The Novel Control Strategy Of Grid-Connected Inverters Under Unbalanced Voltage Condtions

With the rapid development of new energy power generation technology, many countries are to increase photovoltaic and wind power investment. An important component in new energy power generation system is the grid-connected inverter, for the reason that the solar and wind energy must be delivered to the grid with it after they are converted into electric energy. The inverter various control strategies has its unique advantages, such as direct power control and multistage hysteresis control have good dynamic performance, model predictive control is good at low switching frequency. This paper studies several new control strategies of L inverter under unbalanced grid voltage.Firstly, this paper deduces the mathematical models of grid-connected inverter under unbalanced grid voltage, and provide theoretical supports for the design of unbalanced control system. Then the direct power control, multilevel hysteresis control and model predictive control are researched theoretically. These three control strategies specific research are divided into the following points:Firstly, the dynamic performance of these control strategies are researched, and compared with the dynamic performance of the conventional proportional-integral (PI) control; Secondly, these control strategies are also compared with the traditional PI control under low-frequency condition; Then, these control strategies are study to achieve the control targets to suppress the active power second pulsations,suppress the reactive power second pulsations and hold the three-phase current balance under unbalanced grid voltage; Finally, Simulation circuit is built in Matlab/Simulink and an experimental platform is adapted to verify the control effects of different control strategies. experimental results demonstrate the effectiveness and correctnss of these control strategies.