Please choose a matching frequency converter when using a variable frequency motor

A while ago, during the trial operation of a variable frequency motor purchased by a customer, the overcurrent protection device of the frequency converter was triggered and could not be put into normal operation. After understanding and analyzing the feedback from the customer, it was found that the reason was due to the small capacity of the frequency converter.

Nowadays, power electronics technology, as the foundation of energy conservation, material saving, automation, intelligence, and mechatronics integration, is developing towards high-frequency application technology, modular hardware structure, and digital control technology, which has led to the increasingly common use of high-performance variable frequency motors. The matching problem between variable frequency drives and motors has also become a topic of debate.

In most cases, the matching between the frequency converter and the variable frequency motor in the frequency converter powered variable frequency motor system is not a big problem, because on the one hand, customers usually leave a margin when choosing the motor, and when choosing the frequency converter, they will set a sufficiently large safety factor based on the selected motor power.

Today we will briefly explain the matching relationship between the two.Voltage matching: The rated voltage of the frequency converter matches the rated voltage of the motor.

Current matching: For ordinary centrifugal pumps, the rated current of the frequency converter matches the rated current of the motor. For special loads such as deep water pumps, it is necessary to refer to the motor performance parameters to determine the inverter current and overload capacity with high current. The current setting of the frequency converter should not be less than 1.1 times the rated current of the motor, and the maximum current is generally set to 1.5 times the rated current of the motor.

Torque matching: For constant torque loads such as extruders, mixers, and lifting equipment, it is common to increase the capacity of the electric motor and frequency converter to improve low-speed torque and avoid the difficulty of low-frequency compensation; 2. Using high-performance frequency converters or vector frequency converters with torque control function to achieve constant torque operation in low-speed areas and constant power operation in high-speed areas. For variable torque loads such as fans and pumps, low-speed loads have smaller torque, and ordinary functional frequency converters can adapt.

Other precautions

When using a frequency converter to drive a high-speed motor, due to the low reactance of the motor, the increase in high-order harmonics leads to an increase in the output current value. Therefore, the selection of frequency converters for high-speed motors should have a capacity slightly larger than that of ordinary motors.

If the frequency converter needs to operate with a long cable, measures should be taken to suppress the influence of the long cable on the ground coupling capacitance and avoid insufficient output of the frequency converter. Therefore, in this case, the capacity of the frequency converter should be increased by one level or an output reactor should be installed at the output end of the frequency converter.