Power conversion device and power conversion method

Abstract

According to the present invention, when the measured temperature of a switching element on one arm side, which is measured by a temperature sensor, is higher than an estimated temperature based on a temperature increase amount estimated by a first temperature estimation unit, a second temperature estimation unit estimates a predicted temperature of the other switching element on the other arm side by correcting the temperature rise amount of the switching element on the other arm side, which is estimated by the first temperature estimation unit on the basis of the ratio obtained by dividing the difference between the measured temperature and the refrigerant temperature by the temperature increase amount.

Description

Power conversion device and power conversion method

[0001] The present invention relates to a power conversion device and a power conversion method, and is suitable for application to a power conversion device relating to a technique for measuring the temperatures of U-phase, V-phase, and W-phase switching elements, for example.

[0002] In recent years, some power conversion devices installed in vehicles have adopted a configuration in which a temperature sensor is provided on only one of the multiple switching elements of each phase. In such conventional power conversion devices, the temperature of one switching element is estimated based on the temperature measured by the temperature sensor provided on the other switching element, taking into account the heat transfer impedance. The heat transfer impedance is based on the assumption that the cooling system of the switching elements is normal, and varies depending on the refrigerant flow rate, whether the cooling system is air-cooled or water-cooled.

[0003] JP 2011-097812 A

[0004] However, with the technology described in Patent Document 1, the temperature of the switching elements can differ significantly from normal, especially when water runs out in a water-cooled cooling system. In other words, when the cooling system is malfunctioning, the actual temperature of the switching elements tends to be higher in the vertical direction than normal, because the cooling system is not operating normally. However, the calculated value of the temperature of one switching element (hereinafter also referred to as the "estimated temperature") estimated from the temperature of the other switching element of one arm is based on the assumption that the cooling system remains normal, resulting in a discrepancy between the actual temperature of the other switching element and the estimated temperature.

[0005] The present invention has been made in consideration of the above points, and aims to propose a power conversion device and a power conversion method that can accurately estimate the predicted temperature of one switching element based on the temperature measured by a temperature sensor provided in the other switching element, even if an abnormality occurs in the cooling system of the switching element.

[0006] In order to solve this problem, the present invention provides a power conversion device that includes a coolant temperature acquisition unit that acquires the temperature of a coolant that cools a plurality of switching elements that respectively correspond to an upper arm and a lower arm of each phase of the power conversion device; a temperature sensor that measures the temperature of a switching element on one arm side of the plurality of switching elements; a first temperature estimator that estimates an estimated temperature based on an amount of temperature rise of each switching element when the switching element operates based on its drive conditions; and a second temperature estimator that, when the measured temperature measured by the temperature sensor for the switching element on the one arm side is higher than the estimated temperature based on the amount of temperature rise estimated by the first temperature estimator, estimates a predicted temperature of the other switching element on the other arm side by correcting the amount of temperature rise estimated by the first temperature estimator for the switching element on the other arm side based on a ratio obtained by dividing the difference between the measured temperature and the coolant temperature by the amount of temperature rise.

[0007] Furthermore, in the present invention, the power conversion device includes a coolant temperature acquisition step in which a coolant temperature acquisition unit acquires the temperature of a coolant that cools a plurality of switching elements corresponding to each upper arm and a lower arm of each phase of the power conversion device; a switching element temperature measurement step in which a temperature sensor measures the temperature of a switching element on one arm side of the plurality of switching elements; a first temperature estimation step in which a first temperature estimator estimates an estimated temperature based on an amount of temperature rise of each switching element when the switching element operates based on a drive condition of the switching element; and a second temperature estimation step in which, when a measured temperature measured by the temperature sensor for the switching element on the one arm side is higher than an estimated temperature based on the amount of temperature rise estimated by the first temperature estimator, a second temperature estimator estimates a predicted temperature of the other switching element on the other arm side by correcting the amount of temperature rise estimated by the first temperature estimator for the switching element on the other arm side based on a ratio obtained by dividing the difference between the measured temperature and the temperature of the coolant by the amount of temperature rise.

