Cooling structure for inverter for vehicle drive and control system thereof

Abstract

The present application relates to a cooling structure for an inverter for vehicle drive and a control system thereof. The cooling structure for an inverter for vehicle drive includes: a switching element provided in an inverter for vehicle drive; a heat sink connected to the switching element and heat-exchangeable with the switching element; a cooling flow path in which a cooling liquid flows and heat-exchangeable with the heat sink; and an auxiliary cooling module connected to the switching element and heat-exchangeable with the switching element to be heated by heat generation of the switching element or to be cooled together with the switching element.

Description

Technical Field

[0001] The present invention relates to a cooling structure and control system for an inverter for vehicle drive, the cooling structure reflecting the heat generation characteristics of the switching elements included in the inverter. Background Technology

[0002] In recent years, electric vehicles have become a social focus in terms of implementing environmentally friendly technologies and addressing issues such as energy consumption. Electric vehicles operate using motors that receive power from batteries to output power. Therefore, due to their advantages of zero carbon dioxide emissions, very low noise, and the higher energy efficiency of motors compared to engines, electric vehicles are considered environmentally friendly.

[0003] These electric vehicles (EVs) or fuel cell electric vehicles (FCEVs) use electric motors to drive the vehicle, and the motors require inverters. Inverters generate less heat than motors, but the switching elements in the inverter (e.g., insulated-gate bipolar transistors (IGBTs)) have a heating characteristic that results in relatively large temperature variations due to their smaller heat capacity (C = c·m).

[0004] However, existing inverter cooling systems use methods that control the temperature and flow rate of the coolant, similar to engine cooling systems. This cooling system is suitable for engines with relatively slow heat generation characteristics, but it is insufficient to handle the instantaneous heat generation characteristics of inverters.

[0005] Figure 1 The temperature variation of the switching elements under the cooling structure of an existing inverter is shown.

[0006] refer to Figure 1 As the motor load increases, the switching elements begin to heat up, and the temperature of the switching elements rises rapidly in a very short time.

[0007] The existing inverter cooling structure suffers from slow response in controlling the temperature or flow rate of the coolant, and the coolant temperature or flow rate rises after the inverter's switching elements reach a high temperature. Therefore, the switching elements are frequently exposed to higher temperatures when the motor load changes.

[0008] The content described as prior art is provided only to help understand the background of the present invention and should not be considered as corresponding to prior art known to those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to provide a cooling structure and control system for an inverter used in vehicle drive, which reduces temperature variations caused by the heat generated by the switching elements included in the inverter.

[0010] According to an exemplary embodiment of the present invention, a cooling structure for an inverter for vehicle drive may include: a switching element, a heat sink, a cooling flow path, and an auxiliary cooling module. The switching element is disposed in the inverter for vehicle drive; the heat sink is connected to the switching element and is capable of heat exchange with the switching element; coolant flows in the cooling flow path and exchanges heat with the heat sink; the auxiliary cooling module is connected to the switching element and is capable of heat exchange with the switching element, so as to be heated by the heat generated by the switching element, or cooled together with the switching element.

[0011] The switching element may have one surface that contacts the heat sink and another surface that contacts the auxiliary cooling module.

[0012] The auxiliary cooling module can be shaped to surround the switching element, so as to connect to the heat sink and exchange heat with the heat sink.

[0013] The auxiliary cooling module can be the inverter housing, and the switching element can be connected to the inverter housing through a first heat conductor located between the inverter housing and the switching element, and can exchange heat with the inverter housing.

[0014] One side of the first heat conductor can contact the switching element surface, and the other side can contact the inverter housing surface.

[0015] The auxiliary cooling module may include a refrigerant, the phase change temperature of which is within the allowable temperature range of the switching element.

[0016] The phase change temperature of the refrigerant can be the boiling point of the refrigerant, and the refrigerant can cool the switching element while evaporating due to the heating of the switching element.

[0017] The capacity of the refrigerant can be greater than the minimum capacity, which is calculated based on the latent heat of the refrigerant during phase change, the maximum heat generation of the switching element, and the cooling response time.

[0018] The auxiliary cooling module can be connected to the cooling flow path and can exchange heat with the coolant in the cooling flow path through a second heat conductor.

