Toroidal transformer with leakage inductance

Abstract

The present invention relates to a toroidal core transformer, comprising a first toroidal core, a second toroidal core, a primary winding and a secondary winding, the second toroidal core being arranged coaxially within the first toroidal core, the primary winding having first turns which surround the first toroidal core, and the secondary winding having second turns, each second turn surrounding both the first toroidal core and the second toroidal core.

Description

[0001] Description

[0002] title

[0003] Ring transformer with leakage inductance

[0004] State of the art

[0005] The present invention relates to a toroidal transformer and a charging device with a toroidal transformer for potential-free voltage conversion.

[0006] Energy conversion devices such as on-board chargers use transformers that enable potential-free voltage conversion in suitable switching electronics, such as a dual active bridge.

[0007] Such transformers should be compact and cost-effective, operate with low losses, and simultaneously exhibit the desired electrical properties such as leakage and main inductance and transfer ratio. Switching frequencies well above 100 kHz lead to solutions based on ferrite cores, which are prone to core fractures, a risk that must be addressed in the design. On the other hand, one wants to utilize the core material as much as possible by operating it at the highest possible energy densities or magnetic field strengths. This generates considerably larger core losses and thus significantly higher temperature gradients within the core. These temperature gradients, in turn, typically amplify core losses via thermomechanical stresses, so that self-reinforcing positive feedback effects can lead to core fracture.In the past, such core cracks have been observed, or designs were engineered to avoid them by using relatively low core excitation, at the cost of poor core utilization. This undesirable interaction is further exacerbated by irregular core shapes, such as E- or PM-shaped cores, which are more susceptible to cracking due to increased mechanical stress in their critical areas. Ideally, a transformer would be desirable that, while being simple and cost-effective to manufacture, offers a robust design and high electrical and magnetic carrying capacity, combined with low core and winding losses.

[0008] Disclosure of the invention

[0009] The toroidal transformer according to the invention, with the features of claim 1, has the advantage that a high robustness of the toroidal transformer can be achieved in a densely packed design. The toroidal transformer can thus enable a high energy transmission density with low core and winding losses. The toroidal transformer integrates a leakage inductance, which can enable soft switching of the semiconductors of a controlling electronic circuit. This is achieved according to the invention by the toroidal transformer comprising a first toroidal core and a second toroidal core, wherein the second toroidal core is arranged coaxially within the first toroidal core. Furthermore, the toroidal transformer comprises a primary winding and a secondary winding. The primary winding has first turns that enclose the first toroidal core.The secondary winding has two turns, with each second turn enclosing both the first and second toroidal cores. Thus, the first toroidal core forms a primary inductance, and the second toroidal core a leakage inductance, which creates a magnetic flux leakage in the space between the primary and secondary windings. The coaxial arrangement of the second toroidal core within the first toroidal core enables the compact and robust design of the toroidal transformer. Furthermore, arranging the second toroidal core within the first toroidal core reduces the magnetic flux density escaping into the environment, particularly in the areas between the cores where parts of the windings are located and could be inductively heated by external fields. The primary and secondary windings preferably enclose the first and second toroidal cores completely.This allows the available winding and core volume to be used optimally, e.g. by using a single layer of winding, thus minimizing core and winding losses.

[0010] The dependent claims describe preferred embodiments of the invention. Preferably, the second toroidal core is circumferentially divided into several second segments, with a gap arranged between the second segments. Particularly preferably, the second toroidal core is divided into four second segments. The gap preferably extends parallel to an axial direction of the toroidal core transformer. This achieves a reduced effective core permeability and sufficient current-carrying capacity of the ferrite core through shearing.

[0011] Preferably, the first toroidal core is divided into several first segments, with the first segments abutting each other. In particular, the first segments are flush against each other, thus reducing the magnetic resistance of the first toroidal core. The segmented design of the first toroidal core can alleviate mechanical stresses in the first toroidal core, which may be caused by thermal expansion. By reducing these mechanical stresses, the magnetic properties of the first toroidal core can be improved due to reduced stress-induced effects.

[0012] The toroidal transformer preferably comprises a cooling housing that encloses the first toroidal core at least circumferentially. The cooling housing is adjacent to the primary and secondary windings, particularly via a gap filled with thermally conductive potting compound. This allows heat to be dissipated uniformly from the toroidal transformer, resulting in a more homogeneous temperature distribution and reduced mechanical stresses within the transformer. These improvements, in turn, can enhance the magnetic properties and current-carrying capacity of the toroidal transformer.

[0013] The first and / or second toroidal cores are preferably ferrite cores, particularly made of a soft magnetic ferrite. Ferrites have virtually no electrical conductivity, resulting in almost no eddy current losses and thus enabling operation at high frequencies. However, ferrites are brittle and prone to cracking. The inventive design with toroidal cores avoids more complex core shapes with electromagnetically (losses) and thermomechanically unfavorable corners or varying wall thicknesses, and thus enables the robust and cost-effective use of ferrite cores. Alternatively, the first and / or second toroidal core can be made of a material with comparable properties, particularly as a powder core of a low-permeability material.

