Development of a brushless doubly-fed machine for a limited-speed pump drive in a waste-water treatment plant

A 60 hp brushless doubly-fed machine (BDFM) pump drive, which is designed to replace an existing wound-rotor induction machine (WRIM) drive in a waste-water treatment plant, is discussed. Machine structural design as well as controller design are optimized according to the operational demands of the application. This paper focuses mainly on the controller design and implementation for the BDFM pump drive, in a limited-speed range of operation. The performance characteristics of the existing WRIM drive and the projected characteristics of the BDFM drive are presented. The microprocessor based drive controller is capable of performing start-up synchronization, speed control and near unity power factor operation, Additionally, the controller generates a shut-down signal during fault conditions such as power failure and loss of synchronism. Experimental results obtained from a low-power laboratory prototype BDFM are presented to verify the 60 hp design