Fault Identification Method, Device, Equipment and Storage Medium of Power Electronic Transformer

Abstract

The present invention discloses a method, device, equipment and storage medium for fault identification of a power electronic transformer, which is used to solve the problems of poor fault identification ability and low protection sensitivity of the existing power electronic transformer. The method includes: deconstructing the power electronic transformer into three levels, including the overall equipment level, the isolation level and the high-frequency transformer level, and the high-frequency transformer level includes a plurality of high-frequency transformers; judging whether the DC-side voltage of the power electronic transformer is abnormal; if so, calculating the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port and the instantaneous power of the medium-voltage DC side of the overall equipment level; calculating the instantaneous power of the isolation level; calculating the differential current of the high-frequency transformer; and performing fault identification according to the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, the instantaneous power of the medium-voltage DC side, the instantaneous power of the isolation level, the differential current and a preset protection criterion to obtain the fault type of the power electronic transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic transformers, and in particular to a method, device, equipment and storage medium for fault identification of a power electronic transformer. Background Art

[0002] A power electronic transformer (PET), also known as a solid-state transformer (SST) or a power router (PR), is a high-frequency isolation power conversion device that integrates power electronics technology and control technology. It has a topological structure with multiple power conversion stages (input, isolation, and output stages), and can realize functions such as voltage conversion, electrical isolation, power regulation, and renewable energy access. It plays a key role in the distribution network with a high proportion of new energy access. However, the increase in the number of power stages makes its control and fault types more complex, and the traditional current differential protection is not applicable. Therefore, it is urgent to carry out research on the protection of PET.

[0003] With the large-scale access of distributed renewable energy, AC-DC or multi-level DC networking schemes will be widely adopted, and PET will be directly connected to the existing power grid. PET needs to establish an independent protection system to ensure the safety of PET and achieve coordinated control and protection. Subsequently, the industry proposed that on the basis of the three-level partition of the input, isolation, and output stages of PET, it is further refined and divided into blocks, and measurement points are arranged around the protected modules respectively. AC line differential protection, DC low-voltage overcurrent protection, etc. are configured for modules such as PET AC inlets and DC buses, and referring to the protection of AC transformers and converters, it is proposed that the existing mature schemes of rectifier and inverter protection can be directly adopted for the power conversion modules inside PET. Then, the research personnel further introduced the development logic of the hardware protection circuit on this basis, and designed two fault crossing strategies for PET configuration: bridge arm redundancy and bypass redundancy. However, this type of protection scheme has a large number of measurement points and complex communication, and the cooperation between the protections of each module lacks timing logic. In addition, a research team analyzed the internal fault characteristics of high-frequency isolation transformers and confirmed that current differential protection has stronger adaptability at high frequencies. Some scholars also proposed a current differential protection for PET based on dq0 components. This scheme judges whether a fault occurs inside or outside the zone according to the difference between the dq0 values of the currents at both ends of PET. This scheme reduces the number of measurement point configurations, but the improved differential protection extracts high-frequency components for calculation, is vulnerable to noise interference, and has insufficient identification ability for minor faults of PET such as internal short circuits in the isolation stage, and the protection sensitivity is low. Summary of the Invention

[0004] The present invention provides a method, device, equipment and storage medium for fault identification of a power electronic transformer, which is used to solve the technical problems of poor fault identification ability and low protection sensitivity of the existing power electronic transformer.

[0005] The present invention provides a method for fault identification of a power electronic transformer, including:

[0006] Decompose the power electronic transformer into three levels; wherein, the levels include the overall equipment layer, the isolation layer and the high-frequency transformer layer, and the high-frequency transformer layer includes a plurality of high-frequency transformers;

[0007] Judge whether the DC-side voltage of the power electronic transformer is abnormal;

[0008] If so, calculate the instantaneous power of the MVAC input-stage port, the instantaneous power of the LVAC output-stage port and the instantaneous power of the medium-voltage DC side of the overall equipment layer;

[0009] Calculate the instantaneous power of the isolation layer;

[0010] Calculate the differential current of the high-frequency transformer;

[0011] Perform fault identification according to the instantaneous power of the MVAC input-stage port, the instantaneous power of the LVAC output-stage port, the instantaneous power of the medium-voltage DC side, the instantaneous power of the isolation layer, the differential current and a preset protection criterion, and obtain the fault type of the power electronic transformer.

[0012] Optionally, the step of judging whether the DC-side voltage of the power electronic transformer is abnormal includes:

[0013] Obtain the bus-to-ground voltage of the medium-voltage DC side of the power electronic transformer and its first change value;

[0014] Obtain the bus-to-ground voltage of the low-voltage DC side of the power electronic transformer and its second change value;

[0015] Judge whether the DC-side voltage of the power electronic transformer is abnormal by using the bus-to-ground voltage of the medium-voltage DC side, the first change value, the bus-to-ground voltage of the low-voltage DC side, the second change value and a preset setting value.

[0016] Optionally, the step of calculating the instantaneous power of the MVAC input-stage port, the instantaneous power of the LVAC output-stage port and the instantaneous power of the medium-voltage DC side of the overall equipment layer includes:

[0017] Obtain the medium-voltage instantaneous phase voltage value and the medium-voltage instantaneous phase current value of each phase of the MVAC input-stage port in the power electronic transformer;

[0018] Calculate the instantaneous power of the MVAC input stage port using the medium - voltage instantaneous phase voltage value and the medium - voltage instantaneous phase current value;

[0019] Obtain the low - voltage instantaneous phase voltage values and low - voltage instantaneous phase current values of each phase at the LVAC output stage port of the power electronic transformer;

[0020] Calculate the instantaneous power of the LVAC output stage port using the low - voltage instantaneous phase voltage value and the low - voltage instantaneous phase current value;

[0021] Obtain the instantaneous voltage and instantaneous current of the medium - voltage DC side of the power electronic transformer;

[0022] Calculate the instantaneous power of the medium - voltage DC side using the instantaneous voltage and the instantaneous current.

