SMALL SIGNAL STABILITY ANALYSIS OF THREE-PHASE MICROGRID SYSTEM IN THE PRESENCE OF CONSTANT POWER LOADS

Abstract

Small-signal stability is of great concern for three-phase microgrid systems with regulated power converters which are used for connecting multiple distributed energy resources (DERs) and in various motor drive applications. The converters behave as constant-power loads (CPLs) and cause instability issues in the system. An impedance-based method is preferable for the stability analysis of such systems in real-time. Perturbation methods can be used to determine system impedance. The perturbation approach involves injecting various perturbation signals into the system and determining impedance from the measured voltage and current responses. In this thesis, two perturbation signals, quadrature residue binary sequence (QRBS) and quadrature residue ternary sequence (QRTS) are proposed impedance measurements. Next, new adaptive stability improvement methods are proposed to improve the stability using the non-critical CPL and battery energy storage system (BESS). The proposed impedance measurement technique and stability improvement methodologies are validated using simulation and experimental results.