低压微网逆变器的“虚拟负阻抗”控制策略

A Control Strategy of ‘Virtual Negative' Impedance for Inverters in Low-voltage Microgrid

提出基于"虚拟负阻抗"的控制策略对低压微网中的并联逆变器进行控制,该策略包含"虚拟负电阻"和虚拟电感两部分。"虚拟负电阻"用以降低由阻性线路引起的功率耦合,并减小并联系统输出电压降落;虚拟电感使逆变器本身的输出阻抗呈感性,调节系统感抗匹配程度以提高无功分配精度;分析非基频暂态稳定性对"虚拟负电阻"取值范围的限制,提出增大该取值范围的改进方案。改进方案使并联逆变器能稳定运行于基波系统阻抗角位于第二象限的新区域,可提高线路参数漂移和估算不准确时的系统性能。此外,给出用波德图对并联逆变器功率环路进行稳定性分析的方法。仿真和实验结果验证了上述控制策略和方法的有效性。

A novel control strategy based on ＂virtual negative impedance＂ is proposed which is composed of virtual inductor and ＂virtual negative resistor＂. The virtual negative resistor is used to reduce the power coupling and output voltage drop caused by the resistive cabling grid. The virtual inductor is implemented to ensure the output impedance of inverter mainly inductive and also to make the system impedance matched to raise the accuracy of reactive power sharing. The value range of the virtual negative resistor is studied to meet the transient stability and an improved scheme is proposed to increase this value range. The new scheme enables the parallel inverters to work with the impedance angle located in the second quadrant and make the control strategy robust against line parameter drift and uncertain estimation. In addition, the bode-plot method is presented by which the stability analysis of power control loop of parallel inverter is studied. Simulation and experimental results verify the effectiveness of the proposed control strategy and method.