TO IMPROVE EFFICIENCY AND EXTRACTABLE POWER A NEW WIRELESS CHARGING SYSTEM APPLYING PHASE- SHIFT AND AMPLITUDE CONTROL

The efficiency of wireless power transfer is sensitive to the horizontal and vertical distances between the transmitter and receiver coils due to the magnetic coupling change . To transfer power from a transmitter to a mobile receiver over a relatively large air gap wireless power transfer (WPT) is an emerging technology with an increasing number of potential applications.Due to the relatively low efficiency of current Wireless power transfer (WPT) systems However, its widespread application is hampered. In non resonant operation this study presents a concept to maximize the efficiency as well as to increase the amount of extractable power of a WPT system operating. The proposed method is based on actively modifying the equivalent secondary-side load impedance by controlling the phase-shift of the active rectifier and its output voltage level. At the output of the system the presented hardware prototype represents a complete wireless charging system, including a dc–dc converter which is used to charge a battery. Simulation results are shown for the proposed concept in comparison to a conventional synchronous rectification approach. The presented optimization method clearly out performs state-of-the-art solutions in terms of efficiency and extractable power INTRODUCTION Wireless power transfer (WPT) has been an emerging research area for several years and could overcome the inconvenience of EV charging [1]. WPT allows power to transfer from a transmitter coil to a receiver coil over an air gap. Applications for WPT include mobile devices, household facilities, medical implants, and electric vehicles [1–7]. WPT is based on the principle of magnetic resonance couplings Wireless power transfer (WPT) is used in various application fields ranging from a few mill watts in biomedical applications up to several kilowatts of output power in automotive applications. Currently, WPT systems intended to wirelessly charge consumer electronic devices, such as mobile phones or tablet computers, are studied extensively. Various aspects of these systems are defined by several standards which are either based on non resonant or inductive power transfer (IPT), like the Qi standard or on resonant power transfer (RPT), like the Rezence standard. In order to ensure interoperability of different transmitter and receiver devices, these standards define parameters such as the voltage range, the basic circuit structure, and the operating frequency of the system. The main drawbacks of currently available WPT systems for consumer applications are, amongst others, the relatively low overall efficiency and the limited power transfer capability. This results in long charging times which hampers the widespread application of the WPT technology. To overcome these problems, various improvements have been suggested in the literature. Design and optimization methodologies for increasing the efficiency or the maximum transferable power of a WPT link have been proposed WPT systems are frequency-sensitive due to their use of magnetic resonance. Any change in the resonant components, such as inductance, capacitance or load, can influence the operating frequency of the system. Since WPT systems operate in a non-contact manner, the physical spacing between the two coils can vary, resulting in a change in magnetic coupling and eventually shifting the best switching frequency for WPT. In a wireless charging system the efficiency and the amount of power transferred to the output are influenced by the source (transmitter) and load (receiver) impedances. However, this approach does not yield optimal efficiency for the whole operating range, since only the resistive part of the load impedance is altered and thereactive part is not considered at all. Additional improvements to the efficiency of a WPT system are obtained by actively modifying the reactive part of the load impedance. In [23], a phase-shift control approach, instead of a conventional controlling method, is applied to the active rectifier on the secondary side of an RPT system. This technique is used to achieve efficiency improvements by modifying the secondary side resonance frequency, but on the other hand it also impacts the equivalent load impedance. Since the phase-shift is the only control parameter, the resistive as well as the reactive part of the equivalent load impedance are concurrently altered. Hence, these two parameters cannot be controlled separately and the point of maximum efficiency is not reached in general. Furthermore, it might be highlighted that [23] solely investigates an RPT system with a resistive load at the output of the rectifier. INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume VII /Issue 1 / SEP 2016 IJPRES The WPT frequency controls fall into two categories: fixed frequency control and variable frequency control (also called “adaptive frequency control”). A fixed frequency control is normally operated under limited magnetic coupling variances, and a typical input voltage control is used to keep the charging voltage constant [9]. Resonant frequency control, which is a kind of variable frequency control, is designed to improve the WPT’s adaptability for coupling change In contrast, this paper investigates a complete wireless charging system, including a dc–dc converter to regulate the rectified voltage and a battery as load of the system. The acquired simulations and experimental results show that the proposed concept is capable of achieving significant In this study, an advanced optimization strategy for an entire wireless charging system, including an active rectifier and a dc–dc converter charging a battery, is investigated in detail. THEORETICAL ANALYSIS This study focuses on a circuit-based model, but it is worth noting that there exist different other possibilities to model WPT systems. A block diagram of the examined system is shown in Fig. 1. In this section, the methodology for modeling the behavior of the WPT system is introduced and the theoretical conditions for calculating the maximum efficiency and the maximum power transfer are provided. Fig.7. 1 Schematic block diagram of the overall WPT system including an inverter stage driving the primary side resonance circuit, an active rectifier and a dc–dc converter at the secondary side.