What effect does the frequency converter have on the motor?

What effect does the inverter have on the motor?

A variable frequency drive (VFD) is a device that controls the speed and output power of a motor. It mainly controls the motor's speed by changing the motor's power supply frequency and voltage. The VFD has the following effects on the motor:

Speed ​​regulation function: The frequency converter can adjust the speed of the motor as needed to achieve precise speed control, meet the operating requirements under different load conditions, and improve the operating efficiency and stability of the motor.

Energy-saving effect: By adjusting the power supply frequency and voltage of the motor, the inverter can match the motor's operating power with the load, reduce the motor's energy consumption, reduce production costs, and improve energy utilization efficiency.

Improve motor starting performance: The inverter can provide additional starting torque to help the motor start quickly and reach the rated speed, reduce the motor starting time and starting shock, and protect the motor and equipment.

Reduce motor noise: The inverter can reduce motor vibration and noise by adjusting the motor speed and voltage, thereby improving the comfort and safety of the production environment.

The impact of frequency converter on motor

1. Motor efficiency and temperature rise issues

Regardless of the form of motor inverter, it will generate different degrees of harmonic voltage and current during operation, causing the motor to operate under non-sinusoidal voltage and current.

Taking the commonly used sinusoidal wave PWM type inverter as an example, its low harmonics are basically zero, and the remaining high harmonic components are approximately twice the carrier frequency u+1 (u is the modulation ratio).

High harmonics will lead to the consumption of motor stator copper. Rotor copper (aluminum) consumption. Iron loss and additional losses increase, the most significant of which is rotor copper (aluminum) consumption. Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, high-order harmonic voltages cut the rotor bars with a large slip, which will cause a large rotor loss. In addition, the additional copper loss caused by the skin effect must also be considered. These losses will cause the motor to generate additional heat, reduce efficiency, and reduce output power. For example, if an ordinary three-phase asynchronous motor is operated under the non-sinusoidal power supply output by the inverter, its temperature rise will generally increase by 10%-20%.

2. Motor insulation strength problem

At present, many small and medium-sized inverters use the PWM control mode of small and medium-sized inverters. Its carrier frequency is about thousands to several kilohertz rising rate, which is equivalent to applying a large impact voltage to the motor, making the motor turn-to-turn insulation bear a more serious 4 to 6 times voltage superimposed on the motor operating voltage, which will pose a threat to the motor ground insulation. The ground insulation is repeatedly impacted by high voltage, and the motor stator winding is subjected to the rectangular chopping generated by the high-voltage PWM inverter, which accelerates aging.

3. Harmonic electromagnetic noise and vibration

When ordinary asynchronous motors are powered by frequency converters, it makes the electromagnetic, mechanical, vibration and noise caused by ventilation and other factors more complicated. Each time harmonic contained in the frequency conversion power supply interferes with the inherent spatial harmonics of the electromagnetic part of the motor, forming various electromagnetic impact forces. When the frequency of the electromagnetic wave is consistent with or close to the inherent vibration frequency of the motor body, resonance will occur, thereby increasing noise. Due to the wide operating frequency range of the motor and the large speed change range, the frequencies of various electromagnetic waves are difficult to avoid the inherent vibration frequencies of various parts of the motor.

4. Frequent motor starts. Adaptive braking capability

Since the motor uses the inverter power supply, the motor can be started at a very low frequency and voltage without impact current, and can be quickly braked using various braking methods provided by the inverter, thus creating conditions for frequent starting and braking. Therefore, the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating forces, causing fatigue to the mechanical structure and insulation structure, and accelerating aging.