When grid-connected photovoltaic (PV) inverter is connected to weak grid, high equivalent impedance of weak grid can lead to small bandwidth of control system and poor control performance. Aiming at this problem, this paper proposes an adaptive quasi proportion resonant differential (quasi-PRD) control method. This method firstly uses quasi-PRD controller to replace traditional PI controller to realize zero steady-state error tracking and expand system bandwidth. Then, double harmonic current injection method is applied to implement on-line detection of grid impedance. Finally, the detected impedance value is used to on-line adjust controller parameters of quasi-PRD. Simulations and experiments were performed, verifying that the proposed method can not only increase bandwidth and dynamic response speed of control system, but also improve system adaptability for different grid impedance values, and eventually improve power quality.
KEY WORDS :weak grid;quasi-PRD control;grid impedance;adaptive control;
图5
不同控制方式下的并网电流与电压仿真波形
Fig. 5
Voltage and current simulation results under different control strategies
图6
不同控制方式下的并网电流与电压实验波形
Fig. 6
Voltage and current experimental results under different control strategies
图7
基于双谐波电流注入法的电网电阻电感检测结果
Fig. 7
Experimental result of grid resistance and inductance online estimation based on double harmonic current injection method
图8
弱电网下控制器参数不变时的并网电压电流波形
Fig. 8
Voltage and current waveforms with fixed parameters in weak grid
图9
弱电网下自适应调节参数后的并网电压电流波形
Fig. 9
Voltage and current waveforms with and without adaptive control method in weak grid
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