弱电网下基于复数滤波器的并网电压前馈控制策略

随着分布式逆变并网电源的广泛部署,电网所需的传输线路不断增长,再加上配电变压器漏感等因素的影响,电网越来越表现出弱电网特性。在弱电网情况下,为减小电流稳态误差,并网电压比例前馈系统得到了广泛应用,然而由于其引入了与电网阻抗相关的正反馈回路,导致系统相角裕度大幅降低,严重影响并网逆变器的稳定性。以三相LCL并网逆变器为例,通过伯德图分析电网阻抗对并网逆变器稳定性的影响,提出在并网电压比例前馈环节串联复数滤波器的控制方案。分析表明该方案可以提高弱电网条件下并网逆变器的稳定性。最后搭建了三相5 kW并网逆变器仿真模型,验证了该方案的有效性。

Grid voltage feedforward control strategy for weak grid based on complex filter

As the penetration of the distributed energy source in the grid is becoming higher and higher, the grid is increasingly showing the characteristics of weak grid due to some factors like the longer transmission lines and distribution transformer leakage inductance. The proportion feedforward system is widely employed to reduce the current steady-state error in weak grid conditions. The phase margin will be greatly reduced, which affects the stability of grid-connected inverter due to the introduction of the positive feedback loop associated with the grid impedance. Taking the three-phase LCL grid-connected inverter as an example, the influence of the grid impedance on the stability of grid-connected inverter is analyzed by the Bode diagram, and the control strategy that connects a complex filter in series in grid-connected voltage proportional feedforward loop is proposed. The analysis shows that the strategy can improve the stability of grid-connected inverter in a weak grid. Finally, a 5 kW three phase grid-connected inverter simulation model is built to verify the effectiveness of the proposed control strategy. This work is supported by National Natural Science Foundation of China (No. 61703144) and Key Science and Technology Project of Colleges and Universities of Henan Education Department (No. 17A470010).