A hybrid control method for three-phase grid-connected inverters with high quality power

This paper presents a novel control method for three-phase grid-connected inverters used in distributed generation systems. The control system is divided into linear and nonlinear parts. The nonlinear part is further divided into predictable and unpredictable parts. For the linear part, a proportional (P) controller provides output current deadbeat control so that the output current can follow its reference in each pulse width modulation (PWM) period. For the predictable nonlinear part, real-time sampling and predictive techniques are employed to reduce influences of grid voltage harmonics and control delays. An integral (I) controller eliminates the effects of both the unpredictable nonlinear parts and the errors of the P controller on predicting output voltage vector so that the output current closely follows its reference. Further more, the influence of grid voltage harmonics on the inverter output current is analyzed, and the effective method to reduce its influence is developed. Experimental results show that the proposed current control method provides the inverter with an excellent steady-state response and an extremely fast dynamic response, while the quality of the inverter output current is very high.