CN111064353B - Control method for keeping parallel IGBTs thermal stability based on frequency inflection point - Google Patents

Control method for keeping parallel IGBTs thermal stability based on frequency inflection point Download PDF

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CN111064353B
CN111064353B CN201911385419.2A CN201911385419A CN111064353B CN 111064353 B CN111064353 B CN 111064353B CN 201911385419 A CN201911385419 A CN 201911385419A CN 111064353 B CN111064353 B CN 111064353B
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CN111064353A (en
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杨建雄
车延博
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Tianjin University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/26—Testing of individual semiconductor devices
    • G01R31/2607—Circuits therefor
    • G01R31/2608—Circuits therefor for testing bipolar transistors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention belongs to the technical field of power electronic devices, and particularly relates to a control method for keeping parallel IGBTs thermally stable based on a frequency inflection point, which comprises the following steps: in the first step of the method,selecting two IGBTs with the same model, connecting in parallel, recording the switching frequency f and junction temperature difference delta T of the IGBTs, and obtaining the conduction loss difference delta E cond (ii) a Step two, according to the conduction loss difference delta E cond Difference from switching loss Δ E sw Obtaining the frequency inflection point f of the parallel IGBTs 0 Controlling the switching frequency f of the IGBTs in parallel to be less than or equal to the frequency inflection point f 0 . According to the invention, the relation between the switching frequency of the parallel IGBTs and the thermal stability limit is established, the switching frequency is controlled to be lower than or equal to the maximum value of the frequency inflection point, and the loss difference of the parallel IGBTs is reduced along with the increase of the temperature difference, so that the junction temperature of the high-temperature IGBT is further reduced, and the thermal stability of the parallel IGBTs is finally realized.

Description

Control method for keeping parallel IGBTs thermal stability based on frequency inflection point
Technical Field
The invention belongs to the technical field of power electronic devices, and particularly relates to a control method for keeping parallel IGBTs thermally stable based on a frequency inflection point.
Background
The high-voltage IGBT power module is one of core components of a high-voltage direct-current transmission technology, a flexible alternating-current transmission technology, an intelligent switching technology and a high-voltage frequency conversion technology, the power grade of the high-voltage IGBT power module is hundreds kW or even more than dozens of GW, the voltage grade of the high-voltage IGBT power module is more than kV, and the current capacity of the high-voltage IGBT power module is more than hundreds of amperes.
However, the gap between the output capacity of high voltage IGBT power modules and the required capacity for high power conversion applications is increasing. In combination with reliability, economy, etc., it is sometimes not the best solution to choose the highest level IGBT directly. Therefore, multiple IGBT chips are often used in parallel, enabling a specific current capacity and power level. The parallel connection in the power electronics mainly comprises 3 different levels of a device level, a module level and a device level, wherein the parallel connection of the device level and the module level is the most basic and direct, and the power electronics has a better cost performance advantage.
The inventor finds that the switching process of the commonly used IGBT is a main source of device loss, needs to be strictly controlled under the working conditions of high frequency and large current, and particularly needs to pay attention to the consistency of current and junction temperature distribution among parallel devices; in addition, the discreteness of parameters of the IGBT, the asymmetry of the layout of a driving circuit and a main circuit, the difference of temperature and other factors all affect the current sharing during parallel application, so that the heating and the loss among devices are inconsistent, the running junction temperatures of the parallel IGBTs are different, the generated junction temperature difference affects the switching loss and the conduction loss of the IGBT, the distribution of the current and the junction temperature of the IGBT is further affected, and even the devices are overheated and damaged in serious cases, so that serious hidden dangers are brought to the safe running of the converter.
