Current inverter technology-advantages, problems and solutions

In the water supply and sewage industry it has long been the practice of the major pump sets in an installation to have variable speed drives. The benefits obtained from variable speed pumping in terms of energy saving and improved control were appreciated by the water authorities and consulting engineers at an early date. For pumping duties there are currently several types of variable speed drives in service. These include the AC commutator motor, eddy current coupling and DC thyristor drive. In the last ten years the variable frequency inverter drive, operating with a standard squirrel cage induction motor has become the most popular form of drive, virtually replacing all the previous mentioned types. Other applications attracting variable speed operation are aeration blowers and sludge centrifuges which benefit from process control and the inherent soft start from the inverter. The author examines current invertor technology applicable to the above processes.