CN112464443A - Calculation method for IGBT junction temperature fluctuation of power electronic converter - Google Patents

Calculation method for IGBT junction temperature fluctuation of power electronic converter Download PDF

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CN112464443A
CN112464443A CN202011239155.2A CN202011239155A CN112464443A CN 112464443 A CN112464443 A CN 112464443A CN 202011239155 A CN202011239155 A CN 202011239155A CN 112464443 A CN112464443 A CN 112464443A
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葛兴来
张艺驰
肖秀陈
冯晓云
苟斌
宋文胜
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Abstract

The invention discloses a calculation method for IGBT junction temperature fluctuation of a power electronic converter, which specifically comprises the following steps: collecting converter-level variables required by calculating power loss, performing Fourier decomposition on output current at an alternating current side, and acquiring a current expression flowing through the analyzed IGBT; respectively calculating the switching loss and the conduction loss corresponding to the current peak value of the alternating current side, and further obtaining the power loss of the IGBT in the whole fundamental wave period; deducing a junction temperature fluctuation expression in a fundamental wave period by combining a Foster thermal network model, and deriving the junction temperature fluctuation expression to obtain maximum and minimum junction temperature occurrence time points; and calculating the maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to the junction temperature value at the moment and the component value of junction temperature fluctuation at the end of the fundamental wave period. The invention can realize the rapid calculation of the junction temperature fluctuation of the IGBT, and the calculation result is accurate, comprehensive and reliable.

Description

Calculation method for IGBT junction temperature fluctuation of power electronic converter
Technical Field
The invention belongs to the field of reliability analysis and state monitoring of a power electronic converter, and particularly relates to a calculation method for IGBT junction temperature fluctuation of the power electronic converter.
Background
In the last decades, although the industry has been working on power electronic converters with higher efficiency and lower cost, reliability problems have been emerging and become more and more important, since the large amount of unscheduled maintenance of power electronic converters has become one of the main obstacles to reducing energy costs. Meanwhile, in order to improve the competitiveness of the power electronic converter, how to reduce the design margin while meeting the reliability target becomes one of the challenges. An insulated gate bipolar converter (igbt) is known as a 'CPU' of the power electronic converter as a core component of the power electronic converter, and the degree of reliability of the igbt is important for the reliability of the power electronic converter. The reliability of the IGBT is closely related to junction temperature fluctuation, and researches show that: the lifetime of the IGBT will be reduced by half for every 10 ℃ increase in junction temperature fluctuation. Therefore, junction temperature fluctuation calculation of the IGBT is crucial to reliability evaluation of the power electronic converter and operation state monitoring of the converter.
In recent years, some IGBT junction temperature fluctuation calculation methods have been proposed. Zhang Yi, Wang Huai et al propose a thermal modeling simplification method suitable for the periodic power loss of a modular multilevel inverter, namely, a semi-sinusoidal loss curve is used for converting the irregular loss task surface of the IGBT and carrying out discretization equivalence, so that the junction temperature fluctuation of the IGBT is calculated more accurately. J.j.nelson, g.venkataraman et al convert both the power loss function and the thermal network model into the frequency domain, and then calculate the IGBT junction temperature based on frequency domain analysis. Factors such as a modulation strategy, a power factor and the like are considered in the calculation of the IGBT power loss drawn by the motor by M.Ouhab, Z.Khatir and the like, so that the calculation precision of junction temperature is improved. In the case of Wangxiping, Li Shi just et al, the original loss is equalized by using the rectangular pulse loss, and then junction temperature iterative calculation is performed by combining a thermal network, so that the junction temperature can be calculated quickly.
In the currently proposed method for calculating junction temperature fluctuation of the IGBT, a half-sine curve is mostly adopted for power loss calculation for equivalence, so that loss calculation is inaccurate, and errors are introduced by further feeding junction temperature calculation; in addition, the current reliability analysis life model mainly focuses on junction temperature fluctuation, and only needs to calculate the maximum and minimum junction temperature values, so that junction temperature estimation at other time points causes a large amount of calculation redundancy in iterative calculation, and the calculation time and calculation amount of junction temperature are increased seriously.
