SPLIT-CORE COUPLER FOR INDUCTIVE POWER TRANSFER

Abstract

 The subject of the invention is a split-core coupler for inductive power transfer, and more specially the invention relates to the split-core coupler used in wireless charging system in which the supply and receiving side are separated by some insulating gap having a specially designated thickness ensuring relatively large value of the coupling coefficient and, at the same time, enabling for movement of a transmitter relatively to a receiver or vice versa in an improved way. The invention is characterized in that the two parts (A) and part (B) of the split-core transformer are movable connected together during the matching and also during a charging process. The second core column (4) which is placed between the yokes (1) has at least three degrees of freedom in horizontal, vertical and torsional directions or combinations of all these directions during the charging process when the magnetic circuit of the split-core coupler is closed.

Description

[0001] The subject of the invention is a split-core coupler for inductive power transfer, and more specifically the invention relates to the split-core coupler used in wireless charging system in which the suppling and receiving sides are separated by some insulating gap having a specially designated thickness ensuring relatively large value of the coupling coefficient and, at the same time, enabling for movement of a transmitter relatively to a receiver or vice versa in an improved way.

[0002] A compact, strongly coupled Inductive Power Transfer (IPT) system with a split-core coupler having a form of a split-core transformer in which large variations in the alignment between the two parts of the split-core transformer do not result in substantial changes in the magnetic coupling coefficient has potential applications in charging of various types of electric vehicles whose position during the charging process is not perfectly fixed. Potential applications of such a system include charging of electric ships (e.g. ferries), when the ship is attached to the shore (moored) and some movements are still possible due to waves and load changes. Another possible application is fast (flash) charging of electric busses at the bus stops. When combined with automated or assisted parking, the hands-free connection of electrically insulated IPT system is foreseen as an alternative to large and heavy galvanic connectors requiring manual operation.

[0003] In the Inductive Power Transfer IPT systems the acceptable value of the coupling coefficient "k" between the transmitter TR coil and the receiver RE coil is a compromise between the performance, especially efficiency, and the required tolerance of positioning between the transmitter TR and the receiver RE.

[0004] Strongly coupled systems comprise a magnetic core with a relatively small gap. They are characterized by several advantages over loosely coupled systems, such as compactness, high efficiency, and low level of electromagnetic radiation. On the other hand, known IPT systems comprising magnetic cores are not tolerant to variations in the relative position between the TR and RE part as even small alignment variations result in large variations in the coupling coefficient "k", which are difficult to compensate.

[0005] In case of coupling systems requiring a substantial misalignment tolerance of the order of 10 cm, known couplers based on concept of the split-core transformer are thus not applicable. In such cases, known practical applications of the IPT system comprises loosely coupled air coils. In order to reduce electromagnetic radiation and improve magnetic coupling, often some types of shielding or field-focusing elements are applied, however in those systems mechanical positioning tolerance always results in relatively large variations in the coupling coefficient.

[0006] There is known an inductive coupler from European patent EP 0820073 having an antenna and primary winding formed as part of a single structure that can be readily and consistently produced using printed wiring board manufacturing techniques. The coupler has the primary winding and antenna are formed as part of a printed wiring board. A coupler housing having two mating coupler halves secures a center magnetic core and the printed wiring board there between. The coupler housing also secures a cable that is coupled between selected printed circuit layers of the primary winding and a power source for coupling energy to the charging coupler.The charging system described employs a charge port into which an inductive coupler (part) is inserted to charge the vehicle. When the coupler (part) is inserted into the port, the magnetic circuit of the coupler becomes closed. The system works as a plug-socket pair in which the plug has to stay in a fixed position during the charging process. The system described is not intended to tolerate movements of the plug (coupler) with respect to the charging port during the charging process.

[0007] From PCT application WO2015/067816 there is known a movable magnetic core wireless chargers applicable for electrical vehicles. The inductive charging assembly includes a transmitter and a receiver. The transmitter includes a primary coil that is provided for generating an alternating magnetic field. The receiver comprises a secondary coil with a secondary magnetic core for charging a battery of the vehicle when the alternating magnetic field induces an alternating electrical current in the secondary coil. The inductive charging assembly further comprises a pair of movable connection magnetic cores being movable between a charging position and a standby position.
The assembly described comprises three separate functional elements. The transmitter with the primary coil and primary core part, the receiver with the secondary coil and the secondary core part, and the pair of moveable core elements closing the magnetic circuit of the coupler assembly prior to starting the charging cycle. In the standby position, the movable core elements are retracted into the ground of the charging station. In the charging position the moveable core elements becomes attached to the receiver part and stay in generally fixed position during the charging cycle. The movement of the moveable core elements is perpendicular to the plane of the gap in the magnetic circuit. A drawback of the assembly described is that it requires an active mechanical device allowing the moveable core elements to close the magnetic circuit of the coupler. During the charging cycle relative movements of the transmitting at the receiving parts are practically not allowed, which limits the applicability of the solution described to charging of vehicles staying at fixed position during the charging cycle. This is in particular an important limitation in situation of charging a vehicle whose position is not totally fixed, as is the case of the electric ships, or flash charging of electric busses, for example.

