Power device temperature estimation device of inverter

Abstract

To provide a device which can estimate temperature of a power device with high accuracy.SOLUTION: A device 30 is installed in an inverter 10 mounted with a power device 40 to estimate temperature of the power device 40 by temperature of a reflux diode 42. The device 30 comprises: a voltage division unit 32 having a voltage divider circuit constituted of a first element and a second element connected in series; a diode voltage detection unit 33 which detects forward voltage of the reflux diode 42 on the basis of divided voltage of the second element; a diode current detection unit 31 which detects forward current of the reflux diode 42; and a diode temperature estimation unit 34 which estimates the temperature of the reflux diode 42 on the basis of the detected forward voltage, forward current and characteristic data. The first element consists of a diode 32a arranged in parallel with the reflux diode 42 and the second element consists of a resistor 32b.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The disclosed technology relates to an apparatus for estimating the temperature of a power device included in an inverter. [Background technology]

[0002] In recent years, the electrification of automobiles has become remarkable. Accordingly, the output of the drive motors installed in automobiles and the inverters that control them also tends to increase. When the output of the inverter increases, the power devices including the switching elements become hot. Therefore, in order to prevent thermal damage to the inverter, it is necessary to detect the temperature of the switching elements with high accuracy.

[0003] Therefore, it is common to attach a temperature sensor to the board on which the power device is installed to detect the temperature of the switching element. However, in this case, there are problems such as a lack of response in detection and a large error because the temperature sensor is located away from the power device.

[0004] In response to this, a method has been proposed in which the temperature of a freewheeling diode connected in anti-parallel to a switching element is detected and the detected temperature is regarded as the temperature of the switching element (for example, Patent Document 1).

[0005] In detail, the forward voltage when the forward current of the freewheel diode is 1A is detected using a resistor divider circuit consisting of two resistors, and the temperature of the freewheel diode is determined based on the detected value and the relationship between the current-voltage characteristics of the freewheel diode and the temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-208770 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the method of Patent Document 1, a detection signal of the divided voltage value is output to a control unit, and the control unit determines the temperature of the free wheel diode. In general, the voltage that a control unit can tolerate is about several volts. Therefore, when dealing with switching elements that are subjected to high voltages of several hundred volts, such as in an in-vehicle inverter, it is necessary to divide the voltage at a level of 1 / 100.

[0008] In this case, in the above-mentioned resistive voltage divider circuit, the temperature-dependent fluctuation component of the forward voltage of the freewheeling diode to be detected is also divided at a level of 1 / 100.As a result, it becomes necessary to detect minute voltage changes (for example, at the level of 100 μV), making it difficult to estimate the temperature with high accuracy.

[0009] Therefore, the disclosed technology provides a device that can estimate the temperature of a switching element with high accuracy even in an inverter that uses a high voltage. [Means for solving the problem]

[0010] The disclosed technology relates to a power device temperature estimation device that is attached to an inverter in which a power device consisting of a switching element and a free wheel diode connected in anti-parallel to the switching element is implemented, and that estimates the temperature of the power device based on the temperature of the free wheel diode.

[0011] The power device temperature estimation apparatus includes a voltage divider unit having a voltage divider circuit composed of a first element and a second element connected in series and connected in parallel with the free wheel diode, a diode voltage detection unit connected in parallel with the second element and detecting a forward voltage of the free wheel diode based on the voltage division of the second element, a diode current detection unit detecting a forward current of the free wheel diode, and a diode temperature estimation unit having characteristic data related to the voltage, current, and temperature of the free wheel diode and estimating the temperature of the free wheel diode based on the detected forward voltage and forward current and the characteristic data. The first element is a diode arranged in forward parallel with the free wheel diode, and the second element is a resistor.

[0012] That is, this power device temperature estimation device also estimates the temperature of the switching element or power device from the forward voltage of the free wheel diode, similar to Patent Document 1. In the technology of Patent Document 1, the forward voltage of the free wheel diode is detected using a resistive voltage divider circuit composed of two resistors, but this power device temperature estimation device detects the forward voltage of the free wheel diode using a voltage divider circuit composed of a diode and a resistor.

[0013] In other words, the resistor is connected in parallel to a free-wheeling diode whose forward voltage is reduced by the amount of the free-wheeling diode. In other words, with a voltage divider circuit of this configuration, the amount of forward voltage fluctuation caused by temperature change can be detected without being divided. Therefore, since there is no need to detect minute voltage changes, it becomes easier to estimate the temperature and the estimation accuracy is improved.

[0014] The diode voltage detection unit may include a transformer unit that increases a voltage division of the second element.

[0015] This allows the output side of the diode voltage detector to be isolated (insulated) from the high-voltage power circuit of several hundred V. Therefore, even if the power of the voltage divider becomes abnormal, it will not directly affect the output side of the diode voltage detector.

[0016] The diode voltage detection section may include a protection diode connected in parallel with the second element.

[0017] Because the forward voltage of the freewheel diode is high, if the diode (first element) in the voltage divider circuit fails and shorts out, that high voltage acts on the resistor (second element). In that case, there is a risk of damaging the temperature estimation device. On the other hand, if a protection diode is provided, even in such a case, the current can be passed through it from the positive side to the negative side. This prevents an abnormally high voltage from being applied to the resistor. It also prevents an abnormally large current from flowing through the transformer section.

[0018] The inverter may further include a substrate on which the power device is mounted and a heat sink attached to the substrate, and the first element may be arranged separately from the substrate or arranged on the substrate in contact with the heat sink, thereby maintaining a temperature of the first element within an acceptable range for detection of the forward voltage.

[0019] This makes it possible to ignore the effect of temperature changes in the diode that constitutes the first element, simplifying the voltage division calculation.

[0020] The diode temperature estimator may further have a dynamic thermal model for calculating a temperature of the power device, calculate an error and a Kalman gain between an estimated element temperature, which is the temperature of the power device estimated by the diode temperature estimator, and a calculated element temperature, which is the temperature of the power device calculated by the dynamic thermal model, modify the dynamic thermal model by introducing the error and the Kalman gain, and adopt the calculated value by the modified dynamic thermal model as the temperature of the power device.

