The main battery capacity of fuel cell vehicles (FCVs) is about one-tenth that of pure electric vehicles because the primary purpose of the FCV main battery is compensation of fuel cell output power response. The smaller battery capacity may cause regenerative braking to become disabled halfway through a continuous downhill (such as Hakone). Therefore, this paper proposes driving-points of the 1^st or 4^th quadrant on the d-q coordinate system. Unlike conventional high efficiency control, the driving-points are aimed at increasing traction motor losses as may be necessary in order to avoid hard use of the friction brake. This method realizes sufficient braking force without charging the FCV main battery by converting the braking energy into the traction motor and its inverter losses.

The Triple Active Bridge (TAB) DC/DC converter has attracted attention as a power converter for power distribution systems because it has a wide voltage range and bidirectional power transmission and electrical insulation capabilities. As a controller for the converter, the decoupling controller, which uses a front-end compensator, has been proposed. However, the controller design is difficult because the parameters of the compensator change in response to the interference that occurs depending on the operating point. This paper proposes an evaluation method of the interference using a current contour map and the trajectory on a phase plane. As a result, it was shown that the interference intensity is decided depending on the direction of the reference value on the contour map.

A novel prototype of zero-voltage soft-switching (ZVS) high-frequency resonant converter for inductive power transfer (IPT) applications is presented in this paper. By adopting a natural oscillation-based pulse-density-modulation (PDM) scheme, the resonant current of the sending and receiving coils can be continuously regulated under the condition of soft switching; thereby the parasitic oscillation and ringings inherent to the conventional burst-mode PDM can be eliminated effectively. The essential performances on the output power regulation and soft-switching operations are demonstrated in experiment using a class of the 400 W-500 kHz prototype, whereby the validity is evaluated from the practical point of view.

This paper studies a grid-tied inverter using a gallium nitride (GaN) device aiming for passive component size reduction through very-high-switching-frequency operation. This paper proposes to apply a discontinuous current mode (DCM), which does not require dead time and current feedback control that are usually required for a continuous current mode (CCM) operation. These features enable good modulation performance with a MHz-class high-switching-frequency operation without difficulties owing to the very high switching frequency. This paper reports experimental demonstrations of the DCM grid-tied inverter using GaN- high-electron-mobility transistors (GaN-HEMT) with 1-MHz carrier frequency and three different filter components. Output current harmonics and losses are discussed, and it is indicated that chip inductors are promising for DCM-operated low-power inverters.

This paper presents a multiple-input power converter. This converter features a simple circuitry consisting of a single power switch for a single power source, and its transformer core is capable of operating across the entire range up to the flux saturation level. This new converter has an operational constraint in order to avoid saturation of the transformer core. However, it has cost-performance advantage due to the simple circuitry.

We examine the iron loss properties of a nanocrystalline magnetic material (NMM) core excited by pulse width modulation (PWM) inverters with different semiconductors. We report the iron loss characteristics as a function of carrier frequency of the NMM ring core excited by two different inverters, which consist of a silicon-insulated gate bipolar transistor (Si-IGBT) and a gallium nitride-field effect transistor (GaN-FET). The iron losses of the NMM ring core under GaN-FET inverter excitation increase with the increase of carrier frequency owing to the ringing noises generated from the fast switching. However, the iron losses of the Si-IGBT-inverter-excited NMM ring core decrease slightly with increasing carrier frequency. We show that the iron loss properties of NMM ring core depend strongly on power semiconductor characteristics. In addition, to consider the ringing waveform in the NMM ring core by numerical simulations, we focus on a series RLC circuit model. We confirm that the numerical damped oscillation of the ringing calculated based on the series RLC circuit model is consistent with the experimental damped oscillation.

This paper proposes a DC magnetization prevention control in the zero-sequence-cancelling modular multilevel converter (ZC-MMC) as a buffer reactor-less MMC circuit topology. Using the leakage inductance of a zig-zag transformer, the transformer can function as a buffer reactor. By applying a zig-zag connection, DC magnetic flux caused by the zero-sequence DC current flowing through the transformer can be canceled. On the contrary, the core of the transformer is DC-magnetized when a non-zero-sequence DC current is flowing through the transformer. The transformer abnormally heats due to the magnetic saturation of the core caused by DC magnetization. To prevent DC magnetization, DC magnetization prevention control in ZC-MMC was proposed. Using a simulation model and 1-kW experimental setup, DC magnetization prevention control was confirmed.

In this paper, an output voltage accuracy improvement method for an asynchronous PWM inverter is proposed. This method is suitable for control conditions where the ratio of the carrier frequency to output voltage frequency is lower than 9. In such a situation, the inverter output voltage contains disturbance voltage composed of the beat component. The proposed method suppresses the disturbance voltage by adding a compensation term to the voltage command. The details regarding an analytic derivation method of the above compensation term is written in this paper. The validity of the proposed method is confirmed by computer simulation and experiment.

