Temperature estimation system and temperature estimation method

Abstract

To enable estimation of temperatures of a plurality of second monitoring objects to which temperature sensors are not provided.SOLUTION: A temperature estimation system 1 comprises: an electric device 10 including a plurality of first monitoring objects 12 each composed of one or more electronic components, a plurality of temperature sensors 14 each detecting a temperature of the corresponding first monitoring object, and a plurality of second monitoring objects 11, 13 each composed of one or more electronic components; a cooling device 30 having a cooling path 31 through which coolant to cool the plurality of first monitoring objects and the plurality of second monitoring objects flows; and a processor 21 which estimates temperatures of the plurality of second monitoring objects on the basis of the temperatures of the first monitoring objects detected by the temperature sensors 14. The processor 21 estimates the respective temperatures of the second monitoring objects on the basis of the temperatures of the first monitoring objects adjacent in the cooling path 31.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a temperature estimation system for estimating the temperature of an object to be monitored in an electric device, and a temperature estimation method for the temperature estimation system. [Background technology]

[0002] In recent years, efforts to realize a low-carbon or carbon-free society have become more active, and research and development into electrification technologies is being conducted in order to reduce CO2 emissions and improve energy efficiency in vehicles.In order to stabilize the operation of systems equipped with electronic components in electric vehicles and to prevent cost increases, it is important to monitor the temperature of electronic components with a small number of components and prevent them from overheating.

[0003] For example, Patent Document 1 discloses a temperature estimation system that estimates the temperature of a second monitored object, different from a first monitored object, based on the temperature of the first monitored object detected by a temperature sensor. This temperature estimation system includes a cooling device having a cooling path through which a refrigerant flows to cool the first monitored object and the second monitored object, and a temperature sensor that detects the temperature of the first monitored object. A control device of the temperature estimation system derives the amount of heat transferred from the first monitored object to the cooling path based on the temperature of the first monitored object and a first temperature estimate, which is an estimate of the temperature of the first monitored object when the amount of heat transferred from the first monitored object to the cooling path is assumed to be zero, and the temperature of the first monitored object, and estimates a second temperature estimate, which is the temperature of the second monitored object, based on the amount of heat transferred from the first monitored object to the cooling path and the amount of heat generated according to the current operating state of the second monitored object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-160416 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional technology cannot estimate the temperatures of multiple second monitored objects when there are at least two heat-generating electrical components to be cooled by the refrigerant flow path and there are multiple second monitored objects for which no temperature sensor is installed.

[0006] In view of the above background, an object of the present invention is to make it possible to estimate the temperatures of a plurality of second monitoring objects that are not provided with temperature sensors. [Means for solving the problem]

[0007] In order to solve the above problem, one aspect of the present invention is a temperature estimation system (1) comprising: an electrical device (10) having a plurality of first monitored objects (12) each consisting of one or more electronic components, a plurality of temperature sensors (14) each detecting the temperature of a corresponding one of the first monitored objects, and a plurality of second monitored objects (11, 13) each consisting of one or more electronic components; a cooling device (30) having a cooling path (31) through which a refrigerant flows to cool the plurality of first monitored objects and the plurality of second monitored objects; and a processor (20) that estimates the temperatures of the plurality of second monitored objects based on the temperatures of the first monitored objects detected by the temperature sensors, and the processor estimates the temperature of each of the second monitored objects based on the temperatures of the first monitored objects adjacent to each other in the cooling path.

[0008] According to this aspect, the temperature of each second monitored object can be estimated based on the temperature of the first monitored object adjacent to it in the cooling path among the plurality of first monitored objects whose temperatures are detected by the plurality of temperature sensors. Also, by estimating the temperature of the second monitored object based on the temperature of the first monitored object adjacent to it in the cooling path, the temperature of the second monitored object can be accurately estimated.

[0009] In the above aspect, the plurality of second monitored objects may include an upstream second monitored object (13) and a downstream second monitored object (11) arranged upstream and downstream of the plurality of first monitored objects in the cooling path, and the processor may estimate the temperature of the upstream second monitored object based on the temperature of the first monitored object (12U) arranged most upstream in the cooling path among the plurality of first monitored objects, and estimate the temperature of the downstream second monitored object based on the temperature of the first monitored object (12W) arranged most downstream in the cooling path among the plurality of first monitored objects.

