Feed-forward Torque Control of Interior Permanent Magnet Brushless AC Drive for Traction Applications

This paper presents a feed-forward torque control (FTC) technique for interior permanent magnet (IPM) brushless AC (BLAC) drives in traction applications. It is shown that by adopting the Newton-Raphson iterative method for solving the proposed high-order nonlinear relationship between the torque demand, flux-linkage and desirable dq-axis currents, FTC with due account of nonlinear machine parameters can be achieved for IPM BLAC drives. It is also proven that the comparison between the reference voltage magnitudes under maximum torque per ampere (MTPA) and field-weakening (FW) operations together with online base speed determination can be utilized for FW operation activation to achieve full exploitation of the available DC-link voltage during the transition between the constant torque and FW operation regions. Since both the dqaxis current references and the base speed for FW operation activation are computed online, the proposed FTC technique provides flexibility for online parameter update or estimation and is able to cope with wide DC-link voltage variation. The proposed FTC strategy is experimentally validated by measurements on a 10kW wide constant power speed range (CPSR) IPM BLAC machine drive.