[0014] Preferably, the first and second windings, particularly on the first toroidal core, are arranged side by side. Even more preferably, the first and second windings are arranged alternately side by side. This minimizes the interference fields generated outside the transformer and keeps the eddy currents and losses induced in conductive cooler housing materials low. This can enable more efficient operation of the toroidal transformer while requiring less space.

[0015] In an axial direction, the first toroidal core has a first height and the second toroidal core has a second height. The first height is preferably equal to the second height. This can enable a compact and robust design for the toroidal transformer.

[0016] Preferably, the difference between the inner diameter of the first toroidal core and the outer diameter of the second core corresponds to twice the diameter of the primary winding. The diameter of the primary winding is understood to be the outer diameter of the electrical conductor or cable, particularly with insulation or sheathing. This allows the space between the cores to be limited to the dimensions necessary for the winding, thereby minimizing the overall dimensions of the transformer. This close spatial arrangement of the winding and core facilitates heat dissipation from the transformer to the heat sink. For example, in an 11 kW transformer, the dimensions of the first toroidal core can be limited to an outer diameter of approximately 50 mm and the outer diameter of the second toroidal core to approximately 25 mm, with core heights in the range of 30 mm.This allows for high performance of the toroidal transformer even in a small installation space.

[0017] The primary winding and / or the secondary winding preferably comprises a plurality of electrically insulated conductors, which in particular form a high-frequency litz wire. This reduces the winding losses of the toroidal transformer at high switching frequencies.

[0018] In particular, the primary winding and / or the secondary winding comprises a bundle of at least 800 electrical conductors forming a high-frequency litz wire. The turns ratio of the toroidal transformer can be defined by the ratio of the number of electrical conductors in the primary winding to the number of electrical conductors in the secondary winding.

[0019] Preferably, the primary and secondary windings comprise between 10 and 20 turns. In particular, the primary and secondary windings each comprise 15 first turns and 15 second turns. This allows for efficient operation of the toroidal transformer while maintaining cost-effective manufacturing.

[0020] Furthermore, the invention relates to a charging device comprising a previously described toroidal transformer for potential-free voltage conversion. The toroidal transformer forms a leakage field transformer, which, with simple and cost-effective manufacturing, enables reliable voltage conversion in the charging device. The first toroidal core forms a main inductance, and the second toroidal core forms a current-limiting leakage inductance, which can enable soft switching of the semiconductors of a controlling electronic circuit.

[0021] Brief description of the drawings

[0022] A preferred embodiment of the invention is described in detail below with reference to the accompanying drawings. The drawing shows:

[0023] Figure 1 shows a schematic perspective view of a

[0024] toroidal transformer according to a preferred embodiment of the invention and

[0025] Figure 2 is a schematic perspective view of the

[0026] Toroidal transformer with a cooling housing according to the preferred embodiment of the invention.

[0027] Embodiments of the invention Preferably, all identical components, elements and / or units in all figures are provided with the same reference numerals.

[0028] The following section describes in detail a toroidal transformer 1 for a charging device with reference to Figures 1 and 2.

[0029] Figure 1 shows the toroidal transformer 1, which has a first toroidal core 10 and a second toroidal core 20. The second toroidal core 20 is arranged coaxially to the first toroidal core 10 and is located inside the opening of the first toroidal core 10.

[0030] The first toroidal core 10 has a first height h1, which corresponds to a second height h2 of the second toroidal core 20. The first height h1 and the second height h2 are measured along an axial direction XX of the toroidal core transformer 1. Two opposing axial surfaces of the first toroidal core 10 and the second toroidal core 20 can thus be arranged coplanarly to each other.

[0031] The second toroidal core 20 is divided into four second segments 21. The second segments 21 are of equal size and each is separated from the others by a gap 22. The four gaps 22 between the four second segments 21 extend parallel to the axial direction XX. The magnetic resistance of the second toroidal core 20 can be influenced by the width of the gap 22, whereby increasing the width of the gap 22 increases the magnetic resistance of the second toroidal core 20. The gaps 22 are preferably air gaps or filled with a plastic or other electrically non-conductive material such as ceramic or the like.

[0032] The first toroidal core 10 is divided into four first segments 11, which are flush against each other. This allows the first segments 11 to be mechanically decoupled from one another, thus reducing mechanical stresses. The flush contact of the first segments 11 also results in a low magnetic resistance of the first toroidal core 10. The sub-segments can be fixed to each other, for example, by taping or thin, elastic adhesive. Furthermore, the toroidal transformer 1 has a primary winding 30. The primary winding 30 comprises fifteen first turns, each of which encircles the first toroidal core 10.

[0033] Furthermore, the toroidal transformer 1 has a secondary winding 40. The secondary winding 40 comprises fifteen second turns 41, with each second turn 41 enclosing both the first toroidal core 10 and the second toroidal core 20.

