Converter state monitoring method based on IGBT loss

Abstract

The invention discloses a converter state monitoring method based on IGBT (Insulated Gate Bipolar Translator) loss, which relates to the technical field of power electronics, and comprises the following steps: S1, acquiring direct current side input voltage, direct current side input current, alternating current side output voltage and alternating current side output current of a converter, and calculating IGBT power loss and diode power loss; s2, constructing an IGBT module thermal network model, and calculating IGBT junction temperature and IGBT conduction voltage drop; s3, detecting the state of the IGBT by combining the three-phase current output by the AC side of the IGBT and the parameter value of the IGBT element, and carrying out VSC fault positioning; real-time state monitoring is carried out on the converter based on the change of IGBT power loss, power testing is carried out on the IGBT without damaging packaging and stopping, the aging state of the IGBT is monitored by utilizing electrical parameters before and after current conversion, meanwhile, PQ control is introduced, the stability of output power and current is improved, and the reliability of the converter is improved. And a replacement plan of the aged power module is better arranged before the service life of the IGBT is ended.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a converter state monitoring method based on IGBT loss. Background Art

[0002] Power electronic devices, also known as power semiconductor devices, are high-power electronic devices mainly used in power conversion and control circuits. They are known as the heart of electronic equipment. They usually have a current of tens to thousands of amperes and a voltage of hundreds to thousands of volts. They are widely used in aerospace, rail transportation, new energy, home appliances, and other fields.

[0003] Due to the complexity of the operating conditions of the equipment system, power electronic devices are subjected to unbalanced electrical and thermal stress, which can easily cause reliability problems such as aging failure. Once a power electronic device fails, it may cause the equipment system to shut down, resulting in economic losses. In serious cases such as power grids and aviation, which require high reliability, it may cause major safety accidents. IGBT modules are one of the main focus of power electronic system status monitoring strategies. Its common aging failure mode is package failure, and typical manifestations include bond wire breakage and detachment, gate oxide layer degradation, emitter metal layer reconstruction, and solder layer fatigue and voids. The aging process of the package is often accompanied by changes in electrical parameters such as equivalent resistance, parasitic inductance, and inter-electrode capacitance. Therefore, external signals related to the above parameters can be further used to evaluate the health status of the device. These external measurable signals are usually used as health indicators of IGBT modules.

[0004] In the prior art, a full-cycle loss model of an IGBT device is established by analyzing the switching loss, conduction loss data, and temperature data of the IGBT device obtained through big data, automatically detecting the loss and temperature rise of the IGBT device, and sending a shutdown signal to the control circuit module when an abnormality of the IGBT device is detected, thereby improving the safety and reliability of the system;

[0005] Although this solution can improve the safety of the system by real-time monitoring of the working status of IGBT power devices, it requires the establishment of a full-cycle loss model of IGBT devices. This monitoring method is relatively complex and the detection timeliness is not high.

[0006] Therefore, a converter state monitoring method based on IGBT loss is provided to solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a converter state monitoring method based on IGBT loss, which performs real-time status monitoring of the converter based on the change of IGBT power loss, without destroying the package or stopping the IGBT for power testing, and utilizes the electrical parameters before and after the conversion to realize the monitoring of the IGBT aging state, so as to better arrange the replacement plan of the aging power module before the end of the service life of the IGBT.

[0008] To achieve the above object, the present invention provides a converter state monitoring method based on IGBT loss, comprising the following steps:

[0009] S1: Obtain the DC side input voltage, DC side input current, AC side output voltage and AC side output current of the converter, and calculate the IGBT power loss and diode power loss;

[0010] S2: Build the IGBT module thermal network model and calculate the IGBT junction temperature and IGBT on-state voltage drop;

[0011] S3: Detect the IGBT status and locate the VSC fault based on the IGBT AC side output three-phase current and IGBT component parameter values.

[0012] Preferably, in step S1, the IGBT power loss and the diode power loss are calculated by using a formula calculation method, a simulation calculation method or by using a thermal model file in PLECS to obtain the power loss.

