A very fast direct torque control for interior permanent magnet synchronous motors start up

Selection of the stator flux command in direct torque control (DTC) of permanent magnet synchronous motors is very important as it affects machine performance. For steady state operation, it can help to decrease the stator current or machine losses. However, in order to get a fast torque response during motor start up, one needs to change both the stator flux angle and magnitude. In this paper, a method is presented to find the optimal voltage vectors to change both the flux angle and its magnitude that results in high speed dynamics for the torque response. The closed form formula given for the optimal voltage vector is derived based on maximizing the torque change in each sampling time. The simulation results show that the presented method is superior to the conventional DTC. In other words, it is shown that the voltage vectors derived from the switching table for conventional DTC are not the optimal voltage vectors for the situation in which there is a step change in the torque command.