The Study And Realization Of Direct Torque Control System Of Asynchronous Motor Based On DSP

During the recent 20 years, Direct Torque Control (DTC) for asynchronous motor has been developed greatly because of its simple system scheme and excellent static and dynamic performances. In DTC scheme, mathematic model of asynchronous motor is analyzed in the stator reference frame, control system is insensitive to motor parameters, electric motor is controlled directly, the optimum switching mode is achieved to control the inverter. In this dissertation, an improved direct torque control system is presented and simulated after analyzing conventional system. Experiments were carried on the digital signal processor (DSP) control platform to prove the improved scheme.Stator flux observer is a key part of DTC system. Classic u-i model is simple, however the integrator inevitably brings up the error accumulation and DC drift. In this dissertation, a novel modified method of modified programmable low-pass filter, modified programmable cascaded low-pass filter (MPCLPF) is proposed. The MPCLPF method greatly improves the dynamic performance of control system, especially under the low speed condition, by switch the order of rectified and programmable cascaded low-pass filer (PCLPF). In addition, hexagon torque controller is replaced by PI regulator, hexagon flux controller is replaced by flux error proportional saturation controller, and a novel method of space voltage vector selecting is used too. These constitute the improved speed control system of DTC for the asynchronous motor.With the simulation software Matlab/Simulink, the simulation experiment on the improved speed control system of DTC for asynchronous motor is carried. Simulation result shows that the improved system is effective.Special advanced peripherals of TI TMS320F2812 DSP make the design of the control hardware easily, and its high-speed processing capability improved the performance of control system. In the dissertation, software is complied by C language. The software realizes functions of measuring speed of rotation with the method of M/T, sampling stator phase current, observing stator flux and electromagnetic torque, selecting space voltage vector, generating SVPWM, etc.Experiments have been done on the DSP motor control platform. The experimental results show validation of the improved scheme.