[0013] Preferably, the IGBT power loss and the diode power loss are calculated by a formula calculation method, which specifically includes the following steps:

[0014] S11: Calculate the average conduction loss of IGBT In a complete cycle, the average conduction loss of the IGBT is It is expressed as:

[0015]

[0016] Where T sw represents the switching cycle, v ce represents the collector-emitter voltage, i c represents the collector current, δ(t) represents the duty cycle, and δ(t) is expressed as:

[0017] δ(t)=(1±msin(ωt)) / 2

[0018] Where m represents the modulation depth of PWM, ω represents the angular frequency, if the converter is in the rectification state, the δ(t) expression is positive, if the converter is in the inverter state, the δ(t) expression is negative;

[0019] S12: Calculation of IGBT switching losses IGBT switching losses It is expressed as:

[0020]

[0021] in represents the turn-on loss of IGBT, represents the turn-off loss of IGBT, f sw represents the switching frequency, represents the turn-on loss, represents the turn-off loss and turn-on loss and turn-off losses The values ​​are obtained using the module's data sheet. Indicates the current conversion factor of IGBT, Indicates the IGBT voltage conversion factor, It represents the empirical coefficient of IGBT gate resistance R for its turn-on energy consumption, It represents the junction temperature coefficient when turned on. Represents the empirical coefficient of gate resistance R on turn-off energy consumption, Represents the junction temperature coefficient when turned off;

[0022] S13: Calculate the power loss P of IGBT IGBT , IGBT power loss P IGBT It is expressed as:

[0023]

[0024] S14: Calculate the conduction loss of the diode Conduction loss of diode It is expressed as:

[0025]

[0026] where v F Represents the forward voltage drop of the diode, v F It is expressed as:

[0027] v F =K VD (T jD -T 1 )+V F0 (T 1 )+i c [K VD (T jD -T 1 )+R F0 ]

[0028] Where K VD The temperature coefficient of the threshold voltage drop, T1 398.15K, V F0 Represents the threshold voltage drop of the diode at 398.15K, R F0 It represents the on-resistance of the diode at 398.15K;

[0029] S15: Calculate the switching loss P of the diode D_sw , the switching loss of the diode P D_sw It is expressed as:

[0030] P D_sw =P D_on +P D_off

[0031]

[0032] Where P D_on Represents the average turn-on loss during the diode switching cycle, P D_off represents the average turn-off loss during the diode switching cycle, represents the turn-on loss, represents the turn-off loss, K v represents the DC voltage coefficient, It represents the coefficient of IGBT gate resistance R on the turn-off energy consumption of the freewheeling diode;

[0033] S16: Calculate the power loss P of the diode D , the power loss of the diode P D It is expressed as:

[0034] P D =P D_cond +P D_sw .

[0035] Preferably, in step S11, the collector-emitter voltage v ce The value of the junction temperature T j and collector current i c Related, junction temperature T j and collector current i c The linear fitting expression is:

[0036] v ce (T j ,i c )=v ceo (T j )+i c (t)r ce (T j )

[0037] where v ceo represents the threshold voltage of IGBT, r ce Indicates the on-state resistance of the IGBT.

[0038] Preferably, the threshold voltage v ceo and junction temperature T j The relationship is expressed as:

[0039]

[0040] On-state resistance r ce and junction temperature T j The relationship is expressed as:

[0041]

[0042] Where T 1 Set to 25℃, T 2 Set to 125℃, get the collector-emitter voltage v ce for:

[0043]

[0044] Preferably, at 298.15K, the threshold voltage v of the IGBT is ceo and junction temperature T j There is a linear relationship between them, which can be specifically expressed as:

[0045]

[0046] in Indicates the threshold voltage of the IGBT at 298.15K, Indicates the junction temperature coefficient of the threshold voltage of the IGBT;

[0047] On-state resistance r ce The linear relationship with junction temperature is expressed as:

[0048]

[0049] in It represents the on-state resistance of IGBT at 298.15K. Indicates the junction temperature coefficient of the on-state resistance of the IGBT.

[0050] Preferably, in step S3, the IGBT state is detected and the VSC fault location is performed, and the fault results include single-tube fault and double-tube fault. The single-tube fault includes an upper bridge arm single-tube fault and a lower bridge arm single-tube fault. The double-tube fault includes a same-phase double-tube fault and an out-of-phase double-tube fault. The out-of-phase double-tube fault includes an upper bridge arm fault and an out-of-phase bridge arm fault.