[0023] Optionally, the isolation layer includes a dual - active - bridge converter DAB; the instantaneous power of the isolation layer includes the primary - side instantaneous power and the secondary - side instantaneous power; the steps of calculating the instantaneous power of the isolation layer of the isolation layer include:

[0024] Obtain the primary - side voltage, primary - side current, secondary - side voltage, and secondary - side current of the DAB;

[0025] Calculate the primary - side instantaneous power of the DAB using the primary - side voltage and the primary - side current;

[0026] Calculate the secondary - side instantaneous power of the DAB using the secondary - side voltage and the secondary - side current.

[0027] Optionally, the steps of calculating the differential current of the high - frequency transformer include:

[0028] Obtain the transformer primary - side voltage, transformer primary - side current, transformer secondary - side voltage, and transformer secondary - side current of each high - frequency transformer;

[0029] Calculate the primary - to - secondary voltage ratio of the transformer primary - side voltage and the transformer secondary - side voltage;

[0030] Calculate the differential current of the high - frequency transformer using the primary - to - secondary voltage ratio, the transformer primary - side current, and the transformer secondary - side current.

[0031] Optionally, the preset protection criterion includes an overall equipment - layer criterion, an isolation - layer criterion, and a high - frequency transformer - layer criterion; the overall equipment - layer criterion includes an equipment - layer criterion, an AC - side auxiliary criterion, and a DC - side auxiliary criterion; the steps of performing fault identification based on the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, the instantaneous power of the medium - voltage DC side, the instantaneous power of the isolation layer, the differential current, and the preset protection criterion to obtain the fault type of the power electronic transformer include:

[0032] Determine whether the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side satisfy the overall equipment - layer criterion;

[0033] If the overall equipment - layer criterion is satisfied, determine that the power electronic transformer has an internal fault, and determine whether the instantaneous power of the isolation layer satisfies the isolation - layer criterion;

[0034] If the isolation - layer criterion is satisfied, then determine whether the differential current satisfies the high - frequency transformer - layer criterion;

[0035] If the high - frequency transformer - layer criterion is satisfied, determine that the fault type of the power electronic transformer is an inter - turn fault of the high - frequency transformer;

[0036] If the high - frequency transformer - layer criterion is not satisfied, determine that the fault type of the power electronic transformer is an isolation - level fault;

[0037] If the instantaneous power of the isolation layer does not satisfy the isolation - layer criterion, then determine the fault type of the power electronic transformer as an internal input - stage fault or an internal output - stage fault according to the AC - side auxiliary criterion.

[0038] Optionally, it further includes:

[0039] If the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side do not satisfy the overall equipment - layer criterion, then determine whether the instantaneous power of the isolation layer satisfies the isolation - layer criterion;

[0040] If the instantaneous power of the isolation layer does not satisfy the isolation - layer criterion, then determine the fault type of the power electronic transformer as an external DC - side fault or an external AC - side fault according to the DC - side auxiliary criterion;

[0041] If the instantaneous power of the isolation layer satisfies the isolation - layer criterion, then return to the step of determining whether the differential current satisfies the high - frequency transformer - layer criterion.

[0042] The present invention also provides a power - electronic transformer fault identification device, including:

[0043] A deconstruction module, configured to deconstruct the power - electronic transformer into three levels; wherein, the levels include an overall equipment level, an isolation level, and a high - frequency transformer level, and the high - frequency transformer level includes several high - frequency transformers;

[0044] An abnormality judgment module, configured to judge whether the DC - side voltage of the power - electronic transformer is abnormal;

[0045] The device - level instantaneous power calculation module is used to calculate the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side of the overall device layer if so.

[0046] The isolation - layer instantaneous power calculation module is used to calculate the isolation - layer instantaneous power of the isolation layer.

[0047] The differential - current calculation module is used to calculate the differential current of the high - frequency transformer.

[0048] The fault - type determination module is used to perform fault identification based on the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, the instantaneous power of the medium - voltage DC side, the isolation - layer instantaneous power, the differential current, and the preset protection criterion to obtain the fault type of the power - electronic transformer.

[0049] The present invention also provides an electronic device, which includes a processor and a memory:

[0050] The memory is used to store program code and transmit the program code to the processor;

[0051] The processor is used to execute the power - electronic transformer fault - identification method as described in any one of the above according to the instructions in the program code.

[0052] The present invention also provides a computer - readable storage medium, which is used to store program code, and the program code is used to execute the power - electronic transformer fault - identification method as described in any one of the above.

[0053] As can be seen from the above technical solutions, the present invention has the following advantages: The present invention provides a power - electronic transformer fault - identification method, and specifically discloses: deconstructing the power - electronic transformer into three levels; among them, the levels include the overall device layer, the isolation layer, and the high - frequency transformer layer, and the high - frequency transformer layer includes several high - frequency transformers; judging whether the DC - side voltage of the power - electronic transformer is abnormal; if so, calculating the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side of the overall device layer; calculating the isolation - layer instantaneous power of the isolation layer; calculating the differential current of the high - frequency transformer; performing fault identification based on the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, the instantaneous power of the medium - voltage DC side, the isolation - layer instantaneous power, the differential current, and the preset protection criterion to obtain the fault type of the power - electronic transformer. Through the present invention, it is possible to identify internal and external faults at the device level and be able to identify specific fault types, which helps to adopt different fault - isolation methods for different fault types, and subsequently, the control characteristics of the power - electronic transformer can be fully utilized. Description of the Drawings

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0055] Figure 1 It is a step flowchart of a fault identification method for a power electronic transformer provided by an embodiment of the present invention;

[0056] Figure 2 It is a schematic structural diagram of a power electronic transformer provided by an embodiment of the present invention;

[0057] Figure 3 It is a fault identification logic block diagram provided by an embodiment of the present invention;

[0058] Figure 4 It is a structural block diagram of a fault identification device for a power electronic transformer provided by an embodiment of the present invention. Specific Embodiments

[0059] The embodiments of the present invention provide a fault identification method, device, equipment and storage medium for a power electronic transformer, which are used to solve the technical problems of poor fault identification ability and low protection sensitivity of existing power electronic transformers.

