A new double feedback loop control strategy for single-phase voltage-source UPS inverters

This paper proposes a new double feedback loop control scheme for single-phase voltage-source uninterruptible power supply(UPS) inverter with L-C filter. Proportional regulator and proportional-resonant (PR) regulator are applied to the inner current controller and outer voltage controller respectively to guarantee the robustness of the system. In order to improve the dynamic response, a load current feed-forward loop and an output voltage feed-forward loop are added to voltage and current controller respectively. Through the filter inductor current and the filter capacitor voltage, the load current can be computed directly without current sensor. And to reduce the influence of nonlinear load on output voltage, several harmonic resonant compensators are adopted. The mathematical model and the control algorithm of the proposed scheme are described. The digital simulation and experimental results for a 2-kVA inverter indicate that with the proposed strategy, the inverter exhibits satisfactory steady-state and dynamic performances under no matter linear or nonlinear load.