A fault identification and protection method and device for a hybrid DC transformer

Abstract

The application provides a fault identification and protection method and device for a hybrid DC transformer. AC faults can be identified by using three-phase AC voltages on both sides of an AC transformer, and DC faults can be identified by using voltages on the DC side of a converter. The type of fault can be accurately identified, false judgments and missed judgments can be avoided, the response is fast, and fault ride-through control or blocking protection can be matched for different fault types to effectively ensure the safe, stable and reliable operation of the hybrid DC transformer throughout the process. The technical solution provided by the application can take appropriate protection or ride-through control according to the type of fault, thereby improving the fault identification capability, protection action speed, overvoltage suppression capability and fault operation adaptability of the hybrid DC transformer.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, specifically to a method and apparatus for fault identification and protection of a hybrid DC transformer. Background Technology

[0002] As a key piece of equipment for voltage conversion and power transmission between DC systems of different voltage levels, DC transformers play an important role in scenarios such as new energy DC aggregation and transmission, DC grid interconnection, multi-voltage level DC networking, and high-ratio, large-capacity DC energy transmission. To meet the requirements of high-ratio, large-capacity, and isolated DC conversion, hybrid DC transformers, which contain both current-source and voltage-source converter units on the low-voltage side, are gradually becoming a topology with promising engineering applications.

[0003] The energy conversion process of a hybrid DC transformer relies on an AC transformer. When a fault occurs in the intermediate AC transformer or the DC end, the voltage, current and power transmission state inside the hybrid DC transformer will change rapidly. This may lead to overcurrent, overvoltage, power imbalance and rapid increase in device stress in the sending-end converter or receiving-end converter, causing the hybrid isolation DC transformer to fail to operate safely and stably.

[0004] Therefore, there is an urgent need for a technical solution for fault identification and protection of hybrid DC transformers. Summary of the Invention

[0005] This application provides a method and apparatus for fault identification and protection of hybrid DC transformers.

[0006] Firstly, this application provides a fault identification and protection method for a hybrid DC transformer. The hybrid DC transformer includes a DC / AC converter, an AC transformer, and an AC / DC converter connected in sequence.

[0007] Fault identification and protection methods may include: AC faults are identified based on the three-phase AC voltage of the first or second AC side of the AC transformer, and DC faults are identified based on the DC side voltage of the DC / AC converter or AC / DC converter.

[0008] Fault ride-through control or lockout protection is applied to hybrid DC transformers based on the identified fault type.

[0009] Optionally, fault types include AC faults and DC faults.

[0010] AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit ground faults, and three-phase short-circuit faults.

[0011] DC faults include unipolar ground faults and bipolar short-circuit faults.

[0012] In some possible implementations, AC fault identification is performed based on the three-phase AC voltage on the first or second AC side of the AC transformer, including: Sequence component decomposition is performed on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side to obtain the positive sequence voltage component, negative sequence voltage component and zero sequence voltage component of the first AC side or the second AC side.

[0013] AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

[0014] Furthermore, AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side, including: If the amplitude of the positive sequence voltage component is equal to the sum of the amplitudes of the negative sequence voltage component and the zero sequence voltage component, the AC fault is determined to be a single-phase ground fault.

[0015] If the amplitude of the positive sequence voltage component is equal to the amplitude of the negative sequence voltage component, and the zero sequence voltage component is zero, the AC fault is determined to be a two-phase short-circuit ungrounded fault.

[0016] The positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component are equal and none of them are zero, so the AC fault is determined to be a two-phase short-circuit ground fault.

[0017] If the positive sequence voltage component is less than the preset positive sequence voltage threshold, and both the negative sequence voltage component and the zero sequence voltage component are zero, the AC fault is determined to be a three-phase short circuit fault.

[0018] In other possible implementations, DC fault identification is performed based on the DC-side voltage of the DC / AC converter or AC / DC converter, including: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter.

[0019] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is less than the preset first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the preset second voltage threshold, the single-pole grounding fault is determined to be a positive grounding fault.

[0020] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is less than the second voltage threshold, the single-pole grounding fault is determined to be a negative grounding fault.

[0021] The first pole voltage threshold is less than the pole voltage rating of the DC / AC converter or AC / DC converter, and the second pole voltage threshold is greater than the pole voltage rating of the DC / AC converter or AC / DC converter.

[0022] In some other possible implementations, DC fault identification is performed based on the DC-side voltage of the DC / AC converter or AC / DC converter, including: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter.

[0023] The difference between the positive DC-side voltage and the negative DC-side voltage of a DC / AC converter or AC / DC converter is taken as the inter-electrode voltage of the DC / AC converter or AC / DC converter.

[0024] If the inter-electrode voltage of the DC / AC converter or AC / DC converter is less than the inter-electrode voltage threshold of the DC / AC converter or AC / DC converter, the DC fault is determined to be a bipolar short-circuit fault.

[0025] Optionally, the DC / AC converter includes parallel current source converters and modular multilevel converters, while the AC / DC converter is a diode rectifier. Alternatively, DC / AC converters are current source converters, while AC / DC converters are modular multilevel converters. Alternatively, The DC / AC converter is a modular multilevel converter, while the AC / DC converter is a current source converter.

[0026] In one possible implementation, fault ride-through control or blocking protection is applied to the hybrid DC transformer based on the identified fault type, including: In the case of a single-phase ground fault in AC, fault ride-through control is performed on the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter.

[0027] In the event of an AC fault being a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are blocked according to the blocking signal. Alternatively, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are blocked.

[0028] Furthermore, fault ride-through control is performed on the modular multilevel converter based on the actual three-phase AC voltage values, including: Based on the actual values ​​of the three-phase AC voltage and three-phase current of the modular multilevel converter, voltage and current dual closed-loop control is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter.

[0029] The negative sequence voltage reference value of the modular multilevel converter is calculated based on the actual value of the three-phase AC voltage of the modular multilevel converter.

[0030] The control signal is obtained by superimposing and modulating the three-phase AC voltage reference value and the negative sequence voltage reference value of the modular multilevel converter.

[0031] The modular multilevel converter is controlled according to the control signal.

