When an asynchronous motor starts, the slip ratio S is close to 1. At this point, the motor draws a large amount of power, but the power factor is relatively low. As the motor reaches its rated operating condition, the slip ratio S decreases and approaches 0. This means that the motor operates more efficiently, with lower power consumption and a higher power factor.
When using an inverter to start the motor, the output frequency is initially low. This helps ensure that the slip remains within the rated range, allowing the motor to operate at a high power factor throughout the process. In other words, the inverter controls the output frequency to regulate the motor's slip, maintaining optimal performance and efficiency.
If the ratio between the inverter’s output frequency (f) and output voltage (U) is kept constant, the motor’s magnetic flux (Φ) remains stable. This means that the magnetizing current (NIo) stays consistent. However, when the magnetic flux Φ decreases, the magnetizing current also drops, which can affect the motor’s power factor.
To improve the power factor, the key is to control the motor’s slip. When the motor is under heavy load, the inverter can adjust the frequency. Compared to reducing the magnetic flux, this approach effectively reduces reactive current and enhances the power factor. This is why it’s commonly said that "at low frequencies, the output voltage is low, and the reactive current is minimal."
When the motor is pulling a heavy load, the magnetic flux Φ can be reduced by adjusting the frequency-to-voltage ratio. This means lowering the voltage at the same frequency, which reduces the magnetizing current and, consequently, the reactive power. By doing so, the power factor is improved. However, if the frequency is lowered without reducing the voltage, the magnetic flux remains unchanged, and the magnetizing current does not decrease, resulting in no improvement in the power factor.
Servo Lifting Column,Mobile Column Lift,Lifting Column Actuator,Industrial Lifting Equipment
Kunshan Zeitech Mechanical & Electrical Technology Co., Ltd , https://www.zeithe.com