[0010] According to this aspect, the temperature of the upstream second monitored object can be accurately estimated based on the temperature of the first monitored object located immediately downstream thereof, and the temperature of the downstream second monitored object can be accurately estimated based on the temperature of the first monitored object located immediately upstream thereof.

[0011] In the above aspect, it is preferable that the electrical device is a power conversion device (10), each of the first monitored objects is an IPM switching element (12U, 12V, 12W), and the second monitored object includes a capacitor (13) and a reactor (11).

[0012] According to this aspect, the temperature of the capacitor and the temperature of the reactor can be estimated using the detection values ​​of a plurality of temperature sensors that detect the temperatures of the switching elements of the IPM.

[0013] Another aspect of the present invention for solving the above problem is a temperature estimation method in a temperature estimation system (1), the temperature estimation system comprising: an electrical device (10) having a plurality of first monitored objects (12) each consisting of one or more electronic components, a plurality of temperature sensors (14) for detecting the temperatures of the plurality of first monitored objects, and a plurality of second monitored objects (11, 13) each consisting of one or more electronic components; a cooling device (30) having a cooling path (31) through which a refrigerant flows for cooling the plurality of first monitored objects and the plurality of second monitored objects; and a processor (20) for estimating the temperatures of the plurality of second monitored objects based on the temperatures of the first monitored objects detected by the temperature sensors, and the processor estimates the temperatures of each of the second monitored objects based on the temperatures of the first monitored objects adjacent to each other in the cooling path.

[0014] According to this aspect, the processor can estimate the temperature of each second monitored object based on the temperature of the first monitored object adjacent to the second monitored object in the cooling path, among the plurality of first monitored objects whose temperatures are detected by the plurality of temperature sensors. Furthermore, by estimating the temperature of the second monitored object based on the temperature of the first monitored object adjacent to the second monitored object in the cooling path, the processor can accurately estimate the temperature of the second monitored object.

[0015] In the above aspect, the plurality of second monitored objects may include an upstream second monitored object (13) and a downstream second monitored object (11) arranged upstream and downstream of the plurality of first monitored objects in the cooling path, and the processor may estimate the temperature of the upstream second monitored object based on the temperature of the first monitored object (12U) arranged most upstream in the cooling path among the plurality of first monitored objects, and estimate the temperature of the downstream second monitored object based on the temperature of the first monitored object (12W) arranged most downstream in the cooling path among the plurality of first monitored objects.

[0016] According to this aspect, the temperature of the upstream second monitored object can be accurately estimated based on the temperature of the first monitored object located immediately downstream thereof, and the temperature of the downstream second monitored object can be accurately estimated based on the temperature of the first monitored object located immediately upstream thereof. [Effects of the Invention]

[0017] According to the above aspect, it becomes possible to estimate the temperatures of a plurality of second monitoring objects that are not provided with temperature sensors. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of a schematic configuration of a temperature estimation system according to an embodiment. [Figure 2] FIG. 1 is a diagram showing an example of a schematic configuration of a cooling system of a temperature estimation system according to an embodiment. [Figure 3] Block diagram of a temperature estimation function of a temperature estimation system according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0020] <Temperature estimation system> Figure 1 is a diagram showing an example of the schematic configuration of a temperature estimation system 1 according to an embodiment. The temperature estimation system 1 is a system that makes it possible to estimate the temperatures of multiple second monitoring objects, which are different from multiple first monitoring objects, based on the temperatures of multiple first monitoring objects detected by multiple temperature sensors 14 (shown as one in Figure 1) of an electrical device. This makes it possible to acquire the temperatures of multiple second monitoring objects without providing multiple temperature sensors 14 that detect the temperatures of the second monitoring objects, thereby simplifying the configuration.

[0021] The first monitored object and the second monitored object are each composed of one or more electronic components and generate heat when operating (in other words, when power is supplied). In this embodiment, an IPM 12 (Intelligent Power Module) is the first monitored object. A reactor 11 connected to the input side of the IPM 12, which is the first monitored object, is the downstream second monitored object, and a capacitor 13 connected to the output side of the IPM 12 is the upstream second monitored object. However, the objects as the first monitored object and the second monitored object are not particularly limited. In this embodiment, the electric device is a power conversion device 10. However, the electric device is not particularly limited and may be an electrically driven device or an electric control device.

