Resistor-based voltage-withstanding on-state voltage drop measurement circuit for junction temperature monitoring, and monitoring method

Abstract

Disclosed in the present invention are a resistor-based voltage-withstanding on-state voltage drop measurement circuit for junction temperature monitoring, and a monitoring method. The measurement circuit comprises: a high-resistance series high-voltage resistor RL; switching diodes D1 and D2; a low-voltage MOSFET M1; a phase inverter U1; a three-state gate U2; an RC delay circuit consisting of a resistor R1 and a capacitor C1; current-limiting resistors R2 and R3; auxiliary voltage sources VDD and VCC; an operational amplifier U3; and an isolation operational amplifier U4. The monitoring method comprises: designing an on-state voltage drop sampling circuit based on a high-resistance resistor, and performing parameter selection on the basis of an actual application scenario; measuring a collector current and on-state voltage drop model at different junction temperatures under offline conditions, so as to provide a calculation model for online monitoring; and under online conditions, performing online monitoring of junction temperature on the basis of the model obtained by means of performing testing under the offline conditions. The present invention has the advantages of being low cost, having high reliability, and adaptability to on-state voltage drop measurement at a high voltage and within a wide ambient temperature range.

Description

Resistive pressure-bearing on-state voltage drop measurement circuit and monitoring method for junction temperature monitoring Technical Field

[0001] The present invention belongs to the field of online monitoring of junction temperature of power devices, and in particular relates to a resistance-bearing-type on-state voltage drop measurement circuit and a monitoring method for junction temperature monitoring. Background Art

[0002] IGBTs (insulated-gate bipolar transistors) are the most widely used power semiconductor devices in power systems, widely employed in high-power conversion scenarios such as rail transit. IGBT reliability has always been a major constraint on improving converter reliability. According to statistics, over 33% of converter failures are caused by IGBTs. The lifespan and reliability of power semiconductor devices are primarily affected by average junction temperature and temperature fluctuations. Therefore, monitoring and controlling junction temperature is an effective method to improve IGBT lifespan.

[0003] Existing IGBT junction temperature monitoring methods fall into four main categories: built-in thermistor method, optical temperature measurement, thermal impedance network model method, and thermal parameter method. Among these methods, the thermistor method has a slow response speed, the thermistor is located far from the chip, and the measured results differ significantly from the actual IGBT junction temperature, making the resulting temperature less useful. Optical temperature measurement is expensive and requires destructive chip processing, so it is generally used in laboratory environments. The thermal impedance network method cannot directly obtain junction temperature information and is affected by aging, making it unsuitable for online measurement of IGBT junction temperature. Among these methods, thermal parameter methods have attracted considerable attention due to their high accuracy, fast response speed, and strong online monitoring capabilities.

[0004] Among currently available thermal parameters, on-state voltage drop is the most popular due to its excellent overall performance in sensitivity, response speed, and other aspects. It is also the only method currently used in practical engineering applications for online monitoring of IGBT junction temperature. Current on-state voltage drop measurements are divided into low-current and high-current measurements. Low-current on-state voltage drop measurement has become a standard measurement method and is widely used in various offline IGBT measurements due to its extremely high accuracy and the fact that the measured current does not interfere with the IGBT junction temperature. However, during actual converter online operation, the IGBT operates under high current and high voltage conditions. To achieve online monitoring of the IGBT junction temperature using on-state voltage drop, the on-state voltage drop online monitoring circuit must possess excellent high-voltage isolation capabilities and extremely high measurement accuracy.

[0005] At present, the on-line measurement circuit for on-state voltage drop is mainly used for measuring the on-state voltage drop of low-voltage IGBTs. The high-voltage isolation design and circuit reliability of the on-line measurement circuit for on-state voltage drop are important reasons that restrict the application of the measurement circuit in high-voltage occasions. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a resistance-bearing-type on-state voltage drop measurement circuit and monitoring method for junction temperature monitoring.

