It has become an irreversible trend to drive the motor through the inverter. In the actual use process, due to the unreasonable matching relationship between the inverter and the motor, some problems often occur. When choosing an inverter, you should fully understand the load characteristics of the equipment driven by the inverter.

We can divide production machinery into three types: constant power load, constant torque load, and fan and water pump load. Different load types have different requirements for inverters, and we should reasonably match them according to specific conditions.

The torque required by the spindle of the machine tool and the coiler and uncoiler in the rolling mill, paper machine, and plastic film production line is generally inversely proportional to the rotation speed, which is a constant power load. The constant power property of the load should be in terms of a certain speed variation range. When the speed is very low, restricted by the mechanical strength, it will change to a constant torque load at low speed. When the speed of the motor is adjusted by constant magnetic flux, it is constant torque speed regulation; when the speed is weakened, it is constant power speed regulation.

Fans, water pumps, oil pumps and other equipment rotate with the impeller. As the speed decreases, the torque decreases according to the square of the speed, and the power required by the load is proportional to the third power of the speed. When the required air volume and flow rate are reduced, the frequency converter can be used to adjust the air volume and flow rate by means of speed regulation, which can greatly save electricity. Since the power required at high speed increases too fast with the rotation speed, the fan and pump loads should not be run over the power frequency.

TL remains constant or substantially constant at any rotational speed. When the inverter drives a load with constant torque, the torque at low speed should be large enough and have enough overload capacity. If it is necessary to run at low speed at a steady speed, the heat dissipation performance of the motor should be considered to avoid the motor from being burned due to excessive temperature rise.

Issues that should be paid attention to when choosing a frequency converter:

When the power frequency motor is driven by the inverter, the current of the motor will increase by 10-15%, and the temperature rise will increase by about 20-25%.

When using a frequency converter to control a high-speed motor, more harmonics will be generated. And these higher harmonics will increase the output current value of the inverter. Therefore, when selecting a frequency converter, it should be one gear larger than that of an ordinary motor.

Compared with ordinary squirrel cage motors, wound motors are prone to overcurrent tripping problems, and a frequency converter with a slightly larger capacity than usual should be selected.

When using a frequency converter to drive a gear reduction motor, the range of use is limited by the lubrication method of the rotating part of the gear. There is a risk of running out of oil when the rated speed is exceeded.

● The motor current value is used as the basis for inverter selection, and the rated power of the motor is only for reference.

● The output of the inverter is rich in high-order harmonics, which will reduce the power factor and efficiency of the motor.

● When the inverter needs to run with long cables, the influence of the cables on the performance should be considered, and special cables should be used if necessary. In order to make up for this problem, the inverter should enlarge the selection of one or two gears.

●In special occasions such as high temperature, frequent switching, high altitude, etc., the capacity of the inverter will drop. It is recommended that the inverter should be selected according to the first step of enlargement.

● Compared with the power frequency power supply, when the inverter drives the synchronous motor, the output capacity will be reduced by 10~20%.

●For loads with large torque fluctuations such as compressors and vibrators, and peak loads such as hydraulic pumps, you should fully understand the power frequency operation and select a larger frequency inverter.