Improved Weighted Average Current Control Strategy For LCL Grid-Connected Inverters

Abstract

The weighted average current control strategy has attracted much attention because of its lower-order effect on grid-connected inverters. However, the system reverse resonant peak caused by digital control delay causes the traditional WAC control to fail, and the inverter’s adaptation range to the grid impedance under the weak power grid is reduced. In view of this, this article does not start from the point of view of reducing the order of WAC control, but re-examines it from the perspective of grid-side current stability through the well-known capacitive current feedback active damping control method. The analysis shows that the traditional undamped WAC control method has sufficient stability margin under strong grid conditions, while the grid-side current will be in a critical stable state under the capacitive current feedback active damping (CCFAD) control method. It is easy to cause the harmonic resonance of the grid-connected inverter. Furthermore, an improved WAC control strategy is proposed, which enhances the damping effect and robustness of the system by introducing a compensation function in the feedback channel of the machine-side current and the grid-side current. Finally, experiments verify the effectiveness of the proposed control method.

Keywords

• weighted average current control strategy
• digital delay
• capacitive current feedback active damping