[0019] One end of the second heat conductor can be connected to the auxiliary cooling module, and the other end can be connected to the cooling flow path. The other end of the second heat conductor is located downstream of the heat sink based on the flow direction of the cooling flow path.

[0020] The auxiliary cooling module may include a refrigerant whose boiling point is within the allowable temperature range of the switching element, and one end of the second heat conductor may be connected to the auxiliary cooling module, the other end of the second heat conductor may be connected to the cooling flow path, and the first end of the second heat conductor is connected to the upper part of the auxiliary cooling module.

[0021] According to another exemplary embodiment of the present invention, the control system of the cooling structure of the inverter for vehicle drive as described above may include: a circulating pump, a heat exchanger, a cooling fan, and a controller, wherein the circulating pump is disposed in a cooling flow path and configured to circulate coolant in the cooling flow path; the heat exchanger is disposed in the cooling flow path and allows the coolant in the cooling flow path to exchange heat with outdoor air; the cooling fan is configured to rotate to circulate outdoor air around the heat exchanger; and the controller controls the rotational speed of the circulating pump or the rotational speed of the cooling fan based on an input signal received from the driver to control the motor drive.

[0022] According to another exemplary embodiment of the present invention, the control system of the cooling structure for an inverter for vehicle drive as described above may include: a circulating pump, a heat exchanger, a cooling fan, and a controller, wherein the circulating pump is disposed in a cooling flow path and configured to circulate coolant in the cooling flow path; the heat exchanger is disposed in the cooling flow path and allows the coolant in the cooling flow path to exchange heat with outdoor air; the cooling fan is configured to rotate to circulate outdoor air around the heat exchanger; and the controller controls the rotational speed of the circulating pump or the rotational speed of the cooling fan based on the pressure in the auxiliary cooling module. Attached Figure Description

[0023] Figure 1 The temperature variation of the switching elements under the cooling structure of an existing inverter is shown.

[0024] Figures 2 to 4 This diagram illustrates the configuration of a cooling structure for a vehicle-driven inverter according to various exemplary embodiments of the present invention.

[0025] Figure 5 The temperature variation of the switching elements included in the cooling structure of an inverter for vehicle drive according to an exemplary embodiment of the present invention is shown.

[0026] Figure 6 This is a configuration diagram of a control system for a cooling structure of an inverter for vehicle drive according to an exemplary embodiment of the present invention.

[0027] Figure 7 and Figure 8 A schematic diagram showing the rotational speed of a circulating pump and a cooling fan according to an exemplary embodiment of the present invention is shown. Detailed Implementation

[0028] The specific description of the structure and function of the exemplary embodiments of the present invention described herein is illustrative only and is not intended to limit the invention.

[0029] Since various modifications can be made to this invention and it can have several exemplary embodiments, specific exemplary embodiments will be shown and described in detail in the accompanying drawings. However, it should be understood that this invention is not limited to the specific exemplary embodiments, but includes all modifications, equivalents, and substitutions included within the spirit and scope of this invention.

[0030] Terms such as "first" and "second" may be used to describe various components, but these components should not be construed as being limited by these terms. These terms are only used to distinguish one component from another. For example, without departing from the scope of the invention, a "first" component may be named a "second" component, and similarly, a "second" component may be named a "first" component.

[0031] It should be understood that when an element is referred to as "connected to" or "joined to" another element, it can be directly connected to or joined to the other element, or it can be connected to or joined to the other element while having other elements between them. On the other hand, it should be understood that when an element is referred to as "directly connected to" or "directly joined to" another element, it can be connected to or joined to the other element without any other elements between them. Other expressions describing relationships between components should be interpreted similarly, such as "between," "directly between," "adjacent to," "directly adjacent to," etc.

[0032] The terminology used in this specification is for describing specific exemplary embodiments only and is not intended to limit the invention. Unless otherwise expressly stated, the singular forms used herein are intended to include the plural forms. It will be further understood that the terms "comprising" or "having" as used herein specify the presence of the stated feature, step, operation, component, part, or combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0033] Unless otherwise indicated, it should be understood that all terms used in this specification, including technical and scientific terms, have the same meaning as understood by those skilled in the art. It must be understood that terms as defined in dictionaries have the same meaning in the relevant technical context, and they should not be given idealized or overly formal definitions unless the context explicitly indicates otherwise.

