TECHNICAL FIELD

The invention relates to a DC link capacitor for a capacitor arrangement like a switching cell of a power converter as an inverter for a rotary electrical machine like a motor for example in an electric vehicle.

BACKGROUND ART

DC link capacitor are well known to comprise a main body with a capacitive element and two electric terminals. Each one of the electric terminals is arranged to be electrically connected to one bus bar. The DC link capacitor can be integrated into a housing like a heat sink of a power converter. Generally, the DC link capacitor is glued/potted onto the housing such as a heat sink. An additional thermal component can be added to cool the DC link capacitor. This thermal component is a silicon or rubber band that can be arranged between the DC link capacitor and the heat sink or directly onto the bus bar. Any other kind of thermal compound, which is electrically not conductive, could be used. This thermal component allows to increase the cooling of the DC link capacitor. However, the thermal feature is fundamental for high power applications like electric vehicles and the cooling through the thermal component may not be enough.

DISCLOSURE OF INVENTION

Accordingly, an object of the invention is the provision of an improved DC link capacitor. In particular, a solution shall be proposed which allows for high cooling power and provides capacitor that can be easily assembled and compact.

The object of the invention is a DC link capacitor for a switching cell, the DC link capacitor being arranged to be electrically connected between at least two bus bars and comprising a capacitive element and at least two electric terminals, each

SUBSTITUTE SHEET (RULE 26) one being electrically connected to the capacitive element and to one of the bus bars. Further, the DC link capacitor further comprises a plate arranged to cool the capacitive element, the plate comprising a holding part for assembling the DC link capacitor onto a heat sink.

The plate allows to have two functions in one single element. Indeed, the plate is used to cool the DC link capacitor and to mount said DC link capacitor onto the heat sink. Thus, this plate allows to have a more compact and cheaper DC link capacitor. Indeed, the additional thermal element formed by a silicon or rubber band can be removed and the glue can be replaced by the plate.

Further, heat dissipation can be improved because the DC link capacitor is attached directly to the heat sink. Indeed, there is no additional element with no thermal feature like the glue.

According to one embodiment, the plate is arranged at a distance from the electric terminals. The plate and the electric terminals are separate components. Further, there is no electrical contact between the plate and the terminals. Thus, the plate is electrically insulated from the terminals. Similarly, the plate is electrically insulated from the bus bars connected to the terminals. The plate and the bus bars are separate components.

According to one embodiment, a material comprising at least one metallic component forms the plate. The cooling of the DC link capacitor can be increased compared to the cooling of a DC link capacitor containing a silicon or rubber band.

According to one embodiment, the DC link capacitor also comprises an insulated element that surrounds the capacitive element and partially accommodates the plate. The capacitive element can be overmolded into the insulated element. The insulated element can be a resin. The insulated element protects the capacitive element from external elements.

According to one embodiment, a part of the insulated element is arranged between the plate and the capacitive element. Thus, the plate is electrically insulated from the capacitive element. For example, the insulated element can be humidity-tight. In this way, the capacitor can be protected against unfavorable environmental conditions. According to one embodiment, the holding part being outside of the insulated element. Thus, the assembly of the DC link capacitor onto the heat sink is easier.

According to one embodiment, the holding part presents a length in a first direction which is greater than a length in said first direction of the insulated element. Thus, the assembly, in particular by screwing, of the DC link capacitor onto the heat sink is easier. According to another embodiment, the holding part can present a length in a first direction, which is equal to a length in said first direction of the insulated element.

According to one embodiment, the plate surrounds at least partially the capacitive element. Thus, the cooling of the capacitive element is increased.

According to one embodiment, the plate also comprises at least one lateral part extending from the holding part.

According to one embodiment, the lateral part extends inside the insulated element.

According to one embodiment, the plate comprises at least two lateral parts, each one extending from either side of the holding part to partially surround the capacitive element.

The invention also concerns a switching cell comprising a heat sink, at least one power module mounted on the heat sink, at least two bus bars each one being electrically connected to the power module to supply a DC voltage to said module, at least one DC link capacitor, as previously described, electrically connected to the bus bars through the electrical terminal and mounted on the heat sink.