[0060] To make the objectives, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0061] Please refer to Figure 1 , Figure 1 It is a step flowchart of a fault identification method for a power electronic transformer provided by an embodiment of the present invention.

[0062] A fault identification method for a power electronic transformer provided by the present invention may specifically include the following steps:

[0063] Step 101: Decompose the power electronic transformer into three levels; where the levels include the overall equipment layer, the isolation layer, and the high-frequency transformer layer, and the high-frequency transformer layer includes several high-frequency transformers;

[0064] Please refer to Figure 2 , Figure 2The structural schematic diagram of a power electronic transformer provided by an embodiment of the present invention. Figure 2 The five-level power electronic transformer PET shown is divided into three levels, marked with different colors. Among them, dark gray includes the overall equipment layer of the PET, white includes the isolation layer where all DAB cascade units are located, and light gray includes all high-frequency transformer layers. Voltage and current measurement points can be set at different positions, such as Figure 2 shown by the medium gray small squares. The voltage and current of each line can be collected through the voltage and current measurement points.

[0065] Step 102, determine whether the DC side voltage of the power electronic transformer is abnormal;

[0066] In the embodiment of the present invention, the abnormal determination of the DC side voltage of the power electronic transformer can be performed by reading the voltage of the medium-voltage DC bus of the power electronic transformer to the ground and its first change value, and the voltage of the low-voltage DC bus to the ground and its second change value.

[0067] The first change value refers to the instantaneous change value of the voltage of the medium-voltage DC bus to the ground; the second change value is the instantaneous change value of the voltage of the low-voltage DC bus to the ground.

[0068] In one example, step 102 may specifically include the following sub-steps:

[0069] S21, obtain the voltage of the medium-voltage DC side bus of the power electronic transformer to the ground and its first change value;

[0070] S22, obtain the voltage of the low-voltage DC side bus of the power electronic transformer to the ground and its second change value;

[0071] S23, use the voltage of the medium-voltage DC side bus to the ground, the first change value, the voltage of the low-voltage DC side bus to the ground, the second change value and the preset setting value to determine whether the DC side voltage of the power electronic transformer is abnormal.

[0072] In a specific implementation, the voltages of the positive and negative buses of the medium- and low-voltage DC sides to the ground U±MDC, U±LDC and their first change values ΔU±MDC, the first change value ΔU±LDC can be read, and substituted into the formula |ΔU±MDC / U±MDC|>K set0 ∪|ΔU±LDC / U±LDC|>K set0 to check whether it is satisfied. If the judgment is established, step 103 is continued; otherwise, step 102 is looped, where K set0 The setting value of needs to avoid the slight fluctuations of the DC side voltage that may occur under abnormal operating conditions, and at the same time needs to have a high sensitivity to the response of slight faults such as inter-turn short circuits of high-frequency transformers. Generally, the value is taken as 0.2.

[0073] Step 103, if so, calculate the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side of the overall equipment layer;

[0074] MVAC (Medium Voltage AC) usually refers to alternating current with a voltage range between 1 kV and 35 kV.

[0075] LVAC (Low Voltage AC) usually refers to alternating current with a voltage below 1 kV.

[0076] In one example, Step 103 may include the following sub - steps:

[0077] S31, obtain the medium - voltage instantaneous phase - voltage value and medium - voltage instantaneous phase - current value of each phase at the MVAC input - stage port of the power electronic transformer;

[0078] S32, calculate the instantaneous power of the MVAC input - stage port using the medium - voltage instantaneous phase - voltage value and medium - voltage instantaneous phase - current value;

[0079] S33, obtain the low - voltage instantaneous phase - voltage value and low - voltage instantaneous phase - current value of each phase at the LVAC output - stage port of the power electronic transformer;

[0080] S34, calculate the instantaneous power of the LVAC output - stage port using the low - voltage instantaneous phase - voltage value and low - voltage instantaneous phase - current value;

[0081] S35, obtain the instantaneous voltage and instantaneous current of the medium - voltage DC side of the power electronic transformer;

[0082] S36, calculate the instantaneous power of the medium - voltage DC side using the instantaneous voltage and instantaneous current.

[0083] In a specific implementation, the instantaneous power p1 of the MVAC input - stage port can be calculated according to the following formula:

[0084] p1 = p A +p B +p C =u A *i A +u B *i B +u C *i C

[0085] Where p A 、p B 、p C are the three - phase instantaneous powers of the medium - voltage AC - side port, and u A 、u B 、u Cis the medium - voltage instantaneous phase voltage value of each phase at the medium - voltage AC side of the PET, i A 、i B 、i C are the medium - voltage instantaneous phase current values of each phase at the medium - voltage AC side of the PET.

[0086] Calculate the instantaneous power p2 of the LVAC output - stage port according to the following formula:

[0087] p2 = p a + p b + p c = u a * i a + u b * i b + u c * i c

[0088] where p a 、p b 、p c are the three - phase instantaneous powers of the low - voltage AC side port, u a 、u b 、u c are the low - voltage instantaneous phase voltage values of each phase at the low - voltage AC side of the PET, i a 、i b 、i c are the low - voltage instantaneous phase current values of each phase at the low - voltage AC side of the PET.

[0089] Calculate the medium - voltage DC - side instantaneous power p DC :

[0090] p DC = u DC* i DC

[0091] where u DC is the medium - voltage DC - side instantaneous voltage, i DC is the medium - voltage DC - side instantaneous current.

