A Nonlinear Robust Speed Controller for Dual Nonidentical Parallel PMSM System

Connecting permanent magnet synchronous machines (PMSMs) in parallel to a two-level three-leg inverter is a simple but effective way to reduce the required components in a multimachine system. The parallel PMSM system is an affine nonlinear system with external disturbances; therefore, designing a robust controller for it is a challenging issue, especially when machine parameters are not the same. In this article, to deal with the nonlinearity of the system, a Takagi-Sugeno (T-S) fuzzy model is constructed for it first. Then, a nonlinear feedforward controller is introduced to increase the speed tracking performance of the system as well as reduce the complexity of the constructed T-S fuzzy model. To cope with the external disturbances, guaranteed cost control (GCC) techniques and the H-infinity stability analysis method are combined to achieve zero-error speed tracking and external load rejection. In this way, the optimization of GCC is derived, and an H-infinity stability criterion is analyzed based on the T-S fuzzy model instead of the original system. Finally, the feasibility and the performance of the proposed method are tested through an experiment. The experiment results also demonstrated that, compared with the traditional strategy, the proposed method can make the parallel PMSM system consisting of different machines free of unstable risk.