This paper proposes a zero voltage switching (ZVS) method for a bidirectional isolated DC to three-phase AC converter with an indirect matrix converter. The phase shift control method is applied to a primary side converter and a secondary side converter to achieve ZVS and to generate a zero voltage period at the DC-link. A grid current is controlled by the three-phase converter with pulse density modulation based on delta-sigma modulation. From the experimental results, the proposed method reduces switching losses of the whole converter with the bidirectional operation. It is confirmed that the prototype circuit achieves a maximum efficiency of 95.0% with the discharge and charge mode. In addition, the grid current total harmonic distortion is lower than 5.0%.

The output power of solar panels may decrease by degradation due to long-term usage and surface contamination. Methods to detect these problems are necessary for photovoltaic generation to be more widespread. AC impedance methods are used for electrochemical devices to inspect the inside situation of solar panels. In this study, we applied an ac impedance method to solar panels, which have some merits compared with the traditional methods. We added a small ac signal to the duty of a dc-dc converter to implement the ac impedance method. The small ac signal was a white noise generated by a pseudorandom binary sequence (PRBS) such that many frequency points can be measured simultaneously. Unlike traditional methods, this method can examine the solar panels when they are generating power. We measured shaded and nonshaded solar panel impedances and compared with the experimental results. From the results, we can show the potential to distinguish the shaded panel or the unshaded panel based on the difference of the impedance characteristics.

Since smaller thermal-resistance design is indispensable for automotive IGBT modules, the double-sided cooling power module and stacked cooler have been developed. However, it has not known that the FS-IGBT played an extremely important role in exquisite combination of. Therefore, we have reviewed the bottlenecks from the viewpoint of the power semiconductor chips in the power module, named as “Power-Card”, followed by the basic functions the chips should have. Further, we have recognized that the paradigm shift from “Power semiconductor device first” to “Power module first” has strongly pushed forward realization.

This paper describes the low voltage ride through (LVRT) capability of STATCOM using a star-connected modular multilevel converter (MMC). Under unbalanced grid conditions, the phase differences between each phase voltage of STATCOM are not 2π/3. In this case, the dc capacitor voltages diverge without a suitable control against the fault. In this paper, a LVRT control using zero sequence voltage injection is proposed to control the phase differences of the STATCOM output voltages to 2π/3. The proposed control method is verified experimentally.

This paper presents a bidirectional converter with multi-stage FETs featuring voltage balance control function using variable capacitors. The proposed converter is constructed using low-voltage Si-FETs in a series connection, and it improves the voltage balance between the drain-source voltages of the series connected FETs in the OFF period. Using the converter figure of merit (FOM), which can estimate the converter losses from the specifications of the FETs, the effectiveness of the proposed converter is compared to that of a converter using SiC-FETs. The factors of the voltage unbalance are analytically clarified using the equivalent circuit. The principle of voltage balance control function using the variable capacitor is discussed. The experimental results show that the proposed converter can achieve a maximum power conversion efficiency of 99.2%.

This paper proposes a control method for a dual active bridge (DAB) converter, which achieves both a reduction in the non-linear transmission power error due to the dead-time and a reduction in the inductor current with a three-level operation. The non-linear transmission power error is compensated by designing a zero current period in the inductor current with the three-level operation. In addition, an inductor current reduction method for the three-level operation is also proposed. In the non-linear transmission power error compensation method, the inductor current is reduced by suppressing the circulating current by considering the zero-current period to be the dead-time. The validity of the proposed method is confirmed using a 2.0-kW prototype. The experimental results show that the transmission power error is reduced by up to 85.1%. In addition, the inductor current is reduced by up to 64.1% and the loss is reduced by up to 58.6%. Moreover, the DC offset is eliminated by utilizing the voltage polarity reverse phenomenon in the voltage control.

Servo drive motor systems using PWM inverters have become very popular in the industrial market owing to their excellent control over torque, speed and position. Recently, problems of EMI noise and complexity of wiring from 3-phase PWM inverter power line cables have become critical issues in factories. In addition, using the regenerative energy of a motor has become important. A DC bus system can be a solution to these problems and demands. However, the DC bus system for servo drives has a risk of system instability because of interference between the DC bus and the servo drives. In this paper, an impedance-based stability analysis method is proposed that can predict the stability by only using the I/O (impedance) characteristics instead of all the system properties. The experimental results show that this method is useful.

We examined the application of the pulse density modulation (PDM) method to a high-frequency voltage-source inverter for dielectric barrier discharge (DBD). The inverter consists of a full-bridge inverter, step-up transformer, and resonant circuit, and the high-frequency output is supplied to a pair of dielectric electrodes. It is characterized by applying the PDM method to inverter control, and burst controlling the inverter. In this paper, we first describe the specifications and circuit configuration required for a high-frequency voltage-source inverter. Next, we describe the concept of burst frequency setting as a new parameter and the method of constructing a pulse-generating circuit. Finally, a discharge test by prototype inverter is carried out, and it is demonstrate that discharge is stabilized by using PDM.

Firstly, this paper reconstructs a dynamic mathematical model of synchronous reluctance motors (SynRMs) with magnetic dq-cross coupling. This model consists of three self-consistent basic equations of circuit, torque evolution, and energy transmission equations. Secondly, based on the model, this paper reveals analytically that for the SynRMs, there always exists a reference frame called “magnetic salient-pole reference frame” where no magnetic axis-cross coupling occurs, and that the mathematical model in the frame turns out to be formally identical to the ideal one without dq-cross coupling in the dq-synchronous reference frame. Thirdly, this paper proposes new design and realization methods for a current controller, command converter for efficient drive, and salient-pole phase estimator for the SynRMs. The proposed methods perform all the necessary operations in the magnetic salient-pole reference frame instead of the dq synchronous reference frame, and they could achieve high performance and simplicity. The effectiveness and usefulness of the proposed methods are verified through extensive numerical experiments.

A vector control method is necessary for high-efficiency and/or wide-range operations of induction motors. The method requires the phase of the rotor flux, which can be estimated by using the stator and rotor resistances. However, the error between the actual and estimated resistances causes rotor flux estimation error and consequently deteriorates the performance of the vector control. Generally speaking, the influence of the stator resistance error decreases as the speed increases, but not for the influence of the rotor resistance error, which is dependent on the speed. One of the approaches to cope with this problem is to provide the vector control system with robustness against resistance variation. This paper proposes a new slip-frequency vector control method to achieve high robustness to rotor resistance variation; this method has a simple structure similar to simple as the conventional slip-frequency vector control method. The effectiveness and usefulness of the proposed method are verified through extensive experiments.

The paper reports a sprout of 3-degree-of-freedom (DOF) control. The limitation of feedback control including 2-DOF control has been raised for a long time; however, a suitable control theory for overcoming those limitations has still not been formulated. An underlying reason is that the disturbance-suppression performance and noise sensitivity cannot be decoupled. Several researches have tried to tackle this problem using a hardware approach, as a noise level depends on a hardware configuration. It should be noted that the hardware design expands spatiotemporal resolution of a system. This approach helps in reducing noise, namely, it works as the 3rd-DOF for a control system. Therefore, an improvement in the hardware design could be a new angle for solving a mixed-sensitivity problem. This paper quantitatively presents the relation between noise-reduction performance and the spatiotemporal resolution, and provides a foothold for the 3-DOF control.

The reason behind current sharing imbalance natural graphite grade brushes/steel slip-ring systems is clarified in this paper, by introducing the theory of heavily saturated V-I characteristics.