Unified direct-flux vector control of induction motor drives with maximum torque per ampere operation

This paper deals with the Maximum Torque per Ampere (MTPA) operation of induction motor drives using Unified Direct Flux Vector Control (UDFVC). The UDFVC has been introduced in the past as a unified direct flux and vector control approach for both synchronous and asynchronous AC motor drives. The control is implemented in stator flux coordinates with the stator flux being directly controlled by the d_s-axis voltage component, while the machine torque is controlled through q_s-axis current component regulation using the q_s-axis voltage component. The stator flux amplitude is generated using only the torque demand as the input of an MTPA profile that is particular for the AC machine being controlled, without the need of other complex LUTs and motor mapping. In this way, the optimal machine exploitation is reduced to a proper stator flux reference computation that can be done offline using the data from the standard no-load and short-circuit tests. The effectiveness of the proposed solution is verified through intensive experimental tests conducted with a 2.2 kW induction machine. The steady-state MTPA operation, the drive efficiency performance and the transient drive performance are presented.