Inductive power transfer system and its application

Pao Yue-kong Library Electronic Theses Database

Inductive power transfer system and its application


Author: Zhang, Wei
Title: Inductive power transfer system and its application
Degree: Ph.D.
Year: 2014
Subject: Electric power transmission.
Wireless power transmission.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Electronic and Information Engineering
Pages: xxv, 163 p. : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: This thesis aims to optimize the efficiency of an inductive power transfer (IPT) system by identifying and analyzing the circuit characteristics of the loosely coupled transformer of the system. The IPT system is a type of wireless power transmission system being practically non-radiative and commercially available. Compared with conventional wired power transfer, a properly designed IPT system is convenient, safe, reliable and environmentally adaptive. The much lower efficiency of the loosely coupled transformer of the IPT system in comparison to the direct electrical connection of the wired system is the major limitation of its development and application. Therefore, the study of the electrical characteristics of the loosely coupled transformer of the IPT system is the main focus of this thesis. IPT power transfer is based on the Faraday's law of induction. By injecting a changing current to the primary side of a current carrying transmitting winding, a changing magnetic field in space is produced. The changing magnetic field induces a changing current in the physically separated receiving loop of conductor windings. Thus, electrical power is transferred wirelessly via the two physically separated loosely coupled transformer windings. From the perspective of electrical circuits, a changing current can be generated effectively by an assembly of resonant circuits with power-efficient-switching excitation. The loosely coupled transformer windings can be modeled as a loosely coupled transformer with magnetic coupling coefficient k and the coil quality factors Q's. The optimization of the efficiency of the IPT system is thus reduced to the study of the system efficiency among the circuit topologies to generate the sinusoidal voltage or current, the sinusoidal frequency and its interaction with the inductive coupling coefficient k and the quality factor Q's of the conducting windings.
The IPT power converters are thus resonant converters with the loosely coupled inductors compensated with external capacitors to form simple resonant circuits. Resonant power converters are difficult to design due to the narrow region of optimal operating points depending on the operating frequency, load and input-to-output transfer ratio. In this thesis, the optimal operating points for optimal converter power efficiency and load-independent input-to-output transfer ratio operating as an output voltage or current converter are studied. Operating frequencies are identified for the simple output series or parallel compensation techniques. Designs for an operating frequency for either or both of the conditions of optimal converter power efficiency and load-independent input-to-output transfer ratio are given. Finally, an IPT application of roadway powered elective vehicles is studied and a series of sectional tracks is proposed to replace the traditional single long distance track which is inefficient in power transmission. The distance of sequentially excited track section is the focus of sectional track design since it is related with power transfer capability and efficiency. Research is conducted at various vehicle velocities under a sophisticated model of macroscopic dynamics of multi-lane traffic. Two optimal track distances, one for slow moving or stationary vehicle stream near signal lights and the other for high speed situations at freeway, are revealed.

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