A Software-Based Control System to Reduce Conducted CM EMI in Four-Leg Three-Phase Inverters Using the Delay Compensation Technique

Common-Mode (CM) conducted Electro Magnetic Interference (EMI) is a critical issue in automotive power converters, where strict EMC regulations must be met. This paper investigates the Delay Compensation Technique (DCT) applied to traction inverters to reduce CM EMI at low-frequency. Although the four-leg topology enables complementary switching, existing works do not provide a method to finely align the commutation edges, which is required to have CM current pulses canceling out and effectively reducing CM EMI. In this work, an iterative optimization method is introduced for the two-leg case, and then extended to the four-leg inverter with sinusoidal modulation, enabling fast convergence and minimal computational overhead. Experimental validation resulted in 30 dB EMI reduction at 160kHz and in 15-20 dB for frequencies up to a few MHz, with significant benefits in terms of volume reduction of the input EMI filter compared to state-of-the-art techniques.