Field Oriented Control of IPM Drives for Flux Weakening Applications

Interior Permanent Magnet (IPM) drives are adapted to flux-weakening, then to constant power operation over a wide speed range. Most of the control strategies for IPM motor drives are based on the control of the current vector Flux-weakening is obtained by proper current references, that are calculated according to the magnetic model of the motor This approach needs the accurate characterization of the motor and it is sensitive to the inaccuracy and the variation of the model parameters. Moreover, in the case of a variable dc-link, an additional voltage loop is necessary to correct the current references values at different dc-link voltage levels. The direct control of the,flux vector in the stator flux oriented frame, is proposed here, with the aim of obtaining the constant voltage operation of the IPM motor drive in the flux weakening range by means of a very simple control algorithm. The proposed direct, flux control is tested on an IPM motor drive designed for traction. The exploitation of the maximum torque in all the operating speed range is demonstrated. The control is also capable to adapt its flux and current set-points to different dc-link voltage levels with no need of additional voltage regulators. Discrete-time simulation and experimental results are presented and compared showing good accordance.