Study On LPV Direct Torque Control Of Induction Motors

Direct torque control (DTC) system for induction motor has got wide attention because of its advantages such as new thoughts, simple control scheme and excellent performance. The thesis addresses an induction motor model particularly, designs a LPV direct torque control system and studies on this LPV DTC system.Due to the unsatisfactory performance of induction motor at low speed, the DTC system needs improved. The stator flux observation always affects the performance of induction motor in low speed. The preciseness of stator flux observation is the key to stator flux control. Nowadays, there are two stator flux models in the DTC, u-i model and i-u model. In engineering practice, it is always use different stator flux models in different slewing range to estimate the stator flux, but when the u-i model switch to i-u model, there has shake phenomenon. In recent years linear parameter varying (LPV) control has been developed with the development of robust control, and obtained some achievements in non-linear systems control problems. The thesis describes the motor model with the polytopic system, gives a stator flux observation based on LPV control, and establishes a LPV direct torque control system of induction motors.In the thesis, a kind of polytopic LPV rotor current estimator isdesigned, the stator flux and torque are calculated according to the measured value of stator current and the estimation value of rotor current, so that the efficient measurement of the stator flux in the all slewing range is realized. The LPV DCT system escapes the stator flux modle switch between the high speed and low speed, and escapes the shake phenomenon because of the switch. The system has high performance at high speed, but also has large torque ripple in low speed. In order to improve the LPV DCT system, subdivision of stator voltage space vectors is used so that the torque pulsation is decreased, and the excellent dynamic and stead-state performance in high and low speed is achived.In the last, the summarization for the LPV DCT system is made, and some study ways of LPV DTC system are put forward.