|Title:||Modelling and power factor improvement of switched reluctance motor drives|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Electric motors, Linear
|Department:||Department of Electrical Engineering|
|Pages:||xxxiii, 221 p. : ill. ; 30 cm|
|Abstract:||Switched reluctance motor (SRM) drives are found in a number of applications in variable speed drives and are gaining much attention due to their simple and robust structure, low rotor inertia, high power ratio per unit volume, reliability and low cost. With improvements in power electronics and microprocessors, this trend will continue to grow. However, the nonlinearity arising due to the high saturation of the magnetic characteristics complicates the analysis as well as the control of this motor. Consequently, modelling the nonlinear magnetic characteristics is crucial for design, simulation, and control of SRM drives. In addition, the low power factor is a drawback of SRM drives. This thesis is focused on developing accurate models of the nonlinear magnetic characteristics and a new control strategy to improve the power factor. Based on the two-dimensional bicubic spline, a piecewise interpolation model of the nonlinear magnetic characteristics of SRM is presented. This model only needs a small quantity of the known data, to determine the interpolation coefficients. However, it can be used to accurately compute the flux linkage at arbitrary rotor positions and currents. The simulation and experimental results demonstrate that the presented model is accurate. To model analytically the nonlinear magnetic characteristics of SRM, a nonlinear analytical model is proposed. This model is composed of the least squares polynomials with respect to the rotor position and current. It can be employed to accurately describe the nonlinear magnetic characteristics because of the use of the least squares optimization. From a limited number of the given data, the coefficients in the model can be computed not only off line, but also on line. Thus, this model also has a self-training feature. These have been testified to by the simulation and experiment. From the above proposed model, the analytical model of SRMs is developed further. The experiment on the prototype of the SRM drive proves the developed model of SRM. In addition, a hybrid model of SRMs and a position stepping method are developed, based on the two-dimensional bicubic spline and bilinear spline. The former is used to automatically generate a great number of fine rectangular elements and thus it offers the accurate characterization of the nonlinear magnetic behaviours of SRMs. The latter is employed to analytically model the nonlinear magnetic characteristics in each element and hence simplifies the voltage first derivative equation into the analytical model. The experiment verified the effectiveness and accuracy of this model. To take into account the mutual coupling between phase windings, a model of multi-phase SRMs is proposed by introducing the self inductance, mutual inductance, and the connection coefficient. Furthermore, the simulation algorithm for solving this model is developed. The proposed model and simulation algorithm are validated by the simulation and experimental results. To compute the power factor of SRM drives, the simulation model and its algorithm are developed. This model includes the SRM, topology circuit, dc link capacitor, and rectifier circuit. Through the theoretical, simulation, and experimental analyses, the effects of the control and output parameters on the power factor are investigated. From the developed analyses, a new control strategy to improve the power factor is presented, which is that the power factor is improved through optimizing the turn-on and turn-off angles. From the new strategy, two real-time schemes to improve the power factor are developed by means of two optimization techniques. The presented strategy and developed schemes are validated by the simulation and experimental analyses. In summary, four novel models of SRMs are proposed in this thesis. These models have been demonstrated by the simulation and experiment. Furthermore, this thesis investigates the effects of the control and output parameters on the power factor in SRM drives by means of the theoretical, simulation and experimental analyses. A new control concept for improving the power factor in SRM drives is presented and two real-time schemes are developed. These also have been validated by the simulation and experiment.|
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