Differential immersion cooling for semiconductor thermal balancing in power electronic converters

Abstract

A differential immersion cooling system for a power converter including at least one high-temperature semiconductor switch and at least one low-temperature semiconductor switch includes a first flow path adapted to provide immersion cooling to the at least one high-temperature semiconductor switch, a second flow path adapted to provide immersion cooling to the at least one low-temperature semiconductor switch, and a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the at least one high-temperature semiconductor switch and the at least one low-temperature semiconductor switch to improve thermal balancing and increase temperature homogeneity between the at least one high-temperature semiconductor switch and the at least one low-temperature semiconductor switch.

Description

DIFFERENTIAL IMMERSION COOLING FOR SEMICONDUCTOR THERMAL BALANCING IN POWER ELECTRONIC CONVERTERSRELATED APPLICATIONS

[0001] This application claims priority benefit of U.S. Provisional Patent Application Serial No. 63 / 677,266, filed July 30, 2024, the entirety of which is incorporated herein by reference.TECHNICAL FIELD

[0002] This document relates generally to techniques for cooling power electronic converters. More specifically, it is related to the immersion cooling methods in which the heat sources (e.g., semiconductor switches) are immersed in the dielectric cooling fluid. The disclosure is aimed for power electronics composed of a number of individual semiconductor devices with loss unbalance.BACKGROUND

[0003] Power electronic devices naturally produce heat due to their high-frequency operation because of losses dissipated by the semiconductor switches. This undesired heat must be efficiently removed for safe and reliable operation of the system. Most power electronic systems use heat sinks and indirect liquid cooling methods such as cold plate for heat dissipation purposes. Increasing the heat dissipation capability requires utilizing bulky heat sinks or additional heat exchanging systems which in turn will compromise the power density of the whole system.

[0004] Immersion cooling is another cooling technique recently used for power electronic apparatuses. Although thermally conductive and electrically insulating fluid is used in direct contact with the hot switches, the limited power density and the lack of temperature control are the hindrances of such techniques. Additionally, the operational limit of the converters is determined by the hotspot temperature (HST) in the system. As a result, there is still a need in the field for enhanced cooling systems for power electronics converters. This document proposes a novel solution to this requirement.SUMMARY

[0005] Each of the following terms written in singular grammatical form: “a”, “an”, and “the”, as used herein, means “at least one”, or “one or more”. Use of the phrase “One or more”herein does not alter this intended meaning of “a”, “an”, or “the”. Accordingly, the terms “a”, “an”, and “the”, as used herein, may also refer to, and encompass, a plurality of the stated entity or object, unless otherwise specifically defined or stated herein, or, unless the context clearly dictates otherwise. For example, the phrase: “a temperature sensor”, as used herein, may also refer to, and encompass, a plurality of temperature sensors.

[0006] Each of the following terms: “includes”, “including”, “has”, “having”, “comprises”, and “comprising”, and, their linguistic / grammatical variants, derivatives, or / and conjugates, as used herein, means “including, but not limited to”, and is to be taken as specifying the stated component(s), feature(s), characteristic(s), parameter(s), integer(s), or step(s), and does not preclude addition of one or more additional component(s), feature(s), characteristic(s), parameter(s), integer(s), step(s), or groups thereof.

[0007] The phrase “consisting of’, as used herein, is closed-ended and excludes any element, step, or ingredient not specifically mentioned. The phrase “consisting essentially of’, as used herein, is a semi-closed term indicating that an item is limited to the components specified and those that do not materially affect the basic and novel characteristic(s) of what is specified.

[0008] Terms of approximation, such as the terms about, substantially, approximately, etc., as used herein, refers to ± 10 % of the stated numerical value.

[0009] In accordance with the purposes and benefits set forth herein, a new and improved differential immersion cooling system is provided for a power converter including at least one relatively high-temperature semiconductor switch and at least one relatively low-temperature semiconductor switch. The differential cooling system comprises, consists of or consists essentially of: (a) a first flow path adapted to provide immersion cooling to the at least one relatively high-temperature semiconductor switch, (b) a second flow path adapted to provide immersion cooling to the at least one relatively low-temperature semiconductor switch, and (c) a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the at least one high-temperature semiconductor switch and the at least one low-temperature semiconductor switch to improve thermal balancing and increase temperature homogeneity between the at least one high- temperature semiconductor switch and the at least one low-temperature semiconductor switch.

