LARGE SIGNAL STABILITY ANALYSIS FOR DC MICROGRID UNDER DROOP CONTROL BASED ON MIXED POTENTIAL THEORY

Brayton–Moser's mixed potential theory has been used to analyse the large disturbance stability of DC microgrid with constant power load (CPL), such as current-mode controlled BUCK/BOOST converter with CPL or DC system with multi-stage LC filters. However, the stability analysis of other topology of DC–DC converter or multiple converters worked under droop control is rarely involved. Based on this issue, this paper first establishes the mixed potential model of a single bidirectional BUCK/BOOST converter with CPL. Then, the paper gives the method for establishing the mixed potential model of a droop-controlled DC microgrid with multiple bidirectional BUCK/BOOST converters and CPL. Afterwards, the stability criterion of the analytic form of the system under large disturbance is obtained, which shows that the parameters such as system parameters, control parameters, droop coefficients, and CPL power value have the effects on the system's large signal stability. This paper gives and discusses the relationship between system parameters and stability. Thus, instead of calculating and simulating repeatedly, the stability criterion can judge and ensure the stability of the system under large disturbance in the design process. Simulation results demonstrate the correctness of the simple and easily implemented stability criterion.