[0034] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Throughout the drawings, the same reference numerals denote the same components.

[0035] Figures 2 to 4 This diagram illustrates the configuration of a cooling structure for a vehicle-driven inverter according to various exemplary embodiments of the present invention.

[0036] refer to Figures 2 to 4 The cooling structure of an inverter for vehicle drive may include: a switching element 10, a heat sink 20, a cooling flow path 30, and an auxiliary cooling module 40. The switching element 10 is located in the inverter for vehicle drive; the heat sink 20 is connected to the switching element 10 and can exchange heat with the switching element 10; coolant flows in the cooling flow path 30 and exchanges heat with the heat sink 20; the auxiliary cooling module 40 is connected to the switching element 10 and can exchange heat with the switching element 10, either being heated by the heat generated by the switching element 10 or being cooled together with the switching element 10.

[0037] The switching element 10 is a component located in the inverter and can be a semiconductor element such as a transistor or a thyristor. In an exemplary embodiment, the switching element 10 can be a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT).

[0038] The heat sink 20 can be connected to the switching element 10 and can exchange heat with the switching element 10. The heat sink 20 can be connected to the switching element 10 to directly contact the switching element 10 and exchange heat with the switching element 10 through heat conduction or the like, or it can be indirect contact with the switching element 10 and exchange heat with the switching element 10 using a separate medium.

[0039] The coolant can flow in the cooling flow path 30, and the heat sink 20 can be completely located in the cooling flow path 30, or can be inserted into the cooling flow path 30 so that the heat sink 20 is partially exposed to the coolant.

[0040] The auxiliary cooling module 40 can be connected to the switching element 10 and can exchange heat with the switching element 10. Specifically, the auxiliary cooling module 40 can be heated by the heat generated by the switching element 10, or it can be cooled together with the switching element 10. As in the exemplary embodiments described below, the auxiliary cooling module 40 can be integrally coupled to the switching element 10, or it can be indirectly connected to the switching element 10 via a separate medium.

[0041] The heat capacity of the switching element 10 can be increased by the auxiliary cooling module 40 (which is coupled to the switching element 10 and can exchange heat with the switching element 10), thereby delaying the temperature rise of the switching element 10 due to heat generation.

[0042] In an exemplary implementation, such as Figure 2 As shown, the auxiliary cooling module 40 can be formed in the shape of surrounding the switching element 10, and can be connected to the heat sink 20 and exchange heat with the heat sink 20.

[0043] The auxiliary cooling module 40 can simply be a block with a large heat capacity. The heat capacity of the auxiliary cooling module 40 can be greater than that of the switching element 10. The auxiliary cooling module 40 can not only be connected to the switching element 10 and exchange heat with the switching element 10, but also be connected to the heat sink 20 and exchange heat with the heat sink 20. Therefore, the auxiliary cooling module 40, which is heated by the heat generated by the switching element 10, can be cooled by the heat sink 20.

[0044] In another exemplary implementation, such as Figure 3 and Figure 4 As shown, the switching element 10 may have one surface in contact with the heat sink 20 and another surface in contact with the auxiliary cooling module 40. The switching element 10 may be in direct contact with the heat sink 20 and may exchange heat with the heat sink 20 through thermal conduction. On the other surface opposite to the one surface in contact with the heat sink 20, the switching element 10 may be in direct contact with the auxiliary cooling module 40 and may exchange heat with the auxiliary cooling module 40 through thermal conduction.

[0045] The auxiliary cooling module 40 may not be directly connected to the heat sink 20, but may include a separate medium for cooling the auxiliary cooling module 40. The auxiliary cooling module 40 may be indirectly cooled by the switching element 10 or by the ambient outdoor air.

[0046] Specifically, such as Figure 3 As shown, the auxiliary cooling module 40 can be the inverter housing 40, and the switching element 10 can be connected to the inverter housing 40 through the first heat conductor 41 located between the inverter housing 40 and the switching element 10, and can exchange heat with the inverter housing 40.

[0047] The inverter housing 40 can be configured to surround the switching element 10 and the first heat conductor 41 from the outside. The first heat conductor 41 can be made of a material with relatively high thermal conductivity (e.g., a metal such as copper).

