JP7081545B2 - Power converter - Google Patents

Description

This specification discloses a power conversion device in which grease is filled between a module and a cooler.

The power conversion device disclosed in Patent Document 1 includes a module that generates heat when energized, a cooler that cools the module, an insulating plate arranged between the module and the cooler, and a space between the module and the insulating plate. And it is equipped with grease that fills the space between the insulation plate and the cooler. The grease filled between the module and the insulating plate adheres to both to reduce the thermal resistance between them. The grease filled between the insulating plate and the cooler adheres to both to reduce the thermal resistance between them.

Japanese Unexamined Patent Publication No. 2018-06394

In the above power conversion device, when the module is energized, the module generates heat and expands. Therefore, the space between the module and the insulating plate and the space between the insulating plate and the cooler are reduced. As a result, a part of the grease is discharged to the outside of the space. When the power supply to the module is stopped, the temperature of the module drops and the module contracts. A part of the discharged grease returns to the space, but not all the discharged grease returns to the space, and a part of the grease stays outside the space. As a result, a space in which no grease exists is formed in the space between the module and the insulating plate and the space between the insulating plate and the cooler (this is called grease removal). When grease is removed, thermal resistance increases.

This specification discloses a technique for suppressing the occurrence of grease loss.

The technique disclosed herein is a technique useful for suppressing the loss of grease filled in the space between the insulating plate and the cooler, and is a technique useful for suppressing the loss of grease, and the space between the module and the insulating plate. Another technique is used to deal with the grease filled in. This technique is based on the premise that an insulating plate is interposed between the module and the cooler, but it is not a useful technique only when the inclusion is an insulating plate, and the inclusions are present. It is a generally useful technique if it exists. Hereinafter, inclusions such as an insulating plate are referred to as intermediate members.

The power conversion device disclosed in the present specification is arranged between a module that generates heat when energized and has a temperature detector, a cooler in which a refrigerant flows inside to cool the module, and a module and a cooler. It is provided with an intermediate member, a grease filled between the cooler and the intermediate member, and a control unit. The control unit stores a map that converts the detected value of the temperature detection unit into the estimated temperature of grease, and when the estimated temperature of grease converted by the map is equal to or higher than the reference value, the flow rate of the refrigerant flowing through the cooler is calculated. Perform at least one of the process of raising and the process of reducing the current value applied to the module. The insulating plate may be an intermediate member, but a material other than the insulating plate may be an intermediate member.

The grease, which is intended to prevent the grease from coming off by the present technique, is arranged at a position separated from the module by an intermediate member and adjacent to the cooler. Therefore, the grease is more likely to be cooled by the cooler than the grease filled between the module and the intermediate member. The module temperature and the grease temperature are different, and it should be difficult to estimate the grease temperature from the module temperature. However, in reality, it has been confirmed by the inventor that the grease temperature can be estimated from the module temperature, and that the occurrence of grease loss can be sufficiently suppressed within the range of the estimation accuracy. If the grease temperature estimated from the module temperature contains an estimation error, but the estimated temperature is above the reference value, increase the flow rate of the refrigerant flowing through the cooler and / or energize the module. The process of reducing the current value makes it difficult for grease to be discharged to the outside of the space between the intermediate member and the cooler. As a result, it is possible to prevent the grease from coming off.

It is a block diagram of the electric power system of the electric vehicle provided with the electric power conversion device of 1st Embodiment. It is a block diagram which shows the connection relationship between the control part of the power conversion apparatus of 1st Embodiment, and a device. It is a perspective view of the semiconductor device of the power conversion device of 1st Embodiment. It is sectional drawing of the semiconductor device of the power conversion device of 1st Embodiment. It is a figure which shows the relationship between the grease temperature and the grease viscosity. It is a flowchart which shows the temperature drop process of 1st Example. It is a flowchart which shows the temperature drop process of 2nd Example.

(Example)
The power conversion device 10 of the first embodiment will be described with reference to FIGS. 1 to 6. The power conversion device 10 is mounted on an electric vehicle 2 such as a hybrid vehicle or a fuel cell vehicle.

