Nonlinear H/sub /spl infin// speed control of permanent magnet synchronous motors

In this paper, nonlinear H/sub /spl infin// control strategy is applied to speed control of permanent magnet synchronous motors. This motor is increasingly used in many application due to its excellent efficiency, so we need to have some efficient tools to speed control of that. The performance of a permanent magnet synchronous motor is affected by the nonlinear nature of its dynamics. Additionally, some of the parameters are varying during the operation and there is uncertainty in the mechanical parameters of the motor. For these reasons, a robust nonlinear control algorithm seems to be the best choice. Nonlinear H/sub /spl infin// control action has the characteristics of such control, i.e., it has robust performance in response to external disturbances and parameter uncertainty as well as capability in dealing with nonlinear systems. In order to obtain the nonlinear H/sub /spl infin// control law, some inequalities so-called Hamilton-Jacobi-Isaacs (HJI) should be solved. It is so difficult, if not impossible, to find an exact closed solution of HJI inequalities. However, there are some approximate solutions. One of these possible solutions is the use of Taylor series expansion that would be used in this paper. Using this method, the nonlinear H/sub /spl infin// control law of order three is obtained and its performance is compared with that of linearized counterpart, i.e., the first order approximated controller. Simulation results show better performance for higher order approximated controller that of lower order one in response to load torque variations and mechanical parameter uncertainty.