[0021] The temperature of the power device estimated by the diode temperature estimation unit (estimated element temperature) includes switching noise. On the other hand, the dynamic thermal model is not affected by switching, so the calculated element temperature does not include switching noise. Therefore, using a known Kalman filter method, the dynamic thermal model is corrected based on the error between the estimated element temperature and the calculated element temperature and the Kalman gain, and the calculated value based on the corrected dynamic thermal model is used as the temperature of the power device.

[0022] In this way, the dynamic thermal model is successively corrected and the calculated element temperature converges to a true value, so that the diode temperature estimator can estimate the temperature of the power device with reduced switching noise, thereby improving the accuracy of estimating the temperature of the power device.

[0023] The diode temperature estimation unit may further have a dynamic thermal model for calculating a temperature of the power device, and gain setting data relating to a specific output related to noise of the inverter and a gain corresponding to the dynamic thermal model, calculate an error between an estimated element temperature, which is the temperature of the power device estimated by the diode temperature estimation unit, and a calculated element temperature, which is the temperature of the power device calculated by the dynamic thermal model, and obtain the gain from the gain setting data, modify the dynamic thermal model by introducing the error and gain, and adopt the calculated value by the modified dynamic thermal model as the temperature of the power device.

[0024] Calculating the Kalman gain K requires a large computational load. This can cause delays in responsiveness and results in large hardware. However, if changes in switching noise are predicted in advance and the gain is changed accordingly (so-called feedforward control), calculation of the Kalman gain becomes unnecessary, which not only improves the accuracy of estimating the temperature of the power device, but also reduces the computational load and achieves high responsiveness.

[0025] The specific output may be a current value output by the inverter, and the gain setting data may be set so that the gain becomes smaller as the current value increases, or the specific output may be a carrier frequency of the inverter, and the gain setting data may be set so that the gain becomes smaller as the carrier frequency decreases.

[0026] That is, if the current output by the inverter increases, the switching noise increases, and if the current output by the inverter decreases, the switching noise decreases. Also, if the carrier frequency of the inverter decreases, the switching noise increases, and if the carrier frequency of the inverter increases, the switching noise decreases. That is, the current value output by the inverter and the carrier frequency of the inverter are correlated with changes in the switching noise.

[0027] Therefore, by varying the gain depending on these changes, an appropriate gain can be obtained predictively.

[0028] The forward voltage of the free wheel diode may be detected during a period in which the switching element is turned off, regardless of the length of that period.

[0029] The introduction of a dynamic thermal model can suppress the effects of noise. This allows the forward voltage to be detected regardless of the length of the off-period. As a result, there is no restriction on the timing of detecting the forward voltage, and the temperature of the power device can be estimated appropriately.

[0030] A value obtained by averaging a plurality of the forward voltages detected within a preset range of a predetermined electrical angle may be used to estimate the temperature of the free wheel diode.

[0031] This makes it possible to obtain a stable forward voltage, improving the accuracy of estimating the temperature. In addition, since the number of forward voltages that can be detected at a given electrical angle depends on the carrier frequency, the number of forward voltages that can be detected increases as the carrier frequency increases. As described above, the higher the carrier frequency, the smaller the switching noise, and therefore the more stable the forward voltage can be obtained. Effect of the Invention

[0032] According to the disclosed technique, the temperature of the switching elements can be estimated with high accuracy even in an inverter that uses a high voltage, and therefore thermal damage to the inverter can be effectively prevented. [Brief description of the drawings]

[0033] [Figure 1] 1 is a schematic diagram for explaining an electric vehicle to which the disclosed technology is applied. [Diagram 2] FIG. 1 is a schematic diagram for explaining a configuration of a power device temperature estimation apparatus. [Diagram 3] FIG. 11 is a schematic diagram for explaining detection of a forward voltage of a freewheeling diode. [Figure 4] 5 is a schematic diagram for explaining voltage-temperature characteristic data and current correction data; FIG. [Diagram 5] FIG. 1 is a block diagram relating to estimation of the temperature of a power device. [Figure 6] FIG. 4 is a conceptual diagram of first gain setting data. [Figure 7] FIG. 13 is a conceptual diagram of second gain setting data. [Figure 8] 11 is a flowchart relating to temperature management control of a power device. [Figure 9] 9 is a flowchart continuing from FIG. 8. [Figure 10] FIG. 4 is a schematic diagram showing a timing chart relating to on / off of each power device. [Figure 11] FIG. 13 is a conceptual diagram of current limit data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The disclosed technology will now be described, however, the following description is merely exemplary in nature.

[0035] <Application examples of the disclosed technology> Fig. 1 shows an example of a suitable application of the disclosed technology (electric vehicle 1). Electric vehicle 1 is equipped with a drive motor 2 as its drive source. Drive motor 2 is a permanent magnet synchronous motor, and is electrically connected to an inverter 10. Inverter 10 is connected to a drive battery 4 via high-voltage wiring 5. Inverter 10 is also connected to a control device 7 via low-voltage wiring 6 for control.

[0036] The driving battery 4 is composed of multiple lithium ion batteries. The rated voltage of the driving battery 4 is, for example, 300V or higher. The driving battery 4 supplies high-voltage DC power to the inverter 10. The inverter 10 is PWM controlled by the control device 7, and converts the DC power into a three-phase AC current and supplies it to the driving motor 2. This causes the driving motor 2 to rotate.

[0037] A transmission 8 is connected to the rear of the drive motor 2. The rotational power output by the drive motor 2 is changed in speed by the transmission 8 and then transmitted to drive wheels 9 via a propeller shaft, a differential gear, and a pair of drive shafts. This causes the electric vehicle to run.

[0038] As shown in a simplified manner in Fig. 1, the inverter 10 is mounted with a power module 20 including a substrate 20a and a heat sink 20b. A power device temperature estimation apparatus 30 is further assembled to the power module 20 (this will be described separately later). Six power devices 40 are installed on the surface of the substrate 20a. As shown in Fig. 2, each of the power devices 40 includes a switching element 41 and a free wheel diode 42 connected in anti-parallel to the switching element 41.

[0039] A known inverter circuit is provided on the substrate 20a. The inverter circuit converts DC power from the driving battery 4 into three-phase (U-phase, V-phase, W-phase) AC power and outputs it to the driving motor 2 that rotates with three-phase AC. The inverter circuit is provided with a positive electrode side wiring 11 connected to the positive electrode side of the driving battery 4, and a negative electrode side wiring 12 connected to the negative electrode side of the driving battery 4. Three circuits (half-bridge circuits 13) corresponding to each phase are connected in parallel between the positive electrode side wiring 11 and the negative electrode side wiring 12.

