Wireless power transfer systems
Ong, Andrew Chuan En
Date of Issue2018-01-31
Interdisciplinary Graduate School (IGS)
Wireless power transfer (WPT) is a potential technology that enables transmission of electrical power without the necessity of electrical contact. WPT can be employed in a wide variety of applications and this can be achieved due to WPT’s inherent advantages over its wired counterpart. These advantages enable WPT to eliminate numerous drawbacks faced by its wired counterpart. However, even with much research interest in this technology, WPT still need to overcome numerous technical challenges before it can truly be ubiquitous in the modern connected world. This thesis has proposed several approaches to improve WPT’s performance in terms of efficiency, transferred power, etcetera. In addition, a novel control scheme for dynamic WPT (D-WPT) systems without needing external sensors, and this helps solve some complexity and implementation issues of a D-WPT system. WPT systems use inductive coils and its electromagnetic coupling to transfer power wirelessly without electrical contact. These loosely coupled inductive coils are powered by high frequency power sources and cause large leakage inductances and input impedances. By employing compensating capacitors and electromagnetic resonance operation, the input impedance and VA (volt-ampere) rating of the WPT system can be significantly reduced, leading to an increase in the performance in terms of efficiency and power transfer, as well as transfer gap distance. However, there are many different types of compensation circuits available for WPT systems and these compensation circuits perform differently under varied conditions. The thesis dwelled into the circuit analyses on the various compensation circuits and derives the efficiency optimal operating frequencies these WPT systems. Using the optimized operating frequency, the efficiency analysis of these compensation circuits are detailed. Resonant frequency responses of the compensation circuits are used to further differentiate. With these analyses, the efficiency orientated design flow chart for selecting the optimized compensation circuit is derived with consideration for efficiency, load resistances, transferred power, transconductance and voltage gain. Experimental results also verified the usefulness of the flow chart and its respective analyses, which showed efficiency discrepancy of 28% (highest at 500 Ω) equivalent output resistance when comparing between compensation circuits. The LCC compensation circuit is also analyzed and its frequency bifurcation effect is investigated to be significantly mitigated. The LCC compensation circuit also shows significantly higher transferred power and lower harmonic distortion. The concept of Dynamic WPT (D-WPT) is to allow the receiver (Rx) to move freely while receiving power from the D-WPT system wirelessly. The thesis proposes a novel control scheme for the purpose of individual magnetic coupler control using the sensed transient response of the magnetic coupler’s input current. This would improve the D-WPT system’s efficiency, while circumventing the necessity for external positional sensors or auxiliary circuitry. The proposed control algorithm yielded a low standby power to operating power percentage of 7.2% as compared to 44.2% found in existing literatures. Thus, the proposed control algorithm for D-WPT system could be a promising approach to reduce D-WPT system complexity, improve power consumption and EMI/EMC performances during standby mode, as well as power transfer efficiency levels.