[0008] From EP application EP 0878811 there is known a C-shaped fixed core which is provided at a power receiving portion, and a secondary coil is wound on a vertical portion of the fixed core. A moving core is vertically movable in sliding contact with distal end surfaces of horizontal portions of the fixed core. A primary coil, having an air core portion, is provided at a charging coupler. When the charging coupler is attached to the power receiving portion, the moving core is moved downward to extend through the air core portion of the primary coil, and opposite end portions of the moving core are contacted respectively with the horizontal portions of the fixed core. As a result, a magnetic circuit is formed between the primary and secondary coils. The charging coupler is lightweight since it does not have a core. Similarly to the solution described in WO2015/067816 the assembly described comprises three separated functional elements. The transmitter with the primary coil and primary core part housed in the "plug" part, the receiver with the secondary coil and the secondary core part having a c-shaped core member, housed in the charging port being a "socket" and the moveable core element being a movable magnetic bar, closing the magnetic circuit of the coupler assembly prior to starting the charging cycle. The moveable element is located in the "socket" part. The "plug" part stays fixed in the "socket" part during the charging process and no relative movements of the "plug" part with respect to the "socket" part are allowed during the charging process. Therefore The "plug" type is connected with the stationary charging station with a flexible cable and the "plug" part has to be manually inserted to the "socket" part prior to charging.

[0009] There is a need to build a strongly coupled inductive power transfer system, comprising a coupler in the form of a split-core transformer, in which large variations in the mechanical alignment between the two coupler parts has negligible effect on the variation in the magnetic coupling coefficient. Such a solution is foreseen as an enabler for building a highly efficient, compact inductive power transfer system with a large tolerance to misalignment also during the process of power transferring. It can thus combine the advantages of a split core- based strongly coupled system with the misalignment tolerance of a loosely coupled system.

[0010] The essence of the present invention having a form of a split-core transformer with a primary winding and a secondary winding wound on transformer first core column and transformer second core column respectively, wherein the first core column is a part of the transmitter TR having two yokes connected with the column and the second core column is a movable part B of the receiver RE and the movable part B is positioned between the yokes during the engaging process and the two parts A and part B of the split-core transformer are movably connected together during the engaging and also during a charging process. The transformer second core column, which is placed between the yokes, has at least three degrees of freedom in horizontal, vertical and torsional directions or any combination of these directions during the charging process when the magnetic circuit of the split-core coupler is engaged.
Preferably the second column of the split-core coupler has a length "Lc", which is smaller than the distance "Ly" between the facing surfaces of the yokes. In the engaged position of the split-core coupler the second column is positioned between the yokes forming a magnetic circuit of the split-core coupler having gaps at both ends of the second column having the thickness "d_a" and "d_b" respectively.
Preferably the total length of the gap in magnetic circuit of the split-core coupler in the engaged position is a sum of the widths of the two gaps "d_a" and "d_b".
Preferably the sum of the widths of the two gaps "d_a" and "d_b" is constant in the engaged position of the magnetic circuit of the split-core coupler.
Preferably a surface area of faces of each end of the second core column is smaller than the surface area of the adjacent facing surface of the yoke.
Preferably the part A, comprising the yokes and the first core column with a primary winding, is embedded in a protection housing which has a fork-like shape with a horn-shaped entrance for guiding the part B of the split-core coupler into the engaged position.
Preferably the protection housing of the part A is made of an insulating material for protecting the embedded split-core coupler parts against mechanical wear as well against harsh environmental conditions.
Preferably the part B comprising the second core column with the secondary winding is embedded in a protective housing having a horn-like shape which is fitted with the shape of the - part A of the split-core coupler and having dimensions allowing for existing a magnetic gap in the magnetic circuit when the part B of the split-core coupler is in the engaged position.
Preferably the protection housing of the part B is made of an insulating material for protecting the embedded split-core coupler parts against mechanical wear as well against harsh environmental conditions.
Preferably the split-core coupler is a coupler for flash charging system located on the ground.
Preferably the split-core coupler is a coupler for charging system located under the water.

