Online junction temperature monitoring circuit, method and system based on large-current saturation voltage drop method

Abstract

The invention discloses a junction temperature online monitoring circuit, method and system based on a large-current saturation voltage drop method, and relates to the technical field of electronics. The monitoring circuit comprises a high-voltage isolation circuit, a low-pass filter circuit and an analog isolation circuit which are sequentially connected in series; the high-voltage isolation circuit is used for being connected with an IGBT to output a measurement signal used for measuring the junction temperature, then the measurement signal passes through the low-pass filter circuit to ensure that a low-frequency-band signal lower than the cut-off frequency passes through, a signal higher than the cut-off frequency is filtered out, and then the measurement signal processed by the filter passes through the analog isolation circuit to obtain the junction temperature. On one hand, electromagnetic interference on the measurement signal is reduced, and on the other hand, the measurement signal is converted into analog quantity to be input into the measurement equipment, so that the measurement equipment obtains the junction temperature of the IGBT through the measurement signal. According to the invention, the junction temperature measurement precision can be improved.

Description

Technical Field

[0001] The present application relates to the field of electronic technology, and in particular to a junction temperature online monitoring circuit, method and system based on a large current saturation voltage drop method. Background Art

[0002] High-voltage, high-power devices, such as insulated-gate bipolar transistors (IGBTs), are widely used in power conversion systems such as wind power generation, photovoltaics, and electric vehicles. Power electronic devices often operate in harsh environments and face severe reliability challenges. Temperature is the primary cause of failure in high-voltage, high-power devices. Therefore, online monitoring of power device junction temperature plays a crucial role in device reliability assessment.

[0003] At present, the online measurement methods for junction temperature of high-voltage and high-power devices are roughly divided into negative temperature coefficient thermistors, chip integrated sensors, and temperature-sensitive electrical parameter methods. Negative temperature coefficient thermistors require an NTC thermistor to be integrated inside the module. This method requires the NTC thermistor to be installed near the chip to obtain the chip temperature. Once the chip has insulation breakdown, the NTC thermistor will also be broken down by the high voltage. In addition, this method has poor measurement timeliness, and the measured temperature is far from the actual chip temperature. It also needs to be calculated through a thermal network model, which is a cumbersome process. Chip-integrated sensors, such as integrating a PN junction on the chip surface to measure junction temperature, can improve the response time to milliseconds, which can meet the measurement requirements of most working conditions. To obtain a more accurate temperature distribution, more sensors need to be installed on the chip surface, but this will occupy more active area on the chip surface and have higher requirements for the bonding process. The temperature-sensitive electrical parameter method indirectly measures the chip temperature through the temperature-sensitive parameters inside the chip. Different temperature-sensitive parameters are used for measurement according to different working conditions. A device parameter affected by temperature is selected as the characterization quantity, and the corresponding relationship between the characterization quantity and the junction temperature is established through passive heating. This process is called temperature coefficient calibration, or simply calibration. The corresponding relationship between the characterization quantity and junction temperature is also called the calibration relationship. During device operation, the chip's power loss generates heat that actively heats the module. By measuring the characteristic quantity and comparing it with the calibration relationship, the operating junction temperature can be inferred. The temperature-sensitive electrical parameter method is applicable to all modules, offering high feasibility and fast response, and can be used for transient junction temperature measurement.

[0004] Currently, the mainstream online junction temperature measurement method is the temperature-sensitive electrical parameter method. Commonly used temperature-sensitive parameter methods based on on-state characteristics include the saturation voltage drop method under low current, the saturation voltage drop method under load current, the threshold voltage method, the saturation current method, and the short-circuit current method. However, existing conventional measurement circuits still have many shortcomings, such as poor measurement accuracy and high cost. Among them, the 0.5% measurement error of the saturation voltage drop method under load current results in a 4°C junction temperature measurement error. Summary of the Invention

[0005] The present application aims to at least solve the problem of large errors in the online junction temperature measurement method in the prior art, so that the measured junction temperature is more accurate and the circuit reliability is higher.

[0006] The solution of this application example is implemented through the following content.

