Convex Optimization-based Control Design for Parallel Grid-Connected Inverters

Abstract

This paper presents a novel frequency-domain approach towards the control design for parallel grid-connected voltage source inverters (VSIs) with LCL output filters. The proposed method allows to design the controllers of multiple VSIs in a single step, and inherently attenuates the resonances introduced by the output filters and coupling effects while guaranteeing stability. Performance specifications such as desired closed-loop bandwidth, decoupling or robustness towards multimodel uncertainty can be specified through frequency-domain constraints. Furthermore, controllers can be designed in a plugand- play fashion. The designed controllers are equivalent in structure to multivariable PI controllers with filters. As the control design is based on the frequency response of the system, the algorithm is independent of the model order, which allows the use of large and high-order models. The performance of the method is demonstrated on a relevant example of a low-voltage distribution grid with 5 VSIs, and the results are validated both in numerical simulation using MATLAB/Simulink as well as in power-hardware-in-the-loop experiments.

Convex Optimization-based Control Design for Parallel Grid-Connected Inverters