[0011] The advantage of the present invention is that it combines the advantage of the position-tolerant coupler having loosely coupled coils with the advantage of the split core-based coupler having strongly coupled coils. The present invention enables one to build a strongly coupled inductive power transfer system, in which large variations in the mechanical alignment between the two coupler parts prior and during the inductive power transfer process are allowed and do not affect the power transfer efficiency. When the split-core coupler for inductive power transfer described in the present invention is used for the wireless charging of a vehicle, the movements of the vehicle with respect to the charging station are allowed during the charging process. This allows one to build a mechanically simple coupler comprising only two parts which are moveably connected during the charging process, without a need for additional moveable elements closing the magnetic circuit of the coupler prior to the charging process. Thanks to the protective housings the split-core coupler may operate under extremely harsh environmental conditions, including under water operation.
The present invention is presented in the exemplary embodiment on the drawing where:

Fig 1 - shows the coupler in the engaged position in a perspective view,

Fig.2 - shows the coupler without housing in the two sample engaged positions, in a cross-section view

Fig.3 - shows the two parts of the coupler together with the housings in the open position of the coupler, in a semi cross-section of the perspective view

Fig.4 - shows various relative movements of the coupled parts in the engaged position in the perspective views a), vertical relative movements b) horizontal relative movements, and c) torsional relative movements

The split-core coupler comprises two separable parts; a movable part B and a stationary part A. In the presented embodiment the part A is a transmitter TR fixed to the charging station, not presented in the drawing. The part B is a receiver RE fixed to the charged vehicle, also not presented in the drawing. The functions of the parts A and B indicated as the transmitter and the receiver could be swapped without any changes to the essence of the present invention. Part A has two yokes 1 connected together by a column 2. On the column 2 a transformer primary winding 3 is wound. The part B has a column 4 on which a secondary transformer winding 5 is wound. The column 4 with the winding is movably placed between the facing surfaces 1a and 1b of the yokes 1 so that the face surfaces 4a, 4b of the column 4 are placed entirely between facing surfaces 1a and 1b of the yokes 1 during the charging process. The part A of the split-core coupler is placed in a protective housing 6. The yokes 1 and the core column 2 with the primary winding can be embedded in the protection housing 6. The core column 4 with the secondary winding 5 can be embedded in the protective housing 7. The housing 6 has a fork-like shape with a horn-shaped entrance 8, guiding the part B into the engaged position of the split-core coupler. The core column 4 with the secondary winding 5 is embedded in the protective housing 7 having a shape which is fitted with the shape of the protective housing 6 of the stationary part A of the split-core coupler and having dimensions allowing for existence of a gap in the magnetic circuit when the part B of the split-core coupler is in the engaged position.

[0012] The both housings 6 and 7 are made of an insulating material protecting the embedded split-core coupler parts A and B against mechanical wear as well as against harsh environmental conditions. In fig.2 the cross-sectional view of a engaged split-core coupler is presented, without any housing 6 and 7 for better explanation of the invention. In fig.2a) the core column 4 is in an extreme position closing the magnetic circuit of the coupler. In fig.2b) the core column 4 is in an intermediate position closing the magnetic circuit of the coupler.

