基于混合势函数的下垂控制直流微电网大扰动稳定性分析

Large-Disturbance Stability Analysis of Droop-Controlled DC Microgrid Based on Mixed Potential Function

作为未来交直流混合配电网的重要组成部分,直流微电网的稳定性对配电网的安全运行至关重要。混合势函数作为一种非线性电路大扰动稳定性分析的有效工具,已被应用在带恒功率负载的级联系统等方向,但对于含有多个电源的下垂控制直流微电网的稳定性分析则较少涉及。研究了包含VSC和双向非隔离型DC-DC变流器,负荷为恒功率负载的直流微电网的大扰动稳定性。首先,通过对一简单系统应用混合势函数进行理论分析,发现若直接应用混合势函数理论,会导致所求的稳定性判据有较大误差。针对这一问题,提出了一种基于混合势函数理论,适用于下垂控制系统的稳定性判据推导方法,并得出了直流微电网的稳定性判据。该判据表明,下垂控制的直流微电网的大扰动稳定性与各变流器系统参数和各电源输出功率占负载功率比例均有关联。仿真验证了所提方法和稳定性判据的准确性。

As an important part of future hybrid AC/DC distribution networks, stability of DC microgrid is critical to safe operation of distribution networks. Mixed potential function is an effective tool for large signal stability analysis of nonlinear circuits, used to analyze large signal stability of cascade systems with constant power loads. However, stability analysis of droop-controlled DC microgrid is rarely involved. This paper studies large signal stability of a DC microgrid with constant power load, including VSCs and bi-directional non-isolated DC-DC converters. Firstly, this paper theoretically analyzes the mixed potential function of a simple system, and finds out that if the theory is applied directly, it will lead to a wrong stability criterion. Then, a method applying the stability theorem of mixed potential theory under droop control strategy is proposed and the criterion is obtained. The stability criterion shows that the stability of the droop-controlled DC microgrid is related to parameters of each converter and proportion of each power supply. The stability criterion is verified with simulation results.