In general tachometer generators are used to calculate the train running distance in the case of on-board systems. However, this calculation requires the compensation of errors caused by wheel skids and slips. Therefore, we propose a method that combines tachometer generators and inertial sensors to calculate train running distances for communications-based train control systems. As COTS inertial sensors are necessary to reduce initial costs, it is impossible to rely on only inertial sensors. Hence, in order to use lower-precision sensors, it is necessary to minimize the compensation duration. In the proposed method, compensation with inertial sensors is applied only in the case of wheel skids and slips. To realize this requirement, not only a compensation process but also a detection process of the changing condition between the tachometer generators and the inertial sensors is introduced in the proposed method. Simulation analysis results obtained using managed time-stamped data show that it is possible to apply this method to lines having gradients and curves.

The torque feedback control method has been proposed as a control method in the weakening flux region for interior permanent magnet synchronous motors (IPMSM). When applying this control method to the two-level inverter system, a method for determining the voltage margin method has not been studied. In addition, an analytical design method has not been studied. In this paper, a method to design control gains is proposed for the already proposed control feedback method by means of the linearized method. Furthermore a method to determine the voltage margin to secure the torque control performance is proposed. This method is verified by experimental tests with a 1-kW motor system.

In this paper, a power decoupling method for a neutral point clamped (NPC) single-phase AC/DC converter using neutral point voltage control is proposed. In general, single-phase AC/DC converters employ bulky electrolytic capacitors at the DC link in order to smooth the ripple power with twice the utility frequency. The bulky electrolytic capacitor leads to an increased system size and shortens its lifetime. In order to solve these problems, some active power decoupling methods have been proposed. Conventional power decoupling methods absorb the ripple power by using a small film capacitor. However, additional magnetic components are required to realize these methods. The proposed control method uses a T-type NPC circuit with a small film capacitor and decouples the ripple-power with neutral point current control. Hence, the proposed method does not require an additional magnetic component as compared with the conventional methods. The effectiveness of the proposed method is proved using an 800W experimental setup.

A multi-level inverter with a full-bridge clamp circuit is proposed for single-phase three-wire (1P3W) utility connected applications such as PV systems. The proposed inverter consists of two n-level inverters and a full-bridge clamp circuit. The proposed inverter requires only 12 controllable switches to obtain a five-level output voltage even though conventional multi-level converters with the grounded neutral point of the DC-bus require 16 switches. The control strategy for the proposed circuit is also discussed in this paper. The proposed circuit was confirmed to satisfy the FRT (Fault Ride Through) requirements. Finally, in the event of a load unbalance during self-sustained operation, the experimental results confirmed that the grid voltage maintained a balanced state.

In this paper, a method that uses Space Vector Pulse Width Modulation (SVPWM) for reducing the load neutral point potential variation of a three-level V-connection inverter is proposed. In the proposed method, by selecting the vectors that have low load neutral point potential to generate the output voltage command value, the variation range of the load neutral point potential of the V-connection inverter can be reduced. In addition, the load neutral point potential variation influences the magnitude of the load's common-mode leaked current. Moreover, this leaked current is dominant in the generation of conduction noise. Therefore, by reducing the variation range of the load neutral point potential, the proposed SVPWM can be considered capable of reducing conduction noise. Then an experimental comparison of the load neutral point potential variation of the proposed method and the conventional method is analyzed. The results confirm the effect of reducing the load neutral point potential variation by using the proposed method.

A problem in AC-fed railway vehicles is the ripple of the DC-bus capacitor voltage owing to the single-phase power supply. Therefore, beat-less control is required to compensate the effects of voltage ripple in order to obtain smooth torque of the traction motors. This paper deals with a torque current ripple detecting type phase angle modulation beat-less control system for AC-fed railway vehicles. It is difficult to design the control constants theoretically without simulations because of the complexity and nonlinearity of this control system. Therefore, the stability analysis is conducted to establish the design method of this beat-less control system.

The relationship between “surge impedance”, which is defined as the ratio between the maximum transient voltage and current in a time domain, and “impedance” in the frequency domain is discussed based on a set of measured transient responses of an earthing circuit in a traction substation. The frequency characteristics of the results are numerically determined using linearized Laplace transform (LLT). The results indicate that the rise time of the injected impulse current is a key parameter that determines the relationship between the surge impedance and the impedance in a frequency domain. The investigation shows that the surge impedance which can be easily obtainable in a field test is useful for characterizing the transient grounding characteristic by appropriately utilizing the relationship.

The trend in a drive system for dump trucks used in the mining industry is moving away from a mechanical drive system toward an electric drive system because of the increasing efficiency of mining operations. Therefore, an AC drive system for mining dump trucks has been developed. Dump trucks are decelerated by an electrical brake and stopped by a mechanical brake. Dump trucks should be decelerated to a low-speed range by the electrical brake to prevent wear of the mechanical brake. However, the motor torque of dump trucks has to be adjusted in accordance with traveling conditions because they affect the deceleration characteristics of dump trucks. Therefore, a method has been developed for estimating a torque that balances with the slope of a road and controlling the speed of dump trucks in a low-speed range by an electrical brake. The effects of the method have been evaluated using simulations.

