CN113890031B - Flexible direct system IGBT safe working area determination method considering thermoelectric interaction - Google Patents

Flexible direct system IGBT safe working area determination method considering thermoelectric interaction Download PDF

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CN113890031B
CN113890031B CN202111439236.1A CN202111439236A CN113890031B CN 113890031 B CN113890031 B CN 113890031B CN 202111439236 A CN202111439236 A CN 202111439236A CN 113890031 B CN113890031 B CN 113890031B
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igbt
current
boundary
working area
safe working
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CN113890031A (en
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王霄鹤
谢瑞
傅春翔
杨文斌
陈晴
陈雨薇
夏冰清
殷贵
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PowerChina Huadong Engineering Corp Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

The invention discloses a method for determining a safe working area of an IGBT (insulated gate bipolar translator) of a flexible direct system considering thermoelectric interaction, which aims at the defects of extensive type, large allowance and multiple redundancy existing in an IGBT type selection method caused by the fact that the safe working area of the IGBT of the flexible direct system cannot be accurately calculated in the prior art, the safe working area of the IGBT considering the thermoelectric interaction is obtained through theoretical calculation, and the limit of the current and the maximum voltage peak value of the safe boundary of the IGBT and the limit of the maximum junction temperature of the IGBT are considered. The IGBT safe working area calculated by the method can provide a fine IGBT model selection scheme under the condition of ensuring the safe and stable operation of the system, obviously reduces the weight, the volume and the construction cost of a converter station platform, and is beneficial to the flat-price and light development of a flexible direct current transmission system.

Description

Flexible direct system IGBT safe working area determination method considering thermoelectric interaction
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a method for determining an IGBT safe working area of a flexible direct current system considering thermoelectric interaction, wherein the flexible direct current system is a flexible direct current power transmission system.
Background
A voltage source converter based high voltage direct current (VSC-HVDC) transmission technology is also called as a flexible direct current transmission technology, and because the problem of commutation failure does not exist, active and reactive power decoupling control can be realized, direct current power flow inversion is easy, and the flexible direct current transmission technology becomes a preferred scheme for solving the grid connection problem of renewable energy sources. The converter is one of core equipment in a flexible direct current transmission system and comprises multiple circuit topologies such as a two-level converter, a three-level converter and a Modular Multilevel Converter (MMC), wherein the MMC topology utilizes sub-modules to avoid direct series connection of devices, and the limitation of series connection difficulty on power improvement of the converter is broken, so that the converter is widely applied.
Along with the continuous improvement of the voltage grade and the transmission capacity of the flexible direct-current transmission system, the performance requirement of an IGBT power device in the MMC converter is also continuously improved, and the model selection scheme of the IGBT becomes an important factor influencing the whole construction cost of a project. In order to ensure the reliability of the IGBT power device and the converter system, current converter design manufacturers adopt a rough design method with large allowance and multiple redundancies, the reliability of the converter is ensured in a cost-sacrificing mode, the cost, the volume and the weight of the converter are increased, and the flexible direct-current power transmission system is not favorable for the flat-price and light development.
Two main factors restricting the safe and stable operation of the MMC sub-module under the conditions of high voltage and large current are an electric safety boundary and a thermal safety boundary, and a refined selection scheme of the IGBT can be designed under the condition of ensuring the safe and stable operation of the system only by preparing and determining a safe working area of the IGBT.
Disclosure of Invention
The invention aims to overcome the defects of extensive type, large allowance and multiple redundancies of an IGBT type selection method due to the fact that the safe working area of the IGBT of the flexible direct system cannot be accurately determined in the prior art, and provides a method for determining the safe working area of the IGBT of the flexible direct system considering thermoelectric interaction.
