Inverter and motor have a lot of influence, usually we may not be so attention, today we will ask permanent magnet synchronous motor manufacturers from these five aspects to discuss the effect of inverter on the motor.
1. Motor insulation strengthAt present medium and small frequency converters, many are using PWM control.Its carrier frequency is about thousands to tens of kilohertz, which makes the stator winding of the motor have to bear a high voltage rise rate, which is equivalent to applying a very steep shock voltage to the motor, so that the insulation between turns of the motor can withstand a severe test.In addition, the rectangular chopper impulse voltage generated by PWM inverter is superimposed on the running voltage of the motor, which will pose a threat to the insulation of the motor to the ground, and the insulation to the ground will accelerate aging under the repeated impact of high voltage.
2. The motor's adaptability to frequent start and brakingAs a result of the inverter power supply, motor can under low frequency and voltage start, in the form of no impact current and frequency converter is available for braking modes of the brake quickly, create conditions for the realization of the frequent starting and braking, and the mechanical system and electromagnetic system of the motor is in circulation under the action of alternating force, brings to the mechanical structure and insulation structure fatigue and accelerated aging problem.
3. Harmonic electromagnetic noise and vibrationWhen the common induction motor is powered by inverter, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors become more complicated.The time harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces.When the frequency of the electromagnetic wave is the same or close to the natural vibration frequency of the motor body, the resonance phenomenon will occur, thus increasing the noise.Because of the wide range of operating frequency and the wide range of rotating speed, the frequency of various electromagnetic waves is difficult to avoid the natural vibration frequency of each component of the motor.
4. Cooling problem at low speedThe impedance of induction motor is not ideal. When the power frequency is lower, the loss caused by high harmonic is larger.Secondly, when the speed of ordinary asynchronous motor is reduced again, the cooling air volume decreases in proportion to the cubic of the speed, resulting in bad low-speed cooling of the motor and a sharp increase in the temperature rise, which makes it difficult to achieve constant torque output.
5. Efficiency and temperature rise of the motorNo matter which type of inverter, in operation, all produce different degrees of harmonic voltage and current, so that the motor in non-sinusoidal voltage, current operation.Despite the introduction of information, take the currently widely used sinusoidal PWM inverter as an example, its low harmonic is basically zero, the rest of the carrier frequency about one times larger than the high harmonic components: 2u+1 (u is the modulation ratio).The higher order harmonics will cause the increase of stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss.Because the asynchronous motor is close to the fundamental frequency corresponding to the synchronous speed of rotation.Therefore, permanent magnet synchronous motor (PMSM) : after the high harmonic voltage cuts the rotor guide bar with a large slip, a large rotor loss will be generated.In addition, additional copper consumption due to skin effect should be considered.These losses will cause the motor to generate extra heat, reduce the efficiency and reduce the output power. For example, if the ordinary three-phase asynchronous motor is run in the non-sinusoidal power supply output by the inverter, its temperature rise will generally increase by 10% to 20%.