Disclosure of Invention
In order to solve the problems, the invention discloses a calculation method for IGBT junction temperature fluctuation of a power electronic converter.
The invention discloses a calculation method for IGBT junction temperature fluctuation of a power electronic converter, which comprises the following steps of:
step 1: acquiring converter-level variables required by calculating power loss, performing Fourier decomposition on the phase current output by the alternating current side, and acquiring an expression of the current flowing through the IGBT, wherein the expression specifically comprises the following steps:
for phase currents, performing a fourier decomposition can be expressed as:
Figure BDA0002767791540000021
in the formula: c. C0Is a DC component value, ck，dkPeak values of sine and cosine components, respectively, k is the harmonic order, w is the fundamental angular frequency, and w is 2 pi f0，f0Is the fundamental frequency.
In the inverter, the control effect is achieved by controlling the number of times the IGBT is turned on and the on time, and therefore, the current in the IGBT is discontinuous. However, the sum of the currents in the IGBT and the complementary anti-parallel diode on the single-phase arm is equal to the positive (upper IGBT and lower diode) or negative (lower IGBT and upper diode) phase current, and the phase currents flowing in the IGBT and the anti-parallel diode may be equivalent to a half-wave rectified sine wave, and the following relationship is satisfied for the amplitude of each harmonic component in expression (1):
Figure BDA0002767791540000022
Figure BDA0002767791540000023
Figure BDA0002767791540000024
in the formula:
Figure BDA0002767791540000025
the peak value of the phase current.
For a half-sinusoidal phase current flowing through the IGBT, further expressed as:
Figure BDA0002767791540000026
for the half-sine phase current of the analyzed grid-connected inverter, four components are selected to realize better description, namely further expressed as:
Figure BDA0002767791540000027
the external variables required for calculating the IGBT power loss also include: dc bus voltage, switching frequency, fundamental frequency, and power factor.
Step 2: respectively calculating the switching loss and the conduction loss corresponding to the current peak value of the alternating current side, and further obtaining the power loss of the analyzed IGBT in the whole fundamental wave period, wherein the method specifically comprises the following steps:
switching losses and DC sideVoltage VDCCurrent through the IGBT and junction temperature TjIn correlation, the switching loss expression corresponding to the ac side current peak is as follows:
Figure BDA0002767791540000031
in the formula: f. ofswitchingSwitching frequency of IGBT module, Eon、EoffRespectively found in the Datasheet of the IGBT
Figure BDA0002767791540000032
Tj,VDCAnd the corresponding IGBT is subjected to turn-on loss and turn-off loss under the condition.
From the output characteristics of the IGBT and the switching loss curve, the power loss is approximately considered to be linear with the current flowing through the IGBT, from which the switching loss in a single fundamental period can be derived, expressed as:
Figure BDA0002767791540000033
the conduction loss is mainly related to the current flowing through the IGBT and the junction temperature, so the conduction loss at the peak current is expressed as:
Figure BDA0002767791540000034
since the turn-on loss of the IGBT within a single fundamental period is also related to the duty cycle of the IGBT, for the analyzed SPWM modulated lower inverter, the duty cycle is expressed as:
Figure BDA0002767791540000035
in the formula: m is a modulation degree.
Thus, the conduction loss in a single fundamental period is expressed as:
Figure BDA0002767791540000036
the power loss of the IGBT over the entire fundamental period is expressed as:
Figure BDA0002767791540000037
in the formula: pLoss(t) is the power loss for a single fundamental period,
Figure BDA0002767791540000038
the switching losses corresponding to the peak current are,
Figure BDA0002767791540000039
m is the modulation degree, which is closely related to the amplitude of the current of the output phase of the converter.
And step 3: combining with a Foster thermal network model, deducing a junction temperature fluctuation expression in a fundamental wave period, and deriving the junction temperature fluctuation expression to obtain maximum and minimum junction temperature occurrence time points, specifically:
the Foster thermal network model is as follows:
Figure BDA00027677915400000310
in the formula: rTHj，τTHjThermal resistance and thermal time constant of the j-th order, τTHj＝RTHj·CTHj，CTHjThe j-th order heat capacity value, m is the order of the equivalent heat network, the order of the heat network model provided by the data sheet is usually 4, and a specific numerical value of each order of the heat network model is provided.
