Closed-Loop Control of Single-Phase Grid Inverter Using PLL

Simulink model of a closed-loop single-phase grid-connected inverter using PLL for synchronization, stable current control, and unity power

This model demonstrates a closed-loop single-phase grid-connected inverter implemented in MATLAB/Simulink using a PLL-based synchronous reference frame (dq) control strategy. The Phase-Locked Loop extracts the grid phase and frequency, ensuring accurate synchronization between the inverter and the utility grid under steady-state conditions.

Because single-phase systems do not naturally provide orthogonal components, a virtual β-axis signal is generated, enabling the application of Clarke (αβ) and Park (dq) transformations. These transformations convert measured grid voltages and currents into the rotating dq frame, allowing independent and decoupled control of power components using standard control techniques.

In the dq frame, d-axis current control regulates active power injection, while q-axis current control regulates reactive power, enabling unity power factor operation or reactive power support as required. The controlled dq references are transformed back to single-phase quantities using inverse Park and Clarke transformations.

Finally, Sinusoidal PWM (SPWM) is employed to generate gate signals for the inverter switches. The model is structured with clear signal flow and modular blocks, making it suitable for academic study, research, and extension toward practical hardware implementation of grid-connected inverters.