[0032] For example, the negative sequence voltage reference value of the modular multilevel converter is calculated based on the actual value of the three-phase AC voltage of the modular multilevel converter, including: The actual three-phase AC voltage values ​​of the modular multilevel converter are subjected to Clark transformation to obtain the α-axis voltage component and β-axis voltage component of the modular multilevel converter.

[0033] The reference values ​​for the α-axis negative sequence voltage and the β-axis negative sequence voltage of the modular multilevel converter are calculated based on the α-axis voltage components and the β-axis voltage components of the modular multilevel converter.

[0034] The negative sequence voltage reference values ​​of the modular multilevel converter are obtained by performing an inverse Carrack transform on the α-axis negative sequence voltage reference values ​​and the β-axis negative sequence voltage reference values.

[0035] Optionally, the α-axis negative sequence voltage reference values ​​and β-axis negative sequence voltage reference values ​​of the modular multilevel converter satisfy:

[0036]

[0037] in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of a modular multilevel converter. u M_β This represents the β-axis voltage component of a modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

[0038] In another possible implementation, fault ride-through control or blocking protection is applied to the hybrid DC transformer based on the identified fault type, including: In the event of a DC fault being either a positive-to-ground fault or a negative-to-ground fault: if, within a preset first time range, both the positive and negative DC-side voltages of the DC / AC converter or AC / DC converter recover to their respective voltage ranges, the hybrid DC transformer resumes normal operation. Otherwise, the hybrid DC transformer is blocked. The voltage range is defined by a first-pole voltage threshold and a second-pole voltage threshold.

[0039] In the event of a bipolar short-circuit fault in the DC circuit, the energy dissipation device is activated, and the output power of the renewable energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time frame, the energy dissipation device is deactivated, and the renewable energy power station resumes power output, with the hybrid DC transformer returning to normal operation. The energy dissipation device is located on the DC side of the DC / AC converter or AC / DC converter, and the renewable energy power station is connected to the DC side of the DC / AC converter or AC / DC converter.

[0040] Secondly, this application provides a fault identification and protection device for a hybrid DC transformer. The hybrid DC transformer includes a DC / AC converter, an AC transformer, and an AC / DC converter connected in sequence.

[0041] Fault identification and protection devices include: The identification module is used to identify AC faults based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, and to identify DC faults based on the DC side voltage of the DC / AC converter or the AC / DC converter.

[0042] The protection module is used to perform fault ride-through control or lockout protection on hybrid DC transformers based on the identified fault type.

[0043] Optionally, fault types include AC faults and DC faults.

[0044] AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit ground faults, and three-phase short-circuit faults.

[0045] DC faults include unipolar ground faults and bipolar short-circuit faults.

[0046] In some possible implementations, the identification module is specifically used for: Sequence component decomposition is performed on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side to obtain the positive sequence voltage component, negative sequence voltage component and zero sequence voltage component of the first AC side or the second AC side.

[0047] AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

[0048] Furthermore, the identification module is used for: If the amplitude of the positive sequence voltage component is equal to the sum of the amplitudes of the negative sequence voltage component and the zero sequence voltage component, the AC fault is determined to be a single-phase ground fault.

[0049] If the amplitude of the positive sequence voltage component is equal to the amplitude of the negative sequence voltage component, and the zero sequence voltage component is zero, the AC fault is determined to be a two-phase short-circuit ungrounded fault.

[0050] The positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component are equal and none of them are zero, so the AC fault is determined to be a two-phase short-circuit ground fault.

[0051] If the positive sequence voltage component is less than the preset positive sequence voltage threshold, and both the negative sequence voltage component and the zero sequence voltage component are zero, the AC fault is determined to be a three-phase short circuit fault.

[0052] The recognition module is specifically used for: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter.

[0053] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is less than the preset first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the preset second voltage threshold, the single-pole grounding fault is determined to be a positive grounding fault.

[0054] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is less than the second voltage threshold, the single-pole grounding fault is determined to be a negative grounding fault.

[0055] The first pole voltage threshold is less than the pole voltage rating of the DC / AC converter or AC / DC converter, and the second pole voltage threshold is greater than the pole voltage rating of the DC / AC converter or AC / DC converter.

[0056] In some other possible implementations, the identification module is specifically used for: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter.

[0057] The difference between the positive DC-side voltage and the negative DC-side voltage of a DC / AC converter or AC / DC converter is taken as the inter-electrode voltage of the DC / AC converter or AC / DC converter.

[0058] If the inter-electrode voltage of the DC / AC converter or AC / DC converter is less than the inter-electrode voltage threshold of the DC / AC converter or AC / DC converter, the DC fault is determined to be a bipolar short-circuit fault.

[0059] For example, a DC / AC converter includes parallel current source converters and modular multilevel converters, with the AC / DC converter being a diode rectifier. Alternatively, DC / AC converters are current source converters, while AC / DC converters are modular multilevel converters. Alternatively, The DC / AC converter is a modular multilevel converter, while the AC / DC converter is a current source converter.

[0060] In some other possible implementations, the protection module is specifically used for: In the case of a single-phase ground fault in AC, fault ride-through control is performed on the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter.

[0061] In the event of an AC fault being a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are blocked according to the blocking signal. Alternatively, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are blocked.

[0062] Furthermore, the protection module is specifically used for: Based on the actual values ​​of the three-phase AC voltage and three-phase current of the modular multilevel converter, voltage and current dual closed-loop control is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter.

[0063] The negative sequence voltage reference value of the modular multilevel converter is calculated based on the actual value of the three-phase AC voltage of the modular multilevel converter.

[0064] The control signal is obtained by superimposing and modulating the three-phase AC voltage reference value and the negative sequence voltage reference value of the modular multilevel converter.

[0065] The modular multilevel converter is controlled according to the control signal.

[0066] Furthermore, the protection module is specifically used for: The actual three-phase AC voltage values ​​of the modular multilevel converter are subjected to Clark transformation to obtain the α-axis voltage component and β-axis voltage component of the modular multilevel converter.

[0067] The reference values ​​for the α-axis negative sequence voltage and the β-axis negative sequence voltage of the modular multilevel converter are calculated based on the α-axis voltage components and the β-axis voltage components of the modular multilevel converter.

