Speed and Position Controllers Using Indirect Field-Oriented Control: A Classical Control Approach

Torque control for induction motors under the scheme of indirect field-oriented control (IFOC) considering rotor resistance perturbations is analyzed via linear approximations. Several important characteristics of IFOC are elucidated, leading to the design of linear, robust, and performance-based torque, speed, and position controllers. In particular, the resulting controllers are of a low order, robust to rotor resistance perturbations, and are designed according to classical performance specifications, which is a combination of characteristics that have been historically difficult to achieve. General control design guidelines valid for any induction motor are presented. In addition, the stability and minimum phase conditions of the IFOC torque controller are fully derived for any induction motor. These conditions are of prime importance when designing fixed linear speed or position controllers. A case study for a typical motor, including the design of a series of robust controllers and real-time experimental results, is presented. The proposed approach makes use of well-known classical control methods that allow the results presented here to be further extended using any linear single-input-single-output controller design tool, such as H-infinity and quantitative feedback theory.