The power saving principle of the inverter!

I have always heard people say that the inverter can save power, and people who have said it will accept it, but they have not understood why the inverter can save power, and at the same time save more, whether it is more high frequency or more low frequency province. ?

And there are several questions:

1. If two identical motors are working at 50Hz power frequency, one uses the inverter, one does not, and the speed and torque are in the rated state of the motor, then the inverter can save power? How much can I save?

2. If the torque of these two motors does not reach the rated torque of the motor (frequency, speed is still the same 50HZ), how much electricity can save the inverter?

3. The same conditions, how much can be saved under no-load conditions, which provinces are more in these three states?

Answer: The inverter can save power. This is an indelible fact. In some cases, it can save more than 40% of electricity, but in some cases it will be wasted than not connected to the inverter!

The inverter is energy-saving through light load step-down. The drag-to-turn load does not change much because of the speed. Even if the voltage is reduced, it will not be much, so the energy saving is very weak, but it is different in the fan environment. At a small air volume moment, the motor will reduce the speed. We know that the energy consumption of the fan is proportional to the 1.7th power of the speed, so the torque of the motor will drop sharply and the energy saving effect will be obvious. If we use it on the oil well, it will waste more electricity because of the brake resistor used in the return journey (public number: pump housekeeper).

Of course, if the environmental requirements must be adjusted, the energy-saving effect of the inverter is still obvious. In the case of no speed regulation, the inverter will not save power and can only improve the power factor.

1. If two identical motors are working at 50Hz power frequency, one uses the inverter, one does not, and the speed and torque are in the rated state of the motor, then the inverter can save power? How much can I save?

A: For this situation, the inverter can only improve the power factor and does not save power.

2. If the torque of these two motors does not reach the rated torque of the motor (frequency, speed is still the same 50HZ), how much electricity can save the inverter?

Answer: If automatic energy-saving operation is used, the inverter can be stepped down at this time, which can save part of the power, but the power saving is not obvious.

3. The same conditions, how much can be saved under no-load conditions, which provinces are more in these three states?

A: The drag-type load no-load state can not save much power.

For example, about "closed loop control". I think there is room for discussion. The closed-loop concept in the text is too narrow. Closed loop control is not just a feedback from the speed sensor. The frequency control during vector control is closed-loop control, and it is the closed-loop control inside the device. The V/F control belongs to the open-loop control. In addition, the PID regulator feedback control of temperature, pressure, flow and other physical quantities is closed-loop control. The scope. And it can be realized by inverter adjustment. The concept of closed-loop control should not be interpreted as narrow.

For example, the concept of braking, that interpretation is like nonsense, playing with word games, saying that it is equal to not saying the same.

1. Frequency conversion is not everywhere to save power. There are many occasions where frequency conversion does not necessarily save power.

2. As an electronic circuit, the inverter itself consumes power (about 3-5% of rated power).

3. It is a fact that the inverter runs at the power frequency and has a power saving function. But his preconditions are:

First, high power and is a fan/pump type load;

Second, the device itself has a power saving function (software support);

Third, continuous operation in the long run. This is the three conditions that reflect the power saving effect.

Other than that, it doesn't matter if the festival doesn't save electricity. If you do not add preconditions to say that the inverter power frequency operation is energy-saving, it is exaggerated or commercial speculation. Know the original, you will use him skillfully for you. Be sure to pay attention to the use of the occasion and the conditions of use in order to apply correctly, otherwise it is blindly obedient, credulous and "deceived."

4. What is the starting current and starting torque of the motor when the inverter is running?

The inverter is operated, and the frequency and voltage are increased correspondingly with the acceleration of the motor. The starting current is limited to 150% of the rated current (125% to 200% depending on the model). When starting directly with a commercial power supply, the starting current is 6 to 7 times, so a mechanical and electrical impact will occur. It can be started smoothly with the inverter drive (starting time becomes longer). Starting current is 1.2 to 1.5 times of rated current, starting torque is 70% to 120% of rated torque; for inverter with torque automatic enhancement function (public number: pump housekeeper), starting torque For more than 100%, it can be started with full load.

