Vehicle and wireless power transmission system

A method of controlling a-vehicles in a wireless power transmission system including a power transmitter having two transmission electrodes and at least a first vehicle and a second vehicle driven by electric power which is wirelessly transmitted from the power transmitter, the first vehicle and the second vehicle each comprising two reception electrodes for receiving AC power from the two transmission electrodes through capacitive coupling respectively with the two transmission electrodes,

• the method comprising the steps of:
• the first vehicle determining, while the first vehicle is moving with the two reception electrodes being opposed to the two transmission electrodes and the second vehicle is receiving power from the power transmitter, that the second vehicle is receiving power from the power transmitter by detecting that a value of at least one of power, voltage and current in a power receiving circuit connected to the two reception electrodes, or a change rate over time thereof, exceeds a threshold value;
• and
• as a result of the determination that the second vehicle is receiving power from the power transmitter, the first vehicle performing a control process to increase an impedance of the vehicle as viewed from the power transmitter to suppress decrease in efficiency of power transmission to the second vehicle;
• and
• further comprising the steps of:
• the first vehicle determining, while the first vehicle is moving with the two reception electrodes being opposed to the two transmission electrodes and the second vehicle not receiving power from the power transmitter, that the second vehicle is not receiving power from the power transmitter by detecting that the value of at least one of power, voltage and current in a power receiving circuit connected to the two reception electrodes, or a change rate over time thereof, does not exceed a threshold value, and as a result of the determination that the second vehicle is not receiving power from the power transmitter, the first vehicle determining whether the first vehicle needs to receive AC power from the power transmitter and requesting the transmitter to transmit AC power if the first vehicle needs to receive the AC power from the power transmitter;
• and
• if the first vehicle needs to receive the AC power, receiving the AC power from the power transmitter by the two reception electrodes, and converting, in the power receiving circuit, the AC power received by the two reception electrodes into DC power or another form of AC power to supply the DC power or other form of AC power to an electric motor which drives the first vehicle or to a secondary battery which stores electric power for driving the first vehicle.