DTC Drives for Wide Speed Range Applications Using a Robust Flux-Weakening Algorithm

A control scheme for robust flux-weakening operation of direct-torque-control induction motor drive is proposed. The basic idea is to adjust the flux reference on the basis of the torque error, thus determining a spontaneous flux weakening. To exploit the maximum torque capability, it is necessary to estimate the maximum torque that the induction machine is able to generate at any speed. Initially, a basic version of the algorithm, requiring a simple off-line parameter tuning, is presented. Then, the algorithm is improved and completed with the online estimation of the maximum torque, hence avoiding the initial tuning process. The main features of the proposed methods are a little dependence on machine parameters and a smooth transition into and out of the flux-weakening operation mode. Experimental tests demonstrate the effectiveness of the control schemes.