This paper focuses on wireless energy transfer (WET) to a pair of low complex energy receivers (ER), by only utilizing received signal strength indicator (RSSI) values that are fed back from the ERs to the energy transmitter (ET). Selecting the beamformer that maximizes the total average energy transfer between the ET and the ERs, while satisfying a minimum harvested energy criterion at each ER, is studied. This is a nonconvex constrained optimization problem which is difficult to solve analytically. Also, any analytical solution to the problem should only consists of parameters that the ET knows, or the ET can estimate, as utilizing only RSSI feedback values for channel estimation prohibits estimating some channel parameters. Thus, the paper focuses on obtaining a suboptimal solution analytically. It is proven that if the channels between the ET and the ERs satisfy a certain sufficient condition, this solution is in fact optimal. Simulations show that the optimality gap is negligibly small as well. Insights into a system with more than two ERs are also presented. To this end, it is highlighted that if the number of ERs is large enough, it is possible to always find a pair of ERs satisfying the sufficient condition, and hence, a pairwise scheduling policy that does not violate optimality can be used for the WET.
In this paper, a new three-winding planar transformer design with the integrated leakage inductor is proposed for a triple-active-bridge converter. It enables two output voltage levels: a high voltage (HV) output port and a low voltage (LV) output port. The primary and secondary windings are split unevenly in both side legs while the tertiary winding is connected in parallel. The unique winding configuration enables: (i) enhanced efficiency with low volume; and (ii) suppressed parasitic capacitances. Detailed transformer reluctance and loss models are developed in the design process. The core geometry is optimized using a reluctance-model-based mathematical computation. Moreover, comprehensive high-fidelity simulations are conducted to analyse the trade-offs among parasitic capacitances, losses, and inductances. The customized core and the non-overlapping winding boards are assembled, characterized, and tested under various power flow conditions.
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