[0092] Step 104, calculate the isolation - layer instantaneous power;

[0093] In the embodiment of the present invention, the isolation layer may include a Dual Active Bridge (DAB). The DAB consists of two full - bridge circuits, a high - frequency transformer, an inductor, and a capacitor. The two full - bridge circuits are respectively located on the primary side and the secondary side of the transformer, and electrical isolation and voltage matching are achieved through the high - frequency transformer. The isolation - layer instantaneous power includes the primary - side instantaneous power and the secondary - side instantaneous power. Step 104 may specifically include the following sub - steps:

[0094] S41. Obtain the primary side voltage, primary side current, secondary side voltage, and secondary side current of the DAB;

[0095] S42. Calculate the instantaneous power of the primary side of the DAB using the primary side voltage and primary side current;

[0096] S43. Calculate the instantaneous power of the secondary side of the DAB using the secondary side voltage and secondary side current.

[0097] In a specific implementation, the instantaneous power p of the primary side of the DAB can be calculated by the following formula DABP :

[0098] p DABP = u DABP * i DABP

[0099] where u DABP is the primary side voltage of the isolation layer, and i DABP is the primary side current of the isolation layer.

[0100] The instantaneous power p of the secondary side of the DAB is calculated by the following formula DABS :

[0101] p DABS = u DABS * i DABS

[0102] where u DABS is the secondary side voltage of the isolation layer, and i DABS is the secondary side current of the isolation layer.

[0103] Step 105. Calculate the differential current of the high-frequency transformer;

[0104] The differential current is based on Kirchhoff's current law, that is, the sum of the currents flowing into a node is equal to the sum of the currents flowing out of the node. During normal operation or external faults, the differential current should be zero or close to zero; while during internal faults, the differential current will increase significantly.

[0105] In one example, step 105 may include the following sub-steps:

[0106] S51. Obtain the transformer primary side voltage, transformer primary side current, transformer secondary side voltage, and transformer secondary side current of each high-frequency transformer;

[0107] S52. Calculate the primary-secondary side voltage ratio of the transformer primary side voltage and transformer secondary side voltage;

[0108] S53. Calculate the differential current of the high-frequency transformer using the primary-secondary side voltage ratio, transformer primary side current, and transformer secondary side current.

[0109] In specific implementation, the differential current of the primary and secondary coils of each high-frequency transformer can be calculated through |K·i HFITPn +i HFITSn |. Among them, K is the voltage ratio of the primary and secondary sides of the high-frequency transformer, and i HFITPn is the primary current of the nth high-frequency transformer, and i HFITSn is the secondary current of the nth high-frequency transformer.

[0110] Step 106: Perform fault identification based on the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, the instantaneous power of the medium-voltage DC side, the instantaneous power of the isolation layer, the differential current, and the preset protection criterion to obtain the fault type of the power electronic transformer.

[0111] After calculating the relevant power data of different levels of the power electronic transformer, fault identification can be performed according to the calculated power data and the preset protection criterion, so as to obtain the fault type of the power electronic transformer.

[0112] In the embodiment of the present invention, a tracking differentiator can be used to organize the protection criterion. The original traditional differential formula is rewritten by using the formula x1(k + 1) = x1(k) + Tx2(k), x2(k + 1) = x2(k) + hu, where u = fhan(x1, x2, r, h), and it satisfies:

[0113]

[0114] Among them, T is the sampling period, u(k) is the input signal at the kth moment, r is the tracking factor, which determines the speed of the tracking signal, h is the filtering factor, which determines the ability to filter out noise, x1(k) represents the tracking signal, x2(k) is the differential signal of x1(k), d is a dynamic parameter jointly determined by r and h, which is used to control the response speed and noise immunity of the tracking differentiator. A larger r or h will enhance the tracking speed, but may sacrifice smoothness. d0 is the secondary correction parameter of d, which is used as a threshold to judge the amplitude range of the state variable y and distinguish different calculation modes (such as linear and nonlinear regions). y is the linear combination of the state variables x1 (tracking target) and x2 (differential estimation). y is the core intermediate variable, which is used for subsequent condition judgment and calculation of the control input u, reflects the deviation between the system state and the expected trajectory, and fhan is a piecewise nonlinear function, which selects the control strategy according to the amplitude of the intermediate variable a. When a is large (|a| > d), the sign function is used for fast response; when a is small (|a| ≤ d), linear proportional regulation is used to balance the tracking accuracy and smoothness. Assume that the sampling frequency of the embodiment of the present invention is 10 kHz, T takes 10-4 s, r takes 1000, and h takes 0.02. Then the protection criterion is organized as follows:

[0115]

[0116] Among them, C r1 , C r2 , C r3 are the fault identification criteria for the PET device layer, isolation layer, and high-frequency transformer layer mentioned above respectively. P1, P2, and P3 are the active powers of the three ports during normal operation of the PET. K set1 , K set2 , K set3 , K setE , K setDC are the setting thresholds for the overall device layer criterion, isolation layer criterion, high-frequency transformer layer criterion, AC side auxiliary criterion, and DC side auxiliary criterion respectively; , , are p1, p2, and p DC after being processed by the tracking differentiator respectively; , are p DABP , p DABS after being processed by the tracking differentiator respectively; is i DC after being processed by the tracking differentiator; The fault current distortion rate of the E(M) medium-voltage AC side; E(L) is the defined distortion rate index of the low-voltage AC side.

[0117] The criterion setting principle is as follows:

[0118] When the PET is operating, it satisfies the conservation of active power. When a fault occurs inside or outside the zone, the difference in the active power of the PET ports shows an obvious change trend, based on which the internal and external faults can be effectively identified. The active power is usually obtained by the formula P = (∫T0pdt) / T, where P and p represent the active power and instantaneous power of the system respectively, and T represents a cycle. Therefore, the calculation of the active power at power frequency requires at least the instantaneous power values in a 20ms window. However, the PET has a short time requirement for fault identification and cannot obtain the active power in a conventional way.

