IGBT loop stray inductance extraction method based on turn-on loss

Abstract

The invention belongs to the technical field of power electronics, and particularly relates to an IGBT loop stray inductance extraction method based on turn-on loss. The method comprises the following steps: S1, acquiring collector current data and collector-emitter voltage data between a t0 moment and a t1 moment in an IGBT opening process of a loop to be measured; the t0 moment is the moment when the current of the collector begins to rise in the IGBT turn-on process; the t1 moment is the moment when the collector current rises to the load current in the IGBT opening process; s2, calculating the IGBT turn-on loss according to the collector current data and the collector-emitter voltage data obtained in the S1; and S3, obtaining the stray inductance of the to-be-tested IGBT loop according to the IGBT turn-on loss obtained in the S2 and a pre-obtained corresponding relation between the stray inductance of the IGBT loop and the IGBT turn-on loss. According to the invention, the technical problem of inaccurate extraction result of the stray inductance extraction method in the prior art is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a method for extracting stray inductance of an IGBT loop based on turn-on loss. Background Art

[0002] In power electronic devices, the stray inductance of the commutation circuit and the di / dt in it work together, causing the switch device to withstand a very high induced voltage spike during the shutdown transient process, increasing the electrical stress of the device, increasing the system switching loss and electromagnetic interference, and at the same time causing the output voltage to contain a large number of high-order harmonics, affecting system performance. Therefore, it is necessary to accurately calculate the line stray inductance including the IGBT commutation circuit, among which the busbar stray inductance is the most critical.

[0003] At present, the methods for extracting stray inductance can be mainly divided into four categories: analytical method, numerical calculation method, direct measurement method and indirect measurement method.

[0004] The analytical method is generally only applicable to a very small number of specific regular conductors or DC busbars. However, for a commutation circuit composed of multiple sections of conductors and devices with different structures, its stray inductance is usually difficult to calculate.

[0005] The numerical calculation method analyzes and calculates the inductance and capacitance according to the geometric dimensions and material information of the object being measured. However, when the physical structure of the object being measured becomes complex, this method not only takes a long time to calculate, but also has poor convergence.

[0006] Direct measurement methods can be divided into two methods: time domain reflection measurement and frequency domain impedance measurement. The application scope of the time domain reflection method is limited by the complex experimental setup, special hardware and multi-step iteration process. The impedance measurement method is currently limited to single-port measurement between two terminals of the object to be measured. When the other terminals remain suspended, the inductive capacitance between the suspended terminals and the ground will affect the impedance measurement and introduce measurement errors.

[0007] The existing indirect measurement method is mainly based on the volt-ampere characteristic relationship of the inductor. According to the different methods of mathematical processing of the voltage and current waveforms obtained by measurement, the existing indirect measurement method can be divided into differential method and integral method. Among them, the differential method has high requirements on the current waveform, and the experimental waveform usually has high-frequency ripples, which makes it impossible to accurately obtain the current change rate.

[0008] The integration method overcomes the shortcoming of the differential method that it is very sensitive to the shape of the current waveform. However, due to the existence of stray resistance in the loop, the different selection of the integration interval of the integration method will also affect the extraction result of the stray inductance, resulting in inaccurate extraction results.

[0009] In summary, the existing stray inductance extraction method has the problem of inaccurate extraction results. Summary of the invention

[0010] The purpose of the present invention is to provide a method for extracting stray inductance of an IGBT loop based on turn-on loss, so as to solve the technical problem that the extraction results of the stray inductance extraction method in the prior art are inaccurate.

[0011] In order to solve the above technical problems, the present invention provides a technical solution for extracting stray inductance of an IGBT circuit based on turn-on loss: a method for extracting stray inductance of an IGBT circuit based on turn-on loss, the method comprising the following steps:

[0012] S1, obtaining the collector current data and collector-emitter voltage data between time t0 and time t1 during the IGBT turn-on process of the circuit to be tested; time t0 is the time when the collector current starts to rise during the IGBT turn-on process; time t1 is the time when the collector current rises to the load current during the IGBT turn-on process;

[0013] S2, calculate the IGBT turn-on loss based on the collector current data and collector-emitter voltage data obtained in S1;

[0014] S3, obtaining the stray inductance of the IGBT circuit to be tested according to the IGBT turn-on loss obtained in S2 and the correspondence between the IGBT circuit stray inductance obtained in advance and the IGBT turn-on loss.

