Abstract:
This thesis presents the development of power management strategies for a multiple pickup IPT system such that the power supply capacity can be safely reduced without compromising system integrity. Currently multiple pickup IPT systems usually use power supplies with capacities at or above the sum of all pickups’ rated power such that the system is never overloaded. However this approach is expensive in itself and the work presented in this thesis helps reduce the overall system costs. In order to safely reduce the power supply capacity, an understanding of its impact on the pickups is required. This thesis presents a statistical analysis to describe the aggregate power profile in a multiple slow-switching pickup IPT system. Analytical expressions for two parameters have been derived to describe the characteristics of the overloading. Using this knowledge, the optimal power supply capacity can then be chosen – to maximize cost saving and minimize any impact on the pickups for the intended applications. Two novel power management controls have been proposed for the two popular load regulation methods used in materials handling applications, namely: fast-switching and slow-switching. The proposed controls can temporarily stop power transfer to some pickups during an overloading instance such that the power supply capacity can be safely reduced. The IPT frequency is used as the communication channel, removing the need for an extra communication system and therefore requiring minimal adjustments to normal system configurations. It can easily be implemented on existing systems. Experimental results show that both proposed controls are valid under various loading conditions. A new roadway IPT system using a “double-coupled system” (DCS) has been proposed to resolve many of the limitations faced by other currently proposed roadway IPT systems. The proposed system introduces an “intermediary coupler circuit” (ICC) with frequency changing capability between the primary track and each ground transmitter pad such that individual charging sections on the roadway can be controlled independently and only turned on when required to minimize unwanted magnetic leakage fields. The proposed system provides isolation between the power supply and all of the ground transmitter pads, and allows the power supply to run at a lower frequency and feed power to a large number of pads, while the power transfer takes place locally (directly under the vehicle) at a higher frequency. The system can also potentially reduce the impact of dynamic EV powering on the electrical grid at times of traffic congestion. A laboratory scale prototype system has been constructed and tested. The intermediary coupler achieved an efficiency of 92.5% at an output power of 5kW with full system operability. Based on the proposed DCS, potential power management strategies have also been investigated for this dynamic EV powering application. A suitable strategy is proposed which uses a large energy storage capacitor in the ICC to help provide peak power transfer to the EVs while at the same time only requiring a much lower average power transfer from the power supply, therefore allowing cost saving in the power supply and the primary track. By selecting appropriate ICC capacitor values and input power ratings, the proposed strategy requires no active control during normal operation and completely prevents overloading of the power supply, by design.