[0007] In a first aspect, the present application provides a junction temperature online monitoring circuit based on a large current saturation voltage drop method, comprising a high-voltage isolation circuit, a low-pass filter circuit, and an analog isolation circuit connected in series; wherein: The high-voltage isolation circuit includes a first diode, a second diode, a third diode, a fourth diode connected in series, and an IGBT, and a first operational amplifier, wherein the anode of the first diode is electrically connected to a current source, the cathode of the third diode is grounded, the series connection end of the first diode and the second diode is electrically connected to the anode of the fourth diode, and the emitter of the IGBT is grounded; the inverting input end of the first operational amplifier is electrically connected to the anode of the first diode, the non-inverting input end of the first operational amplifier is electrically connected to the series connection end of the first diode and the second diode, and the non-inverting input end of the first operational amplifier is grounded via a first resistor; The low-pass filter circuit includes an RC filter unit and a second operational amplifier connected in series, the other end of the RC filter unit is electrically connected to the output end of the first operational amplifier, and the output end of the second operational amplifier is electrically connected to the input end of the analog isolation circuit; The analog isolation circuit includes a plurality of operational amplifier units connected in series, the input end of the first operational amplifier unit is electrically connected to the output end of the second operational amplifier, and the output end of the last operational amplifier unit outputs the voltage to be measured.

[0008] The measurement signal for measuring the junction temperature when the IGBT is turned on is output through a high-voltage isolation circuit. The measurement signal then passes through a low-pass filter circuit to filter out high-frequency stray signals, making the measurement signal more accurate. The measurement signal processed by the filter is then passed through an analog isolation circuit. On the one hand, this reduces electromagnetic interference on the measurement signal, and on the other hand, it converts the measurement signal into an analog quantity and inputs it into the measurement device, ensuring the accuracy of the measurement signal collected by the measurement device, thereby improving the accuracy of obtaining the junction temperature of the IGBT.

[0009] In the above-mentioned junction temperature online monitoring circuit based on the large current saturation voltage drop method, optionally, the RC filter unit includes a second resistor, a first capacitor, and a second capacitor; wherein: A first end of the second resistor is electrically connected to the output end of the second operational amplifier, and a second end of the second resistor is electrically connected to a non-inverting input end of a second first operational amplifier; The first end of the first capacitor is electrically connected to the output end of the second operational amplifier, and the second end of the second resistor is electrically connected to the negative input end of the second first operational amplifier; A first end of the second capacitor is electrically connected to a second non-inverting input end of the first operational amplifier, and a second end of the second capacitor is grounded.

[0010] The R and C values ​​can be adjusted according to the frequency of the measurement signal to ensure that the cutoff frequency is adapted to the frequency of the measurement signal, so as to filter out high-frequency spurious signals and improve the accuracy of the measurement signal.

[0011] In the junction temperature online monitoring circuit based on the large current saturation voltage drop method as described above, optionally, the resistance of the first resistor is in the megohm level.

[0012] The first resistor is a megohm resistor, which acts as a shunt to protect the operational amplifier in the subsequent stage.

[0013] In the above-mentioned junction temperature online monitoring circuit based on the large current saturation voltage drop method, optionally, the two operational amplifier units are connected in series via a third resistor; wherein: The first operational amplifier unit includes: a third operational amplifier, a fourth resistor and a third capacitor electrically connected to the non-inverting input terminal of the third operational amplifier; an output terminal of the third operational amplifier electrically connected to the third resistor, and the other end of the third capacitor is grounded; the other end of the fourth resistor is electrically connected to the output terminal of the second operational amplifier; The second operational amplifier unit includes: a fourth operational amplifier and a fifth resistor and a fourth capacitor electrically connected to the non-inverting input terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier outputs the measurement signal, and the other end of the fourth capacitor is grounded; the other end of the fifth resistor is electrically connected to the third resistor.

[0014] The analog isolation circuit achieves signal amplification and isolation through two-stage operational amplifiers (U3 and U4), while using resistors and capacitors for voltage division, current limiting and filtering to ensure signal stability and reliability.

[0015] In the junction temperature online monitoring circuit based on the large current saturation voltage drop method as described above, optionally, the second diode is a voltage regulator diode.

[0016] By replacing the two diodes in series with a Zener diode and a diode, the error range of the operational amplifier output voltage Vout and the IGBT's Vce is reduced. Through actual tests, it is found that the measurement error of the measured electrical parameters does not exceed 0.5%, and the data acquisition frequency reaches 200KHz.

[0017] In the junction temperature online monitoring circuit based on the large current saturation voltage drop method as described above, optionally, the reverse resistance of the second diode is in the megohm level.

[0018] The reverse resistance is in the megohm level, and the leakage current is in the μA level, which can ensure that the current flowing through the first diode and the current flowing through the fourth diode are approximately equal. In addition, the first diode and the fourth diode are of the same model, so that the voltage drops of the first diode and the fourth diode are approximately equal, ensuring that there is no interference with the voltage drop measurement when the IGBT is turned on.

