Protection device for vehicle inverters

Abstract

A vehicle inverter protection device for protecting an inverter (101) driving a motor (129) provided in a vehicle as a power source (128) from overheating, comprising: a maximum element temperature calculation unit (403) which calculates a maximum element temperature (T jmax ) of corresponding element temperatures (Tj 1...6 ) of the inverter (101) is calculated, an element temperature output limit coefficient calculation unit (404) which - an output limit (K a ) corresponding to the maximum element temperature (T jmax ) calculated, - a current output limit (K a ) as a current output limit coefficient (k2(i)) when the current output limit value (K a ) is smaller than a previous output limit coefficient (k2(i-1)), and - if the current output limit (K a) is equal to or exceeds the previous output limit coefficient (k2(i-1)), ◯ as the current output limit coefficient (k2(i)) the current output limit value (K a ) when the current output limit (K a ) is equal to the value 1, and ◯ sets a value which is determined by adding a previously determined, predetermined value (K b ) to the previous output limit coefficient (k2(i-1)), where the value is capped at 1, a base torque limit calculation unit (406) which calculates a base torque limit (Tm LMT_b ) is calculated from a map based on an engine speed (ωm) of the engine (129), and a torque limit value determining unit (407) which determines a torque limit value (Tm LMT ) by multiplying the base torque limit (Tm LMT_b ) with the element temperature output limit coefficient (k2).

Description

Technical area

[0001] This invention relates to a protective device for a vehicle inverter. background

[0002] A control device for an electric vehicle including a temperature detecting means for detecting temperatures of individual power devices and outputting corresponding temperature values ​​thereof, and a gate control circuit having a protection function for limiting a current of an inverter based on the highest device temperature among the temperature values ​​output by the temperature detecting means, has been proposed as a conventional device for protecting an inverter element from overheating (see, for example, JP 2001-169401 A).

[0003] Further, in a proposed overheat protection method, switching characteristics of a switching element provided in an inverter, such as a normal on-loss, a switching loss, and a transient thermal impedance, are stored together with a switching element loss calculation formula in a storage device serving as a memory of a control unit, whereupon a CPU of the control unit derives a loss of the switching element from the calculation formula, the normal on-loss, the switching loss, etc., stored in the memory, which are inserted into the calculation formula, using, as variables, an output current approximating a square wave, a control factor, and an output frequency detected in the inverter.The CPU then calculates an element junction temperature using the derived loss and the transient thermal impedance of the memory and implements an output current control of the inverter so that the element junction temperature does not exceed a set temperature (see, for example, JP H09-233832 A).

[0004] JP H11-252 932 A discloses a protective device for the switching elements of an inverter. This device takes into account the fact that temperature sensors are located away from the switching elements to reduce interference. To limit the current, characteristic curves are used whose limit temperatures are shifted to higher temperatures depending on the current delivered by the inverter compared to a characteristic curve used for a temperature sensor located in close proximity to the respective switching element.

[0005] DE 10 2008 046 245 A1 discloses a method for limiting the operating temperature of a motor, in which a maximum permissible current for an electric motor is determined based on a temperature difference between a temperature reference of an inverter module and a temperature T of a semiconductor of the inverter module. The method further determines, via a multidimensional characteristic field based on the maximum permissible current and a maximum permissible flux, a maximum permissible torque. This torque is used to limit a torque command to push the temperature T of the inverter semiconductors below the temperature reference. Summary of the inventionTechnical problem

[0006] However, the following problem occurs in the prior art.

[0007] When an (electric) motor rotates at an extremely low speed while generating a large amount of torque, a large amount of current flows through a specific element for a long period of time. Because the element is switched on and off in synchronization with the motor's rotation, the element temperature becomes oscillatory, varying by a large amount. Therefore, if a torque limit is applied based on the element temperature, the torque variation may increase, leading to a reduction in drivability.

