Patent Application
20130319635
The present invention relates to a cooling device of a circulating-liquid cooling system and a power conversion device that is configured to be coolable by this type of cooling device.
According to a cooling device of a circulating-liquid cooling system, as a coolant (a cooling liquid) of the cooling device, it has been conventionally required to add a required amount of additive to the coolant to reduce the freezing temperature of the cooling liquid to be lower than a minimum temperature in specifications required for the cooling device. The additive for reducing the freezing temperature generally causes degradation in cooling performance. Therefore, there is a problem that, to achieve sufficient cooling performance in a high temperature state, the size of the cooling device becomes large.
Meanwhile, Patent Literature 1 mentioned below discloses the following technique. That is, in a case where an inverter device is connected to a cooling device by a cooling pipe, cooling water from the cooling device is caused to pass through the cooling pipe and circulate therethrough to cool the inverter device, when the temperature of the cooling water is reduced because of a reduction in an outdoor air temperature, the inverter device is caused to perform no-load running to generate heat and the temperature of the cooling water is increased by the heat, thereby preventing freezing of the cooling water.
Patent Literature 1: Japanese Patent Application Laid-open No. H09-199648
However, the technique disclosed in Patent Literature 1 mentioned above is a technique of preventing freezing of a cooling device, and thus there is a problem that when freezing of the cooling device is expected, the inverter device needs to be operated even though the cooling device is in a non-operating state.
It is conceivable to use the technique described in Patent Literature 1 mentioned above and configure a cooling device that allows temporary freezing in its non-operating state. However, according to such a device, for example, in a case where a part of a cooling pipe through which a cooling liquid passes is long, even when the inverter device is caused to perform no-load running to generate heat, while a circulation cooling function is not performed because a part of the cooling pipe is still frozen, the temperature of a semiconductor switching element serving as a cooled body exceeds an allowable maximum temperature. Accordingly, there is a problem that when the inverter device continues running in this state, the semiconductor switching element may be damaged.
In a case of such a device, it is also conceivable that no-load running of the inverter device is temporarily stopped to wait until the temperature of the semiconductor switching element is reduced and then the no-load running is performed again. However, with this method, the inverter device needs to be run and stopped repeatedly and thus there is a problem that it requires a long time to cause the cooling device to be in an operating state.
The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a cooling device that allows temporary freezing in a non-operating state without executing any warming control for preventing freezing and that effectively melts a frozen cooling liquid in a cooling pipe without using any preheating device and the like to be capable of shifting to an operable state in a short time, and a power conversion device including the cooling device.
In order to solve the above problem and in order to attain the above object, in a cooling device regarding the present invention of a circulating-liquid cooling system that connects two of respective elements of a heat exchanger, a circulating pump, and a cooled body by a cooling pipe, the cooled body is arranged between the heat exchanger and the circulating pump, each of a first path length that is a path length between the heat exchanger along the cooling pipe on a side not including the circulating pump and the cooled body and a second path length that is a path length between the circulating pump along the cooling pipe on a side not including the heat exchanger and the cooled body is set to be shorter than a third path length that is a path length between the heat exchanger along the cooling pipe on a side not including the cooled body and the circulating pump, and a metal material having a high conductivity is spirally wound around the cooling pipe so as to contact an outer circumferential surface of the cooling pipe.
The present invention can provide a cooling device that allows temporary freezing in a non-operating state without executing any warming control for preventing freezing and that effectively melts a frozen cooling liquid in a cooling pipe without using any preheating device and the like to be capable of shifting to an operable state in a short time, and a power conversion device including the cooling device.
Exemplary embodiments of a cooling device and a power conversion device according to the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments.
The switching element module 10 is arranged between the radiator 6 and the circulating pump 7. In view of the overall configuration of the cooling pipe 5, the switching element module 10, the radiator 6, and the circulating pump 7 are arranged adjacently. A metal spiral 20 formed by spirally winding a metal material is provided on the cooling pipe 5. This metal spiral 20 is wound so as to closely contact an outer circumferential surface of the cooling pipe 5 and so that spiral parts are closely adjacent to each other, thereby swiftly moving heat generated in the switching element module 10 to every part of the cooling pipe 5.
As shown in
As the cooling liquid in the cooling pipe 5, it is possible to use water, an aqueous solution containing additive (for example, ethylene glycol) that suppresses freezing of the cooling liquid at a low temperature, or an oleaginous solution. A cooling liquid that brings out the significance and effects of the cooling device according to the present embodiment most is water in which an antifreezing liquid such as ethylene glycol is not mixed. Because the antifreezing liquid reduces a heat conductivity of the cooling liquid and its cooling performance, it is preferable to avoid mixing of any impurity with the cooling liquid as much as possible.