[0019] A second aspect of the present application provides a method for online monitoring of junction temperature based on a large current saturation voltage drop method, characterized in that the method is applied to the online monitoring circuit for junction temperature based on a large current saturation voltage drop method as described in any one of the first aspects, and comprises: Obtaining a preset temperature calibration coefficient; wherein the temperature calibration coefficient is used to characterize the corresponding relationship between the junction temperature of the IGBT and the change of the collected voltage; Obtaining a measurement voltage and a corresponding measurement current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on; The junction temperature of the IGBT is determined according to the measured voltage and the temperature calibration coefficient.

[0020] The host computer can provide accurate junction temperature calculation results to ensure the accuracy and reliability of data during the monitoring process. The online monitoring circuit test method of the present application is simple, the data display is intuitive, and the working status of the device under test can be easily judged.

[0021] By using the junction temperature online monitoring circuit based on the large current saturation voltage drop method of the first aspect to measure the IGBT device to be measured, the accuracy of obtaining the junction temperature of the IGBT can be improved.

[0022] The above-mentioned method for online monitoring of junction temperature based on the large current saturation voltage drop method may, optionally, further comprise: after obtaining the measured voltage and measured current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on; Determining whether the measured voltage is the clamping voltage of the IGBT; If so, the measured voltage and the corresponding measured current are discarded; if not, the step of determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient is performed.

[0023] It can avoid inaccurate junction temperature obtained by the junction temperature calculation formula, automatically eliminate the influence of the clamping voltage, and avoid its interference with the junction temperature calculation.

[0024] The above-mentioned method for online monitoring of junction temperature based on the large current saturation voltage drop method, optionally, if not, before determining the junction temperature of the IGBT according to the measured voltage and the temperature calibration coefficient, the method includes: Determine whether the collected measured current is positive; If so, the measured current and the corresponding measured voltage are discarded; if not, the step of determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient is performed.

[0025] By judging the measured current, we ensure that the actual current value flowing through the device under test is used, ensuring the accuracy and reliability of the data during the monitoring process.

[0026] A third aspect of the present application provides a junction temperature online monitoring system based on a large current saturation voltage drop method, characterized by comprising: The junction temperature online monitoring circuit based on the large current saturation voltage drop method as described in any one of the first aspects; The host computer measures the junction temperature of the IGBT by using the online junction temperature monitoring method based on the large current saturation voltage drop method described in any one of the second aspects.

[0027] This application has the following beneficial effects: The detection circuit constructed in the present application includes a high-voltage isolation circuit, a low-pass filtering circuit, and an analog isolation circuit connected in series in sequence; the high-voltage isolation circuit outputs a measurement signal for measuring the junction temperature when the IGBT is turned on, and then the measurement signal passes through a low-pass filtering circuit to filter out high-frequency stray signals, thereby increasing the accuracy of the measurement signal. The measurement signal processed by the filter is then passed through an analog isolation circuit, which, on the one hand, reduces electromagnetic interference to the measurement signal, and on the other hand, converts the measurement signal into an analog quantity and inputs it into the measuring device, thereby ensuring the accuracy of the measurement signal collected by the measuring device, thereby improving the accuracy of obtaining the junction temperature of the IGBT. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, features and advantages of the exemplary embodiments of the present application will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein: Figure 1 A schematic diagram of an online junction temperature monitoring circuit based on a large current saturation voltage drop method provided in an embodiment of the present application; Figure 2 A schematic diagram of an analog isolation circuit according to an embodiment of the present application; Figure 3 Schematic diagram of an online junction temperature monitoring method based on a large current saturation voltage drop method according to an embodiment of the present application; Figure 4 This is a schematic diagram of an online junction temperature monitoring system based on a large current saturation voltage drop method according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the embodiments described are part of the embodiments of the present disclosure, not all of them. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present disclosure.

[0030] IGBT (Insulated Gate Bipolar Transistor), also known as insulated gate bipolar transistor, is tested for junction temperature using existing methods such as saturation voltage drop under low current, saturation voltage drop under load current, threshold voltage, saturation current, and short-circuit current. This results in poor measurement accuracy, as IGBTs experience large voltage fluctuations during switching and are subject to high voltages of thousands of volts when turned off, which can easily damage components in the circuit. Therefore, this application proposes an online junction temperature monitoring circuit based on the high-current saturation voltage drop method to address the issues of poor measurement accuracy and damage to circuit components caused by high voltage during shutdown.