[0119] When the AC system is operating normally, let u A = U A cos(ωt + θ), , where is the power factor angle and θ is the initial phase angle of the A-phase voltage. The power relationship can be obtained as follows:

[0120]

[0121] Among them, p A , p B , p C represent the three-phase instantaneous powers respectively, and u A , uB and u C and i A and i B and i C respectively represent the three-phase instantaneous voltage and current. U A and U B and U C and I A and I B and I C respectively represent the amplitudes of the three-phase instantaneous voltage and current.

[0122] It can be seen from this that the instantaneous power contains information about the active power, and a certain amount of active power can be obtained through the instantaneous power. Moreover, the calculation of the instantaneous power can be completed immediately, with a low requirement for the time window scale, and it is more suitable for constructing the PET protection criterion.

[0123] Since the DAB is equivalent to a transformer with time-delay characteristics and has an isolation effect on faults within milliseconds, the PET is decomposed into two parts, the medium-voltage side and the low-voltage side of the DAB, for transient analysis under faults with the DAB as the boundary.

[0124] When a symmetrical fault of three-phase short circuit occurs on the AC side, the sum of the three-phase instantaneous powers is the active power, and after the fault occurs, it presents as a curve of the change in the active power, as shown in the following formula:

[0125]

[0126] where U, U', I, and I' respectively represent the magnitudes of the amplitudes of the three-phase voltage and current waveforms before and after the fault, and respectively represent the initial phase angles of the three-phase voltage and current waveforms before and after the fault, P and P' represent the steady-state active powers before and after the fault, and τ represents the time constant of this stage, which is related to the circuit structure parameters. When different types of internal faults occur in the PET, only the reference potential point is changed for the external AC side, and the symmetrical characteristics are not damaged. Therefore, they can all be explained by the definition of the active power.

[0127] When an asymmetric fault occurs, the instantaneous power information is no longer equal to the active power all the time. However, there are still significant differences in the amplitude of the instantaneous power during internal and external faults. In addition, to enhance the accuracy of protection, auxiliary criteria are added for both the AC side and the DC side. When a fault occurs in the medium-voltage AC side within the zone, the current flowing through the measuring point is provided by the three-phase AC power supply, and the current frequency remains unchanged at the fault moment. When an external fault occurs, the measured fault current comes from the equivalent capacitor discharge, and at least one phase current frequency shows a sudden change at the fault moment. During an internal fault, the line generates an electromagnetic effect, and the short-circuit current may have transient high-frequency harmonics, interfering with the auxiliary criterion and causing misoperation of the protection. Therefore, a low-pass filtering algorithm is added to the auxiliary criterion to filter out harmonics above 50 Hz. Since the transient high-frequency harmonics are linearly superimposed on the original waveform, it is relatively convenient to filter them out. Under an external fault, the current before and after the fault moment shows a time-domain piecewise function, and the frequency mutation point will be more prominent due to the filtering effect. Therefore, a simple frequency mutation identification function can be constructed as an auxiliary criterion (see the distortion rate function defined in step six). During an internal fault, since there is no frequency mutation, under the same-frequency sine waveform, it is approximately a proportional straight line within 100 μs. The distortion rate E X (M) of the fault current on the medium-voltage AC side is close to the theoretical value of 1, while under an external fault, E X (M) will have a large fluctuation near the fault moment point. The identification region for judging an internal fault should be (1 - K setE , 1 + K setE ), and the setting of the value of K setE should not only consider clearly distinguishing internal and external faults, but also take into account eliminating the problem of excessive filtering of high-frequency harmonics under an internal fault caused by low-pass filtering (that is, the mutation of the filtered current at the fault moment may be weakened by the filtering effect, and the setting value of K setE should not be too large). It is stipulated that when the three-phase criteria of E A (M), E B (M), and E C (M) on the medium-voltage side each meet the condition within the internal identification region (1 - K setE , 1 + K setE ), E(M) is determined to be within the identification region (1 - K setE , 1 + K setE ).

[0128] Among them, the expression of the distortion rate E X (M) of the fault current on the medium-voltage AC side is , where X represents the phase identifier (X ∈ {A, B, C}), i represents the phase current, and j is the sampling point.

[0129] Define the distortion rate index of the low-voltage AC side as E(L), and the threshold setting principle is the same as that for judging E(M).

[0130] For the DC-side auxiliary criterion, when DC faults occur on different sides inside and outside the zone, the DC current flowing through the measuring point comes from the capacitor discharges on different sides. Therefore, there are significant differences in the instantaneous mutation directions of the currents. Thus, when dIDCmes / dt > KsetDC is satisfied, it is an internal fault; otherwise, it is an external fault. Here, IDCmes is defined as the current on the measured medium-voltage DC side, and the reference direction is the direction flowing into the PET. Even though there are obvious positive and negative differences in the current mutation directions under internal and external faults, when setting KsetDC, it is also necessary to consider avoiding interference caused by slight mutations in the current direction under abnormal operating conditions. The setting value can be set to a relatively high positive value to prevent misjudgment of the protection.

