Electromagnetic components for resonant converters

Abstract

The present invention relates to an electromagnetic component for an LLC resonant converter, the electromagnetic component comprising: a first compartment, the first compartment accommodating a single-phase transformer, the secondary winding of the single-phase transformer being wound around a first magnetic core (N1), and the primary winding of the single-phase transformer being wound around the secondary winding; a second compartment, the second compartment accommodating a series inductor of the converter, the series inductor being wound around a second magnetic core (N2), the winding of the series inductor having a first winding, the first winding being wound around the second magnetic core and being electrically connected to a terminal of the primary winding, the other terminal of the primary winding being electrically connected to a second winding of the series inductor, the second winding being wound around the first winding.

Description

Technical Field

[0001] The present invention relates generally to the field of electrical engineering, and more particularly to an electromagnetic assembly for a DC to DC converter in an electric or hybrid vehicle charger. Background Art

[0002] An electric or hybrid vehicle charger generally comprises two conversion stages, namely a first power correction rectifier stage and a second DC to DC conversion stage intended to adapt the voltage rectified by the first stage to the battery voltage. This second conversion stage advantageously comprises a galvanic isolation transformer, one of the roles of which is to ensure the electrical safety of the user when charging the traction battery of such a vehicle.

[0003] When the second conversion stage is an LLC resonant converter, such as Figure 1 As shown, it can be observed that common mode currents occur during operation of the charger, which makes it impossible to meet the requirements for electromagnetic compatibility stipulated in the standards.

[0004] In particular, this resonant converter comprises a transistor bridge with transistors T1, T2, T3 and T4, which is connected at the input to a DC bus whose terminals each have an impedance Zc relative to the body of the vehicle in which the charger is housed. The transistor bridge is connected at the output to an LLC structure comprising a series inductor Lr, a primary winding L1 of a transformer and a capacitor Cr connected in series. The secondary winding L2 of the transformer is connected to the input of a diode bridge, which itself is connected at the output to a smoothing capacitor and to the terminals HV+ and HV- of the vehicle battery. When measuring the performance in terms of electromagnetic compatibility, a line impedance stabilizer network RSIL is inserted between the smoothing capacitor and the battery, and a receiver R is inserted, these actions making it possible to place the charger in a known electrical environment and to perform the measurements.

[0005] During operation, the voltage V across the terminals of transistor T3 A At 0V and the DC bus value V DC The voltage V across the terminals of transistor T4 changes alternately. B Also at 0V and V DC If the B With voltage V A This alternation allows AC current to flow in the primary winding L1 of the converter's transformer.

[0006] When the voltage V across the terminals of transistor T4 B From 0V to value V DC, the presence of common-mode currents can be observed, as indicated by the filled closed dashed arrows, flowing in particular into the stray common-mode capacitances between the connection point B between capacitor Cr and the primary winding L1 of the transformer on the one hand and the vehicle body on the other hand.

[0007] When the voltage V across the terminals of transistor T3 A From 0V to value V DC , the appearance of common-mode current can be observed, as indicated by the non-closed dashed arrows, specifically flowing into:

[0008] - in the stray common-mode capacitance between the connection point A between the drain of transistor T3 and the series inductor Lr on the one hand and the vehicle body on the other hand,

[0009] - It also flows into the stray capacitance Cplr between the series inductor Lr and the secondary winding L2 of the transformer.

[0010] On the one hand, when the voltage V across the terminals of transistor T4 B From 0V to value V DC When, and on the other hand when the voltage V across the terminals of transistor T3 A From 0V to value V DC Therefore, when the receiver R is placed across the terminals of one of the 50Ω resistors of the network RSIL (this resistor is connected to the ground of the vehicle, in this case the receiver R is a measuring instrument used to verify compliance with the electromagnetic compatibility standard), common mode current emissions greater than the authorized threshold are measured.

[0011] There are two main methods known for reducing common-mode current emissions in switched-mode power supplies. The first method is to eliminate the common-mode current at the source by eliminating stray capacitance, while the second method is to filter the current. In this second method, in the case of an LLC resonant converter, the series inductor Lr is usually made symmetrical. To this end, an inexpensive solution is to use the leakage inductance of the transformer as a series inductor, but this is mainly suitable for low-power converters. Another solution described in document EP 2299456 is to integrate the series inductor into the converter in a magnetically and geometrically symmetrical manner, but this solution is expensive and cumbersome. Summary of the invention

[0012] One of the objects of the present invention is to at least partially remedy the drawbacks of the prior art by providing an electromagnetic assembly for an LLC resonant converter which eliminates common mode currents while being compact, inexpensive and capable of being used in high power converters.