[0031] like Figure 1 As shown, this embodiment provides an online junction temperature monitoring circuit based on the high-current saturation voltage drop method, comprising a high-voltage isolation circuit, a low-pass filter circuit, and an analog isolation circuit connected in series. The high-voltage isolation circuit is used to connect to the IGBT output to output a measurement signal for measuring the junction temperature. The measurement signal then passes through the low-pass filter circuit, ensuring that low-frequency signals below the cutoff frequency pass through while filtering out signals above the cutoff frequency. The cutoff frequency of the low-pass filter circuit is set according to the frequency of the measurement signal to ensure that the measurement signal can pass through. The low-pass filter circuit can filter out high-frequency stray signals, making the measurement signal more accurate, thereby ensuring that the junction temperature obtained based on the measurement signal is more accurate. Furthermore, the measurement signal after filter processing passes through the analog isolation circuit, which, on the one hand, reduces electromagnetic interference on the measurement signal, and, on the other hand, converts the measurement signal into an analog quantity and inputs it into the measurement device, which is used by the measurement device to obtain the junction temperature of the IGBT through the measurement signal.

[0032] Specifically, the high-voltage isolation circuit includes a first diode D1, a second diode D3, a third diode D4, a fourth diode D1 and an IGBT connected in series, and a first operational amplifier U1, wherein the anode of the first diode D1 is electrically connected to a current source, the cathode of the third diode D4 is grounded, the series end of the first diode D1 and the second diode D3 is electrically connected to the anode of the fourth diode D1, and the emitter of the IGBT is grounded; the inverting input terminal of the first operational amplifier U1 is electrically connected to the anode of the first diode D1, the non-inverting input terminal of the first operational amplifier U1 is electrically connected to the series end of the first diode D1 and the second diode D3, and the non-inverting input terminal of the first operational amplifier U1 is grounded through a first resistor R5.

[0033] The high-voltage isolation circuit includes a high-voltage part and an isolation part. The first diode D1, the second diode D3, the third diode D4, and the fourth diode D1 connected to the current source and the IGBT are all high-voltage parts. The first operational amplifier U1 and the resistors electrically connected to it constitute the isolation part. The high-voltage circuit part is isolated from the rest of the circuit by the first operational amplifier to ensure that the output measurement voltage is not affected. Among them, the inverting input terminal of the first operational amplifier U1 is electrically connected to the positive electrode of the first diode D1 through the sixth resistor R1, and is electrically connected to the output terminal through the seventh resistor R2. The output terminal of the first operational amplifier U1 is electrically connected to the eighth resistor R3 and the ninth resistor R4 connected in series. The series end of the eighth resistor R3 and the ninth resistor R4 serves as the output end of the high-voltage isolation circuit to output the measurement signal, and the other end of the ninth resistor R4 is grounded.

[0034] When the IGBT is turned on, the current flow path of the current source output of the high-voltage isolation circuit is the current source - the first diode D1, the fourth diode D2, the IGBT, and then back to the current source; since the resistance values ​​of the sixth resistor R1 and the seventh resistor R2 are equal, the current flowing through the sixth resistor R1 and the seventh resistor R2 is equal in magnitude and direction, that is, the measurement voltage output by the operational amplifier at this time V out Approximately equal to the IGBT device being tested V ce (Collector-Emitter Voltage). After the IGBT is turned off, the fourth diode D2 in the circuit is cut off, and the current flows through the first diode D1, the second diode D3, the third diode D4, and then back to the current source. The high-voltage isolation circuit uses the same signal for the first diode D1 and the fourth diode D2, and the ambient temperature of each diode is equal. The virtual short circuit of the first operational amplifier U1 and the improved clamping devices of the second diode D3 and the third diode D4 can make the measured voltage Vout and the IGBT Vce approximately equal, ensuring more accurate IGBT junction temperature measurement through the measured voltage.

[0035] The low-pass filter circuit includes an RC filter unit and a second operational amplifier connected in series. The other end of the RC filter unit is electrically connected to the output of the first operational amplifier U1, and the output of the second operational amplifier U2 is electrically connected to the input of the analog isolation circuit. The measurement signal is filtered by the RC filter unit and amplified by the second operational amplifier U2, facilitating data acquisition by the measurement device.

[0036] The analog isolation circuit includes several operational amplifier units connected in series. The input of the first operational amplifier unit is electrically connected to the output of the second operational amplifier U2, and the output of the last operational amplifier unit outputs the voltage to be measured. The series connection of these operational amplifier units not only amplifies the measurement signal, reducing electromagnetic interference, but also converts the measurement signal into an analog quantity and inputs it into the measurement device, which uses the measurement signal to determine the junction temperature of the IGBT.

