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Solar photovoltaic (PV) arrays in portable applications are often subject to partial shading and rapid fluctuations of shading. In the usual series-connected wiring scheme, the residual energy generated by partially shaded cells either cannot be collected (if diode bypassed) or, worse, impedes collection of power from the remaining fully illuminated cells (if not bypassed). Rapid fluctuation of the shading pattern makes maximum power point (MPP) tracking difficult; generally, there will exist multiple local MPPs, and their values will change as rapidly as does the illumination. In this paper, a portable solar PV system that effectively eliminates both of the aforementioned problems is described and proven. This system is capable of simultaneously maximizing the power generated by every PV cell in the PV panel. The proposed configuration consists of an array of parallel-connected PV cells, a low-input-voltage step-up power converter, and a simple wide bandwidth MPP tracker. Parallel-configured PV systems are compared to traditional series-configured PV systems through both hardware experiments and computer simulations in this paper. Study results demonstrate that, under complex irradiance conditions, the power generated by the new configuration is approximately twice that of the traditional configuration. The solar PV system can be widely used in many consumer applications, such as PV vests for cell phones and music players. Index Terms--Complex illumination, maximum power point tracking (MPPT), partial shading, photovoltaic (PV) solar cell, power converter, solar array.

A one-dimensional transient model of a tubular solid oxide fuel cell stack is proposed in this paper. The model developed in the virtual test bed (VTB) computational environment is capable of dynamic system simulation. This model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. The temperature, the current density, and the gas concentration distribution along the axial direction of the cell are presented. The dynamic behavior of electrical characteristics and temperature under the variable load is simulated and analyzed. For easy implementation in the VTB platform, the nonlinear governing equations are discretized in resistive companion form. The developed model is validated with experimental results and can be used for dynamic performance evaluation and design optimization of the cell under variable operating conditions and geometric condition. [DOI: 10.1115/1.2906114] Keywords: solid oxide fuel cell, SOFC, dynamic model simulation, virtual test bed

Hybrid systems composed of fuel cells and batteries combine the high energy density of fuel cells with the high power density of batteries. A dc/dc power converter is placed between the fuel cell and the battery to balance the power flow between them and greatly increase the peak output power of the hybrid. This paper presents an adaptive control strategy for active power sharing in the hybrid power source. This control strategy can adjust the output current setpoint of the fuel cell according to the state-of-charge (or voltage) of the battery, and is applicable in two topologies of active fuel cell/battery hybrids. The control strategy is implemented in Simulink and then tested under arbitrary load conditions through simulation and experiments. Simulation and experimental results show that the adaptive control strategy is able to adjust the fuel cell output current to adapt to the charge state of the battery, and appropriately distribute the electrical power between the fuel cell and the battery. Experiments demonstrate the generality of the adaptive control strategy. Index Terms--Active power sharing, adaptive control strategy, battery, fuel cell, hybrid power sources, power converter.

A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources. Index Terms--Battery, digital control, fuel cell, hybrid power source, microcontroller, power capacity.

Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales.

This paper describes the basic design, refinement, and verification using finite-element analysis, and operational simulation using the Virtual Test Bed, of a linear machine for an electromagnetic aircraft launcher, for the aircraft carrier of the future. Choices of basic machine format and procedures for determining basic dimensions are presented. A detailed design for a permanent-magnet version is presented, and wound-field coil and induction machine versions are briefly discussed. The long armature-short field geometry is justified, and in particular the impact of this geometry on the scale of the power electronic drive system is examined. Index Terms--Aircraft launcher, linear machine, linear permanent-magnet (PM) synchronous machine, PM machine, power electronic drive, system simulation, track sectioning.

Hybrid fuel cell/battery power sources have potentially widespread uses in applications wherein the power demand is impulsive rather than constant. Interposing a dc/dc converter between a fuel cell and a battery can create two configurations of actively controlled hybrid fuel cell/battery power sources. Those two configurations are compared using both theory and experiment with special attention to the peak power enhancement, and power losses in the converter. Both of the defined configurations were built, using a 35 W polymer electrolyte membrane (PEM) fuel cell, an 8-cell lithium-ion battery pack, and a high-efficiency power converter. Both two configurations yielded a peak power output of 135 W, about 4 times as high as the fuel cell alone could supply, with only a slight (13%) increase of weight. The converter losses were quantitatively analyzed. Which of the two configurations yields a smaller loss depends on the load power demand characteristics including peak power and load duty ratio. The study results provide guidance for the design of hybrid sources according to the particular load power requirements.

