A conduction voltage drop measurement circuit, a junction temperature monitoring method and a power converter

Abstract

The application relates to the technical field of semiconductor power device monitoring, and discloses a conduction voltage drop measurement circuit, a junction temperature monitoring method and a power converter.The conduction voltage drop measurement circuit comprises a first resistor, a second resistor, a third resistor, a first diode, a second diode, a third diode, an enhancement mode NMOS tube, an operational amplifier and a power supply.The application realizes high-voltage protection when the circuit is turned off and accurate measurement when the circuit is turned on through adaptive switch control of the enhancement mode NMOS tube, and the measurement function can be completed without external driving signals, so that the application has the advantages of simple structure, high measurement precision, fast response speed and high safety and can be widely applied to online health monitoring of IGBT devices in the power converter.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor power device monitoring, and in particular to a conduction voltage drop measurement circuit, a junction temperature monitoring method and a power converter. Background Art

[0002] Insulated-gate bipolar transistors (IGBTs), key components in power converters, are widely used in power systems, aerospace, electric vehicles, rail transit, and other fields. As one of the most fault-prone components in converters, approximately 55% of failures are caused by temperature-related factors. Accurately monitoring the junction temperature of power devices has become a key foundation for their lifespan prediction, health management, and reliability assessment.

[0003] Current direct measurement methods for monitoring IGBT module junction temperature have significant limitations. Thermistors can only be attached to the substrate surface of the IGBT module, resulting in significant deviations between the measured temperature and the actual junction temperature. While infrared cameras can achieve non-contact temperature measurement, their application typically requires opening the IGBT package, making them difficult to meet the actual needs of industrial sites.

[0004] The calculation process of the thermal impedance model method in the indirect measurement method is relatively complicated, and its accuracy is easily affected by the changes in the thermal characteristics of the IGBT device after aging and the fluctuations in the heat dissipation circuit parameters. It is difficult to establish a high-precision model for each IGBT separately, which limits its wide application in junction temperature measurement.

[0005] In contrast, methods based on temperature-sensitive electrical parameters have attracted widespread attention due to their high precision, fast response, and robust online monitoring capabilities. Among the currently available temperature-sensitive electrical parameters, on-state voltage drop has become one of the most popular due to its excellent overall performance in terms of sensitivity and response speed.

[0006] However, in practical applications, the collector-emitter voltage of an IGBT varies significantly between its on and off states. This requires the measurement circuit to withstand high voltages to ensure stable operation when the IGBT is off, while also providing high accuracy for measuring small voltage changes during the on state. Current IGBT on-state voltage drop online measurement circuits face significant challenges in achieving high-precision measurement and fast response, due to factors such as high-voltage isolation circuit design, voltage clamping circuit design, and overall circuit complexity. These issues have, to a certain extent, limited the widespread application of on-state voltage drop measurement circuits in practical operating conditions. Summary of the Invention

[0007] The purpose of the present invention is to provide a conduction voltage drop measurement circuit, a junction temperature monitoring method and a power converter, aiming to achieve automatic switching of functional modes according to the operating state of the IGBT without the need for external control signals, provide high-voltage protection when the IGBT is turned off, and provide accurate measurement when the IGBT is turned on.

[0008] To solve the above technical problems, the present invention provides a conduction voltage drop measurement circuit, comprising: a first resistor, a second resistor, a third resistor, a first diode, a second diode, a third diode, an enhancement mode NMOS transistor, an operational amplifier, and a power supply;

[0009] The collector of the IGBT device to be tested is connected to the first end of the first resistor and the first end of the second resistor;

[0010] The second end of the second resistor is connected to the source of the enhancement mode NMOS transistor;

[0011] The drain of the enhancement mode NMOS transistor is connected to the second end of the first resistor, the first end of the third resistor, the input end of the operational amplifier, the cathode of the first diode and the cathode of the second diode;

[0012] The anode of the second diode is connected to the cathode of the third diode;

[0013] The anode of the third diode is grounded and connected to the emitter of the IGBT device to be tested, the second end of the third resistor, the anode of the first diode and the negative electrode of the power supply;

[0014] The gate of the enhancement mode NMOS transistor is connected to the positive electrode of the power supply;

[0015] The inverting input terminal of the operational amplifier is connected to the output terminal, serving as the output terminal of the measurement circuit.

