基于自适应虚拟阻抗控制的孤岛微电网电能质量优化策略

Power Quality Optimization Strategy in Islanded Microgrid Based on Adaptive Virtual Impedance Control

随着大量不对称负载以及非线性负载的接入,孤岛微电网的电能质量问题日益凸显,如何合理分配不平衡和谐波功率成为关键。目前提出的分配策略多致力于实现谐波和负序电流的均分,降低过载风险,但忽略了不同逆变器改善电能质量的差异性。为此,以充分利用逆变器的剩余容量为核心思想,文中提出了一种以改善微电网电能质量为目标的功率分配策略。所提控制策略将剩余容量与输出的非基频功率之差作为输入,自适应调节基波负序和主导谐波频率处的虚拟阻抗,从而保证了逆变器在稳态工况下不过载,并为谐波电流和负序电流分别提供阻抗尽可能小的流通路径,达到改善微电网电能质量的目标。为保证虚拟阻抗调节的稳定性与快速性,基于根轨迹分布确定了虚拟阻抗稳定域范围,并提出了一种改进的变参数积分控制方法。最后,通过仿真和硬件在环实验验证了所提控制策略的可行性与有效性。

With the access of a large number of asymmetric loads and nonlinear loads,the power quality problems of the islanded microgrid are becoming increasingly prominent.It is critical to reasonably distribute the unbalanced and harmonic power.Most of the existing distribution strategies devote to realizing the uniform distribution of harmonic and negative current,which can reduce overload risk.However,the distribution control strategy ignores the difference between different inverters in improving power quality.Therefore,this paper proposes a power distribution strategy aimed at improving the power quality of the microgrid,which takes the core idea of making full use of the residual capacity of inverters.The proposed strategy takes the difference between the residual capacity and the output non-fundamental frequency power as the input,and adaptively adjusts the virtual impedance at the fundamental negative sequence and dominant harmonic frequency to ensure that the inverter is not overloaded under stable conditions.Meanwhile,it can provide the smallest possible flow path of impedance for harmonic current and negative current to achieve the goal of improving the power quality of the microgrid.To ensure the stability and rapidity of the virtual impedance adjustment,the stability region of the virtual impedance is determined based on the root locus distribution,and an improved variable integral control method is also proposed.Finally,the feasibility and the effectiveness of the proposed control strategy are verified by the simulation and the hardware-in-the-loop experiment.