[0008] Here, the inventions described in JP 2001-169401 A and JP H09-233832 A both apply a torque limit according to the element temperature, and therefore, a reduction in drivability occurs when the motor rotates at an extremely low speed while generating a large amount of torque.

[0009] This invention has been designed to solve the above problem, and an object thereof is to provide a protective device for a vehicle inverter capable of protecting an inverter element from overheating while preventing a reduction in drivability. [Problem solving]

[0010] This object is achieved by a protective device for a vehicle inverter having the features according to patent claim 1. Advantageous embodiments emerge from the dependent claims. [Advantageous invention effects]

[0011] In the protective device for a vehicle inverter according to this invention, the inverter element can be protected from overheating by rapidly applying a torque limit according to the maximum element temperature when the maximum element temperature increases, and a reduction in drivability can be prevented even when the maximum element temperature varies in an oscillatory manner to temporarily decrease by gradually removing the torque limit so as to suppress variation in the torque limit. [Brief description of the drawings] [ Fig. 1] Fig. 1 is a view showing an overall configuration of a system including a protective device for a vehicle inverter according to a first embodiment of this invention. [ Fig. 2] Fig. 2 is a view showing an example configuration of a packing structure of a Fig. 1 shows the IGBT chips. [ Fig. 3] Fig. 3 is a block diagram showing a configuration of a motor control unit of the protective device for a vehicle inverter according to the first embodiment of this invention. [ Fig. 4] Fig. 4 is a block diagram showing in detail a configuration of a Fig. 3 shows the torque limit calculation unit. [ Fig. 5] Fig. 5 is a flowchart showing the processing performed by a low-pass filter calculation unit and a first output limit coefficient calculation unit shown in Fig. 4, shows the processing performed. [ Fig. 6] Fig. 6 is a flowchart showing the calculations performed by a maximum element temperature calculation unit and a second output limit coefficient calculation unit provided in Fig. 4, shows the processing performed. [ Fig. 7] Fig. Figure 7 is an illustrative view showing an output limit value K a the protective device for a vehicle inverter according to the first embodiment of this invention. [ Fig. 8] Fig. 8 is a flowchart showing a method for calculating the torque using a minimum value selection unit, a torque limit map and a multiplication unit shown in Fig. 4, shows the processing performed. [ Fig. 9] Fig. 9 is an illustrative view showing torque limit control executed by the protective device for a vehicle inverter according to the first embodiment of this invention in a case where a motor rotates at an extremely low speed. [ Fig. 10] Fig. 10 is an illustrative view showing torque restriction control executed by the protective device for a vehicle inverter according to the first embodiment of this invention in a case where the inverter is not driven. [Description of embodiments]

[0012] A preferred embodiment of a protective device for a vehicle inverter according to this invention is described below using the drawings. Identical or corresponding parts of the drawings are described using identical reference numerals. First embodiment

[0013] Fig. 1 is a view showing an overall configuration of a system including a protective device for a vehicle inverter according to a first embodiment of this invention. Fig. 1, an inverter 101 is configured to drive a three-phase AC motor 129 by controlling on / off IGBTs (Insulated Gate Bipolar Transistors) 102 to 107 serving as a switching element to convert a direct current from a battery 128 into a three-phase alternating current.

[0014] Diodes 108 to 113 are mounted on chips of IGBTs 102 to 107 as element temperature sensors, and the temperatures of the chips are detected by an element temperature detection circuit 121, utilizing the fact that the forward voltages of the diodes exhibit a negative temperature characteristic. Regenerative diodes 114 to 119, which are used to regenerate current, are also connected to IGBTs 102 to 107.

[0015] Note that, to prevent the drawing from becoming overly complicated, only diode 109 is shown connected to element temperature detection circuit 121, and the connections of the other diodes are omitted. However, all diodes are connected to element temperature detection circuit 121.

