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EP3503133A1 - Transformer arrangement - Google Patents

Transformer arrangement Download PDF

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Publication number
EP3503133A1
EP3503133A1 EP18000967.2A EP18000967A EP3503133A1 EP 3503133 A1 EP3503133 A1 EP 3503133A1 EP 18000967 A EP18000967 A EP 18000967A EP 3503133 A1 EP3503133 A1 EP 3503133A1
Authority
EP
European Patent Office
Prior art keywords
transformer
winding
secondary winding
axis
primary winding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP18000967.2A
Other languages
German (de)
English (en)
French (fr)
Inventor
Robert Brezovnik
Drago Dolinar
Martin PETRUN
Jozef Ritonja
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Univerza v Mariboru
Original Assignee
Univerza v Mariboru
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Univerza v Mariboru filed Critical Univerza v Mariboru
Publication of EP3503133A1 publication Critical patent/EP3503133A1/en
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/40—Structural association with built-in electric component, e.g. fuse
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/08—Cooling; Ventilating
    • H01F27/10—Liquid cooling
    • H01F27/16—Water cooling
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/28—Coils; Windings; Conductive connections
    • H01F27/2847—Sheets; Strips
    • H01F27/2852—Construction of conductive connections, of leads
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/28—Coils; Windings; Conductive connections
    • H01F27/2876—Cooling
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/40—Structural association with built-in electric component, e.g. fuse
    • H01F2027/408—Association with diode or rectifier

