Relay protection method and device for converter of low-frequency power transmission system

Abstract

The invention provides a relay protection method and device for a converter of a low-frequency power transmission system, and relates to the field of power equipment operation and maintenance, and the method comprises the steps: determining a current setting value corresponding to each relay protection function according to a topological structure and operation parameters of the low-frequency power transmission system; controlling a power frequency converter transformer valve side alternating-current circuit breaker and a low-frequency bus side alternating-current circuit breaker to carry out valve side connecting line protection according to the obtained valve side electrical parameters and the current setting value; and controlling a power frequency side alternating current circuit breaker and a low frequency side alternating current circuit breaker to perform converter valve protection according to the obtained electrical parameters of the valve body and the current setting value. The complete relay protection configuration method for the modular multilevel matrix converter in the low-frequency power transmission system can be provided, and the safety and stability of the low-frequency power transmission system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power equipment operation and maintenance, in particular to a low-frequency power transmission system converter relay protection method and device. BACKGROUND

[0002] With the development and wide application of high-voltage large-capacity modular multilevel converter technology based on full-controlled devices, a new generation of low-frequency power transmission technology-flexible low-frequency AC power transmission based on flexible AC / AC converter as the core component and pulse width modulation as the theoretical basis has emerged. With the development trend of flexible low-frequency power transmission technology and the technical advantages of future low-frequency power transmission technology in large-capacity long-distance power transmission, flexible low-frequency power transmission is expected to become a new type of power transmission method for the development of new power systems with high proportion of clean energy and high proportion of power electronic devices.

[0003] Among them, the AC / AC converter can realize energy conversion between power frequency and 0~50Hz low frequency, and is the core equipment of flexible low-frequency AC power transmission technology. With the wide application of modular multilevel converter technology in large-capacity power electronic equipment, the prior art proposes to use a new type of modular multilevel matrix converter M3C as a key frequency conversion device in a low-frequency power transmission system. The prior art has carried out a certain degree of research on the low-frequency power transmission system using M3C converter, and proposed an M3C decoupling control strategy to realize independent active and reactive power control on both sides of M3C power frequency and low frequency. In terms of transient control, the fault ride-through strategy is studied for the power / low-frequency side fault of M3C. Obviously, the low-frequency power transmission system using M3C converter is different from the traditional power frequency AC power transmission system, and the traditional power frequency relay protection principle and configuration method is no longer applicable, especially for the converter itself, which needs a customized relay protection configuration scheme. There is an obvious technical gap in the relay protection configuration of the converter for the low-frequency power transmission system scenario.

[0004] This section is intended to provide background or context to the embodiments of the application recited in the claims. The description herein does not constitute admission that the prior art is prior art. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a low-frequency power transmission system converter relay protection method and device, which can provide a complete relay protection configuration method for the modular multilevel matrix converter in the low-frequency power transmission system, and improves the safety and stability of the low-frequency power transmission system.

[0006] To solve the above technical problems, the present application provides the following technical solutions: In a first aspect, the present application provides a low-frequency power transmission system converter relay protection method, comprising: The current setting value corresponding to each relay protection function is determined according to the topological structure and operating parameters of the low-frequency power transmission system; Valve-side connection line protection is performed on the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker according to the obtained valve-side electrical parameters and the current setting value; The power frequency side AC circuit breaker and the low-frequency side AC circuit breaker are controlled for converter valve protection according to the obtained valve body electrical parameters and the current setting value.

[0007] Further, the current setting value corresponding to each relay protection function is determined according to the topological structure and operating parameters of the low-frequency power transmission system, comprising: An electromagnetic transient analysis model of the low-frequency power transmission system is constructed according to the topological structure and operating parameters of the low-frequency power transmission system; The operating maximum value and the fault minimum value corresponding to each relay protection function are generated according to the electromagnetic transient analysis model of the low-frequency power transmission system; The current setting value is determined according to the operating maximum value and the fault minimum value; wherein the fault minimum value < the current setting value < the operating maximum value.

[0008] Further, the operating maximum value and the fault minimum value corresponding to each relay protection function are generated according to the electromagnetic transient analysis model of the low-frequency power transmission system, comprising: A plurality of normal operating conditions of the low-frequency power transmission system in normal operation are determined by using the electromagnetic transient analysis model of the low-frequency power transmission system; The maximum value among the current maximum values corresponding to each normal operating condition is selected as the operating maximum value; A plurality of fault operating conditions of the low-frequency power transmission system are determined by using the electromagnetic transient analysis model of the low-frequency power transmission system; The minimum value among the current minimum values corresponding to each fault operating condition is selected as the fault minimum value.

[0009] Further, the valve-side connection line protection includes power frequency valve-side connection line protection; the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled for valve-side connection line protection according to the obtained valve-side electrical parameters and the current setting value, comprising: The power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled for valve-side connection line differential protection in the valve-side power frequency connection line protection according to the operating current, the braking current and the starting current in the valve-side electrical parameters; The power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled for valve-side connection line zero sequence overvoltage protection in the valve-side power frequency connection line protection according to the valve-side connection line potential transformer voltage and the valve-side zero sequence voltage setting value in the valve-side electrical parameters; Based on the valve-side winding current, AC connection line current transformer current, and the current setting value in the valve-side electrical parameters, control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the power frequency connection line protection. Based on the valve-side winding current in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus to perform valve-side connection line overcurrent protection in the power frequency connection line protection. Based on the current flowing through the starting resistor in the valve-side electrical parameters and the current setting value, the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side are controlled to perform overcurrent protection of the starting resistor in the power frequency connection line protection on the valve side. Based on the total harmonic current of the starting resistor in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform overload protection of the starting resistor in the power frequency connection line protection on the valve side. Based on the low-frequency component of the power frequency side and the power frequency side voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform power frequency side differential frequency protection in the power frequency connection line protection of the valve side.