As can be seen from the power loss expression of the IGBT, the component components of the IGBT are also divided into direct current components and trigonometric function components at different frequencies, and therefore the junction temperature fluctuations at the three components can be calculated and summed separately for the junction temperature fluctuation in a single fundamental wave period.
Taking the sine component as an example for analysis, and performing iterative analysis through discretization, the junction temperature fluctuation expression under the sine component can be obtained as follows:
Figure BDA0002767791540000041
in the formula,. DELTA.TRefjJ is 1, 2, 3 and 4 respectively the component of the junction temperature fluctuation initial value of the analyzed fundamental wave period on the corresponding heat network of each order, the calculation is obtained by the calculation of the last fundamental wave period, the first fundamental wave calculation period of the junction temperature fluctuation of the whole task section, delta TRefjAnd j is 1, 2, 3 and 4, and each component value is 0.
In the same way, the expression of the junction temperature fluctuation under the cosine component and the direct current component is respectively as follows:
Figure BDA0002767791540000042
Figure BDA0002767791540000043
the above is the expression of the junction temperature fluctuation under the fundamental wave period, and for the junction temperature fluctuation calculation under each harmonic component, the frequency and the amplitude of the harmonic component are only required to replace the frequency and the amplitude under the fundamental wave period deduced above.
And for the junction temperature fluctuation of the IGBT, combining the derivation results of the above formula, obtaining the junction temperature fluctuation under each loss component, and summing the junction temperature fluctuations, namely obtaining a final expression of the junction temperature fluctuation.
And (4) obtaining a derivation of the obtained junction temperature fluctuation expression, and enabling the derivation to be equal to 0 to obtain the maximum and minimum junction temperature time points.
And 4, step 4: and calculating the maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to the junction temperature value at the moment and the component value of junction temperature fluctuation at the end of the fundamental wave period.
And 5: calculating maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to a junction temperature value at the moment and a component value of junction temperature fluctuation at the end of the fundamental wave period; and (4) repeating the iteration steps 1 to 4 so as to obtain the junction temperature fluctuation information of the whole analysis task section.
Compared with the prior art, the invention has the beneficial technical effects that:
(1) according to the invention, the power loss of the IGBT can be calculated more quickly and more accurately by the power loss analysis based on the alternating current Fourier decomposition;
(2) the invention estimates the maximum and minimum junction temperature calculation based on the junction temperature characteristic analysis, so that the calculation result is more accurate;
(3) the invention only calculates the junction temperature information which is more concerned in reliability and practical engineering application, avoids a large amount of calculation redundancy in the iterative calculation of the junction temperature, and realizes the rapid calculation of the junction temperature fluctuation.
Drawings
Fig. 1 is a schematic diagram of an equivalent circuit of a grid-connected inverter in the embodiment of the invention.
Fig. 2 shows the phase currents of the IGBTs and diodes on the single-phase leg in an embodiment of the invention.
Fig. 3 is a characteristic curve of turn-on loss at different temperatures of the IGBT module analyzed in the embodiment of the present invention.
Fig. 4 is a turn-off loss characteristic curve of the IGBT module at different temperatures analyzed in the embodiment of the present invention.
Fig. 5 is a conduction output characteristic curve of the IGBT module at different temperatures analyzed in the embodiment of the present invention.
FIG. 6 is a graph of the power loss calculated according to the formula compared to the PLECS simulated power loss in the embodiment of the present invention.
Fig. 7 is a diagram of a Foster thermal network model used in junction temperature calculation in an embodiment of the present invention.
Fig. 8 is a schematic diagram of the conversion of power loss to junction temperature in an embodiment of the present invention.
FIG. 9 is a schematic diagram of discretization under sinusoidal power loss in an embodiment of the present invention.
