Oil-cooled power inverters and methods of operating thereof

Abstract

Described herein are oil-cooled power inverters having various features enabling efficient cooling and compact design. For example, an oil-cooled power inverter may comprise a power inverter PCB comprising a plurality of power transistors thermally coupled to liquid-cooled blocks. Cooling fluid is distributed to the liquid-cooled blocks from a volume partially defined by a manifold and the power inverter PCB. A power inverter board may electrically connect with a plurality of terminals and have pass-throughs enabling cooling liquid to pass from the volume, through the PCB, to the liquid-cooled blocks, while preventing cross-flow of cooling fluid between channels. When the cooling fluid is a dielectric fluid, arrangement of components enables direct contact of the cooling fluid with some electrically active components. The power transistors may be thereby cooled by contact with the liquid-cooled blocks. Arrangement of components enables both efficient liquid cooling and compact design of the oil-cooled power inverter.

Description

Oil-Cooled Power Inverters and Methods of Operating ThereofCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of US Provisional Patent Application 63 / 649,602, filed on 2024-05-20, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Power inverters are devices used to convert direct current (DC) to alternating current (AC). Power inverters are used in various applications, e.g. electric vehicles. In electric vehicles powered by batteries, DC is supplied by the batteries. Power inverters may be used to convert this power to AC for use to power, for example, drive motors or electrical accessories. Cooling can be essential for power inverters, especially their power transistor components. First, Power inverters are not perfectly efficient as some of the electrical energy is lost as heat. Cooling helps dissipate this heat, preventing the power inverter from overheating and ensuring that it operates at its rated efficiency. Cooling is particularly important in compact, high-power inverters that have high levels of heat dissipation but not enough thermal mass for this heat to dissipate into. Furthermore, electronic components (e.g., transistors) have temperature limits beyond which these components can be damaged, or their performance can degrade, thereby requiring constant cooling. Overall, temperature fluctuations (caused by heating) can affect the performance and accuracy of various components of power inverters. Various cooling methods have been proposed for power inverters, e.g., passive cooling (such as heat sinks) and active cooling (such as fans). However, integration of cooling into power inverters, especially compact, high-power inverters, while maintaining the small size of these power inverters has been challenging. Cooling components require a significantamount of space. Furthermore, establishing thermal coupling with various heatgenerating components (e.g., transistors) can be difficult.

[0003] What is needed are new types of power inverters or, more specifically, new arrangements of various components in power inverters enabling efficient cooling during high-power applications.SUMMARY

[0004] Described herein are oil-cooled power inverters having various features enabling efficient cooling and compact design. For example, an oil-cooled power inverter may comprise a power inverter PCB comprising a plurality of power transistors thermally coupled to liquid-cooled blocks. Cooling fluid is distributed to the liquid-cooled blocks from a volume partially defined by a manifold and the power inverter PCB. The power inverter board may electrically connect with a plurality of terminals and have pass-throughs enabling cooling liquid to pass from the volume, throughhe PCB, to the liquid-cooled blocks, while preventing crossflow of cooling fluid between channels. When the cooling fluid is a dielectric fulid, arrangement of components enables direct contact of the cooling fluid with some electrically active components. The power transistors may be thereby cooled by contact with the liquid-cooled blocks. Arrangement of components enables both efficient liquid cooling and compact design of the oil-cooled power inverter.

[0005] Clause 1. An oil-cooled power inverter, comprising: a plurality of terminals; a first DC connector and a second DC connector; a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of power transistors; a manifold comprising a cooling fluid distributor, a cooling fluid inlet comprising a first lumen, a cooling fluid outlet comprising a second lumen, and a cooling fluid sump; and a plurality of transistor cooling blocks fluidically coupled to the manifold, wherein: the cooling fluid inlet is fluidically coupled to the cooling fluid distributor, the cooling fluid outlet is fluidically coupled to the cooling fluid sump, the cooling fluid sump is fluidically coupled to the plurality of transistor coolingblocks, the plurality of power transistors is physically and thermally connected to the plurality of transistor cooling blocks, the manifold is fluidically coupled to the power inverter board, and the cooling fluid inlet, the cooling fluid distributor, the manifold, the power inverter board, and the plurality of transistor cooling blocks together form a liquid-tight volume.

[0006] Clause 2. The oil-cooled power inverter of clause 1, wherein the manifold comprises a plurality of distributor-manifold inlets fluidically coupled to the cooling fluid distributor, a plurality of manifold-block outlets, a first plurality of manifold-passages, a plurality of manifold-block inlets, a plurality of manifoldsump outlets, and a second plurality of manifold-passages, wherein: each one of the first plurality of manifold-passages is fluidically coupled to one of the plurality of distributor-manifold inlets and one of the plurality of manifold-block outlets, each one of the second plurality of manifold-passages is fluidically coupled to one of the plurality of manifold-block inlets and one of the plurality of manifold-sump outlets, and each one of the plurality of manifold-sump outlets is fluidically coupled to the cooling fluid sump.

[0007] Clause 3. The oil-cooled power inverter of clause 2, wherein the power inverter board further comprises a plurality of transistor block inlet passthroughs and a plurality of transistor block outlet passthroughs, wherein: each one of the plurality of transistor block inlet passthroughs is fluidically coupled to one of the plurality of manifold-block outlets, and each one of the plurality of transistor block outlet passthroughs is fluidically coupled to one of the plurality of manifoldblock inlets.

[0008] Clause 4. The oil-cooled power inverter of clause 3, wherein the plurality of transistor cooling blocks comprises a plurality of cooling-block inlets, a plurality of cooling-block outlets, and a plurality of cooling-block passages, wherein each one of the plurality of cooling-block passages is fluidically coupled both to one of the plurality of cooling-block inlets and to one of the plurality of cooling-block outlets.

[0009] Clause 5. The oil-cooled power inverter of clause 4, wherein: each one of the plurality of cooling-block inlets is fluidically coupled to one of the plurality oftransistor block inlet passthroughs, and each one of the plurality of cooling-block outlets is fluidically coupled to one of the plurality of transistor block outlet passthroughs.

[0010] Clause 6. The oil-cooled power inverter of clause 4, further comprising a gasket positioned between the manifold and the power inverter board comprising a plurality of inlet passthroughs and a plurality of outlet passthroughs, wherein each one of the plurality of inlet passthroughs is fluidically coupled either to one of the plurality of cooling-block inlets or to one of the plurality of cooling-block outlets.

[0011] Clause 7. The oil-cooled power inverter of clause 6, wherein the gasket further comprises a plurality of bolt passthroughs.

[0012] Clause 8. The oil-cooled power inverter of clause 1, wherein the cooling fluid inlet is fluidically coupled to an outlet of an external pump and heat exchanger and the cooling fluid outlet is fluidically coupled to an inlet of an external pump and heat exchanger.

[0013] Clause 9. The oil-cooled power inverter of clause 1, wherein the power inverter board further comprises a plurality of capacitors configured to alternatively store a DC power input to the power inverter board and deliver a DC power output to the plurality of power transistors.

[0014] Clause 10. The oil-cooled power inverter of clause 1, further comprising a control electronics board electronically connected to the power inverter board.