[0008] According to the present invention, even if an abnormality occurs in the cooling system of one of the switching elements, the predicted temperature of the other switching element can be accurately estimated based on the temperature measured by the temperature sensor provided in the other switching element.

[0009] 1 is a block diagram showing an example of the configuration of a power conversion device according to the present embodiment; FIG. 2 is a diagram showing an example of current versus temperature rise characteristics for a switching element in the present embodiment; FIG. 3 is a diagram showing an example of a path of current flowing through a switching element; FIG. 4 is a diagram showing an example of temperature change in a switching element; FIG. 5 is a diagram showing an example of temperature change in a switching element; FIG. 6 is a diagram showing an example of temperature change in each switching element of a three-phase upper arm and lower arm; FIG. 7 is a diagram showing an example of the relationship between the current phase and the current of the switching element of each phase; FIG. 8 is a diagram showing an example of current versus temperature rise characteristics when the temperatures of each switching element are different at low frequency; FIG. 9 is a diagram showing an example of temperature change in the switching element of the lower arm at low frequency;

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] Fig. 1 is a block diagram showing an example of the configuration of a power conversion device according to this embodiment. Fig. 2 is a diagram showing an example of the current vs. temperature rise characteristics of a switching element in this embodiment. The power conversion device according to this embodiment is applied to an electric vehicle, for example.

[0012] As shown in FIG. 1 , the power conversion device according to this embodiment includes a DC voltage source 1, a smoothing capacitor 2, a DC voltage sensor 3, a U-phase upper arm switching element Sup, a U-phase upper arm free wheel diode Dup, a U-phase lower arm switching element Sun, a U-phase lower arm free wheel diode Dun, a U-phase temperature sensor Tu, a V-phase upper arm switching element Svp, a V-phase upper arm free wheel diode Dvp, a V-phase lower arm switching element Svn, a V-phase lower arm free wheel diode Dvn, a V-phase temperature sensor Tv, a W-phase upper arm switching element Swp, a W-phase upper arm free wheel diode Dwp, a W-phase lower arm switching element Swn, a W-phase lower arm free wheel diode Dwn, a W-phase temperature sensor Tw, an AC current sensor 4, a motor 5, an angle sensor 6, a control device 7, a gate drive circuit 8, a refrigerant temperature sensor 24, a temperature detection circuit 9, a motor control unit 10, a first temperature estimator 11, a second temperature estimator 12, and a current control unit 13.

[0013] The control device 7 receives a torque command value 14 for the motor 5 from an ECU (Electronic Control Unit) (not shown) or the like for controlling the above-mentioned electric vehicle.

[0014] The DC voltage source 1 is a power supply that supplies a DC voltage to upper arm switching elements Sup, Svp, and Swp of each phase and lower arm switching elements Sun, Svn, and Swn of each phase in the motor 5. The smoothing capacitor 2 is connected in parallel to the DC voltage source 1.

[0015] A DC voltage sensor 3 is connected in parallel to this smoothing capacitor 2, and this DC voltage sensor 3 outputs a DC voltage detection value 15 indicating the measured value of the DC voltage of the DC voltage source 1 to the motor control unit 10.

[0016] In the upper arm, a free wheeling diode Dup is connected in parallel to the collector and emitter of switching element Sup, a free wheeling diode Dvp is connected in parallel to the collector and emitter of switching element Svp, and a free wheeling diode Dwp is connected in parallel to the collector and emitter of switching element Swp. Meanwhile, in the lower arm, a free wheeling diode Dun is connected in parallel to the collector and emitter of switching element Sun, a free wheeling diode Dvn is connected in parallel to the collector and emitter of switching element Svn, and a free wheeling diode Dwn is connected in parallel to the collector and emitter of switching element Swn.

