MXPA95002012A - High frequency transformer that has a waterfall cooled internally with liquid - Google Patents

Abstract

A high frequency transformer (10) has a primary winding (11) comprising a hollow coil of coolant for the transmission of the cooling fluid therethrough, and a secondary winding (12) comprising a plurality of connected coil windings thermally to the primary winding (11) using adhesive (31). The secondary winding (12) may also be comprised of a hollow coil of coolant for the transmission of a cooling fluid therethrough. The present invention uses a hybrid concept, wherein the cooling liquid is used only in one or two turns of the primary and / or secondary windings (11, 12) of the transformer 10. For any winding of transformer (10), the turns The remaining ones of any particular winding are thermally connected to the coolant loop by means of an adhesive (31), and therefore all the turns are cooled, one directly and the rest indirectly. The liquid-cooled refrigerant loop can be connected in series with a normal-design high-frequency winding, without any detrimental effect on electrical losses or performance for both primary and secondary windings / 11, 12). The present invention can also be used in the construction of an inductive coupling probe for an electric vehicle battery charger

Description

HIGH FREQUENCY TRANSFORMER THAT HAS A WATERFALL COOLED INTERNALLY WITH LIQUID BACKGROUND OF THE INVENTION The present invention relates generally to transformers that are used in electric vehicle applications, and more particularly to a high frequency transformer having primary and secondary windings with at least one turn internally cooled with liquid. In the past, high power density transformers had been limited by current due to thermal limitations in the cooling of the transformer's internal copper windings. The cooling has been carried out easily at low frequency (60 and 400 Hz) making the winding as a winding of the hollow tube and pumping a refrigerant (oil, liquid etc.) through it. This can not be done at high frequencies (greater than 10 kHz), due to excessive parasitic current losses introduced by the excessive tube thickness that is required. Therefore, in the past, liquid-cooled transformers had been limited by the inadequate means for cooling the windings. In the design of the transformer, a high-frequency operation is desired to reduce the size of the magnetic core. This is based on the fundamental magnetic equation: E = N * df / dt, where df = NdB. This equation can be rewritten as: Ac = 4INB-108 where: Ac is the cross-sectional area of the core, f is the operating frequency, N is the number of primary turns, and B is the flux density, in Gauss. In this way, if a higher frequency is used to excite the nucleus, the size of the magnetic core can be made smaller. However, this produces a problem with respect to the copper winding. When a smaller copper winding is used, losses in it increase as a result of eddy currents. Stray current losses are a collective term for the redistribution of alternating current in conductors as a function of frequency (surface effect), and the phenomenon where a circuit carrying alternating current can induce circulation currents, without making contact ico, in any conductive material in the immediate vicinity of the circuit (proximity effect). In this way, there is a fundamental limitation on how small the transformer core can be, which is a function of the current losses in the copper windings. The thermal limitations are worse for the inductive coupling transformers of electric vehicles (ie, where the primary winding of the transformer is designed to be physically inserted into a transformer core), since there is relatively poor thermal contact between the primary winding and the core of the secondary transformer. The primary winding of the transformer in this application is referred to as a probe. Metal conduits for coolant normally can not be used in this application, because they are immersed in a high magnetic field, which results in the introduction of large eddy currents. This causes very large losses of power in the liquid conduits and more severe thermal problems, because the element that cools the winding must also be cooled. Therefore, an object of the present invention is to provide a high frequency transformer using at least one internally cooled winding that solves the limitation of copper losses described above.

