Analysis and Compensation of Sigma-Delta ADC Latency for High Performance Motor Control and Diagnosis

High performance motor control and fault diagnosis requires high resolution isolated signal measurement. Sigma-delta ADCs (SD-ADC) are ideal for this purpose but cause remarkable measurement latency which can cause performance degradation and stability issues. In this paper, the effects of current measurement latency caused by a sigma-delta filter module (SDFM) and corresponding latency compensation are discussed in detail. First, the effect of SD-ADC on system phase margin and ADC update delay is analyzed in detail. Consequently, a Kalman filter based technique is proposed to compensate the latency caused by the group delay of the digital filter and increase the phase/gain margin of the system. In addition, three PWM update strategies are proposed and their tradeoffs discussed. The proposed algorithm and measurement results are experimentally verified on a PMSM drive. It is shown that with the proposed solution, Sigma-delta ADC can provide much higher resolution than traditional SAR ADCs and also yield superior diagnostics capability and control.