According to one embodiment, the DC link capacitor is mounted onto the heat sink through the plate by welding or screwing or soldering or riveting. Further, any other fixation technology could be used.

According to one embodiment, the heat sink comprises a cooling chamber containing a cooling fluid.

According to one embodiment, the switching cell can comprise a plurality of individual DC link capacitors being connected in parallel. For example, the switching cell can comprise individual DC link capacitors that are essentially identical. In this way, concatenating capacitors is eased. However, a capacitor arrangement may also comprise different DC link capacitors. The invention also concerns a power converter comprising a switching cell as previously described. For example, the power converter forms an inverter.

Moreover, the invention also concerns a rotary electrical machine comprising a power converter as previously described. The rotary electrical machine is for example an electric motor. The electric motor is for example mechanically coupled to wheels of an electric vehicle.

BRIEF DESCRIPTION OF DRAWINGS

The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

Figure 1 shows a sectional view of an example of a switching cell according to the invention.

Figure 2 is a 3D view of the switching cell of figure 1 in which the control board, the cover, and the spring system are removed.

Figure 3 showing DC link capacitor onto the heat sink with mechanical connection by the plate

Figure 4 is a 3D view of a first example of a DC link capacitor according to the invention in which the insulated element has been made transparent.

Figure 5 is a 3D view of a second example of a DC link capacitor according to the invention in which the insulated element has been made transparent.

Figure 6 is a 3D view of a third example of a DC link capacitor according to the invention in which the insulated element has been made transparent.

Figure 7 is a 3D section view of a power converter comprising an example of switching cell according to the invention.

DETAILED DESCRIPTION

Generally, same parts or similar parts are denoted with the same/similar names and reference signs. Indicating the orientation and relative position is related to the associated figure, and indication of the orientation and/or relative position has to be amended in different figures accordingly as the case may be. In the following description and claims, the various parts and elements will be positioned relative to each other in space with reference to an arbitrarily oriented orthogonal XYZ coordinate system having an X-direction, a Y-direction, and a Z- direction. For the sake of clarity, the X-direction will be referred to as the left-right direction (in the figures, the X-direction arrow points to the left), the Y-direction will be referred to as the front-back direction (in the figures, the Y-direction arrow points to the back), and the Z-direction will be referred to as the bottom-up direction (in the figures, the Z-direction arrow points to the up).

With reference to Figure 1 and Figure 2, the switching cell 100 includes a plurality of power modules 102. In the illustrated example, three power modules 102 are provided. The power modules 102 are, for example, positioned adjacent to each other.

The switching cell 100 further includes an electronic control board 104 for controlling the power modules 102. The electronic control board 104 extends above the power modules 102, for example.

The switching cell 100 further includes a heat sink 106 for cooling the power modules 102. The heat sink 106 includes a cooling chamber 108 defining a coolant flow channel. The cooling chamber 108 has an upper face 112 and a lower face 113, both of which are cooled by the flow of coolant. The power modules 102 are, for example, pressed against the upper face 112 to be cooled.

To keep the power modules 102 against the upper face 112, the switching cell 100 includes, for example, a cover 114 extending over the power modules 102, such as between the control board 104 and the power modules 102. The cover 114 is attached to the heat sink 106, for example, by screws. The switching cell 100 further includes a spring system interposed between the cover 114 and the power modules 102. This spring system is designed to bear on the cover 114 and push the power modules 102 toward the upper face 112. For example, the spring system includes, for each power module 102, a flexible blade 116, compressed between the cover 114 and the power module 102.

The heat sink 106 further includes an inlet hose 118 and an outlet hose 120 for the cooling fluid circulation inside the cooling chamber 108. The hoses 118, 120 are located, for example, on the right and left sides of the cooling chamber 108, respectively, and project vertically downward from the cooling chamber 108.

The switching cell 100 further includes, below the cooling chamber 108, a positive bus bar 128 and a negative bus bar 130 stacked on top of each other. For example, the positive bus bar 128 extends below the negative bus bar 130. Thus, in this example, the positive bus bar 128 forms a lower bus bar and the negative bus bar 130 forms an upper bus bar. An electrically insulating layer can be provided between the bus bars 128, 130 and/or between the bus bar 128, 130 and the heat sink 106.

