Abstract: Permanent-magnet-synchronous-machine (PMSM) drives have been increasingly applied in a variety of industrial applications which require fast dynamic response and accurate control over wide speed ranges. Two control techniques are proposed in this dissertation for PMSM drives, namely flux-weakening control incorporating speed regulation and sliding mode observer with feedback of equivalent control. The research objectives are to extend the operating speed range of the PMSM drive system and improve its control robustness and adaptability to variations of operating conditions as well as dynamic performance. First, a robust flux-weakening control scheme is studied. With a novel current control strategy, the demagnetizing stator current required for the flux-weakening operation can be automatically generated based on the inherent cross-coupling effects in PMSM between its direct-axis and quadrature-axis current in the synchronous reference frame. The proposed control scheme is able to achieve both flux-weakening control and speed regulation simultaneously by using only one speed/flux-weakening controller without the knowledge of accurate machine parameters and dc bus voltage of power inverter. Moreover, no saturation of current regulators occurs under any load conditions, resulting in control robustness in the flux-weakening region. Secondly, a sliding mode observer is developed for estimating rotor position of PMSM without saliency in the implementation of position-sensorless vector control. A concept of feedback of equivalent control is applied to extend the operating range of sliding mode observer and improve its angle-estimation performance. Compared to conventional sliding mode observers, the proposed one features the flexibility to design parameters of sliding mode observer operating in a wide speed range. The estimation error of rotor position can be reduced by properly selecting the feedback gain of equivalent control. In addition, a flux-based sliding mode observer with adaptive feedback gain is investigated. The constant magnitude of equivalent control makes it easier to design the switching gain of discontinuous control in the sliding mode observer. As a result, the problematic chattering phenomenon normally prevailing at low speeds due to high switching gains can be mitigated or even eliminated. The feasibility and effectiveness of the control techniques addressed in this dissertation are verified by both computer simulation and experimental results.