Combined model-based sliding-mode controller for a three-phase voltage source inverter fed induction motor drive

The chattering phenomenon associated with the use of Sliding Mode Controllers (SMC) is considered a major drawback of the robust controllers. Ideally, SMCs are to exhibit infinite switching frequency but this is always compromised by the existence of parasitic dynamics which add to the input relative degree of the system and leads to high but finite switching frequency. The performance and robustness of the controller can be closely linked to the resulting switching frequency. Often, when controlling the speed of induction motors, SMCs are applied and used to generate what is assumed to be smooth control signals. These control signals are used as modulation inputs for various carrier based modulation schemes. In doing so, the sliding action of the controller is disrupted as the SMC´s switching frequency is limited by the finite carrier frequency of the modulation process. This effect is carefully analysed in this paper. An alternative is considered in this paper where SMCs are applied to the inner most control loop without the use of any carrier based modulation schemes.