[0040] Two power devices 40 are connected in series to each of the half-bridge circuits 13. An output wiring 14 that outputs AC power to the drive motor 2 is connected between the two power devices 40. A smoothing capacitor 15 is connected in parallel to the half-bridge circuits 13, 13, 13 between the positive electrode side wiring 11 and the negative electrode side wiring 12 on the input side of the half-bridge circuits 13, 13, 13.

[0041] When the inverter 10 is in operation, each of the switching elements 41 is turned on and off at high speed by PWM control. This generates a current with a pseudo AC waveform, which flows to the drive motor 2 via the output wiring 14 of one of the phases. Then, a current flows from the drive motor 2 to the negative side wiring 12 via the output wiring 14 of the other phase.

[0042] The freewheel diode 42 is provided to prevent the switching element 41 from being damaged by the instantaneous back electromotive force generated when the corresponding switching element 41 is turned off. Therefore, when the corresponding switching element 41 is turned off, a forward voltage is applied to the freewheel diode 42, and a forward current flows.

[0043] The switching element 41, which turns on and off at high speed and interrupts a large current intermittently, generates heat. Therefore, in order to cool the power device 40, a heat sink 20b is attached to the back surface of the substrate 20a as shown in Fig. 1. The heat sink 20b is configured to be cooled by a coolant that is circulated and supplied from a cooling device (not shown).

[0044] The switching element 41 may be damaged if its temperature exceeds an upper limit. For this reason, the temperature of the switching element 41 is detected and the control of the inverter 10 is limited accordingly. However, the amount of heat generated by the switching element 41 varies greatly depending on how often it is turned on and off, and since the switching element 41 is always cooled during operation, the temperature of the switching element 41 varies greatly in a short period of time. Therefore, high responsiveness is required to accurately detect the temperature of the switching element 41 and appropriately manage the temperature.

[0045] The illustrated power device 40 is a metal-oxide-semiconductor field-effect transistor (MOSFET) or a reverse conducting IGBT (RC-IGBT) in which a switching element 41 and a freewheeling diode 42 are integrally configured. Therefore, the temperature of the freewheeling diode 42 can be regarded as the temperature of the switching element 41.

[0046] The power device 40 may be of a type in which the switching element 41 and the free wheel diode 42 are configured separately. Even in this case, the switching element 41 and the free wheel diode 42 configuring the same power device 40 are arranged close to each other on the substrate 20a. Therefore, even in this type, the temperature of the free wheel diode 42 can be considered as the temperature of the switching element 41.

[0047] That is, the temperature of the freewheel diode 42 can be regarded as the temperature of the switching element 41 which constitutes the same power device 40. The temperatures of the freewheel diode 42 and the switching element 41 can also be said to be the temperature of the power device 40. Therefore, the inverter 10 is provided with a power device temperature estimation device 30 which is devised to be able to estimate the temperature of the power device 40 with high responsiveness and accuracy based on the forward voltage of the freewheel diode 42.

[0048] <Power device temperature estimation device> 1, a power device temperature estimation apparatus 30 (also simply referred to as "temperature estimation apparatus 30") according to this embodiment is provided in the power module 20 in a form independent of the substrate 20a. Specifically, the temperature estimation apparatus 30 is attached to the heat sink 20b in a state of being externally attached to the substrate 20a. Note that a part of the temperature estimation apparatus 30 may be integrated with the substrate 20a by being incorporated in the substrate 20a.

[0049] 2, the temperature estimation device 30 is composed of a diode current detection unit 31, a voltage division unit 32, a diode voltage detection unit 33, an AD converter 35, etc. The voltage division unit 32 is composed of a voltage division diode 32a (first element), a voltage division resistor 32b (second element), etc. The diode voltage detection unit 33 is composed of a protection diode 33a, a transformer unit 33b, etc.

[0050] In this temperature estimation apparatus 30, one power device 40 is the estimation target. Specifically, the power device 40 arranged in the lower arm 13a of the U phase is the estimation target. In this case, if there is a difference in temperature between the power devices 40 due to the structure of the power module 20, it is preferable to estimate the power device 40 with the highest temperature.

[0051] Also, a voltage divider 32 or the like may be provided for each of the U, V, and W phases or each of the power devices 40, and a plurality of power devices 40 may be subject to estimation. In this case, although the configuration becomes more complex, thermal damage to the inverter 10 can be prevented with higher accuracy.

[0052] (Diode current detection unit 31) The diode current detection unit 31 is provided corresponding to the power device 40 to be estimated, and detects a forward current flowing through the freewheel diode 42. The diode current detection unit 31 may be any device capable of measuring a current value, such as a current detector or a current sensor.

[0053] 2, the diode current detection unit 31 is installed at a predetermined location on the wiring upstream or downstream of the power device 40 to be estimated. Then, the diode current detection unit 31 detects the current (forward current) flowing through the freewheeling diode 42 while the switching element 41 is off.

[0054] (Voltage dividing section 32) The voltage dividing unit 32 has a function of dividing the high forward voltage of the free wheel diode 42 into two at a predetermined ratio. The voltage dividing diode 32a (first element) and the voltage dividing resistor 32b (second element) are connected in series with each other, and are connected in parallel with the free wheel diode 42 to be estimated. The voltage dividing diode 32a is arranged in forward-parallel in the same direction as the free wheel diode 42. In other words, it is arranged in anti-parallel to the switching element 41.

[0055] When compared at the same forward current, the voltage-dividing diode 32a has a forward voltage slightly lower than that of the free wheel diode 42. The magnitude of the voltage-dividing resistor 32b is selected according to the forward voltage of the voltage-dividing diode 32a.

[0056] The voltage-dividing diode 32a and the voltage-dividing resistor 32b form a voltage-dividing circuit, and this voltage-dividing circuit is used to detect the forward voltage of the freewheeling diode 42. That is, the diode voltage detection unit 33 is connected in parallel with the voltage-dividing resistor 32b, and detects the forward voltage of the freewheeling diode 42 based on the voltage division of the voltage-dividing resistor 32b.

