Parameter Sensitivity Study for Optimization of 1Slot-8Pole Three- Phase Wound Field Switched-Flux Machine Faisal Khan a, Erwan Sulaiman b, Md Zarafi Ahmad c and Zhafir Aizat d Dept. Of Electrical Power Engineering, FKEE, University Tun Hussein Onn Malaysia P.O Box. 8, Parit Raja, Batu Pahat, Johor, Malaysia a faisalkhan@ciit.net.pk, b erwan@uthm.edu.my, c zarafi@uthm.edu.my, d zhafiraizat9@gmail.com Keywords: Switched-Flux machine, deterministic optimization, finite element analysis, robust rotor, non-overlap windings Abstract. This paper presents parameter sensitivity study and performance analysis of 1Slot-8Pole three-phase wound field switched-flux machine (WFSFM). The proposed machine consists of armature slots, field-excitation coil (FEC) slots and 8 rotor poles. All active parts such as armature coil and FEC are located on the stator, while the rotor part consists of only single piece iron. This makes the machine becoming more robust and more suitable to be apply for high speed motor drive system applications. The deterministic design optimization approach is used to treat several design parameters defined in rotor, armature and FEC slot area to achieve better results than initial design. -D finite element analysis (FEA) is used to study various characteristics of machine. Since the initial design fail to attain the maximum torque and power, therefore the performance of machine is enhanced by refinement of several design parameters. After design refinement, WFSFM has achieved the maximum torque of.3 Nm and power of.7 kw at maximum field current density, J e of 3 A/mm and armature current density, J a of 3A rms /mm which is approximately 3 times the torque and times the power of initial design. Introduction In the mid 19s, the first concept of switched-flux machine (SFM) has been founded and printed. stator slots and rotor poles (S-P) permanent magnet (PM) SFM i.e. permanent magnet single-phase limited angle actuator or more well-known as Laws relay has been developed [1], and then single phase generator with stator slots, and or rotor poles (S-/P) has been invented []. Over the last decade, many SFM topologies have been introduced for various application i.e. automotive, domestic appliances, aerospace etc. SFM can be classified into three groups that are Permanent Magnet (PM) SFM, Field Excitation (FE) SFM and Hybrid Excitation (HE) SFM. Permanent magnet and field winding are the main sources of flux in PMSFM and FESFM while in HESFM, both field winding and permanent magnet produces the flux [3-]. In all these SFMs the armature winding and field winding or Permanent magnets are located on the stator. When compare with other SFMs, the FESFM motor has advantages of low cost, simple construction, magnet-less machine, and variable flux control capabilities suitable for various performances. Furthermore, to manufacture the FESFM motors, the PM on the stator of conventional PMSFMs is replaced by DC field excitation coil. In other words, the FESFM motors having salient-rotor structure is a novel topology, merging the principles of the SRMs and inductor generator [-7]. The performance of SFM is enhanced by using segmental rotor configuration in recent research [8]. Segmental rotor is designed in a manner such that to achieve bipolar flux in armature winding, which has neither magnets nor winding. To produce bipolar flux linkages in this way, a toothedrotor structure may be used but it requires overlap windings on the stator [9]. Non-overlap winding has been used in [1] to increase the efficiency by reducing the copper losses and enhanced the speed torque characteristics of SFM. A three-phase SFM using a segmental rotor has been proposed in [11] to improve fault tolerance to a reduction in torque pulsations and power converter rating per