In order to realize the purpose of the invention, the method adopts the following technical scheme:
the method for determining the safe working area of the IGBT of the flexible direct current system considering thermoelectric interaction is characterized by comprising three steps of: determining a safe working area considering the IGBT electrical boundary, determining a safe working area considering the IGBT thermal boundary, and integrating the IGBT safe working area considering the thermoelectric interaction;
the step of determining the safe working area considering the IGBT electrical boundary selectsnDC bus voltmeterCalculating pointV dc1ToV dcnConsidering the limitation of the maximum turn-off current and the maximum voltage peak value of the IGBT, calculating to obtain the IGBT safety boundary current of each voltage calculation point, and calculating according to the DC bus voltageV dcAs abscissa, IGBT safe boundary currentI pkAs ordinate, to obtainnCarrying out curve fitting on sampling points on the electric boundary of each IGBT safe working area to obtain the safe working area considering the electric boundary of the IGBT;
the step of determining the safe working area considering the thermal boundary of the IGBT is to selectiA DC bus voltage calculation pointV dc1ToV dciConsidering the limit of the heat generated by the IGBT conduction loss and the switching loss and the maximum junction temperature of the IGBT, calculating to obtain the IGBT safety boundary current corresponding to each voltage calculation point, and calculating the IGBT safety boundary current according to the direct-current bus voltageV dcAs abscissa, IGBT safe boundary currentI pkAs ordinate, to obtainiCarrying out curve fitting on sampling points on the thermal boundary of each IGBT safe working area to obtain the safe working area considering the thermal boundary of the IGBT;
and integrating the IGBT safe working area considering the thermoelectric interaction model, namely taking the intersection of the safe working area considering the IGBT electric boundary and the safe working area considering the IGBT thermal boundary to obtain the IGBT safe working area considering the thermoelectric interaction model.
Preferably, in order to ensure the integrity of the safe operating area taking into account the electrical boundaries of the IGBT, the selection is madenIn the points, the safety boundary current of one point is required to be the maximum turn-off current of the IGBT, the maximum turn-off current of the IGBT can be referred by a device manual and is generally 2 times of rated current, and when the safety boundary current of a certain point is equal to the maximum turn-off current, the safety boundary currents of which the direct-current bus voltage is smaller than the point are considered to be the maximum turn-off current, so that the calculated amount is reduced. Therefore, in the subsequent calculation process of the IGBT safety boundary current, the recommended value of the first multiple is 2.
Preferably, in order to ensure the integrity of the safe operating area taking into account the thermal boundary of the IGBT, the method is selectediOf the points, the safety margin current required to have one point isThe maximum turn-off current of the IGBT can be consulted through a device manual and is generally 2 times of rated current, and when the safety boundary current of a certain point is equal to the maximum turn-off current, the safety boundary currents of which the direct-current bus voltage is smaller than the point are considered to be the maximum turn-off current, so that the calculated amount is reduced. Therefore, in the subsequent calculation process of the IGBT safety boundary current, the recommended value of the first multiple is 2.
Further: in the step of determining the safe working area considering the IGBT electrical boundary, the IGBT safe boundary current of each voltage calculation point is calculated by adopting the following method:
for DC bus voltage calculation pointV dc1Firstly, selecting the current value of the first multiple of the rated current of the IGBT as the turn-off current, and calculating the voltage peak value of the IGBT at the momentV ce(max)If at this timeV ce(max)If the percentage is less than the first threshold percentage of the rated voltage of the IGBT, the point is a point on the boundary of the IGBT safe working area; if at that timeV ce(max)If the percentage of the rated voltage of the IGBT is larger than the first threshold percentage, selecting the current value of the second multiple of the rated current of the IGBT as the turn-off current, and calculating the voltage peak value of the IGBT at the momentV ce(max)If the second multiple is smaller than the first multiple, and if the second multiple is still larger than the first threshold percentage of the rated voltage of the IGBT, selecting the current value of the third multiple of the rated current of the IGBT as the turn-off current, wherein the third multiple is smaller than the second multiple, and sequentially reducing the current value until the third multiple is smaller than the second multipleV ce(max)The percentage of the first threshold value which is smaller than the rated voltage of the IGBT is selected, and the turn-off current at the moment is used as a calculation point of the voltage of the corresponding direct current busV dc1The IGBT safety boundary current considering the IGBT electric boundary is obtained by repeating the stepsnIGBT safety boundary currents respectively corresponding to the direct current bus voltage calculation points;
the obtained safety working area boundary considering the IGBT electric boundarynPerforming curve fitting on the points to obtain a safe working area considering the IGBT electrical boundary; in the fitting process, when the off-current of a certain boundary point reaches the maximum value, the off-currents of the boundary points with the direct-current bus voltage smaller than the point are all considered to be the sameA maximum value.