[0015] Clause 11. The oil-cooled power inverter of clause 10, further comprising a plurality of riser boards physically connected and electronically connected to both the control electronics board and the power inverter board.

[0016] Clause 12. The oil-cooled power inverter of clause 1, wherein a drain of each one of the plurality of power transistors is electrically connected to one of the plurality of transistor cooling blocks.

[0017] Clause 13. The oil-cooled power inverter of clause 12, further comprising a first busbar positioned between and electrically connected to both the plurality of transistor cooling blocks and the first DC connector.

[0018] Clause 14. The oil-cooled power inverter of clause 1, further comprising a plurality of bus cylinders electrically connected to the power inverter board.

[0019] Clause 15. The oil-cooled power inverter of clause 14, further comprising a second busbar positioned between and electrically connected to both the plurality of bus cylinders and the second DC connector.

[0020] Clause 16. A method of operating an oil-cooled power inverter comprising a plurality of terminals, a first DC connector, a second DC connector, a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of plurality of power transistors, a manifold comprising a cooling fluid distributor, a cooling fluid inlet, a cooling fluid outlet, and a cooling fluid sump, and a plurality of transistor cooling blocks fluidically coupled to the manifold and thermally coupled to the plurality of power transistors, the method comprising: receiving by the power inverter board a direct electrical current; converting by the plurality of power transistors the direct electrical current into an alternating electrical current; and circulating, by an external pump and heat exchanger, a cooling fluid through manifold and the plurality of transistor cooling blocks, thereby transferring heat from the plurality of power transistors.

[0021] Clause 17. The method of clause 16, wherein: the cooling fluid inlet is fluidically coupled to the cooling fluid distributor, the cooling fluid outlet is fluidically coupled to the cooling fluid sump, the cooling fluid sump is fluidically coupled to the plurality of transistor cooling blocks, and circulating the cooling fluid further comprises flowing the cooling fluid into the manifold via the cooling fluid inlet, from the cooling fluid inlet to the cooling fluid distributor, from the cooling fluid distributor to the plurality of transistor cooling blocks, from the plurality of transistor cooling blocks to the cooling fluid sump, and from the cooling fluid sump to the cooling fluid outlet.

[0022] Clause 18. The method of clause 16, wherein the alternating electrical current is a three phase AC.

[0023] Clause 19. The method of clause 16, wherein the oil-cooled power inverter further comprises a control electronics board electronically coupled tothe external pump and heat exchanger and a temperature sensor thermally coupled to the plurality of power transistors and electronically coupled to the control electronics board and the method further comprises: measuring at the temperature sensor a temperature; recording at the control electronics board the measured temperature; determining at the control electronics board whether the measured temperature is above a temperature limit; and signaling by the control electronics board to the external pump and heat exchanger to change a flow rate of the cooling fluid if the measured temperature is above the temperature limit.

[0024] Clause 20. The method of clause 19, wherein the temperature limit is 100 °C.

[0025] Clause 21. The method of clause 16, wherein the oil-cooled power inverter further comprises a control electronics board electronically coupled to the external pump and heat exchanger and a plurality of Hall-effect sensors electronically coupled to the control electronics board and the method further comprises: measuring at the plurality of hall-effect sensors an alternating current flow from the power inverter board; recording at the control electronics board the measured alternating current flow; determining at the control electronics board a predetermined flow rate of the cooling fluid for the measured alternating current flow; and signaling by the control electronics board to the external pump and heat exchangerto change a flow rate of the cooling fluid if the measured rate of change of the alternating current flow is different than the predetermined flow rate.

[0026] Clause 22. A vehicle comprising a liquid-cooled electric motor and an oil- cooled power inverter, the oil-cooled power inverter comprising: a plurality of terminals; a first DC connector and a second DC connector; a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of power transistors; a cooling fluid inlet comprising a first lumen, a cooling fluid distributor fluidically coupled to the cooling fluid inlet; a manifold fluidically coupled to the cooling fluid distributor; a plurality of transistor cooling blocks fluidically coupled to themanifold; a cooling fluid sump fluidically coupled to the plurality of transistor cooling blocks; and a cooling fluid outlet comprising a second lumen and fluidically coupled to the cooling fluid sump, wherein: the plurality of power transistors is physically and thermally connected to the plurality of transistor cooling blocks, the manifold is fluidically sealed to the power inverter board, and the cooling fluid inlet, the cooling fluid distributor, the manifold, the power inverter board, and the plurality of transistor cooling blocks together form a volume fluidically sealed with the exception of the first lumen and the second lumen.

[0027] Clause 23. The vehicle of clause 22, wherein the oil-cooled power inverter is affixed to the liquid-cooled electric motor.

[0028] Clause 24. The vehicle of clause 22, wherein the liquid-cooled electric motor further comprises a plurality of terminals.

[0029] Clause 25. The vehicle of clause 22, wherein: the liquid-cooled electric motor and the oil-cooled power inverter are both fluidically coupled to an external pump and heat exchanger, and the cooling fluid inlet and the cooling fluid outlet are fluidically coupled to the external pump and heat exchanger.

[0030] These and other embodiments are described further below with reference to the figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The included drawings are for illustrative purposes and serve only to provide examples of possible structures and operations for the disclosed inventive systems, apparatus, and methods. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed implementations.

[0032] FIG. 1 is a schematic block diagram illustrating various components of an oil-cooled power inverter and some of their relationships, in accordance with some examples.

[0033] FIG. 2 is a perspective drawing illustrating the relationship of an oil- cooled power inverter with a liquid-cooled electric motor, in accordance with some examples.

[0034] FIG. 3 is a perspective drawing illustrating components of the oil-cooled power inverter with a portion of the inverter housing removed, in accordance with some examples.

[0035] FIG. 4 is a top view drawing illustrating components of the oil-cooled power inverter with a portion of the inverter housing, first busbar, and second busbar removed, in accordance with some examples.

[0036] FIG. 5A is a perspective view drawing illustrating components of the oil- cooled power inverter with a portion of the inverter housing, first busbar, and second busbar removed, in accordance with some examples.

[0037] FIG. 5B is a perspective view drawing illustrating components of the oil- cooled power inverter with a portion of the inverter housing, first busbar, second busbar, and control electronics board removed, in accordance with some examples.

[0038] FIG. 6A is a perspective view drawing illustrating components of the oil- cooled power inverter with a portion of the inverter housing, first busbar, second busbar, control electronics board, a plurality of transistor cooling blocks, and a plurality of bus cylinders removed, in accordance with some examples.

[0039] FIG. 6B is a perspective view drawing illustrating components of the oil- cooled power inverter with the same components removed as in FIG. 6A, and additionally, the plurality of power transistors, the power inverter board, and the plurality of capacitors removed, in accordance with some examples.

[0040] FIG. 7A is a top-view drawing of a cross-section of an oil-cooled power inverter through the cooling fluid inlet, illustrating some internal components of an oil-cooled power inverter, in accordance with some examples.

[0041] FIG. 7B is a schematic cross-sectional side-view of an oil-cooled power inverter at line A-A of FIG. 7A, in accordance with some examples.

[0042] FIG. 7C is a schematic cross-sectional side-view of an oil-cooled power inverter at line B-B of FIG. 7A, in accordance with some examples.

