Symmetric Sliding-Mode Control of Grid-Forming Inverters With Precision Region Under AC and DC Sides Varying

TL;DR

This paper introduces a symmetric sliding-mode control method for grid-forming inverters that improves voltage regulation accuracy and robustness during grid faults and varying conditions by decoupling power dynamics and compensating for inverter asymmetry.

Contribution

It develops a novel symmetric sliding-mode control approach with an explicit voltage precision region and an asymmetry compensation structure, enhancing tracking speed and accuracy under varying AC and DC conditions.

Findings

Faster voltage tracking response demonstrated in simulations and experiments.

Enhanced robustness and accuracy under grid faults and power sharing changes.

Explicit verification of the voltage precision region.

Abstract

Voltage regulation under conventional grid-forming controllers is tightly coupled to power sharing and dc-link dynamics. Consequently, its tracking accuracy deteriorates during grid faults, sudden power sharing changes, or dc-bus voltage varying. To address this issue, a symmetric sliding-mode control (SSMC) method is developed and its voltage precision region is derived. It illustrates how much ac-side power dynamics and dc-link voltage varying can be decoupled from the voltage regulation task, which helps predict when an abnormal entangling appears. While conventional sliding-mode controls address voltage-tracking error through complex sliding surface designs, repetitive correction techniques or special reaching laws, this work identifies that the error at power-line frequency primarily stem from the asymmetry property of inverters with the delay effect and the computational inaccuracy. Guided by this insight, an asymmetry compensation structure is proposed, which avoids added design complexity and directly mitigates voltage tracking error. Furthermore, the control design is supported by a physical and quantitative explanation, aiding in parameter tuning. Simulation and experimental results demonstrate that the proposed method achieves faster tracking responses while maintaining robust and more accurate tracking under both dc-link voltage and ac-side current variations. Conventional grid-forming and classical sliding-mode controllers, which handle these variations separately, cannot match this combined speed and robustness. Furthermore, the voltage precision region is explicitly verified.