SUMMARY OF THE INVENTION To satisfy these and other objectives, the present invention is a high frequency transformer design that partially solves the problem of current losses in the copper windings thereof. The present invention uses a hybrid concept, wherein the internal cooling liquid is used in a small number of turns of the primary and / or secondary windings (referred to as "coolant turns") of the transformer. When reference is made here to the cooling liquid, refers to the flow of a refrigerant through a hollow copper loop. The remaining turns of any particular winding are thermally connected to the coolant turn, thus, for any winding of the transformer all the turns are cooled, one directly and the others indirectly. More specifically, the present invention comprises a high frequency transformer including a primary winding having a hollow conductive coil of coolant for conducting or transmitting therethrough a cooling fluid, and a secondary winding comprising a plurality of coils. conductive turns The secondary winding may also have a hollow conductive coil of coolant to conduct the cooling fluid therethrough. The plurality of the conductor windings of the primary and / or secondary windings are thermally connected to the respective hollow coolant turns thereof. The present concept uses the coolant loop cooled with liquid to provide designs of high frequency, high power, and very high power density transformers. The liquid-cooled refrigerant loop can be connected in series with a normal-design high-frequency helical winding, without any detrimental effect on the losses or electrical performance of the two windings, the primary and the secondary windings. The present invention can also be used for example in the construction of an inductive coupling probe for an electric vehicle battery charger. The present invention is best applied, but not limited to windings with a large surface area, such as flat helix or flat spiral windings, for example, and can be applied directly to any transformer design, and is specifically applied to the design of an inductive coupling transformer for electric vehicles. The cooling of the probe is achieved using non-metallic materials, which have little less than thermal properties. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of the present invention can be more easily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals designate similar structural elements, and in which: Figure 1 is a perspective view of a charging probe forming part of a transformer in accordance with the principles of the present invention; Figure 2 is a side view partly in section of the battery charging apparatus, using a transformer in accordance with the principles of the present invention; Figure 3 shows an over position model illustrating the current against the increase in the frequency of a conductor; Figure 4 illustrates a top view of a transformer in accordance with the principles of the present invention. Figure 5 is a side view of the transformer of Figure 4; Figure 6 is an exploded view of a transformer in accordance with the principles of the present invention; Figure 7 is an exploded view of a transformer in accordance with the principles of the present invention; Figure 8 shows an exploded view of a helical / partially coiled design of the windings that can be used in the transformer of Figure 4; Figure 9 shows an exploded view of a helical / spiral design of the windings that can be used in the transformer of Figure 4; DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings of the figures, Figure 1 is a perspective view of a loading probe 20 or an inductive load coupler 20 forming part of a transformer 10, or of inductive loading apparatus 10. , in accordance with the principles of the present invention. Figure 2 is a partially cross-sectional view of the inductive charging apparatus 10 including a transformer 10 comprising the inductive charging coupler 20 of Figure 1, inserted in a charging port 11 placed in an electric vehicle 17, for example . The charging port 11 includes a housing 12 having an opening 13 into which the inductive charging coupler 20 is inserted. The charging port 11 comprises a secondary core 14 and secondary winding 15 that surrounds the core 14. The charging port 11 is coupled to a battery 16 of the electric vehicle 17 in which it is housed. The charging port 11 includes a plurality of metallized electromagnetic interference fingers (EMI) 18, which project towards the opening 13 and which are adapted to be pressed against the inductive load coupler 20. The EMI fingers 18 may be comprised for example, tinned copper The inductive load coupler 20 is comprised of a plastic housing 22 of the coupler, having two tongue and groove halves of the coupler 22a, 22b, which are configured to provide a handle 23. The load inductive coupler 20 is comprised of a core center magnetic 24 or "elf" 24, which may be comprised for example of ferrite. A primary winding 25 is placed around the center of magnetic core 24. The primary winding 25 is comprised of 3 turns. A flexible hose 26 (FIG. 1), comprising a power cable 26a and refrigerant inlet and outlet line 32, is coupled to the primary winding 25 and to an external power source 27 for energy coupling with the charge coupler. The external power source 27 is generally housed within a charging station 40 which also includes a cooling system 41 comprising a refrigerant pump 42, a refrigerant heat exchanger 43, a cooling fan 44 and a cooling unit 44. 