Contactless Slipring Systems for Wireless Power Transfer in Rotary Applications

Abstract

Inductive Power Transfer (IPT) technology has motivated considerable research and development in the past two decades. This new technology can be used in various wireless power transfer applications with different specifications, necessities, and restrictions. One example application is to deliver electrical power from a static frame to a rotating shaft. This is generally achieved by using mechanical slipring assemblies. However, because of the physical contacts between the stationary brushes and rotating metal rings, frequent maintenance is required due to mechanical and electrical wear and tears. This would significantly increase the system operational cost in applications such as wind turbine pitch control. An alternative solution is to use magnetically coupled coils to achieve contactless power transfer to rotary loads based on inductive power transfer technology. In this thesis three types of contactless slipring systems are proposed and developed based on pulsating, travelling, and rotating magnetic field principles. Full theoretical analysis, computer simulations, and practical experiments have been conducted on both the magnetic field coupling structures and power converter driving circuits to evaluate the proposed systems. Existing single-phase contactless sliprings based pulsating magnetic field have been improved with new pot-core and through-hole magnetic coupling structures, and it is shown that they can increase the magnetic coupling coefficients by up to 45%. A poly-phase system based on axial travelling magnetic field principle is proposed, and shown to be able to transfer about 3.7 times more power than a single-phase system. Another poly-phase system is proposed based on rotating magnetic field principle, and shown to be able to increase the power density by 55% compared to the existing counterpart single-phase system. An improved autonomous current-fed push-pull resonant converter is developed in this thesis to drive the single-phase contactless sliprings. It is shown that the proposed converter can increase the operating frequency to MHz level with full resonance and Zero Voltage Swathing (ZVS). Two new poly-phase current-fed push-pull resonant converters with ZVS operation are proposed and developed to drive the poly-phase contactless sliprings. The former uses an autonomous converter as the driving phase and allows the other phases to follow with a pre-determined phase delay; and the latter is based on full-autonomous operation of all the phases without any additional phase control. Experimental results have demonstrated that these converters can generate good quality currents to excite the magnetic coils of the sliprings to achieve efficient contactless power delivery, which are practically useful for rotary applications such as wind turbine pitch control.