Current Decoupling Scheme of Three-Phase Inverter with Complex Coefficient Controller

In the control of three-phase system, AC signals are always changed into DC signals by synchronous coordinate transformation. A decoupling control scheme in the dq synchronous reference frame (SRF) is proposed to realize active and reactive current decoupling of three-phase inverter. The complex vector control model is established in SRF. Different from the model established in static reference frame, the SRF control model can reflect the coupling characteristic of the active and reactive current. As a result, the PI controller with complex coefficient can be applied to realize current decoupling. In this paper, the coupling characteristic of three-phase system is analyzed. A novel complex PI controller design method is proposed based on the SRF control model and the coefficients are calculated. And its implementation in the control loop is given. Compared with existing PI controllers with real or complex coefficients, the proposed complex PI controller can realize completely the decoupling of the active and reactive current in three-phase system. Besides, the control scheme can make current loop fulfill the expected symmetrical bandwidth, so as to realize a higher effective set-off frequency. As a result, the inverter can achieve well dynamic performance. Finally, the simulation and experimental results are given to verify the theoretical analysis.