Active Cancellation of Periodic DM EMI at the Input of a GaN Motor Inverter by Injecting Synthesized and Synchronized Signals

Active cancellation is a promising solution to reduce the size of passive filter components. Considering power electronic systems in stationary operation and with periodic control signals, the disturbances consist of stable harmonics that can be individually suppressed by destructive sine waves. These sine waves can be superposed to create a synthesized broadband cancellation signal that must be injected in synchronicity with the operation of the power electronic system. Since bothersome effects (like time constants or delay times) can be compensated by appropriate amplitudes and phases of the cancelling sine waves, the active cancellation system can achieve high EMI reductions in a wide frequency range. In this work, the method is applied to a motor inverter with a very large number of differential mode (DM) harmonics. The characteristics of the disturbances are discussed and the challenges for the active EMI cancellation system are elaborated. A suitable method for the determination and generation of the cancellation signal is introduced. This method is applied to a GaN inverter with a synchronous machine in the frequency range from 50 kHz to 30 MHz. The EMI suppression is evaluated by average and peak measurements with an EMI test receiver. The power of the generated cancellation signal is estimated.