[0051] Preferably, if the fault result is a single-tube fault, the power loss peak appears following the single IGBT loss peak; if the fault result is a same-phase double-tube fault, the power loss peak appears periodically following the peak of the corresponding current phase.

[0052] Therefore, the present invention adopts a converter state monitoring method based on IGBT loss of the above structure, which has the following beneficial effects:

[0053] (1) The present invention performs real-time status monitoring of the converter based on the change of IGBT power loss, without destroying the package or stopping the machine to test the power of the IGBT. The electrical parameters before and after the conversion are used to monitor the aging status of the IGBT, so as to better arrange the replacement plan of the aging power module before the end of the service life of the IGBT.

[0054] (2) While calculating the power loss through the formula, the present invention uses software such as PLECS and combines the linear interpolation algorithm to obtain the power loss of the IGBT module under different working conditions, so that the reliability and accuracy of the calculation results are higher;

[0055] (3) The present invention calculates the total input power based on the electrical parameters of the input part, and introduces PQ control to improve the stability of the output power and current, control the reactive power output of the power grid to be 0, adjust the on-resistance of the IGBT in the converter, simulate the corresponding power loss when the internal resistance of the IGBT increases under the aging state, and locate the aged IGBT according to the output waveform.

[0056] The method scheme of the present invention is further described in detail below through the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 A flow chart of a method for monitoring converter status based on IGBT loss according to the present invention;

[0058] Figure 2 is a topological structure diagram of the converter of the present invention;

[0059] Figure 3 The equivalent AC single-phase model circuit diagram of the converter of the present invention;

[0060] Figure 4 This is a schematic diagram of the IGBT volt-ampere characteristic fitting of the present invention;

[0061] Figure 5 This is a schematic diagram of a single-tube fault in the upper bridge arm of the present invention;

[0062] Figure 6 This is a schematic diagram of a single-tube fault in the lower bridge arm of the present invention;

[0063] Figure 7 This is a schematic diagram of the double-tube fault of the upper bridge arm of the present invention;

[0064] Figure 8 This is a schematic diagram of a double-tube fault with different phases and different bridge arms according to the present invention;

[0065] Fig. 9 This is a schematic diagram of a same-phase double-tube fault in the present invention. DETAILED DESCRIPTION

[0066] The method scheme of the present invention is further described below through drawings and embodiments.

[0067] Unless otherwise defined, method terms or scientific terms used in the present invention shall have the common meanings understood by one of ordinary skill in the art to which the present invention belongs.

[0068] The words "include" or "comprises" and the like used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms "inside", "outside", "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly specified and limited, the terms "attachment" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0069] Example

[0070] This embodiment takes the unipolar two-level topology as the research object. The topology has the advantages of simple structure, simple control, low loss, etc., and is widely used in small power energy storage systems. However, due to the limitation of the topology, the DC side energy storage medium voltage is required to be about 750V, and a large number of battery modules need to be connected in series. At the same time, the double frequency fluctuation of the DC bus voltage under the unbalanced power grid will cause the battery pack current to generate a double frequency component, which will damage the battery life.

[0071] like Figure 2 As shown in the figure, the DC side of the single-stage two-level PCS interacts with the three-phase symmetrical AC side grid through a bidirectional DC / AC converter composed of six switching devices, and is connected to the local load or grid through an LC filter. 1 ~S 6 Represents abc three-phase power switch tube, e a 、e b and e c Indicates the three-phase voltage of the AC side power grid, U a , Ub and U c Indicates the output phase voltage of the PCS inverter side, i a 、i b and i c Indicates the output current of the PCS inverter side, i a1 、i b1 and i c1 represents the three-phase current of the PCS grid, L represents the filter inductance at the output side of the PCS inverter, C represents the filter capacitor, and U dc Indicates the DC bus voltage, C dc Represents the DC bus capacitance.