[0016] Furthermore, the IGBTs 102 to 107 are driven by a control device 122 via drive circuits 120. The control device 122 is provided with a microcomputer 123 that performs calculations related to the control of the motor and issues instructions for switching the IGBTs 102 to 107 on and off, and a water temperature detection circuit 125 that detects a temperature of cooling water in the inverter 101 using a thermistor 126. It should be noted that in Fig. 1 only the drive circuit relating to the IGBT 103 is shown.

[0017] Fig. 2 is a view showing an example configuration of a packaging structure of the Fig. 1 shown IGBT chips. In Fig. 2, an IGBT chip 201, solder 202, copper foil 203, an insulation substrate 204, a heat sink 205, grease 206 and a water cooling jacket 207 are laminated in descending order.

[0018] By passing cooling water 208 through a passage provided in the water jacket 207 as a coolant, heat generated in the IGBT chip 201 is dissipated by the cooling water 208. Furthermore, the thermistor 209 serving as a water temperature sensor is embedded in the water jacket 207.

[0019] Fig. 3 is a block diagram showing a configuration of a motor control unit of the protective device for a vehicle inverter according to the first embodiment of this invention. The motor control unit is shown in Fig. 1 shown microcomputer 123.

[0020] First, when a large amount of motor torque is generated and the engine speed is extremely low, an increase in the element temperature is not reflected in the water temperature. Therefore, it is necessary to directly detect the element temperature to suppress the motor torque and thereby protect the inverter element from overheating. Furthermore, in current hybrid vehicles, the same cooling water tends to be used as both the inverter cooling water and the engine cooling water, and as a result, the cooling water temperature may rise even when the inverter is not driven. Therefore, it is necessary to detect the cooling water temperature to suppress the motor torque and thereby protect the inverter element from overheating.

[0021] However, if torque limits are applied simultaneously according to the cooling water temperature and the element temperature, output may be excessively suppressed, resulting in a reduction in drivability. Therefore, in the first embodiment of this invention, torque limitation is appropriately implemented by applying processing for applying a torque limit based on the smaller of a coefficient calculated based on the water temperature and a coefficient calculated based on the element temperature.

[0022] In Fig. 3, the motor control unit includes a torque correction calculation unit 301, a torque limit calculation unit 302, a minimum value selection unit 303, a current control calculation unit 304, and an IGBT drive calculation unit 305.

[0023] The torque correction calculation unit 301 receives a torque command from an external vehicle controller (not shown) via, for example, a CAN (Controller Area Network) not shown, calculates various torque corrections according to the torque command, and outputs the calculated torque correction as a corrected torque.

[0024] The torque limit calculation unit 302 calculates a torque limit value based on, for example, the water temperature of the cooling water detected by the water temperature detection circuit 125, the element temperature detected by the element temperature detection circuit 121, and an engine speed calculated from a signal output by a sensor (not shown) provided in the engine 129.

[0025] The minimum value selecting unit 303 applies a speed limit by comparing the corrected torque output by the torque correction calculating unit 301 with a torque limit value output by the torque limit calculating unit 302, and selecting the smaller value thereof as a target torque.

[0026] The current control arithmetic unit 304 feedback-controls a motor current and outputs a target voltage to achieve the target torque output by the minimum value selection unit 303. The IGBT drive arithmetic unit 305 drives the IGBT to achieve the target voltage output by the current control arithmetic unit 304.

[0027] Note that when the torque limit calculation unit 302 is not provided, the corrected torque calculated by the torque correction calculation unit 301 is output as it is to the current control calculation unit 304 as the target torque, whereupon the target voltage is set based on the target torque.

[0028] Fig. 4 is a block diagram showing in detail a configuration of the Fig. 3 shows the torque limit calculation unit 302. In Fig. 4, the torque limit calculation unit 302 includes a low-pass filter calculation unit 401, a first output limit coefficient calculation unit (a water temperature output limit coefficient calculation unit) 402, a maximum element temperature calculation unit 403, a second output limit coefficient calculation unit (an element temperature output limit coefficient calculation unit) 404, a minimum value selection unit (a limit coefficient selection unit) 405, a torque limit map (a basic torque limit calculation unit) 406, and a multiplication unit (a torque limit determination unit) 407.