A block diagram of the electric power system of the electric vehicle 2 will be described with reference to FIG. The electric vehicle 2 includes a battery 4, a power conversion device 10, and motors 6a and 6b. The power conversion device 10 includes a converter 12, inverters 60a and 60b, capacitors 70 and 72, and a control unit 80 (see FIG. 2).

The converter 12 is a bidirectional DC-DC converter. The low voltage end of the converter 12 is connected to the battery 4. The high voltage end of the converter 12 is connected to the inverters 60a and 60b. The converter 12 includes two switching elements 14a and 14b, two diodes 16a and 16b, and a reactor 18.

The two switching elements 14a and 14b are connected in series between the positive electrode and the negative electrode at the high voltage end of the converter 12. A diode 16a is connected to the switching element 14a in antiparallel. A diode 16b is connected to the switching element 14b in antiparallel. The reactor 18 is connected between the midpoint of the series connection of the two switching elements 14a and 14b and the positive electrode at the low voltage end of the converter 12.

The converter 12 performs a step-up operation for boosting the voltage of the DC power output from the battery 4 and a step-down operation for stepping down the voltage of the DC power output from the inverters 60a and 60b. The switching element 14b and the diode 16a are involved in the boosting operation. The switching element 14a and the diode 16b are involved in the step-down operation. A detailed description of the step-up operation and the step-down operation will be omitted.

Each of the DC ends of the inverters 60a and 60b is connected to the high voltage end of the converter 12. Each of the AC ends of the inverters 60a and 60b is connected to each of the motors 6a and 6b. The motors 6a and 6b are three-phase AC motors.

The inverters 60a and 60b convert the DC power output from the converter 12 into AC power, and supply the converted AC power to the motors 6a and 6b. The inverter 60a includes six switching elements 14c-14h and six diodes 16c-16h. The six switching elements 14c-14h are connected in series by two each. Three sets of series connections are connected in parallel. Each of the six diodes 16c-16h is connected in antiparallel to each of the six switching elements 14c-14h.

The configuration of the inverter 60b is the same as the configuration of the inverter 60b. Therefore, in FIG. 2, the specific configuration of the inverter 60b is not shown. The inverter 60b also includes 6 switching elements and 6 diodes.

A capacitor 70 is connected to the low voltage end of the converter 12. A capacitor 72 is connected to the high voltage end of the converter 12.

As shown in FIG. 2, the control unit 80 controls two switching elements 14a and 14b of the converter 12, six switching elements 14c-14h of the inverter 60a, and six switching elements of the inverter 60b.

The hardware configuration of the power conversion device 10 will be described with reference to FIG. The power conversion device 10 includes a semiconductor device 30. The semiconductor device 30 includes a plurality of (7 in this embodiment) modules 32, a plurality of (8 in this embodiment) coolers 50, a plurality of (14 in this embodiment) insulating plates 52, and grease. It includes 54 (see FIG. 4), connecting pipes 56a and 56b, and a refrigerant circulation device 58 (see FIG. 2). In FIG. 3, only one insulating plate 52 is designated by a reference numeral.

The module 32 and the cooler 50 are alternately laminated in the X direction. Coolers 50 are located at both ends of the semiconductor device 30 in the X direction.

The module 32 has a flat plate shape. The module 32 has a wide surface on the side facing the cooler 50. The module 32 internally houses two switching elements 14 (two of 14a-14h) and two diodes 16 (two of 16a-16h). Specifically, one module 32 houses the switching elements 14a and 14b and the diodes 16a and 16b. The other module 32 accommodates the switching elements 14c, 14d and the diodes 16c, 16d. The other module 32 accommodates the switching elements 14e, 14f and the diodes 16e, 16f. The other module 32 accommodates the switching elements 14g, 14h and the diodes 16g, 16h. Similarly, the other three modules 32 accommodate the six switching elements 14 and the two diodes 16 that make up the inverter 60b. Hereinafter, when the switching elements 14a-14h are shown without distinction, they are referred to as switching elements 14, and when the diodes 16a-16b are shown without distinction, they are referred to as diodes 16.