Fig. 10 is a graph comparing the estimated junction temperature and the plccs simulated junction temperature in an embodiment of the invention.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
The invention discloses a calculation method for IGBT junction temperature fluctuation of a power electronic converter, which comprises the following steps of:
step 1: and collecting converter level variables required by calculating power loss, performing Fourier decomposition on output current of the alternating current side, and acquiring a current expression flowing through the IGBT.
For the analyzed power electronic converter, a three-phase grid-connected inverter with the same scale is taken as an example, and an equivalent circuit diagram is shown in fig. 1, wherein L is a filter inductance value, C is a filter capacitance value, and L is a filter capacitance valuegIs the equivalent impedance value of the grid, Va，Vb，VcThe equivalent voltage is the effective value of the power grid. Due to the working symmetry of the IGBTs in the converter, one of the IGBT modules is selected as an analysis object, and the IGBT of the upper bridge arm of the phase A is selected in the analysis. Table 1 shows the main parameters of the three-phase inverter and the specific type of IGBT used in the inverter, with a rated current of 50A and a rated voltage of 1200V; in addition, the output current of the inverter has an effective value of 25A.
TABLE 1 grid-tied inverter parameters
Figure BDA0002767791540000051
Figure BDA0002767791540000061
The phase current is fourier decomposed and can be expressed as:
Figure BDA0002767791540000062
in the formula: c. C0Is a DC component value, ck，dkPeak values of sine and cosine components, respectively, k is the harmonic order, w is the fundamental angular frequency, and w is 2 pi f0，f0Is the fundamental frequency.
In the inverter, the control effect is achieved by controlling the number of times the IGBT is turned on and the on time, and therefore, the current in the IGBT is discontinuous. However, the sum of the currents in the IGBT and the complementary anti-parallel diode on the single-phase arm is equal to the positive (upper IGBT and lower diode) or negative (lower IGBT and upper diode) phase current, and as shown in fig. 2, the phase current flowing in the IGBT and the anti-parallel diode may be equivalent to a half-wave rectified sine wave, and therefore, the coefficients of the respective components of the current expression satisfy the following relationship:
Figure BDA0002767791540000063
Figure BDA0002767791540000064
Figure BDA0002767791540000065
in the formula (I), the compound is shown in the specification,
Figure BDA0002767791540000066
the peak value of the phase current.
Further, the half-sinusoidal phase current flowing through the IGBT can be expressed as follows:
Figure BDA0002767791540000067
of course, the more harmonic components are selected, the more accurate the phase current flowing through the IGBT is, but the higher calculation load will be brought to the later loss and junction temperature. For the half-sine phase current of the analyzed grid-connected inverter, the selection of four components can realize better description of the half-sine phase current, namely further expressed as:
Figure BDA0002767791540000068
step 2: respectively calculating the switching loss and the conduction loss corresponding to the current peak value of the alternating current side, and further obtaining the power loss of the IGBT in the whole fundamental wave period;
when the current flowing through the IGBT is acquired, the power loss of the IGBT can be calculated. According to the output characteristic and the switching loss curve of the IGBT, the power loss can be approximately considered to be in a linear relation with the current flowing through the IGBT, so that the power loss corresponding to the peak current only needs to be calculated for the power loss calculation of a single fundamental wave period, and the calculation burden brought by loss calculation of switching periods one by one can be avoided.
The power loss of the IGBT includes conduction loss and switching loss. The switching loss calculation for peak current can be expressed as:
Figure BDA0002767791540000071
it can be seen that the switching losses are mainly related to the DC side voltage VDCCurrent through the IGBT and junction temperature TjClosely related, the data sheet gives the switching loss characteristics of the IGBT analyzed at different temperatures, as shown in fig. 3, 4, where the dc side voltage tested is 600V. Therefore, for obtaining the switching loss of the analyzed IGBT corresponding to the voltage, current and temperature, the switching loss can be obtained by searching a loss characteristic curve or by fitting the curve.
