1100 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 6, NOVEMBER 1998 Power Electronic Converters for Switched Reluctance Drives Mike Barnes and Charles Pollock Abstract—A number of power electronic converter circuits exist for switched reluctance machines which are generally applicable to most loads. A larger number of circuits exist which are suitable for particular niche applications, but which have the potential to be the most cost effective within that niche. Due to the variable methods of operation of these circuits and the rapid progress in this field, comparisons of these circuits have so far been limited. This paper attempts to bring together the sum total of converter topologies so far published for switched reluctance drives. A novel classification methodology is presented. The converters are compared using a straightforward total semiconductor VA per phase sum, and the relative cost of the drive system elements is considered. I. INTRODUCTION S WITCHED RELUCTANCE machines have been shown to offer high-efficiency, reliable, robust, easy to manu- facture, and inexpensive motors which can compete with the more conventional brushed dc motor, induction motor, and permanent magnet motor in a variety of applications [1], [2]. Unipolar excitation allows the use of cheaper and more robust converters than conventional inverter drives. Nevertheless, the primary cost of the switched reluctance drive is the power electronic converter; it is thus important to match the converter to the particular application. Previously published comparisons of switched reluctance motor converters [2], [3] have focused on a few of the most common converter circuits. Many of the remaining circuits are worthy of consideration for particular applications and will be discussed in this paper. For each stroke of the motor, the power electronic converter for a switched reluctance motor is required to first provide a positive voltage loop to increase the flux in the phase winding. Second, it must have the ability to reduce the applied voltage if the desired current level is reached. Third, it must apply a negative voltage at turn off, also referred to as a negative voltage loop. The first two requirements are usually met by the equivalent of a step-down or buck circuit operating from a dc-link input. The output smoothing capacitor is usually removed, and the winding of the motor may take the place of the converter inductance and load. The energy recovery circuit is usually in the form of a boost or buck–boost converter. Some circuits can also apply a so-called zero-voltage loop. This is a current Manuscript received August 5, 1997; revised April 1, 1998. Recommended by Associate Editor, D. Torrey. M. Barnes is with the Department of Electrical Engineering and Electronics, UMIST, Manchester, M60 1QD, U.K. C. Pollock is with the Department of Engineering, University of Warwick, Coventry, CV4 7AL, U.K. Publisher Item Identifier S 0885-8993(98)08231-3. Fig. 1. Switched reluctance drive converter classification. freewheel path, which does not include the dc link, and applies only a low negative voltage to the phase winding. The presence of such a path can reduce motor hysteresis losses and power dissipation in the dc-link capacitor during any period when switches in the converter are chopped to reduce the net applied voltage to the phase winding. Drive design strategies to reduce cost are based on nu- merical ratings, relating cost to physical attributes such as capacitance, voltage or current rating, mean time between failure, and kilovoltampere/kilowatt rating. The fewer power electronic components passive or active that can be used to meet a specification, the lower the cost, not only in terms of device cost, but also in terms of required gate drive, protection, heat sinks, and snubbing circuits. Having fewer switches, but these having higher voltage, current, or power dissipation ratings, does not necessarily reduce costs. Particu- larly, an increase in current rating may dramatically increase the package cost beyond any savings that may have been made from a reduced number of switches. The kilovoltampere or kilovoltampere/kilowatt rating of the converter provides a measure of the effectiveness with which the switch rating has been utilized [4] and, hence, relative cost for different converters. 0885–8993/98$10.00  1998 IEEE