| Compared with the internal-combustion forklift, electric forklift has many significant advantages. Its market demand is increasing continuously and has a lot of scope for development. The driving system’s performance of the electric forklift is related to the reliability of the forklift’s operation. Electric forklift is traditionally driven by direct-current dynamo which brings many drawbacks. Nowadays many forklift manufacturers prefer AC-drive rather than DC drive so that the forklift’s performance can be improved. However,the research on the AC drive system of our country is relatively late, and the technology is blockaded by foreign countries, it is urgent to develop a AC-drive system with independent intellectual property rights. This paper is devoted to the study of low-voltage AC-drive system aiming for the complete localization of forklifts.Firstly, an optimal AC-drive control scheme for electric forklift—full AC-drive system is put forward. The mathematical model of asynchronous motor is derivated. The voltage closed loop weak magnetic rise speed algorithm is mainly introduced. The speed range of AC system is raised and the maximum torque output is acquired. The RLSE(Recursive Least Square Algorithm) is derivated in order to identificate the motor parameters online. The algorithm is simple and is easy to realize. Several common PI tuning methods are introduced and the critical proportion method is detailed discussed.Secondly, the simulation experiment is carried out on the basis of theoretical analysis.The simulation environment is Matlab/simulink electrical module. The construction method of the sub module is mainly introduced. S-Function is used to realize non graphical programming. The vector control algorithm, the weak magnetic control algorithm and the parameter identification algorithm verification experiment are carried out according to the system simulation model. The simulation result and the theoretical analysis result are compared as a foundation for the hardware design and software programming.The hardware structure diagram of AC-drive system is carried out and on this basis,control circuit and power circuit are designed. The element selection and the parameter determination are analyzed theoretically which provides the basis for the final determination of the component model. The hardware circuit of LCD is introduced and the power supply module is designed.The system software programming environment and method are introduced. The system software is divided into two parts,the main program and the interrupt service program. To each sub module which is used, the software flow pattern is given, the function and realization method are introduced. The important parameters are set up. Different power section,software variable of different voltage levels are standard unitary processed to ensure that the variable range is consistent and easy for calibration and design.Finally, the grading test experiment is carried out to verify the correctness of the control algorithm. Electrical parameters are detected and calculated in the running states of load and no-load. Experimental results and theoretical analysis are compared in order to obtain AC-drive system with good dynamic and static performance. So the localization of forklifts can be realized. |