This paper proposes a small packaging technique of an iron converter for iron and steel drive system. First, the following measure is applied to decrease the circuit inductance in order to remove the snubber circuit. A smoothing capacitor is moved near an Insulated-Gate Bipolar Transistor (IGBT) unit by splitting the capacitance of a capacitor. A clamp diode is inserted between two IGBTs, and the common-bus is widened. Thus, the opposite effect becomes large, and the inductance decreases. Second, we propose a structure to maintain the current balance for many IGBT units to satisfy the converter capacity. By using these measures, the proposed structure decreases the circuit inductance to 67% that of the conventional one, and the current balance ratio become less than 13%.

The Cockcroft-Walton (CW) circuit, which is well known as a high step-up rectifier, is used in a lot of systems. It is considered that the boost ratio of the circuit decreases according to the load current and the diode junction capacitor. In addition, it is necessary for these rectifiers to use some power factor correctors. This paper investigates the circuit which adds an input inductor. The proposed circuit is focused on LC resonance between the input inductor and the diode junction capacitors. It is numerically and experimentally clarified that the LC resonance improves the boost ratio and the power factor.

In this study, we examined a method of directly molding a bounded magnet into a rotor core and the optimum magnet shape design of an interior permanent magnet synchronous motor (IPMSM). We realized the same size and torque as a conventional IPMSM using a sintered rare-earth magnet.

This paper provides an intensive discussion on a modular multilevel cascade conversion system based on double-star bridge cells (DSBCs), which is referred to simply as a DSBC conversion system. This conversion system is defined as a power conversion system consisting of multiple DSBC converters and medium-frequency isolation transformers. A voltage fluctuation appearing across the floating dc capacitor of each bridge cell is investigated. Theoretical and numerical considerations regarding both circulating currents and the medium frequency lead to a reduction in the peak-to-peak voltage fluctuation. The system is therefore applicable to a wide variety of motor drives with small capacitors. Simulated waveforms verify principles of operation, which are obtained from the 6-kV, 5-MW system consisting of a single DSBC converter for grid connection, two DSBC converters for three-phase star-connected RL loads, and two 560-Hz transformers for galvanic isolation among the grid and the loads.

This paper provides a theoretical and experimental discussion on a modular multilevel triple-star bridge-cell (TSBC) converter with focus on mitigating the capacitor-voltage fluctuation contained in each bridge cell. This paper assumes that the TSBC converter drives an interior permanent magnet synchronous motor rated at 75Hz loaded at the rated torque. A new control method proposed in this paper is characterized by properly superimposing both common-mode voltage and circulating currents in the whole speed range from 0 to 75Hz. Moreover, this paper optimizes the amplitude and frequency of the superimposed common-mode voltage with the help of theoretical analysis, thus resulting in minimizing the voltage fluctuation. This optimized control method can reduce both the voltage fluctuation and the cluster-current amplitude to values below those of existing methods. Experimental waveforms obtained from a three-phase downscaled model verify good start-up performance from a standstill to the rated speed.

This paper proposes a halt sequence for a matrix converter to overcome the over-voltage and over-current problems in the case of system failure during regeneration. A short-circuit operation is performed in order to prevent the regenerating current from flowing into the snubber capacitor. In addition, the motor current is then interrupted the current by the natural turn-off of the freewheeling diode at the current zero-crossing point. The experimental results demonstrated a rise in the snubber voltage that was less than 10% of the rated voltage.

Traditional energy storage systems having lithium-ion battery cells or electric double-layer capacitors (EDLCs) connected in series require a separate charger and cell voltage equalizer. To simplify these energy storage systems, in this paper a transformer-less pulse width modulation (PWM) buck converter integrating a cell voltage equalizer using a voltage multiplier is proposed. The switch count is only two in the proposed converter because of the switchless voltage multiplier. An inductor in a conventional PWM buck converter is replaced with two inductors in the proposed converter in order to produce square wave voltage with an arbitrary amplitude, by which the voltage multiplier is driven. A charge-discharge cycling test using the prototype for three EDLCs connected in series was performed, and the results demonstrated the integrated functions of the proposed converter.

Ph.D. candidates of Power Electronics in Japan (PPEJ) has been established by young engineers, especially Ph.D. candidates of Power Electronics in Japan. The aim of our social group is to enhance research activities related to Power Electronics technologies from the viewpoint of young engineers. Through some events, such as gathering meetings with international Ph.D. candidates, laboratory tours to international research institutes, we are trying to activate Power Electronics Society in Japan.