Three-Phase Seventeen-Level Cascaded Switched-Capacitor Multilevel Inverter for Grid-Connected PV Systems

Abstract

The topology of grid-connected three-phase 17-level Cascaded Switched Capacitor Multilevel Inverter (CSC-MLI) for photovoltaic systems (PV) is proposed in this work. Each phase of the proposed inverter is formed by cascading two identical 9-level SC-MLI basic cells, resulting in a 17-level CSC-MLI configuration to comply with IEEE standards for minimal Total Harmonic Distortion (THD) in grid-tied inverters. The proposed inverter has the feature of self-balancing capacitor voltage ability, self-boosting voltage capability, and limiting the capacitor inrush current during the capacitor charging mode, in addition, the ability of reactive power support. A new hybrid pulse width modulation (PWM) has been implemented with a 2.5 kHz frequency to produce the gate pulses. The proposed three-phase CSC-MLI is connected to a multi-array PV system through a single DC bus bar collector to enable an inherently balanced power share between the CSC-MLI cells and phases. The simulation results show that the proposed inverter achieves a THD of less than 1% in its output current. The MATLAB/Simulink software was employed to simulate the steady-state and dynamic performance of the proposed 12 kW PV grid-connected three-phase CSC-MLI under a variety of environmental conditions and power factors.