[0068] The negative sequence voltage reference values ​​of the modular multilevel converter are obtained by performing an inverse Carrack transform on the α-axis negative sequence voltage reference values ​​and the β-axis negative sequence voltage reference values.

[0069] Optionally, the α-axis negative sequence voltage reference values ​​and β-axis negative sequence voltage reference values ​​of the modular multilevel converter satisfy:

[0070]

[0071] in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of a modular multilevel converter. u M_β This represents the β-axis voltage component of a modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

[0072] In another possible implementation, the protection module is specifically used for: In the event of a DC fault being either a positive-to-ground fault or a negative-to-ground fault: if, within a preset first time range, both the positive and negative DC-side voltages of the DC / AC converter or AC / DC converter recover to their respective voltage ranges, the hybrid DC transformer resumes normal operation. Otherwise, the hybrid DC transformer is blocked. The voltage range is defined by a first-pole voltage threshold and a second-pole voltage threshold.

[0073] In the event of a bipolar short-circuit fault in the DC circuit, the energy dissipation device is activated, and the output power of the renewable energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time frame, the energy dissipation device is deactivated, and the renewable energy power station resumes power output, with the hybrid DC transformer returning to normal operation. The energy dissipation device is located on the DC side of the DC / AC converter or AC / DC converter, and the renewable energy power station is connected to the DC side of the DC / AC converter or AC / DC converter.

[0074] In another aspect, this application also provides a computer device, including: one or more processors.

[0075] A processor is used to execute one or more programs.

[0076] When one or more programs are executed by one or more processors, the fault identification and protection methods described above are implemented.

[0077] Furthermore, this application also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed, it implements the fault identification and protection method described above.

[0078] Compared with the prior art, the beneficial effects of this application are as follows: The fault identification and protection method for hybrid DC transformers provided in this application can identify AC faults based on the three-phase AC voltages of the first or second AC side of the AC transformer, and DC faults based on the DC-side voltage of the DC / AC converter or AC / DC converter. Fault ride-through control or blocking protection is applied to the hybrid DC transformer according to the identified fault type. By using the three-phase AC voltages on both sides of the AC transformer to identify AC faults and the DC-side voltage of the converter to identify DC faults, the method can accurately identify fault types, avoid misjudgments and missed judgments, and provide rapid identification response. Fault ride-through control or blocking protection is matched to different fault types, effectively ensuring the safe, stable, and reliable operation of the hybrid DC transformer throughout the entire process.

[0079] The technical solution provided in this application can take corresponding protection or through-control according to the fault type, thereby improving the fault identification capability, protection action speed, overvoltage suppression capability and fault operation adaptability of hybrid DC transformers.

[0080] This application establishes a unified detection and protection system covering both AC and DC faults, which can overcome the problem of insufficient protection scope caused by setting protection only for a single fault location.

[0081] This application can classify and identify different AC fault types, such as single-phase ground fault, two-phase short-circuit ungrounded fault, two-phase short-circuit ground fault, and three-phase short-circuit fault, through sequence component decomposition, providing a basis for subsequent categorized protection and fault ride-through control.

[0082] This application addresses AC faults such as three-phase short-circuit faults, two-phase short-circuit faults, and two-phase short-circuit-to-ground faults by employing a protection method that combines fault identification blocking and overcurrent blocking. The fault identification blocking is used to improve protection selectivity, while the overcurrent blocking is used to compensate for fault discrimination delay and quickly protect the DC / AC converter, effectively reducing the overcurrent risk of the DC / AC converter under severe faults.

[0083] This application addresses the problem that the DC-side freewheeling inductance may cause transient overvoltage on the valve side during the lockout process of a current source converter. A bridge arm surge arrester is configured on the valve side of the current source converter, and the range of the surge arrester's protection voltage is limited. This ensures that the arrester can not only avoid malfunctions during normal operation, but also reliably operate before the overvoltage reaches the dangerous level of the device during the lockout transient, thereby protecting the bridge arm and power devices.

[0084] This application addresses the issue that single-phase grounding faults are not suitable for simple blocking and shutdown. By utilizing the controllability of voltage source converters, a negative sequence voltage reference value of the modular multilevel converter is added to the three-phase AC voltage reference value of the modular multilevel converter. This cancels the negative sequence component introduced by the fault, suppresses the fault current, and enables fault ride-through, thereby improving the continuous operation capability of the hybrid DC transformer under asymmetrical faults.

[0085] This application further sets corresponding voltage criteria and protection actions for single-pole grounding faults and double-pole short-circuit faults. It can perform maintenance operation, block shutdown, power reduction, power consumption device activation, and operation recovery after fault clearance according to different DC fault types, thereby improving the pertinence and reliability of DC fault handling.

[0086] The technical solution provided in this application can achieve rapid identification, categorized protection, and fault ride-through control under AC and DC fault conditions, thereby enhancing the safety, reliability, and engineering applicability of hybrid DC transformers under complex fault conditions. Attached Figure Description

[0087] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0088] Figure 1 This is a schematic structural diagram of a hybrid DC transformer in an embodiment of this application; Figure 2 This is a schematic flowchart of a fault identification and protection method for a hybrid DC transformer in an embodiment of this application; Figure 3 This is a schematic flowchart illustrating AC fault identification based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, as described in this application. Figure 4 This is a schematic flowchart illustrating fault ride-through control of a modular multilevel converter in an embodiment of this application. Figure 5This is a schematic flowchart illustrating DC fault identification and protection in an embodiment of this application; Figure 6 This is a schematic structural diagram of a fault identification and protection device in the embodiments of this application. Detailed Implementation

[0089] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0090] The terms "first," "second," etc., used in the specification, embodiments, claims, and drawings of this application are for distinguishing purposes only and should not be construed as indicating or implying relative importance or order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as including a series of steps or units. A method, system, product, or apparatus is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0091] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0092] Example 1: This application provides a fault identification and protection method for a hybrid DC transformer. For example... Figure 1As shown, the hybrid DC transformer 100 includes a DC / AC converter 10, an AC transformer 20, and an AC / DC converter 30 connected in sequence. The AC side of the DC / AC converter 10 can be connected to the first AC side of the AC transformer 20, and the AC side of the AC / DC converter 30 can be connected to the second AC side of the AC transformer 20. The hybrid DC transformer 100 can support bidirectional power transmission, thereby achieving either voltage boosting or bucking. Therefore, the DC side of the DC / AC converter 10 can be connected to a renewable energy power plant, and the DC side of the AC / DC converter 30 can be connected to the power grid. Alternatively, the DC side of the DC / AC converter 10 can be connected to the power grid, and the DC side of the AC / DC converter 30 can be connected to a renewable energy power plant.