[0007] The present invention provides a resistance-bearing type conduction voltage drop measurement circuit for junction temperature monitoring, comprising a high-resistance series high-voltage resistor R L , switching diode D1 and switching diode D2, low voltage MOSFET (field effect transistor) M1, inverter U1, tri-state gate U2, RC delay circuit composed of resistor R1 and capacitor C1, current limiting resistor R2 and current limiting resistor R3, auxiliary voltage source VDD and VCC, operational amplifier U3, isolation operational amplifier U4. High resistance series high voltage resistor R L One end is connected to the collector of the IGBT, and the other end is connected to the anode of the switching diode D1. The cathode of the switching diode D1 is connected to the drain of the low-voltage MOSFET M1, and the source of the low-voltage MOSFET M1 is connected to the emitter of the IGBT; the anode of the switching diode D1 is connected in series with a high-value high-voltage resistor R L The connection point is the test point, which is connected to the input end of the operational amplifier U3 of the isolation part. The cathode of the switching diode D2 is connected to the test point, and the anode is connected to the power reference ground; the auxiliary voltage source VDD is connected to the cathode of the switching diode D1 through the current limiting resistor R3.

[0008] In the logic circuit, the input signal of the circuit comes from the IGBT control signal issued by the controller. The signal is inverted by an inverter U1, and then input to the input end of the three-state gate U2 after passing through a series RC delay circuit. The control end input signal of the three-state gate U2 is the control signal of the IGBT; after passing through the three-state gate U2, the control signal becomes an inverted control signal with a delay added to the falling edge of the signal. This control signal is ultimately used to control the switching of the low-voltage MOSFET M1.

[0009] In the circuit of the isolation part, the input signal of the circuit comes from the test point voltage v of the measurement part TP , the operational amplifier U3 is connected as a voltage follower, and its voltage is finally used for on-state voltage drop detection through an isolated operational amplifier U4.

[0010] In addition, the circuit also has output parasitic capacitance C from low voltage MOSFET M1. O , the junction capacitance C of the switching diode D1 and the switching diode D2 R , the input capacitance of the operational amplifier U3 and the PCB parasitic capacitance C S , voltage test point v TP are connected.

[0011] When the IGBT is turned on, the low-voltage MOSFET M1 is turned off according to the control signal. At this time, the switching diode D1 is in a reverse bias state, and the test point voltage v TP is the equivalent IGBT conduction voltage drop v CE-ON When the IGBT is turned off, the low-voltage MOSFET M1 is turned on and off according to the control signal. At this time, the switching diode D1 is in a forward biased state, and the high voltage between the collector and emitter of the IGBT is connected by a high-resistance series high-voltage resistor R L The voltage at the test point is clamped to the conduction voltage drop of the switching diode D1. During the entire process, only the high-resistance series high-voltage resistor R L The IGBT is subjected to high voltage during the shutdown process, and is not subjected to high voltage during the other periods; the control signal of the low-voltage MOSFET M1 is formed by the gate control signal of the IGBT after conditioning by the logic part.

[0012] The present invention provides an IGBT junction temperature online monitoring method based on a resistance-bearing voltage drop measurement circuit, comprising the following steps:

[0013] Step 1: Design based on high-value series high-voltage resistor R L The on-state voltage drop sampling circuit is designed and the parameters are selected according to the actual application scenario.

[0014] According to the actual device power level, select high resistance series high voltage resistor R with different resistance values L , limiting the power dissipation on the resistor to a fixed value, and using the power dissipation combined with the isolation voltage to calculate the high resistance series high voltage resistor R L The resistance value is:

[0015] Where P is the allowable power dissipation on the resistor, V CE is the voltage between the collector and emitter.

[0016] For the selection of switching diodes D1 and D2, any switching diode with a withstand voltage of about 90V and a rated current of mA level can meet the requirements.

[0017] For the selection of operational amplifier U3, the bandwidth is required to be above 1MHz, the input impedance is greater than 1000MΩ, the input capacitance is less than 4PF, and the input bias current level is at the nA level; for the isolation operational amplifier U4, it only needs to meet the system's requirements for isolation voltage.

[0018] For the parameter selection of the RC delay circuit, a delay is added to the low-voltage MOSFET M1 at the moment of the IGBT's turn-on. The delay time of the RC delay circuit is expressed as: T D =RC

[0019] The specific values ​​of the capacitor and resistor parameters can be calculated according to the formula.

[0020] Step 2: Measure the collector current i at different junction temperatures under offline conditions C The on-state voltage drop model provides a calculation model for online monitoring.