[0131] After determining the protection criterion, the fault type can be identified in combination with the protection criterion. Specifically, it can include the following sub-steps:

[0132] S61, judge whether the instantaneous power of the MVAC input-stage port, the instantaneous power of the LVAC output-stage port, and the instantaneous power of the medium-voltage DC side satisfy the overall equipment layer criterion;

[0133] S62, if the overall equipment layer criterion is satisfied, determine that the power electronic transformer has an internal fault, and judge whether the instantaneous power of the isolation layer satisfies the isolation layer criterion;

[0134] S63, if the isolation layer criterion is satisfied, then judge whether the differential current satisfies the high-frequency transformer layer criterion;

[0135] S64, if the high-frequency transformer layer criterion is satisfied, then determine that the fault type of the power electronic transformer is a high-frequency transformer turn-to-turn fault;

[0136] S65, if the high-frequency transformer layer criterion is not satisfied, then determine that the fault type of the power electronic transformer is an isolation-level fault;

[0137] S66, if the instantaneous power of the isolation layer does not satisfy the isolation layer criterion, then judge the fault type of the power electronic transformer as an internal input-stage fault or an internal output-stage fault according to the AC-side auxiliary criterion;

[0138] S67, if the instantaneous power of the MVAC input-stage port, the instantaneous power of the LVAC output-stage port, and the instantaneous power of the medium-voltage DC side do not satisfy the overall equipment layer criterion, then judge whether the instantaneous power of the isolation layer satisfies the isolation layer criterion;

[0139] S68, if the instantaneous power of the isolation layer does not satisfy the isolation layer criterion, then determine the fault type of the power electronic transformer as an external DC-side fault or an external AC-side fault according to the DC-side auxiliary criterion;

[0140] S69, if the instantaneous power of the isolation layer satisfies the isolation layer criterion, then return to the step of judging whether the differential current satisfies the high-frequency transformer layer criterion.

[0141] like Figure 3 As shown, the embodiment of the present invention can identify the fault inside and outside the zone according to the protection criterion and realize the fault type identification. r1 , C r2 , C r3 Combined with the logic combination of auxiliary criteria on the AC and DC sides, the fault type is identified. or When the protection starts. If the judgment criterion C is met r1 , it is judged as an internal fault, and the judgment is continued. If only the judgment criterion C is met r1 Does not satisfy criterion C r2 , then the input level fault or output level fault in the region is further distinguished according to the size of E(M) and E(L); if the judgment criteria C are met at the same time r2 With C r3 , it is further determined that a fault occurs between turns of the high-frequency transformer; if only C r2 Does not meet C r3 , it is determined that there is a short circuit between DAB units at the isolation level. In addition, when the judgment criterion C r1 If it is not satisfied, the criterion C r2 Further supplementary judgment, when criterion C is not met r1 , C r2 When , it is judged as an out-of-zone fault and It is further determined whether the fault outside the zone occurs on the DC side or the AC side. At this point, the protection judgment is completed and the signal is sent to the corresponding protection action unit. The entire judgment process is completed within 2ms after the fault occurs.

[0142] Through the embodiments of the present invention, it is possible to identify faults inside and outside the equipment level area, and to recognize the specific fault type, which helps to adopt different fault isolation methods for different fault types, and subsequently fully utilize the control characteristics of the power electronic transformer.

[0143] See also Figure 4 , Figure 4 A structural block diagram of a power electronic transformer fault identification device provided in an embodiment of the present invention.

[0144] An embodiment of the present invention provides a power electronic transformer fault identification device, comprising:

[0145] A deconstruction module 401 is used to deconstruct the power electronic transformer into three levels; wherein the levels include an overall device level, an isolation level and a high-frequency transformer level, and the high-frequency transformer level includes a plurality of high-frequency transformers;

[0146] The abnormality judgment module 402 is used to judge whether the DC side voltage of the power electronic transformer is abnormal;

[0147] The device - layer instantaneous power calculation module 403 is used to calculate the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, and the instantaneous power of the medium - voltage DC side of the overall device layer if so;

[0148] The isolation - layer instantaneous power calculation module 404 is used to calculate the isolation - layer instantaneous power of the isolation layer;

[0149] The differential - current calculation module 405 is used to calculate the differential current of the high - frequency transformer;

[0150] The fault - type determination module 406 is used to perform fault identification based on the instantaneous power of the MVAC input - stage port, the instantaneous power of the LVAC output - stage port, the instantaneous power of the medium - voltage DC side, the isolation - layer instantaneous power, the differential current, and the preset protection criteria to obtain the fault type of the power - electronic transformer.

[0151] In the embodiment of the present invention, the abnormality judgment module 402 includes:

[0152] The medium - voltage DC - side bus voltage - to - ground and its first change - value acquisition sub - module is used to acquire the medium - voltage DC - side bus voltage - to - ground of the power - electronic transformer and its first change value;

[0153] The low - voltage DC - side bus voltage - to - ground and its second change - value sub - module is used to acquire the low - voltage DC - side bus voltage - to - ground of the power - electronic transformer and its second change value;

[0154] The abnormality determination sub - module is used to determine whether the DC - side voltage of the power - electronic transformer is abnormal by using the medium - voltage DC - side bus voltage - to - ground, the first change value, the low - voltage DC - side bus voltage - to - ground, the second change value, and the preset setting value.

[0155] In the embodiment of the present invention, the device - layer instantaneous power calculation module 403 includes:

[0156] The medium - voltage instantaneous phase - voltage value and medium - voltage instantaneous phase - current value acquisition sub - module is used to acquire the medium - voltage instantaneous phase - voltage value and medium - voltage instantaneous phase - current value of each phase of the MVAC input - stage port of the power - electronic transformer;

[0157] The MVAC input - stage port instantaneous - power calculation sub - module is used to calculate the instantaneous power of the MVAC input - stage port by using the medium - voltage instantaneous phase - voltage value and medium - voltage instantaneous phase - current value;

[0158] The low - voltage instantaneous phase - voltage value and low - voltage instantaneous phase - current value acquisition sub - module is used to acquire the low - voltage instantaneous phase - voltage value and low - voltage instantaneous phase - current value of each phase of the LVAC output - stage port of the power - electronic transformer;

[0159] LVAC output stage port instantaneous power calculation sub-module, which is used to calculate the instantaneous power of the LVAC output stage port by using the low-voltage instantaneous phase voltage value and the low-voltage instantaneous phase current value;

[0160] Instantaneous voltage and instantaneous current acquisition sub-module, which is used to acquire the instantaneous voltage and instantaneous current of the medium-voltage DC side of the power electronic transformer;

[0161] Medium-voltage DC side instantaneous power calculation sub-module, which is used to calculate the instantaneous power of the medium-voltage DC side by using the instantaneous voltage and instantaneous current.

