DC bus voltage EMI mitigation in three-phase active rectifiers using a virtual neutral filter

Grid connected PWM inverters/rectifiers inevitably produce a high frequency switched common mode voltage on their DC bus, which can cause substantial EMI problems. The mitigation strategy proposed in this paper is to couple the Y point of the LCL filter capacitors to the DC bus mid-point to connect a virtual neutral to the DC bus, which significantly reduces the high frequency common mode voltages on the bus. However, additional common mode inductances and capacitances are required for this filter, to limit high frequency circulating currents and define the EMI filter breakpoint. Also, the converter current regulator must be split into differential and common mode sections, to eliminate phase coupling between the phase leg active damping current regulators, and to support damping of the common mode EMI filter resonance. The concept is verified by simulations and experimental results.