[0034] During operation of the toroidal transformer 1 in a charging device, an alternating voltage, particularly with frequencies greater than 100 kHz, is preferably applied to the primary winding 30. Applying the alternating voltage to the primary winding 30 induces an alternating magnetic flux in the first toroidal core 10. This alternating magnetic flux, in turn, induces a voltage in the secondary winding 40. Under secondary-side load, the alternating voltage applied to the primary winding 30 also induces a magnetic leakage flux in the second toroidal core 20.

[0035] The primary winding 30 and the secondary winding 40 are designed as high-frequency stranded wires, which enable the transmission of high frequencies with low winding losses. A high-frequency stranded wire preferably comprises a bundle of over 800 individual electrical conductors.

[0036] The first toroidal core 10 and / or the second toroidal core 20 are preferably made of a soft magnetic ferrite. Soft magnetic ferrites have low electrical conductivity, which reduces eddy current losses at high frequencies and gives the toroidal transformer 1 high transmission efficiency.

[0037] The first toroidal core 10 and the second toroidal core 20 are separated from each other circumferentially by a gap. The width of the gap between the first toroidal core 10 and the second toroidal core 20 preferably has the diameter of a conductor bundle of the primary winding 30.

[0038] Figure 2 shows the toroidal transformer 1, which is arranged in a cooling housing 50. The cooling housing 50 encloses the first toroidal core 10 at least in the circumferential direction U and borders the primary winding 30 and the secondary winding 40.

[0039] The toroidal transformer 1 is preferably encapsulated in a plastic that is particularly thermally conductive, thereby mechanically stabilizing the toroidal transformer 1 and enabling efficient heat dissipation to the cooling housing 50. The cooling housing 50 can, for example, be connected to a cooling element or have self-cooling structures to dissipate heat.

[0040] A first outer diameter d1 of the first ring core 10 is preferably 50 mm and is twice as large as a second outer diameter d2 of the second ring core 20, which is preferably 25 mm.

[0041] The primary windings 30 and the secondary windings 40 can preferably be contacted via a plug or solder connection, which is not shown in Figures 1 and 2.

[0042] By using the toroidal transformer 1 in a charging device, such as an on-board charger, reliable and efficient potential-free voltage conversion can be achieved. The inclusion of a leakage inductance in the form of the second toroidal core 20 in the toroidal transformer 1 allows the voltage-transforming function of the transformer to be combined with the current-limiting function of an inductor in a single compact component. The ring-shaped design of the first toroidal core 10 and the second toroidal core 20 reduces the risk of breakage of either core, thus ensuring high robustness and load-carrying capacity of the toroidal transformer 1.

Claims

Claims 1. Toroidal transformer comprising a first toroidal core (10), a second toroidal core (20), a primary winding (30) and a secondary winding (40), wherein the second toroidal core (20) is arranged coaxially within the first toroidal core (10), wherein the primary winding (30) has first turns (31) enclosing the first toroidal core (10) and wherein the secondary winding (40) has second turns (41), each second turn (41) enclosing both the first toroidal core (10) and the second toroidal core (20).

2. Toroidal transformer according to claim 1, wherein the second toroidal core (20) is divided circumferentially into several second segments (21), wherein a gap (22) is arranged between the second segments (21).

3. Toroidal transformer according to one of the preceding claims, wherein the first toroidal core (10) is divided into several first segments (11), wherein the first segments (11) are in particular flush against each other.

4. Toroidal transformer according to one of the preceding claims, comprising a cooling housing (50) which encloses the first toroidal core (10) at least in the circumferential direction (U), wherein the cooling housing (50) adjoins the primary winding (30) and the secondary winding (40).

5. Toroidal transformer according to any of the preceding claims, wherein the first toroidal core (10) and / or the second toroidal core (20) is a ferrite core.

6. Toroidal transformer according to one of the preceding claims, wherein the first turns (31) and the second turns (41), in particular on the first ring core (10), are arranged next to each other, in particular alternating.

7. Toroidal transformer according to one of the preceding claims, wherein in an axial direction (XX) the first toroidal core (10) has a first height (h1) and the second toroidal core (20) has a second height (h2), wherein the first height (h1) is equal to the second height (h2).

8. Ring transformer according to one of the preceding claims, wherein a difference between an inner diameter of the first ring core (10) and an outer diameter (d2) of the second ring core (20) corresponds to twice the diameter of the primary winding (30).

9. Ring transformer according to one of the preceding claims, wherein the primary winding (30) and / or the secondary winding (40) comprises a plurality of electrically insulated electrical conductors, which in particular form a high-frequency litz wire.

10. Toroidal transformer according to one of the preceding claims, wherein the primary winding (30) and the secondary winding (40) comprise between 10 and 20 turns, in particular 15.

11. Charging device comprising a toroidal transformer (1) according to one of the preceding claims for potential-free voltage conversion.

Images