DC-Link Voltage Balance Control Strategy Based on Multidimensional Modulation Technique for Quasi-Z-Source Cascaded Multilevel Inverter Photovoltaic Power System

A dc-link voltage balancing control strategy for quasi-Z-source cascaded H-bridge (qZS-CHB) inverter photovoltaic (PV) power system is proposed by using multidimensional pulse-width modulation (MD-PWM) technique. The qZS-CHB PV system usually employs proportional-integral (PI) regulators based closed-loop control methods to balance dc-link voltages, combining with distributed maximum power point tracking and grid-tie power control. These require significant control computations and hardware resources for multiple modules based qZS-CHB system. The proposed MD-PWM for the qZS-CHB inverter performs shoot-through behavior based on geometric representation of the output voltage ranges of each H-bridge in coordinate axes. All possible switching sequences of the qZS-CHB inverter are taken into account to choose the most suitable sequence that can balance dc-link voltages of qZS modules in the qZS-CHB PV power system. When compared with the state-of-the-art of voltage balancing control methods, the proposed control strategy has advantages: 1) The computation is low because there is no PI controller, while the stability of the whole system is improved; and 2) there is a reliable balancing capability with fast regulation of dc-link voltages, owing to no extra controller parameters and handling the voltage balance in each control cycle. Simulation and experimental results of qZS-CHB inverter based grid-tie PV power system verify the proposed dc-link voltage balancing control technique.