JP2024080896A - Semiconductor element temperature control method and semiconductor element temperature control device - Google Patents

Abstract

To more definitely suppress the occurrence of a situation in which the temperature of a semiconductor element of an inverter arranged in a cooling system surpasses an upper limit.SOLUTION: A semiconductor element temperature control method includes: calculating a torque command value T*m for stipulating a torque Tm for an electric motor to output; controlling a coolant flow rate WF in a cooling system based on the torque command value T*m; and performing a loss limit processing for limiting operational parameters of an inverter 20 on the basis of the loss P of a semiconductor element. In the loss limit processing, specifically, the method includes: calculating a flow rate response time Δtfr required for the response of a real coolant flow rate WF_R when the coolant flow rate WF is changed through a change in the torque command value T*m; calculating an upper limit loss value Pmax that is a loss where a temperature Tj of the semiconductor element after the flow rate response time Δtfr passes equals to a prescribed upper limit temperature Tj_max; and setting the operational parameters Σ so that the loss P during the time until the flow rate response time Δtfr passes becomes equal to or less than the upper limit loss value Pmax.SELECTED DRAWING: Figure 2

Description

The present invention relates to a semiconductor element temperature control method and a semiconductor element temperature control device.

In a cooling system that cools each heat-generating component mounted on an electric vehicle, a control that changes the refrigerant flow rate based on the amount of heat generated (coolant temperature) according to the driving status of each heat-generating component is known. In particular, a power converter (inverter) that adjusts the power between an on-board DC power source and an AC motor such as a driving motor may be arranged in the cooling system as a heat-generating component. That is, the semiconductor elements that constitute the power module of the inverter are heat sources, and the semiconductor elements are cooled in the cooling system. In this case, when a change in the coolant temperature of the cooling system due to a change in the temperature of the semiconductor elements is detected, the output of a pump arranged in the cooling system is adjusted to increase or decrease the refrigerant flow rate.

However, the control logic that detects changes in the cooling water temperature and increases or decreases the refrigerant flow rate sometimes cannot keep up with changes in the temperature of the semiconductor elements.

In response to this, Patent Document 1 discloses a cooling system that estimates the power loss generated by an inverter by referencing the accelerator opening in an electric vehicle, and controls the refrigerant flow rate based on the estimated power loss.

Patent No. 5258079

However, in the control of Patent Document 1, the response of the actual refrigerant flow rate to a change in the accelerator opening (required output for the electric vehicle) (change in the flow rate command value) is delayed, which can cause the temperature of the semiconductor element to exceed the specified upper limit.

Therefore, the object of the present invention is to more reliably prevent the occurrence of a situation in which the temperature of the semiconductor elements of the inverter arranged in the cooling system exceeds the upper limit value.

According to one aspect of the present invention, a semiconductor element temperature control method is provided that controls the temperature of a semiconductor element of an inverter that is arranged in a specified cooling system and performs power conversion between a power source and an electric motor. In this semiconductor element temperature control method, a torque command value that specifies the torque to be output by the electric motor is calculated, the flow rate of refrigerant in the cooling system is controlled based on the torque command value, and a loss limiting process is performed to limit the operating parameters of the inverter based on the loss of the semiconductor element.

In particular, the loss limiting process calculates the flow rate response time required for the actual refrigerant flow rate to respond when the torque command value changes to change the refrigerant flow rate, calculates an upper limit loss value, which is the loss when the temperature of the semiconductor element matches a predetermined upper limit temperature when the flow rate response time has elapsed, and determines operating parameters so that the loss until the flow rate response time has elapsed is equal to or less than the upper limit loss value.

The present invention makes it possible to more reliably prevent the occurrence of a situation in which the temperature of the semiconductor elements of the inverter arranged in the cooling system exceeds the upper limit value.

FIG. 1 is a diagram illustrating the configuration of a vehicle system according to an embodiment of the present invention. FIG. 2 is a flow chart illustrating a semiconductor element temperature control method. FIG. 3 is a diagram showing a flow rate command value map. FIG. 4 is a flowchart illustrating the loss limiting process in detail. FIG. 5 is a diagram illustrating the response of the actual refrigerant flow rate to a change in the torque command value (flow rate command value). FIG. 6 is a diagram showing an example of a flow rate-temperature map for determining the thermal resistance change coefficient. FIG. 7 is a diagram showing an example of a specific aspect of torque limitation in the loss limiting process. FIG. 8 is a timing chart showing the control results of the comparative example and the embodiment.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a diagram illustrating the configuration of a vehicle system 10 according to one embodiment of the present invention. As shown in the figure, the vehicle system 10 is mounted on an electric vehicle (electric car or hybrid vehicle) and has an inverter 20, a battery 25, a motor 30, a cooling system 40, and a controller 50.

The inverter 20 has a power module 21 and a cooler 22. The power module 21 is composed of multiple semiconductor elements (such as IGBTs) for converting between DC power on the battery side and AC power on the motor side. The cooler 22 is composed of a heat exchanger that dissipates heat from the semiconductor elements using a refrigerant (cooling water) in the cooling system 40.

In particular, the inverter 20 adjusts the power exchanged between the battery 25 and the motor 30 by performing switching operations in the power module 21 based on commands from the controller 50 (torque command value T ^* _m and operating parameters Σ of the inverter 20 described later).

