Analysis and Compensation of Phase Shift Errors of an Open-Loop Current Transducer Considering Eddy Current

Abstract

The open-loop current transducer comprises a magnetic core made of soft magnet material and includes a Hall sensor. Traction motors in applications such as electric vehicles tend to be driven at high speeds. It pushes the inverters to increase the fundamental frequency of the output current above 1 kHz. However, this high frequency current generates eddy currents in the magnetic core of the current transducers. They deteriorate the measurement data thereby resulting the amplitude error and the phase shift error. In this study, the errors of an open-loop current transducer due to eddy currents were analyzed through mathematical modeling and finite element method (FEM). Furthermore, the impact of the error on motor current control was studied. The phase shift error of the current transducer used in this study reaches 3.6 degree when the frequency of current was 1.5 kHz, resulting in about a 20% torque reduction during field-weakening operation at 200 kW, 22500 rpm. In order to correct the error, an online compensation method is proposed based on FEM simulation results. The phase shift error was verified through the experiments with an inductive load. The proposed method was also validated through the experimental results conducted for variable frequencies from 500 Hz to 1.5 kHz.