Showing papers by "Akiyoshi Uchida published in 2017"
10 May 2017
TL;DR: In this paper, the authors investigated the character of the load dependence of efficiency, and made clear that robustness to load variation determines the DDC input voltage by simulation and experiment, but not for single receivers in different coupling conditions.
Abstract: Most batteries require constant voltage to charge; therefore, wireless charging receivers need a constant voltage circuit, commonly a DCDC converter (DDC). On the other hand, Resonant Magnetic Coupling enables multi-receiver charging. As a result, we need to design a wireless charging system for multi-receivers with a DDC. In cases of multi-receiver charging with different positions, the input voltage for a DDC in the stronger coupling receiver rises. Since there is a practical limit of DDC input voltage, we need to design the wireless charging system, not to exceed the limit. Through our work, we investigated the character of the load dependence of efficiency, and made clear that robustness to load variation determines the DDC input voltage by simulation and experiment. In conclusion, efficiency robustness to load variation is advantageous for single receivers, but not for multi-receivers in different coupling conditions.
8 citations
Patent•
21 Dec 2017TL;DR: In this paper, the transmitter groups the receivers into first groups based on degrees of coupling between the transmitter and the respective receivers in an initial state, and starts to transmit the power when the second total time is less than or equal to the first total time.
Abstract: A wireless power supply system includes: a power transmitter; and power receivers configured to receive power through magnetic field resonance or electric field resonance. The transmitter groups the receivers into first groups based on degrees of coupling between the transmitter and the respective receivers in an initial state. The transmitter calculates, for the respective first groups, charging times required to charge the receivers, and a first total charging time for the first groups. The transmitter sets degrees of coupling greater than or equal to the degrees of coupling in the initial state, and again groups the receivers into second groups based on the set degrees. The transmitter calculates, for the respective second groups, charging times required to charge the receivers and a second total for the second groups, and starts to transmit the power when the second total time is less than or equal to the first total time.
2 citations
Patent•
05 Jan 2017
TL;DR: In this article, a power transmission device of noncontact type, which simultaneously charges power receiving devices different in charge power, is presented, and the phase difference between the first and second phases, detected by the first phase-detecting section, is equal to a first target value.
Abstract: PROBLEM TO BE SOLVED: To provide a power transmission device of non-contact type, which simultaneously charges power receiving devices different in charge power.SOLUTION: A power transmission device comprises: a power transmission system coil that receives power from an AC power source; a power receiving system coil having a secondary-side resonance coil that receives power by means of electromagnetic induction from the power transmission system coil due to magnetic field resonance caused between itself and the power transmission system coil, and a secondary-side coil that receives power by means of electromagnetic induction from the secondary-side resonance coil; a first bridge circuit having a switching element connected to the secondary-side resonance coil; a first phase-detecting section that detects a first phase of voltage supplied to the power transmission system coil and a second phase of current flowing in the power receiving system coil; and a first resonance frequency control section that varies the resonance frequency of the power receiving system coil by varying the duty ratio or phase of a pulse voltage that drives the switch element of the first bridge circuit such that the phase difference between the first phase and second phase, detected by the first phase-detecting section, is equal to a first target value.SELECTED DRAWING: Figure 2
1 citations
01 May 2017
TL;DR: In this article, two switches are connected to the resonant capacitance of the receiving resonant coil in parallel and are turned on/off alternately at the transmission frequency to control the receiving power ratio among the receivers.
Abstract: The resonant magnetic coupling (RMC) method has gained tremendous attention for its prospective features such as a large charging range or multiple device charging (multi-charging) application. In multi-charging systems, however, the receiving power ratio among the receivers is determined by coupling coefficient (k) or quality (Q) factor of each resonant coil. Therefore, it is difficult to supply appropriate power from single transmitter to plural receivers at the same time in various situations. To solve this problem, we apply a new efficiency control technique using non-linear devices. Two switches are connected to the resonant capacitance of receiving resonant coil in parallel and are turned on/off alternately at the transmission frequency. With this technique, receiving power ratio among the receivers can be controlled over a wide range at high efficiency.