弱电网下微电网跟网型变流器谐振抑制方法研究

Research on Resonance Suppression Methods for GFL Inverters in Microgrids under Weak Power Grid

  • 摘要: 随着分布式电源大规模接入电网,电网逐步电力电子化呈现弱电网状态。在弱电网下跟网型(Grid following,GFL)变流器容易发生谐振,为此提出基于电网电压前馈(Grid voltage feedback,GVF)+对称锁相环(Symmetric phase-locked loop,SPLL)的GFL变流器谐振抑制方法。首先,建立GFL变流器阻抗模型进行稳定性分析。为了抑制锁相环(Phase-locked loop,PLL)负阻效应,引入考虑PLL的GVF方法,对其进行小信号阻抗建模及稳定性分析。其次,为了消除PLL结构不对称带来的影响,在GVF的基础上引入SPLL进一步提升系统谐振抑制能力。最后,建立GVF+SPLL GFL变流器谐振抑制系统试验平台进行试验测试。通过测试可知,GVF+SPLL方法相比于GVF/未改进方法具有更强的谐振抑制能力,系统谐波含量由原来的21.27%下降至2.14%。同时在电网谐波背景下,GVF+SPLL方法相比于GVF/未改进方法具有更强的谐波抑制能力。

     

    Abstract: With a high proportion of renewable energy generation connected to the power grid, power grid is gradually becoming electrified and presenting a weak power grid state. In weak power grid, GFL converters are prone to occur resonance. Therefore, a GFL converter resonance suppression method based on grid voltage feedforward(GVF)+symmetric phase-locked loop structure(SPLL) is proposed. Firstly, an impedance model is established and stability analysis is done for GFL inverter. To suppress negative resistance effect caused by PLL, GVF method considering PLL is introduced, and small signal impedance modeling and stability analysis are performed on it. Secondly, to eliminate the impact of asymmetric PLL, SPLL is introduced on the basis of GVF to further enhance the system’s resonance suppression ability. Finally, an experimental platform for GVF+SPLL grid following inverter resonance suppression system is established for experimental testing. The experimental results show that GVF+SPLL method has stronger resonance suppression ability, compared to GVF/unimproved method, and system harmonic content has decreased from 21.27% to 2.14%. Meanwhile, under the background of power grid harmonics, the GVF+SPLL method also has stronger harmonic suppression ability compared to the GVF/unimproved method.

     

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