Passive Filter Design to Mitigate Dead-Time Effects in Three-Level T-Type NPC Transformerless PV Inverters Modulated with Zero CMV PWM

Common-mode voltage (CMV) can cause common-mode (CM) current in transformerless PV inverters. In practice, large CM choke is usually required to suppress the CM current. Alternatively, zero common-mode voltage (ZCMV) modulation can be applied to eliminate the CMV. But in practical applications, CMV spikes are inevitable due to the dead-time effect. Such dead-time effect can be mitigated by special PWM sequence design, however, at the expense of increasing switching losses. In this paper, our study addresses this issue by using the DC neutral-point connected LCL (NC-LCL) filter. As the differential-mode (DM) output quality is undermined with ZCMV PWM, the LCL filter parameters must be carefully designed, where both CM and DM filters need to be considered. In addition, filter design for conventional phase disposition (PD) modulation is also included as a comparison. Both simulation results and experimental results are provided for verification.