Study on the Control Strategy of Single-Phase DC/AC Inverter

Single-phase inverters have been extensively researched in static coordinate systems; however, traditional PI controllers cannot achieve accurate control, and proportional resonant regulators are not only complex to operate but also constrained by various conditions. Additionally, it is also difficult to switch single-phase inverters between island operation and grid-connected operation in stationary coordinate systems. This paper aims to addresses these issues. Drawing on the control methods of three-phase inverters in rotating coordinate systems, a mathematical model was established for single-phase inverters in these systems. Their control strategies were defined respectively for island operation, pre-synchronization operation, and grid-connected operation in <italic>dq</italic> coordinate systems. Through coordinate transformation, varying AC quantities were converted into constant DC quantities in <italic>dq</italic> coordinate systems, enabling the use of PI controllers for single-phase inverters to achieve deviation-free control, without the need to design complex controllers. This approach greatly simplifies the implementation of various control strategies for single-phase inverters. These control strategies were verified through both simulations and experiments in dq rotating coordinate systems. The results showed that the single-phase inverter achieved standard sine wave output up to 50 Hz in island operation mode. Under grid conditions suitable for connection, the inverter's output voltage realized phase synchronization with the grid voltage in preparation for grid connection. Furthermore, under grid-connected operation conditions, it transitions from a <italic>V</italic>/<italic>f</italic> control strategy to a <italic>PQ</italic> control strategy. The experimental results have verified the feasibility and correctness of the proposed method.