Flux Polar Control (FPC): a Unified Torque Controller for AC Motor Drives

Transportation electrification is leading to an impressive development of electric drives (eDrives) using either synchronous- (SM) or induction- (IM) motors. However, these eDrive solutions need high-performance torque controllers that must be easy to tune and able to deal with saturated machines. Besides, the torque regulation must be linear for the entire operating speed range, including deep flux-weakening (FW) operation with maximum torque per volt (MTPV) limitation. According to the current state-of-the-art, the torque controllers for traction applications are mainly based on control schemes like current vector control (CVC), direct torque control (DTC), or the more recent direct flux vector control (DFVC). However, these solutions employ inner control loops whose performance depends on the machine's inductances, thus requiring the execution of demanding tuning procedures to adapt the control parameters to the machine's operating point. Moreover, CVC-based torque controllers sometimes rely on demanding multidimensional calibrated maps to linearize the torque regulation and simultaneously perform FW operation with MTPV. In contrast with the torque control solutions mentioned above, this article proposes a unified torque controller for ac motors based on inner flux- and load angle- control loops since their performance is independent of the machine's inductances, i.e., magnetic saturation phenomena. Also, the torque linearization relies on a simple calibrated map providing maximum torque production under inverter current- and voltage- constraints. Experimental results are presented for four different eDrives using both SMs and IM, validating the unifying feature and demonstrating the high dynamic performance of the proposed torque controller.