[0017] A gate drive circuit 8 is connected to each gate of the upper-arm switching elements Sup, Svp, Swp and the lower-arm switching elements Sun, Svn, Swn. The gate drive circuit 8 controls the upper-arm switching elements Sup, Svp, Swp and the lower-arm switching elements Sun, Svn, Swn, and applies AC voltages to the motor 5 from a U-phase output wiring connected to the emitter of the upper-arm switching element Sup (and the collector of the lower-arm switching element Sun), a V-phase output wiring connected to the emitter of the upper-arm switching element Svp (and the collector of the lower-arm switching element Svn), and a W-phase output wiring connected to the emitter of the upper-arm switching element Swp (and the collector of the lower-arm switching element Swn).

[0018] An AC current sensor 4 is provided on each of the output wirings of the U, V, and W phases, and each AC current sensor 4 measures the AC current applied to the output wiring of the U, V, and W phases and outputs the detection result, an AC current detection value 16, to the motor control unit 10. This AC current detection value 16 indicates the value of the AC current input to the motor 5.

[0019] The angle sensor 6 detects the rotation angle of the motor 5 driven by AC current applied to each of the input wirings of the U phase, V phase, and W phase described above, and outputs an angle detection value 17 to the motor control unit 10.

[0020] The motor control unit 10 generates a current command value 22 based on the detected DC voltage value 15, the detected AC current value 16, and the detected angle value 17 of the motor 5, and outputs the current command value 22 to the current control unit 13. The current control unit 13 generates a gate drive signal 23 from the current command value 22, the detected AC current value 16, and the detected angle value 17 of the motor, in order to generate an AC voltage for driving the motor 5.

[0021] The motor control unit 10 also calculates the driving conditions 19 of the switching elements in the process of generating the current command value 22 , and the first temperature estimating unit 11 operates based on these driving conditions 19 .

[0022] The refrigerant temperature sensor 24 is an example of a refrigerant temperature acquisition unit, and is capable of acquiring the temperature of the refrigerant that cools multiple switching elements Sup, Svp, Swp, Sun, Svn, and Swn, each corresponding to the upper arm and lower arm of each of the U phase, V phase, and W phase of the power conversion device (or motor).

[0023] The temperature detection circuit 9 is an example of a refrigerant temperature acquisition unit, and outputs a temperature detection value 18 indicating the temperature of the refrigerant acquired by the refrigerant temperature sensor 24 to the motor control unit 10 and the second temperature estimation unit 12 .

[0024] The temperature sensors Tu, Tv, and Tw are provided on the switching elements Sun, Svn, and Swn on one arm (lower arm) side of the multiple arms out of the multiple switching elements Sup, Svp, Swp, Sun, Svn, and Swn, respectively, but are not provided on the switching elements Sup, Svp, and Swp on the upper arm side. The temperature sensors Tu, Tv, and Tw measure the temperatures of the switching elements Sun, Svn, and Swn on one arm (lower arm) side of the multiple arms out of the multiple switching elements Sup, Svp, Swp, Sun, Svn, and Swn, respectively.

[0025] The first temperature estimation unit 11 estimates a temperature (hereinafter also referred to as the "estimated temperature") based on the temperature rise (ΔTest1, ΔTest2) of each switching element Sup, Svp, Swp, Sun, Svn, and Swn when the switching elements operate based on the driving conditions 19 of the switching elements (see Figure 2).

[0026] When the actual temperature Tact measured by the temperature sensors Tu, Tv, and Tw for the switching elements Sun, Svn, and Swn on the lower arm side is higher than the estimated temperature based on the temperature rise of the arm estimated by the first temperature estimator 11, the second temperature estimator 12 estimates the predicted temperature Test2c (the "corrected estimated temperature" in Figure 2) of the other switching element on the other arm (upper arm) side by correcting the temperature rise ΔTest1 and ΔTest2 estimated by the first temperature estimator 11 for the switching elements on the upper arm side based on the ratio ((Tact - Tc) / ΔTest1) obtained by dividing the difference (Tact - Tc) between the actual temperature Tact and the coolant temperature Tc by the temperature rise ΔTest1 (see Figure 2).

