Frequency Coupling Suppression Control Strategy for Single-Phase Grid-Tied Inverters in Weak Grid

In single-phase voltage source inverters under a weak grid, the frequency coupling, caused by asymmetrical system structure, poses challenge to modeling and controller design. this article, coupling suppression control strategy is presented, where all components in current reference are eliminated. As result, grid-tied inverter directly modeled as simple single-input single-output (SISO) admittance rather than complicated multiple-input multiple-output matrix. The SISO model simple, compact, accurate, which facilitates design-oriented analysis. characteristic analysis shows that Symmetrical phase-locked loop (Sym-PLL) has critical impact on stability grid conditions. To improve stability, prefilter-based impedance-shaping proposed mitigating negative resistor behavior of Sym-PLL. Finally, simulations experimental results validate effectiveness frequency-coupling strategy.