Discrete-time speed servo system design – a comparative study: proportional–integral versus integral sliding mode control
This work presents a comparative study of two approaches for design of high performance discrete-time velocity servo systems with induction motors (IMs). The first approach uses the conventional proportional–integral controller with one-step delayed disturbance compensator (OSDC). The OSDC is based on measurements of the control input and plant states. The second approach uses the discrete-time integral sliding mode (DISM) controller with a first-order disturbance compensator, which is based on switching function signal measurement only. The controlled plant, consisting of IM in the commonly used indirect field-oriented control (IFOC) scheme, is approximated by first-order dynamic model for control design purpose. Comparisons are conducted through simulations considering an ideal case (without unmodelled dynamics) and a regular one, using MATLAB/Simulink models of real IFOC structure elements. The experimental investigation is conducted as well. The performed tests show that both controllers enhanced with the corresponding disturbance compensators are suitable for high-performance control systems design if speed measurement is near noise-free case, with better performance from DISM. If Euler backward difference is applied for speed detection, both control systems need some retuning in order to make a compromise between chattering and tracking accuracy.