Research On The Control Method Of Alternating Frequency-variable Electric Dynamometer Based Direct Torque Control

In industrial production and control area, the dynamometer is widely used. For full-function type dynamometer, squirrel cage induction motor is firstly chosen due to its light rotor, simple and rugged structure and four-quadrant operation. The development of power-electronics and micro-electronic technologies greatly pushes the development on the control techniques of AC motors, the control performances of motors are greatly improved. The direct torque control (DTC) technology of induction machine is a new theory for AC drive following the vector control technology, in contrast to vector control, its main advantage is that it discards the decoupling idea in vector control, controls the motor's flux and torque directly. Its control is easy and the calculating process is very simple. Employing the control method of DTC, using the squirrel induction motor to construct a full-function AC dynamometer system is a better solution scheme. In this thesis the basic principle of the control method of direct torque of the asynchronous motors is further investigated and the systematic structure of the DTC is analyzed. Also this thesis expatiates many basic conception of DTC in detail, which include the voltage space vector, the estimator of flux and torque, harmonious control of flux and torque. The relation between the ripples of flux and torque and the widths of hysteresis band is analyzed and its optimum control strategy is suggested. In this thesis, a kind of current hysteresis band control scheme is presented in order to control the stator current in a limited range at star-up and faulty overcurrent. And then a series of simulation models of DTC of induction machine and dynamometer system under the environment of MATLAB are established to perform all simulations for the proposed control tactics and algorithms, better effect is obtained through simulations. Finally, this thesis selects a squirrel cage induction machine as the load motor, which is linked with the driving machine through a rigid coupling and the DC sides of the main circuits of the two machines are in common DC-bus. The hardware platform of the power dynamometer based on high-speed digital signal processor (DSP) TMS320LF2407A as the controller and intelligent power module (IPM) as the main devices is constructed for experiment studies. This thesis explains the realization of hardware control circuit in detail and the corresponding control system software compiling method. The full digital control of direct torque control system was established. The results of simulations and experiments show that, the dynamometer system which uses squirrel cage induction machine as the load motor, high-speed DSP as the controller, DTC based, has following virtues such as simple structure, the given torque adjusting conveniently and swiftly, the response of the system being quick. Further more, the energy can feed back through common DC-bus or regenerating unit to the networks, it's one of new type dynamometers which is worth to be broadened.