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Back electromotive force (back electromotive force formula of permanent magnet synchronous motor) Back electromotive force refers to the electromotive force generated by resisting the changing trend of current. Back EMF generally appears in electromagnetic coils, such as relay coils, solenoid valves, contactor coils, motors, inductors, etc. Today we will talk about the measurement methods of no-load back EMF of permanent magnet synchronous motor?

1. Reverse dragging method: use the prime mover to drag the motor under test, conduct no-load operation of the generator at synchronous speed, measure the three line voltages at the output end of the machine under test, and take the average value as the no-load back EMF. The original machine can be selected from three-phase synchronous motors with the same number of poles and power, or three-phase asynchronous motors with the same number of poles and frequency. However, during the test, the frequency of three-phase asynchronous motors should be adjusted to reach the synchronous speed of three-phase permanent magnet synchronous motors. In addition, synchronous machines or asynchronous machines with different poles and different frequencies can also be used, but the synchronous speed of the tested machine shall be ensured.

2. Minimum current method: when the tested machine runs no-load at rated voltage and frequency until the mechanical consumption is stable, adjust its external voltage to minimize its no-load current. At this time, the average value of the external terminal voltage is the no-load back EMF of the permanent magnet synchronous motor. However, because the point near the minimum current of the permanent magnet synchronous motor fluctuates greatly, it is difficult to find the minimum value. Through a large number of tests, it is proved that the power factor at the minimum point of the no-load current of the synchronous machine is 1. In this way, the no-load back EMF of the permanent magnet synchronous motor can be determined by observing the power factor.