Definitions

  • Technical problem solved by this invention is to provide a homogeneous distribution of the electric current in the windings of the transformer and the connecting elements, providing a sufficiently large surface on the side of the secondary winding, which is intended to connect an output rectifier and the connection of cooling, as well as to reduce the length of the straight connecting elements, which can be achieved by a proposed partial overlap of the primary and the secondary windings in the area of the so-called winding heads.
  • the known arrangements of high power industrial resistance spot welding systems used for sheet metal joining, among different applications also in the production of car bodies, have a unified structure comprising an input ac-ac converter for supplying a single-phase transformer with one primary and one secondary winding, where secondary winding is divided into two equal parts with the so-called center tap, and an output rectifier.
  • the two power diodes of an output rectifier are connected with both parts of the secondary winding in a way to obtain the sufficiently high output dc welding current as the sum of two currents in both parts of secondary winding.
  • the conventional high power resistance spot welding systems with a dc welding current may differ from each other, while the base structure always includes an adequate voltage source, an input rectifier, a dc bus, an inverter, a single-phase welding transformer with a primary and secondary winding, which is divided into two equal parts with the so-called center tap, and output rectifier, wherein the two rectifier power diodes of an output rectifier are connected so that the dc welding current at the output is the sum of two rectified currents from each part of the secondary winding.
  • the arrangements of an input rectifier and inverter, as well as a transformer and an output rectifier can be different.
  • the primary side of the conventional welding transformer is usually supplied with a pulse width modulated (PWM) voltage with a constant switching period with a frequency of around 1 kHz, may be less or more, but for certain reasons it is bounded up and down.
  • PWM pulse width modulated
  • Existing manufacturers of resistance spot welding systems are using one or, exceptionally, several power diodes in each branch of an output rectifier, where relatively high currents in such power diodes with relatively high internal ohmic resistances results in relatively high Joule loss, hereinafter power loss. High power loss also occurs in massive connections between secondary winding and power diodes, which reduces the efficiency of the entire system.
  • a commonly known fact is that operation by increasing frequency of the PWM supply voltage at the same power of the transformer enables corresponding reduction of the transformer iron core cross-section area, which due to the reduction of dimensions automatically causes the corresponding reduction in the size of the windings and consequently the reduction of weight. It is also commonly known that the dc welding current at the output from an output rectifier decreases with increasing frequency of the supply voltage, which is analytically disclosed in reference DOI 10.1109/ TIE 2017 .2711549, IEEE.
  • the inventors in the US2014/0321184A1 used the known fact and increased the frequency of the supply voltage to 10 kHz keeping a high value of secondary current 20 kA by separating a single secondary winding with a center tap and corresponding output rectifier into the ten smaller secondary windings with center tap and corresponding smaller output rectifiers, realized by MOSFET transistors, all ten secondary windings with output rectifiers connected in parallel.
  • the increase in the number of parallel-connected secondary branches can either increase the value of the secondary welding current at the same frequency of the PWM power supply, or it can increase the frequency of PWM supply voltage by the maintaining unchanged value of the secondary welding current, which enables a suitable geometric reduction of the transformer, and therefore also a reduction of weight.
  • the main disadvantage of the proposed concept in US2014/0321184A1 is the considerably increased complexity of the whole arrangement, which affects the cost and reliability of operation, although allows operation at significantly higher frequencies of PWM supply voltage.
  • a similar arrangement of a transformer with a parallel connection of a plurality of secondary winding coils and one common output rectifier is used in EP 2 749 373 A1 .
  • a so-called sandwich structure is used, in which a certain number of coils of primary winding are connected in serial and are positioned in such a way that placement of respectively connected secondary coils between the coils of primary winding is enabled.
  • Such arrangement is very similar to the one used in US 7 978 040 B2 , but comprises of several parallel connected coils of the secondary winding.
  • the common characteristic of both arrangements is overlapping of the coils of the primary and secondary windings in the direction of the axis, which is parallel to the direction of the magnetic flux in the core of the transformer.
  • the main disadvantage of these solutions is the different arrangement of the coil connections with the so-called positive side and the coil with the so-called negative side of the secondary winding, which causes a large difference in both sides and a highly non-homogeneous current distribution in one of the two sides of the secondary winding.
  • the said arrangement of a transformer with a single primary coil and two coils or two parts of the secondary winding, where the coils are placed concentrically one above another, causes unwanted electromagnetic behavior of the entire system due to the geometric asymmetry.
  • the weight of the transformer which is designed for operation at the certain frequency of the supply voltage, can also be reduced by a certain change of construction in which the so-called sandwiched or pancake construction of the windings from the existing resistance spot welding systems in US 7 978 040 B2 is replaced by the so-called concentric cylindrical construction, as is done in EP 3 232 453 A1 . Due to a good overlap of the primary and the secondary windings in such a cylindrical construction of the welding transformer, this arrangement ensures an excellent magnetic coupling between the individual windings of the transformer, which, in addition to transformer weight reduction and better cooling, can also improve efficiency and improves the electromagnetic properties of the transformer, thus achieving higher dynamics of operation of the welding system.
  • the proposed arrangement of the transformer shows a partially concentric tubular structure, and allows the electrical connection of an output rectifier including the cooling system with an adequate number of straight connections with a sufficiently large cross-section area, which makes it possible to ensure a homogeneous current distribution in windings and connections, and smaller corresponding leakage inductances.
