IGBT junction temperature on-line monitoring circuit based on gate voltage falling time

Abstract

The application discloses an IGBT junction temperature online monitoring circuit based on gate voltage falling time, comprising a high-speed comparison unit, a pulse gating unit and a signal conversion unit; the high-speed comparison unit comprises an isolated input operational amplifier, a high-bit comparison unit, a low-bit comparison unit, input reference units CMPA and CMPB and a logic XOR gate unit; the pulse gating unit comprises a high-speed precision monostable multivibrator unit and a high-speed MOSFET gating unit; and the signal conversion unit comprises a diode clamped second-order RC low-pass detection unit and an isolated output operational amplifier. The falling time is taken as a temperature-sensitive electrical parameter to realize the junction temperature online monitoring of the IGBT, and the application is simple and easy to realize, has high linearity, small volume, low cost and high precision when applied to online monitoring, and has no influence on the main circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to an IGBT junction temperature online monitoring circuit based on gate voltage falling time. BACKGROUND

[0002] As a main power device in industrial applications, the insulated-gate bipolar transistor (IGBT) is widely used in power transmission, rail transportation, electric vehicles and renewable energy power generation. Industrial research on power devices shows that power devices are the devices with the highest failure probability in power electronic devices, accounting for about 31%, and the key factors causing the failure of power devices are temperature, humidity, vibration impact and pollutants, of which about 55% of the power device failures are caused by temperature factors. Therefore, temperature monitoring of power devices is the basis for their health management and optimal control.

[0003] At present, the main power device junction temperature monitoring methods can be summarized into four methods: physical contact measurement method, optical non-contact measurement method, thermal impedance model prediction method and thermal sensitive electrical parameter extraction method.

[0004] Since the internal micro-physical parameters of semiconductor physical devices have a one-to-one mapping relationship with the device temperature, the lifetime of the carrier increases with the increase of the junction temperature, and the mobility of the carrier decreases with the increase of the temperature. Therefore, the characteristics of such semiconductor materials affected by temperature will cause the external macroscopic electrical characteristics of the power device to be measured to show a temperature-related change trend. Such external electrical characteristic parameters affected by the internal junction temperature of the device are called thermal sensitive electrical parameters.

[0005] Common thermal sensitive electrical parameters include: saturation collector-emitter voltage (V ce(sat) ), collector-emitter voltage change rate (du CE / d t ), collector current change rate (di C / d t ), turn-on time / turn-on delay time (t on / t don ), etc.

[0006] However, the current IGBT junction temperature monitoring is mainly based on its conduction voltage drop, other methods have low applicability, and it is not convenient to realize online monitoring of the junction temperature. SUMMARY

[0007] In view of the deficiencies in the prior art, in order to realize online monitoring of the IGBT junction temperature, the application provides an IGBT junction temperature online monitoring circuit based on gate voltage falling time.

[0008] The application discloses an IGBT junction temperature online monitoring circuit based on gate voltage falling time.

[0009] The high-speed comparison unit comprises an isolated input operational amplifier, a high-bit comparison unit, a low-bit comparison unit, input reference units CMPA and CMPB and a logic XOR gate unit; the isolated input operational amplifier is coupled between an IGBT gate G and an IGBT emitter E, the high-bit comparison unit is coupled between an input reference end CMPA and an output end of the isolated input operational amplifier, the low-bit comparison unit is coupled between an input reference end CMPB and the output end of the isolated input operational amplifier, and the logic XOR gate unit is coupled between the high-bit comparison unit and the low-bit comparison unit.

[0010] The pulse gating unit comprises a high-speed precision monostable multivibrator unit and a high-speed MOSFET gating unit; the high-speed precision monostable multivibrator unit is coupled between an output end of the isolated input operational amplifier and a signal ground, and the high-speed MOSFET gating unit is coupled between an output end of the high-speed precision monostable multivibrator unit and an output end of the logic XOR gate unit.

