基于双侧电压反馈控制策略的并网光伏系统电压稳定性研究

Research on Voltage Stability of Grid-Connected Photovoltaic System Based on Double-Side Voltage Feedback Control

针对低电压穿越下并网光伏直流系统不稳定的问题,提出一种改进的双侧电压控制策略。前级变流电路引入电压反馈控制,形成电压反馈与最大功率跟踪(maximum power point tracking,MPPT)的混合控制,结合并网逆变器的电压反馈环路,在电压穿越时,对并网光伏直流系统进行综合控制,同时,为了实现前级电路电压控制和功率控制的自动均衡,基于母线电压实时值设计电压反馈环路和MPPT环路的自适应权重系数。为了证明改进策略在低电压穿越时对直流系统的稳定作用,基于RT-LAB平台搭建并网光伏系统的半实物测试环境,测试结果表明:相比于传统控制策略,在不采用Chopper电阻的情况下,双侧电压反馈控制策略能够在低电压穿越时将直流电压变化量从136 V降低到60.5 V,同时还能将并网冲击功率从3 955 W降低到2 264 W,不仅降低了变流电路的电流应力,还提升了光伏系统在低电压穿越时的稳定工作能力。

In terms of the problem that the grid-connected photovoltaic DC system is unstable during low voltage ride through(LVRT), an improved double-side voltage control strategy is proposed. The voltage feedback control is introduced in the front converter circuits to form a hybrid control including voltage feedback and maximum power point tracking(MPPT). In addition, this paper combines the voltage feedback loop of the grid-connected inverter and comprehensively controls the grid-connected photovoltaic DC system during LVRT. Meanwhile, in order to realize the automatic balance between the voltage control and power control of the front converter, this paper designs adaptive weight coefficients of the voltage feedback loop and MPPT loop based on the actual bus voltage. To verify that the improved control strategy can stabilize the DC system during LVRT, the paper carries out a hardware-in-loop(HIL) test based on the RT-LAB platform. The test result shows that without a Chopper resistor, the double-side voltage feedback control strategy can reduce the variation of DC voltage from 136 V to 60.5 V during LVRT compared with the traditional control strategy, and the grid-connected impulse power can be decreased from 3 955 W to 2 264 W, which not only reduces the current stress of converter circuits but also improves the stability of the photovoltaic system during LVRT.