[0022] As shown in Fig. 1, the temperature estimation system 1 of this embodiment includes a power conversion device 10 electrically connected to a power source 2 and a load 3, a control device 20 that performs overall control of the power conversion device 10, and a cooling device 30 that cools the power conversion device 10. In this embodiment, the temperature estimation system 1 is mounted on an electric vehicle that has a motor as a drive source, such as an electric vehicle or a hybrid electric vehicle. Hereinafter, the electric vehicle on which the temperature estimation system 1 is mounted will be simply referred to as a "vehicle."

[0023] The power supply 2 is a voltage / current source configured to be able to output a predetermined amount of power to the power conversion device 10, and is, for example, a battery serving as a power storage device mounted on a vehicle. More specifically, the power supply 2 can be a high-voltage battery (a so-called drive battery) configured by connecting a plurality of storage cells, such as lithium-ion batteries or nickel-metal hydride batteries, in series or in series-parallel, and capable of outputting a high voltage of 100 to 200 V. Furthermore, the power supply 2 is not limited to such a high-voltage battery, and may also be, for example, a low-voltage battery (a so-called auxiliary battery) capable of outputting a low voltage of about 12 V, a fuel cell, a generator, or the like.

[0024] The load 3 is an electrically powered device that operates using power supplied from the power conversion device 10, and may be, for example, a motor that is a drive source for a vehicle (hereinafter also referred to as a "drive motor"). Furthermore, the load 3 is not limited to such a drive motor, and may be, for example, a motor that drives a fan, a fuel pump, or a compressor mounted on the vehicle (for example, a motor for an air conditioner).

[0025] The power conversion device 10 is a device that generates a predetermined amount of power from power supplied from a power source 2 under the control of a control device 20 and outputs the generated power to a load 3. Specifically, the power conversion device 10 includes a reactor 11, which is an example of a second object to be monitored, an IPM 12, which is an example of a first object to be monitored, a capacitor 13, which is an example of a second object to be monitored, a temperature sensor 14, a voltage sensor 15, and a current sensor 16. For example, the power conversion device 10 is configured by accommodating the reactor 11, the IPM 12, the capacitor 13, the temperature sensor 14, the voltage sensor 15, and the current sensor 16 in the same housing 17 (see FIG. 2 ).

[0026] The IPM 12 has multiple switching elements realized by one or multiple electronic components such as MOSFETs (metal oxide semiconductor field effect transistors) and IGBTs (insulated gate bipolar transistors). The IPM 12 generates a predetermined amount of power by switching these multiple switching elements under the control of the control device 20, and outputs the generated power. Specifically, the IPM 12 converts the DC current flowing from the power source 2 to the load 3 into an AC current, and converts the AC current flowing from the load 3 to the power source 2 into a DC current.

[0027] The reactor 11 is electrically connected to the positive terminal of the power source 2 and the IPM 12. The reactor 11 controls and stabilizes the flow of direct current flowing from the power source 2 to the IPM 12. The reactor 11 also smoothes the current flowing from the IPM 12 to the power source 2, bringing it closer to direct current.

[0028] The capacitor 13 is connected to the output side of the IPM 12 (more specifically, between the IPM 12 and the load 3), and functions as a smoothing capacitor that smoothes the power output from the IPM 12.

[0029] Temperature sensor 14 is a sensor that detects the temperature of IPM 12 and outputs a detection signal indicating the detected temperature of IPM 12 to control device 20. Voltage sensor 15 is a sensor that detects the voltage value of power output from IPM 12 (hereinafter also referred to as "output voltage value") and outputs a detection signal indicating the detected output voltage value to control device 20. Current sensor 16 is a sensor that detects the current value of power output from IPM 12 and outputs a detection signal indicating the detected output current value to control device 20.

[0030] The control device 20 is configured by a computer including a processor 21 configured by a central processing unit (CPU) or the like, a memory 24 such as a RAM 22 or a ROM 23, a storage device 25 such as an HDD or SSD, an input / output port 26, etc. The control device 20 is realized by an ECU (Electronic Control Unit) and controls the entire temperature estimation system 1. The control device 20 may be realized by one ECU or by multiple ECUs operating in cooperation with each other.