[0011] The signal conversion unit comprises a diode clamped second-order RC low-pass detection unit and an isolated output operational amplifier; the diode clamped second-order RC low-pass detection unit is coupled between the high-speed MOSFET gating unit and the signal ground, and the isolated output operational amplifier is coupled to an output end of the diode clamped second-order RC low-pass detection unit.

[0012] The application further discloses an IGBT junction temperature online monitoring method based on gate voltage falling time.

[0013] Step 1: a time base sampling circuit based on the high-speed comparison unit is designed, a falling period waveform is obtained through the pulse gating unit, and the falling period is converted into a constant voltage signal through the signal conversion unit.

[0014] The high-speed comparison unit isolates the IGBT gate voltage through the isolated input operational amplifier, protects the safety of the IGBT, inputs the isolated IGBT signal into the high-bit comparison unit and the low-bit comparison unit, and compares the output of the isolated input operational amplifier with the input reference units CMPA and CMPB, respectively.

[0015] The pulse gating unit inputs the output of the isolated input operational amplifier to the high-speed precision monostable multivibrator unit, sets the RC value within the unit for timing reset, outputs a low level when the equivalent pulse at the IGBT turn-on time is generated, and outputs a high level when the equivalent pulse at the IGBT turn-off time is generated; the high-speed MOSFET gating unit is in the off state after receiving the low level from the high-speed precision monostable multivibrator unit, and in the on state after receiving the high level, outputting the equivalent pulse waveform at the turn-off time.

[0016] The signal conversion unit performs two low-pass filtering operations on the turn-off pulse signal input from the high-speed MOSFET gating unit through a diode-clamped second-order RC low-pass detection unit. At the same time, the clamping diode prevents the subsequent capacitor from discharging into the previous capacitor, thus converting the pulse waveform at the turn-off moment into a constant voltage waveform. The isolated output operational amplifier amplifies the output of the diode-clamped second-order RC low-pass detection unit to protect the circuit safety.

[0017] Step 2: Derive the mathematical expression for the gate voltage fall time and analyze its temperature-sensitive characteristics, and analyze the relationship between the gate voltage fall time and the changes in turn-off current, turn-off voltage and IGBT junction temperature.

[0018] Step 3: Acquire the gate voltage waveform signal, convert the gate voltage fall time into a voltage signal for processing, and obtain a mapping model from the gate voltage fall time to the IGBT junction temperature; compare with the three-dimensional mapping model of the IGBT junction temperature to realize online monitoring of the IGBT junction temperature.

[0019] In step 3, the sampling circuit outputs voltage V. sp With junction temperature T j Turn-off current I c and DC side voltage V dc The relationship between them is:

[0020]

[0021] Where a1, a2, ..., a 22 a 23 All are constant coefficients.

[0022] DC side voltage V dc Assuming a constant voltage, the junction temperature T can be obtained. j The monitoring model is as follows:

[0023] T j =x0V sp +x1I c +x2

[0024] Where x0, x1, and x2 are fitting coefficients.

[0025] IGBT junction temperature can be monitored on line by sampling gate drive voltage waveform.

[0026] The beneficial technical effect of the present application is:

[0027] The present application only uses the falling waveform of IGBT gate voltage off time, and takes the falling time as temperature-sensitive electrical parameter to realize IGBT junction temperature on-line monitoring. Compared with the existing temperature-sensitive electrical parameter method of IGBT, the method is simple and easy to realize. It has high linearity, small volume, low cost, high precision and no influence on main circuit when applied to on-line monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is an equivalent circuit diagram of IGBT cell structure.

[0029] Figure 2 It is a waveform partition diagram of IGBT off time.

[0030] Figure 3 It is a main circuit principle diagram.

[0031] Figure 4 It is a principle diagram of IGBT junction temperature on-line monitoring circuit based on gate voltage falling time of the present application.

[0032] Figure 5 It is a complex frequency equivalent circuit diagram of IGBT junction temperature on-line monitoring circuit based on gate voltage falling time of the present application.

[0033] Figure 6 It is the intermediate output result of IGBT junction temperature on-line monitoring circuit based on gate voltage falling time at different temperatures and the waveform comparison result of gate voltage V ge .