In the prior art, most of influences of temperature on power loss are concentrated on a circuit layout level, and a carrier level inside a device is less involved. Moreover, most of the researches on the temperature characteristics of the IGBT are concentrated on a single power module, and the researches on the interaction influence among the parallel modules are rarely reported. With the development of power electronic systems towards high power, the parallel use problem of devices becomes more and more prominent. Therefore, a control method capable of effectively maintaining the thermal stability of the parallel IGBTs is needed.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the control method for keeping the thermal stability of the parallel IGBTs based on the frequency inflection point is provided, the relation between the switching frequency of the parallel IGBTs and the thermal stability limit is established, the switching frequency is controlled to be lower than or equal to the maximum value of the frequency inflection point, the phenomenon that the device is damaged due to overheating is avoided, and the reliability and the working stability of the parallel IGBTs are effectively improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a control method for keeping parallel IGBTs thermally stable based on frequency inflection points comprises the following steps:
the method comprises the following steps: selecting two IGBTs with the same model, connecting in parallel, recording the switching frequency f and junction temperature difference delta T of the IGBTs, and collecting the voltage U between the collector and the emitter of the IGBTs ce Collector current I at temperature T c(T) And collector current I at temperature T + Δ T c(T+ΔT) Calculating the conduction loss E of the parallel IGBTs at the temperature T cond(T) And conduction loss E at temperature T + DeltaT cond(T+ΔT) Obtaining said E cond(T) And said E cond(T+ΔT) Difference of conduction loss Δ E therebetween cond ；
Step two: calculating the switching loss E of the parallel IGBTs at the temperature T sw(T) And a switching loss E at a temperature T + DeltaT sw(T+ΔT) Obtaining said E sw(T) And said E sw(T+ΔT) Difference in switching loss Δ E between sw According to said difference in conduction loss Δ E cond Difference Δ E from the switching loss sw Obtaining a frequency inflection point f of the parallel IGBTs 0 Controlling the switching frequency f of the parallel IGBTs to be less than or equal to the frequency inflection point f 0 。
Further, in the step one, the conduction loss difference Δ E cond Satisfy the relation:
Figure BDA0002343472220000031
wherein, the Δ I c Representing the difference in collector current, the Δ I, of the parallel IGBTs c Satisfy the relation: delta I c ＝I c(T+ΔT) -I c(T) (ii) a The D represents the switching duty cycle of the parallel IGBTs.
Further, in the second step, the switching loss difference Δ E sw Satisfy the relation:
Figure BDA0002343472220000032
wherein s represents a temperature coefficient of turn-off loss, k sw Representing a constant independent of temperature.
Further, in the second step, when the frequency inflection point f of the parallel IGBTs is obtained 0 While said conduction loss difference Δ E cond Difference Δ E from the switching loss sw Satisfy the relation: delta E cond +ΔE sw ＝0。
Further, in the second step, the frequency inflection point f of the parallel IGBTs 0 Satisfy the relation:
Figure BDA0002343472220000033
further, in the first step, the collector current I of the parallel IGBTs at the temperature T c(T) Satisfy the relation:
Figure BDA0002343472220000034
collector current I of the parallel IGBTs at the temperature of T + delta T c(T+ΔT) Satisfy the relation:
Figure BDA0002343472220000041
wherein, said m 1 M is the same as 2 M, the above 3 M is the same as 4 M is the same as 5 Each representing a correlation coefficient of the collector current temperature characteristic.
Further, in the first step, the conduction loss E of the parallel IGBTs at the temperature T is cond(T) Satisfy the relation:
Figure BDA0002343472220000042
conduction loss E of parallel IGBTs at the temperature of T + delta T cond(T+ΔT) Satisfy the relation:
Figure BDA0002343472220000043
further, in the step one, the conduction loss difference Δ E cond Satisfy the relation:
Figure BDA0002343472220000044
the invention has the beneficial effects that: the invention selects two IGBTs with the same type to be electrified in parallel, records the switching frequency f and the junction temperature difference delta T of the IGBTs in parallel connection, and then records the switching frequency f and the junction temperature difference delta E according to the conduction loss difference delta E cond Difference from switching loss Δ E sw Obtaining the frequency inflection point f of the parallel IGBTs 0 Controlling the switching frequency f of the parallel IGBTs to be less than or equal to the frequency inflection point f 0 On the one hand, when the switching frequency f is less than the frequency inflection point f 0 The junction temperature of the high-temperature IGBT is small, the parallel IGBTs can be in a thermal stable state, and on the other hand, the switching frequency f is equal to the frequency inflection point f 0 The loss difference of the parallel IGBTs is zero, and the junction temperature difference of the parallel IGBTs is kept unchanged, so that the reliability and the working stability of the parallel IGBTs are effectively improved, and the phenomenon that the devices are damaged due to overheating is avoided.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
FIG. 2 is a circuit diagram of the test circuit of the present invention.