[0010] Furthermore, the valve-side connection line protection includes valve-side low-frequency connection line protection; the step of controlling the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value includes: Based on the operating current, braking current and starting current in the valve-side electrical parameters, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform differential protection of the valve-side low frequency connection line in the valve-side low frequency connection line protection. Based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform valve-side low-frequency connection line zero-sequence overvoltage protection. Based on the valve-side winding current, AC connection line current transformer current, and the current setting value in the valve-side electrical parameters, the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform valve-side zero-sequence overcurrent protection in the valve-side low-frequency connection line protection. Based on the valve-side winding current in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform valve-side connection line overcurrent protection in the valve-side low frequency connection line protection. Based on the low-frequency side power frequency component and low-frequency side voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform low-frequency side differential frequency protection in the valve-side low-frequency connection line protection.

[0011] Further, the step of controlling the power frequency side AC circuit breaker and the low frequency side AC circuit breaker for converter valve protection based on the acquired valve body electrical parameters and the current setting value includes: Based on the power frequency side converter chain current in the valve body electrical parameters and the current setting value, control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform bridge arm overcurrent protection in converter valve protection. Based on the low-frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters, the bridge arm reactor differential protection in the converter valve protection is controlled by the power frequency side AC circuit breaker and the low-frequency side AC circuit breaker. Based on the power frequency side converter chain current, low frequency side converter chain current and the current setting value in the valve body electrical parameters, the power frequency side AC circuit breaker and the low frequency side AC circuit breaker are controlled to perform valve differential protection in the converter valve protection. The power frequency side converter chain current, AC connection line current transformer current, and the current setting value in the valve body electrical parameters are used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform the power frequency side differential protection of the converter valve in the converter valve protection; wherein, if the AC connection line current transformer current is greater than the preset action value, the converter is blocked.

[0012] Secondly, this application provides a relay protection device for a low-frequency power transmission system converter, comprising: The current setting unit is used to determine the current setting value corresponding to each relay protection function based on the topology and operating parameters of the low-frequency transmission system. The valve-side connection protection unit is used to control the AC circuit breaker on the valve side and the AC circuit breaker on the low-frequency busbar side of the power frequency converter transformer to perform valve-side connection protection based on the acquired valve-side electrical parameters and the current setting value. The valve body protection unit is used to protect the converter valve based on the acquired valve body electrical parameters and the current setting value.

[0013] Furthermore, the current setting unit includes: The transient model construction module is used to construct an electromagnetic transient analysis model of a low-frequency power transmission system based on its topology and operating parameters. The fault maximum / minimum value determination module is used to generate the maximum operating value and minimum fault value corresponding to each relay protection function based on the electromagnetic transient analysis model of the low-frequency power transmission system. A current setting module is used to determine the current setting value based on the operating maximum value and the fault minimum value; wherein the fault minimum value < the current setting value < the operating maximum value.

[0014] Furthermore, the operational fault extreme value determination module includes: The normal operating condition determination module is used to determine multiple normal operating conditions of the low-frequency transmission system using the electromagnetic transient analysis model of the low-frequency transmission system. The maximum / minimum value determination module is used to select the largest current value from the maximum current values ​​corresponding to each normal operating condition as the operating maximum value; The fault condition determination module is used to determine multiple fault conditions in the low-frequency transmission system by utilizing the electromagnetic transient analysis model of the low-frequency transmission system. The fault minimum value determination module is used to select the minimum current value from the minimum current values ​​corresponding to each fault condition as the fault minimum value.

[0015] Furthermore, the valve-side connection line protection includes valve-side power frequency connection line protection; the valve-side connection line protection unit includes: The valve-side power frequency differential protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line differential protection in the power frequency connection line protection according to the operating current, braking current and starting current in the valve-side electrical parameters. The valve-side power frequency overvoltage protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line zero-sequence overvoltage protection in the power frequency connection line protection according to the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters. The valve-side power frequency zero-sequence overcurrent protection module is used to control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency busbar-side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the power frequency connection line protection according to the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters. The valve-side power frequency connection overcurrent protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection overcurrent protection in the valve-side power frequency connection protection according to the valve-side winding current in the valve-side electrical parameters and the current setting value. The starting resistor overcurrent protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform starting resistor overcurrent protection in the power frequency connection line protection of the valve side based on the current flowing through the starting resistor in the valve side electrical parameters and the current setting value. The starting resistor overload protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform starting resistor overload protection in the power frequency connection line protection of the valve side based on the total harmonic current of the starting resistor in the valve side electrical parameters and the current setting value. The power frequency inter-frequency protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform power frequency inter-frequency quantity protection in the valve-side power frequency connection line protection based on the power frequency side low-frequency component and power frequency side voltage setting value in the valve-side electrical parameters.

[0016] Furthermore, the valve-side connection line protection includes valve-side low-frequency connection line protection; the valve-side connection line protection unit includes: The valve-side low-frequency differential protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform valve-side low-frequency connection line differential protection based on the operating current, braking current and starting current in the valve-side electrical parameters. The valve-side low-frequency overvoltage protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side low-frequency connection line zero-sequence overvoltage protection based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters. The valve-side low-frequency zero-sequence overcurrent protection module is used to control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency busbar-side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the valve-side low-frequency connection line protection based on the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters. The valve-side low-frequency connection overcurrent protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection overcurrent protection in the valve-side low-frequency connection protection according to the valve-side winding current in the valve-side electrical parameters and the current setting value. The low-frequency heterogeneous frequency protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform low-frequency heterogeneous frequency protection in the valve side low-frequency connection line protection based on the low-frequency power frequency component and the low-frequency voltage setting value in the valve side electrical parameters.

[0017] Furthermore, the valve body protection unit includes: The bridge arm overcurrent protection module is used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform bridge arm overcurrent protection in the converter valve protection based on the power frequency side converter chain current in the valve body electrical parameters and the current setting value. The first differential protection module is used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform differential protection of the bridge arm reactor in the converter valve protection based on the low frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters. The second differential protection module is used to control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform valve differential protection in the protection of the converter valve based on the power frequency side converter chain current, the low frequency side converter chain current and the current setting value in the valve body electrical parameters. The third differential protection module is used to control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform differential protection of the converter valve on the power frequency side in the converter valve protection based on the power frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters; wherein, if the AC connection line current transformer current is greater than the preset action value, the converter is blocked.

