The Influence of the LC with Clamping Diodes dv/dt Filter on Current Control of PMSM Drives in Case of Inverter Output Current Sensing and Its Compensation

This paper presents effect of LC with clamping diodes dv/dt filter on current-controlled PMSM drives in case where 3-phase inverter output currents are measured and used in the digital control loop. In particular, this case can be reported in some cases. Firstly, power devices are equipped with integrated pilot current sensors. Secondly, PCB technology based Rogowski coils are installed in inverter leg with analog circuit to feed a signal to microcontroller. Thirdly, hall type current sensors are packaged in inverter output terminal through a bus bar. In those cases, it is inevitable to measure inverter currents because it is hard to move the location of current sensor. In this manner, the effect of filter resonance should be considered properly to control the motor current accurately because the measured inverter output current includes both motor and filter resonant current. If the resonant current of the filter is not compensated properly, it causes the DC offset of motor current which bring about the torque ripples. In order to compensate the offset, inserting a two stage Discrete Fourier Transform (DFT) is used and the calculated offset is subtracted from the sampled current. Judging by simulation and experimental results, it is confirmed that the compensation method eliminates the offset of the motor current effectively, and thereby reducing the torque ripple as well.