The cooler 50 has a flat plate shape. The cooler 50 is made of a metal material such as aluminum. The cooler 50 has a flow path through which the refrigerant flows. The refrigerant is a liquid, for example, LLC (Long Life Coolant).

An insulating plate 52 is arranged between the module 32 and the cooler 50. The insulating plate 52 has a flat plate shape. The insulating plate 52 is an example of an intermediate member, and may not be an insulating plate.

The connecting pipes 56a and 56b connect the coolers 50 adjacent to each other. The connecting pipes 56a and 56b are connected to the refrigerant circulation device 58 (not shown in FIG. 3).

As shown in FIG. 2, the refrigerant circulation device 58 includes a pump 58a. The pump 58a supplies the refrigerant to the cooler 50. The pump 58a is controlled by the control unit 80. The pump 58a is driven according to a command from the control unit 80. As a result, the refrigerant is sent out from the refrigerant circulation device 58.

Returning to FIG. 3, the flow of the refrigerant will be described. The refrigerant sent out from the refrigerant circulation device 58 passes through the connecting pipe 56a and is supplied to the flow paths of all the coolers 50. The refrigerant absorbs heat from the adjacent module 32 while passing through the cooler 50. After that, the refrigerant passes through the connecting pipe 56b and returns to the refrigerant circulation device 58.

Next, with reference to FIG. 4, the structure between the module 32 and the cooler 50 will be described. FIG. 4 is a cross-sectional view of the semiconductor device 30 cut along a plane parallel to the XY plane. The module 32 includes two switching elements 14, two diodes 16, two spacers 40, heat sinks 42, 44, 46, and a main body 48. Actually, the diode 16 is formed inside the switching element 14, and is not shown in FIG.

The two switching elements 14 are arranged in the Y direction. Each of the two switching elements 14 is conducting to each of the two diodes 16. The switching element 14 is, for example, an insulated gate bipolar transistor (that is, an IGBT), a metal oxide semiconductor field effect transistor (that is, a MOSFET), or the like. Although not shown, control terminals are connected to the gate electrode and sense emitter electrode of the switching element 14.

One temperature detecting element 34 is built in one switching element 14. The temperature detecting element 34 is a diode whose resistance value changes according to the ambient temperature. The temperature detecting element 34 is also connected to the control terminal. As shown in FIG. 2, the temperature detecting element 34 is connected to the control unit 80 via the control terminal. The control unit 80 measures the temperature of the switching element 14 by detecting the resistance value of the temperature detecting element 34.

As shown in FIG. 4, a heat sink 42 is connected to the upper surface of one of the switching elements 14 via a solder 38. A heat sink 44 is connected to the upper surface of the other switching element 14 via a solder 38. In FIG. 4, the vertical direction is defined. The heat sinks 42 and 44 are made of copper, aluminum or the like. The heat sinks 42 and 44 have conductivity and thermal conductivity. Although not shown, the positive electrode terminal is connected to the heat sink 42, and the negative electrode terminal is connected to the heat sink 44.

Each of the two spacers 40 is connected to each of the lower surfaces of the two switching elements 14 via a solder 38. The spacer 40 is made of copper, aluminum, or the like. The spacer 40 has conductivity and thermal conductivity.

A heat sink 46 is connected to the lower surfaces of the two spacers 40 via solder 38. The heat sink 46 is made of copper, aluminum, or the like. The heat sink 46 has conductivity and thermal conductivity. Although not shown, the neutral terminal is connected to the heat sink 46.

The main body 48 accommodates two switching elements 14, two diodes 16, two spacers 40, and heat sinks 42, 44, 46. The main body 48 is made of a resin material. The main body 48 covers the surfaces excluding the upper surfaces of the heat radiating plates 42 and 44 and the lower surface of the heat radiating plates 46.

