How to improve the power factor of permanent magnet synchronous motor

The power factor of permanent magnet synchronous motors is often a concern in many industries. Improving the power factor of this motor can achieve the purpose of energy saving and consumption reduction. So how to improve the power factor of permanent magnet synchronous motor? Let’s discuss it together below!

1. Reasons affecting the power factor of permanent magnet synchronous motor

The permanent magnet synchronous motor used on the oil pumping unit is an asynchronously started synchronous motor. It is started by the rotor and then pulled into synchronous operation, similar to an AC synchronous motor. Its operation relies on the mutual attraction between the rotating magnetic field generated by the stator coil in the air gap and the magnets on the rotor, causing the rotor and stator air gap magnetic fields to rotate synchronously and perform work. The rotor is equivalent to a resistance circuit, so the power factor is high. Since there is no excitation current, its no-load loss is small. The power of the motor can reach about 96%, which is higher than that of the three-phase asynchronous motor.

The factors that affect the power factor of permanent magnet synchronous motor are voltage quality (voltage amplitude) and load factor. When the grid voltage is higher than the back electromotive force point of the motor, the permanent magnet motor operates with an inductive load; otherwise, the motor operates with a capacitive load.

Therefore, fluctuations in grid voltage will cause fluctuations in the power factor of the motor, making compensation difficult. If the voltage amplitude is close to the motor's back electromotive force point and the deviation is within the ±2% voltage range, the motor power factor is greater than or equal to 0.9. Otherwise, the power factor is low; in addition, when the load factor of the permanent magnet synchronous motor is less than 25% , the motor power factor is also low.

2. Methods to improve the power factor of permanent magnet motors

After the above analysis, we can take the following measures to make adjustments:

1. Replace the motor appropriately based on the actual measured load factor to ensure that the appropriate load factor is achieved.

2. Stabilize the system voltage, especially at the end of heavy-loaded lines, where the voltage is generally low.

3. Stabilize the single well voltage so that it is close to the no-load back electromotive force of the permanent magnet synchronous motor.

4. When the operating voltage is higher than the back electromotive force point of the permanent magnet motor, capacitor compensation can be added based on the inductive reactive power to improve the power factor of the motor.

5. When the operating voltage is lower than the back electromotive force point of the permanent magnet motor, the transformer tap changer can be adjusted to appropriately increase the amplitude of the secondary voltage so that the motor operating voltage is close to the back electromotive force point, thereby improving its power factor.

6. For heavy-loaded long lines, after adjusting the transformer tap changer, if the secondary voltage amplitude of the transformer is still lower than the back electromotive force point of the permanent magnet motor, the permanent magnet synchronous motor can be replaced and capacitor cabinet compensation can be used.