CN117200224A - Three-phase fault ride-through method for continuous low voltage of hybrid cascade direct current system - Google Patents

Abstract

The invention relates to a three-phase fault ride-through method for continuous low voltage in a hybrid cascade DC system, which includes: calculating the hybrid cascaded DC system according to the three-phase AC voltage on the grid side of the flexible-DC converter transformer of the flexible-DC converter station in the hybrid cascade DC system. The AC voltage amplitude at the receiving end of the cascaded DC system and the detection of the three-phase fault of the near-area AC system of the flexible-to-DC converter transformer; when a three-phase fault of the close-area AC system of the flexible-to-DC converter transformer is detected, the hybrid cascaded DC system The sending end is phase-shifted and maintained for the set phase-shifting time, then the phase-shifting is released and the AC fault recovery process is entered; during the AC fault recovery process, according to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascade DC system, The sending end of the hybrid cascaded DC system adopts square wave power limiting mode or slope power limiting mode to ensure stable frequency, stable voltage and stable power angle at the sending and receiving ends of the hybrid cascaded DC system. The present invention can be widely used in In the field of DC transmission.

Description

A three-phase fault ride-through method for sustained low voltage in hybrid cascaded DC systems

Technical field

The invention relates to the field of DC power transmission, and in particular to a three-phase fault ride-through method for sustained low voltage in a hybrid cascade DC system.

Background technique

China's energy resources and load centers are distributed in reverse directions, and it is necessary to steadily promote the construction of UHV backbone power grids and leverage the transmission capabilities of large UHV power grids. In some load centers in China, such as East China, the demand for DC feed-in continues to increase. However, the intensive DC feed-in outside the region will cause the electrical distance between converter stations to decrease, the short-circuit ratio of multiple feed-ins to decrease, and the simultaneous commutation of multiple DC circuits. The risk of failure is gradually increasing, causing the power grid to face serious security and stability problems. In order to achieve long-distance large-capacity power transmission and multi-point power supply, and solve the problem of reduced short-circuit ratio of multiple feeds at the receiving end, a hybrid cascaded UHV DC transmission method can be used, that is, conventional DC converters and multiple flexible DC converters. The technical solution of cascade connection combines the advantages of conventional DC and flexible DC, which can effectively improve the stability of the AC power grid at the receiving end. It has high reliability, flexible operation mode and wide application prospects. It is the ideal way to build future energy. Key technologies of the Internet.

The hybrid cascaded UHV DC system adopts LCC (grid commutated converter) at the transmitting end. Although the LCC and VSC (voltage source converter) at the receiving end are dispersedly connected to different AC points, the receiving end is usually located in developed areas. , the distance between each drop point is still relatively close, so there are still varying degrees of electrical coupling between each AC drop point. When a single converter fails in the near-area three-phase AC system, it will also cause the grid-side AC bus of other converters to fail. The voltage drops to varying degrees, and the AC bus is prone to sustained low voltage, which causes a chain failure reaction in which the high-end LCC commutation fails and the VSC output power is limited for a long time. The sending end continues to inject the VSC with a serious DC power surplus, eventually leading to the VSC Severe overvoltage or energy dissipation device energy exceeding the limit will cause serious consequences for the VSC to cease operation.

Therefore, how to reduce the DC side surplus power of the VSC converter after a three-phase fault of the near-area AC system at the receiving end of the hybrid cascade DC system, and ensure that the system can achieve the three-phase near-area AC system when sustained low voltage occurs in various operating modes. Fault ride-through is a key issue for the safe and reliable operation of hybrid cascaded DC systems, which has not yet been addressed by existing technologies.

Contents of the invention

In view of the above problems, the purpose of the present invention is to provide a hybrid cascade DC system continuous low voltage three-phase fault ride-through method, which can ensure that the system realizes the three-phase fault ride-through of the near-area AC system when sustained low voltage occurs in various operating modes. .

In order to achieve the above objects, the present invention adopts the following technical solutions: First, a hybrid cascaded DC system provides a continuous low-voltage three-phase fault ride-through method, including:

According to the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer in the hybrid cascaded DC system, calculate the AC voltage amplitude at the receiving end of the hybrid cascaded DC system and detect the near-area AC of the flexible-to-DC converter transformer. System three-phase fault;

When a three-phase fault in the near-area AC system of the flex-DC converter transformer is detected, the sending end of the hybrid cascade DC system shifts the phase and maintains the set phase shift time, then releases the phase shift and enters the AC fault recovery process;

During the AC fault recovery process, according to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascaded DC system, the sending end of the hybrid cascaded DC system adopts the square wave power limiting mode or the slope power limiting mode to ensure The frequency, voltage and power angle of the sending and receiving ends of the hybrid cascade DC system are stable.