An insulating plate 52 is arranged between the module 32 and the cooler 50. The insulating plate 52 is made of an insulating material. The insulating plate 52 prevents the cooler 50 from coming into contact with the upper surfaces of the heat radiating plates 42 and 44, and the cooler 50 from coming into contact with the lower surface of the heat radiating plate 46. This suppresses the conduction between the heat sinks 42, 44, 46 and the cooler 50.

Grease 54 is filled between the module 32 and the insulating plate 52, and between the insulating plate 52 and the cooler 50. The thickness of the grease 54 is several tens of microns. In FIG. 4, the thickness of the grease 54 is exaggerated. The grease 54 promotes heat transfer from the module 32 to the cooler 50. In the following, the grease 54 filled between the module 32 and the insulating plate 52 may be referred to as grease 54a, and the grease 54 filled between the insulating plate 52 and the cooler 50 may be referred to as grease 54b. ..

The grease 54b is arranged at a position farther from the module 32 than the grease 54a filled between the module 32 and the insulating plate 52. Therefore, the heat of the module 32 is less likely to be transferred to the grease 54b than to the grease 54a. Further, the grease 54b is arranged at a position closer to the cooler 50 than the grease 54a. Therefore, the grease 54b is more easily cooled by the cooler 50 than the grease 54a. As a result, the temperature of the grease 54b is lower than the temperature of the grease 54a. Further, since the grease 54a is close to the module 32, the temperature of the grease 54b is substantially equal to the temperature of the module 32.

In the map showing the relationship X1 between the grease temperature and the grease viscosity shown in FIG. 5, the temperature zone of the grease 54b is in a region (the left side portion of the relationship X1) in which the grease viscosity changes significantly when the grease temperature changes. On the other hand, in the relation X1, the temperature zone of the grease 54a is in a region (the right side portion of the relation X1) in which the grease viscosity remains low and does not change significantly even if the grease temperature changes.

Next, the temperature lowering process executed by the control unit 80 of the power conversion device 10 will be described with reference to the flowchart of FIG. Although not shown in FIG. 6, when the user turns on the start switch of the electric vehicle 2, the series of processes of FIG. 6 is executed at predetermined time intervals. Further, when the start switch of the electric vehicle 2 is turned on, the control unit 80 drives the pump 58a of the refrigerant circulation device 58 under the condition that the flow rate of the refrigerant becomes the first flow rate. The control unit 80 stores the first flow rate in advance.

In S2 of the temperature lowering process shown in FIG. 6, the control unit 80 detects the resistance value of the temperature detecting element 34 and measures the temperature of the switching element 14. The control unit 80 acquires resistance values from all (14 in this embodiment) temperature detection elements 34 included in the semiconductor device 30. Therefore, the control unit 80 measures the temperatures of all the switching elements 14.

In the following S4, the control unit 80 selects the maximum temperature from all the measured temperatures of the switching element 14.

In the following S6, the control unit 80 converts the selected maximum temperature into the estimated temperature of the grease 54b by using a map that converts the temperature of the switching element 14 into the estimated temperature of the grease 54b. The control unit 80 stores in advance a map that converts the temperature of the switching element 14 into the estimated temperature of the grease 54b. In the map in which the temperature of the switching element 14 is converted into the estimated temperature of the grease 54b, the estimated temperature of the grease 54b is lower than the temperature of the switching element 14. A map that converts the temperature of the switching element 14 into the estimated temperature of the grease 54b has been specified in advance by experiments.

In the following S8, the control unit 80 determines whether or not the estimated temperature of the converted grease 54b is equal to or higher than the reference value. The control unit 80 stores the reference value in advance. The reference value is a value determined based on a map showing the relationship X1 between the grease temperature and the grease viscosity shown in FIG. 5 and a map (not shown) showing the relationship between the grease viscosity and the progress of grease removal. .. Here, in the relationship X1, the lower the grease temperature, the higher the grease viscosity. On the other hand, in the map showing the relationship between the grease viscosity and the progress of grease removal, the higher the grease viscosity, the more difficult it is for the grease 54 to be discharged to the outside of the space between the module 32 and the cooler 50. The relationship is unlikely to occur. As a result, the reference value is set to a low temperature. Further, a map showing the relationship X1 between the grease temperature and the grease viscosity and a map showing the relationship between the grease viscosity and the progress of grease removal have been specified in advance by experiments. If the estimated temperature of the converted grease 54b is equal to or higher than the reference value (YES in S8), the process proceeds to S10. On the other hand, when the estimated temperature of the converted grease 54b is less than the reference value (NO in S8), the process proceeds to S12.

