FR3092469A1 - Power electronics system for electric or hybrid vehicles - Google Patents

Abstract

The invention relates to a power electronics system (SYS) for an electric or hybrid vehicle, comprising: - a metal casing (CA) comprising a first housing (LOG1) enclosing at least one power electronics component (IND), a lower wall (PAI) of said first housing (LOG1) being cooled by a cooling liquid (WAT) outside of said first housing (LOG1), said cooling liquid (WAT) circulating in a cooling circuit (CR) s 'extending externally to said metal casing (CA), - a second housing (LOG2), in thermal contact with said lower wall (PAI) and in which said cooling liquid (WAT) circulates, said system (SYS) being characterized by that said at least one power electronic component (IND) is immersed in a dielectric coolant (OIL) confined in said first housing (LOG1). Figure for the abstract: Figure 1

Description

Power electronics system for electric or hybrid vehicles

The present invention relates generally to the field of electrical engineering and relates more specifically to a power electronics system for an electric or hybrid vehicle.

Power electronic systems for electric or hybrid vehicles include components that must withstand several tens of amperes and require specific cooling. Conventionally, power switches such as IGBT (Insulated Gate Bipolar Transistor) transistors benefit from optimized thermal conduction by being in direct thermal contact with a water cooling plate. However, certain large-volume components, such as filters, voltage transformers or inductors, releasing less thermal power than IGBT transistors, are generally cooled either by natural air convection in a confined space, or by indirect thermal contact. with a water cooling plate. In the latter case, a very low thermal conductivity resin of the order of 1W/m/°C (Watt per meter per degree Celsius) surrounding these components does not allow good evacuation of the heat by the water cooling plate. . These large-volume components cannot be optimally cooled without generating upper limit temperature constraints of the coolant used, or minimum volume of these components, which increases the cost of the power electronics system that uses them.

The document FR3047109 discloses a power electronics system for an electric or hybrid vehicle charger, in which the casing of an inductor bathes in water from a water plate used for cooling other components. A gasket must be compressed between a choke housing mounting plate and the top wall of the water plate around the choke housing to maintain the system seal. This cooling solution increases the thermal conductance between the inductor and the coolant, but presents the risk of coolant leakage.

One of the aims of the invention is to remedy at least some of the drawbacks of the prior art by providing a power electronics system which efficiently cools its power electronics components, at lower cost and with reduced bulk.

To this end, the invention proposes a power electronics system for an electric or hybrid vehicle, comprising:

- a metal casing comprising a first housing enclosing at least one power electronics component, a lower wall of said first housing being cooled by a cooling liquid outside of said first housing, said cooling liquid circulating in a cooling circuit extending externally to said metal casing,

- a second housing, in thermal contact with said lower wall and in which said cooling liquid circulates,

said system being characterized in that said at least one power electronics component is immersed in a heat transfer dielectric liquid confined in said first housing.

Thanks to the invention, the power electronics component enclosed in the first housing benefits from the cooling liquid used for components with a very high thermal load, while having an autonomous dielectric liquid cooling solution. This dielectric liquid is cooled by the coolant in the second housing, and does not change phase. The solution proposed by the invention is therefore not very complex, inexpensive and compact.

According to an advantageous characteristic of the system according to the invention, internal vertical walls of said first housing comprise circulation ducts arranged vertically.

Said ducts are capable of promoting circulation by convection of said dielectric liquid from an upper part of said first housing towards said lower wall. Compared to a conventional solution for cooling by thermal conduction of a resin with low thermal conductivity (of the order of unity), the system according to the invention makes it possible to create an active and natural circulation of the dielectric liquid in direct contact with the power electronics component to be cooled. In addition, the heat exchange coefficient between the coolant and this component is much higher than air circulation inside the first housing. The transport of calories by this active and natural circulation of dielectric liquid significantly reduces the overall thermal resistance between the power electronics component and the cooling liquid circulating in the second housing. The temperature of the component to be cooled is thus reduced, as well as the compactness of the system, compared to the prior art.

Advantageously, said first housing, said second housing and said ducts are made in a single piece obtained by molding said metal casing. This manufacture of the metal casing increases the thermal conductance between the two housings, reduces the costs of the assembly and the risk of leakage of dielectric liquid. In addition, this massive one-piece part makes it possible to limit vibration problems due to chopped currents that may pass through the power electronics component.

