Abstract
Wireless power transfer (WPT) for electric vehicles is an emerging technology and a future trend. To increase power density, the coupling coefficient of coils can be designed to be large, forming a strongly coupled WPT system, different from the conventional loosely coupled WPT system. In this way, the power density and efficiency of the WPT system can be improved. This paper investigates the dual-side phase-shift control of the strongly coupled series–series compensated WPT systems. The mathematical models based on the conventional first harmonic approximation and differential equations for the dual-side phase-shift control are built and compared. The dual-side phase-shift angle and its impact on the power transfer direction and soft switching are investigated. It is found that synchronous rectification at strong couplings can lead to hard switching because the dual-side phase shift in this case is over 90°. In comparison, a relatively high efficiency and soft switching can be realized when the dual-side phase shift is below 90°. The experimental results have validated the analysis.
Highlights
Compared with the conventional conductive power transfer, wireless power transfer (WPT) [1,2,3,4,5,6] has many advantages, such as safety, automation, convenience, and feasibility to various working environments, such as mining and underwater situations
It is found in strongly coupled WPT systems that this will result in the primary-side inverter working in hard switching, leading to decreasing efficiency and potential circuit seldomly used to regulate the secondary-side charging current due to too much reactive power will be introduced if the phase difference bet mary-side and secondary-side voltages is not 90°
This paper presented the modelling and dual-side phase-shift control of the strongly coupled series–series compensated WPT systems
Summary
Compared with the conventional conductive power transfer, wireless power transfer (WPT) [1,2,3,4,5,6] has many advantages, such as safety, automation, convenience, and feasibility to various working environments, such as mining and underwater situations. The coupling coefficient of the two coupled coils can be designed to be large, forming a strongly coupled WPT system, where the coupling coefficient is normally larger than 0.5 This system has a totally different feature from the conventional loosely coupled WPT systems, whose coupling coefficient is around 0.2. (1) Synchronous rectification is normally conducted to the secondary-side rectifier of the loosely coupled WPT systems to improve efficiency [9,10] It is found in strongly coupled WPT systems that this will result in the primary-side inverter working in hard switching, leading to decreasing efficiency and potential circuit seldomly used to regulate the secondary-side charging current due to too much reactive power will be introduced if the phase difference bet mary-side and secondary-side voltages is not 90°. Phase-shift an and ignoring R1 and R2 when their voltage drops are significantly smaller th we have β U. +1 2 I. . . 2
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