[0018] Thirdly, this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the low-frequency power transmission system converter relay protection method.

[0019] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the low-frequency transmission system converter relay protection method.

[0020] Fifthly, this application provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the low-frequency power transmission system converter relay protection method.

[0021] To address the problems in existing technologies, this application provides a method and device for relay protection of converters in low-frequency power transmission systems. Specifically, it is a complete relay protection configuration method for modular multilevel matrix converters in low-frequency power transmission systems, including multiple protection functions such as valve-side connection line protection and converter valve protection. It innovatively employs an electromagnetic transient analysis model to automatically generate protection setting values, achieving accurate calculation and optimization of relay protection settings. This fills the technological gap in converter protection in the field of low-frequency power transmission, ensuring reliable system operation under normal and fault conditions, effectively preventing equipment damage and system fault escalation, and improving the safety and stability of low-frequency power transmission systems. Furthermore, it has strong engineering applicability, providing technical support for the design, operation, and maintenance of actual power systems, and promoting the widespread application of flexible low-frequency power transmission technology in new power systems. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the M3C main circuit in an embodiment of this application; Figure 2 This is a diagram of the M3C topology from the power frequency / low frequency side perspective in the embodiments of this application; Figure 3 This is a schematic diagram of the valve-side connection line protection zone function configuration in the embodiments of this application; Figure 4 This is a schematic diagram of the functional configuration of the converter valve protection zone in the embodiments of this application; Figure 5 This is a schematic diagram of a low-frequency power transmission system model in an embodiment of this application; Figure 6 This is a flowchart illustrating the automatic generation of setting value parameters in the embodiments of this application. Figure 7 This is a flowchart of the relay protection method for low-frequency power transmission system converters in the embodiments of this application; Figure 8 This is a flowchart illustrating the determination of the current setting values ​​corresponding to each relay protection function in the embodiments of this application; Figure 9 This is a flowchart illustrating the generation of the maximum operating value and the minimum fault value in the embodiments of this application; Figure 10 This is one of the flowcharts for protecting the valve-side connection line in the embodiments of this application; Figure 11 This is the second flowchart of the valve-side connection line protection in the embodiments of this application; Figure 12 This is a flowchart illustrating the protection of the converter valve in this embodiment of the application; Figure 13 This is a structural diagram of the relay protection device for the low-frequency power transmission system converter in the embodiments of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0025] The information collected in the technical solution of this application is information and data authorized by the user or fully authorized by all parties. The collection, storage, use, processing, transmission, provision, disclosure and application of the relevant data all comply with the relevant laws, regulations and standards of the relevant countries and regions, necessary confidentiality measures have been taken, and they do not violate public order and good morals. Corresponding operation portals are provided for users to choose to authorize or refuse.

[0026] Provide users with corresponding operation entry points, allowing them to choose to agree to or reject the automated decision results; if the user chooses to reject, the process will proceed to the expert decision-making process.

[0027] In one embodiment, see Figure 1 , Figure 2 and Figure 7 To improve the safety and stability of low-frequency power transmission systems, this application provides a relay protection method for converters in low-frequency power transmission systems, comprising: S101: Determine the current setting value corresponding to each relay protection function based on the topology and operating parameters of the low-frequency transmission system. S102: Based on the obtained valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to protect the valve-side connection line. S103: Control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to protect the converter valve based on the obtained valve body electrical parameters and the current setting value.

[0028] Understandable Figure 1 This is the main circuit diagram of the M3C. The M3C consists of nine bridge arms and connects two three-phase AC systems of different frequencies. Assume the AC grid voltage on the power frequency side is... v u , v v , v w The current is i u , i v , i w The voltage of the three-phase low-frequency AC grid is v a , v b , v c The grid current is i a , i b , i c .

[0029] Figure 2From the perspective of the power frequency / low frequency side, the M3C topology can be considered as consisting of three sub-converters: phase a sub-converter (containing ua, va, wa converter chains), phase b sub-converter (containing ub, vb, wb converter chains), and phase c sub-converter (containing uc, vc, wc converter chains). These three sub-converters are collectively referred to as phase x (x=a, b, c).

[0030] From the low-frequency side (abc), it can also be viewed as consisting of three sub-converters: the u-phase sub-converter (containing ua, ub, uc converter chains), the v-phase sub-converter (containing va, vb, vc converter chains), and the w-phase sub-converter (containing wa, wb, wc converter chains). These three sub-converters are collectively referred to as the y-phase sub-converter (y = u, v, w).

[0031] Based on the structural characteristics of M3C, a complete relay protection configuration method based on M3C converter is proposed.

[0032] In summary, the converter relay protection includes converter valve protection and valve zone power / low frequency connection line protection, and the configuration of each protection is shown in Table 1.

[0033] Table 1

[0034] To achieve the above protection functions, it is necessary to first determine the current setting value corresponding to each relay protection function. The specific method is described below.

[0035] As described above, the low-frequency transmission system converter relay protection method provided in this application is specifically a complete relay protection configuration method for modular multilevel matrix converters in low-frequency transmission systems. It includes multiple protection functions such as valve-side connection line protection and converter valve protection. Innovatively, it employs an electromagnetic transient analysis model to automatically generate protection setting values, achieving accurate calculation and optimization of relay protection settings. This fills a technological gap in converter protection in the low-frequency transmission field, ensuring reliable system operation under normal and fault conditions, effectively preventing equipment damage and system fault expansion, and improving the safety and stability of low-frequency transmission systems. Furthermore, it has strong engineering applicability, providing technical support for the design, operation, and maintenance of actual power systems, and promoting the widespread application of flexible low-frequency transmission technology in new power systems.

[0036] In one embodiment, see Figure 6 , Figure 8 The step of determining the current setting value corresponding to each relay protection function based on the topology and operating parameters of the low-frequency transmission system includes: S201: Construct an electromagnetic transient analysis model for a low-frequency power transmission system based on its topology and operating parameters; S202: Generate the maximum operating value and minimum fault value corresponding to each relay protection function based on the electromagnetic transient analysis model of the low-frequency power transmission system; S203: Determine the current setting value based on the maximum operating value and the minimum fault value; wherein, the minimum fault value < the current setting value < the maximum operating value.