Advantageously, said ducts are formed by tunnels in said vertical walls of said metal casing, connecting an upper part of said housing to a lower part of said housing. This realization of the ducts promotes the circulation of the dielectric liquid thanks to the temperature differences in the ducts and in the first housing.

Alternatively, said ducts are vertical grooves formed in said vertical walls of said metal casing. This realization of the ducts is simpler than that in the form of tunnels.

Advantageously, said first housing comprises a variable-volume reservoir. This characteristic makes it possible to keep the enclosure of the first housing at atmospheric pressure. Without this characteristic, the pressure due to the variations in volume of the dielectric liquid under the effect of the temperature can rise to 1.3 bars, which requires reinforcing the tightness and robustness of the metal casing.

Preferably, said cooling liquid is glycol water and said heat transfer dielectric liquid is oil or another dielectric liquid with low viscosity and high variation in density. These liquids have the advantage of being inexpensive and good thermal conductors.

Advantageously, the power electronics system according to the invention comprises power switches arranged on a portion of an upper wall of said second housing, said second housing extending under said first housing and laterally beyond said first housing, so that its upper wall defines a platform cooled by said cooling liquid and on which said power switches are arranged. This integration of the power switches in the power electronics system according to the invention makes it possible to reduce its size.

Also advantageously, a thermally conductive elastomer layer is placed between said lower wall and said power electronics component, and/or a deformable plastic part is secured to said power electronics component and to said metal casing. These characteristics make it possible to limit the vibrations of the power electronics component when it is traversed by chopped currents.

Preferably, said first housing comprises at least one coil surrounding a ferromagnetic body. Thus the large volume components of the electric or hybrid vehicle, such as its isolation transformer, are effectively cooled.

Alternatively, said first housing comprises vertical plates on which power electronics components are arranged, said plates electromagnetically separating different groups of electronic components. These components are for example capacities. Such an arrangement also allows easy maintenance of the power electronics system according to the invention.

Preferably, said cooling circuit of the power electronics system according to the invention comprises at least one pump, and a radiator arranged at the front of the vehicle. In other words, the general cooling circuit of the vehicle, or a loop thereof, is used.

Other characteristics and advantages will appear on reading a preferred embodiment described with reference to the figures in which:

represents a power electronics system according to the invention, in this preferred embodiment,

represents a view in horizontal section of the power electronics system according to an embodiment variant of this preferred embodiment,

represents a power electronics system according to the invention, in another variant of this preferred embodiment,

shows a horizontal sectional view of the power electronics system in yet another variant embodiment,

represents a cooling circuit used in the power electronics system according to the invention, in this preferred embodiment,

shows an arrangement of power electronics components in a variant of this preferred embodiment of the invention.

According to a preferred embodiment of the invention represented in FIG. 1 , the power electronics system SYS according to the invention comprises an aluminum casing CA, intended to accommodate various power electronics components of an electric vehicle or hybrid, such as a transformer of a current-DC-DC converter, and power transistors of the IGBT or MOSFET type (from the English “Metal Oxide Semiconductor Field Effect Transistor”).

The aluminum casing CA comprises a first housing LOG1 enclosing an inductance IND formed of a ferromagnetic body CFM around which a winding WIN is wound. The chopped current flowing through this inductor IND is supplied by a sealed connection terminal block, not shown, integrated for example into the cover COUV of the aluminum casing CA, closing the first housing LOG1 in its upper part also in a sealed manner. The aluminum casing CA being arranged in a vertical direction V in this embodiment of the invention, the cover COUV is located on the upper part of the aluminum casing CA, the notions "upper" and "lower" in this application making reference to the position according to this vertical direction V.

The inductor IND being subjected to vibrations due to the chopping of the current flowing through it, a thermally conductive elastomer layer or film CTE is inserted between the ferromagnetic body CFM and a lower wall PAI of the first housing LOG1. This elastomeric film is for example that used in the document FR2996047. As a variant, the inductor IND is not subjected to a chopped current or to vibrations requiring such an elastomer film.

The lower wall PAI of the first housing LOG1 is cooled by the glycol water WAT contained in a second housing LOG2 of the aluminum casing CA. This second housing LOG2 is located under the first housing LOG1 and extends laterally beyond the first housing LOG1, so as to form a platform whose upper wall PS2 is cooled by the glycol water WAT contained in this second housing LOG2.

