Energy-saving air compressors with variable speed control

We developed the variable-speed screw-type air compressor in 1993 and have marketed a range of products with power ratings from 7.5 to 75 kW. Each of these compressors is driven by an induction motor supplied with power through an inverter controlled by the delivery pressure as a feedback signal. The control software which is based on a PID (Proportional, Integral, and Differential) has nonlinear elements for high response speed and stability. This system saves energy by reducing losses and by minimizing delivery pressure to the requirement. A typical user, who on average requires 70% of an air compressor's full capacity, will use 22% less energy with the variable-speed compressor than that consumed by a fixed-speed one. Another advantage of this system is that it greatly reduces fluctuations in the delivery pressure. That is, when the compressor is used with an air receiver of the recommended capacity, the delivery pressure is kept within 0.03 MPa (0.3 bar) of the specified pressure.