Discontinuous PWM Strategy for Reliability and Efficiency Improvements of Single-Phase Five-Level T-Type Inverter

Reliability and efficiency improvements of photovoltaic (PV) inverters have a high potential to decrease the cost of PV energy. Discontinuous pulse width modulation (DPWM) is an effective method to improve both the efficiency and reliability of the power devices of the single-phase five-level T-type neutral point clamped (NPC) inverter. However, applying DPWM gives a negative effect on the lifetime of the dc-link capacitors and thus, reduces the reliability of the inverter from the system-level reliability point of view. This paper proposes the DPWM strategy to improve the lifetime of the dc-link capacitor compared with the conventional DPWM method so that both reliability and efficiency of the single-phase five-level T-type NPC inverter are improved. Through the proposed strategy, the lifetime of the dc-link capacitor is improved, but its negative effects on the efficiency of the inverter and the lifetime of the power devices are negligible. Therefore, the advantages of applying DPWM can be sustained. Simulation and experimental results verify the feasibility and effectiveness of the proposed DPWM strategy.