Coupling Effect Analysis and Design Principle of Repetitive Control Based Hybrid Controller for SVG With Enhanced Harmonic Current Mitigation

Static var generator (SVG) is mostly utilized under polluted grid conditions with certain power quality problems, of which the grid disturbance will lead to the distortion of grid-side current. Hybrid repetitive controller (RC), as an effective method to suppress periodic distortion of grid-connected converters and to improve the dynamic response of conventional RC, has been adopted in existing approaches. However, the physical meaning of existing modeling based on the small gain theorem is not clear. Besides, the conventional design method is difficult to reveal the stability domain and to obtain an optimized repetitive gain, which influences the anti-disturbance performance. In this article, the coupling effect among the controllers of hybrid RC is revealed, showing clear physical meaning, thus the mechanism resulting in the instability problem and delay effect is addressed clearly. Different from existing methods, a simpler design principle is proposed, and a universal stability domain analysis for hybrid RC can be directly obtained and ensure a maximized repetitive gain. A proportional, resonant, and RC (PR-RC) is given as an example to improve the dynamic response of the SVG under $a$ – $b$ – $c$ coordinate. Experimental results demonstrate the correctness and effectiveness of the coupling analysis and parameter design.