[0093] In this embodiment of the application, the DC / AC converter 10 can adopt any of the following structures: The DC / AC converter 10 includes a parallel current source converter (CSC) and a modular multilevel converter (MMC), and the AC / DC converter is a diode rectifier unit (DRU).

[0094] Alternatively, the DC / AC converter 10 is a current source converter (CSC), and the AC / DC converter is a modular multilevel converter (MMC).

[0095] Alternatively, the DC / AC converter 10 is a modular multilevel converter (MMC), and the AC / DC converter is a current source converter (CSC).

[0096] Of course, the DC / AC converter 10 can also adopt other structures, which are not limited in the embodiments of this application.

[0097] like Figure 2 The fault identification and protection method 200 may include the following steps: Step S1: Identify AC faults based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, and identify DC faults based on the DC side voltage of the DC / AC converter or the AC / DC converter.

[0098] Step S2: Perform fault ride-through control or blocking protection on the hybrid DC transformer according to the identified fault type.

[0099] Optionally, fault types include AC faults and DC faults.

[0100] AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit ground faults, and three-phase short-circuit faults.

[0101] DC faults include unipolar ground faults and bipolar short-circuit faults.

[0102] In some possible implementations, in S1, AC fault identification is performed based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, including: like Figure 3 Obtain the three-phase AC voltage from the first AC side or the three-phase AC voltage from the second AC side.

[0103] By performing sequence component decomposition on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side, the positive sequence voltage component, negative sequence voltage component, and zero sequence voltage component of the first AC side or the second AC side can be obtained.

[0104] AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

[0105] Furthermore, AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side, including: If the amplitude of the positive sequence voltage component Equal to the magnitude of the negative sequence voltage component The amplitude of the zero-sequence voltage component The sum of these values ​​determines that the AC fault is a single-phase ground fault.

[0106] If the amplitude of the positive sequence voltage component Equal to the magnitude of the negative sequence voltage component And zero-sequence voltage component If the value is zero, the AC fault is determined to be a two-phase short-circuit ungrounded fault.

[0107] If the positive sequence voltage component Negative sequence voltage component and zero-sequence voltage component If the values ​​are equal and none of them are zero, the AC fault is determined to be a two-phase short-circuit ground fault.

[0108] If the positive sequence voltage component Less than the preset positive sequence voltage threshold And negative sequence voltage components and zero-sequence voltage component All values ​​are zero, indicating that the AC fault is a three-phase short circuit fault.

[0109] Please refer to Table 1 for details: Table 1

[0110] In one possible implementation, S2 includes fault ride-through control or blocking protection for the hybrid DC transformer based on the identified fault type, including: like Figure 3 As shown, in the case of a single-phase ground fault in the AC circuit, fault ride-through control is performed on the modular multilevel converter (MCB) based on the actual three-phase AC voltage values. Specifically, a bridge arm surge arrester can be configured on the CSC valve side. The protection voltage of the bridge arm surge arrester is greater than 1.3 times the sum of the average DC voltage and the maximum DC voltage ripple during normal operation, and less than 0.8 times the withstand voltage of the CSC bridge arm. When the CSC is blocked, the bridge arm surge arrester is used to limit the transient overvoltage on the valve side caused by the energy release of the CSC DC side freewheeling inductor, thus protecting the CSC bridge arm and power devices.

[0111] In the event of an AC fault being a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are blocked according to the blocking signal. Alternatively, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are blocked.

[0112] Furthermore, fault ride-through control is performed on the modular multilevel converter based on the actual three-phase AC voltage values, including: like Figure 4 As shown, based on the actual value of the three-phase AC voltage of the modular multilevel converter... u Mabc and actual value of three-phase current i Mabc A dual closed-loop control of voltage and current is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter. u Mabc_ref .

[0113] Based on the actual value of the three-phase AC voltage of the modular multilevel converter u Mabc Calculate the negative sequence voltage reference value of the modular multilevel converter. u Mn_ref .

[0114] The three-phase AC voltage reference value of the modular multilevel converter u Mabc_ref Negative sequence voltage reference value of modular multilevel converter u Mn_ref The control signal CS is obtained by superimposing and modulating (which can be the closest level approximation modulation).

[0115] The modular multilevel converter is controlled by the control signal CS.

[0116] Figure 4middle, P MMC This represents the actual active power value of the MMC. P MMC_ref This represents the active power reference value for the MMC, which can be set to 0. u Mabc By performing the Parker transformation (i.e., the abc / dq transformation), the d-axis voltage component of the MMC can be obtained. u Md and q-axis voltage component u Mq . u Md_ref This indicates the reference value for the d-axis voltage of the MMC. u Mq_ref This represents the q-axis voltage reference value for the MMC, which can be set to 0. PI indicates proportional-integral control. i Md_ref This indicates the reference value for the d-axis current. i Mq_ref This represents the q-axis current reference value. i Mabc By performing the Parker transformation (i.e., the abc / dq transformation), the d-axis current component of the MMC can be obtained. i Md and q-axis current component i Mq . ω Represents angular frequency. L This represents the inductance value of the bridge arm reactance. The dq / abc transformation is the inverse Parker transformation.

[0117] For example, the negative sequence voltage reference value of the modular multilevel converter is calculated based on the actual value of the three-phase AC voltage of the modular multilevel converter, including: refer to Figure 4 The actual value of the three-phase AC voltage of the modular multilevel converter u Mabc Performing the Clarke transform (i.e., the abc / αβ transform) yields the α-axis voltage component of the modular multilevel converter. and β-axis voltage components .

[0118] Based on the α-axis voltage component of the modular multilevel converter and β-axis voltage components Calculate the α-axis negative sequence voltage reference value of the modular multilevel converter. and β-axis negative sequence voltage reference value .

