Abstract
ABSTRACT:
Electric vehicles are complex electromechanical systems with highly nonlinear dynamics. Hence the electromechanical transmission systems high-performance operation, require nonlinear control design to fully exploit their capabilities. This paper reviews and develops a new approach to Fuzzy-Sliding Mode Control (FSMC) , for the robust control in torque and speed within the dynamic model of a transmission system using induction motor propulsion. There are presented the FSMC control design alternative, the control requirements in torque and speed for the propulsion induction motor, for a traction characteristic as prescribed trajectory. A new approach to indirect Vector Controlled Induction Motors (VCIM) using two nonlinear controllers, one of sliding mode type and the other PI-fuzzy logic based, are described.
The sliding-mode controller acts during the transient state and the PI-fuzzy logic one acts in the steady state. Both controllers are combined within the transmission control drive system, respecting the Takagi-Sugeno fuzzy reasoning principle.
The new control system emphasizes the advantages that the two controllers offer: sliding-mode controller increasing the system stability limits and the PI-fuzzy logic one reducing the chattering in steady-state. Finally, is illustrated the control method on a computer simulated example of a propulsion induction motor within a practical scheme which was implemented using a dSpace TMS-DS1102 digital signal processor.
The electrical drive system is based on the variable-structure control theory. The good performances in the speed/torque robust control is provided by an expert system based on fuzzy reasoning which combines the sliding mode and fuzzy logic controller actions. The expert system has been designed in order to weight the outputs issued from the both nonlinear controllers to get the control action. With this system, a good global stability of the electromechanical transmission is provided. Related to the control system, within the indirect vector control method, the flux component of the induction motor stator current is kept constant.
A short mathematical description related to the control scheme is presented. To obtain the control law, the both controllers are separatelly designed. Afterwards, they are adjusted to achieve good features when they are combined. The inputs to both controllers are the error between the reference speed and the measured speed, and the change in that error. By means of the weighting factor, which is the output of a fuzzy logic system that operates at a higher hierarchical control level, the control actions are combined. It divides the control domain depending on the speed error and change in error.
Results presented in the paper are important from a practical point of view since they provide a detailed framework about the design of the control structure for the traction characteristic and other electrical parameters trajectory tracking task.
The paper represents the sequel and development of Power electronics and Automation research team work.