Ordinary electric motors are designed according to constant frequency and voltage, and cannot fully meet the requirements of frequency converter speed regulation. Therefore, they cannot be used as more frequency conversion motors

1、 The impact of frequency converters on motors mainly lies in their efficiency and temperature rise. The frequency converter can generate varying degrees of harmonic voltage and current during operation, causing the motor to operate under non sinusoidal voltage and current. The higher-order harmonics inside can cause an increase in stator copper loss, rotor copper loss, iron loss, and additional losses of the motor, with the most significant being rotor copper loss. These losses will cause the motor to generate additional heat, reduce efficiency, and output power, and generally increase the temperature rise of ordinary motors by 10-20%.

2、 Insulation strength issues of electric motors.The carrier frequency of the frequency converter ranges from several thousand to over ten kilohertz, making the stator winding of the motor withstand a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, causing the insulation between turns of the motor to withstand a more severe test.

3、 Harmonic electromagnetic noise and vibration.When ordinary motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors become more complex. The harmonics contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces and increasing noise. Due to the wide working frequency range of the motor (official account: pump steward) and the wide speed variation range, it is difficult to avoid the natural vibration frequency of various structural parts of the motor due to the frequency of various electromagnetic force waves.

4、 Cooling issues at low speeds.When the frequency of the power supply is low, the losses caused by higher harmonics in the power supply are relatively large; Secondly, when the speed of the variable motor decreases, the cooling air volume decreases proportionally to the third power of the speed, resulting in the inability of the motor to dissipate heat and a sharp increase in temperature rise, making it difficult to achieve constant torque output.

In response to the above situation, the variable frequency motor adopts the following design:
1) Minimize stator and rotor resistance as much as possible, reduce fundamental copper loss, and compensate for the increase in copper loss caused by higher harmonics
2)The design of the main magnetic field is not saturated, firstly considering that higher harmonics will deepen the magnetic circuit saturation, and secondly considering that the output voltage of the frequency converter can be appropriately increased to increase the output torque at low frequencies
3)Structural design, mainly aimed at improving insulation level; Fully consider the vibration and noise issues of the motor; The forced ventilation cooling is adopted, that is, the main motor Computer fan is driven by an independent motor. The purpose of the forced cooling fan is to ensure the cooling of the motor at low speed.
4)The distributed capacitance of the coil of the variable frequency motor should be smaller, and the resistance of the silicon steel sheet should be larger, so that the impact of high-frequency pulses on the motor is smaller, and the inductance filtering effect of the motor should be better.
5)Ordinary motors, also known as power frequency motors, only need to consider the starting process and the working conditions at one point of the power frequency, and then design the motor; The variable frequency motor needs to consider the starting process and the working conditions of all points within the variable frequency range, and then design the motor.
6)In order to adapt to the PWM width modulation wave output by the frequency converter, which simulates sinusoidal alternating current and contains a large amount of harmonics, a specially made variable frequency motor can actually be understood as a reactor plus an ordinary motor.