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Design studies on less rare-earth and high power density flux switching motors with hybrid excitation/ wound field excitation for HEV drives

Sulaiman, Erwan (2012) Design studies on less rare-earth and high power density flux switching motors with hybrid excitation/ wound field excitation for HEV drives. PhD thesis, Nagoya Institute of Technology.

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Abstract

Hybrid electric vehicles (HEVs), using combination of an internal combustion engine (ICE) and one or more electric motors, are widely considered as the most promising clean vehicles. One example of successfully developed electric machines for HEVs is interior permanent magnet synchronous machine (IPMSM), due to its smaller size and lighter weight providing with design freedom of the vehicles and its higher efficiency contributing to less fuel consumption. As an example, from the historical progress of IPMSM installed on Toyota HEVs, the power density of each motor employed in Lexus RX400h'05 and GS450hC06 has been improved five times and more, respectively, compared to that installed on PriusY97O. ne of the driving forces behind this successful improvement has been the adoption of combination of reduction gear with IPMSM operated at high-speed. However, IPMSM design tends to be difficult because permanent magnet (PM) is embedded in the rotor core. The mechanical strength relies mainly on thickness and number of bridges around PM, but high number of bridges degrades the vximum torque capability due , to increases in leakage flux. Therefore, a new candidate of flux switching machine (FSM) with rugged rotor structure suitable for high-speed operation and the ability to keep high torque and power density is proposed, and examined in this thesis. . This thesis deals with the design studies on high power density hybrid excitation (HE) /field excitation (FE) FSM for HEV drives. Firstly, research background, related works including IPMSM used in HEV, issues of IPMSM for further improvements, and research objectives are discussed in Chapter 1. Then, classifications of FSM and the proposed 12s-10P HEFSM selected for HEV applications are explained in Chapter 2. Under similar restriction and specifications of IPMSM used in HEV, performances of the original 12s- 10P HEFSM are examined. Since the initial performances are far from the target requirements, design improvements using "deterministic optimization method to treat several design parameters are conducted using commercial 2D FEA package, JMAG-Studio ver. 10.0, released by JSOL Corporation. The improved design which successfully achieved the target performances as well as enough mechanical strength being possible to operate at maximum speed of 12,400rlmin is discussed in Chapter 3. b Another infirmity of this motor is the presence of high pole numbers, so that the required PWM frequency becomes very high. To reduce the supply frequency of inverter, various combinations of slot-pole HEFSMs such as 6s-4P, 6s-5P, 6s-7P and 6s-8P are designed .and analyzed in Chapter 4. Among various slot-pole combinations of HEFSMs discussed in Chapter 4, the 6s-5P HEFSM has a better efficiency at high speed operating conditions when compared with other designs, thus it is selected for further analysis. In addition, the problem of high torque ripple of more than 50% in 6s-4P and 6s-8P HEFSMs is difficult to solve. However, to realize high torque and power density, the design motor requires high current density which leads to necessity of complex cooling system to reduce the heat. To overcome this issue, a low-torque, low current density, high-speed and high reduction gear 6s-5P HEFSM-2 is proposed. The target torque is reduced to 210Nm with the introduction of reduction gear ratio of 4:l to get similar torque axle via reduction gear in IPMSM. Since the rotor mechanical strength is strong enough to operate at high speed, the target speed of the motor is increased to 20,000rlmin. Although the 6s-5P HEFSM-2 has successfblly achieved the new target performances, the problem of unbalance pulling force is serious and difficult to overcome. Therefore, the final design of 12s-10P HEFSM discussed in Chapter 3 is selected for hrther analysis. Even though the proposed machine requires high frequency to operate at high .speed, it can be overcome by / introducing high frequency switching devices. In addition, it also has no pulling force as well as very less torque ripple which is suitable for high speed HEV applications. Further design reconsiderations are made and the final performances which achieved the target requirements are demonstrated. Recently the enormous annual usage of rare-earth magnet has increased the price of Neodymium (Nd), Dysprosium (Dy) and Terbium (Tb) which are indispensable to provide the rare-earth magnet with high coercivity as the additives. From view point of cost reduction, the final design 12s-10P HEFSM-2 is analyzed for less rare-earth magnet by reducing the volume of PM in stages. The achieved performances are discussed in Chapter 5. Finally, by removing all PM in the final design HEFSM discussed in Chapter 5, a new ' structure of 12s-10P FEFSM is introduced. The results of the initial and improve design which met the target performances are analyzed and discussed in Chapter 6. The prototype model of FEFSM is manufactured and some preliminary experimental results show the proposed FEFSM with no PM is viable candidate for HEV drives.

Item Type: Thesis (PhD)
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK1001-1841 Production of electric energy or power. Powerplants. Central stations
Depositing User: Normajihan Abd. Rahman
Date Deposited: 05 Jan 2014 04:04
Last Modified: 05 Jan 2014 04:04
URI: http://eprints.uthm.edu.my/id/eprint/4663
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