Hybrid power sources composed of fuel cells and secondary batteries can combine the high energy density of fuel cells with the high power density of batteries. A dc/dc power converter can be placed between the fuel cell and the battery to balance the power flow and greatly augment the peak output power. This paper presents a novel, flexible strategy for multi-objective control of the power converter in the hybrid power source. The control strategy is able to regulate the output current of the fuel cell and the charging current or voltage of the battery while limiting the discharging current of the battery. It can be used in two different configurations without any change. The control strategy is implemented in MATLAB/Simulink and tested by simulation and experiments. Simulation and experimental results show that the multiobjective control strategy is able to select the regulation mode correctly and the fuel cell current, battery current and battery voltage are regulated appropriately. Experiment results demonstrate the great flexibility and generality of the control strategy and validate that the peak power capacity of the active hybrid power source is increased significantly. Simulation and experiment results also show that power converter can be appropriately regulated to meet the multiple objectives required by hybrid power sources. Index Terms--Battery, fuel cell, hybrid power source, multiobjective control, power converter.

An actively controlled battery/ultracapacitor hybrid has broad applications in pulse-operated power systems. A converter is used to actively control the power flow from a battery, to couple the battery to an ultracapacitor for power enhancement, and to deliver the power to a load efficiently. The experimental and simulation results show that the hybrid can achieve much greater specific power while reducing battery current and its internal loss. A specific example of the hybrid built from two size 18650 lithium-ion cells and two 100-F ultracapacitors achieved a peak power of 132 W which is a three-times improvement in peak power compared to the passive hybrid power source (hybrid without a converter), and a seven times improvement as compared to the lithium-ion cells alone. The design presented here can be scaled to larger or smaller power capacities for a variety of applications. Index Terms--Hybrid power source, lithium-ion battery, peak power enhancement, power converter, ultracapacitor.

A state space approach to the design of a maximum power point (MPP) tracking system for photovoltaic energy conversion is presented. The problem of optimal-power control of a nonlinear time-varying system is reduced to an ordinary problem of dynamic system stability in state space by applying MPP conditions in controller design. The resulting tracking system searches for the reference point and tunes the converter for maximum power delivery to a load that may represent an end-user, or an energy-storage element, or a power grid-interface. The proposed design procedure for the MPP tracking system ensures a global asymptotic stability under certain conditions, and a minimum degree of the dynamic feedback. The design is verified using the Virtual Test Bed, demonstrating accurate MPP tracking capability under unpredictable weather change, parameter variation, and load disturbance. The tracking system can be applied either to stand-alone or grid-connected photovoltaic installations, and can be implemented in either analog circuitry or a digital microcontroller. Index Terms--Maximum power point (MPP) tracking, non-linear and time-varying system, photovoltaic energy conversion, state-based approach, system stability.

This paper presents a synergetic controller for pulse current charging of advanced batteries from a fuel cell power source. Pulse current charging protocol that has been shown to have many advantages over the traditional constant current/constant voltage protocol is applied in a fuel cell powered battery-charging station to reduce the total charging time. Strong nonlinearity and dynamics exist in such systems. In this paper, the synergetic control approach is applied to regulate the buck converters that control the pulse charging currents to the many batteries. A practical synergetic controller to coordinate pulse current charging of the battery is synthesized and discussed. It provides asymptotic stability with respect to the required operating modes, invariance to load variations, and robustness to variation of the input and converter parameters. The synergetic controller is then implemented in Simulink. The dynamic characteristics of the synergetic controller are studied and compared with PI controller by conducting system simulation and experimental tests. Simulation and experiment results show the synergetic controller is robust for such nonlinear dynamic system and achieves better performance than the standard PI controller. Index Terms--Asymptotic stability, buck converters, PI controller, pulse current charging, synergetic controller.

This paper presents an effective system design for a fuel-ceil-powered battery-charging station and three control strategies for active power sharing among the batteries. This battery-charging station allows multiple batteries to be simultaneously charged. Three control strategies were investigated to coordinate the active power distribution among the battery-charging branches. The baseline control strategy was equal rate charging. Two advanced control strategies, proportional rate charging and pulse current charging, were compared to the baseline strategy. These control strategies were realized in MATLAB/Simulink, and the current and voltage regulations were implemented using the classical proportional-integral control approach. The system simulation was conducted in the Virtual Test Bed by embedding Simulink objects of the controller and co-simulating with MATLAB. The experimental tests were performed by compiling Simulink codes of the controller and downloading to the dSPACE platform to control real hardware. The simulation and experimental results are given. Experimental tests validate these control strategies. Index Terms--Active power sharing, battery, charging station, control strategy, dSPACE, fuel cell, Simulink, Virtual Test Bed (VTB).