[0029] The low-pass filter arithmetic unit 401 implements filter processing at a water temperature T w of the cooling water, which is detected by the water temperature detection circuit 125, and outputs a filtered water temperature T wfThe first output limit coefficient calculation unit 402 calculates a first output limit coefficient k1 based on a value obtained by subtracting the filtered water temperature T wf , which is output by the low-pass filter arithmetic unit 401, from a pre-stored upper boundary element temperature T* jLMT is determined.

[0030] The maximum element temperature calculation unit 403 calculates a maximum element temperature T jmax from corresponding element temperatures T j1 are j6 and gives the maximum element temperature T jmax The second output limit coefficient calculation unit 404 calculates a second output limit coefficient k2 based on the maximum element temperature T jmax which is output by the maximum element temperature calculation unit 403.

[0031] The minimum value selecting unit 405 compares the first output limit coefficient k1 output by the first output limit coefficient calculating unit 402 with the second output limit coefficient k2 output by the second output limit coefficient calculating unit 404 and outputs the smaller value thereof as an output limit coefficient k.

[0032] The torque limit map 406 is a map that stores an upper limit torque in a normal temperature range, and by referring to the map on the basis of an engine speed ωm, a basic torque limit value Tm is calculated. LMT_b read from the torque limit map. The multiplication unit 407 multiplies the base torque limit value by the output limit coefficient k and outputs a torque limit value Tm LMT out of.

[0033] Fig. Fig. 5 is a flowchart showing the processings executed by the low-pass filter calculation unit 401 and the first output limit coefficient calculation unit 402 shown in Fig. 4 are shown.

[0034] In Fig. 5, the water temperature T w read out (step S501). Next, a low-pass filter processing is performed on the read water temperature T w executed (step S502).

[0035] Next, the first output limit coefficient k1 is calculated (step S503).

[0036] Here, if the thermal resistance from the element temperature to the water temperature is R [°C / W], the upper limit element temperature T* jLMT [°C] and a design water temperature (a temperature at which the application of the limitation has to start) T* w0 [°C], an allowable element heat generation quantity Q LMT[W] at the upper boundary element temperature is expressed by the following equation. QLMT=(T*jLMT−T*w0) / R

[0037] Meanwhile, an allowable element heat generation quantity Q' LMT in a case where the water temperature T wf which is higher than the T* w0 is expressed by the following equation. QLMT=(T*jLMT−T*wf) / R

[0038] Accordingly, the first output coefficient k1 at the water temperature T wf expressed by the following equation. k1=Q'LMT / QLMT=(T*jLMT−Twf) / (T*jLMT−T*w0)

[0039] Next, upper / lower limit clipping is performed on the first output limit coefficient k1 at the lower limit = 0.0, the upper limit = 1.0 (step S504), after which the processing of Fig. 5 is terminated.

[0040] Fig. 6 is a flowchart showing a process executed by the maximum element temperature calculation unit 403 and the second output coefficient calculation unit 404 shown in Fig. 4, shows the processing performed.

[0041] In Fig. 6, the respective element temperatures T j1 are j6 read in (step S601).

[0042] Next, the maximum element temperature T jmax calculated (step S602).

[0043] Next, as in Fig. 7, an output limit value K a from the characteristic map based on the maximum element temperature T jmax read out (step S603).

[0044] Next, the output limit K a compared with a previous value k2 (i-1) of the second output coefficient (step S604) and when the output limit value K ais smaller, or in other words, if the output limit is large, the correction amount K a as a current value k2 (i) of the second output coefficient (step S605).

