The difference between a converter motor and a regular ac motor
Ordinary ac motor speed is fixed, the work in the nominal speed. And rotational speed of variable frequency motor is variable, and it varies with the frequency of the power supply voltage, the motor speed can be controlled, can be adjusted.
The variable frequency motor USES a digital variable (modulation) frequency to control the current or voltage of the motor to achieve the precise tunable of power and speed. But special matching frequency converters are needed. Ordinary ac motor is only through a module (simulated) adjustment current method for constant current speed, can't do it fast speed and load adjustment. But you don't need a special configuration, the general motors box.
From the point of view of the operator, the frequency conversion motor is a bad motor, and the ordinary motor is the good motor. 2) as a result of the inverter output PWM adjustable wide wave simulation sinusoidal alternating current (ac), contains a lot of harmonic, after reactor filter in general need to enter ordinary motor, otherwise ordinary chance fever; 3) in order to adapt to the inverter output PWM adjustable width sinusoidal alternating current (ac) contains a lot of harmonic wave simulation, specialized production of frequency conversion motor, its role in fact can be interpreted as reactor with common motor; 4) that is to say, with the power of variable frequency motor is bigger than ordinary motor iron core section, coil number of turns, wire diameter, higher insulation, a special cooling fan motor; In order to adapt to the need of weak magnetic speed adjustment, the bearing capacity and high speed rotor dynamic balance are considered. 6) this frequency conversion motor does not have a better torque characteristic, but it simply overcomes the need of the ordinary motor to adjust to the PWM for the wide wave analog sinusoidal ac. 7) if the converter motor does not have the above characteristics and requirements, it is a false frequency conversion machine.
Electromagnetic design For common asynchronous motors, the main consideration in redesigning is overload capacity, start-up performance, efficiency, and power factor. And frequency conversion motor, because of the critical slip inverse ratio at power frequency, you can directly start when critical slip is close to 1, therefore, overload capacity and startup performance is not need to think too much, and to solve the key problem is how to improve the ability to adapt the motor of the non sine wave power. Here's how it works: 1) minimize stator and rotor resistance Reducing the stator resistance can reduce the copper consumption of the base wave to compensate for the higher copper consumption. In order to suppress the high harmonics in the current, the inductance of the motor is needed. However, the main effect of the rotor slot leakage resistance is large, and the high frequency harmonic copper consumption increases. Therefore, the size of the leakage resistance of the motor should be adjusted to the rationality of the impedance matching within the entire speed limit. 3) the main magnetic circuit of frequency conversion motor generally designed to unsaturated state, one is to consider will deepen higher harmonic magnetic circuit saturation, 2 it is to consider at low frequency, in order to improve the output torque and appropriate to increase the output voltage of inverter.
The structure design Structure design, main is also considering the non-sinusoidal power characteristics of variable frequency motor insulation structure, the influence of vibration and noise cooling mode, generally pay attention to the following questions: 1) insulation level, which is generally F or higher, strengthens the insulation strength of the ground and turns, especially considering the ability of insulation to withstand shock voltage. 2) to the problem of vibration and noise of the motor, the motor should be fully considered component and overall rigidity, trying to improve its natural frequency, in order to avoid and every force wave resonance phenomenon. 3) cooling mode: the general adoption of forced ventilation cooling, the main motor cooling fan is driven by an independent motor. To prevent shaft current measures, the bearing insulation measures should be applied to the capacity exceeding 160KW motors. Mainly produces magnetic circuit asymmetry, also can produce shaft current, while the rest of the high frequency component generated by the current role in combination, shaft current will increase greatly, which can lead to bearing damage, so often insulation measures. For constant power frequency converter motor, the special lubricating grease should be used to compensate the temperature of the bearings when the speed is over 3000 / min.
