A soft-switched reluctance motor drive circuit with improved performances

Abstract

d L i A simple soft-switched reluctance motor drive circuit was d t Abstract proposed, involving only four switching devices with three motor and the output torque was increasctl by means of shorter currentdevice during powering period, higher efficiency can be performed. 1. birroditcrioii = d L i +~d i windings. The sysleiii yields less EMI, because of soft switching, d t d t = w, -i + L -IFF tail-length. As this system utilizes only one series switching d e d t d L d iEnormous amount of power electronic drives are used for industrid facilities and offices, lately.The switched reluctance motors are also rigorously inivestigated in these days. and various kinds of reluctance motor drive circuits have been presentcd. Electric vehicle is one of the most promised field of reluctance motor applications because of their simple and rigid structure, and tlie future possibility of lower cost than that of induction motors' is also strongly focused point.This motor has relatively high reactance and the stored excited energy has to be retrieved after each powering period. Therefore the energy retrieval period usually 'becomes longer and the shorter retrieval period is desired to obtain higher output power and higher efficiency. For this purpose, some kinds of driving circuits are already proposed. Many of them are utilizing hard switching i:ypes[l]-[3], and they may cause high electro-magnetic intei-ference: (EMI) and lead to rather liigli switching losses. A soft-switched type drivecircuits with resolinill circuit was also reported[4], and it seeins to Iiave less EM1 and less switcliing losses. However, they utilize continuous resonant-switcliings, and may result in high resonant circuit losses. This paper deals with soft-switched type drive-circu.it, including only four switching devices, and has the merits of l o i~ switching losses, low EMJ, and higher efficiency. Fig. 1 shows the structure of the reluctance motor dealt in this paper, and each winding inductance varies according to the rotational angle 0 as sclicinatically depicted iii the figure. It. Relitcfaiice Torqrte GerierafioiiInductance L, of phase-a winding assumed to vary 1ine.arly up and down, during 0 = -30 to +30 degrees. The 0the.r windinginductances and L, also vary as the same way, with thlt 30 degree (mechanical) angle-differences. When the voltage v is applied across the motor winding, tlie fluxlinkage k and v are written iii dh dt v = -where the winding resistance is neglected. As h is rep,resented by the product of inductance L and tlie current i , then the voltage v be comes as follows.

Soft-switching Converters for Electric Vehicle Propulsion

“…Although soft-switching dc-dc converters have been widely accepted by switched-mode power supplies, the corresponding development for EV propulsion is much slower. As the pursuit of power converters having high efficiency and high power density for EV propulsion is highly desirable, the development of soft-switching power converters for motor drives is in progress [Lai, 1997;Murai, 1997;Lai et al, 2005]. Table 1 gives a comparison between hard-switching and soft-switching converters for EV propulsion.…”

“…Compared with the development of soft-switching inverters for ac motors, the development for switched reluctance motor (SRM) drives has been very little [Murai et al, 1997;Cho et al, 1997;Rolim et al, 1999], and suffered from limited research activities in recent years. In fact, motor manufacturers have little activities to further develop SRM and their drives.…”

An Improved Asymmetric Half-Bridge Converter for Switched Reluctance Motor in Low-Speed Operation with Current Regulated Mode

“…The proposed soft-switched converter for three-phase SRMs in [3] involves four switching devices, in which one is specifically assigned for the resonant part. A modified soft-switched circuit in [4] utilizes only three active switches, but requires additional bridge diodes and a resonant tank.…”

“…Another modified converter employs several thyristors for the motor windings and the resonant circuit plus an extra coupled transformer [5]. The introduced soft-switched circuit in [6] has some relocation of its resonant part compared with that in [3]. Although high torque and improved efficiency are claimed to be achieved in [3] and [6], the voltage and current stresses of the switching devices could still be observed in these resonant-based converters.…”

Analysis of Soft-switching Converters for Switched Reluctance Motor Drives for Electric Vehicles

“…In recent years, a number of soft-switching techniques, providing either zero-voltage switching (ZVS) or zero-current switching (ZCS) condition, have been successfully developed for switched-mode power supplies [Ching, 2009] and has been extended to DC motor drives Ching and Chau, 2001;Ching, 2005;Ching, 2006]. Also, a few studies on soft-switching converters for SRM drives have been reported [Murai et al, 1997;Cho et al, 1997;Rolim et al, 1999]. In this paper, two new soft-switching converters for SRM drives, namely the zero-voltage-transition (ZVT) converter, and zero-current-transition (ZCT) converter, are proposed and analysed.…”