This paper focuses on leakage inductances which are bigger than any other parasitic inductances, and studies arelationship between leakage inductance and surge voltage on isolated DC-DC converter. As a result, we confirmed that the mechanism of the surge voltage in current mode DC-DC converter is completely different from that in voltage mode DC-DC converter. Moreover, in voltage mode DC-DC converter, the mechanism of the surge voltage in Forward topology is different from that in Full-bridge topology. Additionally, this paper proposes the equation to bring a peak value of surge voltage and the practical snubber design technique for current mode DC-DC converters. Finally, the validity of the proposed equation and design technique is confirmed by experiments and simulations.

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Non-contact energy transfer system is one of the key technologies of the future electric vehicle charging system.Due to its low coupling coefficient compared to usual transformers, much effort must be applied to improve its efficiency.Especially, series or parallel resonant capacitors are usually applied to improve its rating utilization of the transformer. However,for electric vehicle applications, the relative position between primary and secondary coils can change; therefore, transformer parameters also can change. For that case, the fixed resonant capacitor cannot achieve the maximum efficiency. This paper proposes an active series compensator named MERS applied to the non-contact energy transfer system. The MERS works as aseries variable capacitor in an ac circuit; therefore, can achieve the maximum efficiency of the transformer by optimal equivalent capacitor. A control principle to achieve the optimal operation of the system is described. Experimental results with 1 kW model confirm the operation principle of the proposed method and can achieve a high efficiency off the transformer.

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In this paper we propose a novel chopper circuit topology incorporating series connection of buck and boost choppers. This circuit topology shows various characteristics according to the combination method of operating modes. In these many combinations, we research all operation modes in which the two MOSFETs are on and off at different time. Experimental results show variety of circuit operations by various combinations of operating mode.

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This paper presents a new soft switchingPWMnon-isolated high step-up boost DC-DC converter embedding an edgeresonant switched capacitor (ER-SWC) modular. The DC-DC converter treated here can achieve a high frequency ZCS turn-on and ZVS turn-off operations in active switches and minimization of a reverse recovering current due to ZCS in the freewheeling diode under DCM including CRM operation of input inductor DC current. First of all, detailed operation characteristics and voltage step-up ratio of the proposed soft switching boost DC-DC converter are presented by means of theoretical analysis. For demonstrating the effectiveness of the converter and analysis, a 1[kW]-40[kHz] laboratory prototype is evaluated in experiments, then performances of the converter are discussed from a practical point of view.

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Reduction of switching losses of PWM inverters which are widely used is important to improve their efficiencies.This paper proposes a reduction technique of number of switching times in three-phase PWM inverters. It is based on careful selection of switching vectors in the space vector map, considering their differences which correspond to number of switching times. This is reduced to a simple rule to admit only one-phase for one switching to eliminate unnecessary switching. This rule is equivalent to a rule map among switch vectors on the space vector map. It reduced number of switching times to 2/3 in a 2-level inverter. It is a generalized form of the two-phase modulation method. Furthermore it includes the one-phase modulation method as a special case. The proposed method can be applied also to 3-level inverter.

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An IH cooking heater should have high efficiency heating and accept all metal pans. In order to develop the high efficiency induction heater for all metals, it is necessary to analyze magnetic characteristics of the working coil of IH cooking heater. However such an analysis has not been discussed until now. This paper presents a magnetic analysis for high efficiency induction heating, which can heat not only iron pans but also aluminum pans. The heating performance of IH cooking heater which heats both iron and aluminum pans is discussed with the analysis result of magnetic flux and eddy current distribution.

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[in Japanese]

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This paper proposes a half-bridge inverter based Active Power Quality Compensator (APQC) for electrified railways. The proposed APQC is composed of three-leg structured power switching devices with two DC capacitors. The first-leg is connected to β-phase feeder, and second-leg is to β-phase feeder. These two legs perform a half-bridge inverter based APQC, compensating the reactive, unbalanced active and harmonic currents on two feeders. The third-leg is used to balance two DC capacitor voltages. The basic principle of the proposed half-bridge inverter based APQC is discussed in detail. The validity and excellent practicability of the proposed APQC is confirmed using PSIM software. Simulation results demonstrate that the balanced source currents with the unity power factor are obtained on the primary side of the Scott transformer in the traction substation systems, balancing two dc capacitor voltages.