[0027] That is, the second temperature estimator 12 corrects the temperature estimation values ​​of each switching element Sup, Svp, Swp estimated by the first temperature estimator 11, for example, from the temperature sensors Tu, Tv, Tw of the lower arm switching elements Sun, Svn, Swn and the temperature detection value 18 of the refrigerant temperature sensor 24, and the AC current detection value 16, and calculates the predicted temperature Test2c.

[0028] In the following description, the switching elements Sup, Svp, and Swp of the upper arms Sp of each phase are collectively referred to as switching elements SP unless it is necessary to distinguish them from one another, and the switching elements Sun, Svn, and Swn of the lower arms Sn of each phase are collectively referred to as switching elements SN unless it is necessary to distinguish them from one another.Furthermore, the free-wheeling diodes Dup, Dvp, and Dwp of the upper arms Sp of each phase are collectively referred to as free-wheeling diodes DP unless it is necessary to distinguish them from one another, and the free-wheeling diodes Dun, Dvn, and Dwn of the lower arms Sn of each phase are collectively referred to as free-wheeling diodes DN unless it is necessary to distinguish them from one another.

[0029] An outline of the power conversion method according to this embodiment will be described mainly with reference to FIG. 2 . This power conversion method includes a coolant temperature acquisition step in which a coolant temperature sensor 24 as an example of a coolant temperature acquisition unit acquires the temperature of a coolant cooling a plurality of switching elements corresponding to each of the upper arm Sp and lower arm Sn of each phase of the power conversion device; a switching element temperature measurement step in which temperature sensors Tu, Tv, and Tw measure the temperature of a switching element on one arm (lower arm) Sn side among the plurality of switching elements; a first temperature estimation step in which a first temperature estimator 11 estimates the amount of temperature rise (ΔTest1, ΔTest2) (estimated temperature) of each switching element when the switching element operates based on a driving condition 19 of the switching element; and a second temperature estimator 12 estimates the amount of temperature rise (ΔTest1, ΔTest2) (estimated temperature) of each switching element on the one arm (lower arm) Sn side. and a second temperature estimation step of estimating a predicted temperature (see "corrected estimated temperature" on the second temperature estimation characteristic curve 25) of the other switching element of the other arm (upper arm) by correcting the temperature rise (ΔTest1, ΔTest2) estimated by the first temperature estimator 11 for the switching element on the other arm (upper arm) Sxp side based on a ratio ((Tact-Tc) / ΔTest1) obtained by dividing the difference (Tact-Tc) between the measured temperature (actual temperature Tact) and the coolant temperature Tc by the estimated value (ΔTest1) of the temperature rise of the switching element.

[0030] The motor control unit 10 described above is an example of a drive control unit, and changes the driving conditions 19 of the switching elements. The motor control unit 10 restricts the driving conditions 19 of the switching elements when at least one of the temperatures measured by the temperature sensors Tu, Tv, and Tw and the predicted temperature (corrected estimated temperature) estimated by the second temperature estimator 12 exceeds a predetermined threshold temperature.

[0031] Specifically, when at least one of the temperature detection value 18 and the second temperature estimation value 21 of the switching elements Sun, Svn, and Swn exceeds a predetermined value, the motor control unit 10 changes the driving conditions 19 of the switching elements by limiting the torque of the motor 5, and ultimately controls the temperatures of the switching elements Sup, Svp, Swp, Sun, Svn, and Swn so that they do not rise any further.

[0032] When the rotation speed of the motor 5 is lower than a predetermined value (for example, when it is extremely slow), the motor control unit 10 changes the driving conditions 19 of the switching element based on the temperature estimated by the second temperature estimation unit 12 (the "corrected estimated temperature" in Figure 2), and, for example, keeps it within a threshold temperature or stops the motor 5.

[0033] 3 shows an example of the paths of current flowing through each switching element in a power conversion device. The illustrated example uses the switching elements of one phase of an upper arm Sp and a lower arm Sn as examples, and indicates which switching element the current flows through based on the polarity of the current and the ON / OFF state of the switching element.

