One of the most critical systems in any aerospace vehicle is the electrical power system (EPS). Comprising energy generation, energy storage, power distribution, and power management, EPS is relied upon by every major subsystem for proper operation. To meet the safety requirements of aeronautics and space systems – and provide for their reliability, maintainability, and supportability – advanced health management (HM) techniques for EPS are required. A detailed review of the major EPS component failure modes shows that power generation and energy storage components generally employ some basic HM techniques to estimate and manage remaining life. However, power management and distribution (PMAD) components and systems employ almost no on-board HM techniques. A survey of current aerospace vehicles and platforms will show that power HM systems have employed simple performance and environmental monitoring to provide indications of possible component and subsystem failures, and used redundant components as a "safety net" when failures do occur. More advanced methods that detect fault locations in wiring are used for maintenance purposes and not as an on-board safety system. To move beyond this, future power HM systems need to be "intelligent" and operate autonomously. This means that they need to be able to detect and isolate incipient faults, mitigate failures, or predict impending failures so that mitigating actions can be taken. The historical method of adding HM capabilities after a system has been developed leads to high cost for implementation, limited capabilities, and low reliability in operation. Future aerospace power systems need to incorporate HM capability early in the design cycle for maximum benefit.

This paper presents a modular, fault tolerant dc-dc converter topology that utilizes common duty ratio control to ensure equal sharing of input voltage and output current in input-series output-parallel configuration. The input-series connection allows the use of low voltage MOSFET's optimized for very low $R_{DS,ON}$ resulting in lower conduction losses. The common-duty-ratio scheme does not require a dedicated control loop for input voltage or output current sharing. The fault tolerant protection and control scheme accommodates failure of one or more modules, and ensures input voltage and load current sharing among the remaining healthy modules. The design of a new sensing scheme for detection of fault is presented. The analysis of the topology and the underlying principles are presented. The dependence of peak current from the source and in the protection switch in case of failure of a single converter has been analyzed and the various design tradeoff issues are discussed. The theoretical predictions are validated with simulation and experimental results. The proposed method is simple and gives good dynamic response to changes in input, load, and during fault. This topology is especially suited for space applications where a high level of fault tolerance can be achieved through designed redundancy.

NASA’s new space exploration program demands that vehicles, habitats, and rovers achieve unprecedented levels of reliability, safety, effectiveness, and affordability. Modular and intelligent electrical power systems are critical to achieving those goals. To support this new paradigm, advanced concepts in power management and distribution (PMAD) system technologies are proposed. The concept of modularity in electrical power systems is presented, along with perceived benefits such technology offers. Modular functionality at the power component and system level is discussed along with some recent technical accomplishments. The development of “true modularity” is introduced describing the need for distributed, master-less solutions in developing modular power components. To realize modular power components and systems, a new level of embedded intelligence and communication in power system components will be required. This additional intelligence capability will finally enable the on-board autonomy and health management required for reliable electrical power systems operating far from Earth for long periods. Summary results from recent development efforts are presented along with expected future technology development needs required to support NASA’s ambitious space exploration goals.

A distributed control system (DCS) is developed and hardware verified for a class of digitally controlled modular DC-DC converters. The converters are each independently controlled by its own FPGA-based digital controller. A Control Area Network (CAN) is first set up for the converters to communicate in a master-less peer-to-peer manner. An algorithm is developed to make the converters share the load (current) dynamically in a predetermined manner. More importantly, it makes it possible to for all converters to automatically time-shift their PWM gating signals to minimize the current ripple, which is known as interleaving. An algorithm is developed for this distributed master-less control of power converter system so that the load sharing and interleaving are adjusted autonomously, in real time, as the number of converters changes without prior knowledge.