In the process, the voltage peak value under the corresponding direct current bus voltage and the corresponding turn-off current is calculated by the following methodV ce(max)：
Figure 90170DEST_PATH_IMAGE001
Figure 810739DEST_PATH_IMAGE002
Figure 364211DEST_PATH_IMAGE003
Wherein the content of the first and second substances,V refis the reference voltage given by the data manual,t refis the corresponding current fall time in the data sheet,V dcis the dc bus voltage at the point of computation,t ffor bus voltage to be soughtV dcThe fall time of the current to be lowered,I pkis the off-current for this calculation point,L sthe stray inductance of the power loop can be obtained by looking up a data manual.
Considering the requirements of calculation amount and engineering design margin, the first multiple is preferably a current value which is 2 times of the rated current of the IGBT; the first threshold percentage is preferably 85% of the rated voltage of the IGBT; the maximum value of the off-current is preferably 2 times the rated current. In the step of determining the safe operating area taking into account the electrical boundary of the IGBT, the rated current may be reduced by preferably 0.25 times each time for a factor less than the first time, and if an increase in accuracy is required, the current factor reduced each time may be further reduced. The selection principle for the above preferred values is analyzed in detail in the detailed description.
Further: in the step of determining the safe working area considering the IGBT thermal boundary, the IGBT safe boundary current of each voltage calculation point is calculated by adopting the following method:
for DC bus voltage calculation pointV dc1Firstly, selecting the current value of the first multiple of the rated current of the IGBT as a turn-off current, and respectively calculating the chip junction temperatures of the IGBT1 and the IGBT2 at the momentT 1AndT 2if at this timeT 1AndT 2the second threshold percentages are all smaller than the highest allowable junction temperature of the IGBT, and the point is a point on the boundary of the IGBT safe working area; if at that timeT 1OrT 2If the percentage of the current value of the IGBT is larger than the second threshold value percentage of the highest allowable junction temperature of the IGBT, the current value of the second multiple of the rated current of the IGBT is selected as a turn-off current, and the junction temperature of the chip at the moment is calculatedT 1AndT 2the second multiple is less than the first multiple, if soT 1OrT 2If the percentage is still larger than the second threshold percentage of the highest allowable junction temperature, selecting the current value of the third multiple of the rated current of the IGBT as the turn-off current, wherein the third multiple is smaller than the second multiple, and sequentially decreasing until the third multiple is smaller than the second multipleT 1AndT 2are all less than the second threshold percentage of the highest allowable junction temperature, and the turn-off current at the moment is selected as the corresponding direct current bus voltageV dc1The IGBT safety boundary current considering the IGBT thermal boundary is obtained by repeating the stepsiIGBT safety boundary currents respectively corresponding to the direct current bus voltage calculation points;
the obtained safety working area boundary considering the IGBT thermal boundaryiPerforming curve fitting on the points to obtain a safe working area considering the thermal boundary of the IGBT; in the fitting, when the off-current of a certain boundary point reaches the maximum value, the off-current of the boundary point where the direct-current bus voltage is smaller than the point is considered to be the maximum value.
The IGBT1 is an IGBT switching device connected with the positive electrode of the capacitor in the submodule of the half-bridge converter, the IGBT2 is an IGBT switching device connected with the negative electrode of the capacitor in the submodule of the half-bridge converter, and the junction temperature calculation methods are different due to the fact that the positions of the IGBT switching device and the IGBT switching device are different;
in the process, the chip junction temperatures of the IGBT1 and the IGBT2 under the corresponding direct-current bus voltage and the corresponding turn-off current are calculated by the following methodT 1AndT 2：
Figure 595473DEST_PATH_IMAGE004
Figure 449159DEST_PATH_IMAGE005
Figure 809471DEST_PATH_IMAGE006
Figure 115819DEST_PATH_IMAGE007
Figure 619612DEST_PATH_IMAGE008
wherein the content of the first and second substances,P T1_ConandP T2_Confor turn-on losses of IGBT1 and IGBT2,P T1_SwtandP T2_Swtswitching losses for IGBT1 and IGBT 2;Z T1(j-c)andZ T2(j-c)is the thermal resistance of the chip to the device substrate,Z T1(c-h)andZ T2(c-h)the thermal resistance from the substrate to the radiator can be obtained by looking up a manual;V T1_ConandV T2_Conis the turn-on voltage drop of IGBT1 and IGBT2,V T1_ConandV T2_Conthe device load current and the direct current bus voltage can be expressed in a polynomial form, and for different types of IGBTs, polynomial coefficients are different and can be obtained by referring to a device manual;I pkis the off-current for this calculation point,mas a modulation ratio of the alternating-current voltage,φin order to be the power factor angle,θ 1zero crossing of bridge arm current;K T1A、K T1B、K T1CandK T2A、K T2B、K T2Crepresenting the loss constants of IGBT1 and IGBT2,A T1、B T1、C T1andA T2、B T2、C T2the switching loss factor for IGBT1 and IGBT2, available from device handbooks,f sis the device equivalent switching frequency.