[0031] When the vehicle is driven and traveling, the control device 20 controls the power supplied from the power source 2 to the load 3 by appropriately outputting a predetermined control signal to the power conversion device 10. As a result, the load 3 functions as a drive motor and the vehicle travels. When braking the vehicle while traveling, the control device 20 controls the power supplied from the load 3 to the power source 2 by appropriately outputting a predetermined control signal to the power conversion device 10. As a result, the load 3 functions as a generator and regenerated power is charged to the power source 2.

[0032] The control device 20 controls the power conversion device 10, and the reactor 11, IPM 12, and capacitor 13 generate heat as they operate (in other words, as power is supplied to them). The IPM 12 becomes the hottest among them. The cooling device 30 cools the reactor 11, IPM 12, and capacitor 13 of the power conversion device 10.

[0033] 2 is a diagram showing an example of a schematic configuration of a cooling system of the temperature estimation system 1 according to the embodiment. The cooling device 30 has a cooling path 31 through which a refrigerant (e.g., a cooling water called "LLC") flows to cool the reactor 11, the IPM 12, and the condenser 13. The cooling device 30 also has a radiator 32 as a heat dissipation device that dissipates heat of the refrigerant flowing through the cooling path 31 to the outside air, and a pump 33 that circulates the refrigerant within the cooling device 30.

[0034] The reactor 11, the IPM 12, and the condenser 13 are arranged on the cooling path 31 of the cooling device 30 in a state capable of exchanging heat with the refrigerant flowing through the cooling path 31. The cooling path 31 may be formed inside the housing 17 of the power conversion device 10 as long as it is capable of exchanging heat with the heat-generating electronic components of the power conversion device 10. In another example, the cooling path 31 may be formed by a path-forming member separate from the housing 17. The heat of the reactor 11, the IPM 12, and the condenser 13 is transferred to the refrigerant flowing through the cooling path 31, and then radiated to the outside air by the radiator 32. In this way, the reactor 11, the IPM 12, and the condenser 13, which may generate heat, are cooled by the cooling device 30, and an increase in their temperatures is suppressed.

[0035] A cooling water inlet 17a and a cooling water outlet 17b are formed in the housing 17 of the power conversion device 10. A portion of the cooling path 31 extending from the cooling water inlet 17a to the cooling water outlet 17b of the housing 17 is formed as a single path. In the housing 17 of the power conversion device 10, the capacitor 13, the IPM 12, and the reactor 11 are arranged in this order from the upstream side to the downstream side of the cooling path 31.

[0036] IPM 12 includes switching elements constituting three power modules corresponding to the U-phase, V-phase, and W-phase (hereinafter referred to as U-phase power module 12U, V-phase power module 12V, and W-phase power module 12W) in order to generate three-phase AC power. These three power modules are arranged in a row with respect to cooling path 31. In this embodiment, U-phase power module 12U, V-phase power module 12V, and W-phase power module 12W are arranged in this order from the upstream side to the downstream side of cooling path 31.

[0037] 3 is a block diagram of the temperature estimation function of the temperature estimation system 1 according to the embodiment. On a cooling path 31, a capacitor 13, a U-phase power module 12U, a V-phase power module 12V, a W-phase power module 12W, and a reactor 11 are arranged in this order from upstream to downstream. Temperature sensors 14 for detecting the temperature of the IPM 12 include a temperature sensor 14 for detecting the temperature of the U-phase power module 12U, a temperature sensor 14V for detecting the temperature of the V-phase power module 12V, and a temperature sensor 14W for detecting the temperature of the W-phase power module 12W. Each temperature sensor 14 is an element temperature sensor mounted on a semiconductor substrate of the corresponding power module, and may be, for example, a thermistor.

[0038] The reactor 11 and the IPM 12 are electrically and thermally connected via a first bus bar 19a made of a copper plate or the like. The IPM 12 and the capacitor 13 are electrically and thermally connected via a second bus bar 19b also made of a copper plate or the like. The reactor 11 and the capacitor 13 may also generate heat, but no dedicated sensors are provided to detect their temperatures.

