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Xu, Z.; Li, T.; Zhang, F.; Zhang, Y.; Lee, D.; Ahn, J. Segmental Switched Reluctance Motor. Encyclopedia. Available online: https://encyclopedia.pub/entry/48762 (accessed on 13 December 2025).
Xu Z, Li T, Zhang F, Zhang Y, Lee D, Ahn J. Segmental Switched Reluctance Motor. Encyclopedia. Available at: https://encyclopedia.pub/entry/48762. Accessed December 13, 2025.
Xu, Zhenyao, Tao Li, Fengge Zhang, Yue Zhang, Dong-Hee Lee, Jin-Woo Ahn. "Segmental Switched Reluctance Motor" Encyclopedia, https://encyclopedia.pub/entry/48762 (accessed December 13, 2025).
Xu, Z., Li, T., Zhang, F., Zhang, Y., Lee, D., & Ahn, J. (2023, September 02). Segmental Switched Reluctance Motor. In Encyclopedia. https://encyclopedia.pub/entry/48762
Xu, Zhenyao, et al. "Segmental Switched Reluctance Motor." Encyclopedia. Web. 02 September, 2023.
Segmental Switched Reluctance Motor
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This entry is adapted from the peer-reviewed paper 10.3390/en15239212

Due to the high robustness and control flexibility of switched reluctance motors (SRMs), segmented structures have been widely studied to expand its applications in aerospace and other industrial fields.

switched reluctance motors SRM segmental structure

1. Introduction

With the rapid development of power electronics and the gradual increase in the cost of permanent magnets (PMs), the switched reluctance motor (SRM) has been widely used in critical applications, such as starter/generators for aviation [1], driving systems for electric or hybrid vehicles [2][3][4], and household appliances [5], owing to its special and elaborated structure. Although SRM has lots of merits over induction motors (IM) and permanent magnet synchronous motors (PMSM), its shortcomings of noise, low power density, and radial vibration cannot be ignored. In an ideal SRM, the reluctance varies linearly with stator teeth overlap, generating a constant torque for a constant magnetic motive force (MMF). It is always designed to operate within the magnetic saturation zone of the ferromagnetic material to maximize torque density. However, in practical terms, saturation, magnetic field edge flux, and the rotor’s biconvex pole structure make the constant phase current produce torque and flux as a nonlinear function of rotor position. As a result, the generated torque may contain significant torque fluctuations, while torque ripple is believed to contribute significantly to another shortcoming of SRM, acoustic noise.

In the last few years, the research on the structure of SRMs has focused on segmental, bearingless, and linear types, from the traditional long flux path to the novelty short flux path, as shown in Figure 1. In some industrial applications that require high-speed rotation, conventional switched reluctance motors (CSRMs) typically adopt mechanical bearings to support the shaft of the motor system, causes severe wear on the mechanical bearing under long-term operation and leads to more heating problems. In severe cases, it will affect the uniformity of the air gap between the stator and rotor. It not only affects the efficiency of the motor, but also shortens the useful life of the machine and increases the maintenance burden of the motor and bearings. Moreover, the lubricant required for the mechanical bearings cannot be used in harsh environments such as vacuums and high temperatures. In order to solve the various problems posed by mechanical bearings in high-speed SRMs, air float, liquid float, and magnetic levitation bearings emerged in the community. Although these measures can achieve contactlessness and frictionlessness between shaft and rotor, air float and liquid float technologies must be equipped with special pneumatic and hydraulic systems. However, it will also make the motor larger. When the air pressure or hydraulic system fails, the air float and liquid float bearing will also fail. Consequently, the motor cannot run normally, thereby reducing the reliability of the motor system. The magnetic bearing technology fundamentally changed the traditional support form, with no contact between the shaft and rotor, high speed, high precision, long life, and other characteristics. On this basis, the seminal work of Higuchi proposed the concept of bearingless switched reluctance motors (BSRMs). However, it was not until the late 1990s that a more systematic study of BSRMs was conducted. For example, in [6], Takemoto exploited the similarity between the stator structure of SRMs and magnetic bearings by superimposing the levitation force winding of magnetic bearings on the stator windings of SRMs, such that the motor generates both levitation force and electromagnetic torque to achieve levitation and rotation of the motor rotor, thereby discarding the conventional bearing and reducing the weight of the SRM.

Figure 1. A classification of existing SRM topologies in recent years.

