Jingxin forklift manufacturer introduces the introduction of electric forklift speed control system

by:Jxforklift     2022-02-08
Jingxin forklift manufacturers carry the mission of providing high-quality forklift products and intelligent logistics equipment to users all over the world, and leading the development of China's forklift industry/electric forklifts and intelligent logistics equipment. We hope to get your continued care and support, and we will definitely gain more With more successful experience, we have achieved greater results in the new round of development.   The drive system is the key system of an electric forklift, which is generally composed of a traction motor, a control system (including a motor drive, a controller and various sensors), a mechanical deceleration and transmission device, and wheels. The operating performance of electric forklifts mainly depends on the speed regulation technology of the drive system. At present, electric forklifts have DC and AC drive speed regulation systems.  1. DC speed regulation system   The DC speed regulation system of electric forklifts is composed of direction switch, electric control, accelerator, DC motor, related wiring harness, mechanical transmission device, etc. After the controller receives the instructions for the operation of the forklift from electrical components such as the direction switch and accelerator, it is pulse-width modulated and applied to a DC motor with a certain voltage to drive the forklift.   There are usually two ways to realize the speed regulation of the DC drive speed regulation system of electric forklifts, one is armature control, and the other is excitation control. When the DC motor armature voltage decreases (or increases), the armature current and motor torque will decrease (or increase), causing the motor speed to decrease (or increase). Since the maximum allowable current of the armature is constant and the magnetic field is fixed, the armature voltage can be controlled to keep the maximum torque constant at any speed, but the armature voltage cannot exceed its rated value, that is, the base speed of the motor in the speed region The speed can be adjusted by armature voltage control. On the other hand, when the armature voltage is constant, the excitation voltage of the DC motor must be weakened. Therefore, the motor torque increases and the motor speed also increases. Because the maximum allowable current of the armature is constant, when the armature voltage remains constant When changing time, the induced electromotive force is constant regardless of the speed. Therefore, the maximum power allowed by the motor is constant, and the maximum torque allowed varies inversely with the change of the motor speed. The combination of armature control and excitation control allows the motor to have a wider speed control range. The relationship between the maximum torque and maximum power allowed by the two control methods and the motor speed: when the motor speed is lower than the base speed, the excitation current is kept at the rated value, and the armature is used to control the speed. When the motor speed is higher than the base speed, the armature voltage is maintained at the rated value, and the excitation control is used to adjust the speed.  Second, AC speed regulation system    With the maturity and development of modern control theory of AC motors for electric forklifts, AC variable frequency speed regulation technology has been more and more widely used in the drive system of electric forklifts.   The drive speed regulation system of AC electric forklifts is composed of batteries, AC controllers, induction motors, accelerators, various switches, display instruments, related wiring harnesses, and mechanical transmission devices. The battery pack provides DC power for the entire vehicle. The AC control system is a typical CAN-based system. The CAN interface manages AC controllers, smart displays and other accessories and CAN bus to connect to the vehicle system to provide simple information about the status of vehicle equipment. The AC controller converts the DC power from the vehicle battery into a three-phase AC power with variable frequency and current, and drives the corresponding induction motor. The operator sends instructions through digital control variables (direction switch, seat switch, safety switch, hand brake switch, etc.) and analog control variables (accelerator and brake), and feeds back detection signals through sensors such as speed, temperature, and current to adjust the induction The speed and torque required by the motor drive the forklift.   At present, the more commonly used induction motor variable frequency speed control methods in engineering electric vehicles include constant voltage-to-frequency ratio control, slip frequency control, vector control, and direct torque control. In the domestic electric forklift industry, there are several brands of induction motor controllers such as DANAHER in Sweden, ZAPI in Italy, and CURTIS in the United States. Each system is a control system based on CAN bus. At present, the controller brand of Anhui Yufeng is American CURTIS.   The vector control method based on slip frequency control is based on constant voltage-frequency ratio control. The torque of an asynchronous motor mainly depends on the slip frequency of the motor. In the dynamic process of a sudden change in the operating state, due to the transient current, the torque of the motor will deviate, which hinders the sudden change in the operating state and affects the rapidity of the action. . In the control process, keeping one of the motor rotor, stator and air gap magnetic field unchanged, the motor torque will work the same as in the steady state (mainly determined by the slip frequency), so that the torque current in the dynamic process can be eliminated Fluctuations, thereby improving the dynamic performance of general-purpose inverters. The basic control idea is to control the amplitude, phase and frequency of the stator current to keep the size of the rotating magnetic field of the motor unchanged, thereby changing the control frequency of the magnetic field, and then controlling the stator current vector and the two components separately according to the desired torque. It controls the output frequency of the inverter. This control mode can obtain torque response without delay.
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