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This paper presents the design and development of a transformer isolated high-power dc-dc converter. There are several design issues and challenges. In this paper, we focus on three major issues in high-power dc-dc converters. 1) An energy recovery passive snubber circuit and the selection of pulsewidth modulation control methods are first introduced to reduce the voltage spike and power loss across switching devices. 2) Interleaved winding method is then employed to reduce proximity effect in the transformer winding. 3) The voltage oscillation problem in the secondary rectifier diode is addressed, and solutions are provided. Index Terms--Duty cycle control, proximity effect, skin effect, snubber circuit.

In this paper, three different inverters: conventional pulsewidth modulation (PWM) inverter, dc-dc boosted PWM inverter, and Z-source inverter were investigated and compared for fuel cell vehicle application. Total switching device power, passive components requirement, and constant power speed ratio of each of these inverters were calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, the constant power speed ratio, and the efficiencies of the different inverters for fuel cell vehicle powered by the same fuel cell were conducted. The comparisons show that the Z-source inverter is very promising in applications when the boost ratio is low (1-2). Index Terms--DC-DC power conversion, fuel cells, inverter.

This paper proposes a Z-source inverter system for a split-phase grid-connected photovoltaic system. The operation principle, control method, and characteristics of the system are presented. A comparison between the new and traditional system configurations is performed. Simulation and experimental results are also shown to verify the proposed circuit and analysis. Index Terms--Photovoltaic (PV), power conditioning, MPPT, Z-source inverter.

Compared with conventional field cooling (FC) and zero field cooling magnetization methods, pulsed field magnetization (PFM) is a promising way to magnetize high-temperature superconductors (HTS) with the advantage of dramatically decreasing the size and complexity of the electromagnetic charging system. The effects of the amplitude, width, and ramp rate of the pulsed current are reported. Transient responses of the HTS to pulsed magnetic fields are discussed and analyzed. A series of three pulses was found to be adequate to magnetize the HTS monolith with optimal trapped field if proper pulse amplitudes and widths are applied. Experiments verified that the trapped magnetic fields of HTS by PFM were comparable to those obtained by FC magnetization. Index Terms--High [T.sub.C] superconductors, pulsed current, pulsed field magnetization (PFM), trapped field.

This paper presents a novel control method to lower the harmonic components of the conventional voltage balancing control for the multilevel converters. The harmonic components in the voltage balancing control theory are analyzed in detail. A revised control method based on the line-line voltage redundancy of the three-phase inverter is proposed to lower the harmonic components of both the converter and inverter side. The proposed method can significantly reduce the harmonic components while keeping the switching frequency nearly the same. Simulation and experimental results are provided to show the validity of the theory. Index Terms--Multilevel converter, total harmonic distortion (THD), voltage balancing control.

This paper presents a low-cost approach to power factor correction (PFC) of single-phase diode rectifiers using a series active filter. Comparing with the traditional PFC, the proposed PFC has lower requirements of power device ratings, which leads to lower cost, higher efficiency, and lower electromagnetic interference. It also can eliminate the bulky inductor needed in the traditional PFC. The topology, operation principle, and application issues of the proposed PFC are analyzed in this paper. The control strategy is discussed in detail and simulation results are provided. A 1-kW prototype is built up and the experimental results are presented to verify the analysis. Index Terms--Adjustable-speed drive, heating, ventilating, and air conditioning (HVAC), power factor correction (PFC), series active filter.

The high installation cost is the major obstacle of the commercialization of the solid oxide fuel cell for distributed power generation. This paper presents a new low cost 10-kW converter system to overcome this obstacle. The proposed system consists of an isolated dc-dc converter to boost the fuel cell voltage to 400 V dc and a pulse-width modulated inverter with filter to convert the dc voltage to two split-phase 120-V ac. The dc-dc converter uses phase shifting to control power flow through a transformer with a metal oxide semiconductor field effect transistor full bridge on the low voltage side and a voltage doubler on the high voltage side. One IPM is used to realize the voltage doubler and the dc-ac inverter. Compared to the existing fuel cell converter systems, the proposed circuit has low cost, less component count, smaller size, and reduced dc-dc converter peak current. Simulation and experimental results are demonstrated. Index Terms--DC-DC converter, IPM, solid oxide fuel cell (SOFC), two split-phase, voltage douler.

Power flow control is important in power systems and recently becomes more urgent because of the deregulation and 2003 blackout. This paper presents a novel configuration of unified power flow controller. The proposed configuration has several unique features and advantages over the conventional configuration. As a result, cascade multilevel inverter can be used in the new configuration to lower the cost, volume, and increase the reliability of the system. Analysis and simulation results will be presented. Index Terms--Cascade multilevel inverter, unified power flow controller (UPFC).

A new type of multilevel inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection, but requires only one dc voltage source. This new inverter can operate as a seven-level inverter and naturally splits the power conversion into a higher-voltage lower-frequency inverter and a lower-voltage higher-frequency inverter. This type of system presents particular advantages to Naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9% (without filtering). Index Terms--Cascaded inverter, multilevel inverter, three-level inverter.

This paper presents a regenerative passive snubber circuit for pulse-width modulation (PWM) inverters to achieve soft-switching purposes without significant cost and reliability penalties. This passive soft-switching snubber (PSSS) employs a diode/capacitor snubber circuit for each switching device in an inverter to provide low dv/dt and low switching losses to the device. The PSSS further uses a transformer-based energy regenerative circuit to recover the energy captured in the snubber capacitors. All components in the PSSS circuit are passive, thus leading to reliable and low-cost advantages over those soft-switching schemes relying on additional active switches. The snubber has been incorporated into a 150 kVA PWM inverter. Simulation and experimental results are given to demonstrate the validity and features of the snubber circuit. Index Terms--EMI, PSSS, PWM, soft switching inverters.

A dual half-bridge (DHB) bidirectional dc-dc converter is a new proposed topology that has the advantages of decreased number of devices, soft-switching implementation, low cost, and high efficiency. Typical applications of this converter are the auxiliary power supply in fuel cell vehicles and battery charging and discharging systems where the power density, cost, weight, and reliability are critical factors. A switching-frequency-dependent state-space averaged model of the converter is developed here for either direction of power flow. This averaged model can be used to derive the steady-state characteristics and small signal dynamics of the proposed topology. It also provides a fast simulation tool to investigate the transient response of the converter. The simulated waveforms of the mathematical model are compared with the detailed circuit simulation to verify the accuracy of the modeling.

This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented. Index Terms--Auxiliary power supply, dc-dc converter, fuel cell vehicle, power generation, TDR, ZVS.