A Modified Carrier-Based Discontinuous PWM for Photovoltaic Three-Level Converter with Reduced Common Mode Voltage Ripple

Nowadays, three-level inverters are frequently applied in photovoltaic (PV) systems because of their high efficiency and low harmonics. To improve the power density of transformerless three-level inverters, the high switching frequency is considered which causes lager switching losses. Discontinuous PWM (DPWM) is a solution to reduce switching losses. However, conventional DPWMs cause common mode voltage (CMV) ripple which worsens the reliability of PV systems. To solve this problem, DPWMA is proposed by selecting space vectors which CMV amount are low, but the CMV ripple can be further reduced. In this paper, a modified carried-based DPWM is proposed to reduce CMV ripple of DPWMA. Carrier types of every phase are selected to realize an improved PWM sequence according to switching clamping modes. Finally, the proposed modulation strategy is verified in different modulation index by the simulation.