Energy Characteristics of an Electric Drive with Direct Torque Control for a Permanent-Magnet Synchronous Motor

The article discusses the relevance of developing and studying direct torque-control systems for a permanent-magnet synchronous motor (PMSM). The mathematical description of the electric drive operation is performed in a two-phase coordinate system, which shows the PMSM equivalent circuit with allowance for the losses in the stator magnetic circuit and rotor magnets. The article presents the results of computer simulation of the energy characteristics of two PMSM types (with the same and different stator inductances along the dq axes) as part of an electric drive with a direct torque-control system, for which the dependence of the stator-winding current on the stator flux linkage is selected. The extreme nature of these dependencies is established. For two types of the PMSM magnetic system, algebraic expressions are derived for determining the stator flux-linkage task, ensuring a minimum stator-winding current. An algorithm is developed for finding the minimum stator-winding current using additional flux-linkage task signals. A functional diagram of an electric drive with direct torque control of a PMSM is presented. It contains PI controllers in the torque and flux linkage control loops, the output signals of which are the reference signals for the space-vector modulation system of the stator winding voltage. The results of simulating the electric drive with the proposed algebraic expressions and the developed algorithm for searching for a flux-linkage task that ensures a minimum stator-winding current are presented. The operability of all proposed solutions is established, while the search algorithm is the same for both types of PMSM and ensures the minimization of the stator-winding current in both control zones, while the algebraic expressions for the stator flux-linkage task differ for different types of PMSM and do not ensure a minimum stator-winding current in the entire range of rotation frequency variation.