[0021] When IGBT works in the saturation region, the conduction voltage drop v CE-ON Expressed as:

[0022] Where m is the injection coefficient, k is the Boltzmann constant, and T j is the junction temperature, q is the charge, i C is the collector current, i S is the reverse saturation current, R N is the module package resistance of the IGBT module, R CH is the internal on-resistance of the IGBT.

[0023] Forward voltage drop v CE-ON Find the collector current i C The partial derivative of the conduction voltage drop v CE-ON Collector current i C The rate of change on is expressed as:

[0024] It can be seen that i C On-state voltage drop v CE-ON The rate of change of the collector current i C changes with the change of collector current i C In a small range of change, the rate of change is considered a constant, and the on-state voltage drop is based on the collector current i C It can be expressed as: v through piecewise linearization CE-ON (i C )=k n i C +V INT-n n=1,2...n

[0025] Among them, k n At different collector currents i C Within the range, the conduction voltage drop v CE-ON Collector current i C The rate of change of k CE At a certain collector current i C The specific value in the region, n represents different current ranges; V INT-n is the collector current i C The constant term of the expression in each range; at different collector currents i C In the range, k n and VINT-n The value of k is different; n , according to k CE Expression, when the collector current i C In a small range of variation, k n Considered to be related to the collector current i C It has nothing to do with the junction temperature T j Related constants.

[0026] Calculate k n , using the least squares method to calculate the conduction voltage drop v within a certain current range CE-ON and collector current i C Perform multiple sampling to calculate, expressed as:

[0027] Fitting coefficient R n 2 Expressed as:

[0028] Step 3: Conduct online monitoring of junction temperature based on the model obtained from offline testing under online conditions.

[0029] In the online monitoring experiment, a power cycling experiment based on a Buck circuit is used to verify the online monitoring effect of the proposed monitoring circuit and monitoring method on junction temperature. The Buck power cycling test bench dissipates heat from the IGBT through a heat sink. By changing the power of the heat sink, the IGBT temperature can be increased or decreased while the IGBT is running continuously.

[0030] The beneficial technical effects of the present invention are:

[0031] This invention utilizes a high-resistance series high-voltage resistor in conjunction with an auxiliary low-voltage device to achieve high-voltage isolation between the collector and emitter during IGBT off-time and to measure the on-state voltage drop during IGBT on-time. The proposed circuit offers the advantages of low cost, high reliability, and adaptability to on-state voltage drop measurement over high voltages and a wide range of ambient temperatures. Compared to existing circuits, it has greater potential for online measurement of IGBT junction temperature using on-state voltage drop in high-voltage applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a structural diagram of a resistance-bearing-type on-state voltage drop measurement circuit for junction temperature monitoring according to the present invention.

[0033] FIG2 is a circuit state diagram of the measurement circuit in the IGBT off state and on state.

[0034] Figure 3 shows the ideal waveforms of the key nodes of the measurement circuit.

[0035] Figure 4 shows the output characteristics of the IGBT at different temperatures and the rate of change of the on-state voltage drop versus the collector current at different currents.

[0036] Figure 5 shows the comparison between the actual output characteristic curve and the linearized output characteristic curve within the full current range.

[0037] FIG6 shows the junction temperature-current segment-on-state voltage drop versus current change rate model and the junction temperature-on-state voltage drop-current model.

[0038] Figure 7 is a flow chart of the junction temperature online monitoring strategy.

[0039] Figure 8 shows the waveform during the online monitoring of junction temperature.

[0040] Figure 9 shows the comparison between the monitoring results during the online monitoring of junction temperature and the measurement results of the infrared camera. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] A resistance-bearing type on-state voltage drop measurement circuit for junction temperature monitoring of the present invention is shown in FIG1 , which comprises a high-resistance series high-voltage resistor R L , switching diode D1 and switching diode D2, low voltage MOSFET M1, inverter U1, tri-state gate U2, RC delay circuit composed of resistor R1 and capacitor C1, current limiting resistor R2 and current limiting resistor R3, auxiliary voltage source VDD and VCC, operational amplifier U3, isolation operational amplifier U4. High resistance series high voltage resistor R L One end is connected to the collector of the IGBT, and the other end is connected to the anode of the switching diode D1. The cathode of the switching diode D1 is connected to the drain of the low-voltage MOSFET M1, and the source of the low-voltage MOSFET M1 is connected to the emitter of the IGBT; the anode of the switching diode D1 is connected in series with a high-value high-voltage resistor R L The connection point is the test point, which is connected to the input end of the operational amplifier U3 of the isolation part. The cathode of the switching diode D2 is connected to the test point, and the anode is connected to the power reference ground; the auxiliary voltage source VDD is connected to the cathode of the switching diode D1 through the current limiting resistor R3.