[0043] FIG. 7D is a perspective view showing the relationships of some components of an oil-cooled power inverter on a side that in FIG. 2 is obscured by the liquid-cooled electric motor, in accordance with some examples.

[0044] FIG. 8A is a perspective view showing the relationship of some components of one of a plurality of transistor cooling blocks, in accordance with some examples.

[0045] FIG. 8B is a cross-section view showing the relationship of some components of one of a plurality of transistor cooling blocks, in accordance with some examples.

[0046] FIG. 9 is a process flowchart corresponding to a method of operating an oil-cooled power inverter, in accordance with some examples.

[0047] FIG. 10 is a schematic block diagram illustrating various components of a vehicle and some of their relationships, in accordance with some examples.DETAILED DESCRIPTIONIntroduction

[0048] As noted above, power inverters are devices used to convert DC to AC.Power inverters are used in various applications, e.g., electric vehicles. In electric vehicles powered by batteries, DC is supplied by the batteries. Depending on the type of electric motor powered by the batteries, DC may need to be converted to AC. Also, depending on the type of electrical motor, AC may be provided to the motor as single-phase AC or three-phase AC. In singlephase AC, electrical current is provided with a voltage that oscillates at a set frequency in a sinusoidal waveform. In three-phase AC, electrical current is provided as three oscillating phases over three separate leads. All three phases oscillate at the same set frequency, with each offset in phase 120 degrees from the other two phases. Three-phase AC has benefits for driving electrical motors,including smooth starting and low-vibration operations. Additionally, unlike single-phase AC motors, three-phase AC motors may be controlled down to zero speed at full torque. This is especially desirable for traction motor applications.

[0049] Often in electric vehicles, internal space is at a premium, so compact formats for power inverters are desirable. However, integration of cooling into power inverters, especially compact, high-power inverters, while maintaining the small size of these power inverters can be challenging. Compact power inverters are more difficult to effectively cool. Passive cooling, such as heat sinks, may not provide sufficient removal of heat to maintain an acceptable operating temperature when the power inverter is under the highest load. Active cooling components may require a significant amount of space.

[0050] In the oil-cooled power inverters described below, cooling fluid is distributed through a manifold integrated into the enclosure of the power inverters and cooling blocks. The cooling blocks are thermally coupled to power transistors to effectively remove heat from them during operation. The bodies of the power transistors may be mechanically coupled with the cooling blocks and not be electrically connected with other components of the oil-cooled power inverter when the cooling fluid is a dielectric fluid, such as an oil. Direct coupling of the power transistors with the cooling blocks provides improved heat transfer from the power transistors to the cooling fluid, via the cooling blocks, and increased compactness of the oil-cooled power inverters. Due to the arrangement of channels and seals within the power inverter, the bodies of the power transistors and other power electronics are not directly contacted by the cooling fluid. Control and communication electronics, connectors to power terminals on an electric motor, and DC distribution bus bars are also kept dry. In addition, a power PCB comprising the power transistors serves as one wall of the coolant reservoir to further save weight and space.

[0051] As described below, the power inverter may be affixed to a motor. Affixing the power inverter to the motor saves space within an electric vehicle, and also saves mass. Saving mass is desirable in the design of electric vehiclesbecause accelerating more mass requires more energy, which leads to decreased vehicle range for a given battery charge. Further, locating power inverters close to electric motors reduces resistive power losses over long transmission lines between the motor and the power inverter. In some examples, electrical motors may also be cooled by cooling fluid. In some further examples, the power inverter and the electric motor may use the same cooling fluid, coolant pump, and heat exchanger as already included in the electric vehicle for a liquid-cooled electric motor, saving further mass and space.Examples of Oil-Cooled Power Inverters

[0052] FIG. 1 is a schematic block diagram illustrating components of an oil- cooled power inverter 100 and some of their relationships, in accordance with some examples. The oil-cooled power inverter 100 comprises a plurality of terminals 105, a first DC connector 115, a second DC connector 120, a power inverter board 230, a manifold 155, and a plurality of transistor cooling blocks 190. The power inverter board 230 is electrically connected to the plurality of terminals 105, the first DC connector 115, and the second DC connector 120. The power inverter board 230 comprises a plurality of power transistors 125. The manifold 155 comprises a cooling fluid distributor 150, a cooling fluid inlet 140, a cooling fluid outlet 215, and a cooling fluid sump 210. The cooling fluid inlet 140 comprises a first lumen 145. The cooling fluid outlet 215 comprises a second lumen 220. The plurality of transistor cooling blocks 190 is fluidically coupled to the 155. The cooling fluid inlet 140 is fluidically coupled with the cooling fluid distributor 150. The cooling fluid outlet 215 is fluidically coupled to the cooling fluid sump 210. The cooling fluid sump 210 is fluidically coupled to the plurality of transistor cooling blocks 190. The plurality of power transistors 125 is physically and thermally connected to the plurality of transistor cooling blocks 190. The thermal connection of the plurality of power transistors 125 with the plurality of transistor cooling blocks 190 provides cooling to remove heat generated during operation of the plurality of power transistors 125, as will be described in more detail below. The manifold 155 is fluidically coupled to the power inverter board 230. The cooling fluid inlet 140, the cooling fluiddistributor 150, the manifold 155, the power inverter board 230, and the plurality of transistor cooling blocks 190 together form a liquid-tight volume. As described in more detail below, a cooling fluid may be flown into the liquid- tight volume via the first lumen 145 of the cooling fluid inlet 140 and out of the liquid-tight volume via the second lumen 220 of the cooling fluid outlet 215. The flow of a cooling fluid through components of the oil-cooled power inverter 100, including the cooling fluid inlet 140, the cooling fluid distributor 150, the manifold 155, the cooling fluid sump 210, and the cooling fluid outlet 215 will be described in detail below.

[0053] In some examples, the oil-cooled power inverter 100 further comprises an inverter housing 305. The inverter housing 305 may comprise one or more of the plurality of terminals 105, the power inverter board 230, the cooling fluid inlet 140, the cooling fluid distributor 150, the manifold 155, the plurality of transistor cooling blocks 190, the cooling fluid sump 210, and the cooling fluid outlet 215. In some still further examples, the power inverter board 230, the cooling fluid distributor 150, the manifold 155, the plurality of transistor cooling blocks 190, the cooling fluid sump 210 may be positioned within the inverter housing 305 and the cooling fluid inlet 140 and the cooling fluid outlet 215 extend from within the inverter housing 305 to outside of the inverter housing 305.

