采用传统下垂控制的电压源型逆变器并联构成的微电网,由于其等效输出阻抗较小,当微电网与电网并联运行时,易受到电网并网点电压谐波分量扰动的影响,使微电网并网电流总谐波畸变率升高.提出一种基于分层控制的微电网并网电流电能质量主动提升控制策略,首先利用Park变换将并网点与微电网交流母线的误差电压变换到旋转坐标系下,并在原微电网的二层控制中添加误差电压补偿环路,利用补偿环路中的并联多重谐振控制器对该误差电压进行运算,得到底层电压源型逆变器的谐波电压补偿量,同时在逆变器电压电流内环采用基于旋转坐标系的比例积分与谐振混合控制器,提高逆变器对谐波电压补偿量的跟踪能力,进而减少微电网交流母线与并网点间的谐波电压差,从而降低微电网向电网注入的谐波电流.通过分析表明,本文所述控制策略不仅可减少微电网向电网注入的稳态谐波电流,还可以降低由于并网开关闭合导致电网对微电网的谐波电流冲击.最后,通过仿真和实验验证了所提控制策略的有效性.%Given that the droop controlled inverters based grid-connected microgrid (DCIGC-MG) presents low equivalent output impedance when connecting to the grid, the grid-connecting current (GCC) is distorted easily by the harmonic voltage components at the point of common coupling (PCC), and results in the increase of THDnof GCC. An active harmonic GCC suppression strategy for DCGC-MG based on hierarchical theory was proposed in this paper. Firstly, the voltage error between bus of DCGC-MG and PCC of grid was transferred to dq frame by the Park transformation. Then, an additional compensator consisting of multiple resonant voltage regulators was added into the secondary control to generate the harmonic voltage reference for inverters in the primary level. PI and multiple resonant controllers were adopted as voltage controller in the original primary level to improve the voltage tracking performance of inverter. As a result, the voltage difference between the PCC and system bus decreased, and the GCC is purified. The proposed control strategy not only reduces the steady-state hormonic current injected into the grid by the microgrid, but also suppressed the harmonic inrush currents when the microgrid connects to the distorted grid for protecting inverter. Finally, the simulation and experimental results from scaled-down laboratory prototype have verified the proposed control strategy.
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