Efficient DC Voltage Balancing of Cascaded Photovoltaic System Based on Predictive Modulation Strategy

This article presents a predictive modulation strategy for dc voltage balancing of cascaded H-bridge-based photovoltaic generation systems (CHB-PV). It is intended for improving the efficiency of CHB-PV by reducing the number of switching events. The strategy enables the charge/ voltage estimation and the design of a real-time discharge-order exchange, ensuring discrete dc voltage balancing. The conventional loss-reduced level-shifted-pulsewidth-modulation (LS-PWM) is embedded and used to predict the discharge values and the target dc voltage value. The real-time discharge-order exchange is used to make the individual voltages converge to the target value at intervals of maximum 1/4 fundamental cycle. The voltage spread range introduced by the discrete voltage balancing is also considered and well suppressed by a simple adaptive method. Balancing of the dc voltages is finally achieved in a more discrete way, which makes reduced switching events compared with only using the loss-reduced LS-PWM. Experiment results based on a 2.1 kW/311 V setup are presented to demonstrate the effectiveness of the proposed technologies.