The motor 30 is composed of a three-phase AC motor that functions as a drive source for the electric vehicle and/or as a generator for generating electricity for driving, etc.

The cooling system 40 includes a cooling water pump 41, a radiator 42, and the cooler 22 for the inverter 20 described above.

The cooling water pump 41 circulates the cooling water in the cooling passage of the cooling system 40 at a predetermined cooling water flow rate _WF . In particular, the output of the cooling water pump 41 is adjusted based on a command value for the cooling water flow rate _WF (hereinafter referred to as a "flow rate command value W ^* _F ") received from the controller 50. The radiator 42 dissipates heat from the cooling water by heat exchange with the outside air.

Therefore, by appropriately determining the output (flow rate command value W ^* _F ) of the cooling water pump 41, the amount of cooling provided to the power module 21 (semiconductor element) via the cooler 22 can be adjusted.

The controller 50 is configured by a computer that is composed of, for example, a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output interface (I/O interface), and is programmed to execute the processes described below. More specifically, the functions of the controller 50 are realized by, for example, a vehicle controller that controls each part of the electric vehicle, and a motor controller that controls the driving state of the motor 30 via the inverter 20.

In particular, the controller 50 has a rotation speed/torque command unit 51, a flow control unit 52, and a loss limiting unit 53.

The rotation speed/torque command unit 51 determines a torque command value T ^* _m and a rotation speed command value N ^* _m based on the required output for the electric vehicle, the vehicle speed, etc. The required output is determined according to the amount of accelerator pedal operation by the occupant or a command from a predetermined automatic driving controller.

The flow rate control unit 52 determines the flow rate command value W*F based on the torque command value T ^* _m , the detected value of the coolant temperature _TW obtained by the temperature sensor 60 (hereinafter referred to as the "current coolant temperature _{TW_c} "), the detected value of the motor rotation speed Nm obtained by the rotation speed sensor 61 (hereinafter referred to as the "current motor rotation _{speed Nm_c} "), and the detected value of the DC voltage _Vdc obtained by the voltage sensor 62 (hereinafter referred to as the "current ^DC voltage _{Vdc_c} ").

The loss limiting unit 53 calculates an operating parameter Σ that defines the operation of the inverter 20, based on the current cooling water temperature T _{W_c} , the current motor rotation speed _{Nm_c} , the current DC voltage V _{dc_c} , and a detection value (hereinafter referred to as "current element temperature T _{j_c} ") of the temperature of the semiconductor element (hereinafter referred to as "element temperature T _j ") in the power module 21 obtained by the element temperature sensor 63. The operating parameter Σ includes limit values of the motor torque T _m , the carrier frequency F, the DC voltage V _dc , and/or the gate resistance value _Rg .

The following describes in detail the semiconductor element temperature control method executed by the controller 50.

Figure 2 is a flowchart explaining the semiconductor element temperature control method of this embodiment. Note that each process shown in Figure 2 is repeatedly executed by the controller 50 at a predetermined calculation period.

In step S110, a torque command value T ^* _m is calculated from the required output for the electric vehicle, the vehicle speed, and the like.

Next, in step S120, a process is executed to control the coolant flow rate W _F. More specifically, a flow rate command value W ^* _F is calculated based on the torque command value T ^* _m , the current coolant temperature T _{W_c} , and the current motor rotation speed _{Nm_c} , and the output of the coolant pump 41 is adjusted to realize the flow rate command value W ^* _F .

3 is a diagram for explaining a map for determining the flow command value W ^* _F in this embodiment (hereinafter referred to as the "flow command value map"). As shown in the figure, the flow command value map pre-classifies the cooling water flow rate _WF in stages based on the torque command value T ^* _m , the cooling water temperature _Tw , and the motor rotation speed Nm to determine the flow command value W ^* _F . That is, the flow command value map pre-estimates each scene in which the amount of heat generated in the inverter 20 (switching loss of semiconductor elements) is different according to the torque command value T ^* _m , the cooling water temperature _Tw , and the motor rotation speed Nm, and assigns an appropriate flow command value W ^* _F to each scene.

In particular, in the flow command value map shown in Figure 3, the flow command value W ^* _F is divided into three stages: "high flow", "medium flow", and "low flow" according to the torque command value T ^* _m , the cooling water temperature _Tw , and the motor rotation speed Nm.

More specifically, in the flow command value map shown in Fig. 3, the flow command value W ^* _F is set to be higher as the torque command value T ^* _m is larger (see Figs. 3(a) and 3(b)). The flow command value W ^* _F is also set to be higher as the cooling water temperature _TW is higher (see Fig. 3(a)). Furthermore, the flow command value W*F is set to be higher as the motor rotation speed Nm is lower (see Fig. 3(b)). In particular, in the extremely low rotation speed region where the motor rotation speed Nm is several hundred rpm or less, and in the motor lock region where the motor rotation speed Nm is 0, the amount of heat generated by the semiconductor elements tends to be relatively large, so the flow command value W ^* _F is set to a "medium flow rate" or "high flow rate".

