Research And Design On The Drive System Of Electric Forklift Based On The DTC

As the energy crisis is increasingly serious, energy efficiency technologies were always significant in the field of scientific research. And the development of efficient electric forklift which can replace the inefficient internal combustion forklift became an important research project. Because of the particularity of electric forklift’s motor, generic inverter can not be applied to meet the control requirements of electric forklift. But, its controller’s key technology is currently dominated by a few foreign companies. Thus, there are high economic efficiency and broad market prospects to develop the high-performance electric forklift controller. However, researching on electric forklift drive system is the core of researching the electric forklift. Therefore, the electric forklift drive system base on Direct Torque Control was designed and researched.First, the motor mathematical model in a variety of coordinate are analyzed base on the describing of various coordinate transformation method. The Direct Torque Control based on SVPWM was designed by the analyzing of the traditional Direct Torque Control. Moreover, a model of the magnetic which is more suitable for the control of forklift’s motor was opted after compared of various magnetic models. Then, the simulation for the electric forklift drive system was made, that static performance and dynamic performances are better than the performances of traditional Direct Torque Control as the simulation results showed. The effectiveness and feasibility of this design scheme were verified.Second, the control circuit based on the DSP chip and the power main circuit based on power MOSFET devices in parallel method were designed. A good thermal performance aluminum plate for the main circuit was designed, which can meet the low voltage and high current characteristics of electric forklift motor. Besides, the MOSFET devices parallel flow problem was analyzed and simulated. In additional, the design processes and simulations of MOSFET device buffer circuit are given, as well as its parameter optimization.Third, the experiments were done on the prototype. The results demonstrated the high current distortion and current waveform distortion at zero crossing significantly. After analysising the reasons of the current distortion, a new dead time compensation modulation method was proposed. Dead time’s impact to the voltage vector was analysised and the transition switching state space vector was given. The method to calculate switching times is illustrated through given examples.Finally, this new modulation method was applied to the Direct Torque Control system on the prototype. Specifically, the current waveform became better and the motor run more stably. The feasibility of this design was verified.