[0057] In the conventional voltage divider circuit, a resistor is also used for the first element (resistive voltage divider circuit). In that case, however, when a high voltage of several hundred volts acts on the target switching element 41, the voltage needs to be divided at a level of 1 / 100, and as described above, the fluctuation component accompanying the temperature change in the forward voltage of the free wheel diode 42 to be detected is also divided at a level of 1 / 100. As a result, it becomes necessary to detect minute voltage changes (for example, at the level of 100 μV), which makes it difficult to estimate the temperature with high accuracy.

[0058] In contrast, in the voltage dividing section 32, the first element is a voltage dividing diode 32a. In other words, the voltage dividing resistor 32b has a configuration equivalent to being connected in parallel with a diode whose forward voltage is reduced from the free wheel diode 42 by the voltage dividing diode 32a.

[0059] The circuit configuration of the voltage divider unit 32 is shown in a simplified form in the upper left diagram of Fig. 3. The upper right diagram of Fig. 3 is a graph showing the relationship between the forward voltage Vf and the forward current if of the diode. The solid line shows the forward voltage Vfd of the freewheeling diode 42. The forward voltage Vfd of the freewheeling diode 42 changes relatively little even when the forward current if increases.

[0060] When the temperature of the freewheel diode 42 rises, its forward voltage Vfd shifts downward as shown by the imaginary line and drops (ΔVf) in accordance with the amount of rise in temperature.

[0061] Unlike resistors, diodes have the same and small voltage change ΔVf with respect to temperature even when the magnitude of the forward current is different. For example, in the case of power device 40, the change ΔVf in the forward voltage Vf caused by the temperature rise is about −0.1 V even if the forward current changes in magnitude.

[0062] As shown in Fig. 3, assume that a forward current if_1 flows through the freewheel diode 42 and a forward voltage Vf_1 acts on it. The corresponding switching element 41 is turned off and can be ignored. At this time, assume that the freewheel diode 42 rises from the reference temperature of room temperature and the forward voltage changes from Vfd by ΔVf. In this case, the divided voltage Vrf of the voltage dividing resistor 32b is Vf_1-Vfp as shown in the formula in Fig. 3, and when the temperature change is reflected, it becomes Vfd+ΔVf-Vfp.

[0063] That is, the voltage divider circuit of this configuration can detect the amount of change ΔVf in the forward voltage Vf caused by a temperature change without dividing it. Therefore, it is no longer necessary to detect minute voltage changes, making it easier to estimate the temperature and improving the accuracy of the estimation.

[0064] Incidentally, if the voltage-dividing diode 32a is a resistive voltage-dividing circuit composed of resistors with a resistance value of R0, the fluctuation component due to temperature will be (Rf / R0+Rf)·ΔVf. This pressure, which has been reduced by the voltage division, must be detected.

[0065] Here, the voltage-dividing diode 32a is disposed separately from the substrate 20a, and is configured so that the effect of temperature changes on the forward voltage of the voltage-dividing diode 32a can be substantially ignored (Vfp can be regarded as substantially constant).

[0066] That is, even if the temperature of the voltage-dividing diode 32a changes, it is maintained within an allowable range for detecting the forward voltage Vf_1 of the freewheeling diode 42. When the voltage-dividing diode 32a is disposed on the substrate 20a, it may be configured so that it is disposed in contact with the heat sink 20b and the temperature can be maintained within the allowable range by heat dissipation to the heat sink 20b.

[0067] In this way, the effect of temperature changes on the voltage-dividing diode 32a can be ignored, and the voltage division calculation can be simplified.

[0068] The forward voltage Vfp of the voltage-dividing diode 32a may be detected taking into consideration the temperature change of the voltage-dividing diode 32a. That is, a temperature sensor is installed in the voltage-dividing diode 32a, and the temperature of the voltage-dividing diode 32a is actually measured by the temperature sensor. Data (specific data) relating to the temperature of the voltage-dividing diode 32a and its current-voltage characteristics are stored in advance in the diode temperature estimation unit 34. Then, based on the actually measured temperature of the voltage-dividing diode 32a and the characteristic data, the forward voltage Vf of the voltage-dividing diode 32a taking into consideration the temperature change is detected.

[0069] (Diode voltage detector 33) As described above, the diode voltage detection unit 33 is composed of the protection diode 33a, the transformer unit 33b, etc. The diode voltage detection unit 33 has a function of outputting the divided voltage of the voltage dividing resistor 32b as an analog signal of a predetermined magnitude while being insulated from the circuit of the inverter 10.

[0070] The protective diode 33a is connected in parallel to the voltage dividing resistor 32b in a state in which it is arranged in the opposite direction to the free wheel diode 42 and the voltage dividing diode 32a. Since the forward voltage of the free wheel diode 42 is high, if the voltage dividing diode 32a breaks down and shorts out, the high voltage acts on the voltage dividing resistor 32b. In such a case, the temperature estimation device 30 may be damaged.

[0071] In response to this, by providing such a protective diode 33a, even if the voltage-dividing diode 32a is shorted, a current can be passed from the positive side to the negative side through the protective diode 33a. This makes it possible to prevent an abnormally high voltage from being applied to the voltage-dividing resistor 32b. This makes it possible to prevent an abnormally large current from flowing through the transformer unit 33b. This makes it possible to protect the temperature estimation device 30.

[0072] The AD converter 35 is connected to the voltage dividing section 32 via the transformer section 33b. The AD converter 35 converts the analog signal of the voltage or current input from the transformer section 33b into a digital signal. A load resistor 36 is connected in parallel between the AD converter 35 and the transformer section 33b.

[0073] The transformer unit 33b is made of a known pulse transformer connected in parallel with the voltage dividing resistor 32b, and the AD converter 35 is separated from the voltage dividing unit 32 by the transformer unit 33b. Therefore, the AD converter 35 can be kept independent (insulated) from high-voltage power circuits of several hundred volts. Even if the power of the voltage dividing unit 32 becomes abnormal, the AD converter 35 is not directly affected.

[0074] Moreover, the protective diode 33a prevents a large current from flowing through the transformer unit 33b. Therefore, the transformer unit 33b does not need to be prepared for a large current and can be made smaller. And, since only a relatively small current corresponding to the voltage division of the voltage dividing resistor 32b flows through the transformer unit 33b, the transformer unit 33b can increase the voltage to an appropriate level for the AD converter 35 with a relatively small turns ratio.

