Digital servo system has good dynamic and static characteristic, compared with the traditional control method, has the characteristics of two aspects: on the one hand, the high performance control strategy is widely used in ac servo system. Motor control system based on conventional control theory design defects and deficiencies of the traditional controller design usually need a mathematical model of the controlled object has a very precise, and permanent magnet motor is a nonlinear multivariable system, difficult to box it determine its mathematical model, according to the approximate model of the optimal control in practice often cannot guarantee optimal, by modeling the dynamic, non line and other unforeseen parameters change, the influence of sometimes even lead to control quality serious decline, robustness is not guaranteed. So it is necessary to study a new type of high-performance control strategy, to make up for the flaw and the insufficiency, USES the high performance control strategy of the control system has good adaptive ability and anti-interference ability, can in the parameter time-varying interference and harsh working conditions to ensure system such as good dynamic and steady state performance.