Closed-loop SPWM control for grid-connected buck-boost inverters

DC input voltage of inverters fluctuates dramatically in distributed generation applications such as in a wind energy system. Yet, a high quality ac output is required for grid interconnection under variable source conditions. Previously developed control strategies mainly focused on improvements under load variations, a dc input of relatively small ripples, etc. This paper proposed a closed-loop sinusoidal PWM control method with real-time waveform feedback techniques for a grid-connected buck-boost inverter. The control-to-output function was derived through steady state modeling based on the power balance condition, which provides an approach when the output cannot easily be characterized in a single-stage buck-boost inverter. The closed-loop control model was studied with a newly-invented single-stage buck-boost inverter circuit. Simulations verified the method provided fast dynamic response and robustness under large dc voltage variations, non-ideal grid voltage, and component parametric uncertainties. The controlled inverter achieved a low-THD sinusoidal output with a small ac filter and without a dc link capacitor. Therefore, it is concluded that the proposed method can be a preferred choice for grid-connected buck-boost inverters in distributed generation systems.