Frequency conversion motor & # 8203; 1 a, the influence of the frequency converter for general asynchronous motor, motor power, and the problem of temperature rise regardless of the method of frequency converter in operation have been different degree of harmonic voltage and current, make the motor in non-sinusoidal voltage, power flow operation. There appeared materials to now in use of sine wave type PWM inverter as an example, its low harmonics root is zero, larger than the rest of the carrier frequency times higher harmonic weight: 2 u + 1 (U for the modulation ratio)。 Can lead to higher harmonic motor stator copper loss, rotor copper (Aluminum)Consumption, iron loss and add additional loss, the most obvious is the rotor copper (Aluminum)Consumption. For asynchronous motor is near the base wave frequency corresponding to the synchronous speed of rotation, thus, higher harmonic voltage to a larger slip cutting rotor after conducting bar, will happen a lot of rotor loss. In addition, still need to consider additional copper loss arising from the skin effect. These losses will make motor rated heat, power down, the output power is reduced, such as the general three-phase asynchronous motor running in the inverter output non-sinusoidal power supply conditions, the temperature rise to add 10% ~ 20%. 2 now small and medium frequency converter, motor insulation strength problem, a lot is to choose the PWM control method, its about several thousand to more than 10 KHZ carrier frequency, which makes the motor stator winding to withstand high voltage build-up rate, equivalent to impose great impulse voltage gradient on motor, the turn-to-turn insulation of the motor under relatively strict examination. Other, produced by rectangular chopper in PWM inverter impulse voltage superposition voltage on the motor is running, will pose a threat to ground insulation of motor, to ground insulation under the repeated impact of high pressure can accelerate ageing. 3, harmonic electromagnetic noise and sensation when choosing the inverter power supply general asynchronous motor, can make the electromagnetic, mechanical, ventilation and other elements of the stir and noise have become increasingly complex. Variable frequency power supply is contained in every moment of the harmonic and motor electromagnetic part of the natural space harmonic do to each other, constitute a variety of electromagnetic vibration force. When the electromagnetic wave frequency and motor of the body's inherent in the oscillation frequency, or near, will occur resonance phenomenon, and then increase the noise. Because the motor operating frequency scale, wide speed change big, all kinds of the electromagnetic wave frequency is difficult to avoid the inherent sensation of various components of the motor frequency. 4, motor to start, braking adapt to frequently because selects the inverter power supply, motor can under low frequency and voltage with no impact current method, and can use supplied various inverter braking method for rapid braking, create conditions for complete frequently start and brake, and the mechanical system and electromagnetic system of the motor is in circulation under the effect of alternating force, brings to the mechanical structure and insulation structure fatigue and accelerate the aging problem. 5, when low speed cooling problems first, the impedance of the asynchronous motor is endless ambitions, when power frequency is bottom, the power loss caused by high order harmonic. Secondly, the general asynchronous motor, when the speed is falling and cooling air volume and speed of three times one share is reduced, cause the low speed of a motor cooling conditions deteriorate, temperature rise sharply to add, difficult to finish the constant torque output. Special 1 second, the frequency conversion motor, electromagnetic design for general asynchronous motor, design the function of the priority parameter is overload ability, a function, power and power factor. And frequency conversion motor, is because of the critical slip at power frequency, able to directly start in the critical slip near 1, therefore, overload ability and function is not demand too much, and to deal with the key problem is how to improve the motor of the non sine wave power adaptation ability. Methods generally as follows: 1)As far as possible, the reduction of the stator and rotor resistance. Decrease the stator resistance can drop fundamental copper loss, copper loss caused to compensate for higher harmonic add 2)For possessed of higher harmonic current, should be appropriate to add the inductance of the motor. But rotor slot leakage resistance is larger the skin effect is also big, higher harmonic copper loss also increased. Thus, the motor leakage resistance of intrusive to give attention to two or morethings arrives the rationality of the impedance matching throughout the whole speed adjustment scale. 3)Frequency conversion motor of main magnetic circuit is designed in unsaturated condition, the consideration of higher harmonic is deepening magnetic circuit saturation, 2 it is considering in low frequency, to improve the output torque and proper progress inverter output voltage. 2, structure design, structure design, the first is also considering non-sinusoidal power characteristics of variable frequency motor insulation structure and oscillation, the influence of the noise cooling method, etc, generally pay attention to the following questions: 1)Insulation class, generally for F or higher, strengthen the insulation and line turn insulation strength, especially considering the impact resistance voltage insulation ability. 2)Oscillation of the motor, noise problem, should fully consider the motor components and all the rigidity, vigorously advances the inherent frequency, to avoid resonance occur with all the force wave. 3)Cooling method: forced air cooling is generally selected, the main motor cooling fan with independent motor drive. 4)To prevent shaft current, beyond the capacity of 160 kw motor should choose bearing insulation measures. First is prone to asymmetric magnetic circuit, can also occur shaft current, while the rest of the high frequency weight what is happening with the current combination of effects, the shaft current will greatly add, and then result in bearing damage, so often adopted insulation measures. 5)The constant power variable frequency motor, when the speed beyond 3000 / min, should choose a special grease, high temperature resistant to compensate for the temperature of the bearing