[0048] The first heat conductor 41 can contact the surface of the switching element 10 on one side and the surface of the inverter housing on the other side. The first heat conductor 41 can contact both the switching element 10 and the inverter housing surface, thereby improving the thermal conductivity.

[0049] In another exemplary implementation, such as Figure 4 As shown, the auxiliary cooling module 40 may include a refrigerant, the phase change temperature of which is within the allowable temperature range of the switching element 10.

[0050] Here, the refrigerant can be a two-phase refrigerant that utilizes latent heat through a phase change. That is, the phase change temperature of the refrigerant can be within the allowable temperature range of the switching element 10.

[0051] The permissible temperature range of the switching element 10 can be preset to a temperature range below an upper limit temperature (e.g., 140°C), at which the durability of the switching element 10 decreases sharply with exposure. In an exemplary embodiment, the phase change temperature of the refrigerant can be approximately 80°C.

[0052] The phase change temperature of the refrigerant can be the boiling point of the refrigerant, and the refrigerant can cool the switching element 10 while evaporating due to the heat generated by the switching element 10.

[0053] In other words, the boiling point of the refrigerant is within the allowable temperature range of the switching element 10. Therefore, when the switching element 10 generates heat within the allowable temperature range, the refrigerant can be evaporated through its latent heat and cool the switching element 10.

[0054] The capacity of the refrigerant can be greater than the minimum capacity, which is calculated based on the latent heat of the refrigerant during phase change, the maximum heat generation of the switching element 10, and the cooling response time.

[0055] For example, the required heat absorbed by the refrigerant can be calculated as the product of the maximum heat output of the switching element 10 and the cooling response time. The minimum capacity of the refrigerant can be calculated by dividing the required heat absorbed by the refrigerant by the latent heat of the refrigerant (latent heat per unit mass).

[0056] Here, the cooling response time can be preset by taking into account the responsiveness of the cooling control through the cooling flow path 30 when the switching element 10 heats up. That is, the cooling response time can be between the time point when the heating of the switching element 10 changes and the time point when the cooling control through the cooling flow path 30 changes, for example, it can be preset to 10 seconds.

[0057] The auxiliary cooling module 40 can be arranged to exchange heat with the coolant in the cooling flow path 30 through the second heat conductor 42.

[0058] In other words, the auxiliary cooling module 40 can be arranged to exchange heat with the coolant through the second heat conductor 42, so that it can be cooled by the coolant separately from the switching element 10.

[0059] Specifically, one end of the second heat conductor 42 can be connected to the auxiliary cooling module 40, and the other end can be connected to the cooling flow path 30. The other end of the second heat conductor 42 is located downstream of the heat sink 20 based on the flow direction in the cooling flow path 30.

[0060] The other end of the second heat conductor 42 can be connected to the cooling flow path 30, based on the fact that the coolant flow direction in the cooling flow path 30 is downstream of the heat sink 20, so as to minimize the cooling effect from the heat sink 20. A cooling fin 43 can be formed at the other end of the second heat conductor 42 to extend the area in contact with the coolant in the cooling flow path 30.

[0061] In addition, the auxiliary cooling module 40 may include a refrigerant whose boiling point is within the allowable temperature range of the switching element 10. One end of the second heat conductor 42 may be connected to the auxiliary cooling module 40, and the other end may be connected to the cooling flow path 30. The first end of the second heat conductor 42 is connected to the upper part of the auxiliary cooling module 40.

[0062] One end cooled by the other end of the second heat conductor 42 can be connected to the upper part of the auxiliary cooling module 40 to cool the upper part of the auxiliary cooling module 40. Therefore, gaseous refrigerant, which evaporates in the auxiliary cooling module 40 and is located in the upper part of the auxiliary cooling module 40, can be condensed.

[0063] Figure 5 The temperature variation of the switching elements included in the cooling structure of an inverter for vehicle drive according to an exemplary embodiment of the present invention is shown.

[0064] Further reference Figure 5 In the cooling structure of an inverter for vehicle drive according to an exemplary embodiment of the present invention, the temperature change of the switching element 10 can be delayed and the amount of temperature change can be reduced.