[0034] Figure 7 It is the output result of high bit comparison unit at different temperatures and the waveform comparison result of gate voltage V ge .

[0035] Figure 8 It is the output result of low bit comparison unit at different temperatures and the waveform comparison result of gate voltage V ge .

[0036] Figure 9 It is the fitting result of pulse width at IGBT off time and sampling circuit output voltage of IGBT junction temperature on-line monitoring circuit based on gate voltage falling time of the present application.

[0037] Figure 10 It is the fitting result of IGBT junction temperature on-line monitoring circuit based on gate voltage falling time of IGBT at different temperatures.

[0038] Figure 11The IGBT junction temperature online monitoring circuit based on gate voltage falling time of the application outputs results under different temperatures and different currents at 100V off voltage.

[0039] Figure 12 The IGBT junction temperature online monitoring circuit based on gate voltage falling time of the application outputs results under different temperatures and different currents at 100V off voltage.

[0040] Figure 13 The IGBT junction temperature online monitoring circuit based on gate voltage falling time of the application outputs results under different temperatures and different currents at 100V off voltage. DETAILED DESCRIPTION

[0041] The application will be further described in detail below in combination with the drawings and specific implementation methods.

[0042] The IGBT junction temperature online monitoring circuit based on gate voltage falling time of the application, comprising a high-speed comparison unit 1, a pulse gating unit 2 and a signal conversion unit 3.

[0043] The high-speed comparison unit 1 comprises an isolated input operational amplifier 1-i, a high-bit comparison unit 1-ii, a low-bit comparison unit 1-iii, input reference units CMPA and CMPB (1-iv) and a logic XOR gate unit 1-v; the isolated input operational amplifier 1-i is coupled between the IGBT gate G and the IGBT emitter stage E, the high-bit comparison unit 1-ii is coupled between the input reference end CMPA and the output end of the isolated input operational amplifier 1-i, the low-bit comparison unit 1-iii is coupled between the input reference end CMPB and the output end of the isolated input operational amplifier 1-i, and the logic XOR gate unit 1-v is coupled between the high-bit comparison unit 1-ii and the low-bit comparison unit 1-iii.

[0044] The pulse gating unit 2 comprises a high-speed precision monostable multivibrator unit 2-i and a high-speed MOSFET gating unit 2-ii; the high-speed precision monostable multivibrator unit 2-i is coupled between the output end of the isolated input operational amplifier 1-i and the signal ground, and the high-speed MOSFET gating unit 2-ii is coupled between the output end of the high-speed precision monostable multivibrator unit 2-i and the output end of the logic XOR gate unit 1-v.

[0045] The signal conversion unit 3 comprises a diode clamped second-order RC low-pass detection unit 3-i and an isolated output operational amplifier 3-ii; the diode clamped second-order RC low-pass detection unit 3-i is coupled between the high-speed MOSFET gating unit 2-ii and the signal ground, and the isolated output operational amplifier 3-ii is coupled to the output end of the diode clamped second-order RC low-pass detection unit 3-i.

[0046] The application discloses an IGBT junction temperature online monitoring method based on gate voltage falling time.

[0047] Step 1: a time-based sampling circuit based on a high-speed comparison unit 1 is designed, a falling time period waveform is obtained through a pulse gating unit 2, and a signal conversion unit 3 is used to convert the falling time period into a constant voltage signal.

[0048] The high-speed comparison unit 1 isolates the IGBT gate voltage through an isolated input operational amplifier 1-i, protects the safety of the IGBT, inputs the isolated IGBT signal into a high-bit comparison unit 1-ii and a low-bit comparison unit 1-iii, the high-bit comparison unit 1-ii and the low-bit comparison unit 1-iii compare the outputs of the isolated input operational amplifier 1-i with input reference units CMPA and CMPB (1-iv) respectively, and the comparison results are input into a logic exclusive OR gate unit 1-v to obtain equivalent pulse waveforms of the IGBT turn-on and turn-off processes respectively.

