Capacitor Voltage Ripple Reduction Modulation Method for String Photovoltaic Inverters

This paper proposes a new pulse width modulation (PWM) method for reducing capacitor voltage ripples in H-bridge five-level T-Type inverters for grid-connected single-phase photovoltaic (PV) string inverter applications. The T-Type inverters have been widely employed in several applications due to their superior performance. However, single-phase applications suffer from high voltage ripples over the dc-link capacitors. These ripples cause shortened operating lifetime and reduced reliability of capacitors in addition to distorted output current of the inverter. Thence, a new improved PWM method is developed in this paper for reducing the ripple voltages over the capacitors. The new PWM method employs equally swapped utilization of dc-link capacitors within the line period. In addition, the proposed method is capable of achieving natural voltages balancing among the capacitors. The simulation and experimental verifications of the new proposed PWM have been provided.