Fig. 3 is a waveform diagram illustrating a single IGBT turn-on process.
Fig. 4 is a waveform diagram illustrating a turn-off process of a single IGBT.
FIG. 5 is a schematic diagram of the frequency-loss characteristics of the parallel IGBTs of the present invention.
FIG. 6 is a schematic diagram of junction temperature difference-frequency characteristics under different duty cycles according to the present invention.
Fig. 7 is a graph showing the result of a frequency inflection point characteristic experiment according to the present invention.
Detailed Description
As used in this specification and the appended claims, certain terms are used to refer to particular components, and it will be appreciated by those skilled in the art that a manufacturer may refer to a component by different names. The description and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, and a person skilled in the art can solve the technical problem within a certain error range to substantially achieve the technical effect.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "horizontal", and the like indicate orientations or positional relationships based on those shown in the drawings, only for convenience of description and simplification of description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.
The present invention will be described in further detail with reference to the following drawings and specific examples, but the present invention is not limited thereto.
As shown in fig. 1, a control method for keeping parallel IGBTs thermally stable based on frequency inflection point includes:
the method comprises the following steps: selecting two IGBTs with the same model, connecting in parallel, electrifying, recording the switching frequency f and junction temperature difference delta T of the IGBTs, and collecting the voltage U of the IGBTs between a collector and an emitter ce Collector current I at temperature T c(T) And collector current I at temperature T + Δ T c(T+ΔT) Calculating the conduction loss E of the parallel IGBTs at the temperature T cond(T) And conduction loss E at temperature T + DeltaT cond(T+ΔT) Obtaining E cond(T) And E cond(T+ΔT) Difference of conduction loss Δ E therebetween cond Difference in conduction loss Δ E cond Satisfy the relation:
Figure BDA0002343472220000061
wherein, delta I c Representing the collector current difference, Δ I, of the parallel IGBTs c Satisfy the relation: delta I c ＝I c(T+ΔT) -I c(T) (ii) a D represents the switching duty cycle of the parallel IGBTs.
Step two: calculating the switching loss E of the parallel IGBTs at the temperature T sw(T) And a switching loss E at a temperature T + DeltaT sw(T+ΔT) Obtaining E sw(T) And E sw(T+ΔT) Difference in switching loss Δ E between sw Difference in switching loss Δ E sw Satisfies the relation:
Figure BDA0002343472220000071
wherein s represents the turn-off lossTemperature coefficient of (k) sw Represents a constant independent of temperature, according to the difference of conduction losses deltaE cond Difference from switching loss Δ E sw Obtaining the frequency inflection point f of the parallel IGBTs 0 Controlling the switching frequency f of the parallel IGBTs to be less than or equal to the frequency inflection point f 0 。
Preferably, in step one, the collector current I of the parallel IGBTs at the temperature T c(T) Satisfy the relation:
Figure BDA0002343472220000072
collector current I of parallel IGBTs at temperature T + DeltaT c(T+ΔT) Satisfies the relation:
Figure BDA0002343472220000073
wherein m is 1 、m 2 、m 3 、m 4 、m 5 Each representing a correlation coefficient of the collector current temperature characteristic.
