Patent ID: 9484881
Filing Date: 2016-11-01
CPC Classification: B60L,H02J,H03H,Y02T

Claim Text:
1. An impedance matching device included in a wireless electric power transmission system transmitting electric power by coupling a power transmission antenna with a power reception antenna through an electromagnetic field, the impedance matching device being provided between a power transmission circuit and the power transmission antenna, the impedance matching device comprising: an incident-wave/reflective-wave extraction unit configured to extract incident wave voltage corresponding to an output signal from the power transmission circuit and reflective wave voltage corresponding to a signal reflected from the power transmission antenna; a phase determination unit configured to compare a phase of the incident wave voltage to a phase of the reflective wave voltage to determine which one of the phases is behind or ahead of the other phase; a first matching circuit configured to include a variable inductor element and a variable capacitor element, the variable inductor element being connected in series between the power transmission circuit and the power transmission antenna, the variable capacitor element being connected in parallel closer to the power transmission antenna than the variable inductor element; a second matching circuit configured to include a variable inductor element and a variable capacitor element, the variable inductor element being connected in series between the power transmission circuit and the power transmission antenna, the variable capacitor element being connected in parallel closer to the power transmission circuit than the variable inductor element; a through circuit connected in series between the power transmission circuit and the power transmission antenna; a load value estimation unit configured to estimate a value of a load of a circuit in which the transmitted electric power is consumed, the circuit being connected to the power reception antenna; a storage unit configured to store tables each associated with the value of the load, each of the tables previously storing control values in ascending or descending order of a coupling coefficient corresponding thereto between the power transmission antenna and the power reception antenna, each of the control values corresponding to an inductance value and a capacitance value each needed for matching to a predetermined impedance value by use of the first matching circuit or the second matching circuit; a selection unit configured to select one of the tables corresponding to the value of the load estimated by the load value estimation unit; an adjustment direction determination unit configured to determine, on a basis of the determination by the phase determination unit, a direction of a position for reading out one of the control values from the selected table, the direction indicating whether to select a control value corresponding to a larger coupling coefficient than the coupling coefficient corresponding to the present control value or to select a control value corresponding to a smaller coupling coefficient than the coupling coefficient corresponding to the present control value; a readout position determination unit configured to determine the position for reading out the control value from the selected table based on the direction and a predetermined step width for shifting the position for reading out the control value; a circuit selection unit configured to electrically connect one of the first matching circuit, the second matching circuit and the through circuit based on the determined position; and a control value output unit configured to output the control value at the determined position to the circuit selected by the circuit selection unit.