Further, according to the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer of the flexible-to-DC converter station in the hybrid cascaded DC system, the AC voltage amplitude at the receiving end of the hybrid cascaded DC system is calculated and the flexible-to-DC converter is detected. Three-phase faults in the AC system near the transformer include:

Real-time collection of the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer in the hybrid cascaded DC system;

Calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer;

Based on the three-phase AC voltage collected in real time on the grid side of the flex-to-dc converter transformer, the three-phase fault of the near-area AC system of the flex-to-dc converter transformer is detected.

Further, calculating the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer includes:

Perform CLARK transformation on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer to obtain the two-phase components. and/> , then the AC voltage amplitude/> for:

.

Further, the detection of three-phase faults of the near-area AC system of the flex-to-dc converter transformer based on the three-phase AC voltage on the grid side of the flex-to-dc converter transformer collected in real time includes:

Perform positive and negative sequence PARK transformation on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer to obtain the dq positive sequence voltage component. ,/> and dq negative sequence voltage component/> ,/> ;

According to the dq positive sequence voltage component ,/> and dq negative sequence voltage component/> ,/> , respectively calculate the positive sequence voltage component amplitude/> and negative sequence voltage component amplitude/> :

when satisfied and/> When , it is determined that the flex-DC converter transformer has a three-phase fault in the near-area AC system, where, /> is the positive sequence voltage component amplitude judgment threshold,/> It is the negative sequence voltage component amplitude judgment threshold.

Furthermore, during the AC fault recovery process, according to the continuous low voltage state of the receiving end of the hybrid cascaded DC system and the AC voltage amplitude, the sending end of the hybrid cascaded DC system adopts the square wave power limiting mode or the slope mode. Power limiting mode ensures stable frequency, stable voltage and stable power angle at the sending and receiving ends of the hybrid cascade DC system, including:

During the AC fault recovery process, according to the continuous low voltage state of the receiving end of the hybrid cascaded DC system, the sending end of the hybrid cascaded DC system enters the power limit recovery mode, including square wave power limit mode and slope power limit mode;

The transmitting end of the hybrid cascaded DC system preferentially adopts the square wave power limiting mode. Based on the AC voltage amplitude at the receiving end of the hybrid cascaded DC system, this mode is used to detect when a three-phase fault of the near-area AC system occurs in the hybrid cascaded DC system. Electromechanical-electromagnetic transient joint simulation to determine whether the square wave power limitation mode can ensure the frequency stability, voltage stability and power angle stability of the sending and receiving end AC systems;

When the square wave power limiting mode cannot ensure the stability of the sending and receiving end AC systems, the slope power limiting mode is adopted based on the AC voltage amplitude of the receiving end of the hybrid cascade DC system to ensure the frequency stability of the sending and receiving ends. Voltage stability and power angle stability.

Further, the square wave power limitation mode is: when the power is restored after the phase shift at the sending end of the hybrid cascade DC system, the maximum restored power limit value is set , limiting the maximum recovery power of the sending end of the hybrid cascade DC system to/> and maintain time/> Afterwards, it returns to the pre-fault level;

The slope-type power limiting mode is: the AC voltage amplitude at the receiving end of the hybrid cascade DC system is Communicates to the sending end in real time, and the sending end performs low-voltage current limiting for the station based on the AC bus voltage of the receiving end, and sets the low-voltage current limiting curve of the hybrid cascade DC system/> , where,/> is the rated power of the hybrid cascade DC system under the current operating mode,/> is the margin coefficient.

Further, the method also includes:

Scan the three-phase fault of the near-area AC system of the flexible-DC converter station in the hybrid cascade DC system to obtain the sustained low voltage that maximizes the energy absorption of the energy dissipation device during the recovery process of the three-phase fault of the near-area AC system for more than several milliseconds. AC low voltage amplitude and low voltage duration under voltage operating conditions. The obtained AC low voltage amplitude and low voltage duration are used to determine the maximum recovery power limit value and maintenance time in the square wave power limit mode.