Preferably, in the first step, the conduction loss E of the parallel IGBTs at the temperature T is cond(T) Satisfies the relation:
Figure BDA0002343472220000074
conduction loss E of parallel IGBTs at temperature T + delta T cond(T+ΔT) Satisfy the relation:
Figure BDA0002343472220000075
preferably, in step one, the conduction loss difference Δ E cond Satisfy the relation:
Figure BDA0002343472220000076
preferably, in step two, when obtaining the frequency inflection point f of the parallel IGBTs 0 Time, conduction loss difference Δ E cond Difference from switching loss Δ E sw Satisfy the relation: delta E cond +ΔE sw =0, frequency inflection point f of parallel IGBTs 0 Satisfy the relation:
Figure BDA0002343472220000077
FIG. 2 is a test circuit of the present invention, in which two TO-247 packaged British fly-ash trench gate IGBTs IHW20N120R2 are selected TO be connected in parallel, and during the circuit operation, the switching loss of the IGBT includes turn-on loss and turn-off loss, and during the turn-on process of the IGBT, the collector current rise stage, diode reverse recovery stage and diode reverse recovery blocking stage are included; during the turn-off process of the IGBT, a voltage rising stage between a collector and an emitter, a collector current falling stage and a current tailing stage are included.
FIG. 3 shows u in the turn-on process of a single IGBT ce 、i c A waveform schematic, wherein: u shape dc Is a DC bus voltage, I c Is the load current u ce Is the voltage between the collector and emitter of the IGBT, i c Is collector current, Δ U ce For voltage drop due to stray inductance of the loop, I rrm The reverse recovery current peak. According to the analysis of the internal mechanism of the IGBT turn-on process, the turn-on loss of the IGBT is discussed in three stages.
(1) Collector current rising phase
Figure BDA0002343472220000081
Wherein E is on1 The turn-on loss u at this stage ce1n The voltage between collector and emitter at this stage, i c1n Collector current at this stage, L s Is stray inductance on the loop, t on1 Is the duration of the collector current rise phase, a = U dc I c 2 /2，b＝-L s I c 2 /3。
(2) Diode reverse recovery phase
Figure BDA0002343472220000082
Wherein E is on2 The opening loss, u, at this stage ce2n The voltage between collector and emitter at this stage, i c2n Collector current at this stage, t on2 Is the duration of the diode reverse recovery phase, c = U dc (I rrm 2 +I rrm I c )，d＝-L s (I rrm 2 +I rrm I c )。
(3) Diode reverse recovery blocking stage
Figure BDA0002343472220000091
Wherein E is on3 The opening loss at this stage, e = U dc (I rrm 2 /3+I rrm I c /2)，f＝-L s (I rrm 2 /3+I rrm I c /2)。
Only the current rising slope is related to the IGBT temperature in the parameters related to the turn-on loss, and then the relation between the turn-on loss and the temperature of the IGBT can be obtained:
Figure BDA0002343472220000092
wherein v is GE Is the gate voltage of the IGBT, v GEth Is the threshold voltage, alpha, of the IGBT PNP Is the intrinsic bipolar transistor gain, μ is the carrier mobility, W/L is the ratio of the width to the length of the IGBT channel, C ox Is the capacity of the oxidation electricity,
Figure BDA0002343472220000093
is the temperature coefficient of the turn-on loss, α = a + c + e, β = b + d + f, o and k on Are constant independent of temperature.
FIG. 4 shows u in the IGBT turn-off process ce 、i c A waveform schematic, wherein: u shape cep As stray electricityPeak voltage induced, I tail For trailing current, t tail Is the trailing current duration. According to the analysis of the internal mechanism of the IGBT turn-off process, the turn-off loss of the IGBT is discussed in three stages.
(1)u ce Voltage rising phase
Figure BDA0002343472220000094
Wherein E is off1 Turn-off loss, U, at this stage Gon Is the instantaneous gate emitter voltage, U, of the Miller platform during turn-off Goff Is the gate drive voltage during off-period, R G Is a gate drive resistor, C GC Is a Miller capacitance, C o Is a charge extraction capacitance, g m Is transconductance of the IGBT, t off1 Is the duration of the voltage rise phase, T is the temperature of the IGBT, ω is the temperature coefficient of the turn-off loss of this phase, k 1 Is a constant independent of temperature.
(2)i c Current reduction phase
Figure BDA0002343472220000101
Wherein E is off2 Turn-off loss u at this stage ce2f The voltage between collector and emitter, k, at this stage f Is the collector current slope, i c2f The collector current in this stage, ξ is the temperature coefficient of the turn-off loss in this stage, k 2 And ρ are constants independent of temperature.
