Online feedback-based field weakening control of interior permanent magnet brushless AC drives for traction applications accounting for nonlinear inverter characteristics

This paper presents an online feedback-based (FB) field weakening (FW) control technique for interior permanent magnet (IPM) brushless AC (BLAC) machines with due accounting for nonlinear machine parameters and inverter characteristics in traction applications. The proposed method computes the dq-axis current references online instead of employing predefined look-up tables (LUT) as in the conventional schemes. Thus, it provides the flexibility for online parameter update or estimation to enhance the drive system efficiency. It is shown that in the FB-based FW operation where the machine voltage magnitude is maintained at the voltage hexagon boundary via the voltage FB loop using the ideal FB voltage references which the nonlinear inverter characteristics are neglected, the stator flux reference regulated via the voltage FB loop may not be optimally controlled due to the mismatch between the ideal demand and actual voltages applied to the IPM BLAC machine. For a given torque, it results in a higher current magnitude than the ideal demand, and therefore leads to extra copper losses. To solve this problem, a nonlinear inverter compensation (NIC) method is proposed and experimentally validated by measurements on a 10kW IPM BLAC drive. It is shown that by incorporating the proposed NIC technique, the achievable torque under a given speed can be increased up to 4% and the copper losses under a torque demand and given speed can be reduced up to 4% in the FW operation region.