[0010] In at least some embodiments, the differential immersion cooling system further includes a heat exchanger. The pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.

[0011] In at least some of the many possible embodiments, the differential immersion cooling system further includes a splitter downstream from the pump assembly. The splitter includes (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path. The first feed outlet may be adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet may be adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where Vi>V2.

[0012] At least some embodiments of the differential immersion cooling system include an aggregator downstream of the first and second flow paths. The aggregator includes (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) a return port in communication with the dielectric cooling reservoir.

[0013] The pump assembly may include a first pump in communication with the first flow path and a second pump in communication with the second flow path. The differential immersion cooling system may further include a heat exchanger and wherein (a) the first pump circulates the dielectric cooling fluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump circulates the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.

[0014] Some embodiments of the differential immersion cooling system may further include a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths. Still further, the differential immersion cooling system may further include a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid in the second flow path. The controller may be adapted to receive temperature data from the first andsecond temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.

[0015] In accordance with an additional aspect, a power converter, comprises, consists of or consists essentially of a power board including a plurality of relatively high-temperature semiconductor switches and a plurality of relatively low-temperature semiconductor switches and a differential immersion cooling system. The differential immersion cooling system includes (a) a first flow path adapted to provide immersion cooling to the plurality of relatively high- temperature semiconductor switches, (b) a second flow path adapted to provide a immersion cooling to the plurality of relatively low-temperature semiconductor switch, and (c) a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the plurality of high-temperature semiconductor switches and the plurality of low-temperature semiconductor switches to improve thermal balancing and increase temperature homogeneity across the power board.

[0016] The differential immersion cooling system may further include a heat exchanger. In such embodiments, the pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.

[0017] In at least some embodiments, the differential immersion cooling system further includes a splitter downstream from the pump assembly. The splitter may include (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path.

[0018] The first feed outlet may be adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet is adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where Vi>V2.

[0019] In some embodiments, the differential immersion cooling system further includes an aggregator downstream of the first and second flow paths. The aggregator may include (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) an return port in communication with the dielectric cooling reservoir.

[0020] The pump assembly may include a first pump in communication with the first flow path and a second pump in communication with the second flow path. Still further, the differential immersion cooling system may further include a heat exchanger. In such embodiments, (a) the first pump may circulate the dielectric cooling fluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump may circulate the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.

[0021] The differential immersion cooling system may further include a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths. In addition, in some embodiments, the differential immersion cooling system further includes a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid in the second flow path. In any such embodiments, the controller may be adapted to receive temperature data from the first and second temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.

[0022] In accordance with yet another aspect, a method of improving overall performance of a power electronic converter, comprises, consists of or consists essentially of thermal balancing the power electronic converter by providing differential immersion cooling to the semiconductor switches of the power electronic converter. The method may further include removing more heat from hotter switches of the power electronic converter.

[0023] In accordance with still another aspect, a method of cooling a power electronic converter, comprises, consists of or consists essentially of:(a) providing a first, relatively higher level Li of immersion cooling to relatively high- temperature semiconductor switches arrayed along a first dielectric cooling fluid flow path; and(b) providing a second, relatively lower level L2 of immersion cooling to relatively low- temperature semiconductor switches arrayed along a second dielectric cooling fluid flow path. Inthis way it is possible to provide greater thermal balance across a power board of the power electronic converter.

[0024] The method may further include adjusting a flow rate of dielectric cooling fluid in response to semiconductor switch heating and load conditions. The method may further include

[0025] adjusting a flow rate of dielectric cooling fluid through the first dielectric cooling fluid flow path and the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.

[0026] An additional aspect, relates to a method of cooling a power electronic converter, comprising, consisting of or consisting essentially of: (a) delivering a first stream of dielectric cooling fluid to a first group of relatively high-temperature semiconductor switches, (b) delivering a second stream of dielectric cooling fluid to a second group of relatively low- temperature semiconductor switches, and (c) providing greater cooling to the first group of relatively high-temperature semiconductor switches than the second group of relatively low- temperature semiconductor switches whereby greater thermal balancing is provided across a power board of the power electronic converter.