[0119] The α-axis negative sequence voltage reference value of the modular multilevel converter and β-axis negative sequence voltage reference value Performing an inverse Karak transform (i.e., αβ / abc transform) yields the negative sequence voltage reference value for the modular multilevel converter. u Mn_ref .

[0120] Optionally, the α-axis negative sequence voltage reference values ​​and β-axis negative sequence voltage reference values ​​of the modular multilevel converter satisfy:

[0121]

[0122] in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of a modular multilevel converter. u M_β This represents the β-axis voltage component of a modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

[0123] In other possible implementations, DC fault identification is performed based on the DC-side voltage of the DC / AC converter or AC / DC converter, including: like Figure 5 As shown, the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter are obtained.

[0124] If the positive voltage U+ on the DC side of the DC / AC converter or AC / DC converter is less than the preset first voltage threshold U1, and the negative voltage U- on the DC side of the DC / AC converter or AC / DC converter is greater than the preset second voltage threshold U2, the single-pole grounding fault is determined to be a positive grounding fault.

[0125] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the first voltage threshold U1, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is less than the second voltage threshold U2, the single-pole grounding fault is determined to be a negative grounding fault.

[0126] Among them, the first pole voltage threshold U1 is less than the pole voltage rating of the DC / AC converter or AC / DC converter, and the second pole voltage threshold U2 is greater than the pole voltage rating of the DC / AC converter or AC / DC converter.

[0127] In some other possible implementations, in S1, DC fault identification is performed based on the DC-side voltage of the DC / AC converter or AC / DC converter, including: like Figure 5 To obtain the positive DC-side voltage and negative DC-side voltage of a DC / AC converter or an AC / DC converter.

[0128] The difference between the positive DC-side voltage and the negative DC-side voltage of a DC / AC converter or AC / DC converter is taken as the inter-electrode voltage U of the DC / AC converter or AC / DC converter.

[0129] If the inter-electrode voltage of the DC / AC converter or AC / DC converter is less than the inter-electrode voltage threshold U3 of the DC / AC converter or AC / DC converter, the DC fault is determined to be a bipolar short-circuit fault.

[0130] In another possible implementation, fault ride-through control or blocking protection is applied to the hybrid DC transformer based on the identified fault type, including: like Figure 5 In the event of a DC fault being either a positive or negative ground fault: if, within a preset first time range Δt1, both the positive and negative DC voltages of the DC / AC converter or AC / DC converter recover to their respective voltage ranges, the positive or negative ground fault is determined to be a temporary fault, and the hybrid DC transformer resumes normal operation. Otherwise, the positive or negative ground fault is determined to be a permanent fault, and the hybrid DC transformer is locked out. The voltage range is defined by a first voltage threshold and a second voltage threshold.

[0131] In the event of a bipolar short-circuit fault in the DC circuit, the energy-consuming device is activated, and the output power of the renewable energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time range Δt2, the energy-consuming device is disconnected, and the renewable energy power station resumes power output, with the hybrid DC transformer returning to normal operation. The energy-consuming device is located on the DC side of the DC / AC converter or AC / DC converter, and the renewable energy power station is connected to the DC side of the DC / AC converter or AC / DC converter.

[0132] Example 2: Based on the same inventive concept, this application also provides a fault identification and protection device for a hybrid DC transformer. For a more detailed description of the hybrid DC transformer, please refer to the above and... Figure 1The embodiments in this application will not be described in detail.

[0133] like Figure 6 As shown, the fault identification and protection device 300 includes: The identification module 301 is used to identify AC faults based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, and to identify DC faults based on the DC side voltage of the DC / AC converter or the AC / DC converter.

[0134] Protection module 302 is used to perform fault ride-through control or lockout protection on hybrid DC transformers based on the identified fault type.

[0135] Optionally, fault types include AC faults and DC faults. AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit to ground faults, and three-phase short-circuit faults. DC faults include single-pole ground faults and bipolar short-circuit faults.

[0136] In some possible implementations, the identification module 301 is specifically used for: like Figure 3 Obtain the three-phase AC voltage from the first AC side or the three-phase AC voltage from the second AC side.

[0137] By performing sequence component decomposition on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side, the positive sequence voltage component, negative sequence voltage component, and zero sequence voltage component of the first AC side or the second AC side can be obtained.

[0138] AC faults are identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

[0139] Furthermore, the identification module 301 is used for: If the amplitude of the positive sequence voltage component Equal to the magnitude of the negative sequence voltage component The amplitude of the zero-sequence voltage component The sum of these values ​​determines that the AC fault is a single-phase ground fault.

[0140] If the amplitude of the positive sequence voltage component Equal to the magnitude of the negative sequence voltage component And zero-sequence voltage component If the value is zero, the AC fault is determined to be a two-phase short-circuit ungrounded fault.

[0141] If the positive sequence voltage component Negative sequence voltage component and zero-sequence voltage component If the values ​​are equal and none of them are zero, the AC fault is determined to be a two-phase short-circuit ground fault.

[0142] If the positive sequence voltage component Less than the preset positive sequence voltage threshold And negative sequence voltage components and zero-sequence voltage component All values ​​are zero, indicating that the AC fault is a three-phase short circuit fault.

[0143] Protection module 302 is specifically used for: like Figure 3 As shown, in the case of a single-phase ground fault in AC, fault ride-through control of the modular multilevel converter is performed based on the actual value of the three-phase AC voltage of the modular multilevel converter.

[0144] In the event of an AC fault being a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are blocked according to the blocking signal. Alternatively, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are blocked.

[0145] Furthermore, the protection module 302 is used for: like Figure 4 As shown, based on the actual value of the three-phase AC voltage of the modular multilevel converter... u Mabc and actual value of three-phase current i Mabc A dual closed-loop control of voltage and current is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter. u Mabc_ref .

[0146] Based on the actual value of the three-phase AC voltage of the modular multilevel converter u Mabc Calculate the negative sequence voltage reference value of the modular multilevel converter. u Mn_ref .

[0147] The three-phase AC voltage reference value of the modular multilevel converter u Mabc_ref Negative sequence voltage reference value of modular multilevel converter u Mn_ref The control signal CS is obtained by superimposing and modulating (which can be the closest level approximation modulation).

