Improved Predictive Current Controlled PWM for Single-Phase Grid-Connected Voltage Source Inverters

Inverter-based distributed generators (DG) must meet the power quality requirements set by interconnection standards such as IEEE Standard 1547 before DGs are allowed to interconnect with existing electric power systems. The power quality is highly dependent on the control strategies of the DG inverters. Traditional predictive current controller can precisely control the load current with low distortions, however, has a poor performance under component parameter variations. An improved predictive current controller has been developed by the authors for single-phase grid-connected voltage source inverters (VSI). Aiming to overcoming the drawbacks of the traditional predictive controller, a scheme for improving the robustness of inverter system is proposed along with a dual-timer control strategy and a software phase-lock-loop (PLL). The controller is designed not only to minimize the control error introduced by the control delay but also to provide a faster response for over-current protection. The simulation and experiment results show that the improved predictive controller has a superior performance to the traditional predictive controller, particularly under parameter variations. The single-phase grid-connected VSI implemented with the proposed predictive controller has shown very low current THD in both laboratory tests and in field operation of a small wind turbine system