[0027] The method may further include adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions. In other embodiments the method further includes independently adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions. In other embodiments, the method includes adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme. In still other embodiments, the method further includes independently adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self- adjusting cooling scheme.

[0028] In the following description, there are shown and described several different embodiments of (a) the differential immersion cooling system for a power converter including at least one high-temperature semiconductor switch and at least one low-temperature semiconductor switch , (b) a power inverter incorporating such a differential cooling system, and (c) related methods of improving overall performance of a power electronic converter and cooling a power electronic converter. As it should be realized, the system, the converter and the related methods are capable of other, different embodiments and their several details are capable of modification in various, obvious aspects all without departing from the system, trailer, and method as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive.BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0029] The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate certain aspects of the differential immersion cooling system, the converter and the related methods and together with the description serve to explain certain principles thereof. A person of ordinary skill in the art will readily recognize from the following discussion that alternative embodiments of the system, converter and the related methods may be employed without departing from the principles described below.

[0030] Figure 1A-1C are respective perspective, front and top plan views of a power electronic converter of a type known in the prior art.

[0031] Figures 2A-2C are respective perspective, front and top plan views of a power electronic converter incorporating a first possible embodiment of a new and improved differential immersion cooling system.

[0032] Figure 2D is a schematic of the dielectric cooling fluid circuit for the embodiment shown in Figures 2A-2C.

[0033] Figures 3A-3C are respective perspective, front and top plan views of a power electronic converter incorporating a second possible embodiment of a new and improved differential immersion cooling system.

[0034] Figure 3D is a schematic of the cooperating dielectric cooling fluid circuits and control system for the embodiment shown in Figures 2A-2C.DETAILED DESCRIPTION

[0035] Figures 1A-1C illustrate a conventional power electronic converter C having a power electronic circuit including a power board B held within an enclosure E. The power electronic circuit is the main cause of heat generation in the converter C: that is, other components in the converter generally produce negligible amounts of heat. Significantly, the power board B of the converter C includes both high-temperature (HT) and low-temperature (LT) switches having unbalanced loss distributions. As shown, both types of switches HT, LT are maintained in the single enclosure E.

[0036] In conventional immersion cooling, the entire power board B is immersed in a thermally conductive, insulating cooling fluid. More specifically, the cooling fluid is pumped through the inlet I, absorbs the heat from the switches HT and LT, and exits the enclosure E through the outlet 0. No differential cooling is provided: that is, the same amount of cooling is provided to the HT switches and the LT switches. As a result, even after cooling a thermal imbalance remains between the HT and LT switches. This thermal imbalance tends to promote undesirable thermal expansion issues and, over time, solder joint failures adversely affecting the reliability and service life of the converter.

[0037] Reference is now made to Figures 2A-2D which illustrate a first possible embodiment of the new and improved differential immersion cooling system 10 and a power electronic converter 12 incorporating that system. As shown, the differential cooling system 10 includes an enclosure 14 comprising a first flow path 16 and a second flow path 18. The converter 12 includes a power board 19 including both relatively high-temperature switches HT and relatively low-temperature switches LT. The HT switches are arrayed in and along the first flow path 16. The LT switches are arrayed in and along the second flow path 18. As should be appreciated, the two flow paths are separate and distinct.

[0038] A pump assembly 20 pumps dielectric cooling fluid from the through a downstream splitter 24. More specifically, the splitter 24 includes (a) a single inlet 26, in communication with the pump assembly 20, (b) a first feed outlet 28, in communication with the first flow path 16,and (c) a second feed outlet 30 in communication with the second flow path 18. In one particularly useful embodiment of the system 10, the first feed outlet 28 is adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path 16, while the second feed outlet 30 is adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path 18. More specifically, the first feed outlet 28 and the first flow path 16 may have a greater cross sectional area than the second feed outlet 30 and the second flow path 18 so that the first volume Vi is greater than the volume V2. In this way, differential immersion cooling is provided to the HT switches in the first flow path 16 and the LT switches in the second flow path: that is: more cooling is provided to the HT switches in the first flow path 16 than to the LT switches in the second flow path 18. This tends to reduce or even eliminate any differential heating that would otherwise result from the HT and LT switches due to their unbalanced loss distribution.