This paper investigates the influences of magnetic saturations of main and leakage fluxes for sensor-less vector control systems of an induction machine (IM) on static impedance characteristics using high-frequency voltage signal injection techniques. Furthermore, the amplitude characteristics of rotor slots are investigated by measuring the impedances of high-frequency components with respect to the rotor angle of the IM. The IM is vector-controlled with an ideal voltage source, and the stator impedances of the IM are evaluated from the amplitude ratios of high-frequency voltage to the current, extracted using fast Fourier transform analysis. As a result, the leakage flux saturation saliencies are obtained under the conditions of high-frequency and low-voltage levels, and it is confirmed that the impedance deviations for rotor slots increase under the same conditions as those for leakage flux saturations.

In 2011, planned blackouts were implemented in some areas because of electric power shortage. However, this problem could have been avoided if a system which controls power consumption had existed. Therefore, this paper proposed a new original system that controls domestic power demand. The proposed system controls home electrical appliances, and reduces the electric consumption independently. It is also able to operate effectively even if non-compliant appliances exist together with the system. Therefore, the system combines simplify and flexibility. In addition, we achieved “Power demand control without user's patience” by applying Weber's law. In order to verify the proposed system and algorithm, we built a testing system. As a result of experiments, the proposed system can provide control of the domestic power demand under not only electric power shortage but also popularization of green electric power.

We have proposed a driving method for both a three-phase permanent magnet motor drive and one-degree-of-freedom controlled magnetic suspension using only one three-phase inverter. The suspension winding is connected between the neutral-point of the Y-connected motor winding and the middle point of the voltage sources. Hence, the suspension force is actively controlled by the zero-sequence current. The experimental result showed that the vibration of the magnetic suspension increased under the loaded condition of the motor compared with that under no load. The vibration mainly includes the fundamental and 3rd components of the driving frequency, 1f and 3f. This paper focuses on the positioning accuracy improvement of this magnetic suspension system. We have found that the vibration 1f is caused by the detection error of the current sensor and the three-phase unbalanced resistance and inductance values, and the vibration 3f is caused by the PWM drive. To improve the positioning accuracy, we investigated both the current detection method and the observer-based voltage disturbance compensation. The experimental results demonstrated that these compensations improved the positioning accuracy of the magnetic suspension.

This paper proposes an energy storage system that combines multi-energy storage devices such as a LiB and an EDLC for the power-grid. The proposed control method divides the amplitude of the compensation power reference into the LiB and the EDLC to improve the converter efficiency. A 10-kW prototype system was designed and implemented to validate the proposed architecture and system performance. The experimental results demonstrated that the proposed control method effectively compensated for the power fluctuation from the renewable energy system. The performed simulation analysis confirmed that the proposed system reduced the losses in comparison with the conventional control method.

The switching speed of next-generation power devices based on wide-bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), are more than ten times those of conventional silicon insulated-gate bipolar transistors (Si-IGBT). This may increase the frequency range of electromagnetic noise produced by pulse-width-modulated converters. Further, the operating frequency ranges of noise filters are limited by the parasitic components of passive elements, so it is difficult to realize a high-frequency (HF) noise filter whose operating frequency exceeds several tens of megahertz. This paper proposes a novel and simple analytical method to calculate the winding stray capacitance of an HF three-phase common-mode (CM) inductor for the purpose of estimating its operating frequency range at the design stage. Results of measuring the CM impedance confirm that the proposed method can estimate the operating frequency range of an HF three-phase CM inductor while ensuring practically sufficient precision. Furthermore, the obtained results also show that the reduction in the number of turns does not always contribute to the enhancement of the operating frequency ranges of filter inductors.

This paper focuses on several DC circuit breakers applied to multi-terminal HVDC transmission systems (HVDC grids), investigates their requirements, and compares their circuit design. Several DC circuit breakers are designed to fulfill their requirements, and quantitatively compared under common specifications. The comparison reveals that their operation delay causes the increase in breaking current, resulting in the increase in semiconductor bulb devices and breaking energy. The number of semiconductor bulb devices is also influenced by the configuration of surge arresters. Comparison of lifecycle costs between solid-state and hybrid circuit breakers is also shown. The result shows that the solid-state circuit breakers tend to be low cost if the average current utilization rate is low.

This paper proposes a modulation method to eliminate the DC-offset in transformer current at changing operation modes, which are square waveform, five-level waveform, and square waveform with half of the DC voltage. In the proposed modulation method, the update of phase-shift angle is divided into two steps. From the experiment, the peak of the transformer current due to the DC-offset current is reduced by up to 28.6% compared with the conventional method.