[0148] The modular multilevel converter is controlled by the control signal CS.

[0149] refer to Figure 4 The actual value of the three-phase AC voltage of the modular multilevel converter u MabcPerforming the Clarke transform (i.e., the abc / αβ transform) yields the α-axis voltage component of the modular multilevel converter. and β-axis voltage components .

[0150] Based on the α-axis voltage component of the modular multilevel converter and β-axis voltage components Calculate the α-axis negative sequence voltage reference value of the modular multilevel converter. and β-axis negative sequence voltage reference value .

[0151] The α-axis negative sequence voltage reference value of the modular multilevel converter and β-axis negative sequence voltage reference value Performing an inverse Karak transform (i.e., αβ / abc transform) yields the negative sequence voltage reference value for the modular multilevel converter. u Mn_ref .

[0152] Optionally, the α-axis negative sequence voltage reference values ​​and β-axis negative sequence voltage reference values ​​of the modular multilevel converter satisfy:

[0153]

[0154] in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of a modular multilevel converter. u M_β This represents the β-axis voltage component of a modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

[0155] Optionally, the recognition module 301 is specifically used for: like Figure 5 As shown, the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or AC / DC converter are obtained.

[0156] If the positive voltage U+ on the DC side of the DC / AC converter or AC / DC converter is less than the preset first voltage threshold U1, and the negative voltage U- on the DC side of the DC / AC converter or AC / DC converter is greater than the preset second voltage threshold U2, the single-pole grounding fault is determined to be a positive grounding fault.

[0157] If the positive voltage on the DC side of the DC / AC converter or AC / DC converter is greater than the first voltage threshold U1, and the negative voltage on the DC side of the DC / AC converter or AC / DC converter is less than the second voltage threshold U2, the single-pole grounding fault is determined to be a negative grounding fault.

[0158] Among them, the first pole voltage threshold U1 is less than the pole voltage rating of the DC / AC converter or AC / DC converter, and the second pole voltage threshold U2 is greater than the pole voltage rating of the DC / AC converter or AC / DC converter.

[0159] Optionally, the recognition module 301 is specifically used for: like Figure 5 To obtain the positive DC-side voltage and negative DC-side voltage of a DC / AC converter or an AC / DC converter.

[0160] The difference between the positive DC-side voltage and the negative DC-side voltage of a DC / AC converter or AC / DC converter is taken as the inter-electrode voltage U of the DC / AC converter or AC / DC converter.

[0161] If the inter-electrode voltage of the DC / AC converter or AC / DC converter is less than the inter-electrode voltage threshold U3 of the DC / AC converter or AC / DC converter, the DC fault is determined to be a bipolar short-circuit fault.

[0162] In another possible implementation, the protection module 302 is used for: like Figure 5 In the event of a DC fault being either a positive or negative ground fault: if, within a preset first time range Δt1, both the positive and negative DC voltages of the DC / AC converter or AC / DC converter recover to their respective voltage ranges, the positive or negative ground fault is determined to be a temporary fault, and the hybrid DC transformer resumes normal operation. Otherwise, the positive or negative ground fault is determined to be a permanent fault, and the hybrid DC transformer is locked out. The voltage range is defined by a first voltage threshold and a second voltage threshold.

[0163] In the event of a bipolar short-circuit fault in the DC circuit, the energy-consuming device is activated, and the output power of the renewable energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time range Δt2, the energy-consuming device is disconnected, and the renewable energy power station resumes power output, with the hybrid DC transformer returning to normal operation. The energy-consuming device is located on the DC side of the DC / AC converter or AC / DC converter, and the renewable energy power station is connected to the DC side of the DC / AC converter or AC / DC converter.

[0164] Example 3: Based on the same inventive concept, this application also provides a computer device, which includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to realize the steps of the fault identification and protection method provided in the above embodiments.

[0165] Example 4: Based on the same inventive concept, this application also provides a computer-readable storage medium, specifically a computer-readable storage medium (Memory). A computer-readable storage medium is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the fault identification and protection method provided in the above embodiments.

[0166] Those skilled in the art will understand that the embodiments of the application can be provided as a method, system, or computer program product. Therefore, the application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the application can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0167] The application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0168] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0169] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0170] The above are merely examples of the application and are not intended to limit the application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the application shall be included within the scope of the claims of the pending application.

Claims

1. A fault identification and protection method for a hybrid DC transformer, characterized in that, The hybrid DC transformer includes a DC / AC converter, an AC transformer, and an AC / DC converter connected in sequence. The fault identification and protection method includes: AC faults are identified based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, and DC faults are identified based on the DC side voltage of the DC / AC converter or the AC / DC converter. The hybrid DC transformer is subjected to fault ride-through control or lockout protection based on the identified fault type.

2. The fault identification and protection method according to claim 1, characterized in that, The fault types include AC faults and DC faults; The AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit ground faults, and three-phase short-circuit faults. The DC faults include unipolar ground faults and bipolar short-circuit faults.

3. The fault identification and protection method according to claim 2, characterized in that, The AC fault identification based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer includes: Sequence component decomposition is performed on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side to obtain the positive sequence voltage component, negative sequence voltage component and zero sequence voltage component of the first AC side or the second AC side. The AC fault is identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

4. The fault identification and protection method according to claim 3, characterized in that, The step of identifying the AC fault based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side includes: If the amplitude of the positive sequence voltage component is equal to the sum of the amplitude of the negative sequence voltage component and the amplitude of the zero sequence voltage component, the AC fault is determined to be a single-phase ground fault. If the amplitude of the positive sequence voltage component is equal to the amplitude of the negative sequence voltage component, and the zero sequence voltage component is zero, the AC fault is determined to be the two-phase short-circuit ungrounded fault. If the positive-sequence voltage component, the negative-sequence voltage component, and the zero-sequence voltage component are equal and all are not equal to zero, the AC fault is determined to be the two-phase short-circuit ground fault. If the positive sequence voltage component is less than the preset positive sequence voltage threshold, and both the negative sequence voltage component and the zero sequence voltage component are zero, the AC fault is determined to be a three-phase short circuit fault.

