## 4 Simulation
### Motor Power Distribution  
After 6 s, the material supply of the belt conveyor system is stable, but the material carrying capacity is lower than the full load value. Therefore, it is necessary to adjust the number of motors running and shut down some motors to achieve energy savings. The whole switching process is divided into two steps, which are the deceleration time and shutdown time. This time, t = 6-9 s is selected as the switching time. During this time, the shutdown motor adjusts its output traction according to the preset curve, as shown in Figure 17. The motor speed fluctuation curve is shown in Figure 18. The closed motor needs to output according to the set power. These motors are difficult to control their own speed, and can only rely on the flexible connection of the conveyor belt to constrain the motor speed. At t = 6 s, the multi-motor speed coordination control will be re-adjusted, and the remaining running motors will form the speed coordination control. The fluctuation range of the motor speed dependent on the flexible connection of the conveyor belt is greater than that of the self-adjusting motor speed. However, as the output power of the stopping motor decreases, the whole system gradually achieves new stability, and the speed fluctuation at all motors gradually stabilizes to the set value of 80 r/min.  
Figure 16: Response curve of conveyor belt on a new type of belt conveyor under variable load operation. (**a**) Velocity curve. (**b**) Tension curve.  
Figure 17: Motor traction fluctuation diagram.  
Figure 19 shows the change curve of the motor speed and electromagnetic torque after the number of motors of the belt conveyor is changed. The specific change process of the motor's initial speed and electromagnetic torque is shown in Figure 19a. Since half of the motor is in the process of its own power attenuation in accordance with the set curve, its own speed adjustment ability decreased, the speed of the more obvious decline. The remaining running motor not only bears its original load but also needs to make up for the problem of the insufficient overall output electromagnetic torque caused by the motor with power attenuation. Therefore, it is necessary to increase its own output power and maintain the overall power balance of the belt conveyor. In addition, the remaining running motor still has self-regulation ability, so the motor speed is lower than the closed motor speed.  
Figure 19: Local graph of motor torque and speed fluctuation during multi-motor power redistribution. (**a**) Initial stage. (**b**) Stable period.  
Figure 18: Motor speed fluctuation diagram.  
As shown in Figure 19b, the closed motor will be completely stopped at 9 s. Since the conveyor belt is a flexible object, the remaining running motor reaches stable operation at about 11 s. The speed of each motor is 80 r/min, and the fluctuation is \(\pm\)0.4 r/min. The speed of the conveyor belt fluctuates at \(\pm\)0.021 m/s, and the electromagnetic torque of the remaining motor is finally stabilized at 2.15 kNm.  
In the process of motor power distribution, the power of motor 2 is attenuated, and motor 1 increases the power output to maintain the power balance of the conveying system. Therefore, the conveyor belt between motor 1 and motor 3 is selected to observe the change of tension. Ten observation points are evenly taken between motor 1 and motor 3. The three-dimensional fluctuation of speed and conveyor belt tension is shown in Figure 20. The motor speed and conveyor belt tension fluctuate after the number of motors is switched, and finally stable operation is achieved.