[0072] like Figure 3 As shown, the topological structure diagram of the converter is converted into an equivalent AC single-phase model circuit diagram, where u dc Indicates the DC side voltage, u o Indicates the output voltage of the PCS inverter side, e g Indicates the AC side grid voltage, i o Indicates the output current of the PCS inverter side. Both the DC side and the AC side of the bidirectional DC / AC converter can be controlled. At the same time, the phase relationship of the AC side grid phase voltage and phase current can be controlled to realize the four-quadrant operation of the PCS.

[0073] like Figure 1 As shown, the present invention provides a converter state monitoring method based on IGBT loss, comprising the following steps:

[0074] S1: Obtain the DC side input voltage, DC side input current, AC side output voltage and AC side output current of the converter, and calculate the IGBT power loss and diode power loss;

[0075] The conduction mode of the three-phase bridge inverter circuit is 180° conduction. The upper and lower bridge arms of the same half bridge conduct alternately. The current and voltage waveforms of the IGBT and the freewheeling diode in any phase of U, V, and W are the same and there is only a 120° phase difference. Therefore, only the IGBT and the freewheeling diode in the same half bridge need to be analyzed for loss.

[0076] When the IGBT is in the normal switch-on state, there are four different types of switching mode losses, namely, the loss in the off state, the loss in the on state, the drive loss and the switching loss. Among the above four types of losses, the values ​​of the loss in the off state and the drive loss are very small, so they can be ignored;

[0077] In the inverter circuit, in actual operation, the same phase of the inverter circuit, that is, the same half bridge, conducts electricity alternately between the upper and lower bridge arms. The V of the upper bridge arm in one modulation wave period T is 1 With D 1 On and off are opposite, V1 With D 2 The on-off is the same, a switching cycle T sw V of the same half bridge 1 With D 2 The on and off of V 1 With D 2 It conducts and generates switching loss, conduction loss and cut-off loss, while D 1 Cut-off, resulting in cut-off loss; in the second half D 1 It conducts and generates switching loss, conduction loss and cut-off loss, while V 1 With D 2 Cut-off, resulting in cut-off loss; in the first half of the switching cycle, V 1 conduction and generates switching loss and conduction loss, while D 1 Cut-off, resulting in cut-off loss; in the second half of the switching cycle D 1 conduction and generates switching loss and conduction loss, while V 1 Cut-off, resulting in cut-off loss, of which the cut-off loss can be ignored, and only the switching loss and conduction loss of the IGBT need to be calculated. Similarly, the cut-off loss of the freewheeling diode can also be ignored, and only the conduction loss and turn-off loss need to be calculated.

[0078] In step S1, the power loss of IGBT and diode is calculated by formula calculation method, simulation calculation method or thermal model file in PLECS to obtain power loss. The formula calculation method can calculate power loss with variables such as terminal voltage, phase current, PWM duty cycle, switching frequency, etc. according to driving conditions and power loss parameters and module data sheet. The simulation calculation method makes the fitting result accurate and saves calculation time. The power loss calculation of IGBT with the help of PLECS software has higher credibility and accuracy, and less calculation efficiency and occupied resources. This is because before the IGBT module leaves the factory, the manufacturer will conduct various tests on its products, including all curves of loss calculation, and its test data volume is wider and more;

[0079] The IGBT power loss and diode power loss are calculated by the formula calculation method, which specifically includes the following steps:

[0080] S11: Calculate the average conduction loss of IGBT In a complete cycle, the average conduction loss of the IGBT is It is expressed as:

[0081]

[0082] Where T sw represents the switching cycle, v ce represents the collector-emitter voltage, i crepresents the collector current, δ(t) represents the duty cycle, and δ(t) is expressed as:

[0083] δ(t)=(1±msin(ωt)) / 2

[0084] Where m represents the modulation depth of PWM, ω represents the angular frequency, if the converter is in the rectification state, the δ(t) expression is positive, if the converter is in the inverter state, the δ(t) expression is negative;

[0085] S12: Calculation of IGBT switching losses IGBT switching loss P D_sw This is mainly because the switching loss P is generated because the parasitic inductance inside the module causes the switching from the off state to the on state or the switching from the on state to the off state to be not completed instantly during the commutation process. D_sw , IGBT switching loss It is expressed as:

[0086]