phase. Fig. 1 [9] and [11] shows SMFs having segmented-rotor with non-overlap winding and toothed-rotor with overlap winding at the stator. A single-phase WFSFM machine was comprehensively investigated in [1]. In that machine, armature and field windings are fully pitched and hence the end-winding is long. Two single phase WFSFMs topologies with DC field and AC armature windings having the same coil-pitch of slot-pitches and having different coil-pitches of 1 and 3 slot-pitches respectively are discussed [13]. It is shown that the iron loss and copper loss of WFSFM has been reduced and thus increased the efficiency but it has problem of unbalanced magnetic force. As one alternative to overcome these problems, a new structure of initial design of 1Slot-8Pole three-phase WFSFM with non-overlap armature and field windings is proposed as shown in Fig. 3. From the figure, it is clear that the motor consists of FEC and armature coil located at the stator. The rotor is made of single piece of iron, becoming more robust and more suitable for high speed applications. Based on the topology of 1Slot-8Pole WFSFM illustrated in Fig. 3, design optimization is conducted based on sensitivity of seven design parameters to get maximum performance. This paper compares the performance analysis of initial design and improved design of 1Slot-8Pole WFSFM having toothed-rotor structure and non-overlap armature and field windings. Design specification of proposed 1Slot-8Pole WFSFM The design specifications of proposed 1Slot-8pole WFSSFM are listed in Table 1. The selection of initial design parameters is based on the following assumptions: the initial rotor radius selected is approximately % to 7 % of total machine radius; the FEC slot area and armature coil slot area are set to be trapezoidal shape with same slot area. 8mm 1mm FEC FEC Armature coil mm Rotor Armature coil Fig. 1 Three-phase WFSFM with overlap windings Fig. Three-phase WFSFM with non-overlap windings Fig. 3 Initial design of 1Slot-8Pole Table 1. Initial Design Parameters of 1Slot-8Pole Parameters Values Stator radius [mm] 7 Rotor radius [mm] Air gap length [mm].3 Stator pole width [mm] 8 Armature Slot Area [mm ] 3.11 FEC Slot Area [mm ] 3.11 Field Excitation current [A] 79.13 Armature current [A] 111.9 FEC turns Armature coil turns Filling factor. Stack length[mm] 7 Stator
Design parameters variation procedures The performance analyses of initial design of 1Slot-8Pole WFSFM are investigated. The torque and power obtained are 7. Nm and.9 kw at maximum speed of 31.7 rev/min, which is far from the target requirements. To achieve the requirements, design free parameters X1 to X7 are defined in rotor and stator part as shown in Fig.. Deterministic optimization approach is used to find the maximum performance of machine by adjusting the design free parameters X1 to X7 while keeping the air gap constant. Variation of rotor parameters. The first step is to change the rotor parameters X1, X and X3 while keeping X to X7 constant. Since the torque increases with the increases in rotor radius, X1 is treated and considered as dominant parameter to improve the torque. The torque has maximum value of 1.93Nm when the rotor radius is mm as shown in Fig.. Then keeping X1 at mm, the rotor pole depth X and rotor pole width X3 are adjusted, illustrated in Fig. and achieved the maximum torque. Variation of Armature coil and FEC parameters: Once the maximum torque for X and X3 are determined, the second step is done by changing the armature slot parameters width, X and depth, X while keeping the rotor parameters and FEC slot area constant to get maximum torque, as plotted in Fig. 7. Finally, FEC slot area (width, X and depth, X7) is changed by keeping the other parameters constant for better torque. Fig. 8 shows that maximum torque of 1.1Nm is achieved after completion of 1 st cycle and then,.3nm after completion of nd cycle. The design method above is treated repeatedly by changing X1 to X7 until maximum torque and power are achieved. The final design of this machine which produced the maximum torque and power is shown in Fig. 9. The comparison between the initial and final design parameters are listed in Table. X7 X T[Nm] 1 1 nd cycle Rotor X X3 X Stator 7 8 9 1 11 1 13 1 1 Rotor pole width, X3[mm] Fig. Design parameters of 1Slot-1Pole WFSalR SFM 1 1 1 1 8 X1 nd cycle X. 7.. Rotor radius, X1 [mm] Fig. Torque versus rotor radius Fig. Torque versus rotor pole width 1 1 nd cycle 18 Armature depth, X [mm] Fig.7 Torque versus armature slot depth