[0016] Optionally, a first capacitor is further included, wherein a first end of the first capacitor is connected to the emitter of the IGBT device to be tested, and a second end is connected to the gate of the enhancement mode NMOS tube and the positive electrode of the power supply.

[0017] Optionally, the withstand voltage of the first resistor is greater than the bus voltage, and the resistance of the second resistor is less than the resistance of the third resistor.

[0018] Optionally, the resistance of the first resistor is greater than 1 MΩ.

[0019] Optionally, the resistance of the second resistor is 1%-5% of the resistance of the third resistor.

[0020] Optionally, the voltage value of the power supply is greater than the on-state voltage drop of the IGBT device to be tested.

[0021] Optionally, the first diode is a Schottky diode.

[0022] Optionally, the second diode and the third diode are Zener diodes.

[0023] The present invention also provides a junction temperature monitoring method, which uses the above-mentioned on-state voltage drop measurement circuit to measure the on-state voltage drop of the IGBT, and determines the junction temperature of the IGBT based on the on-state voltage drop.

[0024] The present invention also provides a power converter, comprising an IGBT power device and the above-mentioned on-state voltage drop measurement circuit.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The on-state voltage drop measurement circuit provided by the present invention realizes adaptive switching of the circuit under different working states through circuit topology design. When the IGBT is turned off, the enhancement-type NMOS tube is in the off state, and the circuit can effectively limit the output voltage and clamp it to the set value, ensuring the safety of the measurement circuit; when the IGBT is turned on, the enhancement-type NMOS tube is turned on, and the circuit can quickly and accurately extract the on-state voltage drop of the IGBT. The entire working process does not require the introduction of the IGBT gate drive signal, which simplifies the circuit design and control complexity. Compared with existing measurement circuits, the present invention has significant advantages such as simple structure, high measurement accuracy, fast response speed, and high safety.

[0027] By rationally selecting resistor parameters and diode types, the present invention further optimizes circuit performance. The high voltage resistance and rational resistance configuration of the first resistor ensure safe and reliable operation of the circuit in high-voltage environments; the precise proportional relationship between the second and third resistors ensures measurement accuracy; the use of Schottky diodes improves the circuit's response speed; and the voltage clamping function of the Zener diode enhances the circuit's protection capabilities. This invention enables high-precision online measurement of IGBT on-state voltage drops at different bus voltage levels, providing an effective technical means for power device health management and fault prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is an overall circuit diagram of a conduction voltage drop measurement circuit according to an embodiment of the present invention;

[0029] Figure 2 is an equivalent circuit diagram of the circuit in the IGBT turn-on transient process in an embodiment of the present invention;

[0030] Figure 3 is an equivalent circuit diagram of the circuit in the embodiment of the present invention when the IGBT is in a steady-state conducting state;

[0031] Figure 4is an equivalent circuit diagram of the circuit in the IGBT off state in the embodiment of the present invention;

[0032] Figure 5 This is the first set of experimental waveforms of the circuit on the double-pulse test platform in the embodiment of the present invention;

[0033] Figure 6 This is the second set of experimental waveforms of the circuit in the embodiment of the present invention on the double-pulse test platform. DETAILED DESCRIPTION

[0034] The following, in conjunction with schematic diagrams, provides a more detailed description of a forward voltage drop measurement circuit, a junction temperature monitoring method, and a power converter according to the present invention. These schematic diagrams illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art may modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as generally known to those skilled in the art and is not intended to limit the present invention.

[0035] Based on the teachings of this specification, those skilled in the art may form new technical solutions by cross-combining different implementation methods without generating technical contradictions. Such variations should be deemed to fall within the scope of protection of this application.

[0036] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are greatly simplified and not to exact scale, and are provided solely for the purpose of assisting in the description of the embodiments of the present invention.

[0037] Example 1

[0038] Please refer to Figure 1 The embodiment of the present invention provides a conduction voltage drop measurement circuit comprising: a first resistor R1, a second resistor R2, a third resistor R3, a first diode D1, a second diode D2, a third diode D3, an enhancement type NMOS transistor M1, an operational amplifier AMP, and a power supply V o .