Further, the switching loss within a single fundamental period can be expressed as:
Figure BDA0002767791540000072
as for the conduction loss, the conduction loss is mainly closely related to the output characteristic of the IGBT, and fig. 5 shows the analyzed conduction output characteristic curve of the IGBT module at different temperatures, it can be seen that the conduction loss is mainly related to the current flowing through the IGBT and the junction temperature, and therefore the conduction loss corresponding to the peak current can be represented as:
Figure BDA0002767791540000073
in the formula:
Figure BDA0002767791540000074
to correspond to
Figure BDA0002767791540000075
TjAnd the lower IGBT is conducted and voltage drops.
Besides, it has been mentioned above that the IGBT is intermittently conductive in a single fundamental wave period, and the current flowing through the IGBT is discontinuous, so the conduction loss of the IGBT in a single fundamental wave period is also closely related to the duty cycle of the IGBT, which can be expressed as:
Figure BDA0002767791540000076
in the formula: m is a modulation degree which is closely related to the amplitude of the output current, and the modulation degree is 0.63 when the effective value of the output current of the inverter is 25A.
Considering the duty cycle, the conduction loss in a single fundamental period can be expressed as:
Figure BDA0002767791540000077
further, IGBT power loss P in a single fundamental wave period can be obtainedLoss(t) is:
Figure BDA0002767791540000081
the PLECS (programmable logic controller) software has high confidence degree and high accuracy in the aspects of power loss and thermal characteristic analysis, and is widely accepted by the academic and industrial fields. Therefore, an electrical simulation model is built under MATLAB/Simulink, then joint simulation is carried out by combining PLECS, the simulation result is compared and analyzed with the proposed loss calculation method, and the specific comparison result is shown in FIG. 6. As can be seen from the figure, the proposed loss calculation method can accurately describe the actual loss.
In simulation analysis, for power loss calculation in a single fundamental wave period, higher sampling frequency is needed to calculate the loss in a single switching period one by one, and the proposed loss calculation method only needs to collect the peak value of the output current at the alternating current side and only needs to calculate the power loss under the value, so that repeated iterative loss calculation is avoided, and the calculation amount of the power loss is greatly reduced.
And step 3: deducing a junction temperature fluctuation expression in a fundamental wave period by combining a Foster thermal network model, and deriving the junction temperature fluctuation expression to obtain maximum and minimum junction temperature occurrence time points;
before junction temperature fluctuation calculation, a thermal network model is introduced, and the existing thermal network models are mainly divided into two types, namely a Cauer model and a Foster model. The extraction of the Cauer model parameters usually requires detailed information (such as geometric dimension and material characteristics) of each physical layer of the IGBT module, and the information is usually difficult to collect, so that the application of the Cauer model is limited. The Foster model parameters can be extracted from transient thermal response which is easy to obtain, so the Foster thermal network model is widely applied to rapid junction temperature estimation of the IGBT, and a data manual provides specific parameters of a fourth-order Foster thermal network model, as shown in fig. 7, where P isLossFor power loss of IGBT, TcaseIs the case temperature of the IGBT module, while the thermal network can be described as shown below;
Figure BDA0002767791540000082
in the formula: rTHj，τTHjThermal resistance and thermal time constant of the j-th order, τTHj＝RTHj·CTHj，CTHjIs the j-th order heat capacity value, and m is the order of the equivalent heat networkThe order of the thermal network model provided by the data sheet is typically 4, and the specific values of the thermal network parameters for the power modules of the model analyzed in table 2.
TABLE 2 thermal network parameter values
Figure BDA0002767791540000083
Figure BDA0002767791540000091
As can be seen from the power loss expression of the IGBT, the component components of the IGBT can also be divided into direct-current components and trigonometric function components at different frequencies, so that junction temperature fluctuations in three components can be calculated and summed for junction temperature fluctuations in a single fundamental wave period.
Before solving the junction temperature fluctuation under the three loss components, the required power loss-junction temperature conversion theory is introduced.
When the power loss is a series of rectangular pulses as shown in fig. 8, the power loss can be converted to a junction temperature profile as shown below.