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The reduction of atmospheric CO2 is the greatest subject for the organism on earth. The application of electric energy instead of fossil fuels to advanced transportation is effective for reduction of atmospheric CO2. This paper describes some proposals of challenge of applying power electronics to realize oil-less vehicles such as EVs applied full regenerative braking system.

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The advantages of the variable speed drive of jet-fans have been known from more than twenty years ago. But at present, all jet-fans of the world have been driven at constant speed by the utility power sources. This is because, to realize the induction motor drive through the long cable, some difficult problems must be solved. These problems are the switching surge problem, the EMI problems and the leakage current problems. To solve these problems, we got the sponsorship of the government (MLIT) and started the developments in 2007. And in 2010, we put the variable speed drive of jet-fans into practicaluse. In this paper, the principle of the inverter system for jet-fans, and test results on the actual road tunnel will be presented.

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This paper presents a new LLC multi-resonant DC-DC converter with a reverse resonant LC filte.The proposed DC-DC convert ercircuit can improve the sensitivity of voltage conversion ratio in the step-down area,and then achieve the high performance on output voltage and power regulation by PFM under soft switching conditions.The proposed DC-DC converter can achieve a high frequency Zero Voltage and Zero Current Softswitching (ZVZCS) turn-on and Zero Voltage Soft switching (ZVS) turn-off operations.The theoretical analysis and simulation results of the proposed DC-DC converter are described.Then,the characteristics on the voltage conversion ratio and output power reguration of the conventional LLC resonant DC-DC converter and the proposed DC-DC converter are compared,and the advantageous features in the proposed DC-DC converter are clearly demonstrated.

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This paper presents a soft switching PWM non-isolated boost DC-DC converter embedding an edge-resonant switched capacitor (ER-SWC) modular. The DC-DC converter treated here can achieve a high frequency ZCS turn-on and ZVS turn-off operations in active switches and minimization of a reverse recovering current in the freewheeling diode under DCM including CRM operation of the input DC current. In this paper, the soft switching operating range is described in connection with the output power range as well as the practical design procedure for the circuit parameters.For demonstrating the soft switching operations in detail, a 1[kW]-44[kHz] laboratory prototype designed in accordance with the guideline is evaluated by experiments, then actual performances of the proposed DC-DC converter are discussed from the practical point of view.

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The design of the conventional LC filter has now all depended on trial and error. Therefore, the parameter designdŒsn’t meet our demands. To cover this issue the genetic algorithm is applied.This paper addresses LC filter design in PWM inverter of discrete-time model following control. A multiple-objective geneticalgorithm is used to benefit from computing. The pareto-optimal solution of LC filter is obtained. This algorithm has less possibility to be a local minimum. The pareto ranking method is used for adaptability of genetic algorithm. The validity ofanalysis is demonstrated by the comparison of resistance load to rectifier load. It suggests that the multiple-objective genetical gorithm is practical to optimize a parameter.

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The DC-DC converters are used for a lot of applications, such as HEVs (hybrid electric vehicles) , EVs (electric vehicles) and DC-power grids. However, on the other hand, the DC-DC converter requires further improvements in conversion efficiency, cost and size. There are mainly three types of hard switched DC-DC converters: buck, boost and buck-boost (a single switch-type and a double switch-type) . Comparisons of losses (conduction losses of the switching power devices, and an inductor loss) in these DC-DC converters have been reported. However, as far as the authors know, there has been no comparison of the switching losses in the buck-boost DC-DC converters. Therefore, in this paper, the authors describe a comparison of the switching losses in various DC-DC converters with a simple analysis and computer simulation.

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Although motors that use rare-earth permanent magnets typically exhibit high performance, high costs and concerns about the stability of raw material supplies are leading to their decreased production. However, the performance of such motors is not easily matched without the use of rare-earth permanent magnets. This paper proposes and examinesa permanent magnet assisted synchronous reluctance motor with ferrite magnets that has the same power density as rare-earth permanent magnet synchronous motors. A suitable rotor structure for high torque and high power is also discussed considering demagnetization and mechanical strength.

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