The bus bars 128, 130 are designed to have a DC voltage UDC. The bus bars 128, 130 are both connected to each of the power modules 102 to distribute the DC voltage to the power modules 102.

To hold the bus bars 128, 130 in place, the switching cell 100 includes, for example, a bracket 132. Specifically, the bracket 132 has a bottom 134 on which the bus bars 128, 130 extend. The bracket 132 is attached to the heat sink 106 such that the bus bars 128, 130 extend between the lower face 113 of the cooling chamber 108 and the bottom 134 of the bracket 132. In this manner, the bus bars 128, 130 can be cooled through the lower face 113.

The switching cell 100 further includes DC link capacitors 136 each having thereby two electric terminals 138, 140 respectively connected to the bus bars 128, 130 to receive the DC voltage. These DC link capacitors 136 are designed to smooth the DC voltage UDC and are generally referred to as "DC link capacitor".

The switching cell can comprise a plurality of individual DC link capacitors 136 being connected in parallel. For example, the switching cell can comprise individual DC link capacitors that are essentially identical.

Each power module 102 is, for example, designed to perform a transformation between the DC voltage UDC and a respective AC voltage, for example the AC voltage could be phase voltages of an electrical machine. Each power module 102 has an external connector 202 designed to present this AC voltage. Each power module 102 includes, in addition to the external AC connector 202, an external connector referred to as positive 302 and an external connector referred to as negative 304, designed to be connected to the positive bus bar 128 and the negative bus bar 130, respectively. In the illustrated example, two negative external connectors 304 are provided for each power module 102. These external connectors 202, 302, 304 are, for example, in the form of flat bars.

To perform the voltage transformation, each power module 102 comprise at least one switching arm and thus includes, in a housing 305, two switches 306, 308 connected to each other at a midpoint. The midpoint is connected to the external AC connector 202 to present the AC voltage. The switching arm is connected between the external connectors 302, 304 to present the DC voltage UDC. These switches 306, 308 are shown in Figure 2 schematically for only one of the power modules 102, and not on the others for clarity.

Each switch 306, 308 is preferably a semiconductor controllable switch, such as a transistor switch such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT) or a Gallium Nitride Field Effect Transistor (GaNFET).

Each power module 102 also has control pins 312, allowing in particular the control board 104 to control the switching of the switches 306, 308.

With reference to Figures 4, 5 and 6, each DC link capacitor 136 includes a main body 402. The main body 402 includes, for example, a capacitive element 408 and an insulated element 410 covering the capacitive element 408. The capacitive element 408 is the portion of the capacitor 136 where electrical energy is stored. For example, the capacitive element is a wound metallized plastic film. The insulated element 410 can be an overmold. The insulated element 410 is, for example, made of resin.

Each electric terminal 138, 140 includes an inner portion 404 inside the main body 402 and an outer portion 406 outside of the main body 402. The inner portion 404 of each terminal 138, 140 extends, for example, into the insulated element 410 to join the capacitive element 408. The outer portion 406 of each of the terminals 138, 140 has a connection portion 414 designed to be electrically connected, for example by welding, to a respective one of the bus bars 128, 130.

In the examples illustrated here, both outer portions 406 are arranged side by side on a same side of the DC link capacitor 136. Further in these examples, each inner portion 404 extends in one respective side of the DC link capacitor 136 so that the capacitive element 408 is arranged between them.

Preferably, each terminal 138, 140, or at least its outer portion 406, is formed from a single folded flat plate.

The DC link capacitor 136 further comprises a plate 412 arranged to cool the capacitive element 408. The plate 412 comprises a holding part 416 for assembling the DC link capacitor onto the heat sink 106 and, in this example, two lateral parts 418 extending from the holding part 414. For example, each lateral part 418 extends from either side of the holding part 414 so that the capacitive element 408 is located between the two lateral parts 418.

In the examples illustrated here, each lateral part 418 extends globally perpendicularly to the holding part 416.

The holding part 416 extends outside of the insulated element 410 and the lateral parts 418 extend substantially inside said insulated element 410.

