On the impact of relay circuit losses in four‐coil wireless power transfer systems

Abstract

In wireless power transfer (WPT) systems with more than two coils, the intermediary or relay circuits are used to extend the link distance. Thus, to achieve this extension efficiently in terms of power transfer, these relay circuits must have low losses. However, there are several instances in which there are restrictions in reducing the ohmic losses in all the relay circuits of the system. This is the case of biomedical applications where commonly there are size and access restrictions since one of the circuits can be implanted and also in applications using high-temperature superconductor (HTS) coils due to the difficulty in implementing the necessary cooling system for all the coils of the system. Therefore, in these situations, the designer need to choose which relay circuit will be optimized. In this work, it is presented an analysis on the impact that losses in individual relay circuits have on efficiency, and power transfer, of typical four-coil wireless power transfer systems consisting of circuit 1 (transmitter), relay circuits 2 and 3, and circuit 4 (load). It is shown that the losses on relay circuit 2 have greater impact on efficiency, while the losses of relay circuit 3 have a greater impact on power transfer for a given condition. Practical experiments confirm the developed analysis.

Multiple‐load wireless power transmission system through time‐division multiplexed resonators

“…Many efforts have been made to develop and demonstrate multiple‐receiver WPT systems 14–22 . They are classified based on the number of the transmitters and receivers in the categories: single input–multiple output (SIMO) 14–20 and multiple input–multiple output (MIMO) 21,22 . In this classification, input and output refer to the power transmitter and receiver, respectively.…”

“… 14,15 The second type is to place a transmitter and several receiver coils in a chain one after another (Figure 1B). 16–21 Each of them has its own minuses and pluses.…”

“…These inter‐couplings in this arrangement are considerable and affect the PTE and PDL adversely, 23 especially when the design must be compact and the resonators are placed close together. Furthermore, as the distance between a receiver and the transmitter increases, it receives less power, and the PDL falls sharply for the receivers placed far from the transmitter 17 . So, the number of receivers is restricted; for instance, in the aforementioned paper, there are only two receivers.…”

Operating characteristics of four‐coil magnetic resonant coupling wireless power transfer under different resonant states

“…It has been revealed in other studies 7–9 that the transfer performance of the two‐coil system deteriorates with the increase of the transfer distance due to the weakened magnetic coupling. To extend the transfer distance, MRC‐WPT systems with repeaters positioned between transmitting and receiving coils have been investigated 10–15 . Nevertheless, the transmission efficiency would drop dramatically when the repeater is deviated from a specific position.…”

A simple method to control automatically the performance of three‐coil wireless power transfer systems without direct output measurement

“…[1][2][3][4][5] Starting with the pioneer work of Tesla 6 using WPT systems with only two coils, several other arrangements using three or more coils have been recently researched. [3][4][5][7][8][9][10][11] For instance, typical three-coil WPT systems are composed of three circuits (usually tuned at the same resonance frequency to reduce the losses due to reactive effects), one containing the source, the other containing the load, and one intermediary (relay circuit), where all are coupled to the adjacent ones by their respective mutual inductances.Independently of the number of coils used, a typical WPT system is usually designed aiming optimal efficiency (η), which can be defined as the power delivered to the load circuit divided by the total power supplied by the source. Alternatively, the WPT systems can be designed optimizing their power transfer capability (P Ã ), which can be defined as the power delivered to the load circuit divided by the maximum ideal amount of power which can be delivered to the same load circuit.However, in some applications, the mutual inductance between the coils may vary because the relative position of the coils is not fixed.…”