This invention relates to cooling system for power electronics and, in particular, a cooling system that has a low pressure drop and/or a reduced temperature gradient.
It is well known that electronic circuits generate heat during use. This is particularly true in electrical circuits that transmit and/or convert power because as the electrical power that passes through a circuit increases, the heat that is generated typically increases. Despite the ever increasing efficiency of such circuits and especially within high power electronic converters using in the order of tens to hundreds of kilowatts, the power losses through heat, typically a few kilowatts, need to be dissipated or otherwise removed. This is to avoid degradation or other damage to the circuitry, power modules or other components, and to avoid thermal runaway which occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback.
Initially, air cooled systems were sufficient to dissipate the amount of heat generated, but increasingly these are found to lack the capacity. As such, water cooled systems are preferred and, even more preferred, direct water cooling is used to avoid multiple layers of thermal interfaces. High power electronic converters typically comprise a series of individual power modules in which power is converted, and these power modules are typically soldered or otherwise bonded directly to a plate equipped with pin fins which can contact the cooling fluid, typically water, directly.
Conventional water cooling systems generally provide a flow of cooling water through a chamber into which the pin fins extend, thereby allowing the water to take up heat generated from the power modules mounted on the opposite face of the chamber wall to the pin fins. This however leads to a temperature gradient over the chamber, as the inlet water is cooler than the outlet water, and this can lead to insufficient cooling of components nearer the outlet or unwanted hot spots on the power modules. Such hotspots can lead to reduce performance of the electronics or even damage or failure of components. When the thermal gradient is too high, this can lead to material fatigue, especially when the power modules are subjected to thermal and/or power cycling.
One solution is to increase the flow rate of the cooling water, thereby ensuring appropriate levels of cooling, but this comes at the cost of an increased pressure drop. The pressure drop is caused by the resistance to flow of the pin fins, such that as the fin density/fin size increases so does the pressure drop. Also, the inlet and outlet flow restrictions necessarily cause a pressure drop.
Thus, conventional direct water cooled systems are relatively heavy and large in comparison to the power modules which are to be cooled, and this size makes them difficult to integrate into larger systems, especially hybrid cars for example, where space is limited.
Furthermore, when such a cooling system is required in a racing vehicle, the size and weight of componentry can drastic affect the overall performance of the vehicle.
Thus, it is desirable to improve the cooling system to avoid or at least reduce one or more of the problems identified above.
According to the present invention there is provided a cooling system for power electronics, the system comprising a cooling module having inlet and outlet ends, an inlet side with an inlet channel for receiving, at the inlet end, a flow of cooling fluid and an outlet side having an outlet channel through which, at the outlet end, outlet flow exits the system; and a cooling plate mounted on a face of the cooling module and having a cooling chamber in fluid communication with the inlet and outlet flow channels via a plurality of cooling fluid passages located on opposite sides of the cooling module, such that, in use, flow of cooling fluid in the cooling chamber is from the inlet side to the outlet side.
In this way, the present invention provides a cooling system with reduced temperature gradient from inlet to outlet as well as minimising the pressure drop. The coolant flow is caused to flow across the width of the cooling chamber in a series of relatively short, but wide parallel flow streams.
The present invention also provides a coolant flow distributor comprising a planar base element and a longitudinal divider projecting away from a first face of the planar element such that the first face is divided into two side sections, wherein the divider includes an S-shaped section.
The present invention also provides a coolant flow distributor comprising a planar base element and a longitudinal divider projecting away from a first face of the planar element such that the first face is divided into two side sections, wherein the planar base element includes openings adjacent, or cut outs in, edges of the two side sections.
Where any of the following features relate to the flow distributor, those features may be combined with either or both of the coolant flow distributors referred to above, or with the overall cooling system.
The cooling module may include a cooling jacket and a coolant flow distributor which may be integrally formed or may be discrete elements.
A divider may be provided between the inlet and outlet channels. The divider may define an S-shape to a portion of the inlet and/or the outlet flow channels. The S-shaped portion may be opposite the cooling fluid passages.
The divider may include at least one opening at or adjacent an end of the divider to permit flow between the inlet side and the outlet side.
The inlet and outlet channels may be on the same face of the cooling module.
A plurality of cooling fluid passages may be provided on each of the inlet and outlet sides. There may be the same number of cooling passages on each of the inlet and outlet sides.