[0039] Therefore, the control device 20 of this embodiment includes a coolant temperature estimation unit 27, a heat flow estimation unit 28, and a temperature estimation unit 29 as functional units realized by processing by the processor 21. The processor 21 is configured to estimate the temperatures of the condenser 13 and the reactor 11 based on temperatures detected by the plurality of temperature sensors 14 provided in the IPM 12. This makes it possible to estimate the temperatures of the condenser 13 and the reactor 11, which are the plurality of second monitored objects not provided with dedicated temperature sensors. This will be described in detail below.

[0040] <Temperature estimation method> When the temperature estimation system 1 is started, for example, by turning on the vehicle's ignition power or accessory power, the processor 21 estimates the temperature of the capacitor 13 at a predetermined timing (for example, at a predetermined period) during the start-up period using the estimation method described below.

[0041] First, the processor 21 derives the heat flow rate Q' transferred from the IPM 12 to the cooling water in the cooling path 31. The heat flow rate Q' can be derived, for example, by the following equation (1).

number

[0042] In the above formula (1), the cooling water temperature T w is estimated from the temperature of the IPM 12 by the coolant temperature estimation unit 27. w A coolant temperature estimation map for deriving the coolant temperature T is stored in advance in the storage device 25, and the coolant temperature estimation unit 27 refers to this coolant temperature estimation map to calculate the coolant temperature T w Estimate.

[0043] Then, the heat flow rate estimation unit 28 of the control device 20 calculates the above equation (1) to derive the heat flow rate Q′ transferred from the IPM 12 to the cooling water in the cooling path 31.

[0044] Next, the temperature estimation unit 29 of the control device 20 calculates the heat transfer temperature of the heat transferred from the IPM 12 to the second object to be monitored (the reactor 11 or the capacitor 13) via the first bus bar 19a or the second bus bar 19b. Next, the temperature estimation unit 29 calculates the estimated temperature t i The estimated temperature t of the reactor 11 and the capacitor 13 is calculated. i can be derived, for example, by the following equation (2).

number

[0045] In the numerator of the first term of the above equation (2), the first term represents the amount of heat that flows in, the second term represents the heat loss, and the third term represents the amount of heat that flows through the cooling path 31. The high-temperature side electronic component is the IPM 12, and the low-temperature side electronic component is the reactor 11 or the capacitor 13. The temperature T of the low-temperature side electronic component is L is, for example, the temperature T of the cold-side electronic component calculated most recently (i.e., last time). L If there is no recent value, an initial value stored in the storage device 25 may be used.

[0046] The estimated temperature t of the capacitor 13 is calculated using the above equations (1) and (2). i When calculating the temperature T IPM , the temperature of the hot side electronic component T H , the temperature of the U-phase power module 12U adjacent to the capacitor 13 in the cooling path 31 is used to calculate the temperature T L The estimated temperature t of the capacitor 13 i On the other hand, the previous value or the initial value of the reactor temperature t i When calculating the temperature T IPM, the temperature of the hot side electronic component T H , the temperature of the W-phase power module 12W adjacent to the reactor 11 in the cooling path 31 is used to calculate the temperature T L The estimated temperature t of reactor 11 is i The previous value or the initial value of is used.

[0047] As described above, the temperature estimation system 1 includes a plurality of temperature sensors 14 (14U, 14V, 14W) that detect the temperatures of a plurality of power modules that are first monitored objects. Therefore, the processor 21 can estimate the temperatures of the reactor 11 and the capacitor 13 that are second monitored objects based on the temperatures of the power modules that are adjacent to each other in the cooling path 31. Furthermore, by estimating the temperature of the second monitored object based on the temperature of the first monitored object that is adjacent to each other in the cooling path 31, the processor 21 can accurately estimate the temperature of the second monitored object.

[0048] Processor 21 then estimates the temperature of capacitor 13, which is the second upstream monitoring object, based on the temperature of U-phase power module 12U, which is the most upstream of the multiple power modules, in cooling path 31. Processor 21 also estimates the temperature of reactor 11, which is the second downstream monitoring object, based on the temperature of W-phase power module 12W, which is the most downstream of the multiple power modules, in cooling path 31. This allows processor 21 to accurately estimate the temperatures of capacitor 13 and reactor 11.

