With the field orientation control (FOC) method, a high performance control of the permanent magnet (PM) synchronous motor is achieved. However, the variation of the mechanical parameters of the motor, during operation degrades severely the stability and performance of the overall system and may cause field orientation detuning. This paper presents the design of a central H∞ suboptimal speed controller. Analysis of stability robustness and performance robustness of closed-loop systems is performed. The torque and flux controllers are designed by traditional frequency design methods.

Keywords: Norm, Structure Uncertainty, Performance, Robustness