5. The fault identification and protection method according to claim 2, characterized in that, The step of identifying DC faults based on the DC / AC converter or the DC-side voltage of the AC / DC converter includes: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or the AC / DC converter; If the positive voltage of the DC side of the DC / AC converter or the AC / DC converter is less than a preset first voltage threshold, and the negative voltage of the DC side of the DC / AC converter or the AC / DC converter is greater than a preset second voltage threshold, the single-pole grounding fault is determined to be a positive grounding fault. If the positive voltage on the DC side of the DC / AC converter or the AC / DC converter is greater than the first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or the AC / DC converter is less than the second voltage threshold, the single-pole grounding fault is determined to be a negative grounding fault. Wherein, the first pole voltage threshold is less than the pole voltage rating of the DC / AC converter or the AC / DC converter, and the second pole voltage threshold is greater than the pole voltage rating of the DC / AC converter or the AC / DC converter.

6. The fault identification and protection method according to claim 2, characterized in that, The step of identifying DC faults based on the DC / AC converter or the DC-side voltage of the AC / DC converter includes: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or the AC / DC converter; The difference between the positive DC-side voltage and the negative DC-side voltage of the DC / AC converter or the AC / DC converter is taken as the inter-electrode voltage of the DC / AC converter or the AC / DC converter. If the inter-electrode voltage of the DC / AC converter or the AC / DC converter is less than the inter-electrode voltage threshold of the DC / AC converter or the AC / DC converter, the DC fault is determined to be the bipolar short-circuit fault.

7. The fault identification and protection method according to claim 3, characterized in that, The DC / AC converter includes parallel current source converters and modular multilevel converters, and the AC / DC converter is a diode rectifier; or, The DC / AC converter is a current source converter, and the AC / DC converter is a modular multilevel converter; or... The DC / AC converter is a modular multilevel converter, and the AC / DC converter is a current source converter.

8. The fault identification and protection method according to claim 7, characterized in that, The fault ride-through control or blocking protection of the hybrid DC transformer based on the identified fault type includes: In the case that the AC fault is a single-phase ground fault, the modular multilevel converter is subjected to fault ride-through control based on the actual value of the three-phase AC voltage of the modular multilevel converter. In the event that the AC fault is a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are locked according to the blocking signal; or, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are locked.

9. The fault identification and protection method according to claim 8, characterized in that, The fault ride-through control of the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter includes: Based on the actual values ​​of the three-phase AC voltage and the actual values ​​of the three-phase current of the modular multilevel converter, voltage and current dual closed-loop control is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter; Calculate the negative sequence voltage reference value of the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter; The control signal is obtained by superimposing and modulating the three-phase AC voltage reference value of the modular multilevel converter and the negative sequence voltage reference value of the modular multilevel converter. The modular multilevel converter is controlled according to the control signal.

10. The fault identification and protection method according to claim 9, characterized in that, The calculation of the negative sequence voltage reference value of the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter includes: The actual three-phase AC voltage values ​​of the modular multilevel converter are subjected to Clark transformation to obtain the α-axis voltage component and β-axis voltage component of the modular multilevel converter. The α-axis negative sequence voltage reference value and β-axis negative sequence voltage reference value of the modular multilevel converter are calculated based on the α-axis voltage component and β-axis voltage component of the modular multilevel converter. The negative sequence voltage reference values ​​of the modular multilevel converter are obtained by performing an inverse Carrack transform on the α-axis negative sequence voltage reference values ​​and the β-axis negative sequence voltage reference values.

11. The fault identification and protection method according to claim 10, characterized in that, The α-axis negative sequence voltage reference value and β-axis negative sequence voltage reference value of the modular multilevel converter satisfy the following: in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of the modular multilevel converter. u M_β This represents the β-axis voltage component of the modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

12. The fault identification and protection method according to claim 5, characterized in that, The fault ride-through control or blocking protection of the hybrid DC transformer based on the identified fault type includes: In the case where the DC fault is either a positive ground fault or a negative ground fault: if, within a preset first time range, both the positive DC voltage and the negative DC voltage of the DC / AC converter or the AC / DC converter recover to the voltage range, the hybrid DC transformer resumes normal operation; otherwise, the hybrid DC transformer is locked out; wherein, the voltage range is composed of the first pole voltage threshold and the second pole voltage threshold; In the event that the DC fault is a bipolar short-circuit fault, the energy-consuming device is activated, and the output power of the new energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time range, the energy-consuming device is disconnected, and the power output of the new energy power station is restored, and the hybrid DC transformer resumes normal operation. The energy-consuming device is located on the DC side of the DC / AC converter or the AC / DC converter, and the new energy power station is connected to the DC / AC converter or the DC side of the AC / DC converter.

13. A fault identification and protection device for a hybrid DC transformer, characterized in that, The hybrid DC transformer includes a DC / AC converter, an AC transformer, and an AC / DC converter connected in sequence. The fault identification and protection device includes: The identification module is used to identify AC faults based on the three-phase AC voltage of the first AC side or the second AC side of the AC transformer, and to identify DC faults based on the DC side voltage of the DC / AC converter or the AC / DC converter. The protection module is used to perform fault ride-through control or blocking protection on the hybrid DC transformer according to the identified fault type.

14. The fault identification and protection device according to claim 13, characterized in that, The fault types include AC faults and DC faults; The AC faults include single-phase ground faults, two-phase short-circuit ungrounded faults, two-phase short-circuit ground faults, and three-phase short-circuit faults. The DC faults include unipolar ground faults and bipolar short-circuit faults.

15. The fault identification and protection device according to claim 14, characterized in that, The identification module is specifically used for: Sequence component decomposition is performed on the three-phase AC voltage of the first AC side or the three-phase AC voltage of the second AC side to obtain the positive sequence voltage component, negative sequence voltage component and zero sequence voltage component of the first AC side or the second AC side. The AC fault is identified based on the positive-sequence voltage component, negative-sequence voltage component, and zero-sequence voltage component of the first AC side or the second AC side.