[0013] To this end, the present invention proposes an electromagnetic component for an LLC resonant converter, the electromagnetic component comprising a ferrite structure, wherein the ferrite structure comprises:

[0014] - a first compartment housing a single-phase transformer comprising a secondary winding wound around a first magnetic core and a primary winding wound around said secondary winding,

[0015] - a second compartment housing a series inductor of said LLC resonant converter, the series inductor comprising a winding wound around a second magnetic core,

[0016] The electromagnetic component is characterized in that the winding of the series inductor includes a first winding portion, which is wound around the second magnetic core and electrically connected to a terminal of the primary winding, and the other terminal of the primary winding is electrically connected to a second winding portion of the series inductor, and the second winding portion is wound around the first winding portion, and the terminals of the series inductor and primary winding assembly are formed by the terminals of the first winding portion and the terminals of the second winding portion.

[0017] By means of the invention, the series inductor Lr is shared between two winding parts arranged electrically symmetrically with respect to the primary winding L1 of the transformer, making it possible to eliminate common mode currents. The provision of this symmetry has the advantage, among other things, that it exhibits a small volume, and also reuses the existing ferrite structure of the LLC resonant converter to implement the invention. Since the structure is compact, it is also inexpensive in terms of materials.

[0018] Preferably, the first winding portion and the second winding portion have the same number of turns, so as to make the resonant structure of the converter more symmetrical.

[0019] The invention also relates to an LLC resonant converter, characterized in that the LLC structure of the converter comprises a first capacitor connected in series to the input of the electromagnetic assembly according to the invention, the output of which is connected to a second capacitor of the same value. Such a converter has the same advantages as the electromagnetic assembly according to the invention and enables further limiting of common mode currents by also providing symmetry to the capacitors of the resonant structure of the converter.

[0020] The invention finally relates to a charger for an electric or hybrid motor vehicle, comprising a resonant converter according to the invention, wherein the converter comprises a transistor bridge connected at the input to a DC bus and at the output to the LLC structure, the secondary winding of the transformer of the LLC structure being connected to a rectifier stage, the two terminals of the DC bus having an impedance of the same value relative to the body of the vehicle. Such a charger has the same advantages as the converter according to the invention, while the leakage current is further limited by the symmetry of the impedance of the DC bus with respect to the body. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features and advantages will become apparent from a reading of a preferred embodiment described with reference to the accompanying drawings, in which:

[0022] - has been described with reference to the prior art Figure 1 shows a conventional LLC resonant converter,

[0023] - Figure 2 Shown for Figure 1 The LLC resonant converter is optimized for electromagnetic components,

[0024] - Figure 3 The electromagnetic assembly according to the invention is shown in this preferred embodiment of the invention,

[0025] -as well as, Figure 4 An LLC resonant converter according to the invention is shown in this preferred embodiment of the invention.

[0026] In this application, for simplicity, the same reference numerals are used to identify the same elements that appear in different embodiments or only in different figures. DETAILED DESCRIPTION

[0027] according to Figure 3 A preferred embodiment of the present invention shown reuses the ferrite structure S of the electromagnetic component optimized for LLC resonant converter according to the prior art, such as Figure 2 shown.

[0028] refer to Figure 2 , can be produced by existing technology as follows Figure 1 Electromagnetic components:

[0029] - firstly forming a secondary winding L2 of the transformer around a first central core N1 of the ferrite structure S, the input and output terminals of which correspond to the connection points C and D;

[0030] - the primary winding L1 of the transformer is then formed around the secondary winding L2; the input terminal of the primary winding corresponds to the connection point B;

[0031] - forming a winding of a series inductor Lr around a second central core N2 of the ferrite structure S using the lead-out wires of the primary winding L1 ; the output terminal of the series inductor Lr corresponds to the connection point A.