[0162] In the embodiment of the present invention, the isolation layer includes a dual active bridge converter DAB; the instantaneous power of the isolation layer includes the primary side instantaneous power and the secondary side instantaneous power; the isolation layer instantaneous power calculation module 404 includes:

[0163] Primary side voltage, primary side current, secondary side voltage and secondary side current acquisition sub-module, which is used to acquire the primary side voltage, primary side current, secondary side voltage and secondary side current of the DAB;

[0164] Primary side instantaneous power calculation sub-module, which is used to calculate the primary side instantaneous power of the DAB by using the primary side voltage and the primary side current;

[0165] Secondary side instantaneous power calculation sub-module, which is used to calculate the secondary side instantaneous power of the DAB by using the secondary side voltage and the secondary side current.

[0166] In the embodiment of the present invention, the differential current calculation module 405 includes:

[0167] Transformer primary and secondary side voltage and current acquisition sub-module, which is used to acquire the transformer primary side voltage, transformer primary side current, transformer secondary side voltage and transformer secondary side current of each high-frequency transformer;

[0168] Primary and secondary side voltage ratio calculation sub-module, which is used to calculate the primary and secondary side voltage ratio of the transformer primary side voltage and the transformer secondary side voltage;

[0169] Differential current calculation sub-module, which is used to calculate the differential current of the high-frequency transformer by using the primary and secondary side voltage ratio, the transformer primary side current and the transformer secondary side current.

[0170] In the embodiment of the present invention, the preset protection criterion includes the overall equipment layer criterion, the isolation layer criterion and the high-frequency transformer layer criterion; the overall equipment layer criterion includes the equipment layer criterion, the AC side auxiliary criterion and the DC side auxiliary criterion; the fault type determination module 406 includes:

[0171] Overall equipment layer criterion judgment sub-module, which is used to judge whether the MVAC input stage port instantaneous power, the LVAC output stage port instantaneous power, and the medium-voltage DC side instantaneous power meet the overall equipment layer criterion;

[0172] The first isolation layer criterion judgment sub-module is used to determine that a fault occurs in the power electronic transformer within the zone if the overall equipment layer criterion is met, and to judge whether the instantaneous power of the isolation layer meets the isolation layer criterion;

[0173] The high-frequency transformer layer criterion judgment sub-module is used to judge whether the differential current meets the high-frequency transformer layer criterion if the isolation layer criterion is met;

[0174] The high-frequency transformer turn-to-turn fault determination sub-module is used to determine that the fault type of the power electronic transformer is a high-frequency transformer turn-to-turn fault if the high-frequency transformer layer criterion is met;

[0175] The isolation level fault determination sub-module is used to determine that the fault type of the power electronic transformer is an isolation level fault if the high-frequency transformer layer criterion is not met;

[0176] The in-zone input stage fault or in-zone output stage fault determination sub-module is used to judge that the fault type of the power electronic transformer is an in-zone input stage fault or an in-zone output stage fault according to the AC side auxiliary criterion if the instantaneous power of the isolation layer does not meet the isolation layer criterion.

[0177] In the embodiment of the present invention, the fault type determination module 406 further includes:

[0178] The second isolation layer criterion judgment sub-module is used to judge whether the instantaneous power of the isolation layer meets the isolation layer criterion if the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, and the instantaneous power of the medium voltage DC side do not meet the overall equipment layer criterion;

[0179] The DC side out-of-zone fault or AC side out-of-zone fault determination sub-module is used to determine that the fault type of the power electronic transformer is a DC side out-of-zone fault or an AC side out-of-zone fault according to the DC side auxiliary criterion if the instantaneous power of the isolation layer does not meet the isolation layer criterion;

[0180] The return sub-module is used to return to the step of judging whether the differential current meets the high-frequency transformer layer criterion if the instantaneous power of the isolation layer meets the isolation layer criterion.

[0181] The embodiment of the present invention also provides an electronic device, which includes a processor and a memory:

[0182] The memory is used to store program codes and transmit the program codes to the processor;

[0183] The processor is used to execute the power electronic transformer fault identification method of the embodiment of the present invention according to the instructions in the program codes.

[0184] An embodiment of the present invention also provides a computer-readable storage medium, which is used to store program codes for executing the power electronic transformer fault identification method according to the embodiment of the present invention.

[0185] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be repeated here.

[0186] Each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0187] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a device, or a computer program product. Therefore, the embodiments of the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the embodiments of the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0188] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the method, terminal device (system), and computer program product according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal devices generate a device for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0189] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing terminal device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured product including an instruction device, and the instruction device realizes the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0190] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are executed on the computer or other programmable terminal device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable terminal device provide steps for implementing the functions specified in one process or multiple processes and / or blocks Figure 1 one process or multiple processes and / or blocks Figure 1 steps of the functions specified in one block or multiple blocks

[0191] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention

[0192] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties. And the collection, use and processing of relevant data need to comply with the relevant laws, regulations and standards of relevant countries and regions, and corresponding operation entrances are provided for users to choose to authorize or refuse

[0193] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or terminal device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or terminal device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or terminal device comprising the element

[0194] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention

Claims

1. A method for identifying faults in a power electronic transformer, characterized in that: include: Deconstructing the power electronic transformer into three levels; wherein the levels include an overall device level, an isolation level, and a high-frequency transformer level, wherein the high-frequency transformer level includes a plurality of high-frequency transformers; Determining whether the DC side voltage of the power electronic transformer is abnormal; If so, calculate the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port and the instantaneous power of the medium voltage DC side of the overall equipment layer; Calculating the isolation layer instantaneous power of the isolation layer; Calculating the differential current of the high frequency transformer; Fault identification is performed according to the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, the instantaneous power of the medium voltage DC side, the instantaneous power of the isolation layer, the differential current and a preset protection criterion to obtain the fault type of the power electronic transformer.