[0065] Specifically, compared to the temperature change (dashed line) of the switching element 10 according to the prior art, the temperature change (solid line) of the cooling structure of the inverter for vehicle drive according to an exemplary embodiment of the present invention has the effect that, due to the reduced magnitude of the temperature change ΔT, the highest temperature T of the switching element 10 is reduced. max The temperature rise rate of the switching element 10 decreases, thereby increasing the time Δt for the switching element 10 to reach its maximum temperature.

[0066] Figure 6A configuration diagram of a control system for a cooling structure of an inverter for vehicle drive according to an exemplary embodiment of the present invention; Figure 7 and Figure 8 A schematic diagram showing the rotational speeds of a circulating pump 50 and a cooling fan 61 according to an exemplary embodiment of the present invention is shown.

[0067] refer to Figures 6 to 8 According to another exemplary embodiment of the present invention, the control system for the cooling structure of an inverter for vehicle drive may include a circulation pump 50, a heat exchanger 60, a cooling fan 61, and a controller 70. The circulation pump 50 is disposed in a cooling flow path 30 and circulates coolant in the cooling flow path 30 when driven. The heat exchanger 60 is disposed in the cooling flow path 30 and exchanges heat between the coolant in the cooling flow path 30 and outdoor air. The cooling fan 61 circulates outdoor air around the heat exchanger 60 when rotating. The controller 70 controls the rotational speed of the circulation pump 50 or the rotational speed of the cooling fan 61 based on an input signal received from the driver to control the motor drive.

[0068] The input signal can be a signal received from the driver. In an exemplary embodiment, the input signal can be the amount of pressure applied to the accelerator pedal 90 by the driver. The controller 70 can control the rotational speed of the circulation pump 50 or the rotational speed of the cooling fan 61 based on an accelerator position sensor (APS) indicating the amount of pressure applied to the accelerator pedal 90 received from the accelerator pedal 90.

[0069] Further reference Figure 7 In an exemplary embodiment, the load on the motor (or the amount of pressure applied to the accelerator pedal 90) can be proportional to the required cooling capacity of the switching element 10. Therefore, the rotational speed of the circulating pump 50 or the cooling fan 61 can be controlled to meet the required cooling capacity of the switching element 10, which increases with the increase in motor load. However, when the motor load is below a preset load, the rotational speed of the circulating pump 50 or the cooling fan 61 can be controlled to remain constant.

[0070] Assuming the load on the motor is proportional to the amount of pressure applied to the accelerator pedal 90, the speed of the circulating pump 50 or the speed of the cooling fan 61 can be controlled to be directly proportional to the amount of pressure applied to the accelerator pedal 90.

[0071] This control system can be configured to quickly detect and respond to the heating of the switching element 10, thereby preventing the temperature of the switching element 10 from rising to a high temperature. In this way, the responsiveness of the control system can be improved.

[0072] According to another exemplary embodiment of the present invention, the control system for the cooling structure of the inverter for vehicle drive may include: a controller 70 that controls the rotational speed of the circulating pump 50 or the rotational speed of the cooling fan 61 based on the pressure in the auxiliary cooling module 40.

[0073] The auxiliary cooling module 40 includes a refrigerant whose phase change temperature is within the allowable temperature range of the switching element 10. The auxiliary cooling module 40 may further include a pressure sensor 80 for measuring internal pressure. The controller 70 may control the speed of the circulating pump 50 or the speed of the cooling fan 61 based on the pressure in the auxiliary cooling module 40 measured by the pressure sensor 80.

[0074] When the refrigerant exchanges heat with the switching element 10, it can evaporate in the auxiliary cooling module 40, and the pressure in the auxiliary cooling module 40 may increase as the vapor pressure of the refrigerant increases.

[0075] Further reference Figure 8 As the pressure in the auxiliary cooling module 40 increases, the cooling required by the switching element 10 may increase, and the speed of the circulating pump 50 or the cooling fan 61 can be controlled to meet the required cooling capacity. However, when the motor load is below a preset load, the speed of the circulating pump 50 or the cooling fan 61 can be controlled to remain constant.

[0076] According to this control system, the evaporated refrigerant can be rapidly condensed, thus preparing for the subsequent heating of the switching element 10. In this way, the control system can greatly improve cooling control.