Nasa's resent commitment to Human and Robotic Space Exploration obviates the need for more affordable and sustainable systems and missions. Increased use of modularity and on-board intelligent technologies will enable these lofty goals. To support this new paradigm, an advanced technology program to develop modular, intelligent power management and distribution (PMAD) system technologies is presented. The many benefits to developing and including modular functionality in electrical power components and systems are shown to include lower costs and lower mass for highly reliable systems. The details of several modular technologies being developed by NASA are presented, broken down into hierarchical levels. Modularity at the device level, including the use of power electronic building blocks, is shown to provide benefits in lowering the development time and costs of new power electronic components.

A hybrid phase modulated converter (HPMC) with current doubler rectification has superior soft switching characteristics, high efficiency, and low EMI as compared to a conventional phase modulated converter. It has essentially three modes of operation: (i) continuous conduction mode (CCM); (ii) continuous conduction mode with reversed inductor currents; and (iii) discontinuous conduction mode (DCM). There is never a discontinuity in conduction in the inductors and the definition of DCM is different in itself. In this paper, the various modes are defined, analyzed and design equations derived. The analyses are also verified with a 500 W peak current mode controlled prototype model, switched at 100 kHz and the results are presented. The soft switching behavior of the converter in this mode is also studied and is found to be advantageous.

A hybrid, soft-switching, DC-DC converter has been developed with superior soft switching characteristics, high efficiency, and low electro-magnetic interference. This hybrid topology is comprised of an uncontrolled bridge operating at full pulse-width, and a controlled section operating as a conventional phase modulated converter. The unique topology is able to maintain zero voltage switching down to no load operating conditions. A breadboard prototype was developed and tested to demonstrate the benefits of the topology. Improvements were then made to reduce the size of passive components and increase efficiency in preparation for packaging. A packaged prototype was then designed and built, and several innovative packaging techniques are presented. Performance test data is presented that reveals deficiencies in the design of the power transformer. A simple redesign of the transformer windings eliminated the deficiency. Future plans to improve the converter and packaging design are presented along with several conclusions.

A hybrid phase modulated converter with current doubler rectification has been analyzed. The operating principles in continuous conduction mode are discussed. Various equations and equivalent circuits that aid in design have been derived. How this topology compares against a conventional hybrid resonant converter has been delineated under various design considerations. The zero voltage switching characteristics, filter requirements, small-signal transfer characteristics, device ratings and magnetics size requirement are discussed. Simulation results and experimental verification from a 500 W prototype converter switched at 100 kHz are presented.

The NASA Glenn Research Center and the Cleveland State University have developed a digitally controlled dc-dc converter to research the benefits of flexible, digital control on power electronics and systems. Initial research and testing has shown that conventional dc-dc converters can benefit from improved performance by using digital-signal processors and nonlinear control algorithms.

The motivation behind an advanced technology program to develop intelligent power management and distribution (PMAD) systems is described. The program concentrates on developing digital control and distributed processing algorithms for PMAD components and systems to improve their size, weight, efficiency, and reliability. Specific areas of research in developing intelligent DC-DC converters and distributed switchgear are described. Results from recent development efforts are presented along with expected future benefits to the overall PMAD system performance.

Recent trends in aerospace Power Management and Distribution (PMAD) systems focus on using commercial off-the-shelf (COTS) components as standard building blocks. This move to more modular designs has been driven by a desire to reduce costs and development times, but is also due to the impressive power density and efficiency numbers achieved by today's commercial DC-DC converters. However, the PMAD designer quickly learns of the hidden "costs" of using COTS converters. The most significant cost is the required addition of external input filters to meet strict EMI requirements for space systems. In fact, the high power density numbers achieved by the commercial manufacturers are greatly due to the lack of necessary input filters included in the COTS module. The NASA Glenn Research Center is currently pursuing a digital control technology that addresses this problem with modular DC-DC converters. This paper presents the digital control technologies that have been developed to greatly reduce the input filter requirements for paralleled, modular DC-DC converters. Initial test result show that the input filter's inductor size was reduced by 75%, and the capacitor size was reduced by 94% while maintaining the same power quality specifications.