The cooling fluid passages may provide substantially parallel flow paths across the cooling chamber.
The inlet and outlet channels may extend between the inlet and outlet ends providing substantially longitudinal flow.
In use, cooling fluid flow in the cooling chamber may be substantially perpendicular to the inlet and outlet channel flow.
The cooling plate may be on a first face of the cooling module. A second cooling plate may be provided on a second face of the cooling module. A second set of flow passages may be provided for supplying cooling fluid to the second cooling plate. The or each cooling plate may include one or more internal dividing walls for splitting the respective cooling chamber into multiple sections.
The or each cooling chamber may have a cooling face opposite the cooling module. A plurality of cooling fins may extend into the or each cooling chamber. The cooling fins may be formed on a removable cover plate on the cooling face.
The present invention also provides a power electronics system comprising a cooling system as described above, and power electronics to be cooled by the cooling system mounted on a cooling face of the cooling chamber opposite the cooling module.
The power electronics may comprise a plurality of power modules. Two or more of the flow passages may align with a power module such that cooling fluid flows parallel to an axis of the power module.
The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:
FIG. 1 shows a standard cooling jacket for longitudinal cooling fluid flow;
FIG. 2 shows an exploded view of an example of the present invention;
FIG. 3 shows a schematic cross section through a cooling module;
FIG. 4 shows a schematic plan view of a cooling module with mounted power modules;
FIG. 5 shows a schematic cross section through a twin cooling chamber cooling module;
FIG. 6 shows a schematic representation of the cooling flow through a cooling module;
FIG. 7 shows a perspective view of a cooling system; and
FIGS. 8a and 8b shows an alternative form of flow distributor.
FIG. 1 shows a cooling jacket 10 of a standard design having an inlet 11 and an outlet 12. The inlet and/or outlet may be oriented along the longitudinal axis of the cooling jacket (as shown in solid line in FIG. 1) or may have a different orientation such as perpendicular to the longitudinal axis (as shown in dotted line in FIG. 1). The inlet and/or outlet may comprise one, two or more individual flow paths—one is shown in solid line, two are shown in dotted line. The inlet 11 receives cooling fluid and distributes the fluid into a cooling chamber 13. The cooling fluid passes longitudinally along the cooling chamber 13 and then passes out of the cooling chamber 13 via outlet 12. The outlet cooling fluid is warmer than the inlet cooling fluid because heat is transferred into the cooling fluid due to electronic circuitry/power modules as described in relation to FIG. 2. Arrow 14 indicates not only the direction of the cooling fluid flow, but also represents an increasing temperature gradient from the inlet to the outlet.
FIG. 2 shows an exploded view of a twin cooling module 20 according to the present invention. The cooling jacket 10 of FIG. 1 is substantially unchanged, but in this example, the chamber 13 contains a flow distributor 21 (see FIGS. 3, 4 and 6) which alters the flow of the cooling fluid when compared to the arrangement of FIG. 1. The flow distributor 21 is a substantially planar flow plate 24 having inlet 25 and outlet 26 channels on a first face 27. A divider 28 is provided between the inlet 25 and outlet 26 channels. The arrows 29 of FIG. 2 illustrate how the cooling fluid flow is caused to travel across the cooling chamber from side to side, rather than longitudinally. Walls 31 may be provided to divide the pin fin plate into independent chambers typically associated/aligned with a respective power module. The walls 31 preferably have the same height as the pin fins. This creates a wider, but shorter, flow path across a face of the cooling module leading to reduced temperature gradient across the cooling chamber. This flow will be explained in greater details with reference to later figures.
The cooling jacket 10 and the flow distributor 21 are closed on the upper (in FIG. 2) face by a first pin fin plate 22 defining a main cooling chamber 30. The first fin plate 22 is provided with an array of fins 23 which, when the pin fin plate 22 is fixed to the cooling jacket, extend into the main cooling chamber 30 such that cooling fluid can flow around the fins and take up heat therefrom. The fins 23 are shorter than would typically be used on a conventional fin plate, and are preferably 1mm, rather the more normal 4mm in length. An advantage of the low height is that, due to the relatively larger width, the pressure drop is reduced. The fins may touch face 41 of the flow distributor or may be spaced therefrom. If spaced, the spacing is preferably relatively smaller to ensure maximum coolant flow around the cooling pins. This also helps to minimise the overall height of the cooling module. FIGS. 3 and 5 illustrate that the height of the fins could be the full depth (dotted lines) of the cooling chamber or may extend only over a part of the depth. Power modules or other electronics (see FIGS. 3 to 5, 7) can be affixed to the opposite face of the plate 22 and transfer heat to the pins 23. A seal 29, in this example a sealing gasket, ensures coolant does not leak. The sealing gasket is typically provided within a groove in the fin plate 22 which helps to minimise the overall height of the cooling module.