First, S10 will be described. In S10, the control unit 80 changes the driving condition of the pump 58a to a condition in which the flow rate of the refrigerant becomes the second flow rate. The control unit 80 stores the second flow rate in advance. The second flow rate is larger than the first flow rate. For example, the second flow rate is twice the flow rate of the first flow rate. As a result, the flow rate of the refrigerant flowing through the flow path of the cooler 50 increases. Therefore, the temperatures of the greases 54a and 54b, the insulating plate 52, and the module 32 are lowered.

Next, S12 will be described. In S12, the control unit 80 maintains the driving condition of the pump 58a under the condition that the flow rate of the refrigerant becomes the first flow rate. Specifically, when the driving condition of the pump 58a is a condition in which the flow rate of the refrigerant becomes the second flow rate before S12 is executed, the control unit 80 sets the driving condition of the pump 58a as the first flow rate of the refrigerant. Change to the condition for the flow rate. Further, if the driving condition of the pump 58a is a condition in which the flow rate of the refrigerant becomes the first flow rate before S12 is executed, the control unit 80 does not change the driving condition of the pump 58a.

(effect)
As described above, when the estimated temperature of the grease 54b is equal to or higher than the reference value (YES in S8), in S10, the control unit 80 sets the driving condition of the pump 58a as a second flow rate in which the flow rate of the refrigerant is larger than the first flow rate. Change to the condition that becomes. Therefore, the temperature of the grease 54b is lowered by the refrigerant whose flow rate has increased. As a result, the viscosity of the grease 54b becomes high, and the grease 54b is less likely to be discharged to the outside of the space between the insulating plate 52 and the cooler 50. As a result, it is possible to prevent the grease 54b from coming off.

(Correspondence)
The temperature detection element 34 is an example of a “temperature detection unit”. The insulating plate 52 is an example of an “intermediate member”.

(Second Example)
The second embodiment will be described with reference to FIG. 7. In the second embodiment, the points different from those in the first embodiment will be described, and the same points as those in the first embodiment will be designated by the same reference numerals and the description thereof will be omitted. In the second embodiment, the temperature lowering treatment is different from the temperature lowering treatment of the first embodiment. In the temperature lowering process of the second embodiment, the control unit 80 executes S110 and S112 in place of S10 and S12 of the temperature lowering process of the first embodiment.

First, S110 after YES will be described in S8. In S110, the control unit 80 changes the driving state of the motors 6a and 6b of the electric vehicle 2 to the restricted state. Specifically, the control unit 80 controls each of the switching elements 14 between the converter 12 and the inverters 60a and 60b so that the motor output value is maintained at the first output value. The control unit 80 stores the first output value in advance. The first output value is a value set to suppress the motor output value, and is set to a low value. When the above S110 is executed, the current value flowing through the switching element 14 becomes small. As a result, the temperature of the module 32 drops.

Next, S112 after NO in S8 will be described. In S112, the control unit 80 maintains the drive state of the motors 6a and 6b in the restricted release state. Specifically, if the drive states of the motors 6a and 6b are in the restricted state before S112 is executed, the control unit 80 changes the drive states of the motors 6a and 6b to the restricted state. If the drive states of the motors 6a and 6b are in the restricted release state before S112 is executed, the control unit 80 does not change the drive states of the motors 6a and 6b. In the restricted state, the motor output value changes according to the amount of depression of the accelerator pedal of the electric vehicle 2. That is, in the restricted state, the motor output value is not maintained at the first output value.