[0037] The measurement voltage output by the high-voltage isolation circuit is filtered in turn by the low-pass filter circuit and the analog isolation circuit to filter out high-frequency stray signals and electromagnetic interference. The measurement signal is then converted into an analog quantity through the analog isolation circuit and input into the measuring device, ensuring the accuracy of the measurement signal collected by the measuring device, thereby improving the accuracy of obtaining the junction temperature of the IGBT.

[0038] The detection circuit constructed in the present application includes a high-voltage isolation circuit, a low-pass filtering circuit, and an analog isolation circuit connected in series in sequence; the high-voltage isolation circuit outputs a measurement signal for measuring the junction temperature when the IGBT is turned on, and then the measurement signal passes through a low-pass filtering circuit to filter out high-frequency stray signals, thereby increasing the accuracy of the measurement signal. The measurement signal processed by the filter is then passed through an analog isolation circuit, which, on the one hand, reduces electromagnetic interference to the measurement signal, and on the other hand, converts the measurement signal into an analog quantity and inputs it into the measuring device, thereby ensuring the accuracy of the measurement signal collected by the measuring device, thereby improving the accuracy of obtaining the junction temperature of the IGBT.

[0039] like Figure 1 As shown, as one of the implementation methods, the RC filtering unit includes a second resistor R6, a first capacitor C1, and a second capacitor C2; wherein: the first end of the second resistor R6 is electrically connected to the output end of the first operational amplifier U1, and the second end of the second resistor R6 is electrically connected to the positive input end of the second operational amplifier U2; the first end of the first capacitor C1 is electrically connected to the output end of the first operational amplifier U1, and the second end of the first capacitor C1 is electrically connected to the negative input end of the second operational amplifier U2; the first end of the second capacitor C2 is electrically connected to the positive input end of the second operational amplifier U2, and the second end of the second capacitor C2 is grounded.

[0040] The cutoff frequency of the RC filter unit is determined by the second resistor R6, the first capacitor C1, and the second capacitor C2, as shown in the example:

[0041] in, f0 is the cutoff frequency, R is the resistance of the second resistor R6, and C is the capacitance of the first capacitor C1 and the second capacitor C2. The values ​​of R and C can be adjusted according to the frequency of the measurement signal to ensure that the cutoff frequency is compatible with the frequency of the measurement signal, thereby filtering high-frequency spurious signals and improving the accuracy of the measurement signal. In this embodiment, the measurement signal is a low-frequency signal, and the cutoff frequency can be set to 50 kHz.

[0042] In this embodiment, the resistance of the first resistor R5 in the RC filter unit is in the megaohm range, which can play a shunting role, making the current in the subsequent circuit relatively small, thereby protecting the subsequent operational amplifier.

[0043] like Figure 2 As shown, the present application provides a schematic diagram of an analog isolation circuit, which includes two operational amplifier units, and the two operational amplifier units are connected in series through a third resistor R24; wherein, the first operational amplifier unit includes: a third operational amplifier U3 and a fourth resistor R23 and a third capacitor C16 electrically connected to the non-inverting input terminal of the third operational amplifier U3; the output terminal of the third operational amplifier U3 is electrically connected to the third resistor R24, and the other end of the third capacitor C16 is grounded; the other end of the fourth resistor R23 is electrically connected to the output terminal of the second operational amplifier U2; the second operational amplifier unit includes: a fourth operational amplifier U4 and a fifth resistor R25 and a fourth capacitor C17 electrically connected to the non-inverting input terminal of the fourth operational amplifier U4; the output terminal of the fourth operational amplifier U4 outputs a measurement signal, and the other end of the fourth capacitor C17 is grounded; the other end of the fifth resistor R25 is electrically connected to the third resistor R24.

[0044] Specifically, the first operational amplifier unit is used to amplify the measurement signal, and the second operational amplifier unit is used to isolate the amplified measurement signal. For example, the inverting input (pin 3) of the third operational amplifier U3 is connected to the measurement signal (VA), and the non-inverting input (pin 1) is grounded, forming an inverting amplifier. Through the voltage divider function of the fourth resistor R23 and the third resistor R24, the first operational amplifier U3 amplifies the measurement signal and outputs it to the second operational amplifier unit. The power pins (pins 2 and 7) of the third operational amplifier U3 are connected to a +24V power supply to provide operating voltage.

