Inverter-Current-Feedback Resonance-Suppression Method for LCL-Type DG System to Reduce Resonance-Frequency Offset and Grid-Inductance Effect

Abstract

For the LCL-type grid-connected distributed generation system, the grid-current-feedback active damping (GCFAD) methods have a conflict between the resonance-suppression ability and harmonic-currents amplification. For this, an inverter-current-feedback reso-nance-suppression (ICFRS) method without additional sensors is proposed to reduce resonance-frequency offset and grid-inductance effect due to its unattenuated damping characteristic under high-frequency bandwidth. By analyzing two types of equivalent impedance models of ICFRS and GCFAD with a high-pass filter (HPF), GCFAD can suppress the resonance peak well only with a large resonance-frequency offset and might result in a narrow control bandwidth. However, ICFRS can suppress the resonance peak well with smaller resonance-frequency offset and maintain a high power quality compared with GCFAD. Considering the influence of control delay and grid inductance, the positive/negative critical point of an equivalent virtual resistance of ICFRS derived in the interval of [1/6, 1/3) is obtained, and a robust ICFRS is further proposed to improve system stability by maintaining a positive resistance regardless of grid-inductance variation. The stable-state and dynamic properties of the overall system are analyzed in detail in this paper, and its proper control parameters are selected without a complicated trial. Finally, simulation and experimental results verify the validity of the proposed method.