Research And Design On Direct Torque Control System For Induction Motor Of Electric Forklift

As AC power control technique becomes more and more significant and crucial among the major technologies in the manufacturing of electronic forklift, the requirement of AC drive system for electronic forklift has correspondingly; higher precision, faster response and simpler calculation are the permanent pursuit of the Motor Control System. DTC is the latest high performance AC Variable Speed Drive Control technology following the Vector Control Technology. Direct torque control calculated and controlled AC motor torque in the stator coordinate system, employing the direct control of the stator field, DTC can drastically optimize the inverter switching state; moreover DTC is noted for its brief structure and both excellent static and dynamic performance.This article introduces the basic principles of asynchronous motor direct torque control; by means of the mathematics model of Asynchronous Machine, by analysis of the inverter switching state exhibits Space Voltage Vector; though the study of Space Voltage Vector, this paper gives out the basic structure of the Direction Torque Control System and the detailed introduction of each working unit. Additionally, the paper analyzes the correct selecting method of Space Voltage Vector according to magnetic flux and torque self-control theory.Though the deep analysis of torque ripple of traditional DTC system, the paper analyzes the major factors that influence torque ripple by the way of torque model. Besides, the paper analyzes the features of traditional way of reducing torque ripple in DTC system and the relevant research on improving low speed performance. This paper proposes a DTC solution base on SVPWM; through emulation experiment, it argues that torque ripple and electromagnetic noise can be dramatically reduced with maintaining the normal DTC dynamic performance by adding SVPWM to DTC system. This solution is highly reliable, simple with high precision.The MOSFET parallel connection plan is adopted by designing the main circuit, drive circuit and buffer circuit of the inverter and systematically simulating the buffer circuit and main circuit with optimized parameters. The paper analyzes the problems of current flow equalization in parallel MOSFET and the characteristics of the current flow equalization by simulating MOSFET parallel connection. By designing the control circuit and testing circuit with DSP as the core, the experiment platform of low voltage and high current inverter has been realized in this case. The experiment results demonstrate the feasibility of the SVPWM control strategy applied to the actual system.