  • Choosing the appropriate number of straight connections and their position enables shorter paths for electrical currents, which can reduce the power loss in the windings. Due to the shorter paths and more appropriate arrangement of connections, cooling realization is also easier.
  • the present invention relates to the arrangement of a transformer in the sense of a different construction of the primary and secondary windings, whereby the arrangement of the secondary windings ensures complete overlap of the parts of the primary and secondary windings in the transformer's window, while in the part of the so-called winding heads of the primary and the secondary windings, they overlap only partially, which makes it easier to carry out the connections for an output rectifier, which at the same time become also the elements of the individual secondary winding heads.
  • the modified version of the two turns of secondary winding enables the necessary change of the magnetic and electrical properties of the welding system, and thus enables the achievement of a homogeneous distribution of electrical currents in different parts of the transformer windings and electrical connections and consequently reduces the power loss in the transformer and increases the ability to supply the primary side of the transformer with the voltages with a higher frequency by maintaining the output welding current.
  • the arrangement of the secondary winding according to the present invention at the same time enables a much easier arrangement of the water-cooling of the welding transformer by making the straight sections of the cooling channels of the corresponding dimensions. With implementation of cooling of transformers of smaller powers, the cooling can be replaced by an air-cooling, which additionally simplifies the structure of the transformer.
  • the object of the present invention relates to the improvement of the realization of suitably strong and robust electrical connections at suitable locations and the realization of suitable cooling channels for cooling with a liquid coolant medium.
  • the change in the transformer arrangement in accordance with the present invention reduces the technological complexity of the transformer production and at the same time allows integration, i.e., installation of the rectifier devices of an output rectifier in the winding heads of the two parts of the secondary winding.
  • the rectifier devices of an output rectifier may be a power diodes or transistors, due to relatively low voltages and high currents, preferably MOSFET transistors. Also only a two power diodes can be used, as is the case with existing industrial solutions.
  • the transformer according to the present invention provides the completely straight connections without electrical loops for connecting an output rectifier to the secondary winding, which enables reduction of the respective inductances and ensures a homogeneous distribution of the currents across the entire cross-section area of these connections, In addition, these connections are short and easy to implement, which reduces electrical losses.
  • Figure 1 shows a block diagram of the arrangement of the existing high-power ac-dc converters.
  • Figure 2 shows an electrical circuit diagram of existing welding transformers with an integrated output rectifier.
  • Figure 3 shows a transformer arrangement with an integrated output rectifier.
  • Figure 4 shows the arrangement of the transformer.
  • Figure 5 shows the arrangement of a transformer with a look in cross-section A-A in Figure 4 .
  • Figure 6 shows the arrangement of the windings in Figure 4 .
  • Figure 7 shows the arrangement of a secondary winding of the welding transformer.
  • a block diagram of a resistance spot welding system is shown in Figure 1 and is denoted as a whole by a number 100.
  • a resistance spot welding system comprises of a voltage source 101, an input rectifier 102, and a dc link with a filter 103, an input inverter 104, and a welding transformer with a built-in output rectifier 105,
  • the electrical circuit diagram of the transformer with an integrated output rectifier is schematically shown in Figure 2 and is as a whole denoted by a number 200.
  • the arrangement of the transformer includes a primary circuit 210 and a secondary circuit 220, which are linked with a transformer 230,
  • the primary winding 231 with the number of turns N 1 of the transformer 230 is connected to the primary circuit 210 and is supplied with the primary voltage u 1 232.
  • the primary and the secondary winding 231, 233 of the transformer are magnetically linked - connected by an iron core 236, which can be carried out differently.
  • the primary voltage 232 is pulse width modulated - PWM in different ways.
  • the secondary circuit 220 contains two rectifier devices, 237 and 238, which can be either power diodes or adequate transistors, preferably MOSFET transistors.
  • the center tap A2 240 which with the connection to point A6 244 represent one of the load terminals with the voltage u 2 245, the point A4 242, where are added the currents from the rectifier devices 237 and 238 and A 4 242, which with the connection represent the second terminal point A 5 243 for connection of the load.
  • FIG. 3 Structure of the transformer with a built-in output rectifier to be protected is shown in Figure 3 , which is denoted as a whole by number 30.
  • the rectifier devices 237 and 238 of an output rectifier are mounted in the winding head of the first part of the secondary winding 234 and the winding head of the second part of the secondary winding 235.
  • the first head of the secondary turn 234 is an element 239 with a rectifier device 237, which is mounted between 239 and the element 242 on which the connection 243 is carried out, and comprises of the corresponding number of parallel-connected rectifier devices in the form of power diodes, or transistors, preferably MOSFET transistors.
  • the first head of the secondary turn 235 represent an element 241, so that a rectifier device 238 is mounted between the element 241 and the element 242 on which the terminal point 243 is implemented, comprising the corresponding number of parallel-connected rectifier devices in the form of power diodes, or transistors, preferably MOSFET transistors.
  • the parallel connected power diodes, or transistors, preferably MOSFET transistors, which as a whole represent the rectifier devices 237 and 238, can be also replaced by only two power diodes, as it is the case with the conventional version of the welding system described in US 7 978040 B2 .
  • a primary winding 231 is arranged around the iron core 236 of the transformer.
  • the secondary terminal points A5 and A6 arc according to Fig.
  • each of the two cores 236 are comprising two C-segments
