A Modulation Strategy for Neutral-Point Voltage Ripple Reduction in a Three-Level T-type Inverter

The three-level T-type inverter has been extensively applied for photovoltaic generation of series-connected solar panels. The neutral-point voltage of the T-type inverter may suffer from low-frequency oscillation due to third harmonic current, thus detreating maximum point tracking (MPPT) of series solar panels. This paper proposes a new modulation for the T-type inverter to suppress the neutral-point oscillation even under the condition of unbalanced neutral-point voltage. Thus, the dc-side capacitance of the inverter can be significantly reduced and film capacitors are able to replace electrolytic capacitors to increase the lifetime of the inverter. Simulation results are provided to verify the proposed modulating method.