In the flow command value map, the flow command value W ^* _F is switched when the torque command value T ^* _m changes across a predetermined threshold torque _{Tm_th} (see FIG. 3C). That is, when the torque command value T ^* _m crosses the threshold torque _{Tm_th} , the cooling water flow rate _WF changes in a step manner.

However, due to the response characteristics of the control system for the coolant flow rate _WF (such as a response delay in the output of the coolant pump ⁴¹ ), it takes a certain amount of time (response delay occurs) for the actual coolant _{flow rate WF (} hereinafter referred to as the "actual coolant flow rate _{WF_R} ") to catch up with the flow rate command value W ^* _F when the flow rate command value W*F is switched. Furthermore, in the case of control using the flow rate command value map, the coolant flow rate _WF is required to be changed by a certain amount at the timing crossing the threshold torque _{Tm_th} , so that the effect of the response delay in the actual coolant flow rate _{WF_R} becomes strong.

For this reason, the element temperature _Tj increases during the response period of the actual coolant flow rate _{WF_R} to the flow rate command value W ^* _F , and may exceed the upper limit temperature _{Tj_max} determined from the viewpoint of heat resistance protection. When the element temperature _Tj exceeds the upper limit temperature _{Tj_max} , an output limit is activated to reduce the motor torque _Tm by a certain amount in order to suppress a further increase in the element temperature _Tj , which may cause an uncomfortable feeling to the passengers of the electric vehicle. This situation is particularly likely to occur when the power module 21 is configured with components having a relatively small thermal time constant (relatively fast response), such as a direct-cooled power module or a double-sided-cooled power module.

Therefore, in this embodiment, when the flow command value W ^* _F is switched as necessary, a loss limiting process described below is performed to more reliably prevent the element temperature _Tj from exceeding the upper limit temperature _{Tj_max} .

Returning to FIG. 2, in step S130, it is determined whether loss limiting processing is necessary. More specifically, if the current cooling water temperature T _{W_c} is equal to or higher than a predetermined threshold temperature T _{W_H} , or if the torque command value T ^* _m is equal to or higher than a predetermined threshold torque T _{m_th} , it is determined that loss limiting processing is necessary, and if not, it is determined that loss limiting processing is unnecessary. That is, the determination in step S130 is performed with the purpose of identifying a scene in which the element temperature T _j may exceed the upper limit temperature T _{j_max} . Note that the threshold temperature T _{W_H} and the threshold torque T _{m_th} are respectively determined as the cooling water temperature T _W and the torque command value T ^* _m for switching the flow command value W ^* _F , which are determined in the flow command value map in FIG. 3. On the other hand, the threshold temperature T _{W_H} and the threshold torque T _{m_th} in step S130 may be determined separately from the respective thresholds determined in the flow command value map in FIG. 3.

If the determination result in step S130 is negative, the operation parameter Σ of the inverter 20 is maintained at the basic control value, and the process ends. On the other hand, if the determination result in step S130 is positive, a loss limiting process (S140) is executed. In the loss limiting process, the operation parameter Σ of the inverter 20 is adjusted (limited) so that the element temperature _Tj does not exceed the upper limit temperature _{Tj_max} when the flow command value W ^* _F is switched.

4 is a flow chart for explaining the details of the loss limiting process. As shown in the figure, in the loss limiting process, first, the flow rate response time _Δtfr is calculated.

Here, the flow rate response time _Δtfr means the time required for the actual coolant flow rate _{WF_R} to respond when it is assumed that the torque command value T ^* _m changes from the current control timing t1 and the flow rate command value W ^* _F is switched.

FIG. 5 is a diagram for explaining the response of the actual coolant flow rate _{WF_R} to a change in the torque command value T ^* _m (switching of the flow rate command value W ^* _F ).

As shown in the figure, when the torque command value T ^* _m exceeds the threshold torque _{Tm_th} at the current control timing t1 and the flow command value W ^* _F is switched, the actual cooling water flow rate _{WF_R} reaches the switched flow command value W ^* _F at the response completion timing t2. The flow response time _Δtfr is calculated as the time required for this response (=t2-t1).

In particular, the flow rate response time _Δtfr is calculated according to the torque command value T ^* _m at the current control timing t1 with reference to the response characteristics of the cooling system 40 that are grasped in advance by experiments or the like. Note that a table that defines the relationship between the torque command value T ^* _m and the flow rate response time _Δtfr may be prepared in advance, and the flow rate response time _Δtfr may be obtained by applying the current control timing t1 and the current torque command value T ^* _m to the table. Furthermore, from the viewpoint of further improving the calculation accuracy, a map that correlates the flow rate response time Δtfr with other appropriate parameters (cooling water temperature T _W and motor rotation speed Nm, etc.) in addition to the torque command value T ^* _m may be prepared in advance, and the flow rate response time _Δtfr may be calculated from the torque command value T ^* _m at the current control timing t1 and the parameters with _reference to the map.

Returning to Fig. 4, in step S142, an upper limit loss value _Pmax is calculated. Here, the upper limit loss value _Pmax is calculated as the loss P of the semiconductor element on the assumption that the element temperature _Tj reaches the upper limit temperature _{Tj_max} determined from the viewpoint of heat resistance protection of the semiconductor element when the flow rate response time _Δtfr has elapsed (i.e., when the response completion timing t2 is reached). The loss P is an index value that indicates the magnitude of the switching loss in the semiconductor element (i.e., the magnitude of the heat generation).