  • the so-called core-type construction of transformer could have just a single iron core 236 with two C-segments, having the same iron core cross-section area as that one with the two iron cores.
  • All windings 231, 233 in Figure 3 are electrically isolated between each other and electrically isolated from the iron core 236.
  • FIG 4 shows the arrangement of a transformer that is the subject of the invention.
  • the primary winding 231 is made with a rectangular wire with a cross-section a x b, where ⁇ is a thickness and b is a wire width, concentrically wound around the transformer axis 300.
  • a secondary winding 233 is also wound around the transformer axis 300 and/or an iron core, where on the right and on the left side of the axis 300 on the places, where the primary winding and both parts of the secondary winding do not completely overlap, the well-visible straight parts 234a, 234b, 235a and 235b, which allow simple connection of an output rectifier and the cooling, where the round bores 410 can be used for the cooling.
  • the arrangement of the transformer in Figure 4 comprises of four connecting points for the beginnings and ends of the two parts of the secondary winding 233, otherwise, it is also possible to make a transformer with at least one or more surfaces to connect an output rectifier and the cooling. With the implementation of cooling of transformers of smaller powers, the cooling can be replaced with an air-cooling, which additionally simplifies the structure of the transformer. All windings 231, 233 in Figure 4 are electrically isolated between each other, and are electrically isolated from the iron core 236.
  • Figure 5 shows the transformer from Figure 4 in a cross-section A-A.
  • the primary winding 231 is divided into the three segments, wherein the first segment lies at a distance rp1 and is in the presented arrangement formed of three successive layers of rectangular wires, the second segment lies at a distance rp2 and is in the presented arrangement also formed of three successive layers of rectangular wires, while the third segment is located at a distance rp3 and is in the presented arrangement also formed of three successive layers of rectangular wires, all of said distances relative to the transformer axis 300.
  • Secondary winding 233 comprises of two parts 234 and 235, wherein the first part 234 is concentrically wound around the transformer axis 300 at the distance rs1, while the second part 235 is wound at a distance rs2 around the transformer axis 300.
  • the extensions of the rectangular shape with cooling bores 410 in parts 234a, 234b , 235a, and 235b are located at distances h1, h2, h3 and h4 from the lower edge 430 in the direction of the axis 300 with the cross-section f x d .
  • the first segment of the primary winding and both parts of the secondary winding overlap, the second and third segment of the primary winding also overlap with the first segment of the primary winding, and the overlap of first and second part of the secondary winding with the second and third segment of the primary winding is also in five places, while in four places the overlap is just partial, which enables realization of a straight and short connections of an output rectifier in the direction of the axis 500.
  • All the windings 231, 233 in Figure 5 are electrically isolated from one another, and electrically isolated from the iron core 236.
  • Figure 6 shows an assembled set of primary winding 231 and secondary winding 233 with a separately marked parts 235a, 235b, 234a, and 234b, where four partial overlapping parts between the primary and secondary windings are clearly seen in the right side, which is not relevant from the point of view of the transformer operation. It is important to ensure overlap of the windings in the remaining three-quarters of the primary and secondary windings.
  • the primary winding is carried out with a rectangular wire with a cross-section a x b , but it could also be made with a round wire or wire, which includes parallel-connected round wires or a combination of a rectangular wire and a round wire. All the windings in Figure 6 are electrically isolated from one another, and electrically isolated from the iron core 236.
  • Figure 7 shows the first and the second part 234 and 235 of the secondary coil 233 with four straight extensions, which allow easy connection of an output rectifier and cooling with the liquid coolant.
  • the individual parts of the first and the second part of a secondary coil 234 and 235 in Figure 7 consist of several parts, it is possible to produce both parts in a single piece, which also significantly improves electrical properties.
  • Figure 7 also shows the massive parts 700a, 700b of the two parts of the secondary winding 233, which are along the axis 500 in the length of the iron core L surrounded by an iron corc, and at the same time ensure overlap of the windings in the described area.
  • the solid parts 700c ensure a complete overlap of the windings in the major part of the winding head of the first and second part of the secondary winding in the length l g, while in the smaller part of the winding heads remains without overlap. All the windings 231, 233 in Figure 7 are electrically isolated from one another, and are electrically isolated from the iron corc 236,
  • the transformer arrangement 30 provides a homogeneous distribution of the magnetic fields in an iron core of the transformer 236, which reduces the phenomenon of the unwanted saturation in an iron core.
  • the said arrangement of the transformer with an output rectifier also provides a homogeneous distribution of currents in conductive parts of the windings and a very short distance for connecting an output rectifier, which provides a better system efficiency than the proposed arrangement described in EP3 232 453 A1 .
  • With the proposed arrangement it is also possible to achieve higher values of output welding current under the same operating conditions.
  • the arrangement of the transformer in Figure 4 shows a partial overlap of the primary winding 231 with a secondary winding 233 only in the so-called winding heads on the left side of the transformer, without overlap of the windings heads on the right site of the transformer.
  • a similar system of partial overlap of the primary winding 231 with the secondary winding 233 can also be used for the so-called winding heads on the opposite side, which is, according to Figure 4 , on the right side of the transformer.
  • the right-lying rectifier device 238 in Figure 3 can be moved to the opposite left side of the transformer, while the arrangement of the overlap of the primary and secondary windings along the axis 500 in length L, remains unchanged.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)
EP18000967.2A 2017-12-19 2018-12-13 Transformer arrangement Pending EP3503133A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SI201700337A SI25571A (sl) 2017-12-19 2017-12-19 Izvedba transformatorja