[0054] FIG. 2 is a perspective drawing illustrating the relationship of the oil- cooled power inverter 100 with a liquid-cooled electric motor 970, in accordance with some examples. As shown in FIG. 2, in some examples, cooling fluid inlet 140, cooling fluid outlet 215, first DC connector 115 and second DC connector 120 extend from within inverter housing 305 to the space external to inverter housing 305. As shown in FIG. 2, in some examples, oil-cooled power inverter 100 directly interfaces liquid-cooled electric motor 970. Specifically, a portion of inverter housing 305 directly interfaces liquid-cooled electric motor 970. As noted above, decreasing mass and volume of components of electric vehicles is desirable. Decreasing mass of components may increase vehicle range for a given battery charge. Decreasing the volume of components may increase space available or provide more design flexibility for placement withinthe vehicle for other components such as, for example, battery packs. Affixing the power inverter to the motor saves space within an electric vehicle, and also decreases mass. Further, locating power inverters close to electric motors reduces resistive power losses over long transmission lines between the motors and the power inverters. In some examples, a liquid-cooled electric motor 970 of the electric vehicle may also be cooled by cooling fluid. In some further examples, the power inverter and the liquid-cooled electric motor 970 may use the same cooling fluid, coolant pump, and heat exchanger as already included in the electric vehicle for a liquid-cooled electric motor 970, saving further mass and space. An oil-cooled power inverter 100 and a liquid-cooled electric motor 970 using the same cooling fluid, coolant pump, and heat exchanger is possible when the cooling fluid is a dielectric, or non-electrically conducting, fluid. The non-conductivity of a dielectric fluid prevents unwanted electrical communication, or shorts, between components of the oil-cooled power inverter 100 and the liquid-cooled electric motor 970.

[0055] FIG. 3 is a perspective drawing illustrating components of the oil-cooled power inverter 100 with a portion of inverter housing 305 removed, in accordance with some examples. Shown in FIG. 3, in some examples, oil-cooled power inverter 100 comprises a first busbar 285. First busbar 285 is positioned between and electrically connected to both the first DC connector 115 and plurality of transistor cooling blocks 190. Also shown in FIG. 3, in some examples, oil-cooled power inverter 100 comprises a plurality of bus cylinders 265. Plurality of bus cylinders 265 is electrically connected to the power inverter board 230. A second busbar 280 is positioned between and electrically connected to both the second DC connector 120 and the plurality of bus cylinders 265. First busbar 285 and second busbar 280 are electrically isolated from each other. Plurality of bus cylinders 265, first busbar 285, and second busbar 280 may be formed from a metal selected from the list including aluminum, copper, and steel. In some examples, plurality of bus cylinders 265, first busbar 285, and second busbar 280 may be formed from aluminum. Dimensions of plurality of bus cylinders 265, first busbar 285, and second busbar 280 in directions perpendicular to the direction of the flow throughthese components may be chosen to provide sufficient electrical conductivity to prevent excessive resistive heating during operation of oil-cooled power inverter 100. Direct current electrical power is supplied to oil-cooled power inverter 100 via first DC connector 115 and second DC connector 120. In some examples, direct current electrical power is supplied to oil-cooled power inverter 100 from a battery or a battery pack. In some examples, the drain leg of each transistor of the plurality of power transistors 125 is electrically connected to one of the plurality of transistor cooling blocks 190. Power inverter board 230 is configured to convert direct current supplied to the oil- cooled power inverter 100 into alternating current. In some examples, the alternating current is a single-phase alternating current. In some other examples, the alternating current is a three-phase AC. Alternating current is supplied by the oil-cooled power inverter 100, for example, to liquid-cooled electric motor 970.

[0056] FIG. 4 is a top view drawing illustrating components of the oil-cooled power inverter 100 with a portion of the inverter housing 305, and first busbar 285 and second busbar 280 removed, in accordance with some examples. FIG. 5A is a perspective view drawing illustrating components of the oil-cooled power inverter 100 with a portion of the inverter housing 305, and first busbar 285 and second busbar 280 removed, in accordance with some examples. As shown in FIG. 4, in some examples, oil-cooled power inverter 100 comprises a control electronics board 260. Control electronics board 260 is electronically connected to the power inverter board 230. As shown in FIG. 1, in some examples, control electronics board 260 comprises signal processing electronics 290, communication electronics 295, a plurality of Hall-effect sensors 950, and a plurality of riser boards 270. Plurality of Hall-effect sensors 950 may comprise one, two, three, or even more than three sensors. In a specific example, plurality of Hall-effect sensors 950 comprises two sensors. Plurality of Halleffect sensors 950 is electronically connected to control electronics board 260. Plurality of Hall-effect sensors 950 may be configured to measure the electrical current passing through one or more transistors of the plurality of power transistors 125, thereby providing measurements of current magnitude andpolarity. In a specific example, each one of the two sensors of the plurality of Hall-effect sensors 950 measures current in one phase of the three-phase AC power signal. In this example, control electronics board 260 is configured to calculate the magnitude of the three phases of the three phase AC power passed by the plurality of power transistors 125. Further, control electronics board 260 is configured to provide control signals to power inverter board 230. In some examples, as shown in FIG. 1 and in FIG. 2, oil-cooled power inverter 100 may comprise a low voltage connector 300. Low voltage connector 300 may be configured to provide an electronic connection between control electronics board 260 and other components external to oil-cooled power inverter 100.

[0057] FIG. 5B is a perspective view drawing illustrating components of the oil- cooled power inverter 100 with a portion of the inverter housing 305, first busbar 285, second busbar 280, and control electronics board 260 removed, in accordance with some examples. As shown in FIG. 5B, in some examples, oil- cooled power inverter 100 comprises a plurality of riser boards 270. Plurality of riser boards 270 is physically connected and electronically connected to both the control electronics board 260 and the power inverter board 230. In some examples, plurality of riser boards 270 comprises printed circuit boards (PCBs). The PCBs may electronically connect power inverter board 230 and control electronics board 260. Plurality of riser boards 270 may enable power transfer between power inverter board 230 and control electronics board 260 for operation of either board. Plurality of riser boards 270 may enable transfer of digital control signals or analog signals between power inverter board 230 and control electronics board 260. In addition, plurality of riser boards 270 is configured to maintain the position of control electronics board 260 relative to power inverter board 230 and relative to inverter housing 305.

[0058] Also shown in FIG. 5B is the plurality of power transistors 125 physically connected directly to the plurality of transistor cooling blocks 190. In other words, in some examples, the plurality of power transistors 125 are physically coupled with the plurality of transistor cooling blocks 190 without the use of thermally counductive but electrically insulating components, such as pads orwashers, physically separating the plurality of power transistors 125 from the plurality of transistor cooling blocks 190. As described above, in some further examples, the drain leg of each transistor of the plurality of power transistors 125 is electrically connected to one of the plurality of transistor cooling blocks 190. This configuration is possible in the currently described examples of oil- cooled power inverter 100 when the cooling fluid is a dielectric, or electrically non-conducting, cooling fluid. During opering of the oil-cooled power inverter 100, individual transistor cooling blocks of the plurality of transistor cooling blocks 190 will be at different voltages, whether the oil-cooled power inverter 100 produces single-phase or three-phase AC. If the cooling fluid conducted electricity, it would form electrical shorts between the individual transistor cooling blocks, and therefore, between the power transistors electrically coupled with the individual transistor cooling blocks. Use of a dielectric cooling fluid and directly coupling the plurality of power transistors 125 with the plurality of transistor cooling blocks 190 may provide several benefits. First, thermal conductivity between the plurality of power transistors 125 and the plurality of transistor cooling blocks 190 is greater without the installation of intervening electrically insulating pads or washers. Second, without intervening electrically insulating pads or washers, the plurality of power transistors 125 may be positioned closer to the plurality of transistor cooling blocks 190, thereby increasing compactness.

[0059] The cooling fluid may be selected to have a suitable dielectric constant and dielectric breakdown voltage to prevent electrical shorting between electrically conductive components of the oil-cooled power inverter 100, as noted above. For example, the cooling fluid may have a dielectric constant less than 5, less than 4, less than 3, or even less than 2. For example, the cooling fluid may have a dielectric breakdown of greater than 20 kVRMs, greater than 30 kVRMs, or even greater than 45 kVRMs. The cooling fluid may also be selected to have a sufficient heat capacity for efficienct transfer of heat from components of the oil-cooled power inverter 100. For example, the cooling fluid may have a head capacity of greater than 1 kJ / ( kg K)), greter than 2 kJ / ( kg K)), greater than 2.5 kJ / ( kg K)), or even greater than 3 kJ / (kg K)). The cooling fluid may also beselected to have a sufficient low-temperature viscosity to allow flow through the oil-cooled power inverter 100 at low temperatures the oil-cooled power inverter 100 may be exposed to. For example, the cooling fluid may have a pour point less than -20 °C, less than -30 °C, or even less than -40 °C. Examples of fluids that may be used as the cooling fluid include, but are not limited to, mineral oil, transformer oil, and automatic transmission fluid.

[0060] Also shown in FIG. 5B is plurality of capacitors 235. In some examples, power inverter board 230 comprises a plurality of capacitors 235 configured to alternatively store electrical charge and release electrical charge to other components of power inverter board 230. In some examples, plurality of capacitors 235 is configured to store a DC power input to the power inverter board 230 and deliver a DC power output to the plurality of power transistors 125. In some examples, plurality of capacitors 235 may be configured to filter the alternating current output generated by oil-cooled power inverter 100. Locating plurality of capacitors 235 close to plurality of power transistors 125 is desirable to decrease inductance of the power inverter board 230. The arrangement, which is shown in FIG. 5B of a generally hexagonally packed plurality of capacitors 235 surrounded by plurality of power transistors 125, is one example arrangement with low inductance.

[0061] The flow of cooling fluid in the oil-cooled power inverter 100 will now be described in detail. FIG. 6A is a perspective view drawing illustrating components of the oil-cooled power inverter 100 with a portion of the inverter housing 305, first busbar 285, second busbar 280, control electronics board 260, plurality of transistor cooling blocks 190, and plurality of bus cylinders 265 removed, in accordance with some examples. FIG. 6B is a perspective view drawing illustrating components of the oil-cooled power inverter 100 with the same components removed as in FIG. 6A, and additionally, the plurality of power transistors 125, the power inverter board 230, and the plurality of capacitors 235 removed, in accordance with some examples. As shown in Fig 6A, oil-cooled power inverter 100 comprises a cooling fluid inlet 140. The cooling fluid inlet 140 comprises a first lumen 145.

[0062] FIG. 7A is a top-view drawing of a cross-section of oil-cooled power inverter 100 through the cooling fluid inlet 140, illustrating some internal components of oil-cooled power inverter 100, in accordance with some examples. As shown in FIG. 7A, oil-cooled power inverter 100 comprises a cooling fluid distributor 150 f luidica lly coupled to cooling fluid inlet 140. Fluid entering oil-cooled power inverter 100 via cooling fluid inlet 140 may flow into a center portion of cooling fluid distributor 150 and then flow to the extremities of 150, in other words, from the center towards the outer edges of oil-cooled power inverter 100 shown in FIG. 7A. Possible flow paths of cooling fluid are illustrated in FIG. 7A as dotted line arrows. Manifold 155 is shown with power inverter board 230 attached in FIG. 6A and with power inverter board 230 removed in FIG. 6B, for illustration purposes. Manifold 155 may be formed from a thermally conductive material with sufficient chemical resistivity to the cooling fluid. For example, manifold 155 may be formed from aluminum.

[0063] Manifold 155 comprises a plurality of distributor-manifold inlets 160, a plurality of manifold-block outlets 165, a first plurality of manifold-passages 170, a plurality of manifold-block inlets 175, a plurality of manifold-sump outlets 180, and a second plurality of manifold-passages 185. Each one of the plurality of distributor-manifold inlets 160 is fluidically coupled to the cooling fluid distributor 150. Each one of the first plurality of manifold-passages 170 is, in turn, fluidically coupled to one of the plurality of distributor-manifold inlets 160. Each one of the first plurality of manifold-passages 170 is also fluidically coupled to one of the plurality of manifold-block outlets 165. As shown in FIG. 6A, power inverter board 230 comprises a plurality of transistor block inlet passthroughs 130 and a plurality of transistor block outlet passthroughs 135. Each one of the plurality of transistor block inlet passthroughs 130 is fluidically coupled to one of the plurality of manifold-block outlets 165. Cooling fluid flowing through cooling fluid distributor 150 may flow into the plurality of distributor-manifold inlets 160, from there into first plurality of manifoldpassages 170, and from there into plurality of manifold-block outlets 165.

[0064] FIG. 8A is a perspective view showing the relationship of some components of one of a plurality of transistor cooling blocks 190, in accordancewith some examples. FIG. 8B is a cross-sectional view showing the relationship of some components of one of a plurality of transistor cooling blocks 190, in accordance with some examples. Plurality of transistor cooling blocks 190 comprises a plurality of cooling-block inlets 195, a plurality of cooling-block outlets 200, and a plurality of cooling-block passages 205. Each one of the plurality of cooling-block passages 205 is fluidically coupled both to one of the plurality of cooling-block inlets 195 and to one of the plurality of cooling-block outlets 200. FIG. 8B also illustrates a possible flow path, in some examples, of cooling fluid through one of the plurality of transistor cooling blocks 190 from one of the plurality of cooling-block inlets 195 to one of the plurality of coolingblock outlets 200, indicated by dotted line arrows.

[0065] FIG. 7B is a schematic cross-sectional side-view of the oil-cooled power inverter 100 at line A-A of FIG. 7A, in accordance with some examples. As shown in FIG. 7B, each one of the plurality of transistor block inlet passthroughs 130 is fluidically coupled to one of the plurality of cooling-block inlets 195. FIG. 7C is a schematic cross-sectional side-view of the oil-cooled power inverter 100 at line B-B of FIG. 7A, in accordance with some examples. As shown in FIG. 7C, each one of the plurality of cooling-block outlets 200 is fluidically coupled to one of the plurality of transistor block outlet passthroughs 135. Cooling fluid flowing into plurality of manifold-block outlets 165 may flow through plurality of transistor block inlet passthroughs 130 and enter plurality of transistor cooling blocks 190 via plurality of cooling-block inlets 195. Cooling fluid may then flow through plurality of cooling-block passages 205, absorbing heat from plurality of transistor cooling blocks 190, thereby providing cooling to plurality of power transistors 125 thermally coupled to plurality of transistor cooling blocks 190. Cooling fluid may then flow out of plurality of transistor cooling blocks 190 via plurality of cooling-block outlets 200. Plurality of transistor cooling blocks 190 may be formed from a material having sufficient thermal conductivity and chemical resistance to cooling fluid. In some examples, plurality of transistor cooling blocks 190 is formed from aluminum.

[0066] Each one of the plurality of transistor block outlet passthroughs 135 is fluidically coupled to one of the plurality of cooling-block outlets 200 and toone of the plurality of manifold-block inlets 175. Each one of the second plurality of manifold-passages 185 is fluidically coupled to one of the plurality of manifold-block inlets 175. In some examples, as shown in FIG. 6B, plurality of manifold-block outlets 165 and plurality of manifold-block inlets 175 have openings in the same surface of manifold 155. Each one of the second plurality of manifold-passages 185 is also fluidically coupled to one of the plurality of manifold-sump outlets 180.

[0067] Manifold 155 is fluidically coupled to power inverter board 230. Cooling fluid inlet 140, the cooling fluid distributor 150, the manifold 155, the power inverter board 230, and the plurality of transistor cooling blocks 190 together form a liquid-tight volume, with the exception of the first lumen 145 and the second lumen 220. In other words, power inverter board 230 provides a portion of a cooling fluid enclosure 279 for cooling fluid flowing through oil-cooled power inverter 100. The power inverter board 230 is thereby cooled by thermal contact with the cooling fluid. In some examples, portions of plurality of power transistors 125, plurality of capacitors 235, and other components of power inverter board 230 are exposed to cooling fluid. Specifically, the leads of the plurality of capacitors 235 soldered to the power inverter board 230 are cooled by thermal contact with the cooling fluid. Solder joints electrically connecting the components to power inverter board 230 may also seal power inverter board 230, preventing cooling fluid from passing through power inverter board 230 along vias that penetrate through power inverter board 230. The cooling fluid may be chosen to have suitably low electrical conductivity to prevent electrical shorting between these components through the cooling fluid.

[0068] As shown in FIG. 6B, oil-cooled power inverter 100 comprises a cooling fluid sump 210. Cooling fluid sump 210 is fluidically coupled to the plurality of manifold-sump outlets 180. Oil-cooled power inverter 100 comprises a cooling fluid outlet 215 comprising a second lumen 220. Cooling fluid outlet 215 is fluidically coupled to cooling fluid sump 210. The cooling fluid flowing out of plurality of cooling-block outlets 200 may pass through plurality of transistor block outlet passthroughs 135 and enter plurality of manifold-block inlets 175, flow through second plurality of manifold-passages 185, and then flow intoplurality of manifold-sump outlets 180. The cooling fluid may then flow from plurality of manifold-sump outlets 180 into cooling fluid sump 210 and then into cooling fluid outlet 215.

[0069] In some examples, oil-cooled power inverter 100 comprises a gasket 255 positioned between the manifold 155 and the power inverter board 230.Gasket 255 comprises a plurality of inlet passthroughs 240 and a plurality of outlet passthroughs 245 and a plurality of bolt passthroughs 250. Each one of the plurality of inlet passthroughs 240 is fl uidica lly coupled either to one of the plurality of cooling-block inlets 195 or to one of the plurality of cooling-block outlets 200. In these examples, gasket 255 creates a liquid-tight seal between power inverter board 230 and manifold 155 while permitting passage of cooling fluid between plurality of manifold-block outlets 165 and plurality of transistor block inlet passthroughs 130 and between plurality of transistor block outlet passthroughs 135 and plurality of manifold-block inlets 175. Plurality of inlet passthroughs 240 and plurality of outlet passthroughs 245 prevent mixing or cross-flow of cooling fluid that has not contacted plurality of transistor cooling blocks 190 with cooling fluid that has. Such mixing may lead to increase in temperature of the cooling fluid entering plurality of transistor cooling blocks 190, lowering the efficiency of thermal transfer from plurality of transistor cooling blocks 190 to the cooling fluid. The gasket 255 may be formed from a material that is chemically resistant to cooling fluid and has suitable hardness and service temperature range to maintain a seal at expected operating temperatures. For example, gasket 255 may be formed from a material selected from the list consisting of neoprene, natural rubber, ethylene propylene diene monomer (EPDM) rubber, silicone, nitrile rubber, and a fluoroelastomer.

[0070] In some examples, the cooling fluid inlet 140 is fl uidica lly coupled to an outlet of an external pump and heat exchanger 650, and the cooling fluid outlet is fl uidica I ly coupled to an inlet of an external pump and heat exchanger 650. In these examples, the external pump and heat exchanger 650 supplies cooling fluid to oil-cooled power inverter 100 having a temperature at or below the temperature of plurality of transistor cooling blocks 190. Cooling fluidcirculating through oil-cooled power inverter 100 absorbs heat from plurality of transistor cooling blocks 190 and returns to the external pump and heat exchanger 650 to be cooled.

[0071] FIG. 7D is a perspective view showing the relationships of some components of oil-cooled power inverter 100 on a side that in FIG. 2 is obscured by the liquid-cooled electric motor 970, in accordance with some examples. In some examples, oil-cooled power inverter 100 comprises a resolver 710. Shown in FIG. 7D is a resolver 710, affixed to manifold 155. When present, resolver 710 is electronically coupled with control electronics board 260. Resolver 710 is configured to sense rotational position of liquid-cooled electric motor 970 through its duty cycle. Signals from resolver 710 may provide electronics on control electronics board 260 with information about the position and / or rotation speed of a rotor of liquid-cooled electric motor 970.Examples of Methods for Operating Oil-Cooled Power Inverters

[0072] FIG. 9 is a process flowchart corresponding to method 900 of operating an oil-cooled power inverter 100, in accordance with some examples. Method 900 may commence with (Block 901) receiving by a power inverter board 230 comprising a plurality of power transistors 125 thermally coupled to a plurality of transistor cooling blocks 190 a direct electrical current 910. In some examples, direct current electrical power is supplied to oil-cooled power inverter 100 from a battery or a battery pack.

[0073] Method 900 may proceed with (Block 902) converting by the plurality of power transistors 125 the direct electrical current 910 into an alternating electrical current 920. In some examples, the alternating electrical current 920 is a single-phase alternating current. In some other examples, the alternating electrical current 920 is a three-phase AC. The thermal coupling of the plurality of power transistors 125 with the plurality of transistor cooling blocks 190 provides cooling to remove heat generated during the operation of the plurality of power transistors 125.

[0074] Method 900 may proceed with (Block 903) circulating by an external pump and heat exchanger 650 a cooling fluid 275 through the plurality oftransistor cooling blocks 190, thereby transferring heat from the plurality of power transistors 125. Plurality of transistor cooling blocks 190 comprises a plurality of cooling-block inlets 195, a plurality of cooling-block outlets 200, and a plurality of cooling-block passages 205. Each one of the plurality of coolingblock passages 205 is f luidica lly coupled both to one of the plurality of coolingblock inlets 195 and to one of the plurality of cooling-block outlets 200. The cooling fluid may then flow through plurality of cooling-block passages 205, absorbing heat from plurality of cooling-block inlets 195, thereby providing cooling to plurality of power transistors 125 thermally coupled to plurality of transistor cooling blocks 190. The cooling fluid may then flow out of plurality of transistor cooling blocks 190 via plurality of cooling-block outlets 200. Plurality of transistor cooling blocks 190 may be formed from a material having sufficient thermal conductivity and chemical resistance to cooling fluid. In some examples, plurality of transistor cooling blocks 190 is formed from aluminum. Examples of fluidic coupling of an external pump and heat exchanger 650 with plurality of transistor cooling blocks 190 are described in detail above. Specifically, in some examples, the oil-cooled power inverter 100 further comprises a manifold 155 placed between and fluidically coupled to both the plurality of transistor cooling blocks 190 and the external pump and heat exchanger 650.

[0075] In some examples, the oil-cooled power inverter 100 further comprises a control electronics board 260 and a temperature sensor 940. The control electronics board 260 is electronically coupled to the external pump and heat exchanger 650. The temperature sensor 940 is thermally coupled to the plurality of power transistors 125 and electronically coupled to the control electronics board 260. The method 900 may further comprise (block 904) measuring at the temperature sensor 940 a temperature, recording at the control electronics board 260 the measured temperature, determining at the control electronics board 260 whether the measured temperature is above a temperature limit, and signaling the external pump and heat exchanger 650, by the control electronics board 260, to change a flow rate of cooling fluid 275 ifthe measured temperature is above the temperature limit. In some examples, the temperature limit is 100 °C.

[0076] In some examples, the oil-cooled power inverter 100 further comprises a control electronics board 260 and a plurality of Hall-effect sensors 950. The control electronics board 260 is electronically coupled to the external pump and heat exchanger 650. The plurality of Hall-effect sensors 950 is electronically coupled to the control electronics board 260. Method 900 may further comprise (block 905) measuring at the plurality of hall-effect sensors 950 an alternating current flow from the power inverter board 230, recording at the control electronics board 260 the measured alternating current flow, determining at the control electronics board 260 a predetermined flow rate of cooling fluid 275 for the measured alternating current flow, and signaling the external pump and heat exchanger 650, by the control electronics board 260, to change a flow rate of cooling fluid 275 if the measured rate of change of the alternating current flow is different than the predetermined flow rate.Examples of Electric Vehicles Comprising Oil-Cooled Power Inverters

[0077] Oil-cooled power inverters described herein can be used in electric vehicles. FIG. 10 is a schematic block diagram illustrating components of vehicle 1100 and some of their relationships, in accordance with some examples. Vehicle 1100 comprises a liquid-cooled electric motor 970 and an oil-cooled power inverter 100. The oil-cooled power inverter 100 comprises a plurality of terminals 105, a first DC connector 115, a second DC connector 120, a power inverter board 230, a cooling fluid inlet 140 comprising a first lumen 145, a cooling fluid distributor 150, a manifold 155, a plurality of transistor cooling blocks 190, a cooling fluid sump 210, and a cooling fluid outlet 215. Power inverter board 230 is electrically connected to the plurality of terminals 105, the first DC connector 115, and the second DC connector 120. Power inverter board 230 comprises a plurality of power transistors 125, a plurality of transistor block inlet passthroughs 130, and a plurality of transistor block outlet passthroughs 135. Plurality of power transistors 125 is physically and thermallyconnected to the plurality of transistor cooling blocks 190. Cooling fluid distributor 150 is fluidically coupled to the cooling fluid inlet 140. Manifold 155 comprises a plurality of distributor-manifold inlets 160 fluidically coupled to the cooling fluid distributor 150, a plurality of manifold-block outlets 165, a first plurality of manifold-passages 170, a plurality of manifold-block inlets 175, a plurality of manifold-sump outlets 180, and a second plurality of manifoldpassages 185. Each one of the first plurality of manifold-passages 170 is fluidically coupled to one of the plurality of distributor-manifold inlets 160 and one of the plurality of manifold-block outlets 165. Each one of the second plurality of manifold-passages 185 is fluidically coupled to one of the plurality of manifold-block inlets 175 and one of the plurality of manifold-sump outlets 180.

[0078] Plurality of transistor cooling blocks 190 comprises a plurality of coolingblock inlets 195, a plurality of cooling-block outlets 200, and a plurality of cooling-block passages 205. Each one of the plurality of cooling-block passages 205 is fluidically coupled both to one of the plurality of cooling-block inlets 195 and to one of the plurality of cooling-block outlets 200. Cooling fluid sump 210 is fluidically coupled to the plurality of manifold-sump outlets 180. Cooling fluid outlet 215 comprises a second lumen 220 and is fluidically coupled to the cooling fluid sump 210. Each one of the plurality of transistor block inlet passthroughs 130 is fluidically coupled to one of the plurality of manifold-block outlets 165 and to one of the plurality of cooling-block inlets 195. Each one of the plurality of transistor block outlet passthroughs 135 is fluidically coupled to one of the plurality of cooling-block outlets 200 and to one of the plurality of manifold-block inlets 175.

[0079] Manifold 155 is fluidically sealed to power inverter board 230. Cooling fluid inlet 140, the cooling fluid distributor 150, the manifold 155, the power inverter board 230, and the plurality of transistor cooling blocks 190 together form a cooling fluid enclosure 279 fluidically sealed with the exception of the first lumen 145 and the second lumen 220.In some examples, oil-cooled power inverter 100 is affixed to the liquid-cooled electric motor 970. In some examples, liquid-cooled electric motor 970 furthercomprises a plurality of terminals. In these examples, the plurality of terminals 105 of oil-cooled power inverter 100 are electrically connected to the plurality of terminals of liquid-cooled electric motor 970. In some examples, liquid- cooled electric motor 970 and the oil-cooled power inverter 100 are both fluidically coupled to an external pump and heat exchanger 650. In these examples, cooling fluid inlet 140 and the cooling fluid outlet 215 are fluidically coupled to the external pump and heat exchanger 650.Conclusion

[0080] Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing processes, systems, and apparatuses. Accordingly, the present embodiments are to be considered illustrative and not restrictive.

Claims

CLAIMS1. An oil-cooled power inverter, comprising: a plurality of terminals; a first DC connector and a second DC connector; a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of power transistors; a manifold comprising a cooling fluid distributor, a cooling fluid inlet comprising a first lumen, a cooling fluid outlet comprising a second lumen, and a cooling fluid sump; and a plurality of transistor cooling blocks fluidically coupled to the manifold, wherein: the cooling fluid inlet is fluidically coupled to the cooling fluid distributor, the cooling fluid outlet is fluidically coupled to the cooling fluid sump, the cooling fluid sump is fluidically coupled to the plurality of transistor cooling blocks, the plurality of power transistors is physically and thermally connected to the plurality of transistor cooling blocks, the manifold is fluidically coupled to the power inverter board, and the cooling fluid inlet, the cooling fluid distributor, the manifold, the power inverter board, and the plurality of transistor cooling blocks together form a liquid-tight volume.

2. The oil-cooled power inverter of claim 1, wherein the manifold comprises a plurality of distributor-manifold inlets fluidically coupled to the cooling fluid distributor, a plurality of manifold-block outlets, a first plurality of manifoldpassages, a plurality of manifold-block inlets, a plurality of manifold-sump outlets, and a second plurality of manifold-passages, wherein:each one of the first plurality of manifold-passages is fluidically coupled to one of the plurality of distributor-manifold inlets and one of the plurality of manifold-block outlets, each one of the second plurality of manifold-passages is fluidically coupled to one of the plurality of manifold-block inlets and one of the plurality of manifold-sump outlets, and each one of the plurality of manifold-sump outlets is fluidically coupled to the cooling fluid sump.

3. The oil-cooled power inverter of claim 2, wherein the power inverter board further comprises a plurality of transistor block inlet passthroughs and a plurality of transistor block outlet passthroughs, wherein: each one of the plurality of transistor block inlet passthroughs is fluidically coupled to one of the plurality of manifold-block outlets, and each one of the plurality of transistor block outlet passthroughs is fluidically coupled to one of the plurality of manifold-block inlets.

4. The oil-cooled power inverter of claim 3, wherein the plurality of transistor cooling blocks comprises a plurality of cooling-block inlets, a plurality of cooling-block outlets, and a plurality of cooling-block passages, wherein each one of the plurality of cooling-block passages is fluidically coupled both to one of the plurality of cooling-block inlets and to one of the plurality of coolingblock outlets.

5. The oil-cooled power inverter of claim 4, wherein: each one of the plurality of cooling-block inlets is fluidically coupled to one of the plurality of transistor block inlet passthroughs, and each one of the plurality of cooling-block outlets is fluidically coupled to one of the plurality of transistor block outlet passthroughs.

6. The oil-cooled power inverter of claim 4, further comprising a gasket positioned between the manifold and the power inverter board comprising aplurality of inlet passthroughs and a plurality of outlet passthroughs, wherein each one of the plurality of inlet passthroughs is fluidically coupled either to one of the plurality of cooling-block inlets or to one of the plurality of coolingblock outlets.

7. The oil-cooled power inverter of claim 6, wherein the gasket further comprises a plurality of bolt passthroughs.

8. The oil-cooled power inverter of claim 1, wherein the cooling fluid inlet is fluidically coupled to an outlet of an external pump and heat exchanger and the cooling fluid outlet is fluidically coupled to an inlet of an external pump and heat exchanger.

9. The oil-cooled power inverter of claim 1, wherein the power inverter board further comprises a plurality of capacitors configured to alternatively store a DC power input to the power inverter board and deliver a DC power output to the plurality of power transistors.

10. The oil-cooled power inverter of claim 1, further comprising a control electronics board electronically connected to the power inverter board.

11. The oil-cooled power inverter of claim 10, further comprising a plurality of riser boards physically connected and electronically connected to both the control electronics board and the power inverter board.

12. The oil-cooled power inverter of claim 1, wherein a drain of each one of the plurality of power transistors is electrically connected to one of the plurality of transistor cooling blocks.

13. The oil-cooled power inverter of claim 12, further comprising a first busbar positioned between and electrically connected to both the plurality of transistor cooling blocks and the first DC connector.

14. The oil-cooled power inverter of claim 1, further comprising a plurality of bus cylinders electrically connected to the power inverter board.

15. The oil-cooled power inverter of claim 14, further comprising a second busbar positioned between and electrically connected to both the plurality of bus cylinders and the second DC connector.

16. A method of operating an oil-cooled power inverter comprising a plurality of terminals, a first DC connector, a second DC connector, a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of plurality of power transistors, a manifold comprising a cooling fluid distributor, a cooling fluid inlet, a cooling fluid outlet, and a cooling fluid sump, and a plurality of transistor cooling blocks f luidica lly coupled to the manifold and thermally coupled to the plurality of power transistors, the method comprising: receiving by the power inverter board a direct electrical current; converting by the plurality of power transistors the direct electrical current into an alternating electrical current; and circulating, by an external pump and heat exchanger, a cooling fluid through manifold and the plurality of transistor cooling blocks, thereby transferring heat from the plurality of power transistors.

17. The method of claim 16, wherein: the cooling fluid inlet is f luidica I ly coupled to the cooling fluid distributor, the cooling fluid outlet is fluidica lly coupled to the cooling fluid sump, the cooling fluid sump is fluidically coupled to the plurality of transistor cooling blocks, and circulating the cooling fluid further comprises flowing the cooling fluid into the manifold via the cooling fluid inlet, from the cooling fluid inlet to the cooling fluid distributor, from the cooling fluid distributor to the plurality oftransistor cooling blocks, from the plurality of transistor cooling blocks to the cooling fluid sump, and from the cooling fluid sump to the cooling fluid outlet.

18. The method of claim 16, wherein the alternating electrical current is a three phase AC.

19. The method of claim 16, wherein the oil-cooled power inverter further comprises a control electronics board electronically coupled to the external pump and heat exchanger and a temperature sensor thermally coupled to the plurality of power transistors and electronically coupled to the control electronics board and the method further comprises: measuring at the temperature sensor a temperature; recording at the control electronics board the measured temperature; determining at the control electronics board whether the measured temperature is above a temperature limit; and signaling by the control electronics board to the external pump and heat exchanger to change a flow rate of the cooling fluid if the measured temperature is above the temperature limit.

20. The method of claim 19, wherein the temperature limit is 100 °C.

21. The method of claim 16, wherein the oil-cooled power inverter further comprises a control electronics board electronically coupled to the external pump and heat exchanger and a plurality of Hall-effect sensors electronically coupled to the control electronics board and the method further comprises: measuring at the plurality of hall-effect sensors an alternating current flow from the power inverter board; recording at the control electronics board the measured alternating current flow; determining at the control electronics board a predetermined flow rate of the cooling fluid for the measured alternating current flow; andsignaling by the control electronics board to the external pump and heat exchanger to change a flow rate of the cooling fluid if the measured rate of change of the alternating current flow is different than the predetermined flow rate.

22. A vehicle comprising a liquid-cooled electric motor and an oil-cooled power inverter, the oil-cooled power inverter comprising: a plurality of terminals; a first DC connector and a second DC connector; a power inverter board electrically connected to the plurality of terminals, the first DC connector, and the second DC connector and comprising a plurality of power transistors; a cooling fluid inlet comprising a first lumen, a cooling fluid distributor f luidica lly coupled to the cooling fluid inlet; a manifold f luidica lly coupled to the cooling fluid distributor; a plurality of transistor cooling blocks fluidically coupled to the manifold; a cooling fluid sump fluidically coupled to the plurality of transistor cooling blocks; and a cooling fluid outlet comprising a second lumen and fluidically coupled to the cooling fluid sump, wherein: the plurality of power transistors is physically and thermally connected to the plurality of transistor cooling blocks, the manifold is fluidically sealed to the power inverter board, and the cooling fluid inlet, the cooling fluid distributor, the manifold, the power inverter board, and the plurality of transistor cooling blocks together form a volume fluidically sealed with the exception of the first lumen and the second lumen.

23. The vehicle of claim 22, wherein the oil-cooled power inverter is affixed to the liquid-cooled electric motor.

24. The vehicle of claim 22, wherein the liquid-cooled electric motor further comprises a plurality of terminals.

25. The vehicle of claim 22, wherein: the liquid-cooled electric motor and the oil-cooled power inverter are both fluidica lly coupled to an external pump and heat exchanger, and the cooling fluid inlet and the cooling fluid outlet are fluidica lly coupled to the external pump and heat exchanger.

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