INTRODUCTION

SRM belongs to the electric machine with doubly-salient and singly-excited with concentrated windings. It is rigid and suitable for high-speed operation. Moreover, the rotor of SRM is not equipped with conductors or permanent magnets, this makes it have no cogging torque, and thus it is easy to start. In driving operation, its converter circuit is simple with fault-tolerant capability. The high generating torque and acceleration capabilities make it possess high application potential.

However, SRM has some inherent disadvantages, such as difficult to control with high driving performance owing to nonlinear winding inductance and developed torque characteristics, higher torque ripple and vibration. Some issues for improving the performance of a SRM drive include: (i) Motor design; (ii) Converter: the asymmetric converter has the largest PWM switching flexibility. Hence it is adopted for the developed SRM-driven fan. And the off-the-shelf SRM IPM is used to construct this converter; (iii) Commutation shift: it possesses equivalent field-weakening effect to reduce the back-EMF effect on the current tracking performance; (iv) Voltage boosting: the boosted DC-link voltage can effectively enhance the SRM driving characteristics under high speed; (v) Switching control: the SRM converter switching control approaches can broadly be classified into current-mode control and direct duty-ratio voltage-mode control. The latter is simpler, but it has worse winding current and driving performances. However, it is still applicable for a SRM-driven fan if the proper commutation is set; (vi) Speed control: for facilitating the realization using PWM analog circuits, the direct duty-ratio modes for both the SRM switching scheme and the speed controller are adopted in the established SRM-driven fan.

Till now, there have some practical application examples of SRM drive. For a motor driven cooling fan, its drawn power is proportional to the cubic of speed. Hence, a variable speed motor driven fan may possess great energy saving potential. Traditionally, the single-phase induction motor and the brushless DC motor (BDCM) are the most popularly employed motors for small cooling fans. However, SRM still has the potential as an alternative. And the research has demonstrated the potential of SRM in this application.

For a motor drive powered by the mains, one can apply SMR as the AC front-end to establish the boosted and well-regulated DC-link voltage. The improved driving characteristics in high-speed range with good line drawn power quality can be obtained simultaneously. The surveys for single-phase SMRs can be found . Among various SMRs, Flyback SMR, which belongs to isolated buck-boost SMR, is the best choice for the plants with smaller ratings (<150W). Since it possesses the merits of with isolation, compact, step-up/step-down voltage transfer property, etc. Hence, it is adopted for the established motor driven cooling fan.

The design and implementation of a flyback SMR-fed SRM-driven cooling fan are presented in this report. The employed SRM is rated as three-phase 6/4, 70W, 900rpm. The asymmetric bridge converter is constructed using two off-the-shelf two-phase SRM IGBT IPMs FCAS30DN60BB by the Fairchild Semiconductor. For simplicity, the direct duty-ratio controls for both the PWM switching scheme and the open speed loop are adopted for the established SRM-driven fan. To let the developed fan be powered from the mains with good line drawn power quality, a single-phase flyback SMR front-end is established. The DCM with voltage control is adopted for the ease of realization using analog circuits. Some measured results are provided to evaluate the operation performance of the established flyback SMR-fed SRM-driven fan.


Fig. 1


Fig. 2


Fig. 3


Fig. 4

心得感想

This special topic project report has presented the development of a flyback SMR-fed SRM-driven cooling fan. For compactness, the SRM asymmetric bridge converter is constructed using the off-the-shelf IGBT IPM. All the control schemes of the two power stages are all realized using analog circuits. For the SRM drive, the open speed loop with direct duty ratio control is adopted. As to the single-phase flyback SMR front-end, the DCM with voltage control is applied.

The experimental evaluation has shown that: (1) the developed whole flyback SMR-fed SRM-driven fan possesses good varied speed driving performances with good line drawn power quality characteristics; (2) owing to the highly distorted line drawn current from the mains, the diode rectifier fed SRM-driven fan has larger drawn current, bad power factors and current THDs under the same driving speeds.