[0039] An aggregator 32, downstream of the first and second flow paths 16, 18, includes (a) a first input 34 in communication with the first flow path 16, (b) a second input 36 in communication with the second flow path 18, and (c) a return port 38 in communication with a heat exchanger 22, such as a radiator, to provide cooling to the dielectric cooling fluid. Like the first feed outlet 28, the first input 34 may have a greater cross sectional area than the second input 36 to support the differential cooling. As best shown in Figure 2D, it should be appreciated that the pump 20, the splitter 24, the first and second flow pathways or channels 16, 18, the aggregator 32, the heat exchanger 22 and the return line 42 operate together to form a closed loop through which the dielectric cooling fluid is circulated while providing the desired differential cooling to the HT and LT switches to improve thermal balancing and increase temperature homogeneity across the entire power board 19. In some embodiments, the closed loop may include an optional dielectric cooling fluid reservoir 40 between the heat exchanger 22 and the pump 20.

[0040] Reference is now made to Figures 3A-3D which illustrate a second possible embodiment of the new and improved differential immersion cooling system 100 and a power electronic converter 102 incorporating that system. In this embodiment, the pump assembly 104 comprises a first pump 106 and a second pump 108. The first pump 106 is adapted to pump or circulate dielectric cooling fluid through the inlet 109, the first flow path 110, the outlet 111, theassociated heat exchanger 112, the optional dielectric cooling fluid reservoir 114, if present and the return line 116 in a first circuit 118. In contrast, the second pump 108 is adapted to pump or circulate dielectric cooling fluid through the inlet 119, the second flow path 120, the outlet 121, the associated heat exchanger 122, the optional dielectric cooling fluid reservoir 124, if present, and the return line 126 in a second circuit 128.

[0041] A control system 130 includes a controller 132, in the form of a dedicated microprocessor or computing device, that is adapted to independently control the first and second pumps 106, 108 and the resulting flow of dielectric cooling fluid through the first and second flow paths 110, 120. The control system 130 may further include a first temperature sensor 134, adapted to continuously monitor the temperature of the dielectric fluid in the first flow path 110 and / or the temperature of the HT switches arrayed along the first flow path. Further, the control system 130 may further include a second temperature sensor 136, adapted to continuously monitor the temperature of the dielectric fluid in the second flow path 120 and / or the temperature of the LT switches arrayed along the second flow path. In such an embodiment, the controller 130 receives the temperature data from the first and second temperature sensors 134, 136 and independently adjusts flow rates of dielectric cooling fluid through (a) the first flow path 110 to provide a greater level of cooling to the relatively hotter HT switches arrayed along the first flow path. and (b) the second flow path 120 to provide a lower but sufficient level of cooling to the LT switches arrayed along the second flow path.

[0042] In one particularly useful embodiment, the controller 130 operates in the manner of a closed-loop control system to achieve a self-adjusting cooling scheme for the HT and LT switches found across the power board 140 of the converter 102.

[0043] The differential immersion cooling system 10, illustrated in Figures 2A-2D and the differential immersion cooling system 100, illustrated in Figures 3A-3D both operate so as to provide a new and improved methods for improving the cooling and overall performance of a power electric converter 12, 102. As described above, the method includes thermal balancing the power electronic converter 12, 102 by providing differential immersion cooling to the semiconductor switches HT, LT of the power electronic converter. This includes removing more heat from hotter HT switches of the power electronic converter.

[0044] Still further, the method may include steps of (a) providing a first, relatively higher level Li of immersion cooling to relatively high-temperature semiconductor switches HT arrayed along a first dielectric cooling fluid flow path 16 or 110, and (b) providing a second, relatively lower level L2 of immersion cooling to relatively low-temperature semiconductor switches LT arrayed along a second dielectric cooling fluid flow path 18 or 120 whereby greater thermal balance is provided across a power board 19 or 140 of the power electronic converter 12 or 102.

[0045] Through operation of the controller 132, the method may include adjusting the flow rate of dielectric cooling fluid in either or both of the flow paths 16, 18 or 110, 120, in response to semiconductor switch heating and load conditions. Further, as noted above, this may be accomplished by operation of a closed-loop control system 130 to achieve a self-adjusting cooling scheme.