16. The fault identification and protection device according to claim 15, characterized in that, The identification module is used for: If the amplitude of the positive sequence voltage component is equal to the sum of the amplitude of the negative sequence voltage component and the amplitude of the zero sequence voltage component, the AC fault is determined to be a single-phase ground fault. If the amplitude of the positive sequence voltage component is equal to the amplitude of the negative sequence voltage component, and the zero sequence voltage component is zero, the AC fault is determined to be the two-phase short-circuit ungrounded fault. If the positive-sequence voltage component, the negative-sequence voltage component, and the zero-sequence voltage component are equal and all are not equal to zero, the AC fault is determined to be the two-phase short-circuit ground fault. If the positive sequence voltage component is less than the preset positive sequence voltage threshold, and both the negative sequence voltage component and the zero sequence voltage component are zero, the AC fault is determined to be a three-phase short circuit fault.

17. The fault identification and protection device according to claim 14, characterized in that, The identification module is specifically used for: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or the AC / DC converter; If the positive voltage of the DC side of the DC / AC converter or the AC / DC converter is less than a preset first voltage threshold, and the negative voltage of the DC side of the DC / AC converter or the AC / DC converter is greater than a preset second voltage threshold, the single-pole grounding fault is determined to be a positive grounding fault. If the positive voltage on the DC side of the DC / AC converter or the AC / DC converter is greater than the first voltage threshold, and the negative voltage on the DC side of the DC / AC converter or the AC / DC converter is less than the second voltage threshold, the single-pole grounding fault is determined to be a negative grounding fault. Wherein, the first pole voltage threshold is less than the pole voltage rating of the DC / AC converter or the AC / DC converter, and the second pole voltage threshold is greater than the pole voltage rating of the DC / AC converter or the AC / DC converter.

18. The fault identification and protection device according to claim 14, characterized in that, The identification module is specifically used for: Obtain the positive DC-side voltage and negative DC-side voltage of the DC / AC converter or the AC / DC converter; The difference between the positive DC-side voltage and the negative DC-side voltage of the DC / AC converter or the AC / DC converter is taken as the inter-electrode voltage of the DC / AC converter or the AC / DC converter. If the inter-electrode voltage of the DC / AC converter or the AC / DC converter is less than the inter-electrode voltage threshold of the DC / AC converter or the AC / DC converter, the DC fault is determined to be the bipolar short-circuit fault.

19. The fault identification and protection device according to claim 15, characterized in that, The DC / AC converter includes parallel current source converters and modular multilevel converters, and the AC / DC converter is a diode rectifier; or, The DC / AC converter is a current source converter, and the AC / DC converter is a modular multilevel converter; or... The DC / AC converter is a modular multilevel converter, and the AC / DC converter is a current source converter.

20. The fault identification and protection device according to claim 19, characterized in that, The protection module is specifically used for: In the case that the AC fault is a single-phase ground fault, the modular multilevel converter is subjected to fault ride-through control based on the actual value of the three-phase AC voltage of the modular multilevel converter. In the event that the AC fault is a two-phase short-circuit ungrounded fault, a two-phase short-circuit grounded fault, or a three-phase short-circuit fault, the current source converter and the modular multilevel converter are locked according to the blocking signal; or, in the event of an overcurrent in the modular multilevel converter, the current source converter and the modular multilevel converter are locked.

21. The fault identification and protection device according to claim 20, characterized in that, The protection module is specifically used for: Based on the actual values ​​of the three-phase AC voltage and the actual values ​​of the three-phase current of the modular multilevel converter, voltage and current dual closed-loop control is performed on the modular multilevel converter to obtain the reference value of the three-phase AC voltage of the modular multilevel converter; Calculate the negative sequence voltage reference value of the modular multilevel converter based on the actual value of the three-phase AC voltage of the modular multilevel converter; The control signal is obtained by superimposing and modulating the three-phase AC voltage reference value of the modular multilevel converter and the negative sequence voltage reference value of the modular multilevel converter. The modular multilevel converter is controlled according to the control signal.

22. The fault identification and protection device according to claim 21, characterized in that, The protection module is specifically used for: The actual three-phase AC voltage values ​​of the modular multilevel converter are subjected to Clark transformation to obtain the α-axis voltage component and β-axis voltage component of the modular multilevel converter. The α-axis negative sequence voltage reference value and β-axis negative sequence voltage reference value of the modular multilevel converter are calculated based on the α-axis voltage component and β-axis voltage component of the modular multilevel converter. The negative sequence voltage reference values ​​of the modular multilevel converter are obtained by performing an inverse Carrack transform on the α-axis negative sequence voltage reference values ​​and the β-axis negative sequence voltage reference values.

23. The fault identification and protection device according to claim 22, characterized in that, The α-axis negative sequence voltage reference value and β-axis negative sequence voltage reference value of the modular multilevel converter satisfy the following: in, u M_α n This represents the α-axis negative sequence voltage reference value of the modular multilevel converter. u M_β n This represents the β-axis negative sequence voltage reference value of the modular multilevel converter. u M_α This represents the α-axis voltage component of the modular multilevel converter. u M_β This represents the β-axis voltage component of the modular multilevel converter. u M_α1 express u M_α The α-axis voltage component obtained after one-quarter of a control cycle. u M_β1 express u M_β The β-axis voltage component obtained after one-quarter of a control cycle.

24. The fault identification and protection device according to claim 17, characterized in that, The protection module is specifically used for: In the case where the DC fault is either a positive ground fault or a negative ground fault: if, within a preset first time range, both the positive DC voltage and the negative DC voltage of the DC / AC converter or the AC / DC converter recover to the voltage range, the hybrid DC transformer resumes normal operation; otherwise, the hybrid DC transformer is locked out; wherein, the voltage range is composed of the first pole voltage threshold and the second pole voltage threshold; In the event that the DC fault is a bipolar short-circuit fault, the energy-consuming device is activated, and the output power of the new energy power station is reduced. If the bipolar short-circuit fault is cleared within a preset second time range, the energy-consuming device is disconnected, and the power output of the new energy power station is restored, and the hybrid DC transformer resumes normal operation. The energy-consuming device is located on the DC side of the DC / AC converter or the AC / DC converter, and the new energy power station is connected to the DC / AC converter or the DC side of the AC / DC converter.

25. A computer device, characterized in that, include: One or more processors; The processor is used to store one or more programs; When the one or more programs are executed by the one or more processors, the fault identification and protection method as described in any one of claims 1 to 12 is implemented.

26. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements the fault identification and protection method as described in any one of claims 1 to 12.

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