Research On High-performance Energy Conversion System In Off-grid Photovoltaic Power Generating System

In this paper, some electrical energy transformation technologies in off-grid photovoltaic power generating system are studied. According to different functions, the off-grid power generating system is decomposed into three modules including charging, boosting and inverting. Each module is individually designed in this paper.In the first chapter, some basic principles and domestic and foreign research status of photovoltaic generating system are briefly proposed, which leads to the contents of this paper.In the second chapter, the output characteristics of PV panels and battery charging and discharging characteristics are analyzed, based on which a photovoltaic charging controller with Synchronous Buck circuit is proposed. This charging controller can not only track the maximum power point of PV panels but also monitor the battery charging process and switch among constant current, constant voltage and MPPT charging according to the charging progress.The third chapter presents a high-gain active clamped DC-DC boost converter with coupled inductor and analyses its detail working status in various stages. The converter based on coupled inductor technology tries to enhance the voltage gain and reduce diodes stress by two voltage double cells. The active clamp circuit limits the voltage stress of switches, which makes the use of low voltage and small on-resistance switches possible, by which the conduction losses are reduced and efficiency is improved. In addition, the clever use of transformer leakage inductance and switch parasitic makes soft opening of the switches possible, which can further improve efficiency.In the fourth chapter, the state feedback control and repetitive control ways are analyzed after the establishment of the mathematical model of single-phase full-bridge inverter. A composite control strategy of state feedback control plus repeating control with high dynamic quality and low static error is proposed. In the fifth chapter, the experimental results of the three prototypes are presented and the desired goal is achieved.