[0043] In the logic circuit, the input signal of the circuit comes from the IGBT control signal issued by the controller. The signal is inverted by an inverter U1, and then input to the input end of the three-state gate U2 after passing through a series RC delay circuit. The control end input signal of the three-state gate U2 is the control signal of the IGBT; after passing through the three-state gate U2, the control signal becomes an inverted control signal with a delay added to the falling edge of the signal. This control signal is ultimately used to control the switching of the low-voltage MOSFET M1.

[0044] In the isolation circuit, the input signal of the circuit comes from the test point voltage v of the measurement part. TP , the operational amplifier U3 is connected as a voltage follower, and its voltage is finally used for on-state voltage drop detection through an isolated operational amplifier U4.

[0045] In addition, the circuit also has output parasitic capacitance C from low voltage MOSFET M1. O , the junction capacitance C of the switching diode D1 and the switching diode D2 R , the input capacitance of the operational amplifier U3 and the PCB parasitic capacitance C S , connected to the test point.

[0046] When the IGBT is turned on, the low-voltage MOSFET M1 is turned off according to the control signal. At this time, the switching diode D1 is in a reverse bias state, and the test point voltage v TP is the equivalent forward voltage drop v CE-ON When the IGBT is turned off, the low-voltage MOSFET M1 turns it off and on according to the control signal. At this time, the switching diode D1 is in a forward biased state, and the high voltage between the collector and emitter of the IGBT is connected by a high-resistance series high-voltage resistor R L The voltage at the test point is clamped to the conduction voltage drop of the diode. During the whole process, only the high-resistance series high-voltage resistor R L The IGBT is subjected to high voltage during the shutdown process, and is not subjected to high voltage during the other periods; the control signal of the low-voltage MOSFET M1 is formed by the gate control signal of the IGBT after conditioning by the logic part.

[0047] High resistance series high voltage resistor R L It is the only high-resistance device used in this circuit, and the other auxiliary devices are all low-voltage devices. Using resistors for pressure bearing has the advantages of low cost, high reliability, and good parameter consistency. The other auxiliary devices are all low-voltage devices, which have excellent performance, good parameter consistency, and small parameter changes with temperature, so that the circuit as a whole can work in a wide range of ambient temperatures. At the same time, it is easier to ensure the consistency of performance of different measurement circuits during mass production. L The resistance value ranges from hundreds of kilo-ohms to several megohms. The resistance value is large and will not interfere with the normal operation of the IGBT.

[0048] The present invention provides an IGBT junction temperature online monitoring method based on a resistance-bearing voltage drop measurement circuit, comprising the following steps:

[0049] Step 1: Design a conduction voltage drop sampling circuit based on a high-resistance series high-voltage resistor and select parameters based on the actual application scenario.

[0050] Figure 2 shows the circuit state diagrams of the measurement circuit in the IGBT off state and on state. Figure 2(a) shows the circuit in high-voltage isolation mode, and Figure 2(b) shows the circuit in on-state voltage drop measurement mode.

