Permanent magnet synchronous motors (PMSMs) generate torque ripple through the pulse width modulation (PWM) method of voltage source inverters. In this report, we propose a method to reduce torque ripple during overmodulation in asynchronous PWM. In asynchronous PWM, when the number of pulses decreases during high-speed rotation, three-phase voltage imbalance occurs and torque ripple occurs. By controlling the PWM pulse edge using trapezoidal wave modulation, seamless control from asynchronous PWM down to a single pulse can be achieved. The effectiveness of the proposed method was confirmed by its simulation and experimental results.

In this paper, the offset control of traffic signals is considered using GA. From a practical standpoint, we show results of research on the following issues: (1) shortening the search time, (2) deriving a leveled optimal solution focusing on the upward/downward traffic flow, and (3) examining the derivation method of a better solution. Furthermore, we report the efficiency of GA-neighbor searching method for optimal solution, and utility of a normalized ATT (Average Traffic Time) for the general evaluation.

This paper describes the verification of the transient response occurs on the primary loop used on DWPT system for the SCMaglev. The primary loop has long length, order of several kilometers, and high working frequency, near 10kHz. Therefore, the primary loop has both lumped and distributed circuit characteristics. We propose a simplified method to derive approximate transfer function, represents the lumped and distributed characteristics in desired frequency band. The frequency and transient response characteristics calculated by the transfer function are close to the results obtained from field tests.

This paper proposes a new position sensorless control method for permanent magnet synchronous motors based on current phase convergence. The basic idea of the proposed method is using the instantaneous power based on the p-q theory, which is used in reactive power compensators. The results show that the current phase in d-q coordinate can be estimated using the instantaneous power. Moreover, a new rotor position estimation method has been proposed and validated via simulations and experiments.

This paper deals with time-harmonic problems with complex symmetric matrices in the electromagnetic field analysis. To solve such problems more stably and quickly, the Product-type Krylov Subspace Methods based on the COCG and COCR methods are proposed, and verified in finite element analyses of the time-harmonic eddy current and high-frequency electromagnetic field problems. As a result, in some cases, the number of iterations and the computational time have been reduced.

The switching frequency of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) should be increased to maximize their benefits in power conversion circuits. However, the switching loss increases when the switching frequency is increased. Generally, the gate resistance is designed to be small to reduce the switching loss for one cycle. However, SiC MOSFETs have a higher parasitic gate resistance than Si power devices. This paper proposes reducing the switching losses by “overdriving” the SiC MOSFETs, in which the gate voltage V_g is designed to be higher than the rated gate-source voltage of the SiC MOSFET. The relationship between gate voltage V_g and switching loss is clarified both theoretically and experimentally. Additionally, the effect of “overdrive” on the long-term reliability of SiC MOSFETs is evaluated by conducting continuous switching tests. The results show that “overdrive” can maximize the benefits of SiC MOSFETs based on the expected lifetime of the power conversion circuit.

This article introduces Power Electronics Laboratory at Department of Electrical and Electronic Engineering, School of Engineering, Institute of Science Tokyo.