Considering the requirements of calculation amount and engineering design margin, the first multiple is preferably 2 times of the rated current of the IGBT; the second threshold percentage is preferably 75% and the maximum off-current is preferably 2 times the rated current. The rated current is reduced by a factor of 0.25 times for each time, preferably, the first time or less, and if the accuracy is required to be increased, the current reduced by each time can be further reduced. The selection principle for the above preferred values is analyzed in detail in the detailed description.
By adopting the technical scheme, the invention considers the limit of the IGBT safety boundary current and the maximum voltage peak value and the limit of the IGBT maximum junction temperature in the determination of the IGBT safety working area, can design a refined selection scheme of the IGBT under the condition of ensuring the safe and stable operation of the system, obviously reduces the weight, the volume and the construction cost of a converter station platform, and is beneficial to the flat-price and light development of a flexible direct-current transmission system.
Drawings
FIG. 1 is a typical topology of a half-bridge type MMC sub-module. The IGBT1 and the IGBT2 are respectively an IGBT switching device connected with the positive electrode of the capacitor and an IGBT switching device connected with the negative electrode of the capacitor of the submodule of the half-bridge converter, and the C is a submodule capacitor.
Fig. 2 is a typical topology of a flexible dc power transmission system.
Fig. 3 is a typical topology of a half-bridge type MMC converter.
Fig. 4 is a safety operating region of an IGBT electrical boundary drawn by taking an IGBT device of ABB 4500V2000A as an example.
Fig. 5 is a safety operating region of an IGBT thermal boundary drawn by taking an IGBT device of ABB 4500V2000A as an example.
Fig. 6 is a drawing of an IGBT safe operating area taking ABB 4500V2000A as an example, and taking thermoelectric interaction into account.
Detailed Description
In order to more specifically describe the present invention, the following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings.
The specific implementation of the method is described by taking a flexible direct-current power transmission system as an example. The topology of the flexible direct current transmission system in this embodiment is shown in fig. 2, wherein the topology of the sending-end and receiving-end half-bridge MMC converters is the same, as shown in fig. 3, and each sub-module labeled SM in fig. 3 is the sub-module shown in fig. 1. In the embodiment, the rated direct current voltage of the flexible direct current transmission system is +/-400 kV, the rated power is 1000MW, and the rated current is 1250A, in the embodiment, an ABB 4500V2000A IGBT device is used as a switching device, wherein 4500V2000A is only a specification parameter of the device, and an actual safe working area of the device needs to be determined according to an actual operating condition and a device parameter, so that the number of sub-modules is reasonably selected, which is the main purpose of the invention.
The safe working area of the IGBT is mainly limited by an electric boundary and a thermal boundary, and the device can be considered to be capable of safely and reliably operating only by meeting the requirements of the electric boundary and the thermal boundary.