[0037] Specifically, see Figure 9 The step of generating the maximum operating value and minimum fault value corresponding to each relay protection function based on the electromagnetic transient analysis model of the low-frequency power transmission system includes: S301: Use the electromagnetic transient analysis model of the low-frequency power transmission system to determine multiple normal operating conditions of the low-frequency power transmission system; S302: Select the largest current value from the maximum current values ​​corresponding to each normal operating condition as the operating maximum value; S303: Use the electromagnetic transient analysis model of the low-frequency power transmission system to determine multiple fault conditions in the low-frequency power transmission system; S304: Select the minimum current value from the minimum current values ​​corresponding to each fault condition as the minimum fault value.

[0038] Understandably, the method for determining the setting value is as follows: Because the working principle of converters is relatively complex, the setting values ​​of their related relay protection cannot be obtained manually as in traditional protection methods. Therefore, a new method is proposed: Taking the valve-side connection line overcurrent protection as an example, the electrical quantity selected for this protection is the IVT current on the converter transformer valve side. Explain its setting value. The method for obtaining it.

[0039] The maximum value of IVT under normal operating conditions of the power system is denoted as IVT. nomalmax The minimum value of IVT under fault conditions is denoted as IVT. faultmin Setting value It should meet the following requirements: IVT nomalmax < <IVT faultmin (15) Among them, IVT was determined nomalmax and IVT faultmin The method is as follows: The first step is to establish an electromagnetic transient analysis model.

[0040] When building a model, it is necessary to clarify the topology of the power system; confirm the base capacity and base voltage; and obtain the per-unit impedance values ​​of each voltage level under the maximum and minimum operating modes based on the data; equivalent parameters on the grid side (including positive sequence resistance, reactance, and zero sequence resistance, reactance); line parameters; and parameters on the power source side (usually new energy power plants).

[0041] For example, in a scenario where new energy is transmitted via flexible low-frequency collection in a certain region, the detailed composition and equivalents of each component are as follows: (1) The low-frequency new energy power station model is to equate the wind farm cluster to multiple detailed wind turbine models. The rated power of a single wind turbine is fixed, and the output power is multiplied at the wind turbine outlet step-up transformer. The power is collected through a 35kV collection line, and then the voltage is raised to 220kV through a step-up transformer. The power is then collected through a 220kV collection line and connected to a 20Hz switch station. The 20Hz switch station contains a 20Hz circuit breaker.

[0042] (2) After the low-frequency new energy is collected, it is connected to the 20Hz low-frequency line. The line adopts the π-type equivalent model and the total length of the line can be set.

[0043] (3) Flexible low-frequency power transmission AC switching station includes low-frequency circuit breaker, low-frequency transformer, AC switching valve, grounding transformer, power frequency transformer and power frequency circuit breaker, etc.

[0044] (4) The equivalent model of the power frequency system consists of a power frequency voltage source connected in series with a resistor and an inductor.

[0045] See the low-frequency power transmission system model. Figure 5 As shown, the low-frequency electrical energy generated by the wind turbines flows into the busbar and is then transmitted to the grid connection point via low-frequency transmission lines. The M3C converts the energy to power frequency before connecting it to the regional power grid. After the M3C startup process is complete, voltage vector directional control is activated. Once the M3C establishes a stable low-frequency voltage, the grid-side converter control and the turbine-side converter control of the wind power system are unlocked. The isolation transformer serves as the electrical isolation element.

[0046] Based on the above, an electromagnetic transient analysis model of a low-frequency transmission system including converter transformers is established according to the actual topology and parameters of the power system.

[0047] The second step is to run the analysis model and automatically generate the IVT. nomalmax and IVT faultmin parameter.

[0048] (1) Generate IVT nomalmax

[0049] The electromagnetic transient analysis model of the low-frequency transmission system selects the maximum operating mode under normal operation and sets M states (the specific value of M can be freely set according to actual conditions). The output of the renewable energy power station is different in each state (the output can be freely set according to actual conditions). The analysis model automatically runs the above M states sequentially, reading the IVT each time, until the maximum value of IVT is found. nomalmax .

[0050] (2) Generate IVT faultmin

[0051] The electromagnetic transient analysis model for low-frequency transmission systems selects the minimum operating mode under fault conditions. The fault state is freely selected based on different fault locations (for valve-side connection line overcurrent protection, the fault location is chosen at the valve-side connection line, and the specific fault location can be freely chosen) and different fault types (usually four types: single-phase short-circuit to ground, two-phase short circuit, two-phase short-circuit to ground, and three-phase short circuit). Simultaneously, the output of the renewable energy power station can be freely selected according to actual conditions. N states are generated based on these conditions. These N states are automatically run sequentially on the analysis model, with IVT read each time, until the minimum IVT is found. faultmin .

[0052] Refer to the above steps Figure 6 The process shown is implemented in detail.

[0053] As can be seen from the above description, the low-frequency transmission system converter relay protection method provided in this application can determine the current setting value corresponding to each relay protection function according to the topology and operating parameters of the low-frequency transmission system.

[0054] In one embodiment, see Figure 10 The valve-side connection line protection includes valve-side power frequency connection line protection; the step of controlling the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value includes: S401: Control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency busbar side to perform differential protection of the valve side power frequency connection line in the valve side power frequency connection line protection according to the operating current, braking current and starting current in the valve side electrical parameters. S402: Based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters, control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side power frequency connection line zero-sequence overvoltage protection in the valve-side connection line protection. S403: Based on the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency busbar side to perform valve-side zero-sequence overcurrent protection in the valve-side power frequency connection line protection. S404: Control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency busbar side to perform the overcurrent protection of the valve side connection line in the power frequency connection line protection according to the valve side winding current in the valve side electrical parameters and the current setting value. S405: Based on the current flowing through the starting resistor in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform the starting resistor overcurrent protection in the power frequency connection line protection on the valve side. S406: Based on the total harmonic current of the starting resistor in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform overload protection of the starting resistor in the power frequency connection line protection on the valve side. S407: Based on the low-frequency component of the power frequency side and the power frequency side voltage setting value in the valve-side electrical parameters, control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform power frequency side differential frequency protection in the valve-side power frequency connection line protection.

