Thermally Balanced DPWM Method With Neutral Point Voltage Balancing Capability for Single-Phase Five-Level T-Type NPC Inverters

Discontinuous pulse width modulation (DPWM) is useful to improve the efficiency of a single-phase five-level T-type neutral-point-clamped (5LT-NPC) inverter and the reliability of the power devices. However, depending on how it is applied, the thermal loading imbalance between the two legs of the 5LT-NPC inverter occurs, which results in a reduction in the reliability improvement effect in the power devices by the DPWM. Furthermore, the DPWM strategy should be equipped with the ability to balance the neutral point voltage since the imbalance between the voltages of the two capacitors leads to the distortion of the output current and also the failure of the DC-link capacitor and power devices if its voltage is over the rated value. This paper proposes a Thermally Balanced DPWM (TB-DPWM) method with neutral point voltage balancing capability for the 5LT-NPC. Through the proposed method, the thermal loading balancing between the two legs can be achieved simply without consideration of the power factor. Furthermore, it is also able to balance the neutral point voltage while maintaining the DPWM. The effectiveness and feasibility of the proposed method are verified through the simulations and experiments.