In
A plurality of the switching elements 3 that configure the converter unit 1 and the inverter unit 2 described above are configured by using, for example, a self-extinction semiconductor device such as an IGBT (Insulated Gate Bipolar Transistor). In the case of the switching element 3 according to the present embodiment, as shown in
While
Next, an operation of the cooling device according to the present embodiment at a normal time is explained. In the configuration described above, when the power conversion device is operated, the switching element 3 generates heat. The switching element 3 is cooled by the heat sink 4. Meanwhile, a cooling liquid whose temperature is increased by heat radiation from the switching element 3 via the heat sink 4 is moved in the cooling pipe 5 by the circulating pump 7 and is cooled in the radiator 6 by heat exchange with air. An increase in the temperature of the switching element 3 is suppressed in this way, and a continuous operation of the power conversion device can be performed.
Next, a precondition in the cooling device according to the present embodiment is explained. The precondition is that a freezing temperature of a coolant (a cooling liquid) used for the cooling device according to the present embodiment is higher than a minimum temperature in specifications applied to the cooling device. In a case where the minimum temperature in the specifications applied to the cooling device is −10° C., for example, when water is used as the coolant, for example, a relationship of “minimum temperature (−10° C.)<freezing temperature (0° C.)” is established. Furthermore, in a case where the minimum temperature in the specifications applied to the cooling device is −40° C., for example, even when a required amount of ethylene glycol, for example, is added as an antifreezing agent to the coolant to set the freezing temperature to about −20° C., for example, a relationship of “minimum temperature (−40° C.)<freezing temperature (−20°)” is established.
In a case where the minimum temperature in the specifications applied to the cooling device is −40° C., for example, when an outdoor air temperature is −50° C. because of a severe cold wave that may happen once in ten-odd years, unexpected freezing of the cooling liquid occurs. However, when a cooling device is configured with the precondition described above, that is, when a cooling device is configured while assuming that a cooling liquid is frozen, it is possible to handle such unexpected freezing of the cooling liquid swiftly and without any problem. Furthermore, there is an advantage such that even though the device is not designed to handle events that occur with a very low probability, the device can handle such events. This advantage can greatly contribute to cost reduction and downsizing of the device.
Next, an operation of the cooling device according to the present embodiment at the time of freezing is explained with reference to
When the cooling liquid in the radiator 6 and the circulating pump 7 that have a large heat capacity is melted, any other structures having a large capacity do not exist other than the cooling pipe 5. When the cooling liquid in the radiator 6 and the circulating pump 7 that have a large heat capacity is melted, it is expected that a part of the cooling liquid in the cooling pipe 5c is also melted and the entire cooling liquid is liquefied in a sherbet state. Accordingly, by operating the circulating pump 7 in addition to the switching element module 10, effects of heat transfer are increased and a speed at which the cooling device enters in an operable state can be increased. For example, as shown in
The number of temperature sensors does not need to be two. It is permissible to provide only one temperature sensor, or to provide three or more temperature sensors. The position of the temperature sensor is not particularly limited as long as it is on a circulation path of the cooling liquid, but it is more preferable that the temperature sensor is provided at the periphery part of the radiator 6 or the circulating pump 7.
As shown in
While the present embodiment has explained that the magnitude relationship between the first path length A and the second path length B is not uniquely determined. However, when a different in the heat capacity between the radiator 6 and the circulating pump 7 is large, to allow a structure having a large heat capacity and a structure having a small heat capacity to be melted substantially at the same time, it suffices to arrange a cooling pipe so that a path length of a cooling pipe connected to the structure having a large heat capacity is short.
While the present embodiment has described a material having a high heat conductivity such as copper or silver as the metal material (the metal spiral) that is spirally wound around the cooling tube 5, the metal material is not limited to this type of metal material. For example, it is believed that some carbon nanotubes have a heat conductivity that is ten to ten-odd times larger than that of silver or copper. While the system of supplying carbon nanotubes has not been fully established as of filing of the present application, a technique related to the carbon nanotubes will become a breakthrough technique and it is preferable to use the carbon nanotubes for the cooling device according to the present embodiment.
While the present embodiment has described that the metal material is wound around the entire circumference of the cooling pipe 5 as shown in
As explained above, according to the cooling device of the present embodiment, the cooling performance at a high temperature can be improved without using any additive that reduces a freezing temperature, or even when the additive is used, by suppressing the amount of the additive. Furthermore, any additional device such as a preheating device or a warming device is unnecessary.
According to the cooling device of the present embodiment, because any additive that reduces the freezing temperature is not used, or even when it is used, the amount of the additive can be suppressed, the cooling performance at a high temperature can be improved, and the device can be downsized with the same cooling performance.