[0045] For example, the fourth operational amplifier U4, serving as the amplifier in the second-stage operational amplifier unit, further amplifies the measurement signal and provides isolation, converting it into an analog output signal (VB). The inverting input (pin 6) of the fourth operational amplifier U4 is connected to the output of the third operational amplifier U3, while the non-inverting input (pin 5) is connected to ground via a fifth resistor R25, forming a voltage follower. A voltage follower has high input impedance and low output impedance, stabilizing the signal and providing good isolation. The power pins (pins 6 and 7) are connected to a +24V power supply to provide operating voltage.

[0046] A fourth resistor, R23, is used for voltage division and current limiting. The input measurement signal (VA) is appropriately attenuated before being fed into the inverting input of the third operational amplifier, U3. The fourth resistor, R23, and the input of the third operational amplifier, U3, form a simple voltage divider network, ensuring that the input signal is within the linear operating range of the operational amplifier. Furthermore, a third capacitor, C16, is connected between the non-inverting input of the third operational amplifier, U3, and ground to stabilize the DC bias at the non-inverting input (pin 1), filter out high-frequency noise, and ensure stable DC bias at the input.

[0047] The third resistor R24 ​​is connected between the inverting input terminal and the output terminal of the third operational amplifier U3 to determine the gain of the amplifier. The third resistor R24 ​​is used as a feedback resistor of the third operational amplifier U3 to set the amplification factor together with the fourth resistor R23.

[0048] The fifth resistor R25 serves as a bias resistor for the fourth operational amplifier U4. It is connected between the non-inverting input of the fourth operational amplifier U4 and ground, ensuring a stable DC bias at the non-inverting input (pin 5) of the fourth operational amplifier U4, ensuring that the fourth operational amplifier U4 operates within a suitable linear range. The fourth capacitor C17 serves as a filter capacitor, connected between the power supply pin of the fourth operational amplifier U4 and ground. It is used to filter out power supply noise at the power supply pins (pins 6 and 7) of the fourth operational amplifier U4, ensuring stable power supply for the fourth operational amplifier U4 and reducing the impact of power supply ripple on the signal.

[0049] In addition, a fifth capacitor C10 is included. The fifth capacitor C10 is connected between the output terminal of the third operational amplifier U3 and the ground. It serves as a filter capacitor to filter out high-frequency noise in the output signal of the third operational amplifier U3, further smooth the output signal, and improve signal quality.

[0050] The analog isolation circuit achieves signal amplification and isolation through two-stage operational amplifiers (third operational amplifier U3 and fourth operational amplifier U4), while using resistors and capacitors for voltage division, current limiting and filtering to ensure signal stability and reliability.

[0051] As one embodiment, the second diode D3 is a voltage stabilizing diode, and the reverse resistance of the second diode D3 is in the megohm level. D 3. The third diode D4 serves as a series-connected diode clamping the IGBT. The second diode D3 is implemented using a Zener diode. The Zener diode has a reverse breakdown voltage of approximately 3.2V, a reverse resistance of megohms, and a leakage current of μA. This ensures that the currents flowing through the first diode D1 and the fourth diode D2 are approximately equal. Furthermore, the first and fourth diodes D1 and D2 are of the same model, making the voltage drops across the first and fourth diodes D1 and D2 approximately equal, ensuring that no interference is caused with the voltage drop measurement during IGBT conduction.

[0052] By replacing the two diodes in series with a Zener diode and a diode, the error range of the operational amplifier output voltage Vout and the IGBT's Vce is reduced. Through actual tests, it is found that the measurement error of the measured electrical parameters does not exceed 0.5%, and the data acquisition frequency reaches 200KHz.

[0053] like Figure 3 As shown, based on the same application concept, this embodiment also provides a junction temperature online monitoring method based on the large current saturation voltage drop method, which is applied to any of the above-mentioned junction temperature online monitoring circuits based on the large current saturation voltage drop method, and the method includes the following steps.

[0054] Step S10: obtaining a preset temperature calibration coefficient; wherein the temperature calibration coefficient is used to characterize the corresponding relationship between the junction temperature of the IGBT and the change of the collected voltage.

[0055] Step S20: obtaining a measurement voltage and a corresponding measurement current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on.

[0056] Step S30: determining the junction temperature of the IGBT according to the measured voltage and the temperature calibration coefficient.