[0051] The measurement circuit of the present invention uses the on-off control of the low-voltage MOSFET M1 to realize the forward and reverse bias control of the diode D1, thereby achieving the measurement of the conduction voltage drop and isolation from the high voltage. Figure 3 is a waveform diagram of the key nodes of the measurement circuit. Each signal corresponds to the signal in Figure 1. H and L represent the high and low levels in the logic circuit respectively, and V DC is the DC bus voltage, V GP is the high level of the IGBT drive circuit, which is 20V in this circuit, V GN It is the low level in the IGBT drive circuit. In this circuit, it is -8V. V miller is the Miller platform voltage. V TH is the threshold voltage of low voltage MOSFET M1, V RD is the voltage value of the auxiliary voltage source VDD, V ON is the forward voltage drop of switching diode D1. It takes time for the IGBT voltage to drop from the bus voltage to the forward voltage drop. To prevent this time from interfering with the circuit, a delay is added to the control signal of low-voltage MOSFET M1 at the IGBT's turn-on transient to prevent the high voltage from affecting the measurement. The specific delay time should be designed based on the actual voltage change time of the IGBT used to ensure that the voltage has completely dropped to the forward voltage drop within the delay period. It should also be noted that since the auxiliary voltage source VDD that forces the switching diode D1 to reverse bias is only slightly higher than the forward voltage drop, even if low-voltage MOSFET M1 does not switch, it will not affect the forward voltage drop measurement. However, if low-voltage MOSFET M1 does not turn on when the IGBT is turned off, the test point will be clamped to the voltage of the auxiliary voltage source VDD plus the diode forward voltage drop, thus affecting the circuit's response speed.

[0052] When the IGBT is in the on state, the low voltage MOSFET M1 is turned off, as shown in Figure 2(b). According to Kirchhoff's law, the test point voltage v TP and the circuit node voltage v D It can be expressed as:

[0053] Among them C R 、R L 、C S 、C O , R3 are the circuit parameters in Figure 1. RD is the voltage value of the voltage source VDD in FIG1 .

[0054] It can be seen that the test point voltage v TP Forward voltage drop v CE-ON It shows the first-order low-pass filtering characteristics, and the node voltage v D It is a first-order high-pass filter characteristic. Node voltage v D The voltage at the test point is v TP It shows high-pass filtering characteristics, and the voltage value V RD It shows low-pass filtering characteristics. Since the current limiting resistor R3 is only a current limiting resistor of several hundred ohms, and the voltage value of the voltage source VDD is V RD is a constant value. Therefore, it can be considered that the node voltage v D It can maintain a constant value during the entire low voltage MOSFET M1 off time, so the test point voltage v TP It can be equivalent to a forward voltage drop v CE-ON The first-order low-pass filtering link can be simplified as:

[0055] Since in actual devices, diodes, operational amplifiers, etc. have a certain amount of leakage current, when considering the leakage current, the test point voltage v TP The expression is:

[0056] where R J is the equivalent resistance of the diode leakage current.

[0057] According to the expression of node voltage, in the case of DC circuit breaker or resistive load, its conduction voltage drop is basically a constant value. For a constant conduction voltage drop, its error can be expressed as:

[0058] In actual converters, inductors are often indispensable passive components. In the case of inductive loads, the collector current i C is a ramp signal, and the corresponding on-state voltage drop is also approximately a ramp signal. The error can be expressed as:

[0059] It can be seen that due to the first-order low-pass filtering characteristics of the measurement circuit, when tracking a constant on-state voltage drop, the error only comes from the equivalent resistance caused by the diode leakage current. When tracking the on-state voltage drop of a ramp signal, since the first-order circuit link cannot complete the error-free tracking of the ramp signal, the measurement error is divided into two parts: the error caused by the diode leakage current and the error caused by circuit tracking.

[0060] Furthermore, according to the actual device power level, select high resistance series high voltage resistors R with different resistance values. L , due to the high resistance series high voltage resistor R LWhen the IGBT is turned off, it bears the bus voltage, so it is necessary to ensure that its power and withstand voltage have sufficient safety margin. According to actual needs, the power dissipation on the limiting resistor is a fixed value, and the high resistance series high voltage resistor R is calculated by combining the power dissipation with the isolation voltage. L The resistance value is:

[0061] Wherein, P is the allowable power dissipation of the resistor, which is selected as 4W in this embodiment. In practice, it can be adjusted according to the requirements of the circuit diagram and the heat dissipation conditions. CE is the voltage between the collector and emitter.

[0062] Furthermore, based on the above error analysis, the most important parameter indicators for the selection of switching diodes D1 and D2 are leakage current and junction capacitance C. R At the same time, the stability of various parameters to temperature is also a factor that affects the circuit performance, so the leakage current and junction capacitance C are required. R As small as possible, and the parameters should change as little as possible with temperature. In practice, switching diodes with a withstand voltage of around 90V and a rated current of mA can meet these requirements, so there is no need to make special requirements for the selection of switching diodes.