[0045] If the output limit K a on the other hand, a determination is first made as to whether the output limit K a 1 or not (step S606). If the maximum element temperature has decreased sufficiently so that the output limit value K a is already 1, the current value k2 (i) of the second output limit coefficient is also set to 1, whereupon the output limit is canceled (step S607).

[0046] If the maximum element temperature has not decreased to such an extent that the output limit K a is not yet 1, the current value k2 (i-1) of the second output limit coefficient is set by a predetermined value K bis added to the previous value of the second output limit coefficient k2. Note, however, that the second output limit coefficient is capped at 1 (step S608).

[0047] Finally, the previous value of the second output limit coefficient k2 is updated (step S607), after which the processing of Fig. 6 is terminated.

[0048] Fig. 8 is a flowchart illustrating the processing performed using the minimum value selection unit 405, the torque limit map 406 and the multiplication unit 407 shown in Fig. 4, shows the processing performed.

[0049] In Fig. 8, first, the first output coefficient k1 from the first output limit coefficient calculation unit 402 is compared with the second output limit coefficient k2 from the second output limit coefficient calculation unit 404, and the smaller value thereof is output as the output limit coefficient k (step S701).

[0050] Next, the base torque limit Tm LMT_b calculated from the torque limit map based on the engine speed (step S702).

[0051] Next, the torque limit Tm LMT calculated by multiplying the base torque limit value by the output limit coefficient k (step S703), after which the processing of Fig. 8 is terminated.

[0052] Fig. 9 is an illustrative view showing torque limit control executed by the protective device for a vehicle inverter according to the first embodiment of this invention in a case where the motor rotates at an extremely low speed.

[0053] In Fig. 9. When the motor rotates at an extremely low speed, the current flowing through each individual IGBT is long, and therefore the element temperature of the respective IGBTs varies greatly. Specifically, the IGBT energized synchronously with the rotation of the motor varies such that the element temperature of the energized IGBT rises, while the element temperatures of the non-energized IGBTs decrease. As a result, the element temperature varies vertically. This variation is particularly pronounced in regions where the motor speed is low.

[0054] Meanwhile, water temperature behavior occurs with a delay relative to the element temperature behavior. The causes of this delay are the thermal resistance from the element to the cooling water and the mounting position of the water temperature sensor.

[0055] Here, when the water temperature behavior is taken into account, a temperature gradient remains at the element temperature in the range at which current begins to flow through the elements, and therefore variation occurs in the behavior of the six element temperatures. In this example, an element indicated by a dashed line has the highest temperature, and therefore output limiting must be applied to protect the element indicated by the dashed line from overheating.

[0056] Therefore, in the first embodiment, when the element temperature reaches or exceeds 130 degrees Celsius, for example, the output restriction begins to have such an effect that the torque limit (indicated by a dotted line) decreases, thereby limiting the actual torque (indicated by a solid line). Note that the torque limit continues to decrease over a period in which the element temperature increases.

[0057] When the output is limited so that the element's heat generation decreases and the element temperature begins to drop, the torque limit is reduced in increments of a predetermined value without being affected by the variation in element temperature. This can suppress torque variation and, as a result, prevent a reduction in drivability.

[0058] Fig. 10 is an illustrative view showing torque limit control executed by the protective device for a vehicle inverter according to the first embodiment of this invention in a case where the inverter is not driven.

[0059] As described above, there is a tendency in hybrid vehicles to use a common system as an engine cooling system and electric motor / inverter cooling system with the aim of reducing costs.

[0060] Fig. Figure 10 shows an example of behavior that occurs when the engine operating output is small but the engine operating output is large. In this case, the element temperature varies only slightly, while the water temperature continuously increases in response to increases in the engine temperature.

[0061] Here, in the first embodiment, the output limitation begins to have an effect when the water temperature exceeds, for example, 60 degrees, with the result that the torque limit decreases gently.

