Ordinary Y series three-phase asynchronous motors can not fully meet the requirements of frequency conversion speed regulation, because they are designed according to constant frequency 50hz/60hz. The frequency converter has affected the three-phase asynchronous motor in this way, do you know?
Harmonic electromagnetic noise and vibration
Each time harmonic contained in the variable frequency power supply interferes with the inherent spatial harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the asynchronous motor is powered by a frequency converter, it will make the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors more complicated.
Due to the wide operating frequency range of the motor and the wide range of rotation speed, the frequency of various electromagnetic force waves is difficult to avoid the natural vibration frequency of each component of the motor. When the frequency of the electromagnetic force wave is the same as or close to the natural vibration frequency of the motor body, resonance will occur, thereby increasing noise.
Motor efficiency and temperature rise
Regardless of the type of frequency converter, harmonic voltages and currents of varying degrees are generated during operation, allowing the motor to operate under non-sinusoidal voltages and currents.
Taking the currently commonly used sine wave PWM inverter as an example, the low-order harmonics are basically zero, and the remaining high-order harmonic components that are about twice the carrier frequency are: 2u+1 (u is the modulation ratio) . Higher harmonics will cause the increase of the motor stator copper consumption, rotor copper (aluminum) consumption, iron consumption and additional losses, the most significant is the rotor copper (aluminum) consumption.
Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, the high-order harmonic voltage cuts the rotor bar with a large slip, which will cause a large rotor loss.
In addition, the additional copper consumption due to skin effect needs to be considered. These losses will cause the motor to generate additional heat, reduce efficiency, and reduce output power. For example, if a normal three-phase asynchronous motor is operated under the condition of a non-sinusoidal power supply output by the inverter, its temperature rise will generally increase by 10%-20%.
Y series three-phase asynchronous motor
Dielectric strength of motor
At present, many small and medium frequency converters use PWM control mode. The carrier frequency is about several thousand to more than ten kilohertz, which makes the stator winding of the motor to withstand a very high voltage rise rate, which is equivalent to applying a steep shock voltage to the motor, so that the inter-turn insulation of the motor is subjected to harsher test.
In addition, the rectangular chopping impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which will pose a threat to the motor's insulation to the ground, and the insulation to the ground will accelerate aging under repeated high-voltage shocks.
Cooling at low speed
The impedance of the asynchronous motor is not ideal. When the frequency of the power supply is low, the loss caused by the higher harmonics in the power supply is large.
When the speed of the ordinary asynchronous motor is reduced again, the cooling air volume is reduced in proportion to the cubic power of the speed, which causes the low-speed cooling condition of the motor to deteriorate, the temperature rise increases sharply, and it is difficult to achieve constant torque output.
The adaptability of the motor to frequent starting and braking
After the inverter is used for power supply, the Y series three-phase asynchronous motor can be started at a very low frequency and voltage without rush current, and can be quickly braked by various braking methods provided by the inverter. Starting and braking create conditions. Therefore, the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and insulation structure
Harmonic electromagnetic noise and vibration
Each time harmonic contained in the variable frequency power supply interferes with the inherent spatial harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the asynchronous motor is powered by a frequency converter, it will make the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors more complicated.
Due to the wide operating frequency range of the motor and the wide range of rotation speed, the frequency of various electromagnetic force waves is difficult to avoid the natural vibration frequency of each component of the motor. When the frequency of the electromagnetic force wave is the same as or close to the natural vibration frequency of the motor body, resonance will occur, thereby increasing noise.
Motor efficiency and temperature rise
Regardless of the type of frequency converter, harmonic voltages and currents of varying degrees are generated during operation, allowing the motor to operate under non-sinusoidal voltages and currents.
Taking the currently commonly used sine wave PWM inverter as an example, the low-order harmonics are basically zero, and the remaining high-order harmonic components that are about twice the carrier frequency are: 2u+1 (u is the modulation ratio) . Higher harmonics will cause the increase of the motor stator copper consumption, rotor copper (aluminum) consumption, iron consumption and additional losses, the most significant is the rotor copper (aluminum) consumption.
Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, the high-order harmonic voltage cuts the rotor bar with a large slip, which will cause a large rotor loss.
In addition, the additional copper consumption due to skin effect needs to be considered. These losses will cause the motor to generate additional heat, reduce efficiency, and reduce output power. For example, if a normal three-phase asynchronous motor is operated under the condition of a non-sinusoidal power supply output by the inverter, its temperature rise will generally increase by 10%-20%.
Y series three-phase asynchronous motor
Dielectric strength of motor
At present, many small and medium frequency converters use PWM control mode. The carrier frequency is about several thousand to more than ten kilohertz, which makes the stator winding of the motor to withstand a very high voltage rise rate, which is equivalent to applying a steep shock voltage to the motor, so that the inter-turn insulation of the motor is subjected to harsher test.
In addition, the rectangular chopping impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which will pose a threat to the motor's insulation to the ground, and the insulation to the ground will accelerate aging under repeated high-voltage shocks.
Cooling at low speed
The impedance of the asynchronous motor is not ideal. When the frequency of the power supply is low, the loss caused by the higher harmonics in the power supply is large.
When the speed of the ordinary asynchronous motor is reduced again, the cooling air volume is reduced in proportion to the cubic power of the speed, which causes the low-speed cooling condition of the motor to deteriorate, the temperature rise increases sharply, and it is difficult to achieve constant torque output.
The adaptability of the motor to frequent starting and braking
After the inverter is used for power supply, the Y series three-phase asynchronous motor can be started at a very low frequency and voltage without rush current, and can be quickly braked by various braking methods provided by the inverter. Starting and braking create conditions. Therefore, the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and insulation structure