This second housing LOG2 forms part of a cooling circuit CR represented in FIG . Thus the glycolated water WAT circulates thanks to a pump P, in a network of heat-conducting channels CWG arranged in the second housing LOG2. This WAT glycol water is cooled during its passage through the vehicle's radiator R, located at the front thereof.

On the platform created by the lateral extension of the second LOG2 slot in the CA aluminum casing, there are IP power switches of the IGBT or MOSFET type. They are integrated on a thermally conductive support SUP, for example made of copper, the support SUP itself being glued to the upper wall PS2 of the second housing LOG2. IP power switches are therefore cooled by the free air that surrounds them and by this lateral extension of the AC aluminum casing which acts as a water plate conventionally used to cool this type of power electronics component.

Evacuation of the heat dissipated by the inductance IND in the first housing LOG1 is partly done by conduction of this heat through the lower wall PAI of the first housing LOG1, towards the colder glycol water WAT, which evacuates this heat in the CR cooling circuit.

In order to improve the evacuation of this heat dissipated from the inductance IND towards the lower wall PAI, the inductance IND is immersed in an oil-type heat transfer dielectric liquid OIL. As a variant, a liquid with low viscosity and high variation in density of the Novec 3M® type is used. This type of liquid is more expensive but makes it possible to obtain a higher speed of the flow created by the difference in density.

The heat transfer dielectric liquid OIL is in direct contact with the inductor IND. It circulates in the first housing LOG1 without an electric pump but thanks to the difference in density created by the temperature difference between the inductance IND and the glycol water WAT contained in the second housing LOG2.

Circulation ducts CC are hollowed out in the vertical internal walls PVI of the aluminum casing CA, and allow the passage of the heat transfer dielectric liquid OIL from an upper part PSL of the first housing LOG1 to a lower part PIL of the first housing LOG1. These lateral channels arranged vertically are for example five in number and are arranged angularly and regularly around the inductance IND.

It should be noted that the diameter and the number of oil passages made in the PVI walls of the CA aluminum housing are to be adapted according to the thermal power generated by the power electronics component to be cooled present in the first housing LOG1. The diameter of these ducts is typically in a range of 1mm (millimeter) to 10mm depending on the thermal power to be evacuated. The diameter must be all the more important as the dielectric liquid used is viscous.

The inductance IND to be cooled heats the dielectric heat transfer liquid OIL and thus decreases the density of the dielectric liquid OIL, which then rises in the first housing LOG1 and enters the circulation conduits CC in the upper part PSL of the first housing LOG1. In these CC circulation conduits the dielectric liquid OIL is cooled which increases its density. Having become heavier, it then descends into the circulation ducts CC towards the lower part PIL of the first housing LOG1. This circulation, represented by the solid arrows in FIG. 1 , is carried out without a pump. It is reliable and does not require energy consumption.

In order to compensate for the variation in the volume of the dielectric liquid OIL according to its temperature variations, a deformable reservoir RES is in communication with the first housing LOG1 by a conduit and deforms to store or restore the dielectric liquid OIL from/to the first housing LOG1. This reservoir RES is arranged in a recess EV of the aluminum casing CA and is connected in a sealed manner to the first housing LOG1. This tank RES makes it possible to maintain an atmosphere pressure in the first housing LOG1.

In a variant embodiment, the conduits for the circulation of the dielectric heat transfer liquid OIL are formed by vertical grooves RV on the internal vertical walls PVI of the first housing LOG1, as shown in FIG .

FIG. 3 shows yet another variant embodiment, in which a deformable plastic part PPD is secured on the one hand to the metal casing CA, for example by screws, and to the inductor IND on the other hand, for example by screw. This PPD plastic part blocks the inductance solidly in the vertical direction and the horizontal direction, and absorbs the vibrations of the inductance when it is traversed by a chopped current. The CTE elastomer film is no longer necessary. However, it can be used in combination with this PPD plastic part to further improve vibration absorption.

Figure 4 shows a horizontal section of the power electronics system according to the invention, in yet another alternative embodiment of this preferred embodiment. In this variant embodiment, the oil circulation ducts are made by grooves RV as in FIG . The power electronics component IND to be cooled in this embodiment variant is a transformer whose ferromagnetic body CFM is annular, the windings WIN of the transformer being wound around this annular ferromagnetic body CFM passing inside the ferromagnetic body annular CFM. A PPD deformable plastic part absorbs transformer vibrations by being housed in the CFM ring body. Here it takes the form of a three-pointed star whose points put the CFM annular body under stress and hold it to the aluminum casing by screws located under the PPD deformable plastic part.

