Interleaved PWM control for neutral point balancing in dual 3-level traction drives

This paper presents a new approach for neutral point balancing in dual three-level, T-type, neutral-point-clamped (T-NPC) inverters feeding a dual 3-phase permanent magnet synchronous machine (PMSM). Three-level Space Vector PWM (SVPWM) modulation scheme, without any separate capacitor balancing capability has been employed. However, by synchronously interleaving the switching pulses of both inverters, neutral-point balancing can be achieved over the entire torque/speed range of the traction motor, characterized by varying modulation indexes and load power factors. A control algorithm consisting of two PI loops has been developed in order to eliminate any mismatch between the two 3-level inverters. This technique alleviates the requirements for additional switching to achieve neutral point balancing, resulting in a reduction of both switching loss and AC waveform distortion. Simulation results verifying the proposed control algorithm are presented.