双母线直流微电网的级联稳定性分析

Cascade stability analysis of double-bus DC microgrid

双母线直流微电网因具有供电可靠、负载匹配性高、接入中低压配电网系统灵活方便等特点,逐渐成为未来家庭和楼宇的主要供电架构之一,而级联稳定性分析是其设计中的重要问题。对双母线直流微电网在不同稳态运行模式下的级联小信号稳定性进行分析,利用广义状态空间建模法、传统状态空间平均建模法建立变换器的阻抗模型,根据系统各单元稳态运行模式的源荷属性提出4种模式,并利用阻抗比判据判定系统的小信号稳定性。仿真结果表明,在轻载模式下系统的稳定裕度最小,其中双有源桥、光伏变换器的阻抗特性不受功率交互的影响且一直具有负阻抗特性,而储能单元仅在作为负荷时具有负阻抗特性。对比3种无源阻抗方案以改善负载阻抗特性,提高系统的稳定裕度。实验结果表明:加入无源阻抗后轻载模式的负载电流纹波系数从14.3%下降至1.9%,可见无源阻抗可以改善负载阻抗特性,提高系统的稳定性和抗扰性能。

Double-bus DC microgrid has become one of the main power supply architectures for homes and buildings in the future due to its features of reliable power supply,high load matching and flexible and convenient access to medium and low voltage distribution systems,and the cascade stability analysis is an important issue in its design.The cascade small signal stability of double-bus DC microgrid under different steady-state operation modes is analyzed.The impedance model of the converter is established by the generalised state space modeling method and the conventional state space average modeling method,four modes are proposed according to the source-load property of the steady-state operation modes of each unit in the system,and the small signal stability of the system is determined based on the impedance ratio criterion.Simulative results show that the stability margin of the system is the least in light load mode,in which the impedance characteristics of dual active bridge and photovoltaic converter are not affected by power interac⁃tion and always have negative impedance characteristics,while the energy storage unit only has negative impedance characteristics when it is used as a load.Three passive impedance schemes are compared to improve the load impedance characteristics and increase the stability margin of the system.The experimental results show that the load current ripple coefficient of light load mode decreases from 14.3%to 1.9%after adding the passive impedance,indicating that passive impedance can improve the load impedance characteristics and enhance the stability and anti-interference performance of the system.