Resonance Suppression of High-Frequency AC Drive System with Neutral Non-isolated Filter Based on Digital Delay

The high-speed switching action of GaN power devices will produce a high transient voltage change (dv/dt), resulting in a more serious overvoltage problem at the motor end, destroying the stator winding insulation layer, generating shaft voltage and bearing current to damage the motor bearing. The inverter side series neutral non-isolated LC filter can solve the motor end overvoltage and dv/dt problems caused by GaN HEMT high-speed switch, and significantly reduce the common mode voltage amplitude of the motor side. However, this method will introduce resonance problems into the system. This paper presents a resonant suppression method based on inherent digital control delay, which solves the resonant problem caused by LC output filter. Secondly, the problem of introducing common-mode current into the current loop is analyzed, and its influence on the control system is eliminated by a second-order notch filter. The resonant suppression scheme and common mode current suppression are verified by simulation.