Permanent magnet variable frequency air compressor advantages and disadvantages

the advantage of permanent magnet variable frequency air compressor is that the same control method must be higher than the traditional asynchronous motor. 80% of the air compressors in the market are in variable load state, while the permanent magnet variable frequency air compressor uses variable frequency speed regulation to actively satisfy the user's demand and reduce the loss of useless work according to the amount of gas used. But it is not what working conditions with permanent magnet variable frequency air compressor are energy-saving effect is very obvious. Another 20% of the occasions are full pressure and full load. In this case, the use of variable frequency control asynchronous motor consumes more energy than direct starting, because the frequency converter itself has an additional power loss of 2 ~ 3%, so even if the permanent magnet motor is selected, the energy saving effect will not be obvious. Other advantages of permanent magnet variable frequency air compressor:

1. Reduce the impact, reliable operation

the frequency converter slowly speeds up the starting, which is more stable than the soft starting, completely avoids the current peak value, operates with frequency conversion after the starting operation reaches additional pressure, and carries out stepless variable speed tracking gas production through pressure detection. Under the condition of keeping the pressure unchanged, the gas volume required by the user is output, which reduces the energy consumption in the store and completely prevents the impact of star triangle starting on the power grid and air compressor.

2. Constant voltage power saving

when the general air compressor is in operation, the pressure has been fluctuating within the upper and lower 0.7bar of the additional pressure. Compared with the variable frequency air compressor, the pressure can be stabilized within the upper and lower 0.1bar of the additional pressure. During normal operation, 8.4% of power consumption can be saved (7% more power consumption for every 1bar increase in operating pressure). Especially in the unloading operation, the frequency conversion air compressor saves up to 45% of the power consumption than the general air compressor. At the same time, the quality of gas supply is improved, and the reliability and life of air compressor and gas equipment are improved.

3. AC power supply voltage adaptability

because of the over-modulation technology selected by the inverter, the torque can still be output when the AC power supply is slightly lower to drive the motor. When the voltage is slightly higher, it will not lead to the high voltage of the output motor.

For self-generating occasions, variable frequency drive can show its advantages. According to the characteristics of motor VF (variable frequency air compressor operates under extra voltage in energy-saving state), it has obvious effect on the site with low power grid voltage.

4. Low noise

most of the working conditions of the frequency conversion system are lower than the additional speed of the operation, the main machine mechanical noise and wear down, extend the protection and service life;

if the fan is also driven by frequency conversion, the noise of the air compressor can be significantly reduced.

Integrated permanent magnet variable frequency air compressor

disadvantages of permanent magnet variable frequency air compressor:

1. The motor temperature is too high

permanent magnet motor

because the operating temperature of the oil-cooled head is required to reach 65~80 ℃, the temperature of the motor and the direct coupling shaft of the head is transmitted to the permanent magnet rotor of the motor, and the temperature of the body is transmitted to the motor casing, so that the actual operating environment temperature of the motor reaches about 65 ℃. General motor planning reasonable temperature rise is 80K, then the high motor winding temperature may be 145 ℃, according to 38UH magnetic steel demagnetization (development reversible demagnetization) experiment proves that the demagnetization rate is 2% at 80 ℃; 100 ℃ 5%;120 ℃ is 7%;150 ℃ is 12%. It is clarified that the higher the temperature, the lower the magnetic flux, and the magnetic flux of the magnetic steel is related to the motor power, that is, the higher the motor temperature, the lower the power, the smaller the back electromotive force, and the lower the given voltage of the inverter. The greater the motor current, the higher the winding temperature rise, the greater the resistance, the greater the stator copper loss. The power drops again, so the actual power of the integrated permanent magnet variable frequency air compressor cannot reach the planned value at full pressure and large flow. Give specific examples to illustrate the decline in the power of the integrated permanent magnet variable frequency air compressor common on the market:

(1). It is assumed that the operating environment temperature of the integrated permanent magnet variable frequency air compressor is 70 ℃, the ambient temperature of the split machine motor is 30 ℃, and it is assumed that the temperature rise of the motor during actual operation is 50 ℃ in both cases, the motor has the same electromagnetic planning scheme, and the load of the motor is the same. The operating temperature of the integrated permanent magnet variable frequency air compressor is 120 ℃, and that of the split machine is 80 ℃. The former will operate with a resistance of about 12.7 per cent higher and a copper loss of about 12.7 per cent higher than the latter;

(2). The operating temperature of the split type is assumed to be a control mode in which the direct axis current of the motor is zero: the demagnetization rate of the magnetic steel is 7% and 2% respectively at 120 ℃ and 80 ℃. For this reason, when the motor drags the same load, the stator current of the former will be about 5.38% higher than that of the latter, so the copper loss of the motor will be 11.0% higher;

(3). The total copper loss integrated permanent magnet variable frequency air compressor will be about 25.1 percent higher than the split machine. Based on the 1/3 copper loss in the permanent magnet synchronous motor, the planned power of the general integrated permanent magnet variable frequency air compressor is about 94%, and the power drops to about 93.5 when operating at 120 ℃ (TYB series is about 97%), so the relative power difference is 3.5.

2. demagnetization

permanent magnet motor is afraid of high temperature demagnetization, and demagnetization is determined by magnetic steel. Magnetic steel is afraid of high temperature. The greater the risk of refractory demagnetization (irreversible) at high temperature for a long time, the demagnetization rate in 15 years is not more than 3%. Because NdFeB technology in China has been developed in recent years, it is impossible to verify the life span under high temperature for a long time. There are many cases of magnetic steel demagnetization and failure in the motor industry.

3. Low service life

because of the temperature connection, it can only be planned as an open motor. Many applications of air compressors are relatively poor. Corrosive gases such as dust, moisture and salt spray lead to low service life.

4. High failure rate

because the rotor of the integrated permanent magnet variable frequency air compressor is directly installed on the screw rotor, the bearing on the rotor side of the screw motor has to bear a load more than 2 times larger than the original load, so the bearing and oil seal on the motor side have a life of more than 2 times lower than the original.

5. Maintenance is relatively troublesome

because the rotor of the permanent magnet motor is a permanent magnet, the motor must be removed before the head is removed during the maintenance of the head. The permanent magnet rotor has strong attraction, requires special tools for removal, and the personnel require strong professionalism, otherwise it is very simple. Cause accidents.

6. Manufacturers select small

because the quality of the screw head, the size of the specific power and the selection of the head are very different, the head is the core of the air compressor, and the selection of high-quality head and efficient motor can achieve excellent specific power and reliability. Therefore, any air compressor manufacturer selects high-quality parts to build its own products, which will reflect the quality level of the manufacturer and improve the reliability of the products to build the enterprise brand.