The second aspect is to provide a continuous low-voltage three-phase fault ride-through method for hybrid cascaded DC systems, including:

The three-phase fault detection module of the near-area AC system is used to calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage on the grid side of the flexible-DC converter transformer of the flexible-DC converter station in the hybrid cascade DC system. value and detect the three-phase fault of the near-area AC system of the flexible DC converter transformer;

The AC fault recovery module is used to shift the phase of the sending end of the hybrid cascade DC system and maintain the set phase shift time before releasing the phase shift and entering the AC fault after detecting a three-phase fault of the near-area AC system in the flex-DC converter transformer. recovery process;

The power limit recovery module is used during the AC fault recovery process. According to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascade DC system, the sending end of the hybrid cascade DC system adopts square wave power limiting mode or The slope-type power limiting mode ensures stable frequency, stable voltage and stable power angle at the sending and receiving ends of the hybrid cascade DC system.

In a third aspect, a processing device is provided, including computer program instructions, wherein the computer program instructions, when executed by the processing device, are used to implement steps corresponding to the above three-phase fault ride-through method for continuous low voltage in a hybrid cascade DC system.

In a fourth aspect, a computer-readable storage medium is provided. Computer program instructions are stored on the computer-readable storage medium. The computer program instructions, when executed by a processor, are used to implement the above-mentioned hybrid cascaded DC system with sustained low energy consumption. Corresponding steps for the three-phase fault ride-through method of voltage.

Since the present invention adopts the above technical solutions, it has the following advantages:

1. The present invention proposes a complete set of fault ride-through methods and processes under continuous AC low voltage, which effectively solves the problem of DC side energy dissipation device energy exceeding the limit when the flexible DC AC system fails and causes long-term continuous low voltage, and reduces VSC. The DC side power surplus limits the energy of the energy dissipation device within the allowable range, avoids the investment in primary equipment of the energy dissipation device, and ensures that the three-phase fault ride-through of the near-area AC system under continuous low voltage can be achieved in various operating modes of the system.

2. The square wave power limitation mode proposed by the present invention does not require inter-station communication and can ensure the fault ride-through capability under various operating modes; the slope power limitation mode proposed by the present invention relies on inter-station communication but can retain power transmission to the maximum extent. Ability to reduce power loss, two options can be selected according to system requirements.

To sum up, the present invention can be widely used in the field of direct current transmission.

Description of the drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating preferred embodiments only and are not to be construed as limiting the invention. Throughout the drawings, the same reference numbers refer to the same parts. In the attached picture:

Figure 1 is a schematic diagram of the topology structure of a hybrid cascaded DC system provided by an embodiment of the present invention;

Figure 2 is a schematic flow chart of a method provided by an embodiment of the present invention;

Figure 3 is a schematic diagram for calculating the AC voltage amplitude of the hybrid cascade DC system VSC provided by an embodiment of the present invention;

Figure 4 is a schematic flowchart of a three-phase fault detection method for a hybrid cascaded DC system VSC near-area AC system provided by an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a thorough understanding of the invention, and to fully convey the scope of the invention to those skilled in the art.

It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. The terms "comprises", "includes", "contains" and "having" are inclusive and thus indicate the presence of stated features, steps, operations, elements and/or parts but do not exclude the presence or addition of one or Various other features, steps, operations, elements, components, and/or combinations thereof. The method steps, procedures, and operations described herein are not to be construed as requiring that they be performed in the particular order described or illustrated, unless an order of performance is expressly indicated. It should also be understood that additional or alternative steps may be used.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections shall not be referred to as restricted by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

As shown in Figure 1, the sending end of the hybrid cascade DC system adopts a conventional UHV DC topology, and each pole is composed of a cascade of two twelve-pulse conventional DC converters; the receiving end of the hybrid cascade DC system adopts a hybrid In the cascade DC system topology, each pole consists of a high-voltage end (i.e. 800kV ~ 400kV) twelve-pulse conventional DC converter and multiple low-voltage ends (400kV ~ neutral line) (three shown in the figure) in parallel. Flexible DC converters are cascaded. The flexible DC converters use half-bridge modular multi-level converters. The conventional DC converters at the receiving end and each flexible DC converter are fed into different AC buses. . The hybrid cascaded DC system's sustained low-voltage three-phase fault ride-through method provided by the embodiment of the present invention can effectively reduce the DC side surplus power of the VSC converter under sustained low voltage after a three-phase fault of the AC system in the near area of the system, ensuring that The system can realize AC fault ride-through in various operating modes.

Example 1

As shown in Figure 2, this embodiment provides a hybrid cascade DC system continuous low voltage three-phase fault ride-through method, which includes the following steps:

1) Scan the three-phase fault of the near-area AC system of the flexible-DC converter station in the hybrid cascade DC system, and obtain the three-phase fault of the near-area AC system with a recovery voltage of more than 100 milliseconds that causes the energy dissipation device to absorb the maximum energy during the recovery process. AC low voltage amplitude under continuous low voltage conditions and low voltage duration/> .

