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

Selection of stator flux command in DTC of permanent magnet synchronous motors is very important as it affects the machine performance. For steady state operation, it can help to decrease stator current or machine losses; however, in order to get a fast torque response during motor start up, one needs to change both stator flux angle and magnitude. In this paper, a method is presented to find the optimal voltage vectors to change both flux angle and its magnitude which results in high dynamics for torque response. The closed form formula given for optimal voltage vector is derived based on maximizing torque change in each sampling time. The simulation results show that the presented method is better than using conventional DTC. In other word, 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 torque command.