串联型光伏中压直流变换器及控制策略

Series-connected PV MVDC converter and its control strategy

为满足大型光伏电站串联型光伏中压直流变换器的高升压比和宽输入、输出电压的需求,文章提出了一种新型隔离型buck-boost直流变换电路作为模块拓扑,通过调节占空比,实现直流变换模块升压和降压模式灵活地切换,从而提高变换器的电压运行范围。与常规隔离型buck-boost电路相比,文章拓扑中只有低压侧电路含有可控开关管,简化了拓扑控制,使拓扑更适用于中压场合。文章分析了新型直流变换拓扑工作原理,并推导了不同工况下拓扑的电压增益,提出了适应不同运行工况的变换器控制策略。根据文章策略开发了3 kV/90 kW直流变换模块和20 kV/500 kW串联型光伏直流变换器,测试结果证明设备能够稳定运行。

This paper presents a novel series-connected PV MVDC converter and its control strategy for large scale PV plant.Based on modular configuration of input parallel and output series(IPOS),a novel isolated buck-boost topology is proposed for the module of the converter.By regulating of switches duty cycle,the module can be reconfigured to realize step-up or stepdown mode,thereby increasing the output voltage range of the converter.The traditional isolated buck-boost topology needs to simultaneously control the low voltage side and high voltage side active switches to achieve step-up and step-down operation.In this topology,active switches are only included in the low voltage side of transformer,which simplifies the topology control and makes the topology more suitable for medium-voltage occasions.The operating principles and theoretical derivations of the voltage gain under different operating conditionsare discussed in this paper.The control strategy is designed to adapt to different operation conditions.3 kV/90 kW dcdc module and 20 kV/500 kW series connected PV MVDC converter are developed.The experiment result is presented in the paper.