[0046] The method may also be defined by the steps of:(a) delivering a first stream of dielectric cooling fluid to a first group of relatively high- temperature semiconductor switches HT;(b) delivering a second stream of dielectric cooling fluid to a second group of relatively low-temperature semiconductor switches LT; and(c) providing greater cooling to the first group of relatively high-temperature semiconductor switches HT than the second group of relatively low-temperature semiconductor switches LT whereby greater thermal balancing is provided across a power board 19, 140 of the power electronic converter 12, 102.

[0047] This method further includes independently adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions. In at least some embodiments, the method includes independently adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path 16 or 110 and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path 18 or 120 by operation of a closed-loop control system 130 to achieve a self-adjusting cooling scheme.

[0048] The differential immersion cooling systems and methods disclosed in this document are specifically designed to enhance thermal management in power converters by directly andefficiently cooling the hot switches, the primary heat-generating components. Unlike conventional immersion or air / liquid cooling systems that apply uniform cooling to the entire system, this method utilizes independent and separate cooling channels to achieve thermal balancing and temperature homogeneity across different parts of the circuit. Compared to the state-of-the-art, which often struggles with uneven temperature distribution and bulky cooling setups, the differential immersion cooling systems and methods disclosed herein provide a scalable, more efficient, and performance-optimized thermal solution for high-power electronics.SIMULATION RESULTS

[0049] The operational limit of the converters is determined by the hotspot temperature (HST) in the system. Computational fluid dynamics is a simulation tool used to estimate real- world physical behavior, particularly fluid dynamics. Also, it provides a practical means of understanding and validating the design without needing immediate physical testing.Computational fluid dynamic analysis was used to determine:(a) the temperature distribution of the converter C shown in Figures 1A-1C, equipped with prior art immersion cooling, which indicated a hotspot temperature of 111°C occurring at the HT switches;(b) the temperature distribution of the converter 12 shown in Figures 2A-2D, which indicated a reduced hotspot temperature of 90.3°C occurring at the HT switches; and(c) the temperature distribution of the converter 102 shown in Figures 3A-3D, which indicated a further reduced hotspot temperature of 84.5°C occurring at the HT switches.

[0050] Table 1, below, compares all the studied scenarios in terms of the hotspot temperature (HST). It is observed that utilizing the new differential cooling technique set forth and described in this document leads to effective temperature reduction. Additionally, it should be appreciated that the enclosure volume for circulation of differential cooling fluid represented by the first and second flow paths 16 / 110 and 18 / 120 for this study is only 43% of the enclosure volume for the conventional cooling scheme. This means that the power density of the new technique at least doubles that of the conventional system.Table 1. Comparison of the HST for all the scenariosScenario Inlet Velocity (m / s) HST (°C)ConventionalImmersion Cooling 0.5 111(Figs. 1A-1C)Differential ImmersionCooling, One Inlet 0.5 90.3(Figs. 2A-2C)Differential Immersion _ .P T1-0.5 for HT 0.5 for LTCooling, Two Inlets „ . , „ . , 84.5 Switches Switches(Figs. 3A-3C)Differential Immersion ,c TCooling, Two Inlets ' f' ? 79.2 zr- A Switches Switches(Figs. 3A-3C)Differential Immersion _ „TT„ _ .T„„ 2 for HT 0.5 for LTCooling, Two Inlets „ . , „ . , 75.4° Switches Switches(Figs. 3A-3C)