Figure BDA0002767791540000092
In the formula,. DELTA.Tj(n-1)And PLoss(n-1)Respectively temperature fluctuations and power losses in the previous time interval. Delta Tj(n)Is the temperature fluctuation, P, in the current analysis time intervalLoss(n)Is the power loss in the current analysis interval.
Taking the sine component as an example for analysis, when the power loss is a sine curve, the power loss expression is as follows:
P＝Ppeak_sinsin(2πf0t)
in the formula, wherein Ppeak_sinIs the peak value of the sinusoidal power loss component, f0Is the fundamental frequency of the alternating current.
Randomly selecting a time point T within a single fundamental period analyzed, as shown in FIG. 90Is the fundamental period of the alternating current. Discretizing the power loss curve in the selected time period into n rectangular pulse losses, and expressing junction temperature fluctuation in the currently analyzed time point by using a power loss-junction temperature conversion theory as follows:
Figure BDA0002767791540000093
in the formula,. DELTA.TRefj(j ═ 1, 2, 3 and 4) are respectively the components of the junction temperature fluctuation initial value of the analyzed fundamental wave period (the last value of the junction temperature fluctuation of the last fundamental wave period) on the heat network corresponding to each step, the calculation is obtained by the calculation of the last fundamental wave period, and the first fundamental wave calculation period of the junction temperature fluctuation of the whole task section, delta TRefj(j-1, 2, 3, 4) each component value is 0.
According to the extreme equivalence principle, the more the number of discrete rectangular pulse losses, the better the coincidence ratio of the equivalent power loss curve and the original power loss curve is. According to the newton-lebeniz integration theorem, the expression for the dispersion loss can be converted into the form of a bounded integral as shown below:
Figure BDA0002767791540000101
the same can be said that the junction temperature fluctuations when the losses are cosine as well as dc components can be similarly shown.
When cosine loss:
Figure BDA0002767791540000102
in the formula, Ppeak_cosIs the peak of the cosine power loss component.
When the direct current component is:
Figure BDA0002767791540000103
in the formula, PconstantIs the magnitude of the dc component.
The above analysis is a junction temperature fluctuation expression under the fundamental wave period, and for the junction temperature fluctuation calculation under each harmonic component, the frequency and the amplitude of the harmonic component are only required to replace the frequency and the amplitude under the fundamental wave period deduced above.
For the junction temperature fluctuation of the IGBT in the embodiment, the derivation results of the above formula are combined to obtain the junction temperature fluctuation under each loss component, and the obtained junction temperature fluctuations are summed, namely the final expression of the junction temperature fluctuation is obtained.
The derivation is performed on the expression for obtaining the junction temperature fluctuation, and the derivation is made to be equal to 0, so that the maximum and minimum junction temperature time points can be obtained.
And 4, step 4: calculating maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to a junction temperature value at the moment and a component value of junction temperature fluctuation at the end of the fundamental wave period;
and further obtaining the maximum and minimum junction temperatures according to the obtained junction temperature time points, and further obtaining junction temperature fluctuation concerned by reliability evaluation. Besides, the calculation of the temperature at the moment corresponding to the peak value of the current is mainly used for the loss calculation of the fundamental wave period, and the calculation of the junction temperature fluctuation four-component value at the end of the fundamental wave period is used for the next junction temperature calculation iteration.
Because the fundamental wave frequency is higher, in order to better show the variation process of the junction temperature in a single fundamental wave period, the simulation time of 0.5 second is selected, and the junction temperature profile calculated by the electric-thermal combined simulation and the junction temperature profile obtained by the junction temperature calculation method are compared and analyzed, wherein the comparison result is shown in fig. 10.