[0032] refer to Figure 3 , according to the invention, the ferrite structure S is reused in different ways:

[0033] - Firstly, a secondary winding L2 of the transformer is formed around a first central core N1 of the ferrite structure S, the input and output terminals of which correspond to Figure 4 The connection points C and D;

[0034] - A winding of a first winding portion Lr1 of a series inductor is then formed around the second magnetic core N2; one of the terminals of this first winding portion Lr1 corresponds to Figure 4 The connection point A in

[0035] - The primary winding L1 of the transformer is formed around the secondary winding L2 of the transformer using the wire of the first winding portion Lr1 opposite to the connection point A, and then the second winding portion Lr2 of the series inductor is formed around the first winding portion Lr1 of the series inductor using the remaining wire. The output terminal of the second winding portion Lr2 opposite to its connection to the primary winding L1 corresponds to the connection point B.

[0036] The first winding portion Lr1 and the second winding portion Lr2 are preferably formed with the same number of coil turns so that they have the same value of inductance. The wires used for these windings and winding portions are preferably made of copper.

[0037] Figure 4 The following table shows the Figure 3 The first winding portion Lr1 has a stray capacitance Cplr1 with the secondary winding L2 of the transformer, and the second winding portion Lr2 has a stray capacitance Cplr2 with the same value with the secondary winding L2 of the transformer.

[0038] Therefore, when the voltage V across the terminals of transistor T4 B From 0V to value V DC When , the occurrence of common mode current can be observed, as indicated by the filled closed dashed arrow, in particular flowing into the stray capacitance Cplr2 on the one hand and between point B and the vehicle body on the other hand.

[0039] When the voltage V across the terminals of transistor T3 A From 0V to value V DC , the appearance of common-mode current can be observed, as indicated by the non-closed dashed arrows, specifically flowing into:

[0040] - On the one hand, the stray common mode capacitance between point A and the car body,

[0041] - On the other hand, the stray capacitance Cplr1.

[0042] Therefore, the common-mode currents generated in the two above cases compensate each other to a much greater extent due to the symmetry of the series inductor, even though the series inductor is produced in a highly compact and geometrically asymmetric manner.

[0043] In order to make the LLC resonant converter according to the present invention more symmetrical, the capacitors of the resonant structure are formed by two capacitors Cr1 and Cr2 having the same value, the capacitor Cr1 being connected to point A on the one hand and to the source of the transistor T1 on the other hand, and the capacitor Cr2 being connected to the connection point B on the one hand and to the source of the transistor T2 on the other hand. A From 0V to value V DC When, and on the other hand when the voltage V B From 0V to value V DC The common-mode currents generated when switching will cancel each other out.

[0044] Of course, other embodiments of the invention can be considered, in particular it is possible to use magnetic materials with similar properties other than ferrite or copper in the electromagnetic assembly according to the invention. In addition, variant embodiments are possible, for example, the turns of the winding can use various conductor shapes, or in another variant, a reversible structure can be used instead of the diode bridge of the converter.

Claims

1. An electromagnetic component for an LLC resonant converter, the electromagnetic component comprising a ferrite structure (S), the ferrite structure (S) comprising: - a first compartment housing a single-phase transformer comprising a secondary winding (L2) wound around a first magnetic core (N1) and a primary winding (L1) wound around said secondary winding (L2), - a second compartment housing a series inductor of said LLC resonant converter, said series inductor comprising a winding wound around a second magnetic core (N2), The electromagnetic component is characterized in that the winding of the series inductor includes a first winding portion (Lr1), which is wound around the second magnetic core (N2) and electrically connected to a terminal of the primary winding (L1), the other terminal of the primary winding (L1) is electrically connected to a second winding portion (Lr2) of the series inductor, the second winding portion (Lr2) is wound around the first winding portion (Lr1), and the terminals of the series inductor and primary winding (L1) component are formed by the terminals of the first winding portion (Lr1) and the terminals of the second winding portion (Lr2).

2. The electromagnetic assembly according to claim 1, characterized in that The first winding portion (Lr1) and the second winding portion (Lr2) have the same number of turns.

3. An LLC resonant converter, characterized in that: The LLC structure of the converter comprises a first capacitor (Cr1) connected in series to the input of an electromagnetic assembly as claimed in claim 1 or 2, the output of which is connected to a second capacitor (Cr2) of the same value.

4. A charger for an electric or hybrid motor vehicle, the charger comprising a resonant converter as claimed in claim 3, wherein: The converter comprises a transistor bridge connected at the input to a DC bus and at the output to the LLC structure, the secondary winding (L2) of the transformer of the LLC structure being connected to a rectifier stage, the two terminals of the DC bus having an impedance (Zc) of the same value relative to the body of the vehicle.

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