Real-time implementation of direct torque control scheme for brushless doubly-fed reluctance motors

The paper proposes a direct torque control (DTC) algorithm for the BDFRM and outlines the configuration of a laboratory test facility at Northumbria University for its practical implementation. The simulation and experimental results generated for a small prototype will show that the machine can successfully operate down to zero supply frequency of the inverter-fed (secondary) winding, unlike cage induction or many other traditional AC machines with DTC. This performance advantage of the BDFRM is a consequence of an improved DTC scheme based on a flux estimation technique which doesn´t rely on the secondary voltage integration and therefore avoids related problems at low secondary frequencies, typical for the BDFRM operation. The developed algorithm also allows the machine performance parameters to be optimised in a manner similar to conventional vector controllers but with control actions executed in a stationary reference frame as usual for all DTC methods. The maximum torque per inverter ampere (MTPIA) control strategy has been used as a case study.