The switching of LLC converter becomes hard switching at the time of overload. In this study, we elucidated the mechanism of hard switching and the current path. The reason of hard switching is the commutation of magnetizing current to the secondary side. It is possible to make a judgement whether overload or not from the voltage value at the end of resonance. Voltage value can be obtained from the circuit constants. In this way, it becomes possible to judge the success or failure of soft switching from the circuit constants.

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A steady-state analysis of high frequency-link resonant (HF-R) full-bridge dc-dc converters for inductive power transfer (IPT) systems for automotive and industrial battery charger applications are evaluated in this paper. For transferring power efficiently via the sending and receiving coils in the IPT systems, the inverter and rectifier operations together with output filter arrangement and the resonant tank should be taken into account in under the soft switching condition. The steady-state characteristics of series (S)-type, series / parallel (SP)-type, and series / series (SS)- type resonant full-bridge dc-dc converters are demonstrated and compared on the basis of theoretical and experimental analyses, after which the power converter architecture suitable for IPT systems is discussed from a practical point of view.

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A mobile PV (photovoltaic) system using thin film solar cell is proposed at the first part of this paper. The system is suitable for an emergent power supply at shelters because of the lightweight and portability. At the second part, the efficiency of a boost chopper for each PV module using SiC MOSFET was measured and compared with the converters with Si MOSFET. Finally, prototypes of the boost chopper for each PV module using Si/SiC MOSFET demonstrated the operation with a PV simulator, which shows the converter with SiC MOSFET has an advantage when the irradiation is set to be relatively low.

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A small scale three-phase modular multilevel converter (MMC) system for laboratory study has been developed. A real-time digital simulator is used for the control system. The performance of STATCOM is evaluated in the MATLAB/Simulink software environment. Simulation results demonstrate that the MMC-STATCOM system is able to operate under unbalanced conditions.

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Interior Permanent Magnet Synchronous Motor(IPMSM) is widely used in many industrial applications and household electrical appliances because of its higher efficiency, higher torque density, and wide speed range. In recent years, there has been an increasing interest about motor design technologies that satisfies required specifications in industrial applications. Therefore, it is important to shorten the design period and generalize the method. The period is shorten by using coarse mesh Finite Element Method in this paper. This paper shows usefulness of Genetic Algorithm(GA) coupled with course mesh Finite Element Method for higher torque IPMSM structure.

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Conventionally, using soft magnetic composite in the motor is difficult because hysterisis loss is very large. However, the hysterisis loss of soft magnetic composite is improved in the present technology, so the improvement of efficiency is expected. In addition, iron loss in the PWM driving is greatly affected by the eddy current loss, so reduction of iron loss can be expected by soft magnetic composite which has the small eddy current loss. In this paper, influence on motor characteristics of multi-pole surface PMSM (SPMSM) by a soft magnetic composite and loss of the motor by the PWM drive are discussed. As a result, it is revealed that the iron loss was reduced by using soft magnetic composite in the normal driving range.

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This paper proposes inrush current suppressor using a matrix converter in wind power generation system with squirrel-cage induction machines. The output side of the matrix converter is connected in series to the induction machine through matching transformers. The reference output voltage of the matrix converter is decided by multiplying the induction machine current with the variable control gain. So the matrix converter is behaves as resistors for inrush current. Digital computer simulation is implemented to confirm the validity and practicability of the proposed inrush current suppressor using PSCAD/EMTDC. Simulation results demonstrate that the proposed inrush current suppressor can suppress the inrush current perfectly.

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In recent years, it is remarkable that the increase in power consumption of the consumers belonging to business sector. The consumers belonging the business sector has been introduced demand rate system, so the reduction of power costs by reducing the maximum demand value is noted. Therefore, understanding of the maximum demand value by the prediction of the demand value is important. The conventional prediction, there is method using a time series model, it is effective when there is a periodicity in the data. However, since the power consumption is greatly affected by external factors, using the time series model is difficult to predict. In this paper, we do prediction using a decision tree analysis can be considered the external factors. we focus on the correlation between the demand value data, and the temperature that has a high relationship to power consumption. We performed the power consumption prediction by applying the decision tree and evaluated the accuracy. As a result, it is possible to verify the change in prediction accuracy due to changes in the analytical conditions, and we investigated for improving the accuracy.

