Input Impedance and Stability Analysis of VSC in Integrated On-Board Chargers for Electric Vehicles

This paper deals with a three-phase integrated on-board charger of electric vehicles (EVs) that reutilize the traction motor's stator winding as part of the input filter to form an LCL filter for the front-end voltage source converter (VSC) in dual-stage chargers. This approach imposes additional constraints on the selection of one filter inductance, based on motor specifications, which may affect the control loop stability dynamics, particularly under grid impedance variations. To examine this, the small signal model of the LCL-filtered VSC is developed and its d-q frame based impedance model is derived. The control loops, including the active damping, current, and voltage, are designed, and overall input impedance characteristics are analysed and compared with typical LCL filter based VSC. The system's stability is further assessed through generalized Nyquist criterion under grid impedance variations, and analytical findings are validated in realtime Hardware-in-the-Loop testing.