45 cooling, according to the cooling requirements required. The present invention circulates the liquid refrigerant from the off-frame cooling system 41 at the charging station 40, guiding the refrigerant inlet and outlet lines 32 inside the flexible hose 26 to the charge coupler 20. The refrigerant it may be comprised of a highly dielectric material, such as a polyalphaolefin or Fluoronert. The highly dielectric material shows a high resistance, so that in the refrigerant no current is induced from the magnetic fields or by direct contact with the conductive fields. According to the present invention, a heat exchanger 30 or chamber 30, which conducts coolant, is placed between the primary winding 25. The heat exchanger 30 which conducts coolant, can be attached to the turns of the primary winding 25, using an adhesive 31 conductor or epoxy, for example. The details of the primary winding 25 and the heat exchanger 30 leading to the coolant are discussed below. The housing 22 has a hollow disk-shaped section having substantially flat opposed surfaces, and the tapered handle it extends from the disk section. An opening 34 is placed through each of the opposed flat surfaces of the hollow disk-shaped section. The magnetic core center 24 is positioned in the opening 34 and has opposed flat surfaces substantially coplanar with the substantially flat opposed surfaces of the housing 22. The load coupler 20 is designed to be inserted into the opening 13 of the charging port 11 for coupling the current to the battery 16 from the external power source 27. The coupler has two indentations 28 along its respective sides, which are coupled with two projecting fingers that extend from the loading port, and which provide the user with a tactile sensation when inserted into the cargo port. The tongue-and-groove halves 22a, 22b of the inductive load coupler 20 enclose the primary winding 25 and the magnetic core center 24, and secure the hose 26 in the handle 23. A conductive plastic strip 36 can be placed along an outer portion of the coupler 20 between the handle 23 and the primary winding 25. The conductive plastic strip 36 engages with the metallized electromagnetic interference fingers (EMI) 18 when the coupler 20 is inserted into the loading port 11. A deformation compensator 29 surrounds the the hose 26 at the point where the handle 23 emerges, and is secured by the two tongue and groove halves 22a, 22b of the coupler.

Given the above, a better compression of the present invention will be derived from the compression of the surface effect and the losses by windings in the conductors. The losses by surface effect is an increase in the effective resistance due to the high frequency current carried only by the winding conductor. This occurs because as the frequency increases, the current density increases at the surface of the wound conductor and decreases to zero at the center of the wound conductor. The current is dispersed exponentially within the winding conductor. The portion of the winding conductor that actually carries current is reduced, so that the resistance to high frequency (and the resulting losses) can be several times greater than at low frequency. The depth of penetration (sd) is defined as the distance from the surface of the winding conductor to a point where the current density is 1 / e times the current density at the surface (where e is the base of the natural logarithms ), and is given by sd = > / p / p * μ * / where p is the resistivity of copper and is given by p = 0.69xl0 ~ 6 oh -input at 20 ° C, and μ = 0.4pxl0 ~ 8. When the current in a conductor changes rapidly, as it does at high frequency, the flow within the conductor also changes rapidly. The change in the flow induces a wave of voltage or parasitic voltage, near the surface of the conductor. Because this induced voltage is inside the conductor, it causes a parasitic current coincident with the voltage. This parasitic current reinforces a main current that flows on the surface, but opposite to the center of the conductor. The result is that as the frequency rises, the current density increases on the conductor surface and decreases to zero at the center of the conductor. The current disperses exponentially inside the conductor. The portion of the conductor that actually carries current is reduced, therefore, the resistance at high frequency (and the resulting high losses) can be several times higher than at low frequency. An equation to calculate the losses by the high frequency winding for arbitrary current waveforms is given by: Rac / Rdc (surface effect) = * (e2x-e ~ x + sin (2x) / (e2x + e (-2x) -2cos (2x) .where x is the thickness of the layer / depth of penetration.Although the current density is dispersed exponentially from the surface, the resistance at high frequency is the same, as if the current density were constant from the surface to the depth of penetration, then drops abruptly to zero, consequently, without considering the thickness of the conductor, the minimum resistance (AC resistance at a specific frequency) is limited to the resistance CD at the depth of penetration. In this way, for a layer (spiral) of a helical winding, the thickness of the layer can be as thick as desired, without increasing the losses above the depth of penetration. In depth, the thickness of the layer can be made very thick to allow a structure to transport a refrigerant, as provided by the present invention. However, not all turns of a winding show the proximity effect. Any coil that does not have proximity losses can be used as a coolant loop. A mmf diagram is used as any simple tool to determine which