Power Transfer System

• US 20140300201A1
• Filed: 04/11/2014
• Published: 10/09/2014
• Est. Priority Date: 11/14/2011
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Ichikawa, Keiichi, Goma, Shinji, Suesada, Tsuyoshi, Bondar, Henri
• Granted Patent: US 9,876,362 B2
• Time in Patent Office: Days
• US Class Current: 307/104
• CPC Class Codes: H02J 50/05 using capacitive coupling
• CPC Class Codes: H02J 50/80 involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices

Abstract

A capacitance (Cp) is a capacitance formed between a transmitting-device-side passive electrode and a receiving-device-side passive electrode. A capacitance (Ca) is a capacitance formed between a transmitting-device-side active electrode and a receiving-device-side active electrode. A bridge circuit formed by Z1 to Z4 is connected to a secondary side of a step-up transformer, where Z1 represents an impedance of a first element, Z2 represents an impedance of a second element, Z3 represents an impedance of a series circuit formed by the capacitance (Ca) and a load, and Z4 represents an impedance of the capacitance (Cp). By determining the impedances Z1 to Z4 such that this bridge circuit is balanced, a potential at a receiving-device-side reference potential point is made equal to a ground potential. This reduces variation in receiving-device-side reference potential, reduces noise, and stabilizes the operation of a load circuit on the receiving device side.

Claims

1. A power transfer system comprising:

a power transmitting device having a transmitting-device-side first electrode, a transmitting-device-side second electrode, and a feeding circuit configured to feed an alternating voltage between the transmitting-device-side first electrode and the transmitting-device-side second electrode, wherein

the power transmitting device includes a series circuit between the transmitting-device-side first electrode and the transmitting-device-side second electrode, the series circuit including a first element connected to the transmitting-device-side first electrode and a second element, the first element and the second element being connected in series;

a transmitting-device-side reference potential point connected to a reference potential of the transmitting device, the transmitting-device-side reference potential point being a node between the first element and the second element of the series circuit; and

the series circuit is configured such that a balance condition Z1×

Z4≈

Z2×

Z3 is satisfied at a fundamental frequency of the alternating voltage, where Z1 represents an impedance of the first element, Z2 represents an impedance of the second element, Z3 represents an impedance of the series circuit including a capacitance between the transmitting-device-side first electrode and a receiving-device-side first electrode and a load circuit of a power receiving device, and Z4 represents an impedance including a capacitance between the transmitting-device-side second electrode and a receiving-device-side second electrode of the power receiving device.

2. The power transfer system according to claim 1, further comprising:

the power receiving device having the receiving-device-side first electrode, the receiving-device-side second electrode, and the load circuit, the load circuit configured to receive an alternating voltage generated between the receiving-device-side first electrode and the receiving-device-side second electrode,

wherein a receiving-device-side reference potential point is connected to a reference potential of the receiving device, the receiving-device-side reference potential point being a node between the load circuit and the receiving-device-side second electrode or a midpoint of the load circuit.

3. The power transfer system according to claim 2, wherein the second element of the series circuit has a capacitance connected or formed between the transmitting-device-side second electrode and the transmitting-device-side reference potential point;

and

the balance condition can be satisfied when a voltage ratio V1/V0 is less than 1, where V0 is a first voltage generated between the reference potential of the transmitting device and the reference potential of the receiving device when the capacitance is shorted, and V1 is a second voltage generated between the reference potential of the transmitting device and the reference potential of the receiving device when the capacitance is opened.

4. The power transfer system according to claim 2, wherein the reference potential on the transmitting device side is a ground potential.

5. The power transfer system according to claim 1, wherein the reference potential on the transmitting device side is a ground potential.

6. The power transfer system according to claim 2, wherein a capacitance is connected or formed between the transmitting-device-side reference potential point and the receiving-device-side reference potential point.

7. The power transfer system according to claim 1, wherein the feeding circuit comprises:

an alternating voltage generating circuit, and

a transformer having a primary winding connected to the alternating voltage generating circuit and a secondary winding connected between the transmitting-device-side first electrode and the transmitting-device-side second electrode;

the secondary winding has a lead terminal configured to form a first secondary winding between the transmitting-device-side first electrode and the lead terminal, and form a second secondary winding between the transmitting-device-side second electrode and the lead terminal;

the impedance of the first element is formed by an impedance of the first secondary winding and an impedance of a first capacitor connected in parallel with the first secondary winding; and

the impedance of the second element is formed by an impedance of the second secondary winding and an impedance of a second capacitor connected in parallel with the second secondary winding.

8. The power transfer system according to claim 7, wherein the lead terminal is a center tap of the secondary winding;

and

the secondary winding has

a first lead terminal of the first secondary winding, and

a second lead terminal of the second secondary winding,

the power transfer system further comprising a connection switching circuit configured to switch connection of the transmitting-device-side reference potential to the center tap and one of the first lead terminal and the second lead terminal.

9. The power transfer system according to claim 1, wherein the feeding circuit includes

an alternating voltage generating circuit, and

a transformer having a primary winding connected to the alternating voltage generating circuit and a secondary winding connected between the transmitting-device-side first electrode and the transmitting-device-side second electrode;

the secondary winding has a lead terminal configured to form a first secondary winding between the transmitting-device-side first electrode and the lead terminal, and form a second secondary winding between the transmitting-device-side second electrode and the lead terminal;

the impedance of the first element is formed by an impedance of the first secondary winding; and

the impedance of the second element is formed by an impedance of the second secondary winding,

the power transfer system further comprising an inductor inductively coupled to part of the first secondary winding, and a capacitor connected to the inductor.

10. The power transfer system according to claim 1, wherein the feeding circuit includes

an alternating voltage generating circuit,

a transformer having a primary winding connected to the alternating voltage generating circuit and a secondary winding connected between the transmitting-device-side first electrode and the transmitting-device-side second electrode, and

a series connection circuit formed by a first inductor and a second inductor and connected in parallel with the secondary winding of the transformer;

the impedance of the first element is formed by an impedance of the first inductor; and

the impedance of the second element is formed by an impedance of the second inductor,

the power transfer system further comprising a third inductor inductively coupled to part of the first inductor, and a capacitor connected to the third inductor.

11. The power transfer system according to claim 1, wherein the impedance of the first element is formed by a fixed impedance and a variable impedance connected in parallel with the fixed impedance;

the impedance of the second element is formed by a fixed impedance and a variable impedance connected in parallel with the fixed impedance; and

the variable impedances are set such that the balance condition is satisfied at the fundamental frequency.

12. The power transfer system according to claim 1, wherein the impedances Z1, Z2, Z3, and Z4 are set such that the balance condition is satisfied at a third harmonic frequency of the alternating voltage.

13. The power transfer system according to claim 1, further comprising, at the transmitting-device-side reference potential point, a circuit for injecting a cancellation signal that reduces components caused by deviation from the balance condition.

14. The power transfer system according to claim 1, wherein the transmitting-device-side first electrode is surrounded by and insulated from the transmitting-device-side second electrode. (from original paragraph [0027])

15. The power transfer system according to claim 14, further comprising a transmitting-device-side third electrode that surrounds and is insulated from the transmitting-device-side second electrode. (from original paragraph [0036])

16. The power transfer system according to claim 15, wherein the transmitting-device-side third electrode is connected to the reference potential of the power transmitting device.