Research On Slide Mode Variable-structure Vector Controlled AC Motor

The vector controlled AC motor drive is a multi-variable system featuring time-variant, nonlinear and strongly coupled papameters. With the addition of some nonlinear and random factors such as mechanical friction, vibration and large load fluctuation during its operation the system mathematical model is difficult to be exactly deduced. Therefore modern control theory and advanced control strategy should be applied to overcome the above mentioned influences to make the system robust and to improve the system performance. The method of slide-mode variable structure control is such a strategy that is characterized of low mathematical model precision, insensitiveness to system parameter variation and external disturbances, omission of parameter identifications, fast dynamic response and easy implementation. These advantages make it suitable to high performance vector controlled AC motor drives. The dissertation aims at the application of slide-mode variable structure control to vector controlled AC motor drives.An introduction is made beforehand on the conceptual basis of sliding-mode variable structure control including its design goal, method, as well as the problems of invariability and chattering etc.The scheme of a vector controlled induction motor driving system is then analyzed, and a sliding-mode structure controller is designed to overcome the drawbacks of traditional PI or PID scheme. Aimed at the sensorless vector control of induction driving system, the study is focused on the method of rotor speed identification by sliding mode observer. A novel variable structure MRAS observer is proposed and applied for the speed identification. The thus constructed sensorless vector controlled induction motor drive is studied by simulation.With the study on the strategy of vector control of permanent magnet synchronous motor (PMSM), a number of speed controllers based on advanced control are analyzed and a sliding-mode variable structure controller for the speed control of vector controlled PMSM drive is designed. Aimed at the sensorless vector control of PMSM driving system, the study is focused on the method of speed identification by sliding mode observer. A method for speed identification based on variable structure MRAS is proposed. The thus constructed sensorless vector controlled PMSM drive is studied by simulation.A laboratory platform of AC driving system designed around TI's DSP chip TMS320LF2407A is constructed and the above mentioned control strategies are tested and studied on it.