[0087] Where P Ion represents the turn-on loss of IGBT, represents the turn-off loss of IGBT, f sw represents the switching frequency, represents the turn-on loss, represents the turn-off loss and turn-on loss and turn-off losses The values ​​are obtained using the module's data sheet. Indicates the current conversion factor of IGBT, Indicates the IGBT voltage conversion factor, It represents the empirical coefficient of IGBT gate resistance R for its turn-on energy consumption, It represents the junction temperature coefficient when turned on. Represents the empirical coefficient of gate resistance R on turn-off energy consumption, Represents the junction temperature coefficient when turned off;

[0088] S13: Calculate the power loss P of IGBT IGBT , IGBT power loss P IGBT It is expressed as:

[0089]

[0090] Since the IGBT chip inside the IGBT module is anti-parallel connected with a diode, the heat generated by the diode will also affect the junction temperature of the IGBT, so the power loss of the diode also needs to be taken into account;

[0091] S14: Calculate the conduction loss of the diode Conduction loss of diode It is expressed as:

[0092]

[0093] where v F Represents the conduction voltage drop of the diode, v F It is expressed as:

[0094] v F =K VD (T jD -T 1 )+V F0 (T 1 )+i c [K VD (T jD -T 1 )+R F0 ]

[0095] Where K VD The temperature coefficient of the threshold voltage drop, T 1 398.15K, V F0 Represents the threshold voltage drop of the diode at 398.15K, R F0 It represents the on-resistance of the diode at 398.15K;

[0096] S15: Calculate the switching loss P of the diode D_sw The switching loss of the diode is similar to that of the IGBT. By referring to the energy loss diagram and loss curve in the module data sheet, the switching loss P of the diode can be obtained. D_sw It is expressed as:

[0097] P D_sw =P D_on +P D_off

[0098]

[0099] Where P D_on Represents the average turn-on loss during the diode switching cycle, P D_off represents the average turn-off loss during the diode switching cycle, represents the turn-on loss, represents the turn-off loss, K v represents the DC voltage coefficient, It represents the coefficient of IGBT gate resistance R on the turn-off energy consumption of the freewheeling diode;

[0100] S16: Calculate the power loss P of the diode D , the power loss of the diode P D It is expressed as:

[0101] P D =P D_cond +P D_sw .

[0102] In step S11, the collector-emitter voltage v ce The value of the junction temperature T j and collector current i c The relationship between the two can be obtained by linear fitting using the output characteristic curve in the data sheet of the corresponding module. j and collector current i c The linear fitting expression is:

[0103] v ce (T j ,i c )=v ceo (T j )+i c (t)r ce (T j )

[0104] where v ceo represents the threshold voltage of IGBT, r ce Indicates the on-state resistance of the IGBT.

[0105] Threshold voltage v ceo and junction temperature T j The relationship is expressed as:

[0106]

[0107] On-state resistance r ce and junction temperature T j The relationship is expressed as:

[0108]

[0109] Where T 1 Set to 25℃, T 2 Set to 125℃, get the collector-emitter voltage v ce for:

[0110]

[0111] like Figure 4 As shown in the figure, the solid line and the dotted line represent the volt-ampere characteristic curves of the IGBT at 298.15K and 398.15K respectively. Taking the volt-ampere characteristic curve of the IGBT at 298.15K as an example, the threshold voltage v of the IGBT ceo and junction temperature T j There is a linear relationship between them, which can be expressed as:

[0112]

[0113] in Indicates the threshold voltage of the IGBT at 298.15K, Indicates the junction temperature coefficient of the threshold voltage of the IGBT;

[0114] On-state resistance r ce The linear relationship with junction temperature is expressed as:

[0115]

[0116] in It represents the on-state resistance of IGBT at 298.15K. Indicates the junction temperature coefficient of the on-state resistance of the IGBT.

[0117] S2: Build the IGBT module thermal network model and calculate the IGBT junction temperature and IGBT on-state voltage drop;

[0118] S3: Detect the IGBT status and locate the VSC fault based on the IGBT AC side output three-phase current and IGBT component parameter values.

[0119] In step S3, the IGBT state is detected and the VSC fault is located. The fault results include single-tube fault and double-tube fault. The single-tube fault includes an upper bridge arm single-tube fault and a lower bridge arm single-tube fault. The double-tube fault includes a same-phase double-tube fault and a different-phase double-tube fault. The different-phase double-tube fault includes a same upper bridge arm fault and a different bridge arm fault.