In the step of determining the safe operating area considering the electric boundary of the IGBT, since the IGBT1 and the IGBT2 are in series relationship and the intensities of currents flowing through them are equal, it is only necessary to perform the following steps for any one of them: selecting 5 direct current bus voltage calculation points, wherein the number of the selected calculation points determines the fineness of the safe working area, the more the number of the points is, the higher the fineness is, but the larger the calculation amount is, the fineness can reflect the characteristics of the safe working area, in the embodiment, the 5 points are selected, namely 2800V, 3000V, 3200V, 3400V and 3800V, and the points are named as 2800V, 3000V, 3200V, 3400V and 3800V respectivelyV dc1ToV dc5For each direct-current bus voltage, firstly, selecting a current of a first multiple of the rated current of the IGBT, wherein the maximum overcurrent capacity of the selected IGBT is 2 times of the rated current, so that a rated current value of 2 times (4000A) is selected as a turn-off current of the first multiple, and the maximum overcurrent capacity of the IGBT is obtained by inquiring an IGBT delivery specification; calculating the voltage peak value of the IGBT at the momentV ce(max)If at this timeV ce(max)If the percentage is less than the first threshold percentage of the rated voltage of the IGBT, the point is considered to be a point on the boundary of the IGBT safe working area; the first threshold percentage is determined according to the reliability requirement of the system, the lower the percentage is, the stronger the system reliability is, but the smaller the safe working area is, the higher the system cost is, the recommended selection is 80% -90%, and in this embodiment, the first threshold percentage is selected to be 85% (3825V); if at that timeV ce(max)And if the current is larger than 3825V, selecting the second-time multiple current of the rated current of the IGBT as the turn-off current, wherein the current multiple can be reduced in an equal proportion from the second-time multiple current, the amplitude of each reduction determines the calculation precision, and the smaller the reduction amplitude is, the higher the fineness is, but the larger the calculation amount is. Considering that the purpose of determining the IGBT safe operating region in the present invention is to select a device type, and the device type selection needs to consider a certain margin, in this embodiment, the amplitude of the proportional reduction is selected to be 0.25 times, that is, the second current multiple is 1.75 times (3500A), the third current multiple is 1.5 times (3000A), and so on, according to the 5% to 25% margin in the conventional design. Therefore, a certain engineering margin is considered, and the lower calculation amount of the method can be ensured. Calculating the voltage peak value of the IGBT at the momentV ce(max)If the voltage is still higher than 3825V, selecting the current of third multiple of rated current of IGBT as off-current until the voltage is still higher than 3825VV ce(max)And when the voltage is less than 3825V, selecting the turn-off current and the direct current bus voltage at the moment as a point on the boundary of the IGBT safe working area.
In the process, the voltage peak value under the corresponding direct current bus voltage and the corresponding turn-off current is calculated by the following methodV ce(max)：
Figure 357499DEST_PATH_IMAGE001
Figure 859018DEST_PATH_IMAGE002
Figure 449400DEST_PATH_IMAGE009
Wherein the content of the first and second substances,V refis the reference voltage given by the data manual,t refis the corresponding current fall time in the data sheet,V dcis the dc bus voltage at the point of computation,t ffor bus voltage to be soughtV dcThe fall time of the current to be lowered,I pkis the off-current for this calculation point,L sthe stray inductance of the power loop can be obtained by looking up a data manual.
Repeating the steps to obtain 5 points on the boundary of the IGBT safe working area, then performing curve fitting, and when the safe boundary current of a certain point is equal to the current value of the first multiple of the rated current, considering that the safe boundary current of which the direct-current bus voltage is less than the point is the current value of the first multiple of the rated current, drawing to obtain the safe working area considering the IGBT electrical boundary, as shown in FIG. 4.