More specifically, the upper limit loss value P _max is calculated by the following formula (1).

In the formula, "ΔT _{j_max} " represents the temperature increment from the current element temperature T _{j_c} to the upper limit temperature T _{j_max} , "τ" represents the thermal time constant of the semiconductor element, and "K" represents the thermal resistance change coefficient of the semiconductor element.

The thermal time constant τ is determined in advance according to the thermal characteristics that depend on the type of power module 21. The thermal resistance change coefficient K is a coefficient that is determined as the amount of change in the heat generation (temperature) per flow rate of the semiconductor element.

In particular, the thermal resistance change coefficient K can be determined by referring to a flow rate-element temperature _table (FIG. 6) prepared in advance based on the current cooling water flow rate W _F (a value detected by a flow rate sensor not shown or a flow rate command value W ^* _F ) and the current element temperature T j_c. More specifically, the thermal resistance change coefficient K can be calculated as a rate of change (differential coefficient) at an operating point corresponding to the current cooling water flow rate W _F and the current element temperature T _{j_c} on the curve representing the flow rate-element temperature table shown in FIG. 6.

The upper limit loss value P _max may be calculated using the following equation (2) which is a discretized version of equation (1).

Returning to FIG. 4, in step S143, an operating parameter Σ of the inverter 20 is calculated so that the loss P at the response completion timing t2 is equal to or _less than the upper limit loss value Pmax calculated in step S142.

More specifically, the relationship between the loss P of the semiconductor elements in the inverter 20, the current I, the DC voltage V _dc , and the carrier frequency F can be expressed by the following equation (3) using a predetermined appropriate function f.

Moreover, the relationship between the motor torque T _m , the current I, the DC voltage V _dc , and the motor rotation speed N _m can be expressed by the following equation (4) using a predetermined appropriate function g.

Therefore, by applying the upper limit loss value _Pmax to the loss P in equations (3) and (4) and performing calculations corresponding to the functions f and g, it is possible to determine the operating parameters Σ (more specifically, the motor torque _Tm , the carrier frequency F, and the DC voltage _Vdc ) that satisfy the condition that the loss P coincides _with the upper limit loss value Pmax. Note that maps equivalent to the functions f and g may be prepared in advance to reduce the calculation burden. Below, specific examples of the calculation modes for each operating parameter Σ are described.

[Motor torque]
First, by applying the upper limit loss value P _max , the current DC voltage V _{dc_c} , and the carrier frequency F set at the current control timing t1 to equation (3), the current I (hereinafter referred to as the “upper limit current I _max ”) is calculated assuming that the loss P at the response completion timing t2 matches the upper limit loss value P _max .

Furthermore, by applying the upper limit current _Imax , the current DC voltage _{Vdc_c} , and the current motor rotation speed _{Nm_c} to equation (4), the motor torque _Tm (hereinafter referred to as "upper limit motor torque _{Tm_max} ") is calculated assuming that the loss P at the response completion timing t2 matches the upper limit loss value _Pmax .

Then, the controller 50 adjusts the motor torque _Tm from the current control timing t1 to the response completion timing t2 to a limit torque _{Tm_lim} that is equal to or less than the upper limit motor torque _{Tm_max} .

FIG. 7 shows an example of a specific mode for limiting the motor torque _Tm .

In the example shown in Fig. 7A, the motor torque _Tm in the section from the current control timing t1 to the response completion timing t2 (hereinafter referred to as the "loss limit section [t1, t2]") is limited by a limit torque _{Tm_lim} that is less than the upper limit motor torque _{Tm_max} . Then, the torque control is released at the response completion timing t2.

The limit torque T _{m_lim} is set to an appropriate value for minimizing the torque step that occurs at the entry and completion of the loss limit section [t1, t2] while maintaining the motor torque T _m less than the upper limit motor torque T _{m_max} in the loss limit section [t1, t2].

As a result, the motor torque _Tm is adjusted so that the loss P of the semiconductor element is equal to or less than the upper limit loss value _Pmax in the loss limit section [t1, t2]. Therefore, the element temperature _Tj is maintained equal to or less than the upper limit temperature _{Tj_max} , and the activation of the output limit for heat resistance protection is suppressed. In other words, the occurrence of a sudden change in the motor torque _Tm due to the output limit is suppressed.

7(b) or 7(c), a filter process may be performed to change the motor torque _Tm primarily or secondarily at the start and end of the loss limit section [t1, t2]. This makes it possible to more gently change the motor torque Tm at the start and end of the loss limit section [t1, t2] while maintaining the element _{temperature Tj} at or below the upper limit temperature _{Tj_max} in the loss limit section.

[Carrier frequency]
When using an inverter 20 having a function of switching between multiple carrier frequencies F, it is also possible to employ control logic that selects the carrier frequency F so that the loss P in the loss limit section [t1, t2] is equal to or less than the upper limit loss value _Pmax .

