Implementation of a Four Pole Neutral-Point Clamped Three Phase Inverter with Low Common Mode Voltage Output

This paper describes the implementation of a a Four Pole Neutral-Point Clamped (NPC) Three Phase Inverter that produces virtually no common mode voltage. The low common mode voltage output is achieved by constraining the switch states of the NPC Inverter. This performance is achieved at the expense of reduced voltage utilization and loss of DC link voltage balance control. A fourth pole and associated control are added to balance the upper and lower DC link voltages. The paper describes the control implementations and simulation results compared to measured results used in tuning and commissioning of the system. A 450 V, 78 kW system is implemented in hardware and experimental results are provided showing its differential mode transient and steady state harmonic performance as well as its common mode output voltage.