In the step of determining the safe working area considering the thermal boundary of the IGBT, 8 direct current bus voltage calculation points are selected, the number of the selected calculation points determines the fineness of the safe working area, the more the number of the points is, the higher the fineness is, but the larger the calculation amount is, the fineness can reflect the characteristics of the safe working area, in the embodiment, 8 points are selected, namely 1600V, 1800V, 2100V, 2350V, 2600V, 2800V, 3000V and 4000V, and the points are named as 1600V, 1800V, 2100V, 2350V, 2600V, 2800V, 3000V and 4000VV dc1ToV dc8For each dc bus voltage, first, a current of a first multiple of the rated current of the IGBT is selected, and in this embodiment, the maximum overcurrent capacity of the selected IGBT is considered to be 2 times of the rated current, so that a rated current value of 2 times (4000A) is selected as a turn-off current of the first multiple, and the chip junction temperatures of the IGBT1 and the IGBT2 at that time are respectively calculatedT 1AndT 2(the positions of the IGBT1 and the IGBT2 are shown in figure 1, and the calculation method of the junction temperature is different because the positions of the IGBT1 and the IGBT2 are different), if the calculation method is carried out at the momentT 1AndT 2all are less than the second threshold percentage of the highest junction temperature, the point is considered as the boundary of the IGBT safe working areaA point of (a); the second threshold percentage is determined according to the reliability requirement of the system, the lower the percentage is, the stronger the system reliability is, but the smaller the safe working area is, the higher the system cost is, the recommended selection is 70% -80%, in this embodiment, the second threshold percentage is selected to be 75% (94 ℃) of the highest allowable junction temperature (125 ℃) of the IGBT, and the highest allowable junction temperature of the IGBT is obtained by inquiring the delivery specification of the IGBT; if at that timeT 1OrT 2And if the current is more than 94 ℃, selecting the second-time multiple current of the rated current of the IGBT as the turn-off current, wherein the current multiple can be reduced in an equal proportion from the second-time multiple current, the amplitude of each reduction determines the calculation precision, and the smaller the reduction amplitude is, the higher the fineness is, but the larger the calculation amount is. Considering that the purpose of determining the IGBT safe operating region in the present invention is to select a device type, and the device type selection needs to consider a certain margin, in this embodiment, the amplitude of the proportional reduction is selected to be 0.25 times, that is, the second current multiple is 1.75 times (3500A), the third current multiple is 1.5 times (3000A), and so on, according to the 5% to 25% margin in the conventional design. Therefore, a certain engineering margin is considered, and the lower calculation amount of the method can be ensured. Calculating the junction temperature of the chip at the momentT 1AndT 2if the current is still greater than 94 ℃, selecting the current of third multiple of the rated current of the IGBT as the turn-off current until the current is turned offT 1AndT 2and the current and the direct current bus voltage are selected as one point on the boundary of the IGBT safe working area when the current and the direct current bus voltage are all less than 94 ℃.
In the process, the chip junction temperatures of the IGBT1 and the IGBT2 under the corresponding direct-current bus voltage and the corresponding turn-off current are calculated by the following methodT 1AndT 2：
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Figure 15522DEST_PATH_IMAGE005
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Figure 264155DEST_PATH_IMAGE007
Figure 375331DEST_PATH_IMAGE008
wherein the content of the first and second substances,P T1_ConandP T2_Confor turn-on losses of IGBT1 and IGBT2,P T1_SwtandP T2_Swtswitching losses for IGBT1 and IGBT 2;Z T1(j-c)andZ T2(j-c)is the thermal resistance of the chip to the device substrate,Z T1(c-h)andZ T2(c-h)the thermal resistance from the substrate to the radiator can be obtained by looking up a manual;V T1_ConandV T2_Conis the turn-on voltage drop of IGBT1 and IGBT2,V T1_ConandV T2_Conthe device load current and the direct current bus voltage can be expressed in a polynomial form, and for different types of IGBTs, polynomial coefficients are different and can be obtained by referring to a device manual;I pkis the off-current for this calculation point,mas a modulation ratio of the alternating-current voltage,φin order to be the power factor angle,θ 1zero crossing of bridge arm current;K T1A、K T1B、K T1CandK T2A、K T2B、K T2Crepresenting the loss constants of IGBT1 and IGBT2,A T1、B T1、C T1andA T2、B T2、C T2the switching loss factor for IGBT1 and IGBT2, available from device handbooks,f sis the device equivalent switching frequency.
Repeating the steps to obtain 8 points on the boundary of the IGBT safe working area, then performing curve fitting, and when the safe boundary current of a certain point is equal to the current value of the first multiple of the rated current, considering that the safe boundary current of which the direct-current bus voltage is less than the point is the current value of the first multiple of the rated current, drawing to obtain the safe working area considering the IGBT thermal boundary, as shown in FIG. 5.
And finally, taking intersection of the safe working area considering the IGBT electrical boundary and the safe working area considering the IGBT thermal boundary to obtain the IGBT safe working area considering the thermoelectric interaction, wherein as shown in a hatched area of oblique lines in fig. 6, the selected working point on the hatched area boundary is the optimal working point.