Specifically, for example, from among a plurality of selectable carrier frequencies F, a frequency (hereinafter referred to as "limited carrier frequency F _lim ") is determined that satisfies the condition that the loss P on the left side of equation (3) is equal to or less than the upper limit loss value P _max when the present DC voltage V _{dc_c} and the present current I are applied to the right side of equation (3). Then, the carrier frequency F in the loss limit section [t1, t2] is fixed to the limited carrier frequency F _lim .

As described above, by appropriately limiting the carrier frequency F in the loss limit section [t1, t2], the element temperature _Tj is maintained at or below the upper limit temperature _{Tj_max} , and the operation of the output limit executed from the viewpoint of heat resistance protection is suppressed. In other words, the occurrence of a sudden change in the motor torque _Tm caused by the output limit is suppressed.

[DC voltage]
When using a function for varying the DC voltage _Vdc input from the battery side to the inverter 20 (a boost circuit such as a converter), it is also possible to employ control logic for limiting the DC voltage _Vdc so that the loss P is _equal to or less than the upper limit loss value Pmax in the loss limit section [t1, t2].

Specifically, for example, by applying the upper limit loss value _Pmax , the current current I, and the carrier frequency F set at the current control timing t1 to equation (3), the DC voltage _Vdc (hereinafter referred to as the "limit DC voltage _{Vdc_lim} ") is calculated on the assumption that the loss P at the response completion timing t2 matches the upper limit loss value _Pmax .

Then, the DC voltage _Vdc in the loss limit section [t1, t2] is maintained at the limited DC voltage _{Vdc_lim} . More specifically, the DC voltage _Vdc is basically adjusted to an appropriate value based on the overall efficiency of the inverter 20. Meanwhile, in this embodiment, the DC voltage _Vdc in the loss limit section [t1, t2] is fixed to the limited DC voltage _{Vdc_lim} at which the loss P is equal to or less than the upper limit loss value _Pmax , regardless of the overall efficiency.

As described above, by appropriately limiting the DC voltage _Vdc in the loss limit section [t1, t2], the element temperature _Tj is maintained at or below the upper limit temperature _{Tj_max} , and the operation of the output limit executed from the viewpoint of heat resistance protection is suppressed. In other words, the occurrence of a sudden change in the motor torque _Tm caused by the output limit is suppressed.

[Gate resistance value]
It is also possible to employ a control logic that limits the gate resistance value Rg of the semiconductor element so that the loss P of the semiconductor element is equal to or less than the upper limit loss value _Pmax in the loss limit section [t1, t2].

Specifically, for example, by referring to a map prepared in advance showing the relationship between the loss P and the gate resistance value Rg, a selectable gate resistance value Rg (hereinafter referred to as the "limit gate resistance value Rg _lim ") at which the loss P is equal to or less than the upper limit loss value P _max is determined.

Then, the gate resistance value Rg in the loss limit section [t1, t2] is maintained at the limit gate resistance value Rg _lim . More specifically, the gate resistance value Rg is basically adjusted to an appropriate value based on the overall efficiency of the inverter 20. On the other hand, in this embodiment, the gate resistance value Rg in the loss limit section [t1, t2] is fixed to the limit gate resistance value Rg _lim at which the loss P is equal to or less than the upper limit loss value P _max , regardless of the overall efficiency.

As described above, by appropriately limiting the gate resistance value Rg in the loss limit section [t1, t2], the element temperature _Tj is maintained at or below the upper limit temperature _{Tj_max} , and the operation of the output limit executed from the viewpoint of heat resistance protection is suppressed. In other words, the occurrence of a sudden change in the motor torque _Tm caused by the output limit is suppressed.

The following describes the control results when the above semiconductor element temperature control method is executed.

[Control results]
8 is a timing chart showing an example of a control result when the semiconductor element temperature control method according to the comparative example and the example (present embodiment) is applied. In particular, FIG. 8(a) shows the control result of the comparative example, and FIG. 8(b) shows the control result of the example. Note that, as the comparative example, a semiconductor element temperature control method is assumed in which the above-mentioned loss limiting process (S140) is not executed, and the basic cooling control (S150) is always executed. Also, in the example, in the above-mentioned loss limiting process, control is assumed in which the motor torque _Tm is limited by a limit torque _{Tm_lim} that is less than the upper limit motor torque _{Tm_max} .

In the control of the comparative example shown in Fig. 8A, after time t11 when the motor torque _Tm (torque command value T ^* _m ) increases and reaches the upper limit motor torque _{Tm_max} , the element temperature _Tj increases due to a delayed response of the actual coolant flow rate _{WF_R} to the switching of the flow rate command value W ^* _F . Then, from time t12 when the element temperature _Tj exceeds the upper limit temperature _{Tj_max} , output limitation for heat resistance protection begins to function, and continues until time t13 when the element temperature _Tj falls below the upper limit temperature _{Tj_max} by a certain amount or more. For this reason, a large torque step (circled area in Fig. 8A) occurs around this time t12 to time t13 (output limit section), giving a sense of discomfort to the occupants of the electric vehicle.