[0055] In one embodiment, see Figure 11 The valve-side connection line protection includes valve-side low-frequency connection line protection; the step of controlling the AC circuit breaker on the valve side and the AC circuit breaker on the low-frequency busbar side of the power frequency converter transformer to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value includes: S501: Control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform differential protection of the valve side low frequency connection line in the valve side low frequency connection line protection according to the operating current, braking current and starting current in the valve side electrical parameters. S502: Based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters, control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side low-frequency connection line zero-sequence overvoltage protection in the valve-side low-frequency connection line protection. S503: Based on the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters, control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency busbar-side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the valve-side low-frequency connection line protection. S504: Control the valve-side AC circuit breaker of the power frequency converter transformer and the low-frequency busbar AC circuit breaker to perform valve-side low-frequency connection line overcurrent protection in the valve-side connection line protection according to the valve-side electrical parameters, the valve-side winding current and the current setting value. S505: Based on the low-frequency side power frequency component and low-frequency side voltage setting value in the valve-side electrical parameters, control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform low-frequency side differential frequency protection in the valve-side low-frequency connection line protection.

[0056] It is understandable that the valve-side connection line protection function is as follows. Among them, steps S401 to S407 describe the connection line protection on the power frequency side, while steps S501 to S505 describe the connection line protection on the low frequency side.

[0057] In other words, valve-side connection line protection is divided into power frequency side and low frequency side. Because the converter starts from the power frequency side, it is equipped with a starting resistor compared to the low frequency side. Apart from this device, the configurations of other devices on both sides are basically the same. Therefore, the power frequency connection line on the valve side is used as an example to illustrate the protection configuration. The low frequency connection line is the same as the power frequency side except that it does not require starting resistor protection. See [link to relevant documentation]. Figure 3 As shown.

[0058] 1. Differential protection for valve-side connection lines

[0059] This protection is used to detect ground faults occurring at the valve-side connection line. The protection function measures the current IVT of the converter transformer valve-side winding and the current IVC of the AC connection line CT. When a ground fault occurs at the AC connection line, there is a fault current between the current IVT of the valve-side winding and the current IVC of the AC connection line, resulting in a differential current. The converter valve group corresponding to the fault is locked out, and the AC circuit breaker on the power frequency converter transformer valve side and the AC circuit breaker on the low frequency bus side corresponding to the converter valve are tripped.

[0060] Using the phase current at both ends of the connecting wire (M end and N end) This constitutes a protection system with current reference directions at both ends in opposite directions, and its operating current... and braking current They are respectively:

[0061] In the formula, Represents phases A, B, and C. Starting current I qd The value is taken as 4-6 times the capacitance current of this line under normal operating conditions. The protection criteria are as follows ( k (Proportionality coefficient)

[0062] 2. Zero-sequence overvoltage protection for valve-side connection lines

[0063] Used to detect grounding faults in the connection lines, and for protection purposes, it measures the voltage Uv of the voltage divider on the converter transformer valve side connection line. ), and calculate the zero-sequence voltage on the valve side. This is a preset zero-sequence voltage threshold on the valve side. When a ground fault occurs at the valve-side connection line, and the zero-sequence voltage exceeds a certain value, the corresponding converter valve is locked, tripping the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the corresponding low-frequency bus side of the converter valve. The action criterion is set as follows:

[0064] 3. Valve-side zero-sequence overcurrent protection

[0065] Used to detect grounding faults in the connecting lines, the protection function measures the current IVT of the converter transformer valve side winding and the current IVC of the AC connecting line CT, when the sum of the zero-sequence currents of the two ( If the value exceeds a certain threshold, the protection system will activate, locking the corresponding converter valve and tripping the AC circuit breaker on the power frequency converter transformer valve side and the AC circuit breaker on the corresponding low-frequency bus side. The activation criterion is as follows:

[0066] 4. Overcurrent protection for valve-side connection lines

[0067] This device is used to detect grounding faults at the valve-side connection line. It measures the Inverting Current Transmitted (IVT) on the converter transformer valve side. When the IVT exceeds a certain value, the corresponding converter valve is locked, and the AC circuit breaker on the power frequency converter transformer valve side and the corresponding low-frequency bus side AC circuit breaker are tripped. Its action criterion is:

[0068] 5. Overcurrent protection of starting resistor

[0069] This system is used to detect ground faults in the starting resistor. It measures the current ISR flowing through the starting resistor. When the current exceeds a certain value, the corresponding converter valve is locked, and the AC circuit breaker on the power frequency converter transformer valve side and the corresponding low-frequency bus AC circuit breaker are tripped. The protection action activation criteria are:

[0070] 6. Overload protection for starting resistor

[0071] This system is used to detect overload of the starting resistor and its total harmonic current. If the total harmonic current exceeds a set value, the protection system will activate. The protection activation delay should be sufficient to avoid the effects of transient overloads to prevent false tripping. It should be set using an inverse time-delay principle.

[0072] 7. Frequency anomaly protection

[0073] 1) Power frequency side inter-frequency quantity protection

[0074] When the converter valve is operating normally, the power frequency side and the low frequency side are decoupled, and the low frequency component cancels out the three phases on the power frequency side. When the operation is abnormal, the low frequency component can be detected on the power frequency side. The protection criteria are as follows.

[0075] in, U represents the voltage values ​​of each phase on the power frequency side. set50 This is the power frequency side voltage setting value (preset value).

[0076]

[0077] 2) Low-frequency side inter-frequency quantity protection

[0078] When the converter valve is operating normally, the power frequency side and the low frequency side are decoupled, and the power frequency component cancels out the three phases on the low frequency side. When the operation is abnormal, the power frequency component can be detected on the low frequency side. The protection criteria are as follows.

[0079] in, U represents the voltage values ​​of each phase on the power frequency side. set20 This is the power frequency side voltage setting value (preset value).

[0080]

[0081] Inter-frequency protection actions and alarms. In addition, over-frequency and under-frequency protection for mains frequency and low frequency also needs to be considered. Based on the set values, these actions will trigger alarms or tripping. The criteria are as follows, where the subscripts... H Indicates a high fixed value; subscript L Indicates a low constant value; f Frequency; subscript set This indicates the set value (preset value).