In this embodiment, since the rated current of the system is 1250A, the voltage corresponding to the optimal operating point on the boundary of the safe operating area can be 3400V according to fig. 6, since the rated voltage of the system is ± 400kV, 236 submodules are required to be selected by a single bridge arm in total, and 284 submodules are only required even if 1.2 times of margin is considered, whereas in the existing engineering project, since a calculation method of the IGBT safe operating area in the flexible and straight system is lacked in the prior art, evaluation can be performed only according to half 2250V of the rated voltage of the IGBT, and a certain margin is considered, 400 submodules are selected, so that the construction cost is greatly increased. According to the analysis, the method for determining the safe working area of the IGBT is adopted to select the type of the device, so that the number of sub-modules can be reduced by 29%, and the cost is obviously saved.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

Claims (4)

1. The method for determining the safe working area of the IGBT of the flexible direct current system considering thermoelectric interaction is characterized by comprising three steps of: determining a safe working area considering the IGBT electrical boundary, determining a safe working area considering the IGBT thermal boundary, and integrating the IGBT safe working area considering the thermoelectric interaction;
the step of determining the safe working area considering the IGBT electrical boundary is to select n direct current bus voltage calculation points Vdc1To VdcnConsidering the limitation of the maximum turn-off current and the maximum voltage peak value of the IGBT, calculating to obtain the IGBT safety boundary current of each voltage calculation point, and calculating according to the DC bus voltage VdcIs abscissa, IGBT safe boundary current IpkPerforming curve fitting on the obtained sampling points on the electrical boundaries of the n IGBT safe working areas to obtain the safe working areas considering the electrical boundaries of the IGBT as vertical coordinates;
the step of determining the safe working area considering the IGBT thermal boundary is to select i direct current bus voltage calculation points Vdc1To VdciConsidering the limit of the heat generated by the IGBT conduction loss and the switching loss and the maximum junction temperature of the IGBT, calculating to obtain the IGBT safety boundary current corresponding to each voltage calculation point, and calculating according to the direct-current bus voltage VdcIs abscissa, IGBT safe boundary current IpkPerforming curve fitting on the obtained sampling points on the thermal boundary of the i IGBT safe working areas to obtain the safe working areas considering the thermal boundary of the IGBT as a vertical coordinate;
integrating the IGBT safe working area considering the thermoelectric interaction model, namely taking the intersection of the safe working area considering the IGBT electrical boundary and the safe working area considering the IGBT thermal boundary to obtain the IGBT safe working area considering the thermoelectric interaction model;
in the step of determining the safe working area considering the IGBT electrical boundary, the IGBT safe boundary current of each voltage calculation point is calculated by adopting the following method:
calculating point V for DC bus voltagedc1Firstly, selecting the current value of the first multiple of the rated current of the IGBT as a turn-off current, and calculating the voltage peak value V of the IGBT at the momentce(max)If at this time Vce(max)Less than a first threshold percentage of the rated voltage of the IGBT, the point is a point on the boundary of the IGBT safe working area(ii) a If at this time Vce(max)If the percentage of the rated voltage of the IGBT is larger than the first threshold percentage, selecting the current value of the second multiple of the rated current of the IGBT as the turn-off current, and calculating the voltage peak value V of the IGBT at the momentce(max)If the second multiple is smaller than the first multiple, and if the second multiple is still larger than the first threshold percentage of the rated voltage of the IGBT, selecting the current value of the third multiple of the rated current of the IGBT as the turn-off current, wherein the third multiple is smaller than the second multiple, and sequentially reducing the current value until V is less than the first threshold percentage of the rated voltage of the IGBTce(max)The percentage of the first threshold value which is smaller than the rated voltage of the IGBT is selected, and the turn-off current at the moment is taken as a calculation point V of the voltage of the corresponding direct current busdc1The IGBT safety boundary current of the IGBT electrical boundary is taken into consideration, and the steps are repeated to obtain the IGBT safety boundary currents corresponding to the n direct-current bus voltage calculation points respectively;