Specifically, the process of the three-phase fault scanning method of the near-area AC system is: establishing an electromechanical-electromagnetic hybrid simulation model of the hybrid cascaded DC system. Based on the harsh mode of the AC system, the different DC operating modes and various types of the hybrid cascaded DC system are analyzed. With a VSC input combination, a full-range scan is performed on the three-phase fault of the near-area AC system, and the recovery voltage of the three-phase fault of the near-area AC system is more than 100 milliseconds. During the recovery process, the energy dissipation device absorbs the maximum energy under the continuous low-voltage working condition. AC low voltage amplitude and low voltage duration/> , among which, the harsh mode of the AC system refers to the different wiring and different operating power of the AC system. The so-called "harsh" means that the energy dissipation device absorbs a large amount of energy in this mode. The DC operation mode of the hybrid cascade DC system includes There are seven categories: bipolar full voltage operation, unipolar earth return operation, unipolar metal return operation, bipolar mixed pressure operation, unipolar half voltage earth return operation and unipolar half voltage metal return operation. The VSC input combination refers to the positive and negative poles. The number of VSCs that can be input separately can range from 1 to 3 for each pole.

2) Calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage on the grid side of the flexible-DC converter transformer in the hybrid cascade DC system. As well as detecting three-phase faults in the near-area AC system of flexible DC converter transformers, specifically:

2.1) Real-time collection of the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer in the hybrid cascade DC system.

2.2) Calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer. .

Specifically, as shown in Figure 3, CLARK transformation is performed on the three-phase AC voltage on the grid side of the flex-DC converter transformer collected in real time to obtain the two-phase components. and/> , then the AC voltage amplitude/> for:

(1)

2.3) As shown in Figure 4, based on the three-phase AC voltage collected in real time on the grid side of the flex-to-dc converter transformer, the three-phase fault of the near-area AC system of the flex-to-dc converter transformer is detected:

2.3.1) Perform positive and negative sequence PARK transformation on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer to obtain the dq positive sequence voltage component ,/> and dq negative sequence voltage component/> ,/> .

2.3.2) According to the dq positive sequence voltage component ,/> and dq negative sequence voltage component/> ,/> , respectively calculate the positive sequence voltage component amplitude/> and negative sequence voltage component amplitude/> :

(2)

(3)

2.3.3) Set the positive sequence voltage component amplitude judgment threshold and negative sequence voltage component amplitude judgment threshold .

2.3.4) When satisfied and/> When, it is determined that a three-phase fault of the near-area AC system occurs in the flexible-to-DC converter transformer.

3) When a three-phase fault of the near-area AC system is detected in the flex-DC converter transformer, the sending end of the hybrid cascade DC system shifts phase and maintains the set phase shift time. Then the phase shift is released and the AC fault recovery process is entered.

4) During the AC fault recovery process, according to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascade DC system , the sending end of the hybrid cascaded DC system adopts square wave power limiting mode or slope power limiting mode to ensure that the sending and receiving ends of the hybrid cascaded DC system have stable frequency, voltage stability and power angle stability (frequency stability, voltage stability , power angle stability are both terms, which refer to the ability to return to a specific state within a certain period of time after a disturbance), specifically:

4.1) During the AC fault recovery process, according to the continuous low voltage state of the receiving end of the hybrid cascade DC system, the sending end of the hybrid cascade DC system enters the power limit recovery mode, including square wave power limit mode and slope power limit. model.

4.2) The sending end of the hybrid cascaded DC system preferentially adopts the square wave power limiting mode, based on the AC voltage amplitude of the receiving end of the hybrid cascaded DC system. , using this mode to conduct electromechanical-electromagnetic transient joint simulation when a three-phase fault occurs in the near-area AC system of the hybrid cascade DC system, to determine whether the square wave power limiting mode can ensure the frequency stability and voltage stability of the sending and receiving end AC systems. Stability and angle stability.

Specifically, the square wave power limitation mode is: when the power is restored after the phase shift at the sending end of the hybrid cascade DC system, the maximum restored power limit value is set , limiting the maximum recovery power of the sending end of the hybrid cascade DC system to/> and maintain time/> Afterwards, it returns to the pre-fault level.

More specifically, the maximum recovery power limit value in square wave power limit mode and maintenance time Satisfy:/> ,/> , where,/> is the rated operating power of the system,/> It is the rated AC voltage on the grid side of the flex-DC converter transformer.

4.3) When the square wave power limiting mode cannot ensure the stability of the sending and receiving end AC systems, the AC voltage amplitude of the receiving end based on the hybrid cascade DC system , adopts the slope power limiting mode to ensure the frequency stability, voltage stability and power angle stability of the sending and receiving ends.

