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Control strategies and power electronics in a low-cost electric vehicle propulson system employing a brushless DC machine

Yan, Xinxiang (2000). Control strategies and power electronics in a low-cost electric vehicle propulson system employing a brushless DC machine. PhD Thesis, Northern Territory University.

Document type: Thesis
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Author Yan, Xinxiang
Title Control strategies and power electronics in a low-cost electric vehicle propulson system employing a brushless DC machine
Institution Northern Territory University
Publication Date 2000
Thesis Type PhD
Subjects 0902 - Automotive Engineering
Abstract Battery-powered electric vehicles (BEVs) are a promising part of the solutions to urban pollution and global warming. Existing problems of BEVs are short drive range and high cost. Energy and power control strategies in EV propulsion remain a substantial research topic which require further investigation and power electronics plays a key role in EV development. This thesis studies the control strategies and power electronics for a short range, low cost EV employing high efficiency permanent magnet axial flux brushless dc motor (BDCM). Many of the technologies presented can be used in more general applications. Based on the drive cycle data obtained from an ICE vehicle and its analysis, a novel energy and power management scheme has been proposed. The proposed energy and power management scheme employs the newly developed non-flowing zinc-bromine battery (NFZBB) and ultracapacitors (UCs). NFZBBs are optimized for specific energy, low cost and long life. Ultracapacitors featuring high power density and long life are used to complement the NFZBB to achieve good acceleration performance at low speeds. The thesis shows how combining the two different types of energy storage can optimize the EV propulsion system to achieve high energy for drive range, high power for good acceleration performance, long lifetime, and low cost. A novel multifunctional dc-dc converter topology has been proposed for the overall energy and power control. This single, simple dc-dc converter is used for both the control of the energy which is drawn out of and placed into the ultracapacitors and the speed extension of the BDCM. Several advanced control technologies of BDCM are studied. Zero Voltage Transition (ZVT) soft-switching techniques are utilized in the multifunctional dc-dc converter to achieve high efficiency, reduction of volume and weight, and lower electromagnetic interference (EMI) level. A prototype of the ZVT dc-dc converter with 96% efficiency has been developed. At high power levels, due to large dimensions of ferrite cores and air gaps, the influence of leakage flux and fringing flux on the inductor design within the dc-dc converter becomes significant, and is difficult to predict accurately. With conventional design of high power ferrite cored inductors, difficulty exists in achieving a satisfactory overall performance. A novel design for high power ferrite cored inductors employing a dual-coil or distributed winding scheme is proposed by the author to combat the problems. Results from both 3-Dimensional (3D) finite element analysis (FEA) and measurement verify the viability of the novel design for high power inductors. The proposed inductor design allows better optimization by reducing the localization of saturation, leakage flux, and EMI levels, achieving good utilization of the magnetic cores. A new intelligent gate drive module for high power IGBTs has been developed and presented. This module features high current capacity, powerful functions, high performance, wide application, and convenience of use, and is suitable for high power applications such as in EV drives. The detailed functions, operation, performance, and practical application issues are addressed. A soft-switched on-board EV battery charger with unity power factor has been developed. It employs a zero-current-switching (ZCS) boost converter with power factor correction (PFC) and an asymmetrically controlled zero-voltage-switching (ZVS) half-bridge (HB) dc-dc converter in cascade. Several state-of-the-art power electronics techniques are used. They include power factor correction, a ZVS technique requiring few additional components, control of steady-state duty cycle of the charger's dc-dc converter for high efficiency, a novel active pre-load with minimized power rate, and an optimized charging profile.

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