the voltage peak value V under the corresponding direct current bus voltage and the corresponding turn-off current is calculated by the following methodce(max)：
Figure RE-FDA0003469856270000021
Figure RE-FDA0003469856270000022
Figure RE-FDA0003469856270000023
Wherein, VrefReference voltage given for data handbook, trefIs the corresponding current fall time, V, in the data sheetdcIs the DC bus voltage of the calculation point, tfFor bus voltage V to be solveddcCurrent fall time ofpkThe off-current for this calculation point, LsIs a power loop stray inductance;
in the step of determining the safe working area considering the IGBT thermal boundary, the IGBT safe boundary current of each voltage calculation point is calculated by adopting the following method:
calculating point V for DC bus voltagedc1Firstly, selecting the current value of the first multiple of the rated current of the IGBT as a turn-off current, and respectively calculating the chip junction temperatures T of the IGBT1 and the IGBT2 at the moment1And T2If at this time T1And T2The second threshold percentages are all smaller than the highest allowable junction temperature of the IGBT, and the point is a point on the boundary of the IGBT safe working area; if T is at this time1Or T2If the percentage of the current value of the IGBT is larger than the second threshold value percentage of the highest allowable junction temperature of the IGBT, the current value of the second multiple of the rated current of the IGBT is selected as a turn-off current, and the chip junction temperature T at the moment is calculated1And T2The second multiple is less than the first multiple, if T is present1Or T2If the percentage is still larger than the second threshold percentage of the highest allowable junction temperature, selecting the current value of the third multiple of the rated current of the IGBT as the turn-off current, wherein the third multiple is smaller than the second multiple, and sequentially decreasing until T1And T2Are all less than the second threshold percentage of the highest allowable junction temperature, and the turn-off current at the moment is selected as the corresponding direct current bus voltage Vdc1The IGBT safety boundary current of the IGBT thermal boundary is taken into consideration, and the steps are repeated to obtain the IGBT safety boundary current corresponding to the i direct current bus voltage calculation points respectively;
the IGBT1 and the IGBT2 are respectively an IGBT of the half-bridge converter submodule connected with the positive electrode of the capacitor and an IGBT connected with the negative electrode of the capacitor;
the chip junction temperatures T of the IGBTs 1 and 2 under the corresponding direct-current bus voltage and the corresponding turn-off current are calculated by the following method1And T2：
Figure RE-FDA0003469856270000031
Figure RE-FDA0003469856270000032
Figure RE-FDA0003469856270000033
Figure RE-FDA0003469856270000034
Wherein, PT1_ConAnd PT2_ConFor the turn-on losses of IGBT1 and IGBT2, PT1_SwtAnd PT2_SwtSwitching losses for IGBT1 and IGBT 2; zT1(j-c)And ZT2(j-c)Thermal resistance of the chip to the device substrate, ZT1(c-h)And ZT2(c-h)Is the thermal resistance of the substrate to the heat sink; vT1_ConAnd VT2_ConFor the turn-on voltage drop, V, of IGBT1 and IGBT2T1_ConAnd VT2_ConExpressed as a polynomial form of the device load current and the dc bus voltage; i ispkM is the ac voltage modulation ratio, which is the off current at this calculation point,
Figure RE-FDA0003469856270000035
is the power factor angle, theta1Zero crossing of bridge arm current; kT1A、KT1B、KT1CAnd KT2A、KT2B、KT2CShows the loss constants of the IGBT1 and the IGBT2, AT1、BT1、CT1And AT2、BT2、CT2The switching loss factor of IGBT1 and IGBT2, fsIs the device equivalent switching frequency.
2. The method for determining the safe working area of the IGBT of the flexible direct current system considering thermoelectric interaction, according to claim 1, is characterized in that: in the selected n points, the safety boundary current of at least one point is the maximum turn-off current of the IGBT; the safety margin current of at least one point of the selected i points is the maximum turn-off current of the IGBT.
3. The method for determining the safe working area of the IGBT of the flexible direct current system considering thermoelectric interaction, according to claim 1, is characterized in that: the first time multiple is 2 times of rated current of the IGBT; the first threshold percentage is 85% of the rated voltage of the IGBT; the maximum value of the turn-off current is 2 times of rated current.
4. The method for determining the safe working area of the IGBT of the flexible direct current system considering thermoelectric interaction, according to claim 1, is characterized in that: the first time multiple is 2 times of rated current of the IGBT; the second threshold percentage is 75%, and the maximum value of the off-current is 2 times of the rated current.
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