基于虚拟阻抗的并联VSG改进控制策略研究

Research on Improved Control Strategy of Parallel VSG Based on Virtual Impedance

针对低压配电网中传统虚拟同步发电机(virtual synchronous generator,VSG)控制因逆变器等效输出阻抗和线路阻抗的差异而引起的功率分配不合理以及环流问题,提出了一种基于虚拟阻抗的并联VSG改进控制策略。首先,分析逆变器的功率传输特性和环流特性,设计了虚拟阻抗控制策略,实现了有功与无功的独立控制以及一定的环流抑制。其次,为了消除虚拟阻抗带来的电压跌落并进一步抑制VSG的系统环流,对传统VSG的无功–电压环进行了改进,将输出电压与额定电压的差值作为前馈补偿来校正系统的输出电压。在此基础上,针对不同容量的VSG,制定了多机并联系统参数匹配方法。最后,通过PSCAD/EMTDC软件对离网运行的低压微电网进行仿真分析,结果验证了所提控制策略的正确性。

In the low-voltage distribution network, aiming at the problem of unreasonable power distribution and circulating current caused by the difference between the inverter equivalent output impedance and line impedance in the traditional Virtual Synchronous Generator(VSG) control, an improved parallel VSG control strategy based on virtual impedance is proposed. First, the power transmission characteristics and circulation characteristics of the inverter are analyzed, and the virtual impedance control strategy is designed to realize the independent control of active and reactive power, as well as a certain circulation suppression. Second, in order to eliminate the voltage drop caused by the virtual impedance and further suppress the system circulating current of VSG, the reactive power-voltage loop of the traditional VSG is improved, and the difference between the output voltage and the rated voltage is used as feedforward compensation to correct the output voltage of the system. On this basis,aiming at VSG with different capacities, the parameter matching method of multi machine parallel system is formulated. Finally, the PSCAD/EMTDC software is used to simulate and analyze the off-grid low-voltage microgrid, and the result verifies the proposed control strategy’s correctness.