Today, vector control of induction motors is used considerably in variable-speed drives. In vector control, high performance is realized by decoupling the magnetizing current and the torque current of the induction motor. If the conventional state-equation is used directly for decoupling, the physical operation of the induction motor is difficult to understand from the decoupled state-equation. This is because, in the conventional state-equation, the physical meaning of the coupled terms are not easily discerned. In this paper, we propose a new state-equation using matrix theory whereby the physical meaning of the coupling terms are easily discernable. In addition, decoupling control and current controller design using this new state-equation, are given.

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In order to reduce the interference of the current harmonics in the DC power feeding line to the advanced tram control signaling system, the level of the current harmonics is strictly regulated. Hence the consideration of the harmonic current in the design stage becomes very important. Based on this situation, we have carried out a current harmonics simulation conformed to the real train system by SIMULINK/MATLAB, In this paper, the methods of the SIMULINK description and of the harmonics calculation, and the simulation results in the transient condition as well as in the steady-state one are described. The theoretical analysis of the simulation results is also described.

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PV system output, reflecting irradiation conditions, changes every second. A large number of grid connected PV systems are understood to generate output fluctuations substantial enough to adversely affect utility power quality. Thus the PV system need to have the output fluctuation smoothing system with charge/discharge equipment.
This paper introduces the structure of charge/discharge apparatus equipped PV systems, and describes test results on PV module-scale systems. Effectiveness of the system will be proved.

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In the field of switching power supplies, various Zero-Voltage-Switching (ZVS) circuits have recently been proposed for the reduction of EMI noise. The authors proposed a novel ZVS DC/DC converter of constant frequency PWM control with clamping the device voltage to a DC bus line. Moreover, we proposed a novel Power Factor Correction (PFC) circuit of ZVS operation that is synchronous with the DC/DC converter without using any auxiliary switches. The proposed converter realized high conversion efficiency, high power factor, and low conducted EMI noise.

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The idea to supply several levels of power quality to loads is discussed in this paper. One possible and simple circuit, which enables us to deliver different power quality level to single-phase loads, is proposed. The system can supply three levels of power quality to single-phase loads by use of three-phase four-wire ac system, one inverter and secondary batteries. Performance of the proposed system was verified by simulation results.

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In Japan, we should set up Islanding Protection System when a power-supply unit is connected with grid. It is the equipment detecting whether for the sending off breaker of the substation to be shut and to have become Islanding. we developed Islanding Protection System for a synchronous generator. It uses “Q Control Mode Frequency Shift” method. we are examining the application of it to the inverter. We confirmed the simulation by which it was applied to the inverter was done and it was effective.

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A great deal of research and development work has been done on electric vehicles (EVs) and hybrid electric vehicles (HEVs) in recent years. As a result, EVs and HEVs have been greatly evolved for latest 30 years. Their performance has been improved to 3 or 4 times. Why do they have got such a good performance? A look at the course of research over the years shows that the reason is significant progress in power electronics technologies. In order to spread EVs and HEVs, the technologies will become more important in the future

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Photovoltaic power generation technology (PV) is expected as a promising means to keep the national energy security and solve the various ecological and environmental issues in the future. In this situation, power electronics technologies may have a chance of great contribution for cost reduction and improving performances of PV system to 21st Century, because PV system is composed only from full solid state technologies.

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People with slight disabilities on motion capability can be active in daily life using properly designed motion-assisting devices. Using these devices in various cases would help them as rehabilitation in a broad sense. We developed a robotic orthosis capable of helping human motion by forearm. This orthosis was carefully designed such that mechanical safety for human beings could be ensured. A control scheme for power assistance and motion guide is proposed. The performance of the control scheme is examined by several experiments.

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