analysis of the two topologies, in terms of input and output waveforms, control and efficiency was evaluated. The outcome of the results showed that the ABAC converter was able to reduce weight and volume at high power ratings and inherently control the low voltage current at the same time having nearly the same efficiency as the DAB converter (Xu et al. 2016). This design used modified ABAC topology as preferred in the literature to DAB topology Tarisciotti et al. (2017).The topology shown in Figure 1 was used in this design. From section 4.1, the modification is as shown in the parallel to each other.

The modified ABAC topology has a DC power source linked to the four inductors while each of the four MOSFETS is connected to a working diode. The latter usually acts as a switch to the relevant output of DC-DCDC Converter (Mehdipour et al. 2019). On the other hand, the power input to the significant MOSFETS is normally controlled using the PWM which is also connected to R1, R2, C1, C2 and C3 as indicated in Figure 1. The output side of PWM is connected to MOSFET and an oscilloscope terminal.

The output of the indicated DC-DC Convertor would be connected to the two capacitors in parallel for the purposes of attaining stability while resistors R5 and R6 would regulate the stability of the output voltage (Enrique et al. 2018).

The transformer denoted U2 has the primary to secondary turn ratio 8.7:1, which is used to amplify or modify voltage. Essentially, load resistor is connected to a transformer appearing on the secondary side. Notably, a Multimeter is utilized in measuring the output current as well as voltage.

5. Design Calculations

5.1 Estimation of the Peak Current

The following equation was used to estimate Peak current, :

Where,

Therefore

5.2 Duty Cycle Calculations

The relationship between the input voltage and output voltage is outlined by the following equation:

5.3 Selection of Energy Storage Inductor

5.4 Filter Capacitor Calculations

5.5 Calculations for PWM IC

6. Selected components

6.1 MOSFET Specifications

MOSFET applications and choice was carried out due to their power and frequency characteristics. Due to their low switching losses, less protection is required and fast switching ability, the voltage controlled MOSFET’s are preferred than other types of MOSFETS (Nair et al. 2017). The N channel power MOSFET drain resistance increases with temperature, is protected from breakdown due to its inherent positive temperature coefficient of resistance. It has an operating temperature range of -55 to 175 degrees Celsius; Lead free, Enhanced body diode dI/dt and dV/dt capability. The selected IRFB3206PbF MOSFET of type HEXFET Power MOSFET with a of 60V and drain current of 210A. It has high-speed power switching, uninterruptable power supply, improved Gate and avalanche and Dynamic dV/dt and is Fully Characterized Capacitance and Avalanche. The MOSFET type is used in applications ranging from MHz to KHz such as zero volt switching converter, pulse width modulated inverter and as voltage source.

6.2 CAPACITORS

X7R BME MLCC capacitors are approved and used by NASA for space applications due to their low production costs, high performance and high reliability space applications, X7R BME MLCC are ceramic capacitors, which have a fixed value, the ceramic material is like the dielectric and provides much improved resistance to mechanical stress. The use of BME capacitors enables the use of light and smaller PCB’s and fewer components which is a big advantage for space missions. For resonant circuit applications, the X7R BME MLCC Class 1 capacitors provide high stability and very low losses and offer high capacitance compared to other capacitors. For high volume efficiency for buffer, by-pass and coupling applications, Class2 X7R BME MLCC capacitors are recommended. The capacitor electrical characteristics depend on the ceramic materials used. In order to meet the space specifications, lead free soldering is obligatory for the surface mount components. COTs capacitors are available in wide range of capacitances and sizes. X7R BME MLCC is used in harsh environment conditions, military devices, and avionics and in space. Capacitors for space applications must be robust and reliable at very high temperatures (Nair et al. 2017). Like all other components designed for space applications, capacitors are tested and must withstand vibrations, infrared sun radiation, high vacuum and extremely cold temperatures. There is a chance vibration might not take place in space but all components should overcome the vibrations imposed by the launch vehicle.

6.3 INDUCTORS

The SGIHLP Power Inductors, meets MIL-STD-981 Class S space requirements, it provides the very highest efficiency, very low core loss over a wide range of operating frequencies. The SGIHLP Inductors are fully tested to MIL-STD-981 Group A/B requirements. The power inductors offer excellent inductance, a good range of inductance values from 0.22 µH to 100 µH and can handle high transient current spikes without saturation, operate at high temperatures to 180 °C. Power inductor designed to provide high reliability in space grade applications.

6.4 BYV28-200

The BYV28-200 is an ultrafast rectifier diode with a low forward voltage, ultra-high switching speed, controlled avalanche characteristic, it has the ability to withstand voltage transients, which might be caused by inductors. Avalanche diodes also protect the circuit against surges. The diode is designed to operate in break down at a well-defined reverse voltage without being destroyed when operating within a temperature range of 55 to +175 °C. It operates at high frequency and has low switching losses. Typical application is in high frequency rectification such as in switching mode converters and inverters.

