Control Methods for Permanent-Magnet Synchronous Reluctance Motor Drives

This thesis deals with control methods for synchronous motors with a magnetically salient rotor, such as the synchronous reluctance motors, interior permanent-magnet synchronous motors, and permanent-magnet synchronous reluctance motors. An exact hold-equivalent discrete-time motor model is developed. The motor model is then used in the design and analysis of current controllers and flux observers. A state-feedback current controller with an integral action and reference feedforward is designed directly in the discrete-time domain. The time delays are inherently taken into account in the design. The proposed current control design improves the dynamic performance and robustness especially at high stator frequencies. Furthermore, the saturation characteristics can be properly included in the controller. For sensorless control, a speed-adaptive full-order flux observer is designed and analyzed directly in the discrete-time domain. The proposed sensorless control system enables the operation at very low sampling to fundamental frequency ratios (below ten). For energy-efficient optimal control, a computation method for the control look-up tables is developed. When combined with an identification method for the magnetic model, the proposed method enables the plug-and-play startup of an unknown motor. The developed method is capable of producing optimal references along the maximum torque-per-ampere locus, at the current limit, at the maximum torque-per-volt limit, and in the field-weakening region. Apart from the current controllers, a feedback-linearization stator-flux-oriented control method and its systematic design procedure is developed. Stator-flux-oriented control enables the use of much simpler reference calculation methods. The simplicity of stator-flux-oriented control is tempting for many applications, while better control performance can be achieved with the proposed discrete-time control designs. The developed control methods can be applied in hybrid or electric vehicles, heavy-duty working machines, and industrial applications. The designed controllers and flux observers are experimentally evaluated using a 6.7-kW synchronous reluctance motor drive and a 2.2-kW interior permanent-magnet synchronous motor drive.