Power transmission device and wireless power transmission system

A power transmission device for transmitting power via electric field coupling to a power reception device having a pair of power reception electrodes, the power transmission device comprising:

• first and second power transmission electrodes that respectively oppose the pair of power reception electrodes with a gap therebetween, when the power reception device is positioned adjacent to the power transmission device;
• a voltage detection circuit configured to monitor a voltage of one of the first and second power transmission electrode;
• and
• a control circuit configured to determine an absolute value of a change per a time interval in the monitored voltage and to stop power transmission to the power reception device when the absolute value exceeds a predetermined threshold,
• wherein the control circuit comprises a microcomputer including a computer program that, when executed by the microprocessor, causes the microprocessor to determine the absolute value, compare the absolute value with the predetermined threshold, and stop power transmission by the power transmission device to the power reception device when the absolute value exceeds the predetermined threshold.

A wireless power transmission system comprising:

• a power reception device including a pair of power reception electrodes, and a voltage supply circuit configured to supply a voltage induced in the pair of power reception electrodes to a load;
• and
• a power transmission device including:
• first and second power transmission electrodes that respectively oppose the pair of power reception electrodes with a gap therebetween, when the power reception device is positioned adjacent to the power transmission device;
• a voltage detection circuit configured to monitor a voltage of one of the first and second power transmission electrode;
• and
• a control circuit configured to determine an absolute value of a change per a time interval in the monitored voltage and to stop power transmission to the power reception device when the absolute value exceeds a predetermined threshold
• wherein the control circuit of the power transmission device comprises a microcomputer including a computer program that, when executed by the microprocessor, causes the microprocessor to determine the absolute value, compare the absolute value with the predetermined threshold, and stop power transmission by the power transmission device to the power reception device when the absolute value exceeds the predetermined threshold.

A method for transmitting power via electric field coupling from a power transmitting device having a pair of power transmitting electrodes to a power reception device having a pair of power reception electrodes, the method comprising:

• initiating wireless power transmission from the power transmitting device to the power reception device via electric field coupling between the pair of power transmission electrodes and the power reception electrodes when the power reception device is positioned adjacent to the power transmission device;
• detecting an initial voltage of the one of the first and second power transmission electrode after initiating the wireless power transmission;
• monitoring a voltage of one of the first and second power transmission electrode when the power reception device is positioned adjacent to the power transmission device;
• detecting a subsequent voltage of the one of the first and second power transmission electrode after a time interval;
• determining an absolute value of a change per the time interval in the monitored voltage by calculating a difference between the initial voltage and the subsequent voltage;
• comparing the absolute value to a predetermined threshold;
• and
• stopping power transmission to the power reception device when the absolute value exceeds the predetermined threshold.