2. The method according to claim 1, characterized in that The step of determining whether the DC side voltage of the power electronic transformer is abnormal comprises: Obtaining a medium voltage DC side bus-to-ground voltage of the power electronic transformer and a first change value thereof; Obtaining the low-voltage DC side bus-to-ground voltage of the power electronic transformer and its second change value; The medium voltage DC side bus voltage to ground, the first change value, the low voltage DC side bus voltage to ground, the second change value and the preset setting value are used to determine whether the DC side voltage of the power electronic transformer is abnormal.

3. The method according to claim 1, characterized in that The step of calculating the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port and the instantaneous power of the medium voltage DC side of the overall equipment layer includes: Obtaining the medium voltage instantaneous phase voltage value and the medium voltage instantaneous phase current value of each phase of the MVAC input stage port in the power electronic transformer; Calculating the instantaneous power of the MVAC input stage port by using the instantaneous medium voltage phase voltage value and the instantaneous medium voltage phase current value; Obtaining the low voltage instantaneous phase voltage value and the low voltage instantaneous phase current value of each phase of the LVAC output stage port in the power electronic transformer; Calculating the instantaneous power of the LVAC output stage port by using the low voltage instantaneous phase voltage value and the low voltage instantaneous phase current value; Obtaining the instantaneous voltage and instantaneous current of the medium voltage DC side of the power electronic transformer; The instantaneous power on the medium voltage DC side is calculated using the instantaneous voltage and the instantaneous current.

4. The method according to claim 1, characterized in that The isolation layer includes a dual active bridge converter DAB; the instantaneous power of the isolation layer includes the instantaneous power of the primary side and the instantaneous power of the secondary side; the step of calculating the instantaneous power of the isolation layer of the isolation layer includes: Obtaining a primary voltage, a primary current, a secondary voltage, and a secondary current of the DAB; Calculating the primary-side instantaneous power of the DAB using the primary voltage and the primary current; The secondary side instantaneous power of the DAB is calculated using the secondary side voltage and the secondary side current.

5. The method according to claim 1, characterized in that: The step of calculating the differential current of the high-frequency transformer comprises: Obtaining the transformer primary voltage, transformer primary current, transformer secondary voltage and transformer secondary current of each high-frequency transformer; Calculating a primary-to-secondary voltage ratio of the transformer primary voltage to the transformer secondary voltage; The differential current of the high-frequency transformer is calculated using the primary-to-secondary voltage ratio, the transformer primary current, and the transformer secondary current.

6. The method according to claim 1, characterized in that The preset protection criterion includes an overall equipment layer criterion, an isolation layer criterion, and a high-frequency transformer layer criterion; the overall equipment layer criterion includes an equipment layer criterion, an AC side auxiliary criterion, and a DC side auxiliary criterion; the step of performing fault identification according to the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, the instantaneous power of the medium voltage DC side, the instantaneous power of the isolation layer, the differential current, and the preset protection criterion to obtain the fault type of the power electronic transformer includes: Determine whether the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, and the instantaneous power of the medium voltage DC side meet the overall equipment layer criterion; If the overall equipment layer criterion is met, it is determined that the power electronic transformer has an in-zone fault, and whether the instantaneous power of the isolation layer meets the isolation layer criterion; If the isolation layer criterion is met, determining whether the differential current meets the high-frequency transformer layer criterion; If the high-frequency transformer layer criterion is met, it is determined that the fault type of the power electronic transformer is a high-frequency transformer turn-to-turn fault; If the high-frequency transformer layer criterion is not met, the fault type of the power electronic transformer is determined to be an isolation level fault; If the instantaneous power of the isolation layer does not meet the isolation layer criterion, the fault type of the power electronic transformer is determined to be an intra-zone input level fault or an intra-zone output level fault according to the AC side auxiliary criterion.

7. The method according to claim 6, characterized in that Also includes: If the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, and the instantaneous power of the medium voltage DC side do not meet the overall equipment layer criterion, then determine whether the instantaneous power of the isolation layer meets the isolation layer criterion; If the instantaneous power of the isolation layer does not meet the isolation layer criterion, determining the fault type of the power electronic transformer as a DC side out-of-zone fault or an AC side out-of-zone fault according to the DC side auxiliary criterion; If the instantaneous power of the isolation layer satisfies the isolation layer criterion, the process returns to the step of determining whether the differential current satisfies the high-frequency transformer layer criterion.

8. A power electronic transformer fault identification device, characterized in that: include: A deconstruction module, used for deconstructing the power electronic transformer into three levels; wherein the levels include an overall equipment level, an isolation level and a high-frequency transformer level, and the high-frequency transformer level includes a plurality of high-frequency transformers; An abnormality judgment module, used to judge whether the DC side voltage of the power electronic transformer is abnormal; The device layer instantaneous power calculation module is used to calculate the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port and the instantaneous power of the medium voltage DC side of the entire device layer; An isolation layer instantaneous power calculation module, used to calculate the isolation layer instantaneous power of the isolation layer; A differential current calculation module, used to calculate the differential current of the high-frequency transformer; The fault type determination module is used to perform fault identification according to the instantaneous power of the MVAC input stage port, the instantaneous power of the LVAC output stage port, the instantaneous power of the medium voltage DC side, the instantaneous power of the isolation layer, the differential current and a preset protection criterion to obtain the fault type of the power electronic transformer.

9. An electronic device, characterized in that: The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the power electronic transformer fault identification method according to any one of claims 1-7 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the power electronic transformer fault identification method according to any one of claims 1 to 7.

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