turns can be used to transport refrigerant. For multi-layer windings, the proximity effect is often the dominant effect. The apparent increase in the resistance of the conductor of a winding is caused by eddy currents in it, due to the magnetic fields established on the conductors from the other conductors in the winding. These eddy currents exist even if the winding is an open circuit. Losses exist without a net current flow, giving an infinite resistance. This is the situation with an electrostatic shield and a metal heat exchanger cooled with liquid inserted between the primary winding and the secondary winding. The simplest form of the winding loss equation is given by: Rac / Rdc (proximity effect) = (2/3) * (m2-l) * x * (ex-ß "x + 2sin (x)) / (ex + e (-x) -2cos (2x), where x is the thickness of the layer / depth of penetration and m is the number of layers.This equation shows the drastic increase in losses due to proximity effects, when more layers (turns) are used in the winding of a transformer and, because the thickness of the layer must be maintained at a value equal to or less than the penetration thickness, the multilayer windings (turns) will now be discussed. Proximity can be reduced by interleaving the primary and secondary windings Referring to Figure 3, an over position model is shown, illustrating the current against the increase in frequency in a conductor, and shows a transformer 10 with multilayer windings primary and secondary 11, 12 and a frequency diagram mmf (F) (illustrated above the transformer 10). The primary winding 25 shown in Figure 3 has three turns (Pl, P2; P3), and the secondary winding 15 has four turns (SAI, SA2, SB1, SB2). The secondary winding 15 is arranged in four layers interspersed outside the primary winding 25. The high frequency mmf diagram of Figure 3 shows that there is no field inside the conductors of the primary and secondary windings 11, 12, due to the effect of surface. The fields of the central primary loop, P2, and the secondary loop SAI, and SB1 have low fields of the conductors. The losses in these turns are all due to the surface effect, and not to the effect of proximity. Figure 3 also shows the effect when the thickness of the coil / layer is much greater than twice the depth of penetration. As shown in the primary and secondary coils P2, SAI, and SB1, the current flowing over the layer surfaces is from one amp (surface effect), while in the turns P3, PI, SA2, and SB2, the current is from one amp on one of the layer surfaces (surface effect) and two amps on the other surface (proximity effect). Also, the field between the primary and secondary windings 11, 12, is two ampere-turn, and if a metal is introduced between the primary and secondary windings 11, 12, eddy current losses will result in the metal. Therefore, the SAI, SBl, and P2 turns can be used as the refrigerant turns. Because these turns only experience surface losses, they can be of arbitrary thickness. It has been determined that an optimum thickness can be p / 2 times the depth of penetration. The loop can be thicker, with a minimum penalty for losses. To minimize the proximity effect, the thickness of the uncooled turn is designed to be at least one penetration depth (ie, approximately 8.5 mils at 100 kHz, at 100 ° C). This has a penalty due to the CD resistance. To further optimize the losses, each coil (or layer) can be of variable thickness. This results in an additional reduction in losses due to lower proximity losses. The above discussion illustrates that there are turns inside the windings 11, 12 of the transformer 10 that do not show proximity losses, only the losses by AC resistance of the surface effect, introduced by the operation at high frequency. These turns can be arbitrarily as thick as required, to include the cooling ducts for the liquid to flow through them. For example, using helical coils, a liquid-cooled winding is very compact and provides an optimum surface area for cooling to the remaining coils of windings 11, 12. More than two chilled coils can be used with liquid for the primary windings and secondary 11, 12, interspersing the primary and secondary windings 11, 12. The turns that are cooled with liquid can be easily determined by drawing an mmf diagram of the internal winding fields as shown in figure 3. Figure 4 illustrates a top view of a mode of a transformer in accordance with the principles of the present invention. The transformer 10 is comprised of a primary winding 25 and a secondary winding 15 the secondary winding 15 is formed from two halves, with an upper half placed on the primary winding 25 and a lower half placed under the primary winding 25. The winding primary 25 is comprised of at least one cooling coil having couplings or inlet and outlet ports 19. The cooling loop is usually a hollow tube which can have any desired cross section and which supports good thermal conduction. Figure 5 is a side view of the transformer 10 of Figure 3. Figure 5 illustrates the construction of the transformer 10 in greater detail. The transformer 10 is constructed in such a way that the upper and lower halves of the secondary winding 15 are secured to the exposed surfaces of the primary winding 25 for example., by means of a thermally conductive adhesive. An insulator 37 is placed on the exposed surface of the respective upper and lower halves of the secondary winding 15 and covers the coolant loop of the primary winding 25. The insulator 37 can be attached to the respective windings 11, 12 for example by means of an adhesive or epoxy. Figure 6 is an