[0015] The beneficial effect of the above technical solution is that the technical solution of the IGBT loop stray inductance extraction method based on turn-on loss of the present invention belongs to an improved invention. The present invention calculates the stray inductance based on the data from the moment when the collector current starts to rise to the moment when the collector current rises to the load current during the IGBT turn-on process. In this stage, the collector current change rate is large, and u ce The amplitude changes greatly, and the IGBT junction capacitance and its displacement current have little effect, so this stage is suitable for stray inductance extraction. By directly correlating the turn-on loss and stray inductance, a more accurate stray inductance estimation can be provided. The present invention solves the technical problem of inaccurate extraction results of stray inductance extraction methods in the prior art.

[0016] Furthermore, the pre-obtained corresponding relationship between the stray inductance of the IGBT loop and the turn-on loss of the IGBT is obtained by performing circuit analysis on an equivalent circuit of the IGBT loop.

[0017] Furthermore, the correspondence between the pre-obtained IGBT loop stray inductance and the IGBT turn-on loss is:

[0018]

[0019] Among them, L sis the stray inductance of the IGBT circuit, U dc is the power supply voltage, I L is the load current, t on1 is the duration from time t0 to time t1, P on is the IGBT turn-on loss.

[0020] Furthermore, the correspondence between the pre-obtained IGBT loop stray inductance and the IGBT turn-on loss is:

[0021]

[0022] Among them, L s is the stray inductance of the IGBT circuit, U dc is the power supply voltage, I L is the load current, t r For collector current from 10% I L Up to 90%I L Time required, P on is the IGBT turn-on loss.

[0023] Furthermore, S2 includes: performing data fitting on the collector current data and the collector-emitter voltage data obtained in S1 respectively; and calculating the IGBT turn-on loss according to the fitted data.

[0024] Furthermore, the data fitting method is the least squares method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A topological structure diagram of a double pulse test circuit of an embodiment of a method for extracting stray inductance of an IGBT loop based on turn-on loss of the present invention;

[0026] Figure 2 A linear waveform diagram of the IGBT turn-on transient process according to an embodiment of the IGBT loop stray inductance extraction method based on turn-on loss of the present invention;

[0027] Figure 3 It is a method flow chart of an embodiment of a method for extracting stray inductance of an IGBT loop based on turn-on loss according to the present invention;

[0028] Figure 4 It is a fitting waveform diagram of the collector-emitter voltage in the time period t0-t1 of an embodiment of the method for extracting stray inductance of an IGBT loop based on turn-on loss of the present invention;

[0029] Figure 5 It is a fitting waveform diagram of the collector current in the time period t0 to t1 of an embodiment of the method for extracting stray inductance of an IGBT loop based on turn-on loss of the present invention;

[0030] Figure 6This is the calculation result of the stray inductance at time t1 using different collector currents in the time period t0 to t1 of an embodiment of the IGBT loop stray inductance extraction method based on turn-on loss of the present invention. DETAILED DESCRIPTION

[0031] The present invention calculates the stray inductance based on the data from the moment when the collector current starts to rise to the moment when the collector current first rises to the load current during the IGBT opening process. In this stage, the collector current change rate is large, and u ce The amplitude changes greatly, and the IGBT junction capacitance and its displacement current have little effect, so this stage is suitable for stray inductance extraction. By directly correlating the turn-on loss and stray inductance, a more accurate stray inductance estimation can be provided. The present invention solves the technical problem of inaccurate extraction results of stray inductance extraction methods in the prior art.

