Development of High-Precision Efficiency Measuring Device for High Power Motor Drive Systems

Abstract

In recent years, in the field of power electronics, especially for automobiles, railways, aircraft, etc., the miniaturization and high efficiency of inverters that are the main components of motor drive systems have become important issues. The switching frequency of inverters equipped with wide bandgap power semiconductors typified by SiC and GaN has been increasing steadily, and higher precision power measurement is required for the efficiency measurement of input/out power and conversion across a broader band more than ever before. In particular, although the output power of inverters driving motors includes a switching frequency and its harmonic components, there has been no measuring instrument that can measure these signals accurately until now.

The newly developed current sensor is a manifestation of advanced technology involving winding and magnetic core that achieve a broad band, improved noise resistance performance and common mode rejection ratio (CMRR) via a shield structure, and a magnetic balancing circuit technology that realizes high precision linearity. Through this fusion of technologies, we achieved a very wide measurement bandwidth of DC to 1 MHz (−3 dB) for measuring a large rated current of 2000 A. We also developed a highly accurate measurement system to measure the efficiency of motor drive systems with high precision by incorporating a current sensor phase shift function via a wideband current sensor and power analyzer. As an actual measurement example, we will introduce the measurement results of the motor drive system, and show the effectiveness of the newly developed measurement equipment.