AC power electronic systems: Stability and power quality

This paper presents an overview of ac power electronic system modeling and analysis methods. Characteristics of such systems are first discussed, and their applications and significance in renewable energy and distributed generation (DG), transportation, and other mobile and autonomous power systems are highlighted. Typical stability and power quality problems encountered in these systems are demonstrated by measurements from several practical systems. Small-signal analysis methods, such as phasor-based analysis, transformation into dq reference frame, reduced-order modeling, and harmonic linearization that are applicable to ac power electronic systems, are then reviewed and compared in terms of their applicability and limitations. Small-signal impedance modeling of rectifiers and inverters by harmonic linearization is reviewed in some detail. Limitation of the existing impedance-based system criterion when applied to current-source systems is identified and an extension of the theory is presented for application to grid-parallel inverters.