Research And Design Of The Asynchronous Motor Direct Torque Control System Based On FPGA

With the rapid development of power electronic technology and AC control technology, the AC drive control technology of electric forklift develops rapidly. At the same time, AC control system also transforms from analog control to digital control. Direct torque control is an excellent AC driving control technique, which doesn’t need the precise induction motor model and the complex vector transformations. It has high static and dynamic performance for its direct control method and simple structure. With the rapid development of EDA technology and FPGA devices, complex control algorithm could be realized with a single FPGA chip that has the advantages of high processing speed, good reliability and reconfiguration and has been widely used in recent years. Thus, the significance of researching high-performance electric forklift control system using FPGA can never be overemphasized.This thesis mainly designs a set of direct torque control system which can be applied in electric forklift using FPGA. Firstly, the asynchronous motor’s mathematical model under the three-phase and two-phase stationary coordinate system is discussed in this thesis. The basic concept of the direct torque control, the basic structure and characteristics of traditional direct torque control system and the direct torque control system based on SVPWM are also analyzed. Secondly, based on the analysis of the traditional ideal SVPWM and the SVPWM attached dead zone, SVPWM modulation method is improved. The improved SVPWM eliminates the effect of dead zone on output waveform. The correctness of this novel SVPWM method has been verified through simulated analysis and experiments. Furthermore, the hardware and software of direct torque control system based on the previous theory analysis are designed. Among them, the hardware design includes main power circuit design, drive circuit design, detection of feedback circuit and FPGA control circuit design, software design includes the design of the vector transform module, flux linkage and torque observation module, SVPWM module, digital filter module design, digital PI modules design and speed detection module design etc. And the feasibility of the method was proved by simulating software modules in the RTL-level simulation in Modelsim.Finally, the simulation model of direct torque control system under the Matlab/Simulink is established. The simulation results show that the control system has good dynamic response and steady-state accuracy. And a series of experiments of drive circuit, and direct torque control system are conducted on the hardware platform. The experimental results show that the drive circuit works well, the system runs stably, and has good dynamic performance, which meet the design requirements.