According to the cooling device of the present embodiment, because a pipe made of flexible resin can be used as a cooling pipe, the cooling pipe can be arranged with flexibility.
According to the cooling device of the present embodiment, a metal material is spirally wound around the cooling pipe to closely and adjacently contact the cooling pipe, so that, even when the heat generation source suddenly generates heat, the cooling liquid in the overall cooling device is rapidly liquefied to recover a cooling function. Furthermore, there is adopted a configuration in which a switching element module serving as a heat generation source is arranged between a radiator and a circulating pump. Accordingly, the cooling device can be caused to shift to an operable state before the switching element reaches a maximum allowable temperature.
According to the cooling device of the present invention, because the device is configured while assuming that a cooling liquid is frozen, it is possible to handle such unexpected freezing of the cooling liquid swiftly and without any problem. Furthermore, there is an advantage such that even though the device is not designed to handle events that occur with a very low probability, the device can handle such events. This advantage can greatly contribute to cost reduction and downsizing of the device.
When the flexible cooling pipes 5a and 5b are used as in the first embodiment, while a cooling pipe can be flexibly arranged, the metal spiral 20 needs to be wound around the cooling pipes 5a and 5b. On the other hand, when the metal cooling pipes 5a′ and 5b′ are used as in the present embodiment, any operation of winding the metal spiral 20 around the cooling pipes 5a′ and 5b′ is unnecessary. Furthermore, in a case of the cooling device according to the first and second embodiments, because a distance between the radiator 6 and the heat sink 4 and a distance between the circulating pump 7 and the heat sink 4 are short, a metal pipe having a high heat conductivity can be used.
It is preferable to form the cooling pipes 5a′ and 5b′ by using metal having a high heat conductivity such as silver or copper. When the metal having a high heat conductivity is used, heat transfer between the radiator 6 and the heat sink 4 and between the circulating pump 7 and the heat sink 4 is swiftly performed and thus effects identical to those of the first embodiment can be achieved.
A third embodiment explains a switching element included in the converter unit 1 and the inverter unit 2 of a power conversion device. As the switching element used in the power conversion device, a switching element in which a semiconductor transistor element made of silicon (Si) (an IGBT, a MOSFET, and the like) is connected in antiparallel to a semiconductor diode element also made of silicon is generally used. The techniques explained in the first and second embodiments can be used for an inverter unit and a converter unit each of which includes such a general switching element.
Meanwhile, the techniques explained in the first and second embodiments are not limited to a switching element made of silicon. It is of course possible to include a switching element made of, instead of silicon, silicon carbide (SiC) that has recently attracted attention in the converter unit 1 and the inverter unit 2.
Because silicon carbide has a characteristic that it can be used at a high temperature, when the switching element made of silicon carbide is used as the switching element included in the converter unit 1 or the inverter unit 2, an allowable operating temperature of a switching element module can be raised to be a high temperature. Therefore, when the switching element made of silicon carbide is used, the switching element can be caused to remain in an allowable temperature region even when the amount of heat generation per unit time is increased, and a melting speed of a frozen cooling liquid can be increased as compared to a case where the switching element made of silicon is used.
Silicon carbide (SiC) is an example of a semiconductor referred to as “wide bandgap semiconductor”, because of a characteristic that it has a bandgap larger than silicon (Si). In addition to this silicon carbide, for example, a semiconductor made of a gallium nitride-based material or a semiconductor formed by using diamond are also a wide bandgap semiconductor and characteristics of these materials are similar to those of silicon carbide. Therefore, configurations using a wide bandgap semiconductor other than that made of silicon carbide also form the scope of the present invention.
Because a transistor element and a diode element that are formed of such a wide bandgap semiconductor have a high voltage resistance and a high allowable current density, the transistor element and the diode element can be downsized. By using these downsized transistor element and diode element, a semiconductor module having these elements incorporated therein can be downsized.
Because the transistor element and the diode element formed of a wide bandgap semiconductor also have a high heat resistance, a heat sink can be downsized and a switching element module can be further downsized.
Furthermore, because the transistor element and the diode element formed of a wide bandgap semiconductor have a reduced power loss, the efficiency of the switching element and the diode element can be increased and thus the efficiency of the switching element module can be increased.
As described above, the present invention is useful as a cooling device of a circulating-liquid cooling system and a power conversion device that is configured to be coolable by this type of cooling device.
1 converter unit
2 inverter unit
3 switching element
4 heat sink
5, 5a, 5b, 5c, 5a′,5b′ cooling pipe
6 radiator
7 circulating pump
8 reserve tank
9 blower
10 switching element module
11 overhead line
12 pantograph
13 transformer
14 filter capacitor
15 induction motor
16 IGBT
17 diode
20 metal spiral
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/052942 | 2/10/2011 | WO | 00 | 8/10/2013 |