(3) Current tail stage
Figure BDA0002343472220000102
Wherein E is off3 The turn-off loss at this stage, # is the temperature coefficient of the turn-off loss at this stage, k 3 Is a constant independent of temperature.
Further, the relation between the turn-off loss and the temperature of the IGBT can be obtained as follows:
Figure BDA0002343472220000103
where δ is the temperature coefficient of turn-off loss, ρ and k off Are temperature independent constants and the temperature coefficients of the switching and turn-off losses are approximately equal.
And, the switching loss E of the IGBT sw And the temperature satisfies the following relation:
Figure BDA0002343472220000104
s and k sw Each represents a constant independent of temperature and s represents the temperature coefficient of turn-off loss.
In a switching period, the difference delta E of the total power loss at different temperatures satisfies the relation:
Figure BDA0002343472220000111
as shown in FIG. 5, when IGBTs are operated in parallel, the switching loss difference Δ E between the parallel IGBTs sw The temperature difference delta T of the junction rises, and the influence of the temperature on conduction loss and the conduction voltage drop U ce It is related. In addition, in a switching period, the conduction loss of the parallel IGBTs is influenced by the temperature difference, so that positive feedback and negative feedback exist, under the working condition of large current injection, the IGBT is in a positive temperature characteristic region, the conduction voltage drop of the parallel IGBTs is large, and the conduction loss difference delta E is cond Decreasing with increasing temperature difference. Under the condition of large current injection, the difference delta E of the switching loss is caused by the opposite trend of the switching loss and the conduction loss to the temperature difference sw Proportional to the junction temperature difference Δ T, inversely proportional to the operating frequency, when the total power loss difference Δ E =0, there is a frequency inflection point f of the parallel IGBTs 0 So that the total power loss over a period remains constant, thereby ensuring that the junction temperature difference between the parallel devices does not continue to vary.
Further, by the on-current distribution and switching loss of the IGBT, it is possible to extract the non-turn-offFrequency inflection point f of same current grade with change of junction temperature 0 . By
Figure BDA0002343472220000112
It can be known that the frequency inflection point f 0 Proportional to the duty cycle D, as shown in FIG. 6, frequency inflection point f 0 Rising with increasing duty cycle D. Therefore, when the parallel IGBTs are controlled by the chopping control method, the frequency inflection point characteristic curve should be corrected according to the duty ratio D.
When the duty ratio D is fixed, the smaller the parallel current is, the larger the junction temperature difference delta T is, and the frequency inflection point f 0 The smaller the frequency inflection point f is, at a certain total current in parallel 0 Decreases with the increase of the junction temperature difference Δ T, and as shown in FIG. 7, when the parallel current is 43A and the duty ratio D is 0.99, the frequency inflection point f increases from 25 to 125 0 From 20.8kHz down to 9.4kHz; when the junction temperature difference delta T is 25 and the duty ratio D is 0.99, the frequency inflection point f is formed along with the reduction of the parallel current from 43A to 16A 0 The frequency of the inflection point of the parallel IGBTs is very low when the parallel IGBTs work at a lower point of a positive temperature characteristic zone, if the switching frequency exceeds the maximum value of the inflection point frequency, the loss difference of the parallel IGBTs is increased along with the increase of the temperature difference, the junction temperature of the high-temperature IGBT is further increased easily, and the device can be failed or even the main circuit can be damaged in serious cases.
