Precision control of single-phase PWM inverter using PLL compensation

High-precision control of a single-phase PWM inverter for constant voltage and constant frequency applications, such as uninterruptible power supplies, is presented. The proposed control employs a capacitor current feedback with a phase-locked loop (PLL) compensator that minimises the steady-state error of the output voltage. The PLL compensator utilises the capacitor voltage and current with a phase difference of 901. This concept is similar to the dq transform of the three phase variables, and thus the error of the output voltage can be easily minimised by using a proportional–integral type controller. A computer simulation and experiment have been carried out for the actual single-phase PWM inverter controlled by a digital signal processor, and the results clearly demonstrate the effectiveness of the proposed control.