[0063] Furthermore, regarding the selection of operational amplifier U3, since tracking parameters are static, there are no strict requirements for the operational amplifier's bandwidth. However, its input impedance must be sufficiently large and its input bias current must be low. In practice, operational amplifier U3 is required to have a bandwidth above 1MHz, an input impedance greater than 1000MΩ, an input capacitance below 4pF, and an input bias current in the nanoamp range. As for the isolated operational amplifier U4, since operational amplifier U3 already functions as a voltage follower in the previous stage, it only needs to meet the system's isolation voltage requirements, with no special requirements for operational amplifier performance.

[0064] Furthermore, regarding the parameter selection of the RC delay circuit, since it takes a certain amount of time for the collector-emitter voltage of the IGBT to change from the bus voltage to the conduction voltage drop during the IGBT switching transient. At the moment of IGBT turn-on, the voltage across the collector and emitter of the IGBT drops from the bus voltage to the conduction voltage drop. In order to avoid the influence of the high voltage of the collector and emitter on the measurement, it is necessary to add a delay to the low-voltage MOSFET M1 at this time, so that the circuit starts tracking the conduction voltage drop only after the collector-emitter voltage of the IGBT drops to the conduction voltage drop. When the IGBT is turned off, since the control signal arrives earlier than the rise of the collector-emitter voltage, it will not interfere with the circuit at this time and no special processing is required. Figure 3 shows the waveforms of the working state of the circuit at the key nodes during the IGBT turn-on and turn-off process. The delay time of the RC delay circuit can be expressed as: TD =RC

[0065] In practice, the setting of this time is related to the voltage change time between the IGBT collector and emitter, and needs to be adjusted according to the IGBT switching speed. Generally, a setting of about 2us can fully meet the requirements. The specific values ​​of the capacitor and resistor parameters can be calculated according to the formula.

[0066] Step 2: Measure the collector current i at different junction temperatures under offline conditions C The on-state voltage drop model provides a calculation model for online monitoring.

[0067] It is generally believed that after the IGBT works in the saturation region, the conduction voltage drop v CE-ON It can be expressed as:

[0068] Where m is the injection coefficient, k is the Boltzmann constant, and T j is the junction temperature, q is the charge, i C is the collector current, i S is the reverse saturation current, R N is the module package resistance of the IGBT module, R CH is the internal on-resistance of the IGBT.

[0069] Forward voltage drop v CE-ON Find the collector current i C The partial derivative of the conduction voltage drop v CE-ON Collector current i C The rate of change on is expressed as:

[0070] It can be seen that the collector current i C On-state voltage drop v CE-ON The rate of change of i C changes with the change of collector current i C In a small range of change, the rate of change is considered a constant, and the on-state voltage drop is based on the collector current i C It can be expressed as: v through piecewise linearization CE-ON (i C )=k n i C +V INT-n n=1,2...n

[0071] Among them, k n At different collector currents i C Within the range, the conduction voltage drop v CE-ON Collector current i C The rate of change of k CE At a certain collector current i CThe specific value in the region, n represents different current ranges; V INT-n is the collector current i C The constant term of the expression in each range; at different collector currents i C In the range, k n and V INT-n The value of k is different; n , according to k CE Expression, when the collector current i C In a small range of variation, k n Considered to be related to the collector current i C Independent of junction temperature T j Related constants.

[0072] Based on the piecewise linearization in the previous analysis, calculate k n The basic principle can be expressed as:

[0073] In practical applications, noise is inevitable. To enhance the anti-interference capability, the least square method is used to calculate the conduction voltage drop v within a certain current range. CE-ON and collector current i C Perform multiple sampling to calculate, expressed as:

[0074] Fitting coefficient R n 2 Expressed as:

[0075] Figure 4 shows the output characteristics of the IGBT at different temperatures and the on-state voltage drop versus collector current i at different currents. C It can be seen that the on-state voltage drop of IGBT has obvious positive temperature coefficient area and negative temperature coefficient area under different currents, and the turning point of the two is about 45A. C The rate of change shows a positive temperature coefficient over the entire current range and remains basically stable at high currents.

