Harmonic electromagnetic noise and sensation of single-phase adjustable speed motor
Usually, when the frequency converter is used to supply power for asynchronous motor, the sensation and noise caused by electromagnetic, mechanical, ventilation and other factors will become more and more disorderly. Each time harmonic contained in the variable frequency power supply and some inherent space harmonics of the electromotor electromagnetism are mutually related, forming various electromagnetic exciting forces. When the frequency of the electromagnetic force wave and the natural oscillation frequency of the motor body are close together, resonance image will occur, and then increase the noise. Because of the wide frequency scale of motor operation and the large scale of speed change, it is difficult to avoid the natural sensational frequency of various components of the motor.

Cooling question of single-phase motor at low speed
First of all, the impedance of asynchronous motor is not ideal. When the power frequency is low, the loss caused by high-order harmonics in the power supply is large. Secondly, when the rotating speed of asynchronous motor drops, the cubic component of cooling air volume and rotating speed decreases, which leads to the deterioration of low-speed cooling of motor and the sharp increase of temperature rise, so it is difficult to complete the constant torque output.

Questions about the power and temperature rise of single-phase adjustable speed motor
Regardless of that method, the frequency converter will produce different levels of harmonic voltage and current in operation, so that the motor operates under non sinusoidal voltage and current. Despite the introduction of materials, take the sine wave PWM frequency converter which is widely used at present as an example, its low-order harmonic is basically zero, and the remaining high-order harmonic weight which is about twice of the carrier frequency is 2U + 1 (U is the modulation ratio). High order harmonic will lead to the addition of stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss, the most obvious is rotor copper (aluminum) loss. Because the asynchronous motor rotates at the synchronous speed close to the fundamental frequency, the high-order harmonic voltage will cut the rotor bar with a large slip, which will cause a large rotor loss. In addition, additional copper consumption due to skin effect should be considered. These losses will make the motor rated heating, power reduction and output power reduction. For example, if the normal three-phase asynchronous motor is operated in the non sinusoidal power supply output by the frequency converter, its temperature rise is usually increased by 10% - 20%.

Questions about the insulation strength of single-phase motor
At present, many small and medium-sized inverters use PWM control methods. His carrier frequency is about thousands to tens of kilohertz, which makes the stator winding of the motor to accept a very high rate of voltage rise, which is equivalent to applying a steep impulse voltage to the motor, so that the turn to turn insulation of the motor is subject to more strict detection. In addition, the rectangular chopping impulse voltage generated by PWM frequency converter superimposed on the motor operating voltage will pose a threat to the motor's ground insulation, which will accelerate aging under the repeated impact of high voltage.

The habitual ability of single-phase adjustable speed motor to start and brake frequently
Since the inverter is selected for power supply, the motor can be started at a very low frequency and voltage in a non impact current way, and can use various braking methods provided by the inverter for fast braking, which creates conditions for the completion of frequency starting and braking. Therefore, the mechanical system and electromagnetic system of the motor are in the effect of cyclic alternating force, which brings mechanical layout and insulation layout Fatigue and accelerated aging.