A second fin plate 33 defines a second main cooling chamber 32 and is shown in greater detail in FIG. 5. The second pin fin plate 33, is typically of the same form as first fin plate 22, and can then be affixed to the opposite side of the cooling jacket 10. The form and effect of the flow distributor 21 is shown more clearly in FIGS. 3, 5 and 6.
FIG. 3 is a cross section through a single sided cooling module 60 and illustrates the fluid flow around the flow distributor. The flow distributor 21 has a substantially planar flow plate 24 having a first face 27 and a second face 41. A divider 28 extends away from the first face and, together with a closure 50, defines the inlet channel 25 and the outlet channel 26. The closure 50 may be integrally formed with the divider, such that the flow distributor has an upper planar element 24, the divider 28 and a lower planar element 50. Alternatively, the flow plate 24 and the divider may be integral, with the closure 50 separate, or indeed the closure 50 and the flow divider could be integral, with the flow plate 24 being a separate element (as shown in FIG. 8). The inlet channel 25 receives cooling fluid from the inlet 11 and directs it towards inlet flow passages 45 which extend between the inlet channel 25 and the main cooling chamber 30. The cooling fluid then passes across the main cooling chamber 30, through outlet flow passages 46 and back into the outlet channel 26. The cooling flow then passes along the outlet channel and exits via outlet 12.
The divider 28 takes, in this example, the form of an S-shaped wall. The S-shape is when seen in plan view, i.e. looking perpendicular to the flow plate 24. The divider itself does not necessarily have to be S-shaped, but it is beneficial for there to be an S-shaped wall on the inside of each of the inlet 25 and outlet 26 channels as can be seen in the example of FIG. 8. As shown in FIG. 3, the divider preferably takes the form of a narrow wall and this is beneficial as it allows the greatest size to the inlet and outlet channels, thereby maximising the amount of cooling flow. Furthermore, the S-shape ensures that the inlet flow passages 31 that are further away from the inlet experience substantially the same flow rates and pressures as the flow passages nearer the inlet. The S-shape may be a continuous curve, or may include one or more straight sections in the middle. An alternative form for the flow distributor is shown in FIG. 8.
As can be seen in FIG. 4, power modules 55 are mounted on the outside of fin plate 22 and these can typically lie across the cooling module such that the cooling flow within the cooling module is along the length of the power modules. In this way, the cooling module provides parallel cooling of the various power modules, as each one experiences substantially the same cooling effect. Whilst three of each of flow passages 45, 46 are shown in FIG. 2, a different number could be provided. An equal number on each side is beneficial to maintain a series of substantially parallel flow streams. It may be that the number of flow passages on each side corresponds to the number of power modules to be cooled. In this arrangement, the power modules may be aligned with respective pairs of flow passages. The power modules may mounted individually, or may be part of a single structure which is then mounted onto the fin plate 22. Power modules may be mounted on either or both fin plates. The cooling flow is preferably along an axis of the or each power modules, the axis typically being a longitudinal axis of the power module.
The flow passages 45, 46 are, in FIG. 2, provided by respective openings or recesses in the edge of the flow plate 24 in the flow distributor 21. Alternatively and/or additionally, the flow passages may include flow pathways (not shown) within the cooling jacket or even passages extending through to the cooling jacket and then back into the main cooling chamber. The flow passages may include openings in other components.
