In terms of its design, the speed-regulating motor is dedicated to communication and AC speed regulation. However, the most immediate reason for the prevalence of variable-frequency speed regulation is the simple structure, cheap cost and convenient speed regulation of general asynchronous motors. If it is said that the frequency conversion speed control must be applied to the special frequency conversion motor, then it has caused a contradiction. Isn’t the original simplicity, firmness and durability of the frequency conversion speed control gone?
The harm to the motor and efficiency caused by variable frequency speed regulation, no matter which control measures are selected, the operating voltage single pulse output to the motor terminal is non-sinusoidal alternating current. Therefore, the analysis of the operating characteristics of general asynchronous motors under non-sinusoidal waveforms is the harm caused to the motor during variable frequency speed regulation.
The key is the following multiple aspects: motor loss and high-efficiency non-sinusoidal Torque AC Motors Company supply, in addition to all normal losses caused by the fundamental wave, there will be a lot of additional losses. It is specifically manifested in the increase of motor stator copper loss, motor rotor copper loss and iron loss, which in turn endangers the high efficiency of the motor.
1. The harmonics of the stator copper loss of the motor in the stator winding resistance of the motor make the I2R and increase. When the skin effect is neglected, the copper loss of the motor stator under non-sinusoidal AC current is proportional to the square meter of the total current effective value. If the number of motor stator phases is m1, and the stator resistor of each phase motor is R1, then the total motor stator copper loss P1 is the total motor stator current effective value Irms including the fundamental wave current into the above formula, which must be obtained in the formula The second term means harmonic current loss. According to experiments, it is found that the existence of harmonics and the appearance of the leakage flux against it increase the saturation level of the equivalent circuit of the leakage flux, so the excitation current is enlarged, and the fundamental wave component of the current is also increased.
2. At the frequency of harmonic current, the copper loss of the motor rotor can generally be regarded as the parameter of the motor stator winding resistor, but for the motor rotor of the asynchronous motor, the communication AC resistor is greatly increased due to the skin effect. In particular, the slotted cage motor rotor is particularly serious. The synchronous motor or magnetoelectric motor under the sine wave switching power supply, because the magnetic potential of the harmonic current in the stator room of the motor is not large. The loss caused by the surface winding of the motor rotor is negligible. When the same motor is operated under non-sinusoidal AC switching power supply. The time harmonic current magnetic potential magnetically induces the motor rotor harmonics, just like an asynchronous motor operating close to its fundamental wave at the same speed ratio.
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