[0034] If the switching element of the upper arm Sp is collectively referred to as Sp, the free wheel diode as Dp, the switching element of the lower arm Sn as Sn, and the free wheel diode as Dn, then when the switching element of either the upper arm Sp or the lower arm Sn is ON, the switching element of the other arm is OFF, and ON / OFF is alternately switched at regular intervals. As shown in Figure 3, when the current polarity is +, current flows alternately through the switching element SP and the free wheel diode Dn, while when the current polarity is -, current flows alternately through the free wheel diode Dp and the switching element SN.

[0035] When the rotation speed of the motor 5 is high, that is, when the frequency of the AC current is high, current flows uniformly through the switching element SP, the free wheel diode Dp, the switching element SN, and the free wheel diode Dn, so that the heat generated by each of the switching elements of the upper arm Sp and the lower arm Sn is equal to each other. Note that although the illustrated example is explained using one phase, the same explanation can be given for a three-phase system.

[0036] As an extreme example of a low rotation speed region, when the motor 5 is stopped, the current flowing through the motor 5 becomes direct current. If this embodiment were not applied, when the motor 5 is stopped with the current polarity of a certain phase being positive, current would flow only through the switching element SP and the freewheeling diode Dn, resulting in excessive heat generation, while conversely, no current would flow through the freewheeling diode Dp and the switching element SN, so no heat would be generated.

[0037] 4A to 4C show examples of temperature changes of the switching elements SP and SN, respectively. The illustrated examples show the temperature changes of the switching elements SP and SN when the frequency of the AC current is low.

[0038] 4A, 4B, and 4C show the temperature changes of the upper arm Sp and the lower arm Sn for one phase, respectively. For example, in FIG. 4A, there is a temperature amplitude of about 4° C. at 10 Hz, in FIG. 4B, there is a temperature amplitude of about 30° C. at 1 Hz, and in FIG. 4C, there is a temperature amplitude of about 120° C. at 0.1 Hz.

[0039] 4D shows an example of temperature changes in each of the switching elements Sup, Sun, Svp, Svn, Swp, and Swn in all three-phase arms. Because the temperature peak points differ for each arm, if this embodiment were not applied, it would be necessary to detect or estimate the temperature of each of the switching elements Sup, Sun, Svp, Svn, Swp, and Swn in each arm in order to protect the switching elements Sup, Sun, Svp, Svn, Swp, and Swn from overheating.

[0040] 5 shows an example of the relationship between the current phase assumed in this embodiment and the current of the switching element of each phase. In this embodiment, assuming a state in which the motor 5 is stopped in the current phase shown on the upper right side of FIG. 5, the current frequency is 0 Hz, the U phase (corresponding to "U" in the figure) is at a peak point of positive polarity, and the V phase (corresponding to "V" in the figure) and the W phase (corresponding to "W" in the figure) continue to flow with a current of half the peak of negative polarity.

[0041] 3, whether a current flows through the switching elements SP and SN or the freewheeling diodes Dp and Dn depends on the current polarity. In this embodiment, a U-phase current flows through the switching element Sup of the upper arm Sp, and a V-phase current and a W-phase current flow through the switching elements Svn and Swn of the lower arm Sn.

[0042] Therefore, these three switching elements Sup, Svn, and Swn generate heat, but as already explained, in this embodiment, the temperatures of the switching elements Sup, Svn, and Swn can only be detected by two temperature sensors Tv and Tw provided in the lower arm Sn, and since no temperature sensor is provided for the switching element Sup of the upper arm Sp, its temperature cannot be detected.

[0043] 6 shows an example of current-temperature characteristics when the temperatures of the switching elements are different at low frequencies as assumed in FIG. 5. The driving conditions 19 of the switching elements described above include DC voltage, switching frequency, switching duty indicating the ratio of ON / OFF periods of the switching elements, and flow rate of the cooling medium. These are common to each arm. At low frequencies, the temperature also increases or decreases as the current increases or decreases, and the characteristics are as shown by a first temperature estimation characteristic curve 27.

