Does Air Compressor Controlled by VSD Motor Really Optimize Energy Efficiency?

VSD compressors are highly praised and well-known for their energy-saving capability in the industrial air compressor service, which is achieved by incorporating the characteristics of permanent magnet motor in their design and by precisely matching output power to actual compressed air demand.

However, whether due to shifts or production patterns – the demand for compressed air in most compressed air applications actually fluctuates. Are VSD compressors always the most energy-efficient choice? In this blog post, we consider the pros and cons of VSD compressors and discuss when they are best suited.

Does air compressor controlled by VSD motor really optimize energy efficiency?

How does VSD air compressor work?

The VSD air compressor adopts a permanent magnet synchronous motor and variable frequency control technology. It can adjust the speed at any time according to the load requirements of the air compressor, control the input voltage frequency, maintain the stability of parameters such as pressure, flow, and temperature, thereby improving the working performance of the air compressor.

It can adjust the rotate speed of the air compressor according to the trend of pipeline pressure fluctuations, and can even exempt the air compressor from unloading operations to save electricity.

Ordinary air compressors are controlled in a fixed frequency, which may run at full load all the time and cannot be adjusted according to actual needs. The energy efficiency is low and resulting in energy waste.

The principle of energy efficiency:

The variable frequency speed (VSD control) system regards output pressure as the control object. It is composed of a closed-loop constant pressure control system consisting of frequency converter, pressure sensor and VSD motor.

The working pressure value can be directly set by the operation panel. The instant on-site pressure is detected by the sensor and converted into a 4~20mA current signal and fed back to the frequency converter. The frequency converter compares and calculates data with its built-in PID, thereby adjusting its output frequency to achieve the purpose of constant pressure air supply and energy saving of the air compressor.

VSD air compressor advantages:

1.The inverter adjusts the gas flow rate by adjusting the motor speed, so that the motor output power is proportional to the flow demand, keeping the motor working efficiently, with high power factor, small reactive power loss, and obvious power saving effect.

2.Automatic fast sleep shortens the no-load time, stops the motor completely, and saves energy to the greatest extent. The impact-free starting and low-frequency and high-torque characteristics ensure that the inverter can start and stop with load at any time.

3.Good stability and more silent running sound, When starting and stopping, traditional air compressors will have obvious current shock and mechanical vibration, which will increase the probability of equipment failure. When starting and stopping, the current and mechanical vibration of variable frequency air compressors are very small, so the probability of equipment failure can be reduced.

Do VSD air compressors optimize energy efficiency in all circumstances?

Knowing so much about the advantages of air compressors controlled by VSD motor, do you think that it is the best solution under any circumstances? After all, there should be no more effective way to save costs than improve efficiency of power. However, the fact may be quite opposite.

In most cases, air compressors controlled by VSD motor can indeed achieve energy saving in theory, but in certain circumstances, air compressors controlled by VSD motor will not only fail to help you improve efficiency of power, but will also increase power consumption, increase operating costs and maintenance costs.

Why VSD compressors are not a one-size-fits-all solution?

First, it has a limited work power range.

Air compressors controlled by VSD motor are only at their most efficient when the load is between 40% and 80%. At this point, their performance optimized energy efficiency the most. Outside of this range, the air compressor motor is operating outside its optimum energy efficiency range and is not efficient or cost-effective. If use air compressor controlled by VSD motor incorrectly, it may causes the production cost of same amount of compressed air highly increased.

Second, high temperature will low its performance.

Because the oil-cooled machine head of the air compressor controlled by VSD motor(KOE Seires) has a characteristic operating temperature of 65-80℃, the temperature of the motor and the machine head direct-connected shaft is transferred to the permanent magnet rotor of VSD motor, and the body temperature is transferred to the motor casing, so that the actual VSD motor operating temperature reaches about 65℃.

Generally, Generally, the reasonable temperature rise range of the VSD motor during operation is within 80 ℃, so the actual operating temperature of the VSD motor may reach 145℃. According to the 38UH magnetic steel demagnetization (developmental reversible demagnetization) experiment, the demagnetization rate is 2% at 80℃; 5% at 100℃; 7% at 120℃; and 12% at 150℃.

In other words, the higher the temperature, the lower the magnetic flux of the magnetic steel, and the magnetic flux of the magnetic steel is positively correlated with the motor power, that is, the higher the motor temperature, the lower the output power, the smaller the back electromotive force. And the lower the given voltage of the inverter, the larger the motor current, the higher the temperature rise, the greater the resistance, and the greater the stator copper loss.

So the actual power of the permanent magnet variable frequency air compressor cannot reach the design value at full pressure and large flow. In addition, high temperature will also damage the electronic components and batteries in the air compressor, causing them to age faster and reduce efficiency.

Third, the air compressor repair is very difficult. The overall structure of the variable frequency air compressor is complex. If a fault occurs, it needs to be repaired by professionals. The difficulty is greater than that of traditional air compressor repair. Because the VSD motor rotor is a permanent magnet, the motor must be removed first and then the head during maintenance.

The permanent magnet rotor has a strong suction force and requires special tools. In addition, it requires strong professionalism from maintenance personnel, otherwise it is easy to cause accidents.