Fuel cell power systems offer a unique combination of high efficiency, wide size range, modularity, and compatibility with cogeneration. The development of complete energy systems that realize the benefits offered by fuel cell technology requires a basic understanding of fuel cell system components as well as the associated power electronics for different applications. This paper explains the basic characteristics of a fuel cell system, describes the different types of fuel cells and their current state of development, and discusses the potential application of these systems to transportation and stationary power. Particular emphasis is given to the electrical characteristics of the fuel cell, which is a relatively stiff power source. Power electronic systems are essential for making the fuel cell electrical output compatible with most loads. Options for dc-dc and dc-ac power conversion circuits are given with a discussion of the distinct features of each circuit that can be used for system planning purposes. The interaction between a fuel cell and a single-phase ac inverter load is highlighted because of the widespread applicability of this particular combination.

This paper proposes a new adaptive control technique of the auxiliary branch of the resonant snubber inverter for photovoltaic (PV) applications. By varying the turn-on time of the auxiliary branch based on the load current, the auxiliary resonant current is reduced without the need for any additional components, decreasing the circulating losses and improving system efficiency. An analysis of the resonant snubber inverter operation is discussed. Different control strategies of the auxiliary branch are compared. A 600 W prototype is built to verify operation of the adaptive control technique and to measure the performance improvements. The measured peak and weighted California Energy Commission (CEC) efficiencies are 98.16% and 97.56%, respectively.

In this paper, a detailed design procedure is presented for a bidirectional resonant converter for battery charging application. This converter is similar to the LLC resonant converter with an extra inductor and capacitor in the secondary side. Soft-switching can be ensured in all switches without additional circuitry, and because of that, very high frequency operation is possible, hence; the size of the magnetics and the capacitors can be reduced. In this manuscript, first, an equivalent model for the bidirectional converter is derived for the steady-state analysis. Then, the design methodology is presented. Design of a converter includes finding the transformer turns ratio, design of magnetizing inductance based on ZVS condition, design of resonant inductances and resonant capacitances. To validate the design procedure, a 3.3 kW converter was designed following the guidelines in the proposed methodology as a design example. A prototype was built and tested in the lab. Experimental results verified the design procedure presented.

An inductive power transfer (IPT) system usually consists of four parts: an AC-DC power factor correction (PFC) converter, a high frequency DC-AC inverter, a compensation network comprising a loosely coupled transformer (LCT) and the resonant capacitors, and a rectification output circuit. Due to the relative large air gap, the magnetic coupling coefficient of the IPT system is poor, different from the closely-coupled IPT systems. As a result, the efficiency of the IPT system is always a main concern for different applications. To ensure high power transfer efficiency, these IPT systems should have high tolerance for different gap variation and horizontal misalignment conditions. In this paper, some design considerations to reduce gap and misalignment effects for the IPT system is proposed. By using finite element analysis (FEA) simulation method, the performance of different transmitter and receiver coil dimensions are compared. In order to validate the performance of the proposed design considerations, a hardware prototype is built and the corresponding experiments are carried out. The experimental results shows that the LCT prototype could maintain coupling coefficient between 0.237~0.212 within 40 mm horizontal misalignment.

Using a bidirectional dc-dc converter along with low-voltage energy storage for the high-voltage dc bus and traction motor drives has been a prominent option for hybrid electric and fuel cell vehicles. This paper will describe the significance of energy management power converters and their circuit topology options for efficiency, size, and cost considerations. Whether isolated or nonisolated, soft switching techniques have been widely used in high-power bidirectional dc-dc converters. Through some design examples, the component selection and circuit design optimization are discussed, and their efficiency evaluation results are also given. Major difficulties of developing a high-power bidirectional dc-dc converter are found in lack of high-power passive components and lack of multiphase dc-dc controllers. More development work needs to be done in these areas