光伏并网逆变器集群的谐振原因及其抑制方法

The Cause Analysis and Suppression Method of Resonances in Clustered Grid-connected Photovoltaic Inverters

并网逆变器大规模接入弱电网时可能产生大量低频谐波,严重影响了电网电能质量。针对这一问题,首先分析常规逆变器控制方法在逆变器集群和弱电网情况下的局限性,建立含变压器和电网阻抗的逆变器集群模型,揭示开关管放大非线性干扰、逆变器并网电流参考、周围并联逆变器电流干扰和电网电压扰动对并网逆变器的影响机理,指出高电网阻抗是引起逆变器集群谐振的主要原因。然后从改善逆变器性能的角度出发,提出一种有源谐波电导法,在不改变电路拓扑的情况下,有效抑制逆变器谐波电流的输出,提高了逆变器的抗干扰能力,从而避免谐振现象发生。最后通过仿真复现谐振现象,并证明所提出方法的有效性。

Large amounts of low-frequency harmonics may be found in the situation where inverters connected to a weak grid, which seriously affect the power quality. In order to solve this problem, firstly, the limitation of conventional control in inverter clusters and weak grids was analyzed, and an inverter cluster model was built including the transformers and the grid impedance, revealing the mechanism of effects on the inverter cluster of Err, I＊, Ip and Ug, pointing out that it is mainly the high grid impedance that causes resonance. Then an Active Harmonic Conductance Method was proposed to improve the inverter performance, which can effectively suppress the harmonic current output, and to improve the noise immunity of inverters, thus to avoid resonance, without any changes of the topology. At last, the resonance phenomenon was reproduced to verify the feasibility of the proposed method.