[0075] Specifically, the voltage that the AD converter 35 can tolerate is generally about ±5V. Therefore, the secondary voltage Vad of the transformer unit 33b needs to be within that range. On the other hand, as shown in the lower diagram and formula of FIG. 3, the transformer unit 33b converts the voltage on its primary side (i.e., the divided voltage Vrf of the voltage dividing resistor 32b) and outputs it to the secondary side (Vad=Tvf·Vrf) according to the ratio (turn ratio Tvf:T2 / T1) between the number of turns on the primary side (T1) of the transformer unit 33b connected in parallel with the voltage dividing resistor 32b and the number of turns on the secondary side (T2) of the transformer unit 33b connected to the AD converter 35.

[0076] Since the current flowing through the primary side of the transformer unit 33b is relatively small, the voltage on the primary side can be increased and output to the secondary side by setting the turns ratio Tvf to several times (for example, four times). In this way, the voltage on the secondary side of the transformer unit 33b can be kept within a range of about ±5V. Therefore, the divided voltage Vrf of the voltage dividing resistor 32b, and hence the forward voltage Vf of the freewheeling diode 42, can be detected stably and accurately.

[0077] (Diode temperature estimator 34) The diode temperature estimating unit 34 is configured by an IC chip or the like that is on-board the AD converter 35. That is, the diode temperature estimating unit 34 is provided in the AD converter 35 as a functional component.

[0078] Specifically, the diode temperature estimation unit 34 is composed of known hardware provided in the AD converter 35, such as a processor and a memory, and software, such as programs and data, implemented in the memory. The diode temperature estimation unit 34 estimates the temperature of the freewheeling diode 42 using the detected forward current if and forward voltage Vf through cooperation between the hardware and software.

[0079] That is, the diode temperature estimator 34 has characteristic data related to the current, voltage, and temperature of the freewheeling diode 42. Specifically, as shown by a solid line L1 in the upper graph of Fig. 4, the diode temperature estimator 34 has voltage-temperature characteristic data that specifies the relationship between the forward voltage Vf of the freewheeling diode 42 at a reference forward current if and its temperature td.

[0080] The relationship between the forward voltage Vf of the freewheel diode 42 and its temperature td is relatively small, but changes according to the magnitude of the forward current if (see the upper right diagram in FIG. 3).

[0081] For example, as shown by the phantom line in the upper graph of Figure 4, when the forward current if increases (if+), the temperature td for the forward voltage Vf also increases accordingly. When the forward current if decreases (if-), the temperature td for the forward voltage Vf also decreases accordingly. The change in temperature td for the forward voltage Vf in response to the change in forward current if increases as the forward current if increases.

[0082] Therefore, the diode temperature estimation unit 34 further has current correction data that specifies the relationship between the forward current if and the correction coefficient α of the voltage-temperature characteristic data described above, which is set based on this relationship, as shown in the lower graph of FIG.

[0083] The voltage-temperature characteristic data and the current correction data are stored in the memory of the AD converter 35. The format of the characteristic data can be selected according to the specifications. Instead of the current correction data, voltage-temperature characteristic data for each current value may be used.

[0084] The diode temperature estimation unit 34 estimates the temperature td of the freewheel diode 42 based on the forward current if of the freewheel diode 42 detected by the diode current detection unit 31, the forward voltage Vf detected by the diode voltage detection unit 33, and these characteristic data.

[0085] Specifically, a correction value α is determined from the detected forward current if and the current correction data, and the correction value α is used to correct the voltage-temperature characteristic data to data corresponding to the forward current if. Then, the temperature td of the freewheeling diode 42 is determined from the detected forward voltage Vf and the corrected voltage-temperature characteristic data. As described above, the temperature td of the freewheeling diode 42 is the temperature of both the switching element 41 and the power device 40.

[0086] <Noise countermeasures> The detection of the forward current if and the forward voltage Vf described above is performed during a period when the switching element 41 of the power device 40 to be estimated is off (off period), but the switching element 41 is turned on and off at high speed and the length of the off period also changes. Therefore, the detection is easily affected by noise caused by switching (switching noise).

[0087] For example, since the smaller the off period, the greater the effect of switching noise, detection during a large off period can reduce the effect of switching noise. However, making the off period longer may result in the drive motor 2 not being able to be driven properly, and detection only during a large off period may result in the temperature of the power device 40 not being able to be estimated properly.

[0088] On the other hand, since a large switching noise is superimposed on the forward current if and the forward voltage Vf detected during a small off period, the accuracy of the temperature estimation of the power device 40 decreases. That is, since the temperature of the power device 40 (estimated element temperature) estimated by the diode temperature estimator 34 includes switching noise, it is preferable to reduce the influence of the switching noise in order to estimate the temperature of the power device 40 with high accuracy.

[0089] Therefore, in the temperature estimation device 30, by combining the above-mentioned detection of the forward voltage and forward current of the freewheeling diode 42 and the temperature estimation of the power device 40 based on characteristic data of the freewheeling diode 42 with calculation of the temperature of the power device 40 using a dynamic thermal model, the influence of switching noise can be reduced and the accuracy of estimating the temperature of the power device 40 can be improved.

[0090] 5 shows a block diagram relating to the estimation of the temperature of the power device 40. The diode temperature estimator 34 further includes a dynamic thermal model 38. The diode temperature estimator 34 further includes extended software that combines the dynamic thermal model 38 with the above-mentioned temperature estimation of the power device 40 to estimate the temperature of the freewheeling diode 42. This extended software is configured based on a known Kalman filter.

[0091] The dynamic thermal model 38 can be designed using known thermal fluid analysis software, etc., based on the peripheral structure of the power device 40, such as the substrate 20a and the heat sink 20b, and each factor that contributes to the temperature change of the power device 40, such as the current and voltage output by the inverter 10.

[0092] When the inverter 10 is in operation, a current and a voltage are constantly output to the drive motor 2. At the same time, a coolant is circulated and supplied to the radiator 20b. The dynamic thermal model 38 dynamically calculates the temperature of the power device 40 by detecting and incorporating each of these factors that affect both the heat generation and heat dissipation of the power device 40.

