Challenges
There is a factory on the outskirts of Shenzhen, which is outfitted with several rotary screw air compressors. The factory previously used industrial-grade variable frequency controllers to provide motor control. Motors installed on its rotary screw air compressors were two-pole 55w models.

High operating cost forced the factory to seek energy-saving solutions that require only minimal modifications to its existing operational system. While customers faced the ever-rising operational costs, Easydrive Electric came to save the day. Listed below are several drawbacks that once existed in the old air compressor operating system.

1. Though the motor adopts a star-delta starter to ensure smooth startup, it still requires much electric current to flow through the circuit during starting. Every time operators start the motor, it wastes more money. Additionally, large electric current during startup easily affects the stability of power grid and may also cause safety issues when operating the air compressor.
2. The motor often operates at full load when much energy has been wasted at the outlet valve in the form of compressed air. Such way of operation is uneconomical, involving a huge amount of energy waste.
3. High-frequency operation causes the air compressor to produce a very loud noise.
4. Starting the motor at high frequency produces shock load which is a major cause of motor bearing wear. Premature wear means increased burden of maintenance.
5. In the absence of a load, the electric current that flows through a circuit does not produce any useful work and will go into waste. Traditional mechanical adjustment method provides poor precision in pressure regulation. Wild pressure fluctuations are of frequency occurrence, which results in severe mechanical wear and huge electricity waste.

Solutions
The efforts we have made in response to those challenges involve the addition of a variable frequency drive to the existing air compressor operating system. After the modification, the motor startup signal coming from the central control system is directly routed to the VFD instead of the motor. In this way, the motor can start up at variable frequencies instead of using one same frequency.

As the PID controller receives the feedback signal from the motor, it compares the actual pressure in the motor system with the desired setpoint before allowing the VFD to adjust its frequency accordingly. This integrated motor control system overcomes all the drawbacks of the existing air compressor system by making only small modifications to it.

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VFD Parameter Settings

Mission Accomplished
After the modification is completed, we give the new system a trial run which lasts for 2 hours. During the commissioning process, the VFD starts up the motor smoothly and its PID controller works superbly well with the central PLC system. Calculations find that the new system saves 20.3% more electricity than the old mechanism. But still, there is a drawback to the modified system. Operators might need to take some time when changing the preset pressure setting on the VFD.