考虑恒功率负载与储能单元动态特性的直流微电网系统大信号稳定性分析

Large Signal Stability Analysis of DC Microgrid System Considering Dynamic Characteristics of Constant Power Load and Energy Storage System

直流微电网系统中的负载由闭环控制的变换器连接到母线,通常可视为恒功率负载(CPLs)。恒功率负载在电压变化时呈现负阻抗特性,极易引起系统的不稳定,因此对直流微电网进行大信号稳定性分析是非常必要的。对直流微电网系统进行大信号稳定性分析,同时考虑了恒功率负载的负阻抗特性以及储能单元充放电特性对系统稳定性的影响,应用 Brayton-Moser 提出的混合势函数理论进行稳定性建模,得到大信号稳定性判据。该判据定量描述了母线电压、恒功率负载的功率、储能单元充放电功率等参数与系统大信号稳定性之间的关系。结构简单、便于应用,为保障直流微电网的安全稳定运行提供了重要设计依据。仿真和实验结果表明,在大扰动条件下,满足该判据的系统可以保持稳定运行。

In DC microgrids, the loads are interfaced through power electronic converters. These loads behave as constant power loads (CPLs) with the closed control loop. When the voltage changes, these loads exhibit negative impedance characteristics and may cause instability of the system. Consequently, large signal stability analysis of DC microgrids is very necessary. This paper analyzed the large signal stability of DC microgrid, based on the negative impedance characteristics of the constant power load and the charging and discharging characteristics of the energy storage unit. Brayton-Moser’s mixed potential function is used to obtain the large signal stability criteria. According to the criterion, the influence of the DC bus voltage, the power of constant power loads and the charging and discharging power of the storage units on the system stability are all quantitatively analyzed. The criteria are very simple and easy to be used, and provide design basis for ensure the stability of DC microgrid. The experiment and simulation results indicate the system can maintain stable under large disturbance conditions.