[0044] For example, if the flow rate of the refrigerant decreases due to an abnormality in the cooling system, the actual temperature is expected to be higher than the first temperature estimation characteristic curve 27. This expected temperature characteristic is defined as the second temperature estimation characteristic curve 25.

[0045] 5, the current in the U phase is the largest, whereas the temperatures can be detected in the V and W phases as described above. If the temperature rise of the switching element Svn of the lower arm Sn of the V phase estimated by the first temperature estimation characteristic curve 27 is ΔTv_mdl, the actually detected temperature is Tv, and the coolant temperature is Tc, the second temperature estimation characteristic curve 25 can be obtained by expanding the first temperature estimation characteristic curve 27 in the vertical direction by the following coefficient: ΔTv_act / ΔTv_mdl, where ΔTv_act=Tv-Tc

[0046] In the first temperature estimation characteristic curve 27, if the temperature rise corresponding to the current value of the U-phase is ΔTu_mdl, the temperature of the switching element Sup of the upper arm Sp of the U-phase can be estimated by the following formula: ΔTu_est=ΔTu_mdl×(ΔTv_act / ΔTv_mdl)

[0047] 7 shows an example of temperature changes of the switching elements Sun, Svn, and Swn of the lower arm Sn at low frequencies. The illustrated example shows an example in which only the temperature changes of the switching elements Sun, Svn, and Swn of the lower arm Sn of each phase are extracted from the example of the time-temperature characteristics shown in FIG.

[0048] As shown in the figure, the temperature of the switching elements Sun, Svn, and Swn of any one of the phases can be detected, and therefore, by applying this embodiment, it is possible to estimate the temperature of the switching elements of the upper arm Sp, eliminating the need to provide a temperature sensor for the switching elements of the upper arm Sp.

[0049] FIG. 8 shows an example of the current versus temperature characteristic shown in FIG. 6 when the frequency is low and the cooling refrigerant is stopped.

[0050] Generally, the refrigerant temperature sensor 24 is often installed upstream of the refrigerant flow path. Therefore, as shown in the example, the detected refrigerant temperature remains Tc, but if the refrigerant temperature around the switching element rises to temperature Tc' due to heat generation by the element, the relationship between current and temperature rise will be as shown by curve 26.

[0051] On the other hand, the second temperature estimator 12 recognizes the refrigerant temperature as Tc, and therefore outputs a second temperature estimation characteristic curve 25 whose intersection is the temperature Tv1 of the switching element Svn. Therefore, according to this embodiment, the estimated temperature increase ΔTu_est of the U-phase is estimated to be higher than the actual temperature, and protection action against overtemperature of the switching element is activated earlier.

[0052] As described above, the power conversion device according to this embodiment includes the refrigerant temperature sensor 24 that acquires the temperature of the refrigerant cooling the multiple switching elements Sup, Sun, Svp, Svn, Swp, and Swn corresponding to the upper arm and lower arm of each phase of the motor 5, the temperature sensors Tu, Tv, and Tw that measure the temperature of the switching elements Sun, Svn, and Swn on one arm (lower arm) side of the multiple switching elements Sup, Sun, Svp, Svn, Swp, and Swn, the first temperature estimator 11 that estimates an estimated temperature based on the temperature rise amounts ΔTest1 and ΔTest2 of each switching element when operating based on the driving conditions 19 of the switching elements, and the temperature sensor 24 that measures the temperature of the switching elements Sun, Svn, and Swn on one arm (lower arm) side of the multiple switching elements Sup, Sun, Svp, Svn, Swp, and Swn. and a second temperature estimator 12 that, when a measured temperature (actual temperature Tnmax) measured by the temperature sensors Tu, Tv, and Tw is higher than an estimated temperature based on the amount of temperature rise estimated by the first temperature estimator 11, estimates a predicted temperature Test2c (corresponding to the "corrected estimated temperature" shown in FIG. 2 ) of the other switching elements Sup, Svp, and Swp on the other arm (upper arm) side by correcting the amount of temperature rise (ΔTest1, ΔTest2) estimated by the first temperature estimator 11 for the switching elements on the other arm (upper arm) side based on a ratio ((Tact-Tc) / ΔTest1) obtained by dividing the difference (Tact-Tc) between the measured temperature (actual temperature Tact) and the refrigerant temperature Tc by the amount of temperature rise (ΔTest1).