[0057] The preset temperature calibration coefficient represents the relationship between the IGBT's junction temperature and the sampled voltage. This method is implemented using a host computer. Before using the host computer system, you need to configure the host computer, which stores the junction temperature calculation formula. First, set the storage path for the sampling file (measured voltage and current). Then, enter the measured voltage and the preset temperature calibration coefficient into the junction temperature calculation formula to obtain the corresponding junction temperature.

[0058] In addition, before conducting the test, it is necessary to confirm whether the ADC sampling board used to collect the measurement signal is connected and fixed, and finally start sampling. The host computer system can display the collected voltage and current in real time, and obtain the junction temperature value of the measuring device (IGBT) through the data calculator based on the collected voltage, current, and preset temperature calibration coefficient.

[0059] In addition to connecting and fixing the ADC sampling board, it is also necessary to check whether the ADC sampling board and the components in the junction temperature online monitoring based on the large current saturation voltage drop method can work normally, whether there is a short circuit, and whether the current source cannot be open. You can first test whether the high-voltage isolation circuit on the ADC sampling board can normally output the IGBT's saturation voltage drop Vce, and then check in turn whether the cutoff frequency of the low-pass filter circuit corresponds to the frequency of the measurement signal.

[0060] like Figure 4 As shown, after obtaining the measured voltage and measured current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on, the method further includes the following steps.

[0061] Determine whether the measured voltage is the clamping voltage of the IGBT.

[0062] If so, the measured voltage and the corresponding measured current are discarded; if not, the step of determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient is performed.

[0063] If not, before determining the junction temperature of the IGBT according to the measured voltage and the temperature calibration coefficient, the method includes the following steps.

[0064] Determine whether the collected measured current is positive.

[0065] If so, the measured current and the corresponding measured voltage are discarded; if not, the step of determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient is performed.

[0066] In practical applications, to protect the monitoring circuit's downstream circuitry, the high-voltage isolation circuit outputs a clamping voltage when the device under test (IGBT) is off. The saturation voltage drop (measurement voltage) is output only when the device under test is on. Directly incorporating the clamping voltage into the junction temperature calculation formula will result in significant errors.

[0067] Therefore, when executing the above steps, the host computer needs to determine the state of the IGBT, specifically by measuring the voltage. If the measured voltage is the clamping voltage, the IGBT is in the off state, and this sampling data needs to be skipped (discarding the measured voltage and corresponding measured current). If so, the subsequent steps of determining the IGBT junction temperature based on the measured voltage and the temperature calibration coefficient are continued. This can avoid inaccurate junction temperature calculated using the junction temperature calculation formula, automatically eliminate the influence of the clamping voltage, and prevent its interference with the junction temperature calculation.

[0068] Furthermore, the current sampling value represents the bus current, not the current flowing directly through the device under test. Therefore, the host computer must perform additional calibration to ensure that the current value actually flowing through the device under test is used. Specifically, it determines whether the collected measured current is positive. If so, the sampled data is skipped (discarding the measured voltage and corresponding measured current). If not, the step of determining the IGBT junction temperature based on the measured voltage and temperature calibration coefficient is executed.

[0069] By judging the measured current, we ensure that the actual current value flowing through the device under test is used, ensuring the accuracy and reliability of the data during the monitoring process.

[0070] Through this series of logical judgments and data processing, the host computer can provide accurate junction temperature calculation results, ensuring the accuracy and reliability of the data during the monitoring process. The online monitoring circuit test method of this application is simple, the data display is intuitive, and the working status of the device under test can be easily determined.

[0071] Based on the same application concept, this embodiment also provides an online junction temperature monitoring system based on the large current saturation voltage drop method, including: any of the above-mentioned online junction temperature monitoring circuits based on the large current saturation voltage drop method and a host computer; the host computer uses any of the above-mentioned online junction temperature monitoring methods based on the large current saturation voltage drop method to measure the junction temperature of the IGBT.

[0072] The upper computer is used to measure the online monitoring circuit, measure the device under test and display the measurement results intuitively, which can easily determine the working status of the device under test.

[0073] In the above description of the present application, the terms "first" or "second" and the like used to refer to numbers or ordinal numbers are used only for convenience of description and are not to be understood as explicitly or implicitly indicating relative importance or implicitly indicating the number of the indicated technical features. At the same time, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, for example, two, three or more, etc., unless otherwise specifically defined.

