Programmable controller solves the problem of synchronous control of distributed vehicle drives

When the vehicle drive motor adopts decentralized drive, the motor speed asynchronism may cause the vehicle body to run uncoordinatedly, and then the motor speed may deviate from the normal value, which may cause equipment damage in severe cases. Therefore, it is of practical significance to solve the problem of motor speed asynchronism caused by decentralized drive of vehicle drive motor.
This paper introduces an advanced and practical control method using PLC to solve the motor speed synchronization when the vehicle is decentralized driven.

2 Problem Statement

At present, vehicle operation equipment generally adopts two modes: centralized drive (see Figure 1) and decentralized drive (see Figure 2). The relationship between the centralized drive inverter and the motor is "one to many"; the relationship between the two in decentralized drive is "one to one".

The advantages of "one-to-many" are simple control, easy operation and maintenance, but the centralized drive layout requires a large space in the vehicle body. When the vehicle load is large or the vehicle body space is limited, the "one-to-one" decentralized drive method is usually adopted because of its compact structure and simple layout. However, one-to-one has high requirements for the inverter and motor, especially the synchronization problem is difficult to solve. If the motor speed is inconsistent, the inverter will work in the opposite direction, and the output current will be too large to cause tripping, affecting the working efficiency of the vehicle and the service life of the electrical equipment. If the speed deviation is too large, it will cause the vehicle body to deform, affecting the use.

The pulse signal collected by the encoder enters the PLC through the high-speed counting module FM350-1 and is converted into motor speed data. The signals of the two motor encoders are compared, and the motor speed difference is adjusted through the PID adjustment module to give the speed value of motor 2 MW1000.

MW1000 needs to be converted into a signal that the inverter can accept. Since the corresponding 4-20mA value of PLC is 0-27648, and the inverter receiving range value is 0-8192, MW1000/27648×8192 is sent to the analog output channel and converted into a current signal that the inverter can accept to control the inverter of traction motor 2. The PID algorithm is the most commonly used mathematical algorithm in industrial control. Its basic formula is as follows:

Pou （tt） =Kp×（et） +Ki×Σ（et） +Kd×[ （et） - （et- 1） ]

Where: Kp—proportional adjustment coefficient. It reflects the deviation of the system in proportion. Once the system has deviation, the proportional adjustment will immediately take effect to reduce the error.

Ki —Integral adjustment coefficient. It enables the system to eliminate steady-state errors and improve the degree of non-difference. The strength of the integral action depends on the integral time. The smaller the constant Ti is, the stronger the integral action is. Kd —Differential adjustment coefficient. The differential action reflects the rate of change of the system deviation signal. It is predictive and can predict the trend of deviation change. Therefore, it can produce advanced control effects. Before the deviation is formed, it has been eliminated by the differential adjustment action. In order to reduce external interference caused by factors such as power system fluctuations, when compiling the control algorithm, it is necessary to consider the use of integral links, that is, using a continuous and stable input signal over a period of time instead of a certain instantaneous value input signal for PID operation to eliminate cumulative errors and make the number of revolutions adjustable within a certain range. In this way, traction motor 1 and traction motor 2 can be well synchronized and controlled with high synchronization accuracy, thereby ensuring the stability of the operating mechanism.

4 Control results

The PLC host computer monitoring program is compiled using STEP7, and Wincc collects speed values ​​and draws curves. The time interval for data extraction is 15ms. In fact, the speeds of traction motor 1 and traction motor 2 are the same, but in order to reflect the tracking and fluctuation of traction motor 2, they are specially separated here. The upper one is the speed curve of traction motor 1, and the lower one is the speed curve of traction motor 2 (see Figure 4). When the speed of traction motor 1 changes, traction motor 2 can respond in time, track, and quickly reach stability. Experiments show that the control method using PLC and inverter can meet higher synchronization requirements, fast response, and small speed fluctuation.

5 Conclusion

该控制方法已在各种炉下车辆中应用。实际应用中, 走行同步起动效果明显, 车辆运行平稳。实践证明, 采用PLC 解决车辆分散驱动时电机速度同步的控制方法应用效果较好, 是一种理想的调速控制方法, 满足了生产工艺要求, 减少了设备的维修维护费用, 保证了车辆发挥正常的生产效率, 经济效益显著。随着PLC 与变频器控制方法的广泛应用, 必将更好地提高传动系统对