[0049] The pulse gating unit 2 inputs the output of the isolated input operational amplifier 1-i into a high-speed precision monostable multivibrator unit 2-i, sets the value of an internal RC for timing reset, outputs a low level when the equivalent pulse is generated at the IGBT turn-on moment, and outputs a high level when the equivalent pulse is generated at the IGBT turn-off moment, a high-speed MOSFET gating unit 2-ii is in an off state after receiving the low level of the high-speed precision monostable multivibrator unit 2-i, and is in an on state after receiving the high level, and outputs the turn-off moment equivalent pulse waveform.

[0050] The signal conversion unit 3 performs twice low-pass filtering on the turn-off pulse signal input by the high-speed MOSFET gating unit 2-ii through a diode clamping second-order RC low-pass detection unit 3-i, meanwhile, the clamping diode prevents the rear-stage capacitor from discharging to the front-stage capacitor, so that the turn-off moment pulse waveform is converted into a constant voltage waveform, and an isolated output operational amplifier 3-ii isolates and amplifies the output of the diode clamping second-order RC low-pass detection unit 3-i to protect the safety of the circuit.

[0051] Step 2: a mathematical expression of the gate voltage falling time is derived, and the temperature-sensitive characteristics, the change relationship between the gate voltage falling time and the turn-off current, the turn-off voltage and the IGBT junction temperature are analyzed.

[0052] Step 3: a gate voltage waveform signal is collected, the gate voltage falling time is converted into a voltage signal for processing, a mapping model from the gate voltage falling time to the IGBT junction temperature is obtained, and the IGBT junction temperature online monitoring is realized by comparing with an IGBT junction temperature three-dimensional mapping model.

[0053] The IGBT cell equivalent circuit structure is as shown in Figure 1As shown, these internal parasitic capacitances and resistances vary with junction temperature and cause the associated temperature-sensitive electrical parameters to change. Thus, the junction temperature can be extracted from the temperature-sensitive electrical parameters associated therewith.

[0054] The turn-off process is shown in the following five stages. Figure 2 As shown, the five stages are as follows.

[0055] The first stage (t0-t1): The time interval can be expressed as:

[0056]

[0057] The second stage (t1-t2): V ce starts to rise, C GC starts to decrease, and the displacement current I gc is generated at the same time. ce is small and C GC is large, the limited displacement current limits the discharge process, so V ce rises slowly. When V ce equals V ge , C GC drops sharply, and V ce rises rapidly.

[0058] The third stage (t2-t3): The time interval can be expressed as:

[0059]

[0060] The fourth stage (t3-t4): The time interval of the stage can be expressed as:

[0061]

[0062] The fifth stage (t4-t5): The IGBT is completely turned off, and the space charge region is established. However, due to the recombination of hole carriers, I c has a tailing effect, and the speed of its decline is determined by the lifetime of the carriers.

[0063] In the IGBT turn-off process, according to the V ge waveform, the gate voltage falling time t down =t4-t0 is determined.

[0064]

[0065] The BUCK circuit of the circuit adopted in the present application adopts an IGBT chip FF100R12KS of Infineon, and the circuit schematic diagram is as shown in Figure 3The gate voltage falling time is only determined by the gate drive voltage waveform, so in order to sample the gate drive circuit waveform, the IGBT junction temperature online monitoring circuit based on the gate voltage falling time is designed, as shown in Figure 4 The complex frequency domain equivalent circuit is shown in Figure 5 .

[0066] Figure 6 The intermediate output results of the IGBT junction temperature online monitoring circuit based on the gate voltage falling time at different temperatures are compared with the gate voltage V ge waveform. Figure 7 The high-bit comparison unit 1-ii output results at different temperatures are compared with the gate voltage V ge waveform. Figure 8 The low-bit comparison unit 1-iii output results at different temperatures are compared with the gate voltage V ge waveform. Therefore, it is proved that the IGBT junction temperature online monitoring circuit based on the gate voltage falling time designed by the application can extract the IGBT gate voltage waveform, and the gate voltage falling time at the turn-off time can be equivalent to the corresponding pulse waveform.