[0039] Specifically, the connection relationship between the measurement circuit and the IGBT device T1 to be measured is as follows:

[0040] The collector C of the IGBT device T1 to be tested is connected to one end of the first resistor R1 and one end of the second resistor R2; the other end of the second resistor R2 is connected to the source of the enhancement mode NMOS transistor M1; the drain of the enhancement mode NMOS transistor M1 is respectively connected to the other end of the first resistor R1, one end of the third resistor R3, the input end of the operational amplifier AMP, the cathode of the first diode D1, and the cathode of the second diode D2; the anode of the second diode D2 is connected to the cathode of the third diode D3; the anode of the third diode D3 is grounded and respectively connected to the emitter E of the IGBT device T1 to be tested, the other end of the third resistor R3, the anode of the first diode D1, and the power supply V o The gate of the enhancement mode NMOS tube M1 is connected to the power supply V o The inverting input terminal of the operational amplifier AMP is connected to the output terminal and serves as the output terminal of the measurement circuit.

[0041] Furthermore, the measurement circuit further includes a first capacitor C1, a first end of the first capacitor C1 is connected to the emitter E of the IGBT device T1 to be measured, and a second end is connected to the gate of the enhancement mode NMOS transistor M1 and the power supply V o positive electrode.

[0042] Furthermore, the first resistor R1 is a high-resistance high-voltage resistor. Specifically, the withstand voltage of the first resistor R1 is greater than the bus voltage V DC , the resistance of the first resistor R1 is greater than 1MΩ, and the resistance of the second resistor R2 is less than the resistance of the third resistor R3.

[0043] In this embodiment, the first resistor R1 is a high-resistance high-voltage resistant resistor, which not only ensures sufficient voltage resistance but also effectively reduces the static power consumption of the circuit.

[0044] The embodiments of the present invention address the technical problem of measurement circuits struggling to simultaneously withstand high voltages and achieve accurate measurements. By selecting a high-voltage-resistant first resistor, R1, the circuit is able to withstand bus voltage without breakdown when the IGBT is off. By configuring the resistance relationship between the second and third resistors, R2 and R3, adaptive impedance switching is achieved in the circuit's different operating states, providing an accurate voltage measurement path when the IGBT is on and an effective voltage clamping function when the IGBT is off.

[0045] The resistance of the second resistor R2 is 1%-5% of the resistance of the third resistor R3. Preferably, the resistance of the second resistor R2 is 1% of the resistance of the third resistor R3, ensuring the measurement accuracy and response speed of the circuit. The main function of the second resistor R2 is to suppress the large current surge generated by the enhancement mode NMOS transistor M1 during the switching transient process, thereby protecting the stable operation of the circuit.

[0046] Furthermore, the power supply V o The voltage value is greater than the on-state voltage drop of the IGBT device T1 to be tested, ensuring that the enhanced NMOS transistor M1 can achieve reliable switching control during circuit operation, solving the technical problem that traditional circuits require external drive signals.

[0047] In a specific example, the first diode D1 is a Schottky diode, which has a smaller junction capacitance and a faster switching speed. This choice effectively reduces the equivalent capacitance C of the measurement node S. Vs This improves the circuit's response speed and solves the technical issue of slow response in traditional circuits. The second diode D2 and the third diode D3 are Zener diodes with identical electrical characteristics. The stable reverse breakdown characteristics of the Zener diodes provide reliable voltage clamping for the circuit, effectively suppressing voltage spikes generated by switching transients and ensuring the safety of the measurement circuit.

[0048] The first capacitor C1 and the power supply V o Together they provide a stable bias voltage for the gate of the enhancement mode NMOS transistor M1. The first capacitor C1 plays a coupling and filtering role in the circuit, ensuring the stability of the gate voltage and improving the reliability of the circuit operation.

[0049] For details, please refer to Figure 2 - Figure 4 , the working principle of this embodiment is as follows:

[0050] Working mechanism of IGBT off state:

[0051] Please refer to Figure 4 When the IGBT device T1 is in the off state, its collector-emitter voltage V CE Equal to bus voltage V DC At this time, to ensure that the enhancement mode NMOS tube M1 is reliably turned off, the circuit parameters must meet the following conditions:

[0052] ;

[0053] Among them, R M_off is the equivalent resistance of the enhanced NMOS tube M1 when it is turned off, V M_this the threshold voltage of M1. Since the resistance of the first resistor R1 is much larger than that of other resistors, and when M1 is turned off, R M_off At this time, the equivalent resistance of the back-end circuit of the measurement node S is relatively small compared to the front-end circuit, and the input voltage of the operational amplifier AMP is clamped near the preset voltage value.

