Robust Decentralized PI Controller Design for Permanent Magnet Synchronous Generator

Abstract

This article considers the problem of controller design for a grid-connected wind energy conversion system (WECS) employing a variable-speed permanent magnet synchronous generator (PMSG). The system architecture comprises of two back-to-back converters connecting the PMSG to the grid. The variable-speed control of the PMSG using the machine-side converter employs a multi-input multioutput (MIMO) inner-loop current control. Although there are sophisticated control strategies to address MIMO design requirements, their practical deployment is often hindered by implementation complexity and computational demands for higher order controllers. In contrast, conventional proportional–integral (PI) controllers remain attractive for embedded applications because of their simplicity and easy hardware realizability. However, traditional PI control approaches rely on current-loop decoupling through feedforward compensation and thereby design in the single-input single-output framework, leading to suboptimal performances. To overcome this, a MIMO control design framework is proposed that explicitly considers the coupling in the system model. The controller design employs a two-stage approach: 1) designing the decentralized inner-loop current controllers in a MIMO framework and then 2) the outer-loop speed controller design. The structured PI controller requires the controller to be designed in a static output feedback framework. Simple weight functions in H∞ robust control framework are chosen for the current-loop controller design to simplify the output feedback design criterion. While achieving robustness to disturbance rejection, the simultaneous regional pole placement criterion is used to ensure well-damped transient responses. Experiments on a laboratory-scale PMSG-based WECS validate the effectiveness of the proposed control design method that outperforms conventionally designed PI controllers in both transient and steady-state performances. © 2020 IEEE.