[0067] Figure 9 The pulse width of the IGBT junction temperature online monitoring circuit based on the gate voltage falling time at the turn-off time is compared with the sampling circuit output voltage fitting result. Therefore, it is proved that the output voltage of the IGBT junction temperature online monitoring circuit based on the gate voltage falling time designed by the application has a good linear relationship with the IGBT gate voltage falling time at the turn-off time.

[0068] Figure 10 The fitting graph of the sampling circuit output voltage and the junction temperature relationship experimental result under the condition of 400V / 40A. Under the turn-off voltage and current of 400V / 40A, the IGBT is heated by using a constant temperature heating table with a constant temperature gradient of 30-130℃, and experimental tests are carried out at each temperature gradient to verify the influence of the working junction temperature of the IGBT on the turn-off process. From Figure 6 It can be seen that under the condition of 400V / 40A, V sp has a linear relationship with the junction temperature T j . Therefore, it is proved that the output voltage of the IGBT junction temperature online monitoring circuit based on the gate voltage falling time designed by the application has a good linear relationship with the IGBT junction temperature.

[0069] Therefore, the relationship between the sampling circuit output voltage V sp and the junction temperature T j , the turn-off current I c and the DC side voltage V dc is:

[0070]

[0071] wherein a1, a2, ···, a 22 , a 23 are constant coefficients.

[0072] Since it is difficult to solve T sp directly from the expression of V j , a weight factor is set to ignore the polynomials with small impact factors. Meanwhile, for the convenience of subsequent experimental verification of the fitting accuracy of the junction temperature model, the DC side voltage V dc is regarded as a constant voltage, and the monitoring model of the junction temperature T j is obtained as follows:

[0073] T j = x0V sp + x1I c + x2

[0074] wherein x0, x1 and x2 are fitting coefficients.

[0075] Figure 11 The IGBT junction temperature online monitoring circuit output results based on the gate voltage falling time under different temperatures and different currents at the off voltage of 100V are shown in the figure. As shown in the figure, the error coefficient R 2 is 99.24%.

[0076] Figure 12 The three-dimensional fitting diagram of the IGBT junction temperature online monitoring circuit output results based on the gate voltage falling time and the IGBT junction temperature and off current is shown in the figure. Figure 13 The three-dimensional fitting diagram of the IGBT junction temperature online monitoring circuit output results based on the gate voltage falling time and the IGBT junction temperature and off voltage is shown in the figure. Therefore, by obtaining the test results of the IGBT under different voltage and current levels, the junction temperature monitoring model under any off condition is obtained by interpolation fitting according to the aforementioned junction temperature model. The experimental results of the proposed monitoring method are shown in Table 1.

[0077] Table 1 Experimental verification results

[0078]

[0079]

[0080] The data in Table 1 show that the gate voltage falling time model can be used for online measurement of the junction temperature, and the IGBT junction temperature online monitoring circuit based on the gate voltage falling time designed by the application can accurately extract and convert the gate voltage falling time, and the maximum error and error percentage are 3.3℃ and 4.5%, respectively. This means that the IGBT junction temperature online monitoring circuit based on the gate voltage falling time has excellent performance.