A digital signal processor (DSP) solution is proposed to control an H-bridge DC-DC isolated output power converter. The multiple mode digital controller is evaluated with an existing Westinghouse 1-kW power stage. The digital controller was developed using the dSPACE [1] rapid prototype development system and MATLAB/Simulink. It is evaluated using a real-time digital control development platform that included the actual Westinghouse converter power stage. Preliminary digital controller performance is presented that warrants continued investigation and development of this application of digital control and supports the use of the DSP as a viable component in Power Management and Distribution (PMAD) applications.

A battery charge regulator based on the series-connected boost regulator (SCBR) technology has been developed for high-voltage spacecraft applications. The SCBR regulates the solar array power during insolation to prevent battery overcharge or undercharge conditions. It can also be used to provide regulated battery output voltage to spacecraft loads if necessary. This technology uses industry-standard dc-dc converters and a unique interconnection to provide size, weight, efficiency, fault tolerance, and modularity benefits over existing systems. The high-voltage SCBR shown in the photograph has demonstrated power densities of over 1000 watts per kilogram (W/kg). Using four 150-W dc-dc converter modules, it can process 2500 W of power at 120 Vdc with a minimum input voltage of 90 Vdc. Efficiency of the SCBR was 94 to 98 percent over the entire operational range. Internally, the unit is made of two separate SCBR s, each with its own analog control circuitry, to demonstrate the modularity of the technology. The analog controllers regulate the output current and incorporate the output voltage limit with active current sharing between the two units. They also include voltage and current telemetry, on/off control, and baseplate temperature sensors. For peak power tracking, the SCBR was connected to a LabView-based data acquisition system for telemetry and control. A digital control algorithm for tracking the peak power point of a solar array was developed using the principle of matching the source impedance with the load impedance for maximum energy transfer. The algorithm was successfully demonstrated in a simulated spacecraft electrical system at the Boeing PhantomWorks High Voltage Test Facility in Seattle, Washington. The system consists of a 42-string, high-voltage solar array simulator, a 77-cell, 80-ampere-hour (A-hr) nickel-hydrogen battery, and a constant power-load module. The SCBR and the LabView control algorithm successfully tracked the solar array peak power point through various load transients, including sunlight discharge transients when the total load exceeded the maximum solar array output power.

Current trends in satellite design are focused on developing small, reliable, and inexpensive spacecraft. To that end, a modular power management and distribution system (PMAD) is proposed which will help transition the aerospace industry towards an assembly line approach to building spacecraft. The modular system is based on an innovative DC voltage boost converter called the Series Connected Boost Unit (SCBU). The SCBU uses existing DC-DC converters and adds a unique series connection. This simple modification provides the SCBU topology with many advantages over existing boost converters. Efficiencies of 94-98%, power densities above 1,000 W-c/kg, and inherent fault tolerance are just a few of the characteristics presented. Limitations of the SCBU technology are presented, and it is shown that the SCBU makes an ideal photovoltaic array regulator. A modular design based on the series connected boost unit is outlined and functional descriptions of the components are given.

Current trends in satellite design are focused on developing small, reliable, and inexpensive spacecraft. To that end, a modular power management and distribution system is proposed which will help transition the aerospace industry towards an assembly line approach to building spacecraft. The modular system is based on an innovative DC voltage boost converter called the series connected boost unit (SCBU). The SCBU uses any isolating DC-DC power converter and adds a unique series connection. This simple modification provides the SCBU topology with many advantages over existing boost power converters. Efficiencies of 94-98%, power densities above 1,000 W/kg and inherent fault tolerance are just a few of the characteristics presented. Limitations of the SCBU technology are presented and it is shown that the SCBU makes an ideal photovoltaic array regulator. A set of photovoltaic power system requirements are presented that can be applied to almost any low Earth orbit satellite. Finally, a modular design based on the series connected boost unit is outlined and functional descriptions of the components are given

The Power Management and Distribution (PMAD) DC Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power System (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power DC to DC converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD DC Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions.