Patent Application
20140198453
1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for more efficiently cooling electrical components.
2. Discussion of the Background
Power converters are widely used for diverse range of applications to control energy flow or convert voltage, current or frequency necessary for connecting to a motor or a generator, or interfacing with an utility grid. Some of those applications include motor drives for oil and gas, metal, water, mining and marine industries, as well as power/frequency converters for renewable energy (wind, solar), and electric power industries.
Some of the core components of a power converter (or a variable frequency drive, which is a special type of power converter driving electric motors) are the power semiconductor switches. The power semiconductor switches generate power losses during their operation, i.e., conducting currents and switching currents on and off. Examples of those power semiconductor switches include but are not limited to an Integrated Gate Commutated Thyristor (IGCT), Insulated Gate Bipolar Transistor (IGBT), Injection-Enhanced Gate Transistor (IEGT), Thyristor (ETT or LTT), diode in press-pack package (silicon wafers in hockey-puck like ceramic housing) or IGBT, Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET), diodes in plastic module package, etc. The capability, performance and reliability of these power semiconductor switches are sensitive to their junction temperature due to reasons such as reduced turn-off capability at higher junction temperature, localized hot spots due to concentrated current conduction, etc.
To achieve the cooling of such switches and to keep their junction temperature within their operation limit, liquid cooling is an effective means for removing the heat generated from power losses during power switch operation. Liquid cooling, e.g., water cooling, uses a liquid flow to remove heat from a cooling component (e.g., heat sink or cold plate) attached to an electrical component (e.g., power semiconductor switch). Because of the direct contact between surfaces of the cooling component and the electrical component, heat is transferred from the element having a higher temperature (electrical component) to the element having a lower temperature (cooling component). The liquid is provided around and/or through the cooling component to disperse the heat transferred to the cooling component. The liquid flow is then taken to a place to be cooled, away from the electrical component. Such a place may be a water-to-water or water-to-air heat exchanger that dissipates the heat to a cooling tower or ambient air.
It is noted that for a power module the baseplate is galvanic isolated from electrodes of the power semiconductor switches while for press-pack devices the pole face of the power semiconductor switch is electrically connected to the electrodes of the power semiconductor switches. This arrangement implies that to avoid an electrical short circuit, de-ionized water needs to be used for heat sinks for press-pack switches if the liquid cooling circuit connects different electrical components together.
An example of a cooling system 10 is shown in
To form a liquid cooling circuit for a given number of liquid cooled electrical components, the cooling components that are in contact with or are part of the electrical components are fluidly connected to each other. An exemplary cooling topology is shown in
A parallel branch 35 may include an incoming pipe 20, a pressure compensator 36, a heat sink 16, another pressure compensator 40 and an outgoing pipe 22. A series branch 37 may include an incoming pipe 38, multiple heat sinks 16, connecting pipes 42 and outgoing pipes 44. It is noted that a series branch includes two or more heat sinks or equivalent devices linked in series. Thus, the cooling system 10 includes various type of connections, such as serial or parallel or combinations of serial and parallel connections.
Serial liquid connections for all cooling components have less total liquid flow but higher pressure drop than parallel connections. Consequently, this would lead to a pump with a larger head and higher stress on the cooling components. This makes the liquid cooling circuit prone to leakage due to a higher pressure. Another negative factor for a serial liquid loop is that the temperature downstream of the cooling loop keeps increasing as heat accumulates from one cooling stage to the next. This heat deteriorates the cooling effect for components in the downstream of the cooling loop. Therefore it is desirable to place power semiconductor switches that have a higher dissipation power and are more sensitive to junction temperature upstream of the liquid cooling loop.
The parallel liquid connections for all cooling components lead to less pressure drop than a serial liquid connection. However, the parallel liquid connections have a higher total liquid flow, i.e., a larger amount of liquid is needed. An important limiting factor for this arrangement is that since all paralleled cooling branches must have the same ΔP (pressure drop), the resultant liquid flow for each branch may not be the needed value. To solve this issue, a complicated design is needed by introducing either additional ΔP balancing elements (such as a coil 36 or 40) or carefully designing the diameter of each paralleled cooling branch. Alternatively, a flow regulating valve may be manually controlled to adjust the flow distribution to ensure the right amount of flow is achieved for each paralleled liquid branches.
Returning to
For this specific arrangement, the outgoing pipes 22 of the heat sinks from the column 12a are directly connected to the first water outlet manifold 32 so that the high temperature liquid is not reused for cooling elements of columns 12b and 12c. However, because the temperature of the cooling liquid from the connecting pipes 42 is not high, this cooling liquid is used to cool the cooling components of column 12c before the cooling liquid is being provided to the second water outlet manifold 33.
However, the cooling arrangement of
Another cooling arrangement is illustrated in
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.
According to one exemplary embodiment, there is a liquid cooling system for a power conversion apparatus. The liquid cooling system includes a first cooling stage that includes first cooling components of the power conversion apparatus, wherein the cooling components are connected to form parallel cooling branches; a mixing manifold configured to be fluidly connected to the parallel cooling branches so that cooling liquid streams from the parallel cooling branches are mixed in the mixing manifold; and a second cooling stage that includes second cooling components, and the second cooling stage is connected in series with the first cooling stage in terms of a cooling liquid that flows through the cooling system. The cooling liquid streams from the first cooling stage are mixed together in the mixing manifold before being delivered to the second cooling stage.
According to another exemplary embodiment, there is a power conversion apparatus that includes a power stack including first and second electrical components; an inlet manifold fluidly connected to a first cooling stage of the power conversion apparatus and configured to provide a cooling fluid to the first cooling stage for cooling down the first electrical components associated with the first cooling stage; a mixing manifold fluidly connected to the first cooling stage and configured to (i) receive from the first cooling stage heated cooling liquid streams having different temperatures, (ii) mix the heated cooling liquid streams to substantially have a single temperature, and (iii) provide the mixed cooling liquid streams to a second cooling stage of the power conversion apparatus for cooling down second electrical components associated with the second cooling stage; and an outlet manifold fluidly connected to the second cooling stage of the power conversion apparatus and configured to receive mixed cooling liquid streams from the second cooling stage.
According to still another exemplary embodiment, there is a method of cooling a power conversion apparatus. The method includes providing a cooling liquid to an inlet manifold; transferring the cooling liquid from the inlet manifold to heat sinks of a first cooling stage of the power conversion apparatus, wherein the heat sinks are provided on parallel cooling branches; cooling the heat sinks of the first cooling stage; receiving at a mixing manifold heated cooling liquid streams having different temperatures from the parallel cooling branches of the first cooling stage; mixing the heated cooling liquid streams in the mixing manifold; providing the mixed cooling liquid streams to heat sinks of a second cooling stage of the power conversion apparatus; and collecting mixed cooling liquid streams from the second cooling stage at an outlet manifold connected to the second cooling stage.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of water cooled three-column power stacks. However, the embodiments to be discussed next are not limited to these power stacks, but may be applied to other stacks or power conversion devices that have components that need to be cooled.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
According to an exemplary embodiment, there is a manifold cooling system for cooling down a multi-column power stack. The manifold cooling system includes a liquid inlet manifold, a liquid outlet manifold and a liquid mixing manifold. Cooling components fluidly connect the manifolds for circulating a cooling liquid through the manifolds. As defined later, the cooling components are grouped in parallel and series branches. Electrical components are attached or provided with some of the cooling components. The liquid mixing manifold collects cooling liquid streams from parallel branches, mixes them up and then provides the mixed cooling liquid to the remaining branches for cooling.
The novel cooling systems to be discussed next advantageously provide consistent and more uniform thermal performance for power semiconductor switches that are being cooled downstream of a liquid loop regardless of operation conditions. Such operating conditions include power losses that are not uniformly distributed at the power semiconductor switches that need to be cooled by the liquid cooling loop and power losses that are time dependent, i.e., depend on the circuit operation principle, the power source (such as power grid), and/or the load (such as motor and compressor) conditions. Under these conditions, it is desirable to have a most effective cooling system for power semiconductor switches upstream and downstream of the liquid loop, taking advantage of the fact that some devices dissipate less heat than the others in the paralleled liquid cooling arrangement. By mixing the cooling liquid after cooling the parallel branches and before delivering the liquid to the downstream power semiconductor switches, it allows the liquid temperature to be averaged at a lower value than the liquid temperature from maximum liquid temperature from the highest power dissipation branch.
In addition, the exemplary embodiments to be discussed next, provide an elegant way in solving potentially mismatched ΔP among parallel cooling branches. In this regard, no additional ΔP balancing elements are needed in the novel embodiments. Further, there is no need to carefully design the diameter of each paralleled cooling branch or to provide flow regulating valves to adjust the flow distribution to ensure the right amount of flow is achieved for each paralleled liquid branches.
According to an exemplary embodiment illustrated in
Returning to
A liquid inlet manifold 90 and a liquid outlet manifold 92 may be also provided for providing and removing, respectively, the cooling liquid from the cooling system. Thus, the parallel branches fluidly connect the liquid inlet manifold 90 to the mixing manifold 84 and the series branches fluidly connect the mixing manifold 84 to the liquid outlet manifold 92. Further, it is noted that some branches 87a-k fluidly connect the inlet manifold 90 to the outlet manifold 92 without connecting to the mixing manifold 84, where k is a number equal or larger than zero.
The embodiment shown in
In an exemplary embodiment illustrated in
A heat sink 160 may be a metal block that has an inlet 162 and an outlet 164 connected to each other by a channel 166 as shown in
Still with regard to
It is noted that the mixing manifold 112 may receive streams of heated cooling liquid from all heat sinks 160 of the first column 152. Thus, if one or more power semiconductor switches of the first column 152 operate at a higher temperature than the other power semiconductor switches of the same column, the streams of cooling liquid coming from these components are mixed together in the mixing manifold 112, thus bringing the cooling liquid to a substantially constant temperature before being distributed to the series branches 106a-m. In other words, streams of cooling liquid having different temperatures in the first cooling stage 104 are mixed together to provide a cooling liquid with a substantially uniform temperature to the branches of the second cooling stage 106.
In an exemplary embodiment, a mechanism 118 may be provided inside the liquid mixing manifold 112 or connected to the liquid mixing manifold 112 for enhancing the mixing of the streams of cooling liquid. Such mechanism 118 may be, for example, a synthetic jet. A synthetic jet can be implemented in a number of ways, such as with an electromagnetic driver, a piezoelectric driver, or even a mechanical driver such as a piston. Each driver moves a membrane or diaphragm up and down many times per second, sucking the surrounding fluid into a chamber and then expelling it.
The liquid mixing manifold 112 may have different shapes depending on the mechanical arrangement of the columns in the power conversion apparatus 100.
After mixing the liquid streams collected from the heat sinks of the first cooling stage 104, the liquid mixing manifold 112 may deliver the mixed cooling liquid to another set of incoming piping 120. The incoming piping 120 connect the liquid mixing manifold 112 to heat sinks of the second cooling stage 106 and the second column 154. The incoming piping 120 may be connected in series with other piping as discussed later. As the power semiconductor switches of columns 154 and 156 may operate at a lower temperature than the switches of column 152, the cooling liquid from the heat sinks associated with the electrical components of the second column 154 are provided via intermediate piping 122 to the heat sinks associated with the electrical components of the third column 156. From here, a set of outgoing piping 124 (connected in series with incoming piping 120 and intermediate piping 122) take the heated cooling liquid to the liquid outlet manifold 110. The heated cooling liquid may be cooled through a heat exchanger (not shown) and returned to the liquid inlet manifold 108 or discharged.
The embodiment shown in
The embodiment shown in
As previously discussed, the liquid mixing manifold may have a V shape as shown in
In another exemplary embodiment, not all the heat sinks (or other cooling components) of a cooling section are connected to the liquid mixing manifold. For example,
One or more of the novel exemplary embodiments discussed above advantageously provide even temperature distribution to the liquid streams supplied for the cooling of the power semiconductor switches. Also, one or more of these embodiments provide a better distribution of the liquid flow and/or reduce a structure of the cooling system when switching elements of various columns heat at different temperatures.
According to an exemplary embodiment, the following rules may be implemented for a power conversion apparatus. For parallel branches, place the cooling components (e.g., heat sinks) with equal pressure drop in parallel connections for high loss, temperature sensitive (e.g., current carrying and turn-off capability, failure, etc.) electrical components. The maximum number of cooling components in parallel is limited by the maximum allowable flow rate of the cooling system. The cooling components for most temperature sensitive and high loss electrical components are placed in parallel in the first cooling stage of the cooling system, subsequently connected to an inlet of the mixing manifold.
For series branches, the cooling components with different pressure drops and those attached to less temperature sensitive electrical components, may be placed in series to reduce a flow rate. The maximum number of cooling components that may be connected in series is limited by the total allowable pressure drop and maximum inlet temperature of the last stage. Multiple series branches of cooling components (preferably configured according to the electrical circuit topology, such as phase A, B, C components in series connection) may be connected in parallel.
Regarding the use of the mixing manifold, if losses of those electrical components attached to the parallel cooling components vary depending on the operating conditions, the cooling liquid streams are mixed in the mixing manifold before delivering the cooling liquid further to the downstream cooling components.
The mixing manifold may be made of aluminum, copper, stainless steel, Teflon, or silicon rubber hose.
According to an exemplary embodiment illustrated in
The disclosed exemplary embodiments provide a system and a method for better cooling a multi-column power stack and/or power converter with multi-cooling branches. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN2011/001351 | 8/15/2011 | WO | 00 | 2/13/2014 |
