Modelling and field-oriented control of a synchronous reluctance motor with rectangular stator current excitation

The rotor saliency of the axially laminated synchronous reluctance motor (SynRM) produces a rectangular air-gap flux density distribution. Optimal torque / rms ampere is achieved from machine if a rectangular stator current distribution interacts with this flux. The impact of rectangular stator currents on the design and control of the SynRM are considered. A design model is developed that assumes rectangular stator currents. The design model is based on an existing lumped element model of the SynRM magnetic circuit that has been extended to include saturation effects. All stator and rotor dimensions are included in the design model. The key dimensions are identified and a simple iterative algorithm is determined for optimising these values. A 5.0kW experimental motor is designed and built with an optimal torque / unit mass ratio. The designed motor has a nine-phase concentrated winding to approximate the ideal rectangular stator current distribution. Finite element analysis and static tests demonstrate the validity the design model. Generalised voltage and torque expressions are developed for the nine-phase machine. An orthogonal transformation is obtained to isolate the direct and quadrature, harmonic components of the stator inductance matrix. This transformation is applied to the standard stator voltage and torque equations to determine the equivalent d-q harmonic component equations. Two field-oriented control strategies are developed for the multiphase SynRM drive. A simple stator reference frame control strategy is implemented and performance results presented. A transformed frame vector controller is demonstrated to have theoretically superior performance to the stator reference frame controller but could not be implemented due to the excessive computational requirement for this strategy