A Universal Droop Control for Grid-Connected Cascaded Inverters

Decentralized control of cascaded inverters attracts much attention due to its high flexibility and scalability. In the grid-connected mode, the existing decentralized control methods either tend to destabilize under grid-voltage dip or fail to provide primary voltage/frequency support. To address this issue, this article proposes a universal droop control of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\omega/P\text{-} Q$</tex-math></inline-formula> & <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V/Q$</tex-math></inline-formula> with grid voltage adaptability and active support capability. Specially, the system robustness is improved by adding reactive power item into the frequency droop control law. Meanwhile, it can also realize grid-forming support and autonomous power balance, which offers a universal control framework for practical cascaded PV/storage application. Finally, the experimental results validate the proposed control strategy.