[0074] Although multiple embodiments of the present application have been shown and described herein, it will be appreciated by those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art can conceive of many changes, modifications, and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The accompanying claims are intended to limit the scope of protection of the present application, and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A junction temperature online monitoring circuit based on a large current saturation voltage drop method, characterized in that: It includes a high-voltage isolation circuit, a low-pass filter circuit, and an analog isolation circuit connected in series; wherein: The high-voltage isolation circuit includes a first diode, a second diode, a third diode, a fourth diode connected in series, and an IGBT, and a first operational amplifier, wherein the anode of the first diode is electrically connected to a current source, the cathode of the third diode is grounded, the series connection end of the first diode and the second diode is electrically connected to the anode of the fourth diode, and the emitter of the IGBT is grounded; the inverting input end of the first operational amplifier is electrically connected to the anode of the first diode, the non-inverting input end of the first operational amplifier is electrically connected to the series connection end of the first diode and the second diode, and the non-inverting input end of the first operational amplifier is grounded via a first resistor; The low-pass filter circuit includes an RC filter unit and a second operational amplifier connected in series, the other end of the RC filter unit is electrically connected to the output end of the first operational amplifier, and the output end of the second operational amplifier is electrically connected to the input end of the analog isolation circuit; The analog isolation circuit includes a plurality of operational amplifier units connected in series, the input end of the first operational amplifier unit is electrically connected to the output end of the second operational amplifier, and the output end of the last operational amplifier unit outputs the voltage to be measured.

2. The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to claim 1, characterized in that: The RC filter unit includes a second resistor, a first capacitor, and a second capacitor; wherein: A first end of the second resistor is electrically connected to the output end of the first operational amplifier, and a second end of the second resistor is electrically connected to the non-inverting input end of the second operational amplifier; A first end of the first capacitor is electrically connected to the output end of the first operational amplifier, and a second end of the first capacitor is electrically connected to the negative input end of the second operational amplifier; A first end of the second capacitor is electrically connected to the non-inverting input terminal of the second operational amplifier, and a second end of the second capacitor is grounded.

3. The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to claim 2, characterized in that: The resistance of the first resistor is in the megohm level.

4. The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to claim 1, characterized in that: The two operational amplifier units are connected in series via a third resistor; wherein: The first operational amplifier unit includes: a third operational amplifier, a fourth resistor and a third capacitor electrically connected to the non-inverting input terminal of the third operational amplifier; an output terminal of the third operational amplifier electrically connected to the third resistor, and the other end of the third capacitor is grounded; the other end of the fourth resistor is electrically connected to the output terminal of the second operational amplifier; The second operational amplifier unit includes: a fourth operational amplifier and a fifth resistor and a fourth capacitor electrically connected to the non-inverting input terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier outputs the measurement signal, and the other end of the fourth capacitor is grounded; the other end of the fifth resistor is electrically connected to the third resistor.

5. The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to claim 1, characterized in that: The second diode is a voltage stabilizing diode.

6. The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to claim 5, characterized in that: The reverse resistance of the second diode is in the megohm level.

7. A junction temperature online monitoring method based on a large current saturation voltage drop method, characterized in that: Applied to the junction temperature online monitoring circuit based on the large current saturation voltage drop method according to any one of claims 1 to 6, the method comprising: Obtaining a preset temperature calibration coefficient; wherein the temperature calibration coefficient is used to characterize the corresponding relationship between the junction temperature of the IGBT and the change of the collected voltage; Obtaining a measurement voltage and a corresponding measurement current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on; The junction temperature of the IGBT is determined according to the measured voltage and the temperature calibration coefficient.

8. The method for online monitoring junction temperature based on the large current saturation voltage drop method according to claim 7, characterized in that: After obtaining the measured voltage and measured current output by the monitoring circuit when the IGBT in the monitoring circuit is turned on, the method further includes: Determining whether the measured voltage is the clamping voltage of the IGBT; If so, the measured voltage and the corresponding measured current are discarded; if not, the step of determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient is performed.

9. The method for online monitoring of junction temperature based on the large current saturation voltage drop method according to claim 8, characterized in that: If not, before determining the junction temperature of the IGBT based on the measured voltage and the temperature calibration coefficient, the method includes: Determine whether the collected measured current is positive; If so, the measured current and the corresponding measured voltage are discarded; If not, the step of determining the junction temperature of the IGBT according to the measured voltage and the temperature calibration coefficient is performed.

10. A junction temperature online monitoring system based on a large current saturation voltage drop method, characterized in that: include: The junction temperature online monitoring circuit based on the large current saturation voltage drop method according to any one of claims 1 to 6; A host computer, wherein the host computer measures the junction temperature of the IGBT using the online junction temperature monitoring method based on the large current saturation voltage drop method according to any one of claims 7 to 9.

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