[0032] Embodiment of the method for extracting stray inductance of IGBT loop based on turn-on loss:

[0033] Based on the analysis and comparison of various existing stray inductance extraction methods, the present invention sorts out multiple stages of the transient process of opening and closing the commutation circuit based on a double pulse test circuit. First of all, an obvious current change rate is a prerequisite for extracting stray inductance. Therefore, a time period with a large current change during the shutdown process should be selected. After analysis, this time period is from the moment when the collector current begins to drop rapidly to the moment when it decreases to the tail current. However, since the size and waveform of the tail current are affected by factors such as the shutdown time, rated current, and device temperature, it is impossible to accurately obtain the value, which brings errors to subsequent calculations. Therefore, the loss during the IGBT opening process is selected to extract the stray inductance, and the most favorable stage for the extraction of stray inductance during the opening transient process is found.

[0034] During the turn-on process of the IGBT, the speed of change of the current is hindered due to the presence of stray inductance, resulting in increased energy loss during the turn-on process. Therefore, by analyzing the IGBT turn-on loss, the influence of stray inductance can be inferred. In practical applications, due to the presence of factors such as signal noise, measurement error, and system nonlinearity, the traditional method may introduce certain errors. In contrast, the method based on IGBT turn-on loss can provide a more accurate estimation of the inductance value by directly correlating the turn-on loss and stray inductance. In addition, the method based on IGBT turn-on loss can extract and calculate the inductance value in real-time operation. By real-time monitoring and analyzing the turn-on loss during the switching process, the estimated value of the stray inductance can be obtained in real time. This is very useful for real-time control and fault diagnosis, and changes or abnormalities in the inductance value can be detected in time.

[0035] The IGBT loop stray inductance extraction method based on turn-on loss in this embodiment is based on Figure 1The equivalent circuit shown in FIG. 1 is implemented based on the equivalent circuit shown in FIG. 1 , in which the upper IGBT of the bridge arm is the control object, and the lower IGBT is reliably turned off, using only its anti-parallel diode. s is the stray inductance of the entire loop, and the test load is a resistive and inductive load.

[0036] A method flow chart of a method for extracting stray inductance of an IGBT loop based on turn-on loss in this embodiment is shown in FIG. Figure 3 As shown:

[0037] Step 1: Establish a double pulse test circuit model and use this circuit to measure the collector current i during the IGBT turn-on process c and collector-emitter voltage u ce variable.

[0038] Step 2: Analyze the current i of the IGBT during the turn-on process c Waveform and voltage u ce Waveform, such as Figure 2 As shown, the IGBT turn-on waveform is linearized and the turn-on process is divided into three stages. The stage that is most suitable for extracting stray inductance is selected. The selection basis is:

[0039] Stage t0~t1: Due to the combined effect of the loop stray inductance and the current change rate, a depression is generated, and the collector current change rate is large. The collector current i c Rapidly rise to the load current I L , and u ce The amplitude changes greatly, and the IGBT junction capacitance and its displacement current have little effect, so this stage is suitable for stray inductance extraction, where t0 is the collector current i c At the start of the rise, t1, the collector current i c To increase the load current I L time.

[0040] During the t1-t2 phase, the lower tube enters the reverse recovery phase at t1, and its reverse current i d Continue to increase, the reverse recovery current and collector current i c superposition, so that i c A current spike I max , this stage i c >i load The distribution of excess carriers in the diode is different from that when it remains in the on state, which has a certain impact on the commutation circuit.

[0041] During the period from t2 to t3, the reverse recovery process of the freewheeling diode is about to end, and the collector current begins to decrease. During this process, the IGBT terminal voltage further decreases, and the diode voltage increases at the same time, reaching a steady state at time t3. The diode voltage u dEqual to bus voltage U dc This stage is obviously affected by the sweeping and recombination of excess carriers in the diode and is not suitable for stray inductance extraction.

[0042] Based on the above analysis, the period from t0 to t1 is taken as the time period for extracting stray inductance.

[0043] Because the turn-on process is linearized when analyzing the turn-on loss, the collector current i c The rate of change of remains unchanged, and the rate of change in this stage has nothing to do with the current size, but only with the temperature. c The rising rate K i for:

[0044]

[0045] Among them, I L is the load current, t r For collector current from 10% I L Up to 90%I L The duration of the stage t0 to t1 is t on1 =1.25t r .