The plate 412 extends at distance from the capacitive element 408. Therefore, there is no electrical contact between the plate and more particularly between the lateral parts 418 and said capacitive element 408. Further, part of the insulated element 410 can be arranged between the plate 412, and in particular the lateral parts 418, and the capacitive element 408.

The plate 412 extends at distance from the electric terminals 138, 140. Therefore, there is no electrical contact between the plate and more particularly between the lateral parts 418 and said electric terminals 138, 140. Further, part of the insulated element 410 can be arranged between the plate 412, and in particular the lateral parts 418, and the electric terminals 138, 140.

The plate 412 extends at distance from the bus bars 128, 130. Therefore, there is no electrical contact between the plate and said bus bars 128, 130.

In the example illustrated in figures 4 to 6, the plate 412 comprises an opening 420 arranged to accommodate at least partially at least one electric terminal 138, 140. This opening 420 allow to increase the heat exchange surface between the plate 412 and the capacitive element 408 avoiding any electrical contact between them. The opening 420 can be formed into a lateral part 418 of the plate 412. More precisely here, each lateral part 418 comprise one opening 420 accommodating partially one electric terminal 138, 140.

For example, the opening 420 can be a notch.

The DC link capacitor 136 is securely attached to the heat sink 106 through the holding part 416 of the plate 412.

In the example of figure 4, the holding part 416 of the plate 412 is attached to the heat sink 106 by welding or soldering. An optimal thermal exchange between the plate and the heat sink is reached with this configuration. To do that, the holding part 416 comprise a flat surface 422 directly in contact with the heat sink 106. The length and the width of the holding part 416 can be smaller than the respective length and width of the insulated element 410.

In the example of figures 5 and 6, the holding part 416 of the plate 412 is attached to the heat sink 106 by screwing or riveting. To do that, the holding part 416 comprise holes 426. The holes can be arranged on an extension part 428 extending from a central body 430 of the holding part 416. The extension part 428 extends, here, in a plan comprising the central body 430.

In the example of figure 5, the holding part 416 comprises 4 holes 426 each one arranged on an extension part 428. Further here, each extension part 428 extends from one corner of the central body 430 so that the holding part 416 presents a H shape.

In the example of figure 6, the holding part 416 comprises 4 holes 426 arranged by couple on two extension parts 428. Further here, each extension part 428 extends in two opposite directions of the same axis so that the central body 430 is arranged between both extension parts 428.

Further, the holding part 416 can comprises indexing means 424, like openings, to correctly positioned the DC link capacitor 136 onto the heat sink 106.

The plate 412 is formed of a material comprising at least one metallic component. For example, the plate is formed of aluminum or steel or copper.

Preferably, the plate 412 is formed from a single plate, meaning it is a one- piece element. For example, the plate 412 is formed by folding a flat plate to formed the lateral parts 418. For the need of the manufacturing process, the plate 412 and more particularly the lateral parts 418, can comprises process notches 432.

A simplified example of manufacturing process for the DC link capacitor 136 is as followed: the plate 412 is first shaped, then the plate is positioned compared to the capacitive element 408 and the electric terminals 138, 140, then all said elements are overmolded by the insulated element 410.

For each DC link capacitor 136, the positive terminal 138 is connected, for example by welding, to a connection portion of the upper bus bar 130. The negative terminal 140 is connected, for example by welding, to a connection portion of the lower bus bar 128.

With reference to Figure 7, the switch cell 100 is for example designed to be part of an electrical system, for example a power converter line an inverter 702.

The inverter 702 includes, for example, an electromagnetic compatibility (EMC) filter 704 connected between the two bus bars 128, 130 and a general housing 706 into which the EMC filter 704 and the switching cell 100 are located.

The general housing 706 includes, for example, a main portion 708 having a top opening 710 and a cover (not shown) adapted to close the top opening 710. The general housing 706 further includes, for example, a lower opening 712 for passage of the DC link capacitors 136 and a cover 714 for closing the lower opening 712.

The inverter 702 is for example designed to be part of a rotary electrical machine like an electric motor. The electric motor is for example mechanically coupled to wheels of an electric vehicle.

It is noted that the invention is not limited to the embodiments disclosed hereinbefore, but combinations or various modifications of the different variants are possible in the light of the teaching which has just been disclosed.