[0013] The column 4 has length "L_c" which is smaller than the distance "L_y" between the facing surfaces 1a and 1b of the yokes 1. In the engaged position of the split-core coupler the column 4 is positioned between the yokes 1 forming the magnetic circuit having two gaps in-between the column 4 and yokes 1. The two gaps have the widths "d_a" and "d_b" respectively. The total length of the gap in magnetic circuit of the split-core coupler in the engaged position is a sum of the widths of the two gaps "d_a" and "d_b". The sum the widths of the two gaps "d_a" and "d_b" is not dependent on the relative position of the part A and part B of the coupler as long as the column 4 is positioned between the yokes 1. The surface area of faces 4a and 4b of each ends of the column 4 is smaller than the surface area of the adjacent surfaces 1a and 1b of the yokes 1. Thanks to the protective housings 6 and 7 the split-core coupler may operate under extremely harsh environmental conditions, including operation underwater.
In the operational conditions of the invention, prior to the charging process, the moveable part B is inserted into the stationary part A to close the magnetic circuit of the split-core coupler. In the engaged position of the split-core coupler the column 4 of the part B is positioned between the yokes 1 of the part A. Since the surface area of each end face 4a and 4b of the column 4 is smaller than the surface area of the adjacent facing surfaces 1a and 1b of the yokes 1, movements of the part B with respect to part A do not substantially affect the magnetic parameters of the split-core coupler, as long as the horizontal, vertical, and torsional movements or combination of these movements are within the split-core coupler design limits, what is presented in fig.4. Those limits depend on the surface area 1a and 1b of the yoke 1 with respect to the surface area of the end face 4a and 4b of the column 4. Limits in the horizontal direction are illustrated in fig.2. Fig. 2a shows the extreme position of the part B in the part A so that the magnetic circuit of the split-core coupler remains closed. The fig. 2b shows the other position of the part B in the part A allowed by dimensions of the housings 6 and 7 of the split-core coupler, not presented in fig.2. The difference between the positions of part B in fig. 2a and 2b indicates the range of the movement of the part B in the part A in horizontal direction for which the value of the inductive coupling coefficient "k" remains generally constant. It is obvious the person skill in the art that the similar rules is applicable to the movement of the part B in the part A in the vertical an torsional directions. In addition to the large tolerance of the split-core coupler to movements of the part B in the directions indicated in fig. 4, there is also a tolerance of the split-core coupler along the direction of the column 4 length. This tolerance is defined by the clearance between the housing 6 of the stationary part A and the housing 7 of the moveable part B. Within allowed mechanical limits defined, the total gap thickness, being the sum of "d_a" and "d_b," is constant.
The split-core coupler described above is a single-phase device comprising one pair of columns and one set of windings (one in the part A and one in part B). It is obvious to those skilled in the art that a similar, multi-phase coupler can be built based the same principle, which is not shown in the figures. As an example a three-phase coupler comprising three columns and three windings in the parts A and B respectively can be proposed.

Claims

1. A split-core coupler for inductive power transfer having a form of a split-core transformer with a primary winding (3) and a secondary winding (5), first core column (2), and on second core column(4), wherein first core column (2) is a stationary part (A) of the transmitter TR having two yokes (1) connected with the column (2) and the second core column (4) is a movable part (B) of the receiver RE of the split-core coupler and the movable part (B) is positioned between the yokes (1) during the engaging process, characterized in that the two parts the stationary part (A) and the movable part (B) of the split-core transformer are moveably connected together during the engaging and also during the charging process and the second core column (4) placed between the yokes (1) has at least three degrees of freedom in horizontal, vertical and torsional directions or combinations of all these directions during the charging process when the magnetic circuit of the split-core coupler is engaged.

2. A split-core coupler according to claim 1, characterized in that the length "Lc" of the second core column (4), , is smaller than the distance "Ly" between the facing surfaces (1a, 1b) of the yokes (1) and in the closed position of the split-core coupler the second core column (4) is positioned between the yokes (1) forming a magnetic circuit of the split-core coupler having gaps at the both ends of the column (4) having the widths "d_a" and "d_b" respectively.

3. A split-core coupler according to claim 2, characterized in that the total length of the gap in magnetic circuit of the split-core coupler in the engaged position is a sum of the widths of the two gaps "d_a" and "d_b".

4. A split-core coupler according to claim 3, characterized in that the sum of the widths of the two gaps "d_a" and "d_b" is constant in the engaged position of the magnetic circuit of the split-core coupler.

5. A split-core coupler according to claim 1, characterized in that a surface area of each end face (4a) and (4b) of the second core column (4) is smaller than the surface area of the adjacent facing surface (1a, 1b) of the yoke (1).

6. A split-core coupler according to claim 1, characterized in that the yokes (1), the first core column (2) with the primary winding (3) is embedded in a protection housing (6) which has a fork-like shape with a horn-shaped entrance (8) for guiding the part (B) of the split-core coupler into the closed position.

7. A split-core coupler according to claim 6, characterized in that the protection housing (6) is made of an insulating material for protecting the embedded split-core coupler parts against mechanical wear as well against harsh environmental conditions.

8. A split-core coupler according to claim 1, characterized in that the second core column (4) with the secondary winding (5) is embedded in a protective housing (7) having a shape which is fitted with the shape of the stationary part (A) of the split-core coupler and having dimensions allowing for existing a magnetic gap in the magnetic circuit when the part (B) of the split-core coupler is in the closed position.

9. A split-core coupler according to claim 8, characterized in that the protection housing (7) is made of an insulating material for protecting the embedded split-core coupler parts against mechanical wear as well against harsh environmental conditions.

10. A split-core coupler according to claim 1, characterized in that it is a coupler for flash charging system located on the ground.

11. A split-core coupler according to claim 1, characterized in that it is a coupler for charging system located under the water.

Drawing