[0051] This document may be said to relate to the following:1. A differential immersion cooling system for a power converter including at least one high-temperature semiconductor switch and at least one low-temperature semiconductor switch, comprising: a first flow path adapted to provide immersion cooling to the at least one high- temperature semiconductor switch; a second flow path adapted to provide immersion cooling to the at least one low- temperature semiconductor switch; and a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the at least one high- temperature semiconductor switch and the at least one low-temperature semiconductor switch to improve thermal balancing and increase temperature homogeneity between the at least one high- temperature semiconductor switch and the at least one low-temperature semiconductor switch.2. The differential immersion cooling system of item 1, further including a heat exchanger, wherein said pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.3. The differential immersion cooling system of item 2, further including a splitter downstream from the pump assembly, said splitter including (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path.4. The differential immersion cooling system of item 3, wherein the first feed outlet is adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet is adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where Vi>V2.5. The differential immersion cooling system of item 4, further including an aggregator downstream of the first and second flow paths, said aggregator including (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) a return port in communication with the heat exchanger.6. The differential immersion cooling system of item 1, wherein the pump assembly includes a first pump in communication with the first flow path and a second pump in communication with the second flow path.7. The differential immersion cooling system of item 6, further including a heat exchanger and wherein (a) the first pump circulates the dielectric cooling fluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump circulates the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.8. The differential immersion cooling system of item 7, further including a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths.9. The differential immersion cooling system of item 8, further including a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the at least one high-temperature semiconductor switch in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the at least one low- temperature semiconductor switch in the second flow path.10. The differential immersion cooling system of item 9, wherein the controller is adapted to receive temperature data from the first and second temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.11. A power converter including the differential immersion cooling system of any of claims 1-10.12. A power converter, comprising: a power board including a plurality of relatively high-temperature semiconductor switches and a plurality of relatively low-temperature semiconductor switches; and a differential immersion cooling system including (a) a first flow path adapted to provide immersion cooling to the plurality of high-temperature semiconductor switches, (b) a second flow path adapted to provide immersion cooling to the plurality of low-temperature semiconductor switch, and (c) a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the plurality of high-temperature semiconductor switches and the plurality of low-temperature semiconductor switches to improve thermal balancing and increase temperature homogeneity across the power board.13. The power converter of item 12, wherein the differential immersion cooling system further includes a heat exchanger, and wherein said pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.14. The power converter of item 13, wherein the differential immersion cooling system further includes a splitter downstream from the pump assembly, said splitter including (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path.15. The power converter of item 14, wherein the first feed outlet is adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet isadapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where V V2.16. The power converter of item 15, wherein the differential immersion cooling system further includes an aggregator downstream of the first and second flow paths, said aggregator including (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) a return port in communication with the heat exchanger.17. The power converter of item 12, wherein the pump assembly includes a first pump in communication with the first flow path and a second pump in communication with the second flow path.18. The power converter of item 15, wherein the differential immersion cooling system further includes a heat exchanger and wherein (a) the first pump circulates the dielectric cooling fluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump circulates the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.19. The power converter of item 18, wherein the differential immersion cooling system further includes a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths.20. The power converter of item 19, wherein the differential immersion cooling system further includes a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the plurality of relatively high-temperature semiconductor switches in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the plurality of relatively low-temperature semiconductor switches in the second flow path.21. The power converter of item 20, wherein the controller is adapted to receive temperature data from the first and second temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.22. A method of improving overall performance of a power electronic converter, comprising: thermal balancing the power electronic converter by providing differential immersion cooling to the semiconductor switches of the power electronic converter.23. The method of item 22, further including removing more heat from hotter switches of the power electronic converter.24. A method of cooling a power electronic converter, comprising: providing a first, relatively higher level Li of immersion cooling to relatively high- temperature semiconductor switches arrayed along a first dielectric cooling fluid flow path; and providing a second, relatively lower level L2 of immersion cooling to relatively low- temperature semiconductor switches arrayed along a second dielectric cooling fluid flow path whereby greater thermal balance is provided across a power board of the power electronic converter.25. The method of item 24, further including adjusting a flow rate of dielectric cooling fluid in response to semiconductor switch heating and load conditions.26. The method of item 24, further including adjusting a flow rate of dielectric cooling fluid through the first dielectric cooling fluid flow path and the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.27. A method of cooling a power electronic converter, comprising: delivering a first stream of dielectric cooling fluid to a first group of relatively high- temperature semiconductor switches; delivering a second stream of dielectric cooling fluid to a second group of relatively low- temperature semiconductor switches; and providing greater cooling to the first group of relatively high-temperature semiconductor switches than the second group of relatively low-temperature semiconductor switches whereby greater thermal balancing is provided across a power board of the power electronic converter.28. The method of item 27, further including adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions.29. The method of item 27, further including independently adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions.30. The method of item 27, further including adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.31. The method of item 27, further including independently adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.