[0049] Furthermore, the processor 21 can estimate the temperatures of the capacitor 13 and the reactor 11 using the detection values ​​of a plurality of temperature sensors 14 (14U, 14V, 14W) provided to detect the temperatures of the switching elements of the IPM 12. Therefore, there is no need for dedicated sensors to estimate the temperatures of the capacitor 13 and the reactor 11, which makes it possible to reduce the number of parts, cut costs, and simplify the system configuration.

[0050] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment or modified example, and can be widely modified and implemented. For example, the first monitored object and the second monitored object are not limited to the above example. In the above embodiment, the temperature of one first monitored object is used to estimate the temperature of the second monitored object, but the temperatures of two first monitored objects may also be used. In addition, the specific configuration, arrangement, quantity, material, etc. of each component and part can be changed as appropriate within the scope of the present invention. Furthermore, not all of the components shown in the above embodiment are necessarily required, and can be selected as appropriate. [Explanation of symbols]

[0051] 1: Temperature estimation system 2: Power supply 3: Load 10: Power conversion device (an example of an electrical device) 11: Reactor (an example of a second monitored object) 12: IPM (example of the first monitored object) 12U: U-phase power module (first monitored object) 12V: V-phase power module (first monitored object) 12W: W-phase power module (first monitored object) 13: Capacitor (an example of a second monitored object) 14: Temperature sensor 14U: Temperature sensor 14V: Temperature sensor 14W: Temperature sensor 20: Control device 21: Processor 30: Cooling device 31: Cooling path T IPM : Temperature of IPM12 (temperature of adjacent first monitored object) T H : Temperature of the hot side electronic component (temperature of the first adjacent monitored object) t i : Estimated temperature of the second monitored object

Claims

1. an electrical device including a plurality of first monitored objects each composed of one or more electronic components, a plurality of temperature sensors for detecting the temperature of the corresponding first monitored object, and a plurality of second monitored objects each composed of one or more electronic components; a cooling device having a cooling path through which a refrigerant flows to cool the plurality of first monitored objects and the plurality of second monitored objects; a processor that estimates temperatures of the plurality of second monitored objects based on the temperatures of the first monitored objects detected by the temperature sensor; the electric device is a power conversion device, each of the first monitored objects is a switching element of an IPM, and each of the second monitored objects includes a capacitor and a reactor; The processor estimates the temperature of each of the second monitored objects based on the temperature of the first monitored object adjacent to the cooling path.

2. the plurality of second monitored objects include an upstream second monitored object and a downstream second monitored object that are arranged upstream and downstream of the plurality of first monitored objects in the cooling path, respectively; The processor: estimating a temperature of the upstream second monitoring object based on a temperature of a first monitoring object arranged most upstream of the cooling path among the plurality of first monitoring objects; 2. The temperature estimation system according to claim 1, wherein the temperature of the downstream second monitored object is estimated based on the temperature of the first monitored object located furthest downstream in the cooling path among the plurality of first monitored objects.

3. an electrical device including a plurality of first monitored objects each composed of one or more electronic components, a plurality of temperature sensors for detecting temperatures of the plurality of first monitored objects, and a plurality of second monitored objects each composed of one or more electronic components; a cooling device having a cooling path through which a refrigerant flows to cool the plurality of first monitored objects and the plurality of second monitored objects; a processor that estimates temperatures of the plurality of second monitored objects based on the temperatures of the first monitored objects detected by the temperature sensor; A temperature estimation method for a temperature estimation system, wherein the electric device is a power conversion device, each of the first monitored objects is a switching element of an IPM, and the second monitored objects include a capacitor and a reactor, A temperature estimation method, wherein the processor estimates the temperature of each of the second monitored objects based on the temperature of the first monitored object adjacent to the cooling path.

4. the plurality of second monitored objects include an upstream second monitored object and a downstream second monitored object that are arranged upstream and downstream of the plurality of first monitored objects in the cooling path, respectively; the processor: estimating a temperature of the upstream second monitoring object based on a temperature of a first monitoring object arranged most upstream of the cooling path among the plurality of first monitoring objects; 4. The temperature estimation method according to claim 3, wherein the temperature of the downstream second monitored object is estimated based on the temperature of the first monitored object that is located furthest downstream in the cooling path among the plurality of first monitored objects.

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