A twin cooling chamber cooling module 80 is shown in FIG. 5 in which, instead of the closure 50, a second fin plate 33 is provided. The equivalent function of the closure 50 is provided by a further planar element 61 which, together with the plate 24, sandwich the divider 28. This second fin plate may be identical to fin plate 22 and defines, along with the further planar element 61, the second main cooling chamber 32. No second divider is required. Corresponding second inlet 63 and second outlet 64 flow passages are formed to allow cooling fluid flow from the inlet channel 25 to pass across the second main cooling chamber 32 in the same manner as described above in relation to main cooling chamber 30. The second inlet 63 and second outlet 64 flow passages may take the matching form to the first inlet 25 and first outlet 26 passages, and may be the same in number. However, they could also be different in number or form, depending upon the cooling requirement from the second main cooling chamber 32.
FIG. 6 illustrates the flow paths through the twin cooling chamber module 80 of FIG. 5. The inlet coolant flow is received into the wider end of the inlet chamber 25 and is caused to flow towards the narrower end. As the flow path narrows along the inlet chamber, part of the coolant flow is caused to enter the inlet flow passages 45 but due to the reducing size of the inlet channel, the pressure of the remaining coolant in the inlet channel does not alter significantly. This occurs all along the inlet channel, thereby ensuring that the flow through each inlet flow passage is substantially identical in pressure and flow rate. This ensures that the cooling module can provide an even cooling effect across its length. The coolant then flows into, and across the width of, each of the main cooling chambers 30, 32 before passing into respective outlet flow passages 46 and then recombining in the outlet flow channel 26. The widening of the outlet flow channel towards the outlet helps to maintain a constant flow rate and pressure in the outlet coolant flow. Divider holes 86 and 87 can be provided in the divider, typically at or adjacent one or both ends of the divider. The effect of the hole(s) is to eliminate vortex generation and therefore regions of static flow. Such static flow is not refreshed by new coolant and so hot spots could form. The holes are sized to permit a small amount of coolant flow directly across the divider to prevent vortex formation, but the bulk of the coolant flow is still caused to flow along the inlet channel and through the flow passages so as to be used for cooling within the cooling chamber(s).
FIG. 7 shows an alternative form of the twin cooling chamber module 80 and, in particular, this figure shows the inlet 11 and outlet 12. In this example, the inlet includes a substantially circular inlet opening 81 into which coolant flows, the opening leading to a diverging inlet manifold 83 which allows the inlet flow to enter the inlet channel 25 across substantially the whole width of the channel. This ensures a smoother flow of inlet cooling fluid with fewer recirculating eddies and the like which can adversely affect the cooling profile of the cooling module. The outlet has a similar form, with a converging outlet manifold 84 receiving coolant fluid across substantially the whole width of the outlet channel 26 and directing it to the outlet opening 82. The use of substantially the whole width ensures that cooling fluid does not become trapped in a region of the outlet channel, which would lead to areas that do not provide the correct level of cooling.
The gradual change in the cross section of the flow path, within the inlet and outlet manifolds and within the inlet and outlet channels minimises regions with high pressure drop, thereby resulting in smoother cooling fluid flow. Other factors that assist in minimising pressure drop within the system include no sharp corners or significant obstacles within the flow path, and the large width of the cooling flow within the main cooling chambers relative to distance the flow travels across the cooling chambers.
FIGS. 8a and 8b shows an alternative form to the flow distributor 21, being used in a single cooling chamber cooling module. The form shown here could be used in a twin cooling chamber cooling module as well. In this example, the cooling jacket is formed from two parts, a lower part 90 which includes an integrally formed flow distributor 21 defining the inlet 25 and outlet 26 channels, and an upper section 91 which includes the coolant inlet 11 and outlet 12 and which also includes a central planar section 92 which functions in a similar manner to the flow plate of FIG. 3. The divider 28 in this example is not a narrow wall along the entire length, but rather has a varying width. The divider still provides an S-shape to the inner wall of each of the inlet 25 and outlet 26 channels. Although not shown, the divider holes 86, 87 of FIG. 6 could still be incorporated in the arrangement of FIG. 8.
FIG. 8a shows the upper 91 and lower 90 parts joined together, whereas FIG. 8b shows only lower part 90 and illustrates the inlet 25 and outlet 26 channels.
The flow distributor 21 could be formed integrally with the cooling jacket 10 or within the lower section of FIG. 8, and may be formed by 3-D printing or casting. Alternatively, they may be separate elements, in which case, the flow distributor is preferably mounted by way of an interference fit within the cooling jacket. One or more resilient elements (not shown) may be placed between the cooling jacket and the flow distributor to assist with the interference fit.
The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.
Patent Application
20220015271