[0052] The differential immersion cooling systems 10, 100 and related methods described herein, provide a number of benefits and advantages. These include:• Enhanced Thermal Management: Efficiently removes more heat from hotter switches. Maintains uniform and homogenous temperature distribution. Prevents thermal runaway and allows operation at higher power ratings.• Adaptive and Intelligent Cooling: Incorporates a closed-loop control system to adjust flow rate dynamically. Enables a self-regulating cooling scheme based on real-time thermal conditions.• Improved Reliability: Minimizes thermal expansion and solder joint failures due to better thermal balancing. Increases overall system reliability, especially in converters with unbalanced loss distributions (e.g., T-Type, NPC, and active NPC converters).• Higher Power Density: Requires significantly less cooling fluid than conventional immersion methods. Allows for a more compact design, contributing to increased power density.• Extended Component Lifespan: Reduced operating temperatures prolong the lifespan of semiconductor switches and the entire converter system.

[0053] The uniqueness of the approach lies in its differential cooling design, which not only improves heat dissipation at critical hotspots but also reduces thermal gradients within thesystem. This results in: increased maximum output power, enhanced reliability through consistent thermal performance, and higher power density enabled by a more compact and purpose-built cooling architecture.

[0054] Although the differential immersion cooling systems, power converters and related methods of this disclosure have been illustratively described and presented by way of specific exemplary embodiments, and examples thereof, it is evident that many alternatives, modifications, or / and variations, thereof, will be apparent to those skilled in the art. For example, a flow control valve, under operational control of the controller 132, could be used as the splitter 24 to divide the flow of dielectric cooling fluid from a single pump 20 between the two flow paths 16, 18 arrayed with HT and LT switches in order to provide the differential cooling. It is intended that all such alternatives, modifications, or / and variations, fall within the spirit of, and are encompassed by, the broad scope of the appended claims.

Claims

What is claimed:

1. A differential immersion cooling system for a power converter including at least one high-temperature semiconductor switch and at least one low-temperature semiconductor switch, comprising: a first flow path adapted to provide immersion cooling to the at least one high- temperature semiconductor switch; a second flow path adapted to provide immersion cooling to the at least one low- temperature semiconductor switch; and a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the at least one high- temperature semiconductor switch and the at least one low-temperature semiconductor switch to improve thermal balancing and increase temperature homogeneity between the at least one high- temperature semiconductor switch and the at least one low-temperature semiconductor switch.

2. The differential immersion cooling system of claim 1, further including a heat exchanger, wherein said pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.

3. The differential immersion cooling system of claim 2, further including a splitter downstream from the pump assembly, said splitter including (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path.

4. The differential immersion cooling system of claim 3, wherein the first feed outlet is adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet is adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where Vi>V2.

5. The differential immersion cooling system of claim 4, further including an aggregator downstream of the first and second flow paths, said aggregator including (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) a return port in communication with the heat exchanger.

6. The differential immersion cooling system of claim 1, wherein the pump assembly includes a first pump in communication with the first flow path and a second pump in communication with the second flow path.

7. The differential immersion cooling system of claim 6, further including a heat exchanger and wherein (a) the first pump circulates the dielectric cooling fluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump circulates the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.

8. The differential immersion cooling system of claim 7, further including a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths.

9. The differential immersion cooling system of claim 8, further including a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the at least one high-temperature semiconductor switch in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the at least one low-temperature semiconductor switch in the second flow path.

10. The differential immersion cooling system of claim 9, wherein the controller is adapted to receive temperature data from the first and second temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.

11. A power converter including the differential immersion cooling system of any of claims 1-10.

12. A power converter, comprising: a power board including a plurality of relatively high-temperature semiconductor switches and a plurality of relatively low-temperature semiconductor switches; and a differential immersion cooling system including (a) a first flow path adapted to provide immersion cooling to the plurality of high-temperature semiconductor switches, (b) a second flow path adapted to provide immersion cooling to the plurality of low-temperaturesemiconductor switch, and (c) a pump assembly adapted to circulate a dielectric cooling fluid through the first flow path and the second flow path whereby differential cooling is provided to the plurality of high-temperature semiconductor switches and the plurality of low-temperature semiconductor switches to improve thermal balancing and increase temperature homogeneity across the power board.