It can be seen that the proposed junction temperature fluctuation calculation method can achieve accurate calculation of junction temperature fluctuation, and also exhibits accurate estimation in the transient process of junction temperature, wherein in the calculated maximum and minimum junction temperature information, the value with the largest deviation from the simulation is also less than 0.5 ℃. Simultaneously acquiring simulation time and calculation time of the method, wherein the simulation time and the calculation time are respectively as follows: 0.4s and 0.3s, it can be seen that the proposed junction temperature fluctuation calculation method can calculate the key junction temperature information at a faster speed, that is, for a task profile with a simulation time of 0.5s, the proposed algorithm can be completed in less time, so that the proposed junction temperature calculation method can be integrated into a control system of a converter to realize real-time estimation of the junction temperature, and meanwhile, the proposed calculation method only calculates four junction temperature information in a single fundamental wave period, so that excessive information storage is not required, and the problem that the existing junction temperature calculation method cannot be implemented on line due to the information storage problem is solved. In addition, when the junction temperature reaches a steady state, the junction temperature appears constant-amplitude periodic fluctuation, so that the maximum and minimum junction temperature time points in each fundamental wave period are fixed, and the initial value components of the junction temperature fluctuation in the fundamental wave period are also kept consistent, the junction temperature can be directly assigned to the next fundamental wave period without carrying out iterative calculation again on the junction temperature, and thus, the calculated junction temperature information of the previous fundamental wave period can be further reduced.
It is worth noting that: in the proposed junction temperature fluctuation calculation method, after power loss is obtained, errors cannot be caused to junction temperature calculation based on the proposed junction temperature calculation method, so the junction temperature calculation errors are mainly caused by the loss calculation errors, the loss error is determined by the number of selected harmonic components, the more the number is, the more accurate the loss is, the more accurate the calculated junction temperature is, but the calculation burden of the junction temperature calculation is further increased. Therefore, based on the proposed junction temperature calculation method, the key point for calculating the junction temperature of the current transformer in other operating modes or under a modulation strategy is to select a proper harmonic component.

Claims (5)

1. A calculation method for IGBT junction temperature fluctuation of a power electronic converter is characterized by comprising the following steps:
step 1: acquiring converter-level variables required by calculating power loss, performing Fourier decomposition on the phase current output by the alternating current side, and acquiring the current flowing through the IGBT, wherein the expression is as follows:
Figure FDA0002767791530000011
in the formula:
Figure FDA0002767791530000012
the peak value of the phase current;
step 2: respectively calculating the switching loss and the conduction loss corresponding to the current peak value of the alternating current side, and further obtaining the power loss of the IGBT in the whole fundamental wave period, wherein the expression is as follows:
Figure FDA0002767791530000013
in the formula: pLoss(t) is the power loss for a single fundamental period,
Figure FDA0002767791530000014
the switching losses corresponding to the peak current are,
Figure FDA0002767791530000015
the conduction loss corresponding to the peak current is M, and M is a modulation degree which is closely related to the amplitude of the current of the output phase of the current transformer;
and step 3: deducing a junction temperature fluctuation expression in a fundamental wave period by combining a Foster thermal network model, and deriving the junction temperature fluctuation expression to obtain maximum and minimum junction temperature occurrence time points;
and 4, step 4: and calculating the maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to the junction temperature value at the moment and the component value of junction temperature fluctuation at the end of the fundamental wave period.
2. The calculation method for the IGBT junction temperature fluctuation of the power electronic converter as claimed in claim 1, wherein the step 1 specifically comprises:
for phase currents, performing a fourier decomposition can be expressed as:
Figure FDA0002767791530000016
in the formula: c. C0Is a DC component value, ck，dkThe peak values of the sine component and the cosine component are respectively, and k is the harmonic frequency; w is the fundamental angular frequency, and w is 2 pi f0，f0Is the fundamental frequency;
due to the unidirectional conductivity of the IGBT, conduction is only in half a period of the phase current, and therefore the current flowing through the IGBT assumes a half sinusoidal waveform, satisfying the following relationship for the amplitude of each harmonic component in expression (3):
Figure FDA0002767791530000017
Figure FDA0002767791530000021
Figure FDA0002767791530000022
in the formula:
Figure FDA0002767791530000023
the peak value of the phase current;
for a half-sinusoidal phase current flowing through the IGBT, further expressed as:
Figure FDA0002767791530000024
for the half-sine phase current of the analyzed grid-connected inverter, four components are selected to realize better description, namely further expressed as:
Figure FDA0002767791530000025
the external variables required for calculating the IGBT power loss also include: dc bus voltage, switching frequency, fundamental frequency, and power factor.