The segmental structure is a new topology based on the optimization of the flux path of the CSRM, of which the basic idea is to convert the stator or rotor from the previous conventional continuous iron core structure into discontinuous segments embedded in an isolator made of non-magnetic material to form a special short flux path which will reduce the coupling of adjacent phase fluxes and core losses. This idea was pioneered proposed by Lawerson, who divided the rotor of a synchronous reluctance motor (SynRM) into several discontinuous segments and replaced the magnetically conductive material in the center of the rotor with a non-magnetic material. It aims at increasing the magnetic utilization of SynRM by having more than half of the magnetic iron structure carry machine flux with short flux paths at any time during machine operation. Instead of the use of the conventional rotor teeth structure, it is constructed from a series of discrete segments. This method paved the way for the future research on the segmented switched reluctance motor (SSRM) [7].

2. Segmental Rotor Switched Reluctance Motor

Segmental rotor switched reluctance motors are designed to shorten the magnetic flux path (Figure 2), reduce iron loss, and increase motor torque by splitting the conventional convex rotor structure into several discontinuous rotor blocks and embedding them in a non-magnetic isolator made of magnetic isolation material. Common configurations are 6/5[8], 12/8[9], 12/10[10], 16/10[11] and axial flux 12/10[12]，etc. According to the winding connection can be divided into whole pitch winding and centralized winding structure. It is worth noting that if a centralized winding connection is used, the stator usually adopts a hybrid stator pole structure. The wide teeth were defined as excitation poles and the narrow teeth were defined as auxiliary poles. All conductors in each stator slot are coupled only to their own MMF-driven flux. The mutual coupling between adjacent phases is small, increasing the electrical utilization and reducing the MMF requirements of the motor. The winding generated flux flows downward from the excitation pole, through the rotor segment, and returns from the adjacent auxiliary pole to either side of the excitation stator pole, with a short flux path.

Figure 2. Common structures of segmental rotor switched reluctance motors

3. Segmental Stator Switched Reluctance Motor

Analogously, the block stator switched reluctance motor divides the stator of the motor into multiple discontinuous stator blocks (Figure 3), forming an interference fit with the casing for fixation. Common types include C-type stator [13][14], E-type stator[15], and axial modular stator structures [16][17][18].

Figure 3. Common structures of segmental stator switched reluctance motors.

4. Double Stator Segmented Switched Reluctance Motor

In order to optimize the electromagnetic force in the air gap to produce the tangential electromagnetic force and weaken the radial electromagnetic force as much as possible, some researchers proposed the double-stator segmental switched reluctance motors (DSSRM) [19][20][21][22][23][24][25][26][27], as shown in Figure 4. Otherwise, a new double-stator segmental rotor BSRM with CW windings which combines the advantages of a short flux path and no flux reversal in a segmental rotor bearingless SRM [28][29], which not only weakens the coupling between the torque and the levitation system, but also improves the torque output capability compared with the conventional double-stator BSRM.
 
Figure 4. Common structures of double stator SSRM.

5. Segmented Switched Reluctance Motor with Permanent Magnet assisted

Some researchers have proposed that the performance of the motor can be improved by embedding permanent magnets between the stator teeth, stator yoke, or stator tooth poles [30][31][32][33][34], as shown in Figure 5.
 
Figure 5. Common structures of PM assisted SSRM.

6. Segmental Rotor Linear Switched Reluctance Motor

Linear switched reluctance motors (LSRM) are also an important branch of SRMs with structural variants similar to rotation SSRMs. The stator structure can still be divided into two structures according to windings' connections, i.e., equal-tooth and unequal-tooth forms. What is more, there are double mover structures with FPW and CW, and double mover segmented LSRM with toroidal windings [35][36][37], as shown in Figure 6.

 Figure 6. Common structures of segmental rotor LSRM.

7. Conclusion

The SSRM, emerging as a new structure of the SRM, inherits the advantages of the traditional structure of SRM and improves the performance of the motor. It furthermore has the advantages of shorter flux path, low weight, and reduced core loss. Further improvement in fault tolerance and reliability also increases its applications in electric/hybrid vehicles and aerospace. There are many ontological structures of the SSRM, which are ultimately evolved from the most basic segmental rotor and segmental stator structures. In a novel design of the SRM in which a toothed rotor is replaced with one containing a series of discrete segments, the segments' rotor achieves isolation between adjacent rotor poles, and the cylindrical rotor structure reduces wind resistance when the motor is running at high speed. The segmental stator achieves magnetic, thermal, and electrical isolation between adjacent phases, which improves core utilization, reduces costs, and improves fault tolerance. Based on the two basic structures, new types of SRMs, such as segmental rotor BSRM, HESSRM, axial segmental SRM, and double-stator SSRM, have gradually evolved. In this research, researchers analyze and summarize the existing structural topology design of the SSRM. However, due to the specificity of their structures, there is still a long way to go for large-scale industrial applications. 

References

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  7. P.J. Lawrenson; L.A. Agu; A new unexcited synchronous machine. null 1963, 110, 1275-1275.
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Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register : Zhenyao Xu , Tao Li ,
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