A novel neutral point balancing technique for SVPWM switched 3-level inverter for AC drives

A novel SVPWM technique is proposed for the neutral point balancing application of three level inverter fed AC motor drives which are operating as both in motoring and regenerative mode. The neutral-point voltage will be balanced by PWM control according to the direction of neutral-point current. The neutral-point current direction is calculated by sensing the output current of each phase. Based on Neutral point current and unbalance in the neutral point voltage, duration of small vectors are changed in a sub-cycle. The state of neutral point voltage is decided by hysteresis-band control. With the proposed PWM technique, there will not be a complete elimination of P or N vectors, because of which symmetry in the switching's maintained and hence only one switching at a time is maintained in a given sub-cycle. This method is verified by simulation of three-level converter fed IM drive operating as both motoring and regenerative mode.