[0076] Test point voltage v TP The real waveform and linearized waveform in the full current range are shown in Figure 5. It can be seen that the collector current i C The waveform is divided into three stages: low current (5A-30A), medium current (30A-60A), and high current (greater than 60A). In the low current stage, every 5A is set as a current interval, in the medium current stage, every 10A is set as a current interval, and in the high current stage, every 20A is set as a current interval. It can be seen that the linearized waveform has a good description effect.

[0077] Figure 6 shows the junction temperature-current segment-conduction voltage drop to current change rate model and the junction temperature-conduction voltage drop-current model. In the inductive load, the conduction voltage drop v CE-ON And the test point voltage v TP There is a stable error, so k is used n As a thermal parameter. It can be seen that in the small current range, k n is much larger than in the high current range, where k n When dividing the current range, the current range needs to be very narrow in low currents and can be wider in high currents.

[0078] Step 3: Conduct online monitoring of junction temperature based on the model obtained from offline testing under online conditions.

[0079] Figure 7 shows the flow chart of the junction temperature online monitoring strategy. Since there is a large ripple interference in the circuit in the actual process, the fitting coefficient R is used to determine the 2 This can improve the reliability of data and thus the accuracy of monitoring.

[0080] In the online monitoring experiment, a power cycle experiment based on the Buck circuit was used to verify the online monitoring effect of the proposed monitoring circuit and monitoring method on the junction temperature. The Buck power cycle test bench dissipates heat from the IGBT through a heat sink, and by changing the power of the heat sink, the IGBT is heated up and cooled down while the IGBT is running continuously. In the present invention, the IGBT is set to a cycle of 60s, with 40s for heating and 20s for cooling. Figure 8 shows the waveform during the online monitoring of the junction temperature, and Figure 9 shows the comparison between the monitoring results and the measurement results of the infrared camera during the online monitoring of the junction temperature. It can be seen that the online monitoring strategy has a good online monitoring effect on the junction temperature, and the error of the monitored temperature does not exceed 3.5°C.

Claims

1. A resistance-bearing pressure-type on-state voltage drop measurement circuit for junction temperature monitoring, characterized in that: Contains high resistance series high voltage resistor R L , switching diode D1 and switching diode D2, low voltage MOSFET M1, inverter U1, tri-state gate U2, RC delay circuit composed of resistor R1 and capacitor C1, current limiting resistor R2 and current limiting resistor R3, auxiliary voltage source VDD and VCC, operational amplifier U3, isolation operational amplifier U4; high resistance series high voltage resistor R L One end is connected to the collector of the IGBT, and the other end is connected to the anode of the switching diode D1. The cathode of the switching diode D1 is connected to the drain of the low-voltage MOSFET M1, and the source of the low-voltage MOSFET M1 is connected to the emitter of the IGBT; the anode of the switching diode D1 is connected in series with a high-value high-voltage resistor R L The connection point is the test point, which is connected to the input terminal of the operational amplifier U3 of the isolation part. The cathode of the switching diode D2 is connected to the test point, and the anode is connected to the power reference ground. The auxiliary voltage source VDD is connected to the cathode of the switching diode D1 through the current limiting resistor R3. In the logic circuit, the circuit's input signal comes from the IGBT control signal sent by the controller. The signal is inverted by an inverter U1 and then input to the input of a tri-state gate U2 after passing through a series RC delay circuit. The control input signal of the tri-state gate is the IGBT control signal. After passing through the tri-state gate U2, the control signal becomes an inverted control signal with a delay added to the falling edge of the signal. This control signal is ultimately used to control the switching of the low-voltage MOSFET M1. In the isolated circuit, the input signal comes from the test point voltage of the measurement part. The operational amplifier U3 is connected as a voltage follower, and its voltage is finally used for on-state voltage drop detection through an isolated operational amplifier. In addition, the circuit also has output parasitic capacitance C from low voltage MOSFETM1 O , the junction capacitance C of D1 and D2 R , the operational amplifier input capacitance and the PCB parasitic capacitance C S , connected to the test point.