Figure 6 shows the first housing LOG1 in yet another alternative embodiment of the preferred embodiment described in this application. In this variant, the first housing LOG1 is parallelepipedic and comprises several vertical plates PLA on which are fixed power electronic components COP, such as capacitors or super-capacitors. COP components can also be fixed directly to the vertical walls PVI of the first housing LOG1. PLA plates are for example solid metal plates or metal grids and separate different groups of COP components according to their electromagnetic emission characteristics. This arrangement makes it possible to suppress or limit the electromagnetic radiation between the various groups of COP components.

It should be noted that other variants of this preferred embodiment are of course possible. For example, the casing CA is alternatively made of cast iron, which allows the system according to the invention to be massive enough not to require an elastomer film or a plastic part to limit the vibrations of the inductive component IND, the casing not undergoing so no vibration. In another variant, the casing CA is made in several pieces assembled by screwing, in particular the first housings LOG1 and LOG2 are for example two separate parts joined together. In yet another variant, the second CWG housing does not have CWG channels but directly a glycol water tank. A coolant other than glycol water can of course be used to cool the power electronics placed on the AC housing platform, for example non-glycol water.

Claims (12)

Power electronics system (SYS) for electric or hybrid vehicles, comprising:
- a metal casing (CA) comprising a first housing (LOG1) enclosing at least one power electronic component (IND), a lower wall (PAI) of said first housing (LOG1) being cooled by a cooling liquid (WAT) outside said first housing (LOG1), said cooling liquid (WAT) circulating in a cooling circuit (CR) extending externally to said metal casing (CA),
- a second housing (LOG2), in thermal contact with said lower wall (PAI) and in which said cooling liquid (WAT) circulates,
said system (SYS) being characterized in that said at least one power electronic component (IND) is immersed in a dielectric coolant (OIL) confined in said first housing (LOG1). Power electronics system (SYS) according to claim 1, characterized in that internal vertical walls (PVI) of said first housing (LOG1) have circulation ducts (CC) arranged vertically. Power electronics system (SYS) according to claims 1 and 2, characterized in that said first housing (LOG1), said second housing (LOG2) and said conduits (CC) are made in a single piece obtained by molding said housing metallic (CA). Power electronics system (SYS) according to any one of claims 2 to 3, characterized in that said conduits (CC) are formed by tunnels in said vertical walls (PVI) of said metal casing (CA), connecting a upper part (PSL) of said housing to a lower part (PIL) of said housing. Power electronics system (SYS) according to any one of claims 2 to 3, characterized in that said conduits are vertical grooves (RV) formed in said vertical walls (PVI) of said metal casing (CA). Power electronics system (SYS) according to any one of claims 1 to 5, characterized in that said first housing (LOG1) comprises a variable volume reservoir (RES). Power electronics system (SYS) according to any one of claims 1 to 6, characterized in that said cooling liquid (WAT) is glycol water and said dielectric coolant (OIL) is oil. or another dielectric liquid with low viscosity and large variation in density. Power electronics system (SYS) according to any one of claims 1 to 7, characterized in that it comprises power switches (IP) arranged on a portion of an upper wall (PS2) of said second housing ( LOG2), said second housing (LOG2) extending under said first housing (LOG1) and laterally beyond said first housing (LOG1), so that its upper wall (PS2) defines a platform cooled by said cooling liquid (WAT) and on which said power switches (IP) are arranged. Power electronics system (SYS) according to any one of claims 1 to 8, characterized in that a thermally conductive elastomeric layer (CTE) is disposed between said bottom wall (PAI) and said electronics component. power (IND), and / or a deformable plastic part (PPD) is secured to said power electronic component (IND) and to said metal casing (CA). Power electronics system (SYS) according to any one of claims 1 to 9, characterized in that said first housing (LOG1) has at least one coil (WIN) surrounding a ferromagnetic body (CFM). Power electronics system (SYS) according to any one of claims 1 to 9, characterized in that said first housing (LOG1) comprises vertical plates (PLA) on which are arranged power electronic components (COP ), said plates (PLA) electromagnetically separating different groups of electronic components (COP). Power electronics system (SYS) according to any one of claims 1 to 11, wherein said cooling circuit (CR) comprises at least one pump (P), and a radiator (R) arranged in front of the vehicle.