[0082]

[0083] As can be seen from the above description, the low-frequency power transmission system converter relay protection method provided in this application can control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value.

[0084] In one embodiment, see Figure 12 The step of controlling the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side for converter valve protection based on the acquired valve body electrical parameters and the current setting value includes: S601: Control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform bridge arm overcurrent protection in the converter valve protection according to the power frequency side converter chain current in the valve body electrical parameters and the current setting value. S602: Based on the low-frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters, control the power frequency side AC circuit breaker and the low-frequency side AC circuit breaker to perform differential protection of the bridge arm reactor in the converter valve protection. S603: Based on the power frequency side converter chain current, low frequency side converter chain current and the current setting value in the valve body electrical parameters, control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform valve differential protection in converter valve protection. S604: Control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform differential protection of the converter valve in the converter valve protection according to the power frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters; wherein, if the AC connection line current transformer current is greater than the preset action value, the converter is blocked.

[0085] It is understandable that steps S601 to S604 describe the protection of the converter valve.

[0086] The protection zone of the converter valve mainly extends from the current transformer (CT) on the power frequency side starting resistor to the current transformer (CT) on the low frequency bus. Here, CT refers to the current transformer. The configuration primarily considers two main types of equipment: valve groups and reactors, with differential and overcurrent protection included. A schematic diagram of the configuration is shown below. Figure 4 As shown. The current direction for protection in this area is set to point towards the converter valve. In the diagram and the following formulas, the suffix or subscript "50" for current I represents the power frequency side, and "20" represents the low frequency side; "ua, ub, uc, va, vb, vc, wa, wb, wc" represent the converter chain, see details. Figure 2 IVC stands for AC connection line CT current, subscript... A、B、C This represents phases A, B, and C. For example, This represents the current flowing through the magnetic flux linkage ua on the power frequency side, and so on. SET All are setpoint values.

[0087] 1. Bridge arm overcurrent protection

[0088] This device is used to detect short-circuit faults in the converter and grounding faults in the low-frequency side lines. It measures the current on the power frequency side arm of the converter valve; if the current exceeds a set value, it activates to lock the converter valve and trip the AC circuit breaker on the power / low-frequency side. The activation criteria are as follows:

[0089] This protection requires consideration of the converter valve's tolerance capabilities, and the coordination of multi-stage protection action settings and timing.

[0090] 2. Differential protection for bridge arm reactors

[0091] This protection is used to protect reactors and connected AC busbars from grounding faults. Its operating principle employs a phase-differential design, using an OR logic for the three phases. When the single-phase differential current exceeds a set value, the protection trips quickly, locking the converter valve and tripping the start-up / low-frequency side AC switch. Its operating principle is as follows:

[0092] 3. Valve differential protection

[0093] This protection is used for grounding faults within the converter valve. Its protection principle employs a segmented differential approach, calculating the differential current from the currents on both sides of the same bridge arm. Using an OR logic across the nine bridge arms, when the single-phase differential current exceeds a set value, the protection operates quickly, locking the converter valve and tripping the start-up / low-frequency side AC switch. Its operating principle is as follows:

[0094] 4. Differential protection on the power frequency side of the converter valve

[0095] The protection operates over a short lead area from the start-up resistor valve's current transformer (CT) on the power frequency side to the power frequency side of the converter valve arm. It uses a phase-differential protection mechanism with an OR logic across the three components. When the differential current exceeds a set value, the protection trips quickly, locking the converter valve and tripping the AC switch on the power / low frequency side. Its operating principle is as follows:

[0096] 5. Converter overcurrent protection

[0097] This protection is used to protect the converter valve and the AC line on the low-frequency side from grounding short-circuit faults. When the current IVC50 of the CT on the power frequency connection line of the valve side exceeds a certain value, the protection will activate and lock the converter. This protection serves as a backup protection for the differential protection on the power frequency side of the converter valve.

[0098] As can be seen from the above description, the low-frequency power transmission system converter relay protection method provided in this application can control the power frequency side AC circuit breaker and the low-frequency side AC circuit breaker to protect the converter valve based on the obtained valve body electrical parameters and the current setting value.

[0099] Based on the same inventive concept, this application also provides a low-frequency transmission system converter relay protection device, which can be used to implement the method described in the above embodiments, as shown in the following embodiments. Since the principle of the low-frequency transmission system converter relay protection device in solving the problem is similar to that of the low-frequency transmission system converter relay protection method, the implementation of the low-frequency transmission system converter relay protection device can refer to the implementation of the software performance benchmark determination method, and repeated details will not be elaborated further. As used below, the terms "unit" or "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the system described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0100] In one embodiment, see Figure 13 To improve the safety and stability of low-frequency power transmission systems, this application provides a converter relay protection device for low-frequency power transmission systems, comprising: The current setting unit 701 is used to determine the current setting value corresponding to each relay protection function based on the topology and operating parameters of the low-frequency transmission system. The valve-side connection protection unit 702 is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency busbar side to perform valve-side connection protection based on the acquired valve-side electrical parameters and the current setting value. The valve body protection unit 703 is used to protect the converter valve based on the acquired valve body electrical parameters and the current setting value.

[0101] In one embodiment, the current setting unit includes: The transient model construction module is used to construct an electromagnetic transient analysis model of a low-frequency power transmission system based on its topology and operating parameters. The fault maximum / minimum value determination module is used to generate the maximum operating value and minimum fault value corresponding to each relay protection function based on the electromagnetic transient analysis model of the low-frequency power transmission system. A current setting module is used to determine the current setting value based on the operating maximum value and the fault minimum value; wherein the fault minimum value < the current setting value < the operating maximum value.

[0102] In one embodiment, the operational fault maximum / minimum value determination module includes: The normal operating condition determination module is used to determine multiple normal operating conditions of the low-frequency transmission system using the electromagnetic transient analysis model of the low-frequency transmission system. The maximum / minimum value determination module is used to select the largest current value from the maximum current values ​​corresponding to each normal operating condition as the operating maximum value; The fault condition determination module is used to determine multiple fault conditions in the low-frequency transmission system by utilizing the electromagnetic transient analysis model of the low-frequency transmission system. The fault minimum value determination module is used to select the minimum current value from the minimum current values ​​corresponding to each fault condition as the fault minimum value.

