Vladan P. Vujičić

Minimization of Torque Ripple and Copper Losses in Switched Reluctance Drive

This paper presents a control technique for torque-ripple minimization in the switched reluctance motor (SRM) drive, based on a torque-sharing function (TSF) concept. In the proposed method, the reference torque is directly translated into the reference current waveform using the analytical expression. Optimization criteria of a TSF that are concerned with secondary objectives, such as minimization of copper losses or maximization of drive performance, are described. In addition, a novel family of TSFs is introduced. An optimal TSF can be easily extracted from the proposed family to satisfy one of the secondary objectives or to create balance between more of them. Control performances of the two extracted TSFs and the two optimized conventional (linear and sinusoidal) TSFs are compared. These four TSFs keep the copper losses to nearly the theoretical minimum. Each of them provides approximately the same operation efficiency of the considered three-phase 6/4 SRM drive. However, due to extension of the commutation angle between adjacent phases, TSFs from the proposed family provide better torque-speed characteristics. Moreover, one of them expands the possible speed range of torque-ripple-free drive operation, and another one, which provides the best torque-speed characteristics, reduces the peak phase current.

A simple nonlinear model of the switched reluctance motor

The paper presents a simple nonlinear model of the switched reluctance motor (SRM) which requires a minimum of precalculated or measured input data. Therefore, it is convenient for use in earlier stage of SRM design in order to minimize time for finding optimal configuration. Moreover, it is shown that this model produces accurate torque shape for given current, and accurate flux linkage-current relationships. This also provides reliable results in dynamic regime. The simulation and experimental results are compared for available three-phase 6/4 motor.

Asymmetrical switched reluctance motor for a wide constant power range

In this paper the systematic approach to the design of a asymmetrical three-phase switched reluctance motor (SRM) with wide constant power range is described. It is shown that the SRM configuration with an unequal number of turns per phases may provide a wider constant power range than a corresponding symmetrical one. If the stator pole widths are unequal, the constant power range may be further extended. In these considerations, the maximal volt-ampere characteristics of the power converter are kept on the same level. The results are obtained using a suitable SRM model whose validity has been experimentally verified. The experimental results for the referent symmetrical SRM drive and asymmetrical one with an unequal number of turns per phase are also presented.

Modeling of a Switched Reluctance Machine Based on the Invertible Torque Function

This paper presents a switched reluctance machine model based on an invertible expression representing the torque-phase current relationship. The model can be useful for real-time control in high-performance applications when the command current is derived from the torque command. The two angular functions that the model requires as input can easily be calculated from the known static torque-position characteristics for two currents. However, the paper also proposes the analytical models of the angular functions. The result is a geometry-based analytical model, with all parameters derived from machine geometry and material properties. Simulation and experimental results illustrate that the model provides very high accuracy.

Simple Sensorless Control for High-Speed Operation of Switched Reluctance Generator

High-speed operation of the switched reluctance generator (SRG) in discontinuous conduction mode (DCM) as well as in continuous conduction mode (CCM) is considered in this paper. Very simple control method of SRG that enables stable SRG operation in CCM without using the rotor position information is proposed. Although the conventional SRG power converter can be used to implement this sensorless method, two more suitable converter topologies are also proposed. These topologies are based on diode bridge rectifiers and do not contain switch components. The output power of SRG is controlled by regulating the dc excitation current. The simulation results show that the proposed control method provides much more output power of SRG at high speeds than conventional control in DCM, and the same power as conventional control in CCM. Experimental results confirm validity and effectiveness of the proposed control method.

Review of marine current speed and power coefficient — Mathematical models

The knowledge of the mathematical models of ocean currents and of power coefficients is necessary for a complete marine current generator systems modeling. Review of these models is the topic of this paper. For any of the listed marine current mathematical models, simulation results of marine current velocity as a function of time is presented. Also, using the mathematical model of ocean currents based on the first order Stockes model, the time-dependence of the marine current speed, as a function of the ocean depth, across horizontal and vertical axis, is presented. On the other hand, as the marine current turbines are similar in many aspects to wind turbine technologies, mathematical models of the wind power coefficients are used for mathematical description of the marine power coefficients. The experimental results of the marine power coefficient are fitted using the proposed mathematical equation. All mentioned mathematical models are implemented, and simulation results obtained, using the software package MATLAB.