13. The power converter of claim 12, wherein the differential immersion cooling system further includes a heat exchanger, and wherein said pump assembly circulates the dielectric cooling fluid from the heat exchanger through the first and second flow paths and back to the heat exchanger.

14. The power converter of claim 13, wherein the differential immersion cooling system further includes a splitter downstream from the pump assembly, said splitter including (a) a single inlet in communication with the pump assembly, (b) a first feed outlet in communication with the first flow path, and (c) a second feed outlet in communication with the second flow path.

15. The power converter of claim 14, wherein the first feed outlet is adapted to deliver a first volume Vi of the dielectric cooling fluid to the first flow path and the second feed outlet is adapted to deliver a second volume V2 of the dielectric cooling fluid to the second flow path where V V2.

16. The power converter of claim 15, wherein the differential immersion cooling system further includes an aggregator downstream of the first and second flow paths, said aggregator including (a) a first input in communication with the first flow path, (b) a second input in communication with the second flow path, and (c) a return port in communication with the heat exchanger.

17. The power converter of claim 12, wherein the pump assembly includes a first pump in communication with the first flow path and a second pump in communication with the second flow path.

18. The power converter of claim 15, wherein the differential immersion cooling system further includes a heat exchanger and wherein (a) the first pump circulates the dielectric coolingfluid from the heat exchanger through the first flow path and back to the heat exchanger in a first circuit and (b) the second pump circulates the dielectric cooling fluid from the heat exchanger through the second flow path and back to the heat exchanger in a second circuit.

19. The power converter of claim 18, wherein the differential immersion cooling system further includes a controller adapted to independently control operation of the first pump and the second pump and the flow of the dielectric cooling fluid through the first and second flow paths.

20. The power converter of claim 19, wherein the differential immersion cooling system further includes a first temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the plurality of relatively high-temperature semiconductor switches in the first flow path and a second temperature sensor adapted to monitor a current temperature of the dielectric cooling fluid or the plurality of relatively low-temperature semiconductor switches in the second flow path.

21. The power converter of claim 20, wherein the controller is adapted to receive temperature data from the first and second temperature sensors and independently adjust flow rates of the dielectric cooling fluid through the first and second flow paths based upon temperature data and load conditions.

22. A method of improving overall performance of a power electronic converter, comprising: thermal balancing the power electronic converter by providing differential immersion cooling to the semiconductor switches of the power electronic converter.

23. The method of claim 22, further including removing more heat from hotter switches of the power electronic converter.

24. A method of cooling a power electronic converter, comprising: providing a first, relatively higher level Li of immersion cooling to relatively high- temperature semiconductor switches arrayed along a first dielectric cooling fluid flow path; and providing a second, relatively lower level L2 of immersion cooling to relatively low- temperature semiconductor switches arrayed along a second dielectric cooling fluid flow path whereby greater thermal balance is provided across a power board of the power electronic converter.

25. The method of claim 24, further including adjusting a flow rate of dielectric cooling fluid in response to semiconductor switch heating and load conditions.

26. The method of claim 24, further including adjusting a flow rate of dielectric cooling fluid through the first dielectric cooling fluid flow path and the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.

27. A method of cooling a power electronic converter, comprising: delivering a first stream of dielectric cooling fluid to a first group of relatively high- temperature semiconductor switches; delivering a second stream of dielectric cooling fluid to a second group of relatively low- temperature semiconductor switches; and providing greater cooling to the first group of relatively high-temperature semiconductor switches than the second group of relatively low-temperature semiconductor switches whereby greater thermal balancing is provided across a power board of the power electronic converter.

28. The method of claim 27, further including adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions.

29. The method of claim 27, further including independently adjusting a flow rate of the first and second streams of dielectric cooling fluid in response to semiconductor switch heating and load conditions.

30. The method of claim 27, further including adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.

31. The method of claim 27, further including independently adjusting a flow rate of the first stream of dielectric cooling fluid through the first dielectric cooling fluid flow path and a flow rate of the second stream of the dielectric cooling fluid through the second dielectric cooling fluid flow path by operation of a closed-loop control system to achieve a self-adjusting cooling scheme.

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