[0093] The dynamic thermal model 38 may be stored as a calculation program in the memory of the AD converter 35. Furthermore, a heat generation map set based on the relationship between the current and voltage output by the inverter 10 and the amount of heat generated by the power device 40, and a heat dissipation map set based on the relationship between the flow rate and temperature of the refrigerant and the amount of heat dissipation by the power device 40 may be stored in the memory of the AD converter 35 and referenced as necessary.

[0094] The diode temperature estimation unit 34 determines the current and voltage (power) output by the inverter 10 from their command values, actual measurement values, etc. At the same time, the flow rate and temperature of the coolant supplied to the radiator 20b are also determined from their command values, actual measurement values, etc. Then, by introducing these factors that affect both the heat generation and heat dissipation of the power device 40 into a dynamic thermal model 38, the temperature of the power device 40 is calculated successively.

[0095] The diode temperature estimator 34 uses a known Kalman filter to calculate an error between the temperature of the power device 40 calculated by the dynamic thermal model 38 (calculated element temperature) and the estimated element temperature, and calculates an optimal gain K (Kalman gain K) that minimizes the error. Then, the calculated error and Kalman gain K are introduced into the dynamic thermal model 38, and a correction term related to noise in the dynamic thermal model 38 is changed. By doing so, the diode temperature estimator 34 corrects the dynamic thermal model 38. After that, the calculated value obtained by the corrected dynamic thermal model 38 is adopted as the temperature of the power device 40.

[0096] As a result, the dynamic thermal model 38 is successively corrected and the calculated element temperature converges to a true value, so that the diode temperature estimator 34 can estimate the temperature of the power device 40 with reduced switching noise. Therefore, the accuracy of estimating the temperature of the power device 40 is improved.

[0097] Since the dynamic thermal model 38 is not affected by switching, the calculated element temperature does not include switching noise. In contrast, as described above, the estimated element temperature actually measured includes switching noise. Therefore, the error between the calculated element temperature and the estimated element temperature consists of a model error caused by the dynamic thermal model 38 and a noise error caused by the switching noise.

[0098] In this case, in the case of the Kalman filter, the model error is minimized while the noise error is minimized. Specifically, the covariance of these errors is calculated, and the gain K at which this value is minimized is determined as the optimal gain K, that is, the Kalman gain K.

[0099] However, in this case, the calculation of the covariance imposes a large computation load, which may cause a delay in response. Also, the hardware may become large and may not be able to be incorporated into the AD converter 35.

[0100] Therefore, a configuration may be adopted in which a change in the switching noise is predicted in advance and the gain K is changed accordingly (so-called feedforward control). In this way, it becomes unnecessary to calculate the Kalman gain K, and therefore it is possible to improve the estimation accuracy of the temperature of the power device 40, reduce the calculation load, and achieve high responsiveness.

[0101] (Combination of feedforward control) Specifically, as indicated by the dashed line in FIG. 5, an appropriate gain K is predicted based on the current and voltage output by the inverter 10, and the magnitude of the gain K is changed.

[0102] The diode temperature estimator 34 further includes a predetermined gain setting data. The above-mentioned extension software is configured to use the gain setting data. The gain setting data includes data on the correlation between a specific output related to the noise, i.e., switching noise, of the inverter 10 and a gain K (also called a predictive gain K to distinguish it from the Kalman gain K) corresponding to the dynamic thermal model 38.

[0103] For example, the switching noise increases as the current output by the inverter 10 increases, and the switching noise decreases as the current output by the inverter 10 decreases. Therefore, the current value output by the inverter 10 is correlated with the change in the switching noise (corresponding to a specific output).

[0104] The diode temperature estimation unit 34 has gain setting data (first gain setting data) relating to the correlation between the current value i output by the inverter 10 and the predictive gain K, as shown in Fig. 6. The first gain setting data is set so that the predictive gain K decreases as the current value i output by the inverter 10 increases.

[0105] In addition, the lower the carrier frequency of the inverter 10, the larger the switching noise becomes, and the higher the carrier frequency of the inverter 10, the smaller the switching noise becomes. Therefore, the carrier frequency of the inverter 10 is correlated with changes in the switching noise (corresponding to a specific output).

[0106] The diode temperature estimation unit 34 has gain setting data (second gain setting data) relating to the correlation between the carrier frequency fr of the inverter 10 and the predictive gain K as shown in Fig. 7. The second gain setting data is set so that the predictive gain K becomes smaller as the carrier frequency fr of the inverter 10 becomes lower.

[0107] The diode temperature estimator 34 may also be provided with gain setting data (third gain setting data) relating to the correlation between both the current value and carrier frequency output by the inverter 10 and the predictive gain K. In this way, although the amount of data increases, it is possible to obtain the predictive gain K corresponding to the changes in both of these specific outputs.

[0108] The diode temperature estimation unit 34 predicts an appropriate gain K based on the current value and carrier frequency output by the inverter 10 and the first gain setting data or the second gain setting data (or the third gain setting data), and acquires a predictive gain K.

[0109] For example, when a current value output by the inverter 10 is input, the diode temperature estimator 34 obtains a predictive gain K corresponding to the current value from the first gain setting data. As a result, if the current value output by the inverter 10 is reduced, the predictive gain K is increased accordingly, and if the current value output by the inverter 10 is increased, the predictive gain K is decreased accordingly.

[0110] Similarly, when the carrier frequency of the inverter 10 is input, the diode temperature estimator 34 obtains a predictive gain K corresponding to the carrier frequency from the second gain setting data. As a result, if the carrier frequency of the inverter 10 becomes higher, the predictive gain K becomes larger accordingly, and if the carrier frequency of the inverter 10 becomes lower, the predictive gain K becomes smaller accordingly.

[0111] The diode temperature estimator 34 introduces the thus obtained predictive gain K and the error between the estimated element temperature and the arithmetic element temperature into the dynamic thermal model 38, and modifies the noise-related correction term of the dynamic thermal model 38. By doing so, the diode temperature estimator 34 modifies the dynamic thermal model 38. After that, the calculated value obtained by the modified dynamic thermal model 38 is adopted as the temperature of the power device 40.

