One inverter carries several or even dozens of motors at the same time, and the speed of all motors is controlled by the output frequency of the same inverter. Theoretically, the speed of all motors is the same, and the speed can be increased and decreased at the same time. However, due to the difference in motor manufacturing or the size of the load carried by the motor, the actual operating speed of each motor is different, and there is no mechanism to correct this difference in the system, and it is impossible to install a mechanism to correct the difference. When there is no connection between some devices, this control method will definitely produce accumulated errors. The inverter can be regarded as a power supply. In some rigidly connected systems, the load of the motor that runs slightly faster will be heavier and the load of the motor that runs slightly slower will be light, but because the same inverter is driven, the load will be heavy. The difference rate becomes larger and the slip rate becomes smaller when the load is light. In this way, there will be a certain degree of automatic correction capability, which will eventually make each motor keep running in synchronization, but the load distribution is uneven. Generally, the motor should be selected when selecting the motor. Power amplification level. For applications that require rapid braking, in order to prevent overvoltage during stop, a braking unit and braking resistor should be added. Some low-power inverters have built-in braking units, so you only need to connect a braking resistor.
The significance of choosing the correct motor capacity: If the motor capacity is too large, the motor efficiency is low and the capacity is wasted; if the motor capacity cannot be fully utilized; if the capacity is too small, the motor will overheat and the motor life will be reduced. The insulation material of each motor limits its maximum allowable temperature. If the operating temperature exceeds the allowable temperature, the insulation life will be shortened by half for every 8°C increase. Therefore, the appropriate capacity must be selected. When selecting the motor, in addition to the capacity, the type, current type, speed, etc. of the motor must also be selected.
When studying the heating of a motor, the difference between the temperature of the motor and the ambient temperature is often referred to as the "temperature rise". Obviously, motors using different insulating materials have different maximum allowable temperature rises. The temperature rise marked on the nameplate of the motor refers to the difference between the maximum allowable temperature of the insulating material used and 40°C, or it is called the rated temperature rise. When selecting the motor power, in addition to considering heat generation, sometimes it is also necessary to consider whether the overload capacity of the motor is sufficient, because the short-term overload capacity of various motors is limited.
The selection of a motor should be comprehensively considered from various aspects such as DC and AC, mechanical characteristics, speed regulation and starting performance, and price. The general principles are: ① First consider the three-phase squirrel cage asynchronous motor, which is mainly suitable for strong mechanical characteristics and no speed requirements. Production machinery such as dragging of production machinery, ordinary machine tools and water pumps with a power of less than 100KW. ② When the on-site power supply capacity is small, the motor power is large, and the speed change is required during operation, the wound type motor should be selected. Because of its good mechanical characteristics, it is more suitable for some lifting equipment, hoisting equipment, etc. ③ The structure of the slip motor can be divided into two types: vertical and horizontal. The horizontal shaft is horizontal, and the vertical one is vertical to the ground. Under normal circumstances, when the speed regulation requirement is within the range of 1:10, and the speed can be adjusted continuously, the slip motor can be selected. Vertical motors should be avoided as much as possible. Only when vertical operation is required is it necessary to simplify the transmission device. Choose a vertical motor, on the other hand, the price of a vertical motor is relatively higher.
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