3. The calculation method for the IGBT junction temperature fluctuation of the power electronic converter as claimed in claim 2, wherein the step 2 specifically comprises:
switching losses and DC side voltage VDCCurrent through the IGBT and junction temperature TjIn correlation, the switching loss expression corresponding to the ac side current peak is as follows:
Figure FDA0002767791530000026
in the formula: f. ofswitchingSwitching frequency of IGBT module, Eon、EoffRespectively found in the Datasheet of the IGBT
Figure FDA0002767791530000027
Tj,VDCThe corresponding IGBT is subjected to turn-on loss and turn-off loss under the condition;
from the output characteristics of the IGBT and the switching loss curve, the power loss is approximately considered to be linear with the current flowing through the IGBT, from which the switching loss in a single fundamental period can be derived, expressed as:
Figure FDA0002767791530000028
the conduction loss is mainly related to the current flowing through the IGBT and the junction temperature, so the conduction loss at the peak current is expressed as:
Figure FDA0002767791530000029
since the turn-on loss of the IGBT within a single fundamental period is also related to the duty cycle of the IGBT, for the analyzed SPWM modulated lower inverter, the duty cycle is expressed as:
Figure FDA0002767791530000031
in the formula: m is a modulation degree;
thus, the conduction loss in a single fundamental period is expressed as:
Figure FDA0002767791530000032
4. the calculation method for the IGBT junction temperature fluctuation of the power electronic converter as claimed in claim 3, wherein the step 3 is specifically as follows:
the Foster thermal network model is as follows:
Figure FDA0002767791530000033
in the formula: rTHj，τTHjThermal resistance and thermal time constant of the j-th order, τTHj＝RTHj·CTHj，CTHjThe j-th order heat capacity value, m, the order of the equivalent heat network, the order of the heat network model provided by the data manual is 4, and a specific numerical value of each order of the heat network model is provided;
as can be seen from the power loss expression of the IGBT, the component components of the IGBT are also divided into direct-current components and trigonometric function components at different frequencies, so that junction temperature fluctuations under three components can be calculated and summed for junction temperature fluctuations within a single fundamental period;
in the sinusoidal component, iterative analysis is carried out through discretization, and the junction temperature fluctuation expression under the sinusoidal component is obtained as follows:
Figure FDA0002767791530000034
in the formula,. DELTA.TRefjJ is 1, 2, 3 and 4 respectively the component of the junction temperature fluctuation initial value of the analyzed fundamental wave period on the corresponding heat network of each order, the calculation is obtained by the calculation of the last fundamental wave period, the first fundamental wave calculation period of the junction temperature fluctuation of the whole task section, delta TRefjJ is 1, 2, 3, 4, each component value is 0;
in the same way, the expression of the junction temperature fluctuation under the cosine component and the direct current component is respectively as follows:
Figure FDA0002767791530000035
Figure FDA0002767791530000036
the above is the expression of the junction temperature fluctuation under the fundamental wave period, and for the junction temperature fluctuation calculation under each harmonic component, the frequency and the amplitude of the harmonic component are only required to replace the frequency and the amplitude under the fundamental wave period deduced above;
for the junction temperature fluctuation of the IGBT, the derivation result of the above formula is combined to obtain the junction temperature fluctuation under each loss component and sum the junction temperature fluctuation, namely a final expression of the junction temperature fluctuation;
and (4) obtaining a derivation of the obtained junction temperature fluctuation expression, and enabling the derivation to be equal to 0 to obtain the maximum and minimum junction temperature time points.
5. The calculation method for IGBT junction temperature fluctuation of the power electronic converter as claimed in claim 3, further comprising the following steps:
and 5: calculating maximum and minimum junction temperature values according to the acquired time points, wherein the current peak value corresponds to a junction temperature value at the moment and a component value of junction temperature fluctuation at the end of the fundamental wave period; and (4) repeating the iteration steps 1 to 4 so as to obtain the junction temperature fluctuation information of the whole analysis task section.
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