[0112] As a result, the dynamic thermal model 38 is corrected successively and the calculated element temperature converges to the true value, so that the diode temperature estimator 34 can estimate the temperature of the power device 40 with reduced switching noise. This improves the accuracy of estimating the temperature of the power device 40. Moreover, since it is no longer necessary to calculate the Kalman gain K, the calculation load can be reduced and high responsiveness can be achieved. As a result, the hardware can be made smaller, so that it can be easily incorporated into the AD converter 35.

[0113] <Specific Example of Temperature Management of Power Device 40 by Temperature Estimation Apparatus 30> 8 and 9 show an example of temperature management control of the power device 40 by the temperature estimation device 30 to which noise countermeasures have been implemented. In this temperature estimation device 30, noise countermeasures are implemented by combining the above-mentioned feedforward controls.

[0114] When the electric vehicle 1 is keyed in and power is supplied to the on-board electrical equipment, the temperature estimation device 30 starts reading relevant data such as the current output by the inverter 10 (step S1). The temperature estimation device 30 always executes temperature management control processing while the inverter 10 is operating, that is, while power is being supplied to the on-board electrical equipment (Yes in step S2). When the inverter 10 stops, the temperature estimation device 30 stops processing the temperature management control (No in step S2).

[0115] When the inverter 10 is operating and power is being output to the drive motor 2, the temperature estimation apparatus 30 (diode temperature estimation unit 34) preferably executes, in parallel, a process of estimating the temperature of the power device 40 based on the temperature of the freewheeling diode 42, a process of calculating the temperature of the power device 40 using the dynamic thermal model 38, and a process of acquiring the predictive gain K. This allows temperature estimation in a short time, resulting in excellent responsiveness.

[0116] (Processing for Estimating Temperature of Power Device 40 Based on Temperature of Freewheel Diode 42) In the process of estimating the temperature of the power device 40 based on the temperature of the freewheeling diode 42, the temperature estimation apparatus 30 first performs a process of averaging the forward voltages Vf detected during a predetermined period (step S3). Specifically, a plurality of forward voltages detected within a predetermined range of electrical angle that is set in advance are averaged. The value thus obtained (average Vf value) is used to estimate the temperature of the freewheeling diode 42.

[0117] 10 shows a timing chart relating to the on / off of each power device 40 arranged in the lower arm 13a of each of the U, V, and W phases. The hatched portions indicate on periods, and the portions therebetween indicate off periods. As shown in FIG. 2, in this temperature estimation apparatus 30, the estimation target is the U-phase power device 40, and therefore the forward voltage Vf is detected during the off periods (R1 and R2).

[0118] As described above, the detection of the forward voltage Vf is more affected by switching noise as the off period becomes shorter, so the effect of switching noise can be reduced by detecting the forward voltage Vf during a long off period (e.g., R2). However, if detection is limited to a long off period, the timing is significantly restricted, and the temperature of the power device 40 cannot be appropriately estimated.

[0119] In contrast, in the case of the temperature estimation device 30, the influence of noise can be suppressed by the above-mentioned noise countermeasures. As a result, the forward voltage Vf can be detected regardless of the length of the off period. For example, the forward voltage Vf can be detected even during the period R1, which is the shortest off period.

[0120] Therefore, in the temperature estimation device 30, a predetermined period, for example, an electrical angle of 120° (period of R3), is set in advance, and the forward voltage Vf is detected during each successive off period within that range, and these forward voltages Vf are averaged. In this way, it is possible to obtain a stable forward voltage Vf.

[0121] The number of forward voltages Vf that can be detected at a given electrical angle depends on the carrier frequency. The higher the carrier frequency, the more forward voltages Vf that can be detected. As mentioned above, the higher the carrier frequency, the smaller the switching noise, so a more stable forward voltage Vf can be obtained.

[0122] The temperature estimation device 30 corrects the characteristic data according to the detected forward current if (step S4). That is, as shown in Fig. 4, a correction value α is specified from the detected forward current if and the current correction data, and the voltage-temperature characteristic data is corrected to data corresponding to the forward current if using the correction value α.

[0123] Then, the temperature estimation device 30 estimates the element temperature Tsw based on the acquired Vf average value and the corrected voltage-temperature characteristic data (step S5). The temperature estimation device 30 acquires the element temperature Tsw estimated in this way as an estimated element temperature Tsw1 (step S6).

[0124] (Temperature calculation process of power device 40 using dynamic thermal model 38) In the temperature calculation process of the power device 40 using the dynamic thermal model 38, the temperature estimation device 30 calculates the element temperature Tsw using the dynamic thermal model 38 (step S7). That is, the current and voltage (power) output by the inverter 10 are identified from their command values, actual measurement values, etc. At the same time, the flow rate and temperature of the coolant supplied to the radiator 20b are also identified from their command values, actual measurement values, etc. Then, these factors that affect both the heat generation and heat dissipation of the power device 40 are introduced into the dynamic thermal model 38. In this way, the temperature estimation device 30 calculates the temperature of the power device 40.

[0125] The temperature estimation device 30 acquires the element temperature Tsw estimated in this way as a calculated element temperature Tsw2 (step S8).

[0126] The temperature estimation device 30 calculates the error between the acquired estimated element temperature Tsw1 and the calculated element temperature Tsw2 (step S9). Since it is merely a subtraction, there is almost no computational load.

[0127] (Acquisition process of predictive gain K) The temperature estimation device 30 predictively obtains a gain K from the current and voltage (power) output by the inverter 10 based on a specific output (current value, carrier frequency) associated with the noise (step S10).

[0128] Specifically, when a current value output by the inverter 10 is input, the diode temperature estimator 34 obtains a predictive gain K corresponding to the current value from the first gain setting data. Alternatively, when a carrier frequency of the inverter 10 is input, the diode temperature estimator 34 obtains a predictive gain K corresponding to the carrier frequency from the second gain setting data. The temperature estimation device 30 preferentially adopts a predictive gain K based on either the current value or the carrier frequency depending on the situation.

[0129] In addition, when the diode temperature estimation unit 34 has the third gain setting data, when the current value and carrier frequency output by the inverter 10 are input, the diode temperature estimation unit 34 obtains a predictive gain K corresponding to the current value and carrier frequency from the third gain setting data.

[0130] When the process of calculating the error between the estimated element temperature Tsw1 and the calculated element temperature Tsw2 and the process of obtaining the predictive gain K are completed, as shown in FIG. 9, the temperature estimation device 30 introduces the calculated error and the obtained predictive gain K into the dynamic thermal model 38 (step S11).

