A modified DPWM scheme for capacitor voltage balancing in three level NPC traction inverter for electric vehicles

Abstract

A discontinuous pulse width modulation (DPWM) strategy for variable load power factor (PF) with capacitor voltage unbalance control in a three level neutral point clamped (NPC) traction inverter drive for electric vehicles (EVs) is developed and presented in this paper. It is shown that the addition of an appropriate offset signal with the reference DPWM signals generates compensating neutral current in the desired direction which can be used to mitigate existing unbalance in two dc link capacitor voltages. Minimum switching losses at variable load PF is attained by positioning the clamped regions of the reference auxiliary signals according to the PF. Detailed performance analysis of the scheme for traction inverter drive for induction motor (IM) is carried out through simulation, and the experimental results are presented to verify the effectiveness of the proposed scheme.