[0046] Step 3: Based on Figure 1 The circuit analysis of the topological circuit shown in the figure can obtain the collector-emitter voltage u during the period t0 to t1. ce , collector current i c The expression of turn-on loss and stray inductance can be used to derive the mathematical relationship between turn-on loss and stray inductance. ce and collector current i c The expression is:

[0047]

[0048] i c =K i t (3)

[0049] Among them, U dc is the power supply voltage, L s is the stray inductance of the IGBT circuit to be tested.

[0050] Step 4: Based on the measured collector-emitter voltage u during the period t0 to t1 during the IGBT turn-on process ce and collector current i c The waveform is fitted with a polynomial curve to obtain the voltage fitting function and the current fitting function expressions. The specific steps are as follows:

[0051] The data of collector-emitter voltage and collector current in the time period t0-t1 during the IGBT turn-on process are imported into Matlab, and the waveforms of voltage and current are fitted by the least square method based on polynomials. The fitting order is set to 4, and the fitting waveforms of voltage and current during the turn-on process are obtained, as shown in Figure 2. Figure 4 , Figure 5 As shown, the fitting function expressions of the collector-emitter voltage and collector current during the turn-on process are obtained.

[0052] Then integrate the product of the fitting function of voltage and current to obtain the turn-on loss P of the IGBT device. on , whose expression is:

[0053]

[0054] Among them, u ce (t) is the voltage fitting function, i c (t) is the current fitting function, t0 is the moment when the collector current starts to rise during the IGBT turn-on process, and t1 is the moment when the collector current first rises to the load current during the IGBT turn-on process.

[0055] Step 5: Substitute equations (2) and (3) into And simplifying it, we can get:

[0056]

[0057] The specific derivation process is as follows:

[0058] (1) The current i c Substituting the expression of (t) into the voltage u ce (t) In the expression:

[0059]

[0060] Simplifying further:

[0061]

[0062] (2) Calculate the power loss expression.

[0063] will u ce (t) and i c Substituting (t) into the power loss formula yields:

[0064]

[0065] Expand and decompose the integral:

[0066]

[0067] Separate the two integral terms:

[0068]

[0069] (3) Calculate each integral term.

[0070] The first integral term:

[0071]

[0072] Assume t0 = 0 and t1 = t r ,but:

[0073]

[0074] The second integral term:

[0075]

[0076] (4) Substitute the integral result into the power loss expression:

[0077]

[0078] Simplifying, we get:

[0079] P on =0.4U dc I L t r -0.1024L s I L 2 Further, the stray inductance L of the circuit to be tested can be obtained s The calculation formula is:

[0080]

[0081] Among them, U dc is the power supply voltage, I L is the load current, t on1 is the duration from time t0 to time t1, P on is the turn-on loss of the IGBT.

[0082] It should be noted that in actual calculations, the collector current can be approximately 10% I L The corresponding time is taken as t0, and the collector current is 90% I L The corresponding time is taken as t1, and the stray inductance L can be calculated as follows s :

[0083]

[0084] The turn-on loss P during the time period t0 to t1 is calculated by using formula (4). onSubstituting into equation (5), we can get the stray inductance value L s .

[0085] The following is a simulation example to further illustrate the IGBT loop stray inductance extraction method of the present invention.

[0086] A Matlab / Simulink simulation experiment platform was built for simulation verification. The simulation parameters are shown in Table 1.

[0087] Table 1 Basic parameters of simulation system

[0088]

[0089] The data of collector-emitter voltage and collector current in the time period t0-t1 of the IGBT turn-on process are imported into Matlab, and the waveforms of voltage and current are fitted by the least square method based on polynomials. The fitting order is set to 4, and the fitting waveforms of voltage and current in the turn-on process are obtained, as shown in Figure 2. Figure 4 , Figure 5 As shown, the fitting function expression of the collector-emitter voltage and collector current in this time period during the turn-on process is obtained, and it is substituted into formula (4) to calculate the turn-on loss as 0.2321mJ. Then it is substituted into formula (5) to obtain the stray inductance value at this time as 179nH. Then it is substituted into formula (5) to calculate the stray inductance value at this time. Figure 4 , Figure 5 With collector current i c 88A (88A is approximately 10% I L ) is taken as t0, the collector current i c 171.2A (171.2A is approximately 90% I L ) time is taken as t1.