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EP3503133A1 true EP3503133A1 (en) 2019-06-26

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EP18000967.2A Pending EP3503133A1 (en) 2017-12-19 2018-12-13 Transformer arrangement

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SI (1) SI25571A (sl)

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4571669A (en) * 1983-09-13 1986-02-18 Honda Giken Kogyo Kabushiki Kaisha Transformer with rectifier
US5160820A (en) * 1990-03-30 1992-11-03 Honda Giken Kogyo Kabushiki Kaisha Welding transformer and method of manufacturing same
JPH0638223U (ja) * 1992-06-16 1994-05-20 株式会社電元社製作所 抵抗溶接用変圧器
US6369680B1 (en) 1997-04-02 2002-04-09 Expert Maschinenbau Gmbh Transformer
US7978040B2 (en) 2007-01-08 2011-07-12 Robert Bosch Gmbh Winding element for a coil winding and transformer arrangement
EP2749373A1 (en) 2012-02-29 2014-07-02 Koyo Giken Inc. Welding transformer, welding transformer assembly, welding device, and resistance welding method
US20140321184A1 (en) 2011-10-31 2014-10-30 Fronius International Gmbh Synchronous rectifier
EP3232453A1 (en) 2016-04-14 2017-10-18 Robert Bosch Gmbh Transformer arrangement

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4571669A (en) * 1983-09-13 1986-02-18 Honda Giken Kogyo Kabushiki Kaisha Transformer with rectifier
US4571669B1 (en) * 1983-09-13 1996-08-27 Honda Motor Co Ltd Transformer with rectifier
US5160820A (en) * 1990-03-30 1992-11-03 Honda Giken Kogyo Kabushiki Kaisha Welding transformer and method of manufacturing same
JPH0638223U (ja) * 1992-06-16 1994-05-20 株式会社電元社製作所 抵抗溶接用変圧器
US6369680B1 (en) 1997-04-02 2002-04-09 Expert Maschinenbau Gmbh Transformer
US7978040B2 (en) 2007-01-08 2011-07-12 Robert Bosch Gmbh Winding element for a coil winding and transformer arrangement
US20140321184A1 (en) 2011-10-31 2014-10-30 Fronius International Gmbh Synchronous rectifier
EP2749373A1 (en) 2012-02-29 2014-07-02 Koyo Giken Inc. Welding transformer, welding transformer assembly, welding device, and resistance welding method
EP3232453A1 (en) 2016-04-14 2017-10-18 Robert Bosch Gmbh Transformer arrangement

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ROBERT BREZOVNIK ET AL: "Impact of the Switching Frequency on the Welding Current of a Spot-Welding System", IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS., vol. 64, no. 12, 1 December 2017 (2017-12-01), USA, pages 9291 - 9301, XP055711025, ISSN: 0278-0046, DOI: 10.1109/TIE.2017.2711549 *

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