提高直流微电网稳定性的并网换流器串联虚拟阻抗方法

Grid Converter Series Virtual Impedance Method for Improving DC Microgrid Stability

保证直流微电网稳定运行的核心是控制直流母线电压稳定。为解决附加虚拟惯性控制和恒功率负载削弱系统阻尼、导致直流母线电压产生高频谐振的问题,从阻抗匹配的角度出发,利用有源阻尼的思想,提出并网换流器串联虚拟阻抗的方法。首先对并网换流器的控制系统进行小信号建模,得到输出阻抗,分析并提取输出阻抗的尖峰量,在控制系统中将该尖峰函数以虚拟阻抗的形式补偿到原阻抗,达到减小输出阻抗的目的。其次针对不同虚拟惯性系数和负载功率,给出了虚拟阻抗的具体计算过程,利用Middlebrook判据对串联虚拟阻抗后系统的稳定性进行判断。最后,在Matlab/Simulink中建立直流微电网模型并进行时域仿真,在RT-LAB实时仿真平台进行实验测试,验证了串联虚拟阻抗方法的有效性。

The key measure to maintain stable operation of DC microgrid is to control stability of DC bus voltage. In order to solve the problem that additional virtual inertia control and constant power load would weaken system damping and cause high frequency oscillation of DC bus voltage, from the perspective of impedance matching, a method of grid converters series virtual impedance is proposed using the idea of active damping. Firstly, a small signal model of the grid inverter control system is built to obtain output impedance. Then the peak of output impedance is analyzed and extracted. The peak function is compensated to previous impedance in the control system to reduce the amplitude of the output impedance. Secondly, the specific calculation process of virtual impedance is given for different virtual inertia coefficients and load powers. Stability of the system with series virtual impedance is judged with Middlebrook criterion. Finally, a DC microgrid model is built and simulated in Matlab/Simulink, and an experimental test is performed on RT-LAB real-time simulation platform, thus validity of the series virtual impedance is verified.