Incremental torque control of a synchronous reluctance motor servo drive

Recently, owing to certain advantages of synchronous reluctance motor (SynRM), electric drives based on it are being investigated extensively. This dissertation concerns the control aspects of a SynRM servo drive fed by a voltage source inverter (VSI). Major contents, results and contributions are summarized as follows: (1) An extensive literature review on modern electric drives was carried out. It is concluded that (a) The existing control algorithms broadly falls into two categories: Averaging Torque Control (ATC) and Instantaneous Torque Control (InsTC); (b) A constraint should be imposed in the control to account for the nonlinearity of electromagnetic torque production in electric motors; (c) A transition from analog control to digital control is under way because of certain advantages of digital control; (d) modern control theory and advanced digital signal processing techniques are finding more and more application in electric drives. (2) Based on comparisons of dynamics level of different parts of the power subsystem, it is concluded that only the electric motor dynamics should be modeled. Three time-varying discrete models of the motor dynamics are developed and evaluated by digital simulations. (3) Extended from ATC and InsTC strategies, a fully digital control strategy, called Incremental Torque Control (IncTC), is proposed. IncTC is based on the incremental torque characteristics of VSI-fed SynRM, and consists of a incremental torque speed controller and incremental torque modulator IncTC features fastest response, and is robust, and digital-implementation oriented. Various constraint can be imposed in IncTC to optimize the performance of SynRM. Extensive simulation is carried out to investigate the validity and features of IncTC, and also provide guidelines for its DSP-based implementation. (4) A TMS320C30 DSP based experimental system of the proposed IncTC is developed. The system consists of a 2-pole 1.5 kW SynRM with an axial-laminated anisotropic rotor, an intelligent IGBT module and a TMS320C30 DSP board. This system has been tested with 2 kHz sampling frequency for various operating conditions. Experimental results show that the proposed IncTC is valid and holds great promise. (5) An effective algorithm for the position and speed estimation based on phase current measurements is proposed and verified with digital simulation. In the algorithm, only current sensors are needed, and position and speed are estimated independently. Furthermore, the angular position is directly represented in its sine and cosine values, which are really employed in the controller.