(effect)
As described above, when YES in S8 (that is, when the estimated temperature of the grease 54b is equal to or higher than the reference value), in S10, the control unit 80 limits the driving states of the motors 6a and 6b of the electric vehicle 2. change. As a result, the current value flowing through the switching element 14 becomes small. Therefore, the temperature of the module 32 is lowered, and the temperature of the grease 54b is lowered. As a result, the viscosity of the grease 54b becomes high, and the grease 54b is less likely to be discharged to the outside of the space between the insulating plate 52 and the cooler 50. As a result, it is possible to prevent the grease 54b from coming off.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

(Modification example)
(1) In the modification of the first embodiment described above, when the estimated temperature of the grease 54b is equal to or higher than the reference value (YES in S8), the control unit 80 uses S10 of the first embodiment and S110 of the second embodiment. You may do both. That is, the control unit 80 changes the drive condition of the pump 58a to a condition in which the flow rate of the refrigerant becomes a second flow rate larger than the first flow rate, and changes the drive state of the motors 6a and 6b of the electric vehicle 2 to the restricted state. You may. As a result, the flow rate of the refrigerant increases and the current value flowing through the switching element 14 decreases. Further, in this modification, the control unit 80 executes both S12 of the first embodiment and S112 of the second embodiment.

(2) In the above embodiment, in S6, the control unit 80 converts the selected maximum temperature into the estimated temperature of the grease 54b by using the map that converts the temperature of the switching element 14 into the estimated temperature of the grease 54. In the modified example, the map for converting the temperature of the switching element 14 to the estimated temperature of the grease 54b is a map when the temperature of the switching element 14 is rising and a map when the temperature of the switching element 14 is decreasing. Both may be included. The map when the temperature of the switching element 14 is rising is a map used when a current is flowing through the switching element 14. Further, the map when the temperature of the switching element 14 is low is a map used when no current is flowing through the switching element 14. The control unit 80 determines whether or not a current is flowing through the switching element 14 based on a command from the control unit 80 to turn the switching element 14 on and off.

(3) In the above embodiment, in S8, the control unit 80 compares the estimated temperature of the grease 54b with one reference value. However, the control unit 80 may compare the estimated temperature of the grease 54b with the two reference values. Specifically, first, the control unit 80 determines whether or not the estimated temperature of the grease 54b is equal to or higher than the first reference value. Next, the control unit 80 determines whether or not the estimated temperature of the grease 54b is equal to or higher than the second reference value. The control unit 80 changes the drive conditions of the pump 58a (or the drive states of the motors 6a and 6b) based on the comparison result between the estimated temperature of the grease 54b and the two reference values. Further, the number of reference values is not limited to two, and may be three or more.

Although the technique of this embodiment can cope with the omission of the grease 54b, the omission of the grease 54a is not perfect. It is necessary to take another measure to prevent the grease 54a from coming off. Since another measure can be taken for the grease 54a, it has technical value in itself to be able to deal with the omission of the grease 54b.

The technical elements described herein or in the drawings exhibit their technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

2: Electric vehicle 4: Battery 6a, 6b: Motor 10: Power conversion device 12: Converter 14, 14a-14h: Switching element 16, 16a-16h: Diode 18: Reactor 30: Semiconductor device 32: Module 34: Temperature detection element 38: Solder 40: Spacer 42, 44, 46: Heat sink 48: Main body 50: Cooler 52: Insulation plate 54, 54a, 54b: Gris 56a, 56b: Connecting pipe 58: Refrigerator circulation device 58a: Pump 60a, 60b: Inverter 70, 72: Condenser 80: Control unit

Claims (1)

A module that generates heat when energized and has a temperature detector,
A cooler in which the refrigerant flows inside to cool the module,
An intermediate member arranged between the module and the cooler,
The grease filled between the cooler and the intermediate member,
A map for converting the detected value of the temperature detection unit into the estimated temperature of the grease is stored, and when the estimated temperature of the grease converted by the map is equal to or higher than the reference value, the refrigerant flowing through the cooler is used. A power conversion device including a control unit that executes at least one of a process of increasing the flow rate and a process of reducing the current value of energizing the module.

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