Modeling and analysis of a feedback control strategy for three-phase voltage-source utility interface systems

This paper presents the steady-state and dynamic analysis of a novel feedback control strategy for a three-phase voltage-source utility interface power convertor system with a third order T-filter. The control scheme employs an inner capacitor current feedback loop and an outer capacitor voltage control loop to ensure that the harmonic content of both the capacitor voltage and utility current is within the acceptable total harmonic distortion. The utility interface system is analyzed by establishing a general model using state-space analysis. Employing the concept of state-space averaging technique, the steady-state performance of a balanced three-phase system is obtained in terms of system parameters. The dynamic response of the control strategy is then examined by developing a linearized model of the system equations employing perturbation technique and small signal approximation. Based on the bode plot of the system transfer function, a control loop regulator is selected to improve the dynamic response of the system. It is shown in the paper that the proposed scheme offers many advantages for utility interface systems; it is robust and insensitive to parameter variations. In addition, due to the use of the inner current loop, the system has fast dynamic response. Moreover, it is compatible with both large and weak AC network applications and capable of feeding the utility current at any desired power factor