On the other hand, in the control of the embodiment shown in FIG. 8B, in the section (loss limit section) from time t21 to time t22 where the motor torque T _m (torque command value T ^* _m ) increases, the motor torque T _m sticks to the limit torque T _{m_lim} . Therefore, in the loss limit section, the element temperature T _j can be maintained at or below the upper limit temperature T _{j_max} , and output limitation for heat resistance protection is avoided. In particular, the torque step before and after the loss limit section is suppressed compared to the torque step in the output limit section of the comparative example. Therefore, the discomfort felt by the occupant of the electric vehicle can be reduced compared to the control of the comparative example. Furthermore, in this embodiment, by changing the motor torque _Tm at the time of entering the loss limit section (time t21) and at the time of completing the loss limit section (time t22) in a filter-like (smooth) manner (see solid line graph), the change in motor torque _Tm at the time of entering the loss limit section (time t21) and at the time of completing the loss limit section (time t22) can be made more gradual than when this is changed in a ramp-like manner (see dashed line graph), thereby further reducing the discomfort felt by the occupant of the electric vehicle.

The effects of the semiconductor element temperature control method of this embodiment described above are summarized below.

In this embodiment, a semiconductor element temperature control method is provided that controls the temperature of a semiconductor element of an inverter 20 that is arranged in a specified cooling system 40 and performs power conversion between a power source (battery 25) and an electric motor (motor 30).

In this semiconductor element temperature control method, a torque command value T ^* _m that specifies the torque (motor torque _Tm ) to be output by the motor 30 is calculated (S110), the refrigerant flow rate (cooling water flow rate _WF ) in the cooling system 40 is controlled based on the torque command value T ^* _m (S120), and a loss limiting process (S140) is executed to limit the operating parameter Σ of the inverter 20 based on the loss P of the semiconductor element.

In particular, in the loss limiting process, a flow rate response time Δtfr required for a response of the actual refrigerant flow rate (actual cooling water flow rate _{WF_R} ) when the torque command value T ^* _m changes to change the cooling water flow _{rate WF is} calculated (S141), an upper limit loss value _{Pmax which} is the loss P when the temperature of the semiconductor element (element temperature _Tj ) after the flow rate response time _Δtfr has elapsed (response completion timing t2) matches a predetermined upper limit temperature _{Tj_max} is calculated (S142), and an operating parameter Σ is determined so that the loss P until the flow rate response time _Δtfr has elapsed is equal to or less than the upper limit loss value _Pmax (S143).

As a result, in a scene where the coolant flow rate _WF is changed in response to a change in the torque command value T ^* _m (a scene where the coolant temperature _TW and the element temperature _Tj increase), the element temperature _Tj can _be maintained at or below the upper limit temperature _{Tj_max} even if a response delay occurs in the actual coolant flow rate _{WF_R} . That is, it is possible to more reliably prevent the element temperature _Tj of the inverter 20 arranged in the cooling system 40 from exceeding the upper limit temperature _{Tj_max} . Therefore, in this scene, the occurrence of a torque step due to the activation of the output limit for thermal protection of the semiconductor element is suppressed, and the discomfort felt by the vehicle occupants can be reduced.

In addition, in order to avoid such output restriction activation, the control value of the cooling water flow rate _WF (the output of the cooling water pump ⁴¹ ₎ can be reduced to suppress an increase in energy efficiency, compared to a case in which the cooling water flow rate _WF (flow rate command value W ^* _F ) is set high from the beginning relative to the requirement based on the torque command value T*m.

Furthermore, the operating parameter Σ includes the output torque of the motor (motor torque _Tm ). In the loss limiting process, an upper limit output torque (upper limit motor torque _{Tm_max} ) at which the loss P becomes the upper limit loss value _Pmax is calculated, and the motor torque _Tm during the period until the flow rate response time _Δtfr has elapsed (loss limit section) is adjusted to be equal to or lower than the upper limit motor torque _{Tm_max} (particularly the limit torque _{Tm_lim} ).

This realizes a more specific control logic for implementing restrictions on the motor _torque ^Tm , which is one of the operating parameters Σ, from the viewpoint of maintaining the element temperature _Tj below the upper limit temperature _{Tj_max} in a scene where the cooling water flow rate _WF is changed in response to a change in the torque command value T* _m .

In particular, by setting the limit torque _{Tm_lim} to a value relatively close to the upper limit motor torque _{Tm_max} , it is possible to more reliably reduce the torque step that occurs compared to when output limiting for thermal protection is activated, while still satisfying the condition that the element temperature _Tj does not exceed the upper limit temperature _{Tj_max} .

Furthermore, the operating parameter Σ includes a plurality of mutually switchable carrier frequencies F that are set in the inverter 20. Then, in the loss limiting process, one limit carrier frequency F _lim at which the loss P is equal to or smaller than the upper limit loss value P _max is selected, and the carrier frequency F is maintained at the limit carrier frequency F _lim until the flow rate response time Δt _fr has elapsed.

This realizes a specific control logic for implementing a restriction on the carrier frequency _F , which is one of the operating parameters _Σ , from the viewpoint of maintaining the element temperature _Tj at or below the upper limit temperature ^Tj_max in a scene where the cooling water flow rate _WF is changed in response to a change in the torque command value T*m. In particular, when the inverter 20 having a function of switching between a plurality of carrier frequencies F is employed, the operation of the output restriction for thermal protection can be suppressed.

