High frequency inductive power transfer operation using active transceivers

Abstract

Near-field Wireless Power Transfer is the transmission of energy through a dielectric via the means of inductive or capacitive coupling. Such systems become more versatile if they can operate with dynamically variable and large air-gaps. This thesis is primarily concerned with the attainment of the information to assess the state of operation of a transmitter or receiver, allowing each side to be operated as a re-configurable transceiver. One of the key elements in designing such systems is the ability to evaluate the state of the transceivers and the link. The magnitude and phase of the induced voltage in an IPT pad contain information about the state of all the coupled transceivers or foreign objects. This information can be useful to shut the system down if a foreign object is detected, or to actively control the power flow and tuning of an IPT system. Together with the choice of an appropriate frequency synchronisation technique, this can be also used to enable the transition from the classic active-passive IPT arrangements, which employ an inverter and a passive rectifier, to active-active arrangements, where both sides of the system are re-configurable transceivers. This leads to several advantages, including improved low coupling operation, active minimisation of reactive power flow across the link and bidirectional system operation. This work proposes a set of techniques to increase the capabilities of IPT systems in terms of safety, monitoring and controllability and provides the underpinning technology to enable active-active operation of Megahertz IPT systems. This is achieved through different techniques for induced voltage estimation and synchronisation. Synchronisation is achieved with a speed of 1.6 seconds and a maximum error of 2◦. Induced voltage is estimated within 120 ms with an average error of 0.62 V (1.6 %). The key achievements of this work are the development of an induced voltage estimation technique for live system monitoring, the design and analysis of three synchronisation techniques for bidirectional HF-IPT operation and the assessment of practical applications for these techniques.