A new phase-domain induction machine model for use in power system dynamic simulation is developed with the aid of a symbolic tool. The symbolic tool can automatically construct a time-domain power system component model in the resistive companion form (RCF) that is widely used in time-domain simulators. The automatic differentiation technique (ADT) is utilized within the context of a symbolic modeling language, and the tool has been implemented for the virtual test bed (VTB) simulation environment. The new induction machine model was used to study start-up transients of an induction motor. The new model was verified by comparing the simulation results to those obtained from a standard d-q model. This paper also demonstrates that a symbolically assisted technique can provide an efficient and rapid path for developing complex nonlinear device models for power system simulations. Index Terms--Automatic differentiation, dynamic response, electric machines, induction machines, power system modeling, power system simulation, power systems, resistive companion form, symbolic tool, symbolically assisted simulation.

The theory of synergetic control was introduced in a power electronics context in a previous paper. In this paper, we review the theory, then focus on some practical aspects with reference to both simulations and actual hardware. In particular, we address management of the current limit condition and solve it with several different approaches. Adaptive and other control laws are also introduced to improve the control performance. The various controls are evaluated by applying the classical voltage reference step test and the step load test. Index Terms--Current limit, dynamic parameter adaptation, integral error term, nonlinear control, switching converter, synergetic control theory.

A study is presented on the design and testing of spacecraft power systems using the virtual test bed (VTB). The interdisciplinary components such as solar array and battery systems were first modeled in native VTB format and validated by experiment data. The shunt regulator and battery charge controller were designed in Simulink according to the system requirements and imported to VTB. Two spacecraft power systems were then designed and tested together with the control systems.

The process for designing digital controls for power electronics is typically quite convoluted and affords many opportunities for errors to occur. We present here a new and Complete method for rapid prototyping of digital controls that allows rapid realization of new designs. The approach uses a collection of tools that include both software (the virtual test bed (VTB) and Matlab/Simulink) and hardware (dSpace DSP). An example application of the methodology completes the discussion. Index Terms--Digital controls, dSpace DSP, power electronics, rapid prototyping, virtual test bed.

An approach to model the solar cell system with coupled multiphysics equations (photovoltaic, electro-thermal, direct heating and cooling processes) within the context of the resistive-companion method in the Virtual Test Bed computational environment is presented. Appropriate across and through variables are defined for the thermal terminal of the system so that temperature is properly represented as a state variable, rather than as a parameter of the system. This allows enforcement of the system power conservation through all terminals, and allows simultaneous solutions for both the electrical potentials and the system temperature. The thermal port built accordingly can be used for natural thermal coupling. The static and dynamic behaviors of the solar array model based on the approach are obtained and validated through comparison of simulation results to theoretical predictions and other reported data. The electro-thermal modeling method developed here can be generally used in the modeling of other devices, and the method to define the across and through variables can also be generalized to any other interdisciplinary processes where natural coupling is required. Index Terms--Electro-thermal modeling, resistive companion method, solar energy conversion, Virtual Test Bed simulation.

Conventional air-magnetic circuit breakers, which are widely used in low-voltage applications, utilize magnetic forces that are produced by blowout coils, the geometry of the arcing contacts, or both. The magnetic forces act to push the arc off the contacts into an arc chute, which consists of a number of metal plates. The arc chute causes the arc to be split into a number of smaller arcs, thereby facilitating the process of extinguishing the arc. In the last 20 years, the technology of circuit breakers has dramatically advanced, now including mature devices based on gas-blast (such as [SF.sub.6]) and vacuum interruption. At the same time, the technology of power electronic devices has evolved rapidly, leading to suggestions of a purely static circuit breaker based on solid-state electronic devices. Recently, several different proposals have appeared for current-limiting devices to be used in conjunction with or in replacement of conventional circuit breakers. The technologies involved in these proposals have ranged from very familiar (series reactors) to quite innovative (conductive polymer devices). Several of these proposed technologies have been used to a limited extent in commercial products, but they are very likely to see increasing applications as the technology matures. This paper begins with a short review of conventional circuit breaker action for background, then reviews the recent literature for current-limiting technologies that could be applied to low-voltage electric power systems. The paper concludes with a description of work underway for further development of conductive polymer current limiters.

The transient current interruption mechanism in a magnetically delayed vacuum switch (MDVS) is studied. Experiments are performed wherein the voltage and current characteristics of anMDVS, such as the trigger current amplitude and trigger voltage, are measured. The streak and framing images of the transient discharge are also obtained using an image converter camera. Results show that the transition from proper switch closure to the high-loss opening phase occurs via an ion erosion processsimilar to that in a plasma-opening switch.