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When selecting the matching inverter for the inverter motor, the following two verification tests should be carried out based on the detailed analysis of the load characteristics of the motor under the actual working conditions:

1) the electromagnetic compatibility of the inverter itself;

2) No load, load, speed control process of vibration and noise performance characteristics.

1 constant torque load

When variable frequency speed regulation is carried out under constant torque load, the resistance torque on the motor output shaft remains unchanged when the motor speed is increased or decreased, but the maximum value of the increased speed is not allowed to exceed the rated speed, otherwise the motor will be burned due to overload operation. In the process of speed up regulation, there is not only resistance torque, but also inertia torque to prevent the speed change, so that the torque on the motor shaft exceeds the rated torque of the motor, which may lead to shaft breaking or various electrical faults caused by overheating of the winding. The so-called constant torque speed regulation actually refers to the constant torque on the motor output shaft when the speed is adjusted to any speed and stable operation, which has the ability to drive constant torque load. In the process of motor acceleration or deceleration, in order to shorten the transition time, the motor shaft should be able to generate enough acceleration or braking torque within the allowable range of motor mechanical strength and motor temperature rise, so that the motor can quickly enter the constant torque operation state.

2 constant power load

The torque speed characteristic of constant power refers to the constant power provided by the motor when the running speed of equipment or machinery changes. For example, rolling mill, lathe, winding machine and conveying equipment all have the characteristics of low speed and high torque, small torque and high speed, that is, the motor should have the ability to drive variable torque and constant power load.

When the voltage of the motor increases with the increase of frequency, if the voltage of the motor has reached the rated voltage of the motor, it is not allowed to continue to increase the voltage with the increase of frequency, otherwise the motor insulation will be broken down due to overvoltage. For this reason, after the motor reaches the rated voltage, even if the frequency increases, the motor voltage remains unchanged. The output power of the motor is determined by the product of the rated voltage and rated current of the motor. The current no longer changes with the change of frequency, that is, the motor reaches the operation state of constant voltage, constant current and constant power.

In addition to the load of constant power and constant torque, the power consumed by some equipment changes sharply with the operating speed. For example, for fans and pumps, the resistance torque is proportional to the second to third power of the running speed, that is, the square torque reducing load characteristic, so only the energy-saving frequency converter needs to be selected according to the rated point; For the starting frequency converter used for power frequency motor, the performance requirements of the whole starting process from static speed to normal running speed should be considered.