Furthermore, the operating parameter Σ includes a variable DC voltage _Vdc input to the inverter 20. Then, in the loss limiting process, a limit DC voltage _{Vdc_lim} at which the loss P coincides with the upper limit loss value _Pmax is determined, and the DC voltage _Vdc is maintained at the limit DC voltage _{Vdc_lim} until the flow rate response time _Δtfr has elapsed.

This realizes a specific control logic for limiting the DC voltage ^Vdc , _which is one of the operating parameters Σ, from the viewpoint of maintaining the element temperature _Tj at or below the upper limit temperature _{Tj_max} in a scene where the cooling water flow rate _WF is changed in response to a change in the _torque command value T*m. In particular, when a configuration (a boost circuit such as a converter) that adjusts the DC voltage _Vdc input to the inverter 20 is adopted, it is possible to suppress the operation of output limiting for thermal protection.

Furthermore, the operation parameter Σ includes a plurality of mutually switchable gate resistance values Rg that are set in the inverter 20. Then, in the loss limiting process, one limit gate resistance value Rg _lim at which the loss P is equal to or less than the upper limit loss value P _max is selected, and the gate resistance value Rg is maintained at the limit gate resistance value Rg _lim until the flow rate response time Δt _fr has elapsed.

This realizes a specific control logic for limiting the gate resistance value ^Rg _{, which is one of the operating parameters Σ, from the viewpoint of maintaining the element temperature Tj at or below the upper limit temperature Tj_max in a scene where the cooling water flow rate WF is} changed in response to a change in the torque command value T*m. In particular, when a function for varying the gate resistance value Rg is adopted, it is possible to suppress the operation of output limiting for thermal protection.

Furthermore, in this embodiment, the flow command value W* _F is determined from the torque command value T ^* _m , the cooling water temperature T _W , and the motor rotation speed _Nm by referring to a flow command value map (FIG. 2) in which the cooling water flow rate WF is divided into stages in advance based on the torque command value T ^* _m , the refrigerant temperature (cooling water temperature T _W ) of the cooling system 40, and the motor rotation speed _Nm . Then, the cooling water flow _{rate WF is} controlled based on ^{the determined flow command value W* F} _.

As a result, a plurality of scenes in which the element temperature _Tj is different in level can be classified in stages in advance through the torque command value T ^* _m , the coolant temperature _TW , and the motor rotation speed _Nm , and the coolant flow rate _WF can be controlled based on the flow rate command value W ^* _F appropriately assigned to each scene. Therefore, rough control in which the coolant flow rate _WF (flow rate command value W ^* _F ) is actually changed less frequently in response to changes in the torque command value T ^* _m can be realized, and the effect of response delay of the coolant flow rate _WF can be reduced. Then, by executing the loss limiting process on the premise of such basic flow rate control, even when the torque command value T ^* _m changes and the flow rate command value W ^* _F is switched, the element temperature _Tj is prevented from exceeding the upper limit temperature _{Tj_max} , and the operation of output limiting for thermal protection is suppressed.

In this embodiment, the loss limiting process is executed when the cooling water temperature T _W is equal to or higher than a predetermined threshold temperature T _{W_th} or the torque command value T ^* _m is equal to or higher than the threshold torque T _{m_th} (if S130 is Yes). On the other hand, when the cooling water temperature T _W is lower than the threshold temperature T _{W_th} and the torque command value T ^* _m is lower than the threshold torque T _{m_th} (if S130 is No), the loss limiting process is not executed and the operating parameter Σ is maintained at the basic control value.

This realizes a specific control _logic for appropriately estimating a scene in which the element temperature _Tj may exceed the upper limit temperature _{Tj_max} due to a response delay of the actual cooling water flow rate _{WF_R} among scenes in which the flow command value W ^* _F specified in the flow command value map is switched, and for executing the loss limiting process only in the scene in question. In other words, the scenes in which the loss limiting process is executed during flow control can be limited to a necessary range, and the calculation load or the map capacity (memory area) used for calculation can be reduced.

Furthermore, in this embodiment, a controller 50 is provided that functions as a semiconductor element temperature control device suitable for executing the above-mentioned semiconductor element temperature control method. This semiconductor element temperature control device is arranged in a specified cooling system 40 and controls the temperature of the semiconductor element of the inverter 20 that performs power conversion between the power source (battery 25) and the electric motor (motor 30).

In particular, this semiconductor element temperature control device has a torque calculation unit (rotation speed/torque command unit 51) that calculates a torque command value T ^* _m that specifies the torque to be output by the motor 30 (motor torque _Tm ), a flow rate control unit 52 that controls the refrigerant flow rate (cooling water flow rate _WF ) in the cooling system 40 based on the torque command value T ^* _m , and a loss limiting unit 53 that limits the operating parameter Σ of the inverter 20 based on the loss P of the semiconductor element.

Then, the loss limiting unit 53 calculates a flow rate response time Δtfr required for a response of the actual refrigerant flow rate (actual cooling water flow rate W _{F — R )} when the torque command value T ^* _m changes to change the cooling water flow rate _WF (S141), calculates an upper limit loss value P max which is the loss P when the temperature of the semiconductor element (element temperature T _j ) after the flow rate response time _Δtfr has elapsed (response completion timing t2) matches a predetermined upper limit temperature T _{j_max} (S142), and determines an operating parameter _Σ so that the loss P until the flow rate response time _Δtfr has elapsed is equal to or less than the upper limit loss value P _max (S143).