[0120] When the converter is operating normally, the on-resistance Ron of the six IGBTs is the same, and the loss is maintained at about 20. Figure 5 As shown, when a single-tube fault occurs, this embodiment assumes that the IGBTs of the upper and lower bridges of phase A are aged, and their Ron increases, while the Ron of the other bridge arms remains unchanged, and the overall loss and the peak value of the corresponding fault phase Ia appear at the same time, and the peak value of the overall loss always follows the peak value of the single IGBT loss;

[0121] like Figure 6 As shown in the figure, when the current is reversed, the aging IGBT will also experience a small loss peak when it is subjected to reverse voltage. When the lower bridge arm ages, the peak value of the total IGBT loss corresponds to the negative half-axis peak point in one cycle of Ia, and a small peak value will also appear in the positive half-cycle during the reverse cutoff stage. Based on this rule, we can realize the positioning monitoring of IGBT aging.

[0122] like Figure 7As shown in the figure, assuming that the upper bridge arm IGBTs of different sizes are aged, first set the No. 1 and No. 3 tubes to age, and their on-resistance Ron increases to the same value. The power loss will have two peaks, but the peaks are not equal. The positions of the two peaks correspond to the positions where the positive half-axis peaks of Ia and Ib appear, and the power loss peak corresponding to the peak of Ia will be slightly smaller than the power loss peak corresponding to Ib.

[0123] The reason for this is that when the first small peak appears, Ia and the corresponding No. 1 IGBT power reach their peaks. At this time, the No. 3 tube is in the power decline stage (Ib is in the decline stage) and is about to decline to the valley, so the peak here has not reached the maximum. When the second peak appears, Ib and the corresponding No. 3 IGBT power reach their peaks. At this time, the No. 1 tube is about to reach the peak of the reverse current, so there will also be a small peak in power, and the overall power loss reaches the maximum at this time.

[0124] like Figure 8 As shown, out-of-phase and out-of-bridge-arm IGBT aging occurs, and the overall loss peak appears at the positive half-axis peak of Ia and the negative half-axis peak of Ib;

[0125] like Fig. 9 As shown in the figure, when a same-phase double-tube fault occurs, the power loss peak also appears periodically following the peak value of the corresponding current phase.

[0126] Therefore, the present invention adopts the above-mentioned converter state monitoring method based on IGBT loss, and performs real-time status monitoring of the converter based on the change of IGBT power loss. There is no need to destroy the package or shut down the IGBT for power testing. The electrical parameters before and after the conversion are used to monitor the aging state of the IGBT. At the same time, PQ control is introduced to improve the stability of the output power and current, so as to better arrange the replacement plan of the aging power module before the end of the service life of the IGBT.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the method scheme of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary method personnel in the field should understand that they can still modify or replace the method scheme of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified method scheme to deviate from the spirit and scope of the method scheme of the present invention.

Claims

1. A method for monitoring converter status based on IGBT loss, characterized in that: The following steps are involved: S1: Obtain the DC side input voltage, DC side input current, AC side output voltage and AC side output current of the converter, and calculate the IGBT power loss and diode power loss; S2: Build the IGBT module thermal network model and calculate the IGBT junction temperature and IGBT on-state voltage drop; S3: Detect the IGBT status and locate the VSC fault based on the IGBT AC side output three-phase current and IGBT component parameter values.

2. The method for monitoring converter status based on IGBT loss according to claim 1, characterized in that: In step S1, the IGBT power loss and the diode power loss are calculated by using a formula calculation method, a simulation calculation method or by using a thermal model file in PLECS to obtain the power loss.