6.5 UC3842

UC3842 is a fixed current mode PWM controller. It is specially designed for Off-Line and DC-to-DC converter applications with minimum external components. These integrated circuits feature a trimmed oscillator for precise high gain error amplifier, current sensing comparator, a temperature compensated reference, duty cycle control, and a high current totem-pole output for driving a Power MOSFET. Moreover, some other features include temperature compensated reference and current sensing. In addition, protective features consisting of input and reference under voltage lockouts each with hysteresis, a latch for single pulse metering, programmable output dead time, and cycle−by−cycle current limiting, are included. These devices are available in either a 14−pin plastic surface mount (SOIC−14) or 8−pin dual−in−line and surface mount (SOIC−8) plastic package. The SOIC−14 package is designed in a manner that is has separate power and ground pins for the totem pole output stage. The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX843B is modelled for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off). The UVLO provides a very stable DC-DC converter operation.

UC3842 Features:

Trimmed Oscillator for Precise Frequency Control

Current Mode Operation to 500 kHz

Oscillator Frequency Guaranteed at 250 kHz

Latching PWM for Cycle−By−Cycle Current Limiting

Automatic Feed Forward Compensation

Internally Trimmed Reference with Under-voltage Lockout

Low Start up and Operating Current

Under-voltage Lockout with Hysteresis

High Current Totem Pole Output

This is a Pb−Free and Halide−Free Device.

The UC3842 can operate within 100% duty cycle.

This integrated pulse width modulator was chosen due to its good electrical performance and low costs.

6.6 Transformer

A high power planar transformer with the input voltage of 80V, maximum secondary current 50A, output voltage of 800V, primary to secondary ratio was 1:10, and the magnetizing inductance of 5H was used. Both primary and secondary windings resistance was 1Ω. Planar transformer features:

Small, low height

have excellent temperature characteristics

have a low leakage inductance

high power density

good thermal characteristics

Controlled parasitic (leakage inductance and capacitance)

have excellent repeatability properties

High efficiency ca. 99%

Compact and very light

8. Future Space Challenges and Solutions

The biggest challenge to humankind is to be able to stay in space. Technologies in high power conversion, high power systems and components, power generation, distribution and storage are vital and require improvements to keep humans for a certain period in space. Space is a very dangerous and unfriendly place. It starts with isolation from families, risks of cancer through exposure to radiation, a diet composed of frozen dried foods, lack of enough room for exercising which leads to deteriorating of bones and muscles. Tests carried out on Mars reveal that without gravity working on your body results in the loss of body minerals, loss of muscle strength, endurance due to lack of exercises. There are also chances of vision problems caused by the pressure put on eyes caused by fluids shifting up to the head. Six months is considered the maximum time humans can stay in space with exception of Scott Kelly who spent a year a year in space aboard the International Space Station. Scott Kelly’s results are currently used by scientists to analysing the changes in humans after one year. The analysed data is important for researchers and scientist to plan future missions such as to Mars.

The space challenges are not only on humans, they also affect the selection, design and future testing of electronics components for space. Considering space missions such as to Mars where temperatures can exceed 2000°C, travelling speed of 20,000mph and exposure to extreme radiation, the selection of the electronics components and the power electronics converters for microgrids in space are crucial. The first task for space electronics to overcome is the vibration caused by the launch vehicle. Severe demands are placed on the rocket and its payload. Extreme noise and vibrations are generated by the rocket launchers. In space large shocks occur when the satellite separates from the rocket. These large shocks can cause damage on circuit boards and other electrical equipment. The challenge is to deeply understand the launch environment to ensure the shock and vibration requirements are met. Thorough inspection and simulation under the extreme harsh conditions experienced during the launch and the expected space conditions using precise equipment. Testing the electronics components thoroughly is the only way to be sure they survive the vibrations during launch, high and low space temperatures, ultra-low vacuum, electromagnetic interference and radiation. The other biggest challenge is the mission duration, the electronics components are expected to work under these extreme conditions for several years.

9. Conclusion

In this research into the design of power electronic converters for or space microgrids, based on existing power electronic components is evaluated. The electrical system attached to the extra-terrestrial base operates in a similar way to a microgrid, while integrated s modules include solar boards meant for core energy production and the batteries as storing units. In addition, electric vehicles such as aircraft as well as satellites constitute part of the extra-terrestrial basis loads. To tackle the power supplying issue, the microgrids concept as an isolated energy system is presented by different companies. From a space-qualified point of view, different design aspects of a power converter including the non-isolated/ isolated, hard-switched/soft-switched and voltage-fed/current-fed are usually considered. There are several companies including API Technologies, BAE Systems. CISSOID, Cobham and 3D plus offer radiation-hard converters, voltage controllers or associated power ICs for implementation in-space use. These transformers may be either isolated or non-isolated but are usually are equipped with voltage step-down feature. These transformers, which are normally fabricated by means of hybrid or PCB-based structure, are mainly presented by power supply producers.

One the other hand, semiconductor producers with radiation-hard features also fabricate non-isolated converters and shifting regulators constructed either like monolithic ICs or multi-chip components. They likewise manufacture associated chips including linear controllers, block functions for fashioning DC/DC transformers and shifting regulators. All in all, this paper can help envision the incredible application range of power electronics components in space by using simple-concept high-tech power converters. Since there are entirely different environmental conditions in each different space station and extra-terrestrial basis including harsh radiation and temperature conditions, a specific power electronics design may be required for each condition following space-qualified designing and manufacturing principles. So as to efficiently discover the solar system and more through establishment of a space basis, it could be understood that the standards have been improved for conditions of power efficiency, low mass, and small scale, in addition to fabrication innovative power electronics components and elements. Extreme radiations and severe temperature conditions await humankind as they explore through the galaxy.

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