[0131] Then, as described above, the dynamic thermal model 38 is modified, and the element temperature Tsw is estimated using the modified dynamic thermal model 38 (steps S12, S13).

[0132] Specifically, the dynamic thermal model 38 is modified by changing a correction term related to noise in the dynamic thermal model 38 using the predictive gain K and the error. After that, the calculated value obtained by the modified dynamic thermal model 38 is adopted as the final estimated element temperature Tsw of the power device 40.

[0133] The temperature estimation device 30 determines whether the element temperature Tsw estimated in this way exceeds a predetermined temperature Ts (step S14). Specifically, data (current limit data) indicating the relationship between the maximum current value that the inverter 10 can output and the element temperature Tsw, as shown in Fig. 11, is preset in the temperature estimation device 30 (diode temperature estimation unit 34).

[0134] Then, the temperature estimation device 30 refers to the current limit data, and if the estimated element temperature Tsw exceeds the temperature Ts (Yes in step S14), it reduces the maximum current value that the inverter 10 can output in accordance with the element temperature Tsw, and manages the current so that it does not exceed that value (step S15).

[0135] If the estimated element temperature Tsw is equal to or higher than Tmax, the inverter 10 is stopped from operating so that it does not output current. On the other hand, the temperature estimation device 30 refers to the current limit data, and if the estimated element temperature Tsw does not exceed the temperature Ts (No in step S14), the maximum current value is set as normal (a constant value) and the current is managed so as not to exceed that value. Then, the process returns to step S2 and the process of estimating the element temperature Tsw is repeated.

[0136] In this way, with this temperature estimation device 30, it is possible to accurately estimate the temperature of the switching element 41 even in the inverter 10 that uses a high voltage. Therefore, by using this temperature estimation device 30 to manage the temperature of the switching element 41, it becomes possible to effectively prevent thermal damage to the inverter 10.

[0137] The disclosed technology is not limited to the above-described embodiment, but includes various other configurations. For example, although the embodiment shows an example of application to the electric vehicle 1, the disclosed technology can also be applied to a hybrid vehicle. [Explanation of symbols]

[0138] 1. Electric vehicles 2 Drive motor 4. Driving battery 10 Inverter 20 Power Module 20a Board 20b radiator 30 Power device temperature estimation device 31 Diode current detection section 32 Voltage divider 32a Voltage divider diode (first element) 32b Voltage dividing resistor (second element) 33 Diode voltage detector 33a Protection diode 33b Transformer section 34 Diode temperature estimation section 35 AD converter 36 Load Resistance 38 Dynamic Thermal Model 40 Power Devices 41 Switching element 42 Freewheeling diode

Claims

1. A power device temperature estimation apparatus is provided to an inverter in which a power device is mounted, the power device including a switching element and a free wheel diode connected in anti-parallel to the switching element, the power device temperature estimation apparatus estimating a temperature of the power device based on a temperature of the free wheel diode, a voltage dividing section including a voltage dividing circuit connected in parallel with the freewheeling diode, the voltage dividing circuit being configured with a first element and a second element connected in series; a diode voltage detection unit connected in parallel to the second element and configured to detect a forward voltage of the freewheeling diode based on a voltage division of the second element; a diode current detection unit for detecting a forward current of the free wheel diode; a diode temperature estimator that has characteristic data relating to a voltage, a current, and a temperature of the free wheel diode and estimates a temperature of the free wheel diode based on the detected forward voltage and forward current and the characteristic data; Equipped with the first element is a diode arranged in forward and parallel with the freewheeling diode, and the second element is a resistor.

2. 2. The power device temperature estimation apparatus according to claim 1, The power device temperature estimating apparatus, wherein the diode voltage detection unit has a transformer unit that increases a voltage division of the second element.

3. 2. The power device temperature estimation apparatus according to claim 1, the diode voltage detection unit has a protection diode connected in parallel with the second element.

4. The power device temperature estimation apparatus according to any one of claims 1 to 3, the inverter further includes a substrate on which the power device is mounted and a heat sink attached to the substrate; a first element disposed on the substrate in contact with the heat sink, the first element being disposed separately from the substrate, or disposed on the substrate in contact with the heat sink, thereby maintaining a temperature of the first element within an acceptable range for detection of the forward voltage.

5. 2. The power device temperature estimation apparatus according to claim 1, a diode temperature estimator further having a dynamic thermal model for calculating a temperature of the power device, the diode temperature estimator calculating an error and a Kalman gain between an estimated element temperature, which is the temperature of the power device estimated by the diode temperature estimator, and a calculated element temperature, which is the temperature of the power device calculated by the dynamic thermal model, correcting the dynamic thermal model by introducing the error and the Kalman gain, and adopting the calculated value by the corrected dynamic thermal model as the temperature of the power device.

6. 2. The power device temperature estimation apparatus according to claim 1, a diode temperature estimator further having a dynamic thermal model for calculating a temperature of the power device, and gain setting data relating to a specific output related to noise of the inverter and a gain corresponding to the dynamic thermal model, the diode temperature estimator calculates an error between an estimated element temperature, which is the temperature of the power device estimated by the diode temperature estimator, and a calculated element temperature, which is the temperature of the power device calculated by the dynamic thermal model, and acquires the gain from the gain setting data, corrects the dynamic thermal model by introducing the error and gain, and adopts the calculated value using the corrected dynamic thermal model as the temperature of the power device.

7. 7. The power device temperature estimation apparatus according to claim 6, The specific output is a current value output by the inverter, and the gain setting data is set so that the gain becomes smaller as the current value becomes larger.

8. 7. The power device temperature estimation apparatus according to claim 6, The specific output is a carrier frequency of the inverter, and the gain setting data is set so that the gain becomes smaller as the carrier frequency becomes lower.

9. The power device temperature estimation apparatus according to any one of claims 5 to 8, The power device temperature estimating apparatus according to claim 1, wherein the forward voltage of the free wheel diode is detected during a period in which the switching element is turned off, regardless of the length of that period.

10. 10. The power device temperature estimation apparatus according to claim 9, a power device temperature estimation apparatus that estimates a temperature of the free wheel diode by averaging a plurality of the forward voltages detected within a preset range of a predetermined electrical angle.

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