In a DC traction power supply system, the overload setting value of a DC circuit breaker is conventionally decided by a 130% value of monthly maximum value of traction load. In this paper, a novel method to derive the overload setting value by statistical calculations of the loads is proposed. It was confirmed that the proposed method can provide a more reasonable threshold value in some traction substations.

Sensorless control based on a pattern matching method is proposed for interior permanent magnet synchronous motors (IPMSMs), which have non-sinusoidal inductance spatial distribution at a standstill and very low speed regions. By using the pattern matching method, closed-loop-position sensorless control is possible for IPMSMs even under the heavy load condition, but atypical position error occurs. A previous study examined why position control errors are generated in the pattern matching method.

This paper presents three improvement methods for the position control error by considering the cause of the position control error. In addition, characteristics of each proposed method are clearly explained, and their effectiveness is presented by simulation and experimental results.

This paper proposes a new V/f control method for permanent magnetic synchronous motors (PMSMs) without a position sensor. The proposed method uses state feedback control based on an n-t coordinate system, and controls rotational speed and the voltage amplitude. The t-axis is a tangent line of a constant voltage ellipse, and the n-axis is a normal line of the ellipse. The t-axis current is utilized to place the poles of the transfer function at the desired position at low speed and high speed conditions. The effectiveness of the proposed method was verified by simulation and experimental results.

To improve the resolution of a magnetic absolute encoder, we propose a new magnetic encoder with an eccentric structure. Since the proposed magnetic encoder consists of only one eccentrically rotating multi-pole magnet and four Hall elements, its structure is very simple and cost efficient. By calculating the absolute offset by combining the look-up table and least squares method, it is possible to calculate the absolute angle even when a multipolar magnet is used for resolution improvement. Furthermore, since the quadrature signal can be calculated, it is possible to configure the converter using the conventional method, and it is very versatile. Experimental results show that the proposed method can achieve both improvements of accuracy by increasing the number of pole pairs and calculation of absolute angle.

A segment type switched reluctance motor (SRM) has been proposed herein, with the aim of high torque density and low level vibration and acoustic noise. A 4-phase segment type SRM is designed and constructed for reducing the large torque ripple of the 3-phase one. The torque ripple and efficiency characteristics are measured by using the test machine and a full bridge type drive system. The torque ripple is reduced from 200%, of the 3-phase SRM, to approximately 40%. Furthermore, performance characteristics under unipolar excitation as well as bipolar excitation are compared.

This paper proposes a technique to reduce capacitor currents in the dc link of PWM double inverters with current sensors in series with low-side switches. In the proposed technique, the phase difference between carrier signals in each inverter of the PWM double inverters is set to 180 degrees, and the voltage references of double inverters are shifted in accordance with the difference between the voltage reference of the medium value and that of the minimum value. The conventional and proposed technique are compared using the experimental results. Compared to the conventional technique, the proposed technique can reduce capacitor currents in the dc link of double inverters, while maintaining the harmonics of the inverter output current.

This paper proposes a compensation method for the non-liner error of the transmission power caused by dead-time in a dual active bridge (DAB) converter with three-level operation including zero-voltage phase. The non-liner error of the transmission-power is compensated by using three-level operation. From the experimental results, the error of the transmission power caused by dead-time is reduced by 78.9%.

This paper proposes a PWM control strategy for a three-phase induction motor (IM) drive using a dual current source inverter (DCSI). This DCSI can drive IM with parallel connected CSIs, which consist of three legs with six switching devices. In DCSI, one of the CSI circuits generates the torque current component by using the reference PWM pattern, and the another outputs the exciting current component produced by employing a phase-shifted PWM pattern. The experiments prove that the proposed DCSI with a dual PWM pattern can drive IM by using only a single DC power supply.

Our research interests include cell equalizers for energy storage systems, differential power processing converters for photovoltaic panels, multiport converters, etc. Students are actively involved in their respective research projects to improve and strengthen their skills everyday. For more details, please visit our laboratory website (http://pel.ee.ibaraki.ac.jp/index.html).