Improving the start and restart behavior through state recognition of AC drives

The paper presents control strategies for abnormal operating conditions of AC motor drive systems. These improve the total performance as well as the ruggedness of the system. Two methods to start a rotating motor through state recognition are described. Two cases are distinguished according to whether the back EMF exists or not. In either case, normal operation can be reestablished as fast as possible on return of the power supply following a power interruption. Discussions and experimental results are presented for both failure conditions, based on V/f control and on sensorless field oriented control.