3. The method for monitoring converter status based on IGBT loss according to claim 2, characterized in that: The IGBT power loss and diode power loss are calculated by the formula calculation method, which specifically includes the following steps: S11: Calculate the average conduction loss of IGBT In a complete cycle, the average conduction loss of the IGBT is It is expressed as: Where T sw represents the switching cycle, v ce represents the collector-emitter voltage, i c represents the collector current, δ(t) represents the duty cycle, and δ(t) is expressed as: δ(t)=(1±msin(ωt)) / 2 Where m represents the modulation depth of PWM, ω represents the angular frequency, if the converter is in the rectification state, the δ(t) expression is positive, if the converter is in the inverter state, the δ(t) expression is negative; S12: Calculation of IGBT switching losses IGBT switching losses It is expressed as: in represents the turn-on loss of IGBT, represents the turn-off loss of IGBT, f sw represents the switching frequency, represents the turn-on loss, represents the turn-off loss and turn-on loss and turn-off losses The values ​​are obtained using the module's data sheet. Indicates the current conversion factor of IGBT, Indicates the IGBT voltage conversion factor, It represents the empirical coefficient of IGBT gate resistance R for its turn-on energy consumption, It represents the junction temperature coefficient when turned on. Represents the empirical coefficient of gate resistance R on turn-off energy consumption, Represents the junction temperature coefficient when turned off; S13: Calculate the power loss P of IGBT IGBT , IGBT power loss P IGBT It is expressed as: S14: Calculate the conduction loss of the diode Conduction loss of diode It is expressed as: where v F Represents the conduction voltage drop of the diode, v F It is expressed as: v F =K VD (T jD -T1)+V F0 (T1)+i c [K VD (T jD -T1)+R F0 ] Where K VD Represents the temperature coefficient of the threshold voltage drop, T1 is 398.15K, V F0 Represents the threshold voltage drop of the diode at 398.15K, R F0 It represents the on-resistance of the diode at 398.15K; S15: Calculate the switching loss P of the diode D_sw , the switching loss of the diode P D_sw It is expressed as: P D_sw =P D_on +P D_off Where P D_on Represents the average turn-on loss during the diode switching cycle, P D_off represents the average turn-off loss during the diode switching cycle, represents the turn-on loss, represents the turn-off loss, K v represents the DC voltage coefficient, It represents the coefficient of IGBT gate resistance R on the turn-off energy consumption of the freewheeling diode; S16: Calculate the power loss P of the diode D , the power loss of the diode P D It is expressed as: P D =P D_cond +P D_sw 。 4. The method for monitoring converter status based on IGBT loss according to claim 3, characterized in that: In step S11, the collector-emitter voltage v ce The value of the junction temperature T j and collector current i c Related, junction temperature T j and collector current i c The linear fitting expression is: v ce (T j ,i c )=v ceo (T j )+i c (t)r ce (T j ) where v ceo represents the threshold voltage of IGBT, r ce Indicates the on-state resistance of the IGBT.

5. The method for monitoring converter status based on IGBT loss according to claim 4, characterized in that: Threshold voltage v ceo and junction temperature T j The relationship is expressed as: On-state resistance r ce and junction temperature T j The relationship is expressed as: Where T1 is set to 25°C and T2 is set to 125°C, the collector-emitter voltage v ce for:

6. The method for monitoring converter status based on IGBT loss according to claim 4, characterized in that: At 298.15K, the threshold voltage v of the IGBT ceo and junction temperature T j There is a linear relationship between them, which can be specifically expressed as: in Indicates the threshold voltage of the IGBT at 298.15K, Indicates the junction temperature coefficient of the threshold voltage of the IGBT; On-state resistance r ce The linear relationship with junction temperature is expressed as: in It represents the on-state resistance of IGBT at 298.15K. Indicates the junction temperature coefficient of the on-state resistance of the IGBT.

7. The method for monitoring converter status based on IGBT loss according to claim 1, characterized in that: In step S3, the IGBT state is detected and the VSC fault is located. The fault results include single-tube fault and double-tube fault. The single-tube fault includes an upper bridge arm single-tube fault and a lower bridge arm single-tube fault. The double-tube fault includes a same-phase double-tube fault and a different-phase double-tube fault. The different-phase double-tube fault includes the same upper bridge arm fault and the different bridge arm fault.

8. The method for monitoring converter status based on IGBT loss according to claim 7, characterized in that: If the fault result is a single-tube fault, the power loss peak follows the single IGBT loss peak. If the fault result is a same-phase double-tube fault, the power loss peak follows the peak of the corresponding current phase and appears periodically.

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