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The hybrid electric vehicle has been advanced for environmental problems. It is realized an improvement in fuel efficiency by balancing both the characteristics of an electric motor and an internal combustion engine. In our laboratory, the hybrid electric vehicle has been remodeled from a commercial engine vehicle. Authors are also advancing research that focuses on improving the exercise performance by using engines with two electric motors. The hybrid electric vehicle is a four-wheel-drive vehicle (4WD). Authors are aiming to achieve the method of traction control of 4WD. In order to suppress slip at the time of idling wheel, it is controlled the rotation speed of wheels by using both the mechanical mechanism of the center differential gear and characteristic of the electric motor (generator). The characteristic of this system suppress the rotation of the front wheel by using a generator as an electric motor when the front wheel slipping. Then, this generator is attached to the rear wheel’s output side of the transfer. Slip ratio is detected by using the rotational speed difference between the front wheels and rear wheels. In this paper, authors introduce the principle of the proposed methods and remodeling manufacturing process that was performed in order to achieve the traction control. In addition, it is reported the experiment results.

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This paper presents the non-isolated step-down (buck) type switched mode DC-DC converter prototype operating under a principle of advanced delta-sigma modulation processing circuit, which is based upon double stage cascade delta-sigma modulation strategy developed by the authors. The switching noise level reduction characteristics of the delta-sigma modulated DC-DC converter mentioned above are illustrated and discussed as compared with those of buck DC-DC converter prototype operating under the conditions of conventional carrier-based PWM one in addition to a one-stage delta-sigma modulation control scheme. Of these, it is particularly noted that the switching noise peaks vs. frequency characteristics of two-stage delta-sigma modulation processor-based buck DC-DC converter treaded here are more superior and effective from a practical point of view.

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This paper provides the high efficienncy middle-ca pacity Uninteerruptible Powwer System (UUPS) design and test results. This U PS is a doub le conversionn type UPS annd it has a trransformer-lesss design for three-phase three-wire lloads. Capacitty range of th is UPS is 100 0-225kVA and it achieves hiigh efficiency y 97.0% with bbidirectional switch neuttral point clammp topology ffor low voltagge. In additionn, UPS size is one of the smmallest in midddle-capacity UPS categoory. This midddle-capacity UPS can be built a parallel redundant UPS system. It provides hhigh quality power suppply and reliabiility.

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In recent years, various storage battery systems, such as home battery system, V2H/V2G system, and UPS system, have spread rapidly all over the world. We propose a new power conversion system for use in the previously-stated storage battery systems. This paper describes operation analysis of this system for bi-directional power conversion with fundamental grid-interconnection. Good output follow-up controllability characteristics of the proposed system are shown through computer simulation results.

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This paper proposes a fast parallel circuit simulation method for a power electric system by applying an explicit integration formula to selected energy storage elements such as inductors and capacitors. The forward Euler (FE) formula is applied to selected series inductors and parallel capacitors. Then an implicit formula such as the backward Euler (BE) formula is applied for stable numerical integration, and the optimum step size is selected for each subcircuit. A parallel processing method that utilizes thread processing techniques based on OpenMP application program interfaces with a multicore CPU and shared-memory system reduces its processing time. A new general algorithm based on a thread processing technique, a subcircuit memory processing technique, and a binary variable step size method is described to utilize numerical processing at each time step synchronously and efficiently. Then a new automatic partitioning method of a system into subcircuits is described. This paper also proposes how to process a PE system with a DSP-based digital control principle. The proposed method is applied to power electronic systems. It is investigated how the proposed method works and shown for effectiveness of parallel simulation by the circuit partitioning.

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Suppression of subsynchronous torsional interaction(SSTI) in electrical power system achieved with insertion of an inverter to transmission line in series. Active power of the transmission line is sensed and filtered by three sets of bandpass filters to get the torsional signal for feedback. The output signal of controller is converted to voltage reference signals for each phase by dq inverse transformation and the voltage reference signals are input to PWM control circuit to generate the gate firing signals for the inserted inverter. Simulation results show the control is effective to suppress the SSTI

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The full-bridge type bidirectional DC/DC converter is considered to be a promising topology for large capacity DC/DC conversion. Bidirectional DC/DC converter have two operation modes : Current-Mode and Voltage-Mode. It is well known that large surge voltage is generated at switching devices with current mode operation. The main factor of surge voltage is the leakage inductance of the transformer. The purpose of the study is the suppression of the surge voltage caused by the leakage inductance. In this paper we propose a novel control strategy which reduce the surge voltage of switching devices at current mode operation. Finally, experimental results of laboratory model which applied the new control strategy are presented, in which the reduction of surge voltage is realized.

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