Offline Compensation Method for Current Scaling Gains in AC Motor Drive Systems With Three-Phase Current Sensors

Abstract

This article proposes an offline compensation method for current scaling gains in the AC motor drive systems with three-phase current sensors. Many articles have been presented about the current scaling gain compensations of inverters. Most of them can be adopted during rotations. Those were studied for two-phase current sensing. Applications, such as elevators and hoist cranes, generally measure three-phase currents directly using three current sensors in preparation for a fault in any one of them. In this article, we present a compensation method for a three-phase current sensing system. This article analyzes the effect of current scaling gain errors on the neutral current that is calculated with measured stator currents. Based on the analysis, a compensation strategy for the current scaling gains is presented. The proposed method is applicable only at a standstill. It can be used for initial commissioning since it works at a standstill regardless of whether the rotor is locked or not. The experiments that demonstrate the validity of the proposed method were carried out in an elevator system as well as a laboratory. The proposed method is simple to be implemented and it requires no additional hardware.