【Daily Question 20090221】Why can inverters improve the power factor?

There is a large capacitor between rectification and inversion, which serves to improve the power factor. For inverters, it serves the purpose of rectification and filtering.

The reason for the increase in power factor is that the filtering capacitors inside the inverter generate reactive power, which is supplied for the motor to consume. As the power factor increases, the actual input current of the inverter decreases, thereby reducing the line losses between the power grid and the inverter as well as the copper losses in the transformer. At the same time, as the load current decreases, the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can handle a greater load.

Mainly, it involves adding a large varistor to improve the power factor

The solution I came up with was to add a large varistor, thereby improving the power factor.

The reason for the increase in power factor is that the filtering capacitors inside the inverter generate reactive power, which is supplied for the motor to consume. As the power factor increases, the actual input current of the inverter decreases, thereby reducing the line losses between the power grid and the inverter as well as the copper losses in the transformer. At the same time, as the load current decreases, the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can handle a greater load.

The reason for the increase in power factor is that the filtering capacitors inside the inverter generate reactive power, which is supplied for the motor to consume. As the power factor increases, the actual input current of the inverter decreases, thereby reducing the line losses between the power grid and the inverter as well as the copper losses in the transformer. At the same time, as the load current decreases, the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can handle a greater load.

The inverter’s DC circuit has filter capacitors, which allows the power factor to be improved to 99%. An inverter can change the frequency! This can be determined using the formula for power factor!

During the start-up of an asynchronous motor, when the slip rate S is close to 1, a large slip results in high reactive power and a low power factor； 2. When an asynchronous motor is operating at its rated capacity, the slip rate S is close to 0; a low slip results in low reactive power and a high power factor ； 3. When starting the motor, the frequency output by the inverter is low, which ensures that the slip of the asynchronous motor remains within the rated slip range; thus, the motor operates at a high power factor at all times ； 4. Therefore, it can be said that the inverter changes the output frequency to keep the slip of the asynchronous motor within the rated slip range, thereby ensuring a high power factor for the motor’s operation ；

If the ratio of the inverter’s output frequency f to the output voltage U remains constant, then the motor flux Φ is a constant value; in other words, the excitation current (NIo) stays unchanged； 2. The excitation current (NIo) decreases only when the motor flux Φ decreases ； 3. Therefore, the main way in which inverters improve the power factor is by controlling the slip rate of the asynchronous motor ； 4. When the asynchronous motor is under a situation of overloading, the frequency converter can adjust the frequency-to-voltage ratio, reducing the motor flux Φ; this helps to reduce reactive current and improve the power factor ；

Reduce the frequency and voltage, but keep the frequency-to-voltage ratio constant; this ensures that the magnetic flux Φ in the motor core remains unchanged, equal to the magnetic flux Φ specified in the motor’s design, that is, the magnetic flux Φ at the power frequency； 2. When a large motor is used to drive a small one, it is possible to reduce the motor flux Φ, that is, to change the value of the frequency-to-voltage ratio; in other words, at the same frequency, the voltage can be appropriately reduced, thereby lowering the excitation current ； 3. Therefore, reducing the frequency of 1 lowers the voltage, but does not reduce the flux Φ; the excitation current remains unchanged, and the reactive power stays the same ； 4. Therefore, the change in the voltage-frequency ratio for 2 leads to a reduction in the motor flux Φ, a decrease in the excitation current, a reduction in reactive power, and an improvement in the power factor ；

To improve the power factor, the inverter can change the frequency! This can be determined using the formula for the power factor

There is a large capacitor between the rectifier and the inverter, which serves to improve the power factor. For inverters, it serves the purpose of rectification and filtering.

There is a large capacitor between rectification and inversion, which serves to improve the power factor. For inverters, it serves the purpose of rectification and filtering.

The reason for the increase in power factor is that the filtering capacitors inside the inverter generate reactive power, which is supplied for the motor to consume. As the power factor increases, the actual input current of the inverter decreases, thereby reducing the line losses between the power grid and the inverter as well as the copper losses in the transformer. At the same time, as the load current decreases, the power distribution equipment such as transformers, switches, contactors, and wires that supply power to the inverter can handle a greater load. To improve the power factor, the inverter can change the frequency! Based on the formula for the power factor, it can be seen that reducing the frequency lowers the voltage, but the frequency-to-voltage ratio remains constant; this ensures that the magnetic flux Φ in the motor’s core stays unchanged, equal to the magnetic flux Φ specified during the motor’s design, that is, the magnetic flux Φ at the line frequency ； 2. When a large motor is used to drive a small one, it is possible to reduce the motor flux Φ, that is, to change the value of the frequency-to-voltage ratio; in other words, at the same frequency, the voltage can be appropriately reduced, thereby lowering the excitation current ； 3. Therefore, reducing the frequency of 1 lowers the voltage, but does not reduce the flux Φ; the excitation current remains unchanged, and the reactive power stays the same ； 4. Therefore, the change in the voltage-frequency ratio for 2 leads to a reduction in the motor flux Φ, a decrease in the excitation current, a reduction in reactive power, and an improvement in the power factor ； 5. If the ratio of the inverter’s output frequency f to the output voltage U remains constant, then the motor flux Φ is a constant value; in other words, the excitation current (NIo) does not change ； 6. Only when the motor flux Φ decreases does the excitation current (NIo) decrease ； 7. Therefore, the main way in which inverters improve the power factor is by controlling the slip rate of the asynchronous motor ； 8. When the asynchronous motor is under a situation of overloading, the inverter can adjust the frequency-to-voltage ratio, reducing the motor flux Φ; this helps to reduce reactive current and improve the power factor ；

(1) Improve the natural power factor. The natural power factor is the power factor of electrical equipment without any compensation. Methods to improve the natural power factor include: ① Proper selection of asynchronous motors ； ②Avoid operating power transformers under light load ； ③Reasonably arrange and adjust the process flow to improve the operating conditions of mechanical and electrical equipment ； ④Where the production process conditions permit, synchronous motors should be used in place of asynchronous motors. (2) Use artificial compensation for reactive power. Artificial compensation is achieved by installing reactive power compensation devices. The most commonly used such device by electricity consumers is the power capacitor, also known as a shunt capacitor, phase-shifting capacitor, or electrostatic capacitor.

Because the inverter is used to rectify alternating current into direct current, thereby preventing the motor from affecting the power grid

The inverter’s DC circuit has filter capacitors, which enables an improvement in the power factor

Variable frequency cannot improve the power factor of the motor. If you don’t believe it, you can do a measurement. When the same motor is operated for one hour with a frequency converter and without one, it is definitely the motor connected to the frequency converter that uses more electricity. What people mean when they say that inverters save electricity by improving the power factor is, in essence, the following. It refers to the electricity saved when he operates at a lower frequency. To give an example. A fan rotates at 3,000 revolutions per minute across the entire frequency range, that is, at its maximum wind speed. If a low wind speed is needed now, the oldest method is to close the wind damper. In this way, the motor still operates across the full frequency range. But with an inverter, I can reduce the frequency to achieve a lower wind speed, allowing the motor to operate at a speed below 3000 revolutions per minute. The voltage of the motor is proportional to its frequency. If the motor frequency decreases, then the motor voltage also decreases. At the same time, his power also decreased while the power factor increased.

Can it be improved? Who can provide data support to conduct a specific analysis and explain the principle behind it?

This is mainly because the inverter contains large electrolytic capacitors, which can effectively compensate for the reactive power of inductive loads, thereby improving the motor’s power factor. The commonly used reactive power compensator in electricity systems is the power capacitor.