2. The resistance-bearing-type on-state voltage drop measurement circuit for junction temperature monitoring according to claim 1, characterized in that: When the IGBT is turned on, the low-voltage MOSFET M1 is turned off according to the control signal. At this time, the switching diode D1 is in a reverse bias state, and the test point voltage v TP is the equivalent forward voltage drop v CE-ON When the IGBT is turned off, M1 turns it off and on according to the control signal. At this time, the switching diode D1 is in a forward biased state, and the high voltage between the collector and emitter of the IGBT is connected by a high-resistance series high-voltage resistor R L The voltage at the test point is clamped to the conduction voltage drop of the diode. During the whole process, only the high-resistance series high-voltage resistor R L The IGBT is subjected to high voltage during the shutdown process, and does not undergo high voltage during the other periods; the control signal of the low-voltage MOSFET M1 is formed by the gate control signal of the IGBT through conditioning by the logic part.

3. An IGBT junction temperature online monitoring method based on the resistance-bearing pressure-type on-state voltage drop measurement circuit according to claim 1, characterized in that: The following steps are involved: Step 1: Design a conduction voltage drop sampling circuit based on a high-resistance series high-voltage resistor and select parameters according to the actual application scenario; According to the actual device power level, select high resistance series high voltage resistor R with different resistance values L , limiting the power dissipation on the resistor to a fixed value, and using the power dissipation combined with the isolation voltage to calculate the high resistance series high voltage resistor R L The resistance value is: Where P is the allowable power dissipation on the resistor, V CE is the voltage between the collector and emitter; For the selection of switching diodes D1 and D2, switching diodes with a withstand voltage of about 90V and a rated current of mA level meet the requirements; The operational amplifier U3 must have a bandwidth of 1 MHz or higher, an input impedance greater than 1000 MΩ, an input capacitance less than 4 pF, and an input bias current in the nA range. The isolation operational amplifier U4 must only meet the system's isolation voltage requirements. Regarding the parameter selection of the RC delay circuit, a delay is added to the low-voltage MOSFET M1 at the moment the IGBT is turned on. The delay time of the RC delay circuit is expressed as: T D =RC The specific values of the capacitor and resistor parameters can be calculated according to the formula; Step 2: Measure the collector current and on-state voltage drop model at different junction temperatures under offline conditions to provide a calculation model for online monitoring; When IGBT works in the saturation region, the conduction voltage drop v CE-ON Expressed as: Where m is the injection coefficient, k is the Boltzmann constant, and T j is the junction temperature, q is the charge, i C is the collector current, i S is the reverse saturation current, R N is the module package resistance of the IGBT module, R CH is the internal on-resistance of the IGBT; Forward voltage drop v CE-ON Find the collector current i C The partial derivative of the conduction voltage drop v CE-ON Collector current i C The rate of change on is expressed as: It can be seen that the collector current i C On-state voltage drop v CE-ON The rate of change of the collector current i C changes with the change of collector current i C In a small range of change, the rate of change is considered a constant, and the on-state voltage drop is based on the collector current i C It can be expressed as follows through piecewise linearization: v CE-ON (i C )=k n i C +V INT-n n=1,2...n Among them, k n At different collector currents i C Within the range, the conduction voltage drop v CE-ON Collector current i C The rate of change of k CE At a certain collector current i C The specific value in the region, n represents different current ranges; V INT-n is the collector current i C The constant term of the expression in each range; at different collector currents i C In the range, k n and V INT-n The value of k is different; n , according to k CE Expression, when the collector current i C In a small range of variation, k n Considered to be related to the collector current i C It has nothing to do with T j Related constants; Calculate k n , using the least squares method to calculate the conduction voltage drop v within a certain current range CE-ON and collector current i C Perform multiple sampling to calculate, expressed as: Fitting coefficient R n 2 Expressed as: Step 3: Conduct online monitoring of junction temperature based on the model obtained from offline testing under online conditions. In the online monitoring experiment, a power cycling experiment based on a Buck circuit is used to verify the online monitoring effect of the proposed monitoring circuit and monitoring method on junction temperature. The Buck power cycling test bench dissipates heat from the IGBT through a heat sink. By changing the power of the heat sink, the IGBT temperature can be increased or decreased while the IGBT is running continuously.

Images