[0090] In this embodiment, the collector current i c The moment of 88A is taken as t0, and the corresponding moments of different current values ​​in the time period of t0 to t1 are selected as t1 used in the actual calculation of stray inductance. The influence of selecting different t1 moments on the calculation results is analyzed. The calculation results are as follows Figure 6 shown.

[0091] Depend on Figure 6 It can be seen that during the time period t0-t1 of the IGBT turn-on process, no matter which t1 is selected as the time for calculating the stray inductance, the calculated stray inductance value is relatively stable, about 180nH, with little variation, which effectively verifies the accuracy of this solution.

[0092] The present invention has the following characteristics:

[0093] 1. By quantitatively analyzing the relationship between stray inductance and IGBT turn-on loss, the stray inductance value is calculated. Compared with the existing technology, the high requirements of the differential method on the current waveform, which leads to the problem of not being able to accurately obtain the current change rate, and the different selection of the integral interval of the integral method will also affect the extraction result of the stray inductance. The stray inductance value can be calculated in a more efficient way, thereby saving time and resource costs.

[0094] Second, the method based on IGBT turn-on loss is a non-invasive measurement method. It does not require circuit changes or the addition of additional sensors, so it will not affect or interfere with the normal operation of the system. This is very advantageous for systems that have been put into operation or for applications that require online monitoring and maintenance of the system.

[0095] 3. Traditional differential and integral methods usually require offline data processing and calculation, and cannot obtain the inductance value in real time. However, the method based on IGBT turn-on loss can estimate the inductance value in real time by monitoring the turn-on loss during the switching process in real-time operation. This is very useful for real-time control and fault diagnosis.

[0096] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments without creative work, or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for extracting stray inductance of an IGBT circuit based on turn-on loss, characterized in that: The method comprises the following steps: S1, obtaining the collector current data and collector-emitter voltage data between time t0 and time t1 during the IGBT turn-on process of the circuit to be tested; time t0 is the time when the collector current starts to rise during the IGBT turn-on process; time t1 is the time when the collector current rises to the load current during the IGBT turn-on process; S2, calculate the IGBT turn-on loss based on the collector current data and collector-emitter voltage data obtained in S1; S3, obtaining the stray inductance of the IGBT circuit to be tested according to the IGBT turn-on loss obtained in S2 and the correspondence between the IGBT circuit stray inductance obtained in advance and the IGBT turn-on loss.

2. The method for extracting stray inductance of an IGBT circuit based on turn-on loss according to claim 1, characterized in that: The correspondence between the pre-obtained stray inductance of the IGBT loop and the turn-on loss of the IGBT is obtained by performing circuit analysis on the equivalent circuit of the IGBT loop.

3. The method for extracting stray inductance of an IGBT circuit based on turn-on loss according to claim 1 or 2, characterized in that: The correspondence between the pre-obtained IGBT loop stray inductance and the IGBT turn-on loss is: Among them, L s is the stray inductance of the IGBT circuit, U dc is the power supply voltage, I L is the load current, t on1 is the duration from time t0 to time t1, P on is the IGBT turn-on loss.

4. The method for extracting stray inductance of an IGBT circuit based on turn-on loss according to claim 1 or 2, characterized in that: The correspondence between the pre-obtained IGBT loop stray inductance and the IGBT turn-on loss is: Among them, L s is the stray inductance of the IGBT circuit, U dc is the power supply voltage, I L is the load current, t r For collector current from 10% I L Up to 90%I L Time required, P on is the IGBT turn-on loss.

5. The method for extracting stray inductance of an IGBT circuit based on turn-on loss according to claim 1, characterized in that: S2 includes: Perform data fitting on the collector current data and collector-emitter voltage data obtained by S1 respectively; Calculate the IGBT turn-on loss based on the fitted data.

6. The method for extracting stray inductance of an IGBT circuit based on turn-on loss according to claim 5, characterized in that: The data fitting method is the least squares method.

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