[0054] IGBT turn-on transient response mechanism:

[0055] Please refer to Figure 2 , during the IGBT conduction process, V CE Rapidly decreases, causing the voltage V at the measuring node S to S At this time, the enhanced NMOS tube M1 is still in the off state and can be modeled as taking into account the parasitic capacitance C ds Equivalent model of dV S The change of / dt forces the current to flow through the parasitic capacitance of M1, causing V S Rapidly decreases. When V S Drop to V o -V M_th When , M1 starts to conduct, realizing automatic switching of the circuit state.

[0056] IGBT conduction state measurement mechanism:

[0057] Please refer to Figure 3 When the enhancement mode NMOS tube M1 is turned on, the first resistor R1 has a large resistance, and the equivalent resistance R M_on Small, and the resistance of the second resistor R2 is only 1% of the resistance of the third resistor R3. At this time, the voltage V S Accurately reflect the on-state voltage drop of IGBT:

[0058] ;

[0059] This solves the technical problem that traditional circuits find it difficult to accurately measure small voltage changes in high-voltage environments.

[0060] IGBT turn-off transient protection mechanism:

[0061] When the IGBT device T1 under test switches from the on state to the off state, V CE Rapidly rises, measure the voltage V at node S S At the same time, it rises. Due to dV S The / dt change rate is fast, and the charging current will introduce a large voltage spike at point S. The voltage clamping function of the second diode D2 and the third diode D3 effectively suppresses this voltage spike, limiting it to a reasonable range and ensuring the safety of the measurement circuit.

[0062] For further information, please refer to Figure 5and Figure 6 , and further verified the circuit provided by the embodiment of the present invention on a double-pulse test experimental platform.

[0063] The experimental results show that the measurement circuit can quickly and accurately respond to the change of the on-state voltage drop of the IGBT, and realize the online tracking and high-precision measurement of its voltage value. The measurement waveform shows that the circuit output V out It can accurately track the conduction state of the IGBT and show good dynamic response characteristics during the switching transient process.

[0064] In summary, the on-state voltage drop measurement circuit described in this embodiment resolves the fundamental contradiction between high-voltage isolation and accurate measurement in traditional measurement schemes. Through adaptive switching control of the enhanced NMOS transistor M1, it can automatically switch operating modes according to the operating state of the IGBT: providing reliable high-voltage protection when the IGBT is off, clamping the voltage at the measurement point within a safe range; and achieving precise voltage measurement with mV accuracy when the IGBT is on, completely breaking away from the constraints of traditional circuits requiring external drive signals and significantly simplifying system complexity. Thanks to the fast switching characteristics of the first diode D1 and the appropriate resistor ratio design, the circuit's response time can reach the μs level, enabling rapid tracking of voltage changes during the IGBT switching process. The dual voltage clamping protection formed by the second diode D2 and the third diode D3 effectively suppresses voltage spikes generated by switching transients, ensuring stable operation of the measurement circuit in harsh electromagnetic environments. The high-resistance first resistor R1 ensures sufficient voltage resistance while keeping the circuit's static power consumption to an extremely low level. The overall solution has a small number of components, low cost, and is easy to integrate. It can be widely used in converter systems of different power levels and can be adapted to various application scenarios from low voltage to high voltage through simple parameter adjustments.

[0065] Example 2

[0066] An embodiment of the present invention provides a junction temperature monitoring method, which can use the on-state voltage drop measurement circuit described in the first embodiment to measure the on-state voltage drop of the IGBT, and determine the junction temperature of the IGBT based on the on-state voltage drop.

[0067] Specifically, the junction temperature monitoring method includes the following steps:

[0068] S1: Connect the IGBT device to be tested using the on-state voltage drop measurement circuit to establish a measurement system.

[0069] S2: During the normal operation of the IGBT, the output signal V of the measurement circuit is collected in real time. out ;

[0070] S3: Converting the measured on-state voltage drop value into a corresponding junction temperature value according to a pre-calibrated curve of the relationship between on-state voltage drop and junction temperature;

[0071] S4: Use the junction temperature monitoring results for IGBT health status assessment, fault prediction or protection control.