[0053] In this way, even if the cooling system of one of the switching elements is malfunctioning, the predicted temperature of the other switching element can be accurately estimated based on the temperature measured by the temperature sensors Tu, Tv, and Tw provided only on the switching element Sun, Svn, and Swn, thereby preventing the actual temperature of the other switching element Sup, Svp, and Swp from becoming too high even if the cooling system of the switching element is malfunctioning.

[0054] The power conversion device according to this embodiment includes a motor control unit 10 as an example of a drive control unit that changes the drive conditions 19 of the switching elements. The motor control unit 10 limits the drive conditions of the switching elements when either the temperatures measured by the temperature sensors Tu, Tv, and Tw or the predicted temperature (the corrected estimated temperature) estimated by the second temperature estimator 12 exceeds a predetermined threshold temperature. Here, limiting the drive conditions of the switching elements can be, for example, keeping the temperature within the threshold temperature or stopping the motor. In this way, it is possible to prevent failure of the switching elements due to overtemperature.

[0055] In this embodiment, when the rotation speed of the motor 5 is lower than a predetermined value (for example, when the rotation speed is extremely low), the motor control unit 10 changes the driving conditions 19 of the switching elements based on the predicted temperature (corresponding to the "corrected estimated temperature" in FIG. 2 ) estimated by the second temperature estimator 12. In this way, when the rotation speed of the motor 5 is lower than a predetermined value (for example, when the rotation speed is extremely low), there is a risk that the switching elements of the upper arm may generate excessive heat, but by changing the driving conditions 19 of the switching elements based on the predicted temperature, it is possible to prevent excessive heat generation in practice.

[0056] Motor control unit 10 generates a current command value 22 based on a detected DC voltage value 15 indicating the value of the DC voltage of DC voltage source 1, a detected AC current value 16 indicating the value of the AC current input to motor 5, and a detected angle value 17 of motor 5, and also calculates driving conditions 19 for the switching elements in the process of generating current command value 22. In this way, motor control unit 10 can prevent switching elements Sup, Svp, Swp, Sun, Svn, and Swn from being excessively heated by driving motor 5, thereby preventing failure of switching elements Sup, Svp, Swp, Sun, Svn, and Swn.

[0057] The motor control unit 10 outputs the drive conditions 19 of the switching elements calculated as described above to the first temperature estimator 11. In this way, the first temperature estimator 11 can estimate the temperatures taking the drive conditions 19 into consideration, and therefore the first temperature estimator 11 can estimate the temperatures of the switching elements Sup, Svp, and Swp more accurately.

[0058] It should be noted that the present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the spirit and scope of the appended claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations.

[0059] In the above-described embodiment, a three-phase power conversion device has been described as an example, but it is not necessarily three-phase, and the present embodiment can be applied to any power conversion device having more than two phases.

[0060] The present invention can be applied to a power conversion device relating to a technique for measuring the temperatures of U-phase, V-phase, and W-phase switching elements.