Although the embodiments of the present invention have been described above, the above embodiments merely show some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined in any manner possible.

For example, in order to simplify the control logic, the judgment in step S130 in FIG. 2 may be omitted, and the loss limiting process (S140) may be executed during flow control (S120) regardless of the current coolant temperature T _{W_c} or the torque command value T ^* _m .

In the above embodiment, the detection value of the element temperature sensor 63 is used as the current element temperature T _{j_c} . However, instead of this, a configuration may be adopted in which the current element temperature T _{j_c} is estimated based on appropriate parameters that can be obtained in the vehicle system 10.

10 Vehicle system 20 Inverter 21 Power module (semiconductor element)
22 Cooler 25 Battery 30 Motor 40 Cooling system 41 Cooling water pump 42 Radiator 50 Controller 51 Rotation speed/torque command unit 52 Flow rate control unit
53 Loss Limitation Section

Claims (8)

A semiconductor element temperature control method for controlling the temperature of a semiconductor element of an inverter arranged in a predetermined cooling system and performing power conversion between a power source and an electric motor, comprising:
Calculating a torque command value that defines a torque to be output by the electric motor;
a flow rate of a refrigerant in the cooling system is controlled based on the torque command value;
performing a loss limiting process for limiting an operating parameter of the inverter based on a loss of the semiconductor element;
In the loss limitation process,
calculating a flow rate response time required for an actual refrigerant flow rate to respond when the torque command value changes to change the refrigerant flow rate;
calculating an upper limit loss value which is the loss when the temperature of the semiconductor element coincides with a predetermined upper limit temperature when the flow rate response time has elapsed;
determining the operating parameters so that the loss during the flow rate response time elapses is equal to or less than the upper limit loss value;
A method for controlling the temperature of semiconductor devices. 2. A semiconductor device temperature control method according to claim 1, comprising:
the operating parameters include an output torque of the electric motor;
In the loss limitation process,
Calculating an upper limit output torque at which the loss becomes the upper limit loss value;
adjusting the output torque to be equal to or lower than the upper limit output torque until the flow rate response time has elapsed;
A method for controlling the temperature of semiconductor devices. 2. A semiconductor device temperature control method according to claim 1, comprising:
The operating parameters include a plurality of carrier frequencies that are set in the inverter and that are mutually switchable;
In the loss limitation process,
Selecting one limited carrier frequency at which the loss is equal to or less than the upper limit loss value;
maintaining the carrier frequency at the limited carrier frequency until the flow rate response time has elapsed;
A method for controlling the temperature of semiconductor devices. 2. A semiconductor device temperature control method according to claim 1, comprising:
the operating parameters include a variable DC voltage input to the inverter;
In the loss limitation process,
determining a limiting DC voltage at which the loss coincides with the upper limit loss value;
maintaining the DC voltage at the limited DC voltage until the flow rate response time has elapsed;
A method for controlling the temperature of semiconductor devices. 2. A semiconductor device temperature control method according to claim 1, comprising:
the operating parameters include a plurality of mutually switchable gate resistance values set for the inverter;
In the loss limitation process,
selecting a limit gate resistance value at which the loss is equal to or less than the upper loss limit value;
maintaining the gate resistance value at the limited gate resistance value until the flow rate response time has elapsed;
A method for controlling the temperature of semiconductor devices. A semiconductor device temperature control method according to any one of claims 1 to 5,
determining a flow command value from the torque command value, the refrigerant temperature, and the motor rotation speed by referring to a flow command value map in which the refrigerant flow rate is divided into stages in advance based on the torque command value, the refrigerant temperature of the cooling system, and the motor rotation speed;
controlling the refrigerant flow rate based on the determined flow rate command value;
A method for controlling the temperature of semiconductor devices. 7. A semiconductor device temperature control method according to claim 6, comprising:
When the refrigerant temperature is equal to or higher than a predetermined threshold temperature or when the torque command value is equal to or higher than a threshold torque, the loss limiting process is executed;
if the coolant temperature is less than the threshold temperature and the torque command value is less than the threshold torque, maintaining the operating parameters at basic control values without performing the loss limiting process;
A method for controlling the temperature of semiconductor devices. A semiconductor element temperature control device that controls the temperature of a semiconductor element of an inverter that is arranged in a predetermined cooling system and performs power conversion between a power source and an electric motor,
a torque calculation unit that calculates a torque command value that defines a torque to be output by the electric motor;
a flow rate control unit that controls a refrigerant flow rate in the cooling system based on the torque command value;
a loss limiting unit that limits an operating parameter of the inverter based on a loss of the semiconductor element,
The loss limiting unit is
calculating a flow rate response time required for an actual refrigerant flow rate to respond when the torque command value changes to change the refrigerant flow rate;
calculating an upper limit loss value which is the loss when the temperature of the semiconductor element coincides with a predetermined upper limit temperature when the flow rate response time has elapsed;
determining the operating parameters so that the loss during the flow rate response time elapses is equal to or less than the upper limit loss value;
Semiconductor element temperature control device.

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