[0103] In one embodiment, the valve-side connection line protection includes valve-side power frequency connection line protection; the valve-side connection line protection unit 702 includes: The valve-side power frequency differential protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line differential protection in the power frequency connection line protection according to the operating current, braking current and starting current in the valve-side electrical parameters. The valve-side power frequency overvoltage protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line zero-sequence overvoltage protection in the power frequency connection line protection according to the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters. The valve-side power frequency zero-sequence overcurrent protection module is used to control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency busbar-side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the power frequency connection line protection according to the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters. The valve-side power frequency connection overcurrent protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection overcurrent protection in the valve-side power frequency connection protection according to the valve-side winding current in the valve-side electrical parameters and the current setting value. The starting resistor overcurrent protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform starting resistor overcurrent protection in the power frequency connection line protection of the valve side based on the current flowing through the starting resistor in the valve side electrical parameters and the current setting value. The starting resistor overload protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform starting resistor overload protection in the power frequency connection line protection of the valve side based on the total harmonic current of the starting resistor in the valve side electrical parameters and the current setting value. The power frequency inter-frequency protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform power frequency inter-frequency quantity protection in the valve-side power frequency connection line protection based on the power frequency side low-frequency component and power frequency side voltage setting value in the valve-side electrical parameters.

[0104] In one embodiment, the valve-side connection line protection includes valve-side low-frequency connection line protection; the valve-side connection line protection unit 702 includes: The valve-side low-frequency differential protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform valve-side low-frequency connection line differential protection based on the operating current, braking current and starting current in the valve-side electrical parameters. The valve-side low-frequency overvoltage protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side low-frequency connection line zero-sequence overvoltage protection based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters. The valve-side low-frequency zero-sequence overcurrent protection module is used to control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency busbar-side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the valve-side low-frequency connection line protection based on the valve-side winding current, AC connection line current transformer current and the current setting value in the valve-side electrical parameters. The valve-side low-frequency connection overcurrent protection module is used to control the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection overcurrent protection in the valve-side low-frequency connection protection according to the valve-side winding current in the valve-side electrical parameters and the current setting value. The low-frequency inter-frequency protection module is used to control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform power frequency inter-frequency quantity protection in the low-frequency connection line protection of the valve side based on the low-frequency power frequency component and the low-frequency voltage setting value in the valve side electrical parameters.

[0105] In one embodiment, the valve body protection unit 703 includes: The bridge arm overcurrent protection module is used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform bridge arm overcurrent protection in the converter valve protection based on the power frequency side converter chain current in the valve body electrical parameters and the current setting value. The first differential protection module is used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform differential protection of the bridge arm reactor in the converter valve protection based on the low frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters. The second differential protection module is used to control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform valve differential protection in the protection of the converter valve based on the power frequency side converter chain current, the low frequency side converter chain current and the current setting value in the valve body electrical parameters. The third differential protection module is used to control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to perform differential protection of the converter valve on the power frequency side in the converter valve protection based on the power frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters; wherein, if the AC connection line current transformer current is greater than the preset action value, the converter is blocked.

[0106] From a hardware perspective, in order to improve the safety and stability of low-frequency power transmission systems, this application provides an embodiment of an electronic device for implementing all or part of the converter relay protection method for the low-frequency power transmission system. The electronic device specifically includes the following components: The system comprises a processor, a memory, a communications interface, and a bus; wherein the processor, memory, and communications interface communicate with each other via the bus; the communications interface is used to realize information transmission between the low-frequency transmission system converter relay protection device and core business systems, user terminals, and related databases and other related equipment; the logic controller can be a desktop computer, tablet computer, or mobile terminal, etc., and this embodiment is not limited to these. In this embodiment, the logic controller can be implemented with reference to the embodiments of the low-frequency transmission system converter relay protection method and the embodiments of the low-frequency transmission system converter relay protection device, the contents of which are incorporated herein, and repeated details will not be described again.

[0107] In one embodiment, the relay protection method function for low-frequency transmission system converters can be integrated into a central processing unit (CPU). The CPU can be configured to perform the following control: S101: Determine the current setting value corresponding to each relay protection function based on the topology and operating parameters of the low-frequency transmission system. S102: Based on the obtained valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to protect the valve-side connection line. S103: Control the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side to protect the converter valve based on the obtained valve body electrical parameters and the current setting value.

[0108] As described above, the low-frequency transmission system converter relay protection method and device provided in this application is specifically a complete relay protection configuration method for modular multilevel matrix converters in low-frequency transmission systems. It includes multiple protection functions such as valve-side connection line protection and converter valve protection. Innovatively, it employs an electromagnetic transient analysis model to automatically generate protection setting values, achieving accurate calculation and optimization of relay protection settings. This fills a technological gap in converter protection in the low-frequency transmission field, ensuring reliable system operation under normal and fault conditions, effectively preventing equipment damage and system fault expansion, and improving the safety and stability of low-frequency transmission systems. Furthermore, it has strong engineering applicability, providing technical support for the design, operation, and maintenance of actual power systems, and promoting the widespread application of flexible low-frequency transmission technology in new power systems.

[0109] Embodiments of this application also provide a computer-readable storage medium capable of implementing all steps of the low-frequency transmission system converter relay protection method with the execution subject as a server or client in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all steps of the low-frequency transmission system converter relay protection method with the execution subject as a server or client in the above embodiments.

[0110] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, apparatus, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention 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.

[0111] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (devices), and computer program products according to embodiments of the invention. 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 illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0112] 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 1 The function specified in one or more boxes.

[0113] 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.

[0114] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A relay protection method for a converter in a low-frequency power transmission system, characterized in that, include: Determine the current setting value corresponding to each protection function based on the topology and operating parameters of the low-frequency transmission system; Based on the obtained valve-side electrical parameters and the current setting value, the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side are controlled to protect the valve-side connection line. Based on the obtained valve body electrical parameters and the current setting value, the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side are controlled to protect the converter valve.