Therefore, the control method of the present invention makes the switching frequency f of the parallel IGBTs less than or equal to the frequency inflection point f 0 And the reliability of the parallel device is effectively improved. Controlling the switching frequency f to be lower than the frequency inflection point f 0 Of IGBTs in parallel, frequency inflection point f when the IGBTs are operated at the higher point of the positive temperature characteristic region 0 The loss difference of the parallel IGBTs is reduced along with the rise of the temperature difference, the junction temperature of the high-temperature IGBT is further reduced, and finally the parallel IGBTs are in a thermal stable state; controlling the switching frequency f to be equal to the frequency inflection point f 0 The loss difference of the parallel IGBTs is zero, and the junction temperature difference of the parallel IGBTs is kept unchanged.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious modifications, substitutions or alterations based on the present invention will fall within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (8)

1. A control method for keeping parallel IGBTs stable thermally based on frequency inflection points is characterized by comprising the following steps:
the method comprises the following steps: selecting two IGBTs with the same model, connecting in parallel, recording the switching frequency f and junction temperature difference delta T of the IGBTs, and collecting the voltage U between the collector and the emitter of the IGBTs ce Collector current I at temperature T c(T) And collector current I at temperature T + Δ T c(T+ΔT) And calculating the conduction loss E of the parallel IGBTs at the temperature T cond(T) And conduction loss E at temperature T + Δ T cond(T+ΔT) Obtaining said E cond(T) And said E cond(T+ΔT) Difference of conduction loss Δ E therebetween cond ；
Step two: calculating the switching loss E of the parallel IGBTs at the temperature T sw(T) And a switching loss E at a temperature T + Δ T sw(T+ΔT) Obtaining said E sw(T) And said E sw(T+ΔT) Switching loss difference Δ E therebetween sw According to said difference in conduction loss Δ E cond Difference Δ E from the switching loss sw Obtaining a frequency inflection point f of the parallel IGBTs 0 Controlling the switching frequency f of the parallel IGBTs to be less than or equal to the frequency inflection point f 0 。
2. The frequency inflection point-based control method for maintaining thermal stability of IGBTs in parallel as claimed in claim 1, wherein:
in the first step, the conduction loss difference Δ E cond Satisfies the relation:
Figure FDA0002343472210000011
wherein, the Δ I c Representing the difference in collector current, the Δ I, of the parallel IGBTs c Satisfies the relation: delta I c ＝I c(T+ΔT) -I c(T) (ii) a The D represents the switching duty cycle of the parallel IGBTs.
3. The method of claim 2 for frequency knee-based control of the thermal stability of IGBTs in parallel, wherein:
in the second step, the switching loss difference Δ E sw Satisfy the relation:
Figure FDA0002343472210000021
wherein s represents a temperature coefficient of turn-off loss, k sw Representing a constant independent of temperature.
4. The frequency inflection point-based control method for maintaining thermal stability of IGBTs in parallel as claimed in claim 3, wherein:
in the second step, when the frequency inflection point f of the parallel IGBTs is obtained 0 While said conduction loss difference Δ E cond Difference Δ E from the switching loss sw Satisfy the relation: delta E cond +ΔE sw ＝0。
5. The method of claim 4 for frequency knee-based control of the thermal stability of IGBTs in parallel, wherein:
in the second step, the frequency inflection point f of the parallel IGBTs 0 Satisfy the relation:
Figure FDA0002343472210000022
6. the frequency inflection point-based control method for maintaining thermal stability of IGBTs in parallel as claimed in claim 2, wherein:
in the first step, the parallel IGBTs are at the temperature TCollector current I c(T) Satisfies the relation:
Figure FDA0002343472210000023
collector current I of the parallel IGBTs at the temperature of T + delta T c(T+ΔT) Satisfy the relation:
Figure FDA0002343472210000024
wherein, said m 1 M, the above 2 M is the same as 3 M is the same as 4 M, the above 5 Are each indicative of a correlation coefficient of the collector current temperature characteristic.
7. The method of claim 6 for frequency knee-based control of the thermal stability of IGBTs in parallel, wherein:
in the first step, the conduction loss E of the parallel IGBTs at the temperature T cond(T) Satisfy the relation:
Figure FDA0002343472210000031
conduction loss E of parallel IGBTs at temperature T + delta T cond(T+ΔT) Satisfies the relation:
Figure FDA0002343472210000032
8. the frequency inflection point-based control method for maintaining thermal stability of IGBTs in parallel as claimed in claim 7, wherein:
in the step one, the conduction loss difference Δ E cond Satisfy the relation:
Figure FDA0002343472210000033
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