exploded view of a mode of a transformer 10 in accordance with the principles of the present invention. The transformer 10 of Figure 6 has planar, primary and secondary helical windings 11, 12 although a spiral shape or other shape having a relatively large surface area can be used. The primary winding 25 is a flat tube having conical portions 38 for transition to the round output couplings 19. The secondary winding 15 for example, is comprised of a thin copper lamella, and is attached or adhered to the primary winding 25 by an adhesive, for example, such as an epoxy. Thermal limitations are worse for inductive coupling transformers for an electric vehicle (ie, where the primary winding of the transformer is designed to be physically inserted into a transformer core), because there is a relatively poor thermal contact between the primary winding 25 and the transformer core of the secondary winding 15. In this application, the primary winding 25 of the transformer 10 is referred to as a probe or vane. Metal coolant heat exchangers usually can not be used in this application because they are immersed in a high magnetic field, which would result in the introduction of large eddy currents. This causes very large losses of power in the liquid conduits and thermal problems, because the coolant loop must also be cooled. It is only practical to use a metallic coil of coolant as the central loop. By way of example, FIG. 8 shows an exploded view of a helical / partially spiral design that can be used in the transformer 10 of FIG. 4, and FIG. 9 shows an exploded view of a helical / spiral design of windings. which may be used in the transformer 10 of Fig. 4. In Fig. 8, the windings comprise three turns each, while in Fig. 9, the windings comprise four turns each. The coil cooled with air or liquid is the outermost loop of each design. In this way a new and improved high frequency transformer has been described, having primary and secondary windings with at least one turn internally cooled with liquid. It will be understood that the above-described embodiment is only illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Clearly, numerous other arrangements can be readily developed by those skilled in the art without departing from the scope of the invention.

Claims (10)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as property. CLAIMS 1. A high frequency transformer characterized in that: a primary winding comprises a hollow metallic coil of the coolant for the transmission of a cooling fluid therethrough; and a secondary winding comprising a plurality of conductive turns which are coupled to the primary winding.
2. 2. The high-frequency transformer according to claim 1, wherein the hollow metallic coil of coolant is characterized by a helical plane winding.
3. 3. The high frequency transformer according to claim 1, wherein the hollow metallic coil of coolant is characterized by a spiral flat winding. The high frequency transformer according to claim 1, wherein the primary winding is further characterized by an additional plurality of conductive turns. The high-frequency transformer according to claim 4, wherein the additional plurality of conductive turns of the primary winding is characterized in that they are thermally bonded by means of an adhesive to the hollow metallic coil of coolant. The high frequency transformer according to claim 2, wherein the primary winding is further characterized by a further plurality of conductive turns comprising each spiral plane windings. The high frequency transformer according to claim 1, wherein the primary winding is characterized by an inductive coupling probe which is used in a battery charger for electric vehicle. The high frequency transformer according to claim 1, wherein the secondary winding is characterized by a hollow conductive loop of coolant for the transmission of the cooling fluid therethrough and which is an outer turn of the secondary winding. The high frequency transformer according to claim 8, wherein the secondary winding is further characterized by an additional plurality of conductive turns. The high-frequency transformer according to claim 9, characterized in that the additional plurality of conductive turns of the secondary winding are thermally bonded by means of an adhesive to the respective hollow conductive coil of the coolant thereof. SUMMARY OF THE INVENTION A high frequency transformer (10) has a primary winding (11) comprising a hollow coil of coolant for the transmission of the cooling fluid therethrough, and a secondary winding (12) comprising a plurality of conductive loops thermally bonded to the primary winding (11) using adhesive (31). The secondary winding (12) may also be comprised of a hollow coil of coolant for the transmission of a cooling fluid therethrough. The present invention uses a hybrid concept, wherein the cooling liquid is used only in one or two turns of the primary and / or secondary windings (11, 12) of the transformer 10. For any winding of transformer (10), the turns The remaining ones of any particular winding are thermally connected to the coolant loop by means of an adhesive (31), and therefore all the turns are cooled, one directly and the rest indirectly. The liquid-cooled refrigerant loop can be connected in series with a normal-design high-frequency winding, without any detrimental effect on electrical losses or performance for both the primary and secondary windings (11, 12). The present invention can also be used in the construction of an inductive coupling probe for an electric vehicle battery charger.