Output impedance modeling and stability criterion for parallel inverters with average load sharing scheme in AC distributed power system

The stability criterion of cascaded AC system is usually used to check the stability of AC distributed power system (DPS) by dividing it into a source and a load subsystem. However, the output impedance (admittance) of these subsystems should be obtained, and the stability of subsystems should be checked before applying stability criterion of cascaded AC system. Parallel operation of inverters in source subsystem complicates the output impedance of source subsystem, and can cause source subsystem operating alone instable. In this paper, the output impedance of the inverters operating in parallel with average load sharing scheme is modeled by the I/O character of each inverter operating stand-alone, and a stability criterion was proposed to predict the stability of parallel inverters based on Generalized Nyquist Criterion (GNC). The output impedance model and stability criterion proposed for parallel inverters were verified by simulation results.