FPGA Based Motor Inverter Control for Strictly Synchronous Digital Active EMI Cancellation

Many modern motor inverters use fast switching transistors to reduce losses. Due to steep switching waveforms and high frequencies, these systems represent a significant source of electromagnetic interference (EMI). Usually, large and heavy passive filters are used to suppress the EMI. Active EMI filters (AEF) can reduce the size and weight. Digital AEFs with synthesized anti-noise injection can reach very high performance when the injected anti-noise is synchronized to the EMI that has to be measured in advance. Unavoidable delays between EMI measurement and anti-noise injection lead to reduced suppression at higher frequencies. A prediction of future EMI allows compensation of delays and thus synchronous injection. In motor inverters, the control signals contain important EMI information for predicting the needed anti-noise signal. As the control signal is created first, knowledge on it can give sufficient advance for anti-noise processing. Furthermore, for a high noise suppression a strict temporal relation between EMI and anti-noise is needed. This can be achieved, e.g., if motor control and anti-noise signal generation are implemented with a common clock or on a single signal processing system. As several investigations have shown that a field-programmable gate arrays (FPGA) combined with fast digital-to-analog and analog-to-digital converters are appropriate for anti-noise signal generation, it is obvious to also implement the noise generation algorithm on the same FPGA. In this work first, a synchronous motor control and digital AEF system are discussed. Especially, a digital adaptive notch filter has been developed that is operated synchronously with the noise source. The performance of this filter is discussed.