[0062] According to the first embodiment, it is possible to obtain the above-described protective device for a vehicle inverter, which can protect the inverter element from overheating by making the element temperature output limit coefficient calculation unit quickly apply a torque limit according to the maximum element temperature when the maximum element temperature increases, and which can prevent a reduction in drivability even when the maximum element temperature varies in an oscillatory manner to temporarily decrease by gradually canceling the torque limit so that the variation in the torque limit is suppressed.

[0063] Furthermore, the protection device for a vehicle inverter also includes the water temperature output limit coefficient calculation unit, which calculates the water temperature output limit coefficient based on the water temperature of the cooling water in the inverter, and the limit coefficient selection unit, which selects and outputs the smaller output limit coefficient of the element temperature output limit coefficient and the water temperature output limit coefficient. The torque limit determination unit determines the torque limit by multiplying the base torque limit by the element temperature output limit coefficient or the water temperature output limit coefficient selected by the limit coefficient selection unit. Therefore, the element is doubly protected against overheating according to both the water temperature and the element temperature, and is therefore more reliably protected.In addition, to ensure that the element is not overprotected, either the element temperature output limit coefficient or the water temperature output limit coefficient is selected and as a result, the output performance of the element can be maintained at an appropriate level.

[0064] In addition, the water temperature output limit coefficient calculation unit calculates the water temperature output limit coefficient based on a ratio between the value obtained by subtracting the water temperature of the cooling water from the predetermined upper limit element temperature and the value obtained by subtracting the design water temperature at which the application of the torque restriction is to start from the upper limit element temperature.

[0065] As a result, the element can be adequately protected from overheating based on the water temperature.

Claims

[1] A vehicle inverter protection device for protecting an inverter (101) driving a motor (129) provided in a vehicle as a power source (128) from overheating, comprising: a maximum element temperature calculation unit (403) which calculates a maximum element temperature (T jmax ) of corresponding element temperatures (Tj 1...6 ) of the inverter (101) is calculated, an element temperature output limit coefficient calculation unit (404) which - an output limit (K a ) corresponding to the maximum element temperature (T jmax ) calculated, - a current output limit (K a ) as a current output limit coefficient (k2(i)) when the current output limit value (K a ) is smaller than a previous output limit coefficient (k2(i-1)), and - if the current output limit (K a) is equal to or exceeds the previous output limit coefficient (k2(i-1)), ◯ as the current output limit coefficient (k2(i)) the current output limit value (K a ) when the current output limit (K a ) is equal to the value 1, and ◯ sets a value which is determined by adding a previously determined, predetermined value (K b ) to the previous output limit coefficient (k2(i-1)), where the value is capped at 1, a base torque limit calculation unit (406) which calculates a base torque limit (Tm LMT_b ) is calculated from a map based on an engine speed (ωm) of the engine (129), and a torque limit value determining unit (407) which determines a torque limit value (Tm LMT ) by multiplying the base torque limit (Tm LMT_b ) with the element temperature output limit coefficient (k2). [2] A protective device for a vehicle inverter according to claim 1, further comprising: a water temperature output limit coefficient calculation unit (402) that calculates a water temperature output limit coefficient based on a water temperature of cooling water in the inverter; and a limit coefficient selection unit (405) that selects and outputs a smaller output limit coefficient of the element temperature output limit coefficient and the water temperature output limit coefficient, wherein the torque limit determining unit determines the torque limit by multiplying the base torque limit by the element temperature output limit coefficient or the water temperature output limit coefficient as selected by the limit coefficient selecting unit. [3] The protective device for a vehicle inverter according to claim 2, wherein the water temperature output limit coefficient calculation unit calculates the water temperature output limit coefficient based on a relationship between a value obtained by subtracting the water temperature of the cooling water from a predetermined upper limit element temperature and a value obtained by subtracting a design water temperature, which is a water temperature at which application of the torque restriction is to start, from the upper limit element temperature.

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