1mm 1 1 nd cycle 1mm 1mm 19 1 3 FEC depth, X7 [mm] mm Fig.8 Torque versus FEC slot depth Fig. 9 Improved design of 1Slot-8Pole WFSFM Improvement of various characteristics of 1Slot-8Pole WFSFM Cogging Torque. The cogging torque analyses for both designs are shown in Fig. 1. The initial design of 1Slot-8Pole WFSFM has high peak to peak cogging torque of approximately 7 Nm. As high cogging torque causes vibration in machine and makes it noisy, therefore by following various steps of changing the design parameters, the cogging torque of 1Slot-8Pole WFSFM is reduced to approximately Nm. Torque and Power versus speed characteristics. The torque and power versus speed curves of initial and improved design of 1Slot-1Pole WFSFMs are plotted in Fig. 11 and 1. At the base speed of 31.7 rev/min and.7 rev/min, the maximum torque of 7.1 Nm and.3 Nm is obtained and torque starts to decrease if the machine is operated beyond the base speed. The power accomplished by initial design of 1Slot-8Pole WFSFM at base speed is.9 kw and starts to reduce until 1.1 kw at higher speed of 8.8 rev/min due to increase in iron loss while the power 3 1-1 - -3-1 8 1 18 3 3 Electrical cycle [Degrees] Fig.1 Cogging Torque P [kw] Initial design Improved design 8 Speed [rev/m] Fig.11 Torque and power vs. speed for initial design 3 1 1 1 P[kW] 8 Speed [rev/min] Fig.1 Torque and power vs. speed for improved design Table. Initial and Improved Design Parameters of 1Slot- 8Pole WFSalR SFM Parameters Initial Improved X1 Rotor radius [mm] X Rotor depth [mm] 18. 17. X3 Rotor pole width [mm] 1 X Armature coil width [mm] 13 1 X Armature coil depth [mm] 1.. X FEC width [mm] 13 11 X7 FEC depth [mm] 1. 1. Ag Air gap length [mm].3.3 S a Armature coil slot area[mm ] 3.11 1.3 S fec FEC slot area [mm ] 3.11 17.3 T Average torque [Nm] 7..3 P Power [kw].9.7
achieved by improved design is.7 kw at maximum torque and base speed of.7 rev/min. Conclusion In this paper, parameter sensitivity study for design optimization and performance analysis of 1Slot-8Pole are presented and clearly demonstrated. The proposed design has a robust rotor structure and non-overlap windings. As a result the motor can be used for high speed applications and efficiency will increase due to reduction of copper losses. The shape of the proposed motor is very simple which paves better way of design optimization compared to other machines. The torque and power are increased to an acceptable condition by design refinement. Further optimization techniques will be applied in future to reduce the cogging torque and increase the flux linkage, average torque and power. References [1] Laws AE. An electromechanical transducer with permanent magnet polarization, Technical Note No.G.W., Royal Aircraft Establishment, Farnborough, UK, 19 [] Rauch SE, Johnson LJ., Design principles of flux-switching alternators, AIEE Trans., 7 (19) 11-18. [3] F.Khan, E. Sulaiman, M.Z. Ahmad, Coil test analysis of wound-field three-phase flux switching machine with non-overlap winding and salient rotor, IEEE 8th International Power Engineering and Optimization Conference (PEOCO), (1) 3-7. [] Sulaiman E, Kosaka T, Matsui N., Design optimization and performance of a novel -slot - pole PMFSM with hybrid excitation for hybrid electric vehicle, IEEJ Trans. Ind. Appl., 13 (1) 11-18. [] E. Sulaiman, M. Z. Ahmad, T. Kosaka, and N. Matsui, Design Optimization Studies on High Torque and High Power Density Hybrid Excitation Flux Switching Motor for HEV, Procedia Engineering, 3(13) 31 3. [] J. H. Walker, The theory of the inductor alternator, J. IEE, 89 (19) 7 1. [7] T. J. E. Miller, Switched Reluctance Machines and Their Control, Hillsboro, OH: Magna Physics, 1993. [8] B.C. Mecrow, E.A. El-Kharashi, J.W. Finch, and A.G.Jack, Segmental rotor switched reluctance motors with single-tooth windings, IEE Proc. on Power Applications,1(3) 91-99. [9] Erwan Bin Sulaiman, Takashi Kosaka and Nobuyuki Matsui, Design Study and Experimental Analysis of Wound Field Flux Switching Motor for HEV Applications, XXth International Conference on Electrical Machines (ICEM), (1) 19-17 [1] A. Zulu, B.C. Mecrow, M. Armstrong, Topologies for three-phase Wound field Segmented- Rotor flux switching Machines th IET International Conference on Power Electronics, Machines and Drives (PEMD), (1) 1- [11] Ackim Zulu, Barrie C. Mecrow, and Matthew Armstrong, A Wound-Field Three-Phase Flux-Switching Synchronous Motor With All Excitation Sources on the Stator, IEEE Transactions on Industry Applications, (1) 33-371 [1] C. Pollock, H. Pollock, R. Barron, J. R. Coles, D. Moule, A. Court, and R. Sutton, Fluxswitching motors for automotive applications, IEEE Trans. Ind. Appl., () 1177-118. [13] Y. J. Zho, and Z. Q. Zhu, Comparison of low-cost single-phase wound-field switched-flux machines, 13 IEEE International Electric Machines & Drives Conference (IEMDC), (13) 17-18