Impedance criterion based virtual inductor control method for improving inverter system stability

As the energy market increased, microgrid becomes a reliable application of renewable energy source. In the microgrid, inverter behavior is a significant concern to assure system operation reliability. The modeling of a traditional voltage source inverter system and its equivalent output impedance are set up, open loop stability and the boundary condition are represented in this paper. With the output impedance model, impedance stability criterion is employed to assess system stability. Furthermore, filter parameters impacts to the output impedance and system stability are certified by time-domain anslysis approach. Based on the negative incremental impedance characteristic, an AC constant power load model is described to study the degeneration of system stability by impedance specification approach. In order to damp the inverter equivalent output impedance and improve system stability, a virtual inductor control method, which is used to decrease the equivalent filter inductor, is proposed. With this method, the system dynamic response is enhanced and harmonic component at switching frequency is effectively suppressed. The availability of the proposed method is verified by simulation and experimental results.