Experimental Study Of Direct Torque Control Of Ac Motors And Linear Motor Static Characteristics

With the development of power electronics and microprocessor, AC drives have been improved greatly, which have already taken the place of DC drives gradually and are applied to numerous fields. Now, AC drives are developed towards digital, intelligent, integrated system. At present AC drives are focusing on field orient control (FOC)> direct torque control(DTC) and space vector pulse width modulation (SVPWM). Since DTC has been developed about 20 years ago, it has become the most important area in the field of AC drive for its advantages of direct control and short adjusting time. At the lower realization of AC drives, SVPWM is the dominated technic, which is fit for digital realization and has high efficiency compared with sine pulse width modulation(SPWM). In this thesis, it is focused on DTC and SVPWM.First, a method of symmetry space vector pulse width modulation(SSVPWM) is put up to improve the capacity of SVPWM. To test the feasibility of SSVPWM, an AC drives control with constant ratio between the voltage and frequency is performed. The result of experiment proved the function of SSVPWM in decreasing the harmonic of current. Then, to increase the efficiency of AC drive, an optimized control is developed. During the analysis of optimum control, the base of copper waste and iron waste are firstly analyzed, then the relation between the copper waste and voltage and the relation between the iron waste and current are discussed. Finally, an optimized control of constant ratio of the voltage and frequency is developed.The second part focuses on DTC, which involves are the flux and torque control. During the control of flux, the idea of FOC is used to decrease the response time of flux. As a result a FOC control of AC driver is performed first. Because the change of torque is arose mainly by the change of angle between the stator flux and rotor flux, the torque is controlled by changing the angle between the stator flux and rotor flux to decrease the response time of torque.The third part focuses on linear-motor drive. First, an analysis on the thrust and vertical force is discussed. Then, an experiment about the static characteristic of linear-motor is performed to better learn the characteristic of linear-motor. Finally, some conclusions for linear-motor drive are drawn based on controlling the change of vertical force.