5. In the same factory, the large motors move together, and the inverter stops during operation. Why?

When the motor starts, the starting current corresponding to the capacity will flow. The transformer on the stator side of the motor will produce a voltage drop. When the motor capacity is large, the voltage drop will have a large influence. The inverter connected to the same transformer will make an undervoltage or instantaneous stop. The judgment, and thus the protection function (IPE) action, causes the operation to stop.

6. Is there a limit to the installation direction when installing the inverter?

The structure of the inside and the back of the inverter takes into account the cooling effect. The relationship between the upper and lower sides is also important for ventilation. Therefore, for the unit type, the longitudinal position is placed in the disc and hung on the wall, and installed as vertically as possible.

7. Is it possible to use a soft start without directly applying the motor to a fixed frequency inverter?

It is ok at very low frequencies, but if the given frequency is high, the conditions for direct start of the commercial power supply are similar. A large starting current (6 to 7 times rated current) will flow, and the motor will not start because the inverter cuts off the overcurrent.

8. What problems should I pay attention to when the motor runs over 60Hz?

(1) Machines and devices are required to operate at this speed (mechanical strength, noise, vibration, etc.).

(2) The motor enters the constant power output range, and its output torque should be able to maintain its operation (the output power of the shaft such as the fan and pump increases proportionally to the cube of the speed, so pay attention when the speed is slightly increased).

(3) The problem of bearing life is to be fully considered.

(4) For motors with medium capacity or above, especially 2-pole motors, it is necessary to discuss with the manufacturer carefully when operating above 60 Hz.

9. Can the inverter drive the gear motor?

Depending on the structure of the reducer and the way it is lubricated, there are a number of issues to be aware of. In the structure of the gear, 70 to 80 Hz is usually considered as the maximum limit. When oil lubrication is used, continuous operation at low speed is related to the damage of the gear.

10. Can the inverter be used to drive a single-phase motor? Can I use a single-phase power supply?

The machine basically can't be used. For the single-phase motor of the governor switch-start type, it will burn out under the speed range below the operating point.

Auxiliary winding; for capacitor starting or capacitor operation, capacitor explosion will be induced. The power supply of the inverter is usually three-phase, but for small-capacity, it also has a single-phase power supply.

11. What is the power consumed by the inverter itself?

It is related to the model, operating status, frequency of use, etc. of the inverter, but it is difficult to answer. However, the efficiency of the inverter below 60 Hz is about 94% to 96%, so that the loss can be estimated, but the built-in regenerative braking type (FR-K) inverter, if the braking loss is also taken into account, the power consumption It will become larger, and attention must be paid to the design of the operation panel.

12. Why can't I use it continuously in the whole area of ​​6~60Hz?

Generally, the motor is cooled by the blades on the outer fan or the rotor end ring mounted on the shaft. If the speed is lowered, the cooling effect is lowered, so that the same heat as the high-speed operation cannot be withstood, and the load torque at a low speed must be reduced, or A large-capacity inverter is combined with a motor or a dedicated motor.

13. What should you watch out for when using a motor with a brake?

The brake excitation circuit power supply should be taken from the input side of the frequency converter. If the brake is operating when the inverter is outputting power, it will cause an overcurrent cut. Therefore, the brake should be actuated after the inverter stops outputting.

14. I want to use the inverter to drive the motor with the capacitor for improving the power factor. The motor does not move.

The current flowing into the inverter improves the power factor. Because the charging current causes the inverter overcurrent (OCT), it cannot be started. As a countermeasure, please operate the capacitor after removing it, or even improve the power factor. On the input side of the inverter. It is effective to connect an AC reactor.

15. How long does the inverter last?

Although the inverter is a stationary device, it also has consumption devices such as a filter capacitor and a cooling fan. If they are regularly maintained, it is expected to have a life of more than 10 years.