The air compressor frequency conversion transformation system using D31 inverter has been put into operation for more than two years, and has achieved good economic and social benefits:

• The control device operates reliably and has a low failure rate; 

• The air pressure is stable, so that the system pressure change of the pipe network is kept within the range of ±0.2bar, which effectively improves the quality of the working conditions; 

• Enhance the reliability of the system, reduce the noise of the air compressor, and prolong the service life of the compressor; 

• The economic benefits are remarkable, the energy cost is reduced by 44.3%, and the maintenance cost is significantly reduced. The statistics of actual operation show that it can save  651,900 kWh of electricity a year. Calculated at 0.3 yuan per kilowatt-hour, about 195,600 yuan in electricity savings. The electricity bill is saved by more than 20%, and the invested funds can be recovered in about half a year.