[0072] The relationship between the on-state voltage drop and junction temperature generally exhibits a negative temperature coefficient, meaning that the on-state voltage drop decreases as the junction temperature increases. For a typical IGBT device, the temperature coefficient is approximately -2mV / °C to -3mV / °C. Through precise temperature calibration, a junction temperature measurement accuracy of ±5°C can be achieved.

[0073] Furthermore, an embodiment of the present invention also provides a power converter, including an IGBT power device and the on-state voltage drop measurement circuit described in the first embodiment.

[0074] The on-state voltage drop measurement circuit described in the embodiments of the present invention can be widely used in various power converters, including but not limited to inverters, rectifiers, choppers, and AC speed regulators. In a power converter, the measurement circuit provides real-time on-state voltage drop monitoring for each IGBT power device. The monitoring results can be used to determine the degree of IGBT aging based on the changing trend of the on-state voltage drop. When the on-state voltage drop exceeds the normal range, a warning signal is promptly issued. When an abnormality is detected, protective action is triggered to prevent device damage.

[0075] In summary, the core innovation of the present invention lies in resolving the fundamental contradiction of traditional measurement circuits: how to accurately measure small voltage changes while withstanding high voltages. The present invention achieves this technological breakthrough by introducing an enhanced NMOS transistor as an adaptive switch, combined with a carefully designed resistor network and diode protection circuit. Experimental verification shows that the circuit can operate stably at different bus voltage levels, and its measurement accuracy and response speed are superior to existing technologies. It provides an ideal technical solution for online health monitoring and fault prediction of IGBT power devices, which will significantly improve the reliability and safety of power electronic equipment. It has important engineering value and broad application prospects.

[0076] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A conduction voltage drop measurement circuit, characterized in that: include: A first resistor, a second resistor, a third resistor, a first diode, a second diode, a third diode, an enhancement mode NMOS transistor, an operational amplifier, and a power supply; The collector of the IGBT device to be tested is connected to the first end of the first resistor and the first end of the second resistor; The second end of the second resistor is connected to the source of the enhancement mode NMOS transistor; The drain of the enhancement mode NMOS transistor is connected to the second end of the first resistor, the first end of the third resistor, the input end of the operational amplifier, the cathode of the first diode and the cathode of the second diode; The anode of the second diode is connected to the cathode of the third diode; The anode of the third diode is grounded and connected to the emitter of the IGBT device to be tested, the second end of the third resistor, the anode of the first diode and the negative electrode of the power supply; The gate of the enhancement mode NMOS transistor is connected to the positive electrode of the power supply; The inverting input terminal of the operational amplifier is connected to the output terminal, serving as the output terminal of the measurement circuit; in, ; Where V DC is the bus voltage, V o is the power supply voltage, R M_off is the equivalent resistance of the enhanced NMOS transistor when it is turned off, V M_th is the threshold voltage of the enhancement mode NMOS transistor, R1 is the resistance value of the first resistor, R2 is the resistance value of the second resistor, and R3 is the resistance value of the third resistor; The resistance of the first resistor is greater than 1 MΩ, and the resistance of the second resistor is 1%-5% of the resistance of the third resistor.

2. The on-state voltage drop measurement circuit according to claim 1, wherein: It also includes a first capacitor, a first end of which is connected to the emitter of the IGBT device to be tested, and a second end of which is connected to the gate of the enhancement mode NMOS tube and the positive electrode of the power supply.

3. The on-state voltage drop measurement circuit according to claim 1, wherein: The withstand voltage of the first resistor is greater than the bus voltage, and the resistance of the second resistor is less than the resistance of the third resistor.

4. The on-state voltage drop measurement circuit according to claim 1, wherein: The voltage value of the power supply is greater than the on-state voltage drop of the IGBT device to be tested.

5. The on-state voltage drop measurement circuit according to claim 1, wherein: The first diode is a Schottky diode.

6. The on-state voltage drop measurement circuit according to claim 1, wherein: The second diode and the third diode are Zener diodes.

7. A junction temperature monitoring method, characterized in that: The on-state voltage drop measurement circuit according to any one of claims 1 to 6 is used to measure the on-state voltage drop of the IGBT, and the junction temperature of the IGBT is determined according to the on-state voltage drop.

8. A power converter, characterized in that: The invention comprises an IGBT power device and the on-state voltage drop measurement circuit according to any one of claims 1 to 6.

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