2. The relay protection method for low-frequency power transmission system converters according to claim 1, characterized in that, The determination of the current setting values ​​corresponding to each protection function based on the topology and operating parameters of the low-frequency transmission system includes: An electromagnetic transient analysis model of a low-frequency power transmission system is constructed based on its topology and operating parameters. Based on the electromagnetic transient analysis model of the low-frequency power transmission system, the maximum operating value and minimum fault value corresponding to each protection function are generated; The current setting value is determined based on the maximum operating value and the minimum fault value; wherein the minimum fault value < the current setting value < the maximum operating value.

3. The relay protection method for low-frequency power transmission system converters according to claim 2, characterized in that, The process of generating the maximum operating value and minimum fault value corresponding to each protection function based on the electromagnetic transient analysis model of the low-frequency power transmission system includes: The electromagnetic transient analysis model of the low-frequency power transmission system is used to determine multiple normal operating conditions of the low-frequency power transmission system. The maximum current value among the maximum current values ​​corresponding to each normal operating condition is selected as the operating maximum value; Multiple fault conditions of the low-frequency power transmission system are determined using the electromagnetic transient analysis model of the low-frequency power transmission system. The minimum current value corresponding to each fault condition is selected as the minimum fault value.

4. The relay protection method for low-frequency power transmission system converters according to claim 1, characterized in that, The valve-side connection line protection includes valve-side power frequency connection line protection; the step of controlling the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value includes: Based on the operating current, braking current and starting current in the valve-side electrical parameters, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform differential protection of the valve-side power frequency connection line in the valve-side power frequency connection line protection. Based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform valve-side power frequency connection line zero-sequence overvoltage protection in the valve-side connection line protection. Based on the valve-side winding current, AC connection line current transformer current, and the current setting value in the valve-side electrical parameters, control the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus side AC circuit breaker to perform valve-side zero-sequence overcurrent protection in the power frequency connection line protection. Based on the valve-side winding current in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus to perform valve-side connection line overcurrent protection in the power frequency connection line protection. Based on the current flowing through the starting resistor in the valve-side electrical parameters and the current setting value, the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side are controlled to perform overcurrent protection of the starting resistor in the power frequency connection line protection on the valve side. Based on the total harmonic current of the starting resistor in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve-side of the power frequency converter transformer and the AC circuit breaker on the low-frequency bus side to perform overload protection of the starting resistor in the power frequency connection line protection on the valve side. Based on the low-frequency component of the power frequency side and the power frequency side voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform power frequency side differential frequency protection in the power frequency connection line protection of the valve side.

5. The relay protection method for low-frequency power transmission system converters according to claim 1, characterized in that, The valve-side connection line protection includes valve-side low-frequency connection line protection; the step of controlling the AC circuit breaker on the valve side and the AC circuit breaker on the low-frequency busbar side of the power frequency converter transformer to perform valve-side connection line protection based on the acquired valve-side electrical parameters and the current setting value includes: Based on the operating current, braking current and starting current in the valve-side electrical parameters, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform differential protection of the valve-side low frequency connection line in the valve-side low frequency connection line protection. Based on the valve-side connection line voltage divider voltage and valve-side zero-sequence voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform valve-side low-frequency connection line zero-sequence overvoltage protection. Based on the valve-side winding current, AC connection line current transformer current, and the current setting value in the valve-side electrical parameters, the power frequency converter transformer valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform valve-side zero-sequence overcurrent protection in the valve-side low-frequency connection line protection. Based on the valve-side winding current in the valve-side electrical parameters and the current setting value, control the AC circuit breaker on the valve side of the power frequency converter transformer and the AC circuit breaker on the low frequency bus side to perform valve-side connection line overcurrent protection in the valve-side low frequency connection line protection. Based on the low-frequency side power frequency component and low-frequency side voltage setting value in the valve-side electrical parameters, the power frequency converter valve-side AC circuit breaker and the low-frequency bus-side AC circuit breaker are controlled to perform low-frequency side differential frequency protection in the valve-side low-frequency connection line protection.

6. The relay protection method for low-frequency power transmission system converters according to claim 1, characterized in that, The method of controlling the AC circuit breaker on the power frequency side and the AC circuit breaker on the low frequency side according to the obtained valve body electrical parameters and the current setting value to protect the converter valve includes: Based on the power frequency side converter chain current in the valve body electrical parameters and the current setting value, control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform bridge arm overcurrent protection in converter valve protection. Based on the low-frequency side converter chain current, AC connection line current transformer current and the current setting value in the valve body electrical parameters, the bridge arm reactor differential protection in the converter valve protection is controlled by the power frequency side AC circuit breaker and the low-frequency side AC circuit breaker. Based on the power frequency side converter chain current, low frequency side converter chain current and the current setting value in the valve body electrical parameters, the power frequency side AC circuit breaker and the low frequency side AC circuit breaker are controlled to perform valve differential protection in the converter valve protection. The power frequency side converter chain current, AC connection line current transformer current, and the current setting value in the valve body electrical parameters are used to control the power frequency side AC circuit breaker and the low frequency side AC circuit breaker to perform the power frequency side differential protection of the converter valve in the converter valve protection; wherein, if the AC connection line current transformer current is greater than the preset action value, the converter is blocked.

7. A relay protection device for a converter in a low-frequency power transmission system, characterized in that, include: The current setting unit is used to determine the current setting value corresponding to each protection function based on the topology and operating parameters of the low-frequency transmission system. The valve-side connection protection unit is used to control the AC circuit breaker on the valve side and the AC circuit breaker on the low-frequency busbar side of the power frequency converter transformer to perform valve-side connection protection based on the acquired valve-side electrical parameters and the current setting value. The valve body protection unit is used to protect the converter valve based on the acquired valve body electrical parameters and the current setting value.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the low-frequency power transmission system converter relay protection method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the low-frequency transmission system converter relay protection method according to any one of claims 1 to 6.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instruction is executed by the processor, it implements the steps of the low-frequency transmission system converter relay protection method according to any one of claims 1 to 6.

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