Claims

1. An IGBT junction temperature on-line monitoring circuit based on gate voltage falling time, characterized in that, The circuit comprises a high-speed comparison unit (1), a pulse gating unit (2) and a signal conversion unit (3); The high-speed comparison unit (1) comprises an isolated input operational amplifier (1-i), a high-bit comparison unit (1-ii), a low-bit comparison unit (1-iii), an input reference unit CMPA and CMPB (1-iv) and a logic XOR gate unit (1-v); the isolated input operational amplifier (1-i) is coupled between the IGBT gate G and the IGBT emitter E, the high-bit comparison unit (1-ii) is coupled between the input reference end CMPA and the output end of the isolated input operational amplifier (1-i), the low-bit comparison unit (1-iii) is coupled between the input reference end CMPB and the output end of the isolated input operational amplifier (1-i), and the logic XOR gate unit (1-v) is coupled between the high-bit comparison unit (1-ii) and the low-bit comparison unit (1-iii); The pulse gating unit (2) comprises a high-speed precision monostable multivibrator unit (2-i) and a high-speed MOSFET gating unit (2-ii); the high-speed precision monostable multivibrator unit (2-i) is coupled between the output end of the isolated input operational amplifier (1-i) and the signal ground, and the high-speed MOSFET gating unit (2-ii) is coupled between the output end of the high-speed precision monostable multivibrator unit (2-i) and the output end of the logic XOR gate unit (1-v); The signal conversion unit (3) comprises a diode-clamped second-order RC low-pass detection unit (3-i) and an isolated output operational amplifier (3-ii); the diode-clamped second-order RC low-pass detection unit (3-i) is coupled between the high-speed MOSFET gating unit (2-ii) and the signal ground, and the isolated output operational amplifier (3-ii) is coupled to the output end of the diode-clamped second-order RC low-pass detection unit (3-i).

2. An IGBT junction temperature on-line monitoring method based on gate voltage falling time, characterized in that, The IGBT junction temperature online monitoring circuit based on gate voltage falling time according to claim 1 comprises the following steps: Step 1: design a time-based sampling circuit based on the high-speed comparison unit (1), obtain the falling period waveform through the pulse gating unit (2), and convert the falling period into a constant voltage signal through the signal conversion unit (3); The high-speed comparison unit (1) isolates the IGBT gate voltage through the isolated input operational amplifier (1-i) to protect the safety of the IGBT, and inputs the isolated IGBT signal to the high-bit comparison unit (1-ii) and the low-bit comparison unit (1-iii); the high-bit comparison unit (1-ii) and the low-bit comparison unit (1-iii) compare the output of the isolated input operational amplifier (1-i) with the input reference unit CMPA and CMPB (1-iv) respectively; the comparison results are input to the logic XOR gate unit (1-v) to obtain the equivalent pulse waveform of the IGBT turn-on and turn-off process respectively. The pulse gating unit (2) inputs the output of the isolated input operational amplifier (1-i) to the high-speed precision monostable multivibrator unit (2-i), sets the value of the unit RC for timing reset, outputs low level when the equivalent pulse is generated at the IGBT opening moment, and outputs high level when the equivalent pulse is generated at the IGBT closing moment; the high-speed MOSFET gating unit (2-ii) is in the off state after receiving the low level of the high-speed precision monostable multivibrator unit (2-i), and is in the on state after receiving the high level, and outputs the off moment equivalent pulse waveform; The signal conversion unit (3) performs twice low-pass filtering on the off pulse signal input by the high-speed MOSFET gating unit (2-ii) through the diode clamped second-order RC low-pass detection unit (3-i), and the clamped diode makes the rear capacitor not discharge to the front capacitor, so that the off moment pulse waveform is converted into a constant voltage waveform; the isolated output operational amplifier (3-ii) isolates and amplifies the output of the diode clamped second-order RC low-pass detection unit (3-i) to protect the safety of the circuit; Step 2: derive the mathematical expression of the gate voltage falling time and analyze its temperature-sensitive characteristics, and analyze the change relationship between the gate voltage falling time and the off current, the off voltage and the IGBT junction temperature; Step 3: collect the gate voltage waveform signal, convert the gate voltage falling time into a voltage signal for processing, obtain the mapping model from the gate voltage falling time to the IGBT junction temperature, and compare with the IGBT junction temperature three-dimensional mapping model to realize the online monitoring of the IGBT junction temperature.

3. The IGBT junction temperature online monitoring method based on gate voltage falling time according to claim 2, characterized in that, The step 3 sampling circuit output voltage V sp The relationship between the junction temperature T j , the off current I c and the DC side voltage V dc is: wherein a1, a2, ···, a 22 , a 23 are constant coefficients; The DC side voltage V dc The junction temperature T j The monitoring model is: T j = x0V sp + x1I c + x2 Wherein, x0, x1 and x2 are fitting coefficients; By sampling the gate drive voltage waveform, the online monitoring of the IGBT junction temperature can be realized.

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