[0061] 1... DC voltage source, 2... Smoothing capacitor, 3... DC voltage sensor, 4... AC current sensor, 5... Motor, 6... Angle sensor, 7... Control device, 8... Gate drive circuit, 9... Temperature detection circuit, 10... Motor control unit, 11... First temperature estimator, 12... Second temperature estimator, 13... Current control unit, 14... Motor control command, 15... DC voltage detection value, 16... AC current detection value, 17... Motor angle detection value, 18... Temperature detection value, 19... Switching element drive condition, 20... First temperature estimation value, 21... Second temperature estimation value, 22... Current command value, 23... Gate drive signal, 24... Refrigerant temperature sensor

Claims

1. A power conversion device comprising: a coolant temperature acquisition unit that acquires the temperature of a coolant that cools a plurality of switching elements corresponding to an upper arm and a lower arm of each phase of a power conversion device; a temperature sensor that measures the temperature of one of the plurality of switching elements on one arm; a first temperature estimation unit that estimates an estimated temperature based on an amount of temperature rise of each of the switching elements when the switching elements operate based on their driving conditions; and a second temperature estimation unit that, when a measured temperature measured by the temperature sensor for the switching element on the one arm side is higher than an estimated temperature based on the amount of temperature rise estimated by the first temperature estimation unit, estimates a predicted temperature of the other switching element on the other arm side by correcting the amount of temperature rise estimated by the first temperature estimation unit for the switching element on the other arm side based on a ratio obtained by dividing the difference between the measured temperature and the coolant temperature by the amount of temperature rise.

2. A power conversion device as described in claim 1, further comprising a drive control unit that changes the drive conditions of the switching element, wherein the drive control unit limits the drive conditions of the switching element when either the measured temperature by the temperature sensor or the predicted temperature estimated by the second temperature estimation unit exceeds a predetermined threshold temperature.

3. The power conversion device according to claim 1, characterized in that the drive control unit changes the drive conditions of the switching element based on the predicted temperature estimated by the second temperature estimation unit when the rotation speed of the motor is lower than a predetermined value.

4. The power conversion device according to claim 2 or 3, characterized in that the drive control unit generates a current command based on a DC voltage detection value indicating the value of the DC voltage of a DC voltage source, an AC current detection value indicating the value of the AC current input to the motor, and a motor angle detection value, and calculates the drive conditions of the multiple switching elements in the process of generating the current command.

5. The power conversion device according to claim 4, characterized in that the drive control unit outputs the calculated drive conditions for the plurality of switching elements to the first temperature estimation unit.

6. A power conversion method for a power conversion device comprising: a coolant temperature acquisition step in which a coolant temperature acquisition unit acquires the temperature of a coolant that cools a plurality of switching elements corresponding to an upper arm and a lower arm of each phase of the power conversion device; a switching element temperature measurement step in which a temperature sensor measures the temperature of a switching element on one arm side of the plurality of switching elements; a first temperature estimation step in which a first temperature estimation unit estimates an estimated temperature based on an amount of temperature rise of each switching element when the switching element operates based on a driving condition of the switching element; and a second temperature estimation step in which, when a measured temperature measured by the temperature sensor for the switching element on the one arm side is higher than an estimated temperature based on the amount of temperature rise estimated by the first temperature estimation unit, a second temperature estimation step in which a second temperature estimation unit estimates a predicted temperature of the other switching element on the other arm side by correcting the amount of temperature rise estimated by the first temperature estimation unit for the switching element on the other arm side based on a ratio obtained by dividing the difference between the measured temperature and the coolant temperature by the amount of temperature rise.

7. The power conversion method according to claim 6, characterized in that a drive control unit that changes the drive conditions of the switching element limits the drive conditions of the switching element when either the measured temperature by the temperature sensor or the predicted temperature estimated by the second temperature estimation unit exceeds a predetermined threshold temperature.

8. The power conversion method according to claim 6, characterized in that the drive control unit changes the drive conditions of the switching element based on the predicted temperature estimated by the second temperature estimation unit when the rotation speed of the motor is lower than a predetermined value.

9. The power conversion method according to claim 7 or 8, characterized in that the drive control unit generates a current command based on a DC voltage detection value indicating the value of the DC voltage of a DC voltage source, an AC current detection value indicating the value of the AC current input to the motor, and an angle detection value of the motor, and calculates the drive conditions of the multiple switching elements in the process of generating the current command.

10. The power conversion method according to claim 9, characterized in that the drive control unit outputs the calculated drive conditions for the plurality of switching elements to the first temperature estimation unit.

Images