[0077] The controller 70 according to an exemplary embodiment of the present invention can be implemented using a non-volatile memory (not shown) and a processor (not shown), the non-volatile memory being configured to store data relating to algorithms configured to control the operation of various components of the vehicle or software instructions for reproducing the algorithms; the processor being configured to perform the operations described below using the data stored in the respective memory. Here, the memory and processor can be implemented as separate chips. Alternatively, the memory and processor can be implemented as a single chip integrated with each other. The processor can consist of more than one processor.

[0078] According to the cooling structure and control system of the inverter for vehicle drive of the present invention, the switching elements included in the inverter can have increased heat capacity.

[0079] Therefore, by preventing sudden changes in the temperature of the switching element, the durability of the switching element can be improved.

[0080] In addition, the heating of the switching elements can be detected in advance, and the inverter's cooling control can be configured to respond quickly to the heating.

[0081] Although specific embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various modifications and alterations can be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A cooling structure for a vehicle-driven inverter, comprising: Switching elements are disposed in an inverter used for vehicle drive; A heat sink is connected to the switching element and configured to exchange heat with the switching element; A cooling flow path in which coolant flows to exchange heat with the heat sink; as well as An auxiliary cooling module is connected to the switching element and is capable of exchanging heat with the switching element to be heated by the heat generated by the switching element, or to be cooled together with the switching element; The auxiliary cooling module includes a refrigerant, and the phase change temperature of the refrigerant is within the allowable temperature range of the switching element. The capacity of the refrigerant is greater than or equal to the minimum capacity, which is calculated based on the latent heat of the refrigerant during phase change, the maximum heat generation of the switching element, and the cooling response time.

2. The cooling structure for an inverter for vehicle drive according to claim 1, wherein, The phase change temperature of the refrigerant is the boiling point of the refrigerant; The refrigerant cools the switching element as it evaporates due to the heat generated by the switching element.

3. The cooling structure for an inverter for vehicle drive according to claim 1, wherein, The auxiliary cooling module can exchange heat with the coolant in the cooling flow path through the second heat conductor.

4. The cooling structure for an inverter for vehicle drive according to claim 3, wherein, The first end of the second heat conductor is connected to the auxiliary cooling module, the second end of the second heat conductor is connected to the cooling flow path, and the second end of the second heat conductor is arranged at the downstream point of the heat sink based on the flow direction of the cooling flow path.

5. The cooling structure for an inverter for vehicle drive according to claim 3, wherein, The auxiliary cooling module includes a refrigerant, the boiling point of which is within the allowable temperature range of the switching element. The first end of the second heat conductor is connected to the auxiliary cooling module, the second end of the second heat conductor is connected to the cooling flow path, and the first end of the second heat conductor is connected to the upper part of the auxiliary cooling module.

6. A cooling structure for an inverter used in vehicle drive, comprising: Switching elements are disposed in an inverter used for vehicle drive; A heat sink is connected to the switching element and configured to exchange heat with the switching element; A cooling flow path in which coolant flows to exchange heat with the heat sink; as well as An auxiliary cooling module is connected to the switching element and is capable of exchanging heat with the switching element to be heated by the heat generated by the switching element, or to be cooled together with the switching element; The auxiliary cooling module has a shape that contacts and surrounds the switching element, and is connected to the heat sink and is capable of exchanging heat with the heat sink.

7. The control system for the cooling structure of the inverter for vehicle drive according to claim 1, comprising: A circulating pump is located in the cooling flow path and configured to circulate the coolant in the cooling flow path; A heat exchanger is installed in the cooling flow path and allows the coolant in the cooling flow path to exchange heat with the outdoor air; A cooling fan configured to rotate to circulate outdoor air around the heat exchanger; as well as The controller controls the speed of the circulating pump or the speed of the cooling fan based on the input signal received from the driver to control the motor drive.

8. The control system for the cooling structure of the inverter for vehicle drive according to claim 1, comprising: A circulating pump is located in the cooling flow path and configured to circulate the coolant in the cooling flow path; A heat exchanger is installed in the cooling flow path and allows the coolant in the cooling flow path to exchange heat with the outdoor air; A cooling fan configured to rotate to circulate outdoor air around the heat exchanger; as well as The controller controls the speed of the circulating pump or the speed of the cooling fan based on the pressure in the auxiliary cooling module.

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