Specifically, the slope-type power limiting mode is: convert the AC voltage amplitude at the receiving end of the hybrid cascade DC system into Communicates to the sending end in real time, and the sending end performs low-voltage current limiting for the station based on the AC bus voltage of the receiving end, and sets the low-voltage current limiting curve of the hybrid cascade DC system/> , where,/> is the rated power of the hybrid cascade DC system under the current operating mode,/> It is the margin coefficient. By setting this coefficient to ensure that the DC side power emitted by the sending end is less than the power capacity that the receiving end can absorb, to avoid surplus power, it is recommended to be 0.9 to 1.

Taking the three-phase fault ride-through of a continuous low-voltage near-area AC system of a hybrid cascade DC system with ±800kV/8000MW and a receiving end including a single LCC and three VSCs as an example, the method of the present invention will be further described in detail.

1) Establish an electromechanical-electromagnetic hybrid simulation model of the hybrid cascade DC system. Based on the harsh method of the AC system, conduct various operating modes of the hybrid cascade DC system and the three-phase faults of the near-area AC system under various VSC input combinations. Global scan. In this embodiment, the electromechanical-electromagnetic hybrid simulation (ADPSS, PSASP) platform is used to complete the DC modes such as bipolar full voltage, bipolar half voltage, unipolar full voltage, unipolar half voltage and metal loop, and consider each input VSC combination (123, 12, 23, 13, etc.), considering the most severe winter peak mode, conduct a full-field scan of the three-phase faults of the VSC near-area AC system, and obtain the most severe low-voltage operation of the three-phase faults of the DC system near-area AC system The mode is 1+2 operation mode (the high-voltage side LCC is put into operation, and the low-voltage side two VSCs are put into operation). In this operation mode, the most severe low voltage amplitude during the three-phase fault recovery process of the VSC near-area AC system is 0.72pu (standard The unitary value is the rated AC voltage amplitude), and the maximum low voltage duration is 0.9s.

2) Calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage on the grid side of the flexible-DC converter transformer in the hybrid cascade DC system. and detection of three-phase faults in near-area AC systems of flexible DC converter transformers. In this embodiment, the positive sequence voltage component amplitude judgment threshold/> and negative sequence voltage component amplitude judgment threshold are taken to be 0.8pu and 0.2pu respectively. When the amplitude of the positive sequence voltage component/> and negative sequence voltage component amplitude/> satisfy and/> When, it is determined that a three-phase fault of the near-area AC system occurs in the flexible-to-DC converter transformer.

3) When a three-phase fault in the near-area AC system is detected in the flex-DC converter transformer, the sending end of the hybrid cascade DC system shifts and maintains the phase. After a certain time, the phase shift is released and the AC fault recovery process is entered. In this embodiment,/> Set to 70ms.

4) During the AC fault recovery process, according to the continuous low voltage state of the receiving end of the hybrid cascade DC system and the AC voltage amplitude of the receiving end of the hybrid cascade DC system, as well as the obtained AC low voltage amplitude and low voltage duration , the sending end of the hybrid cascaded DC system adopts the square wave power limiting mode or the slope power limiting mode to ensure the frequency, voltage and power angle stability of the sending and receiving ends of the hybrid cascaded DC system. In this embodiment, it is calculated that the square wave power limitation mode can ensure the frequency stability, voltage stability and power angle stability of the sending and receiving ends of the hybrid cascade DC system. Therefore, this power limitation recovery mode is adopted, where the maximum recovery power Limit value/> Set to 0.7pu (the base value per unit is/> ), maintenance time/> Set to 1s. Finally, after adopting the square wave power limiting mode, the three-phase faults of the near-area AC system of the flexible-DC converter station of the hybrid cascade DC system were scanned again and it was found that the method of the present invention effectively reduced the VSC DC side power surplus. , limiting the energy of the VSC DC side energy dissipation device within the allowable range, ensuring that the three-phase fault ride-through of the near-area AC system under continuous low voltage can be achieved in various operating modes of the system.

Example 2

This embodiment provides a hybrid cascade DC system continuous low voltage three-phase fault ride-through method, including:

The fault scanning module is used to scan the three-phase fault of the near-area AC system at the flexible-DC converter station in the hybrid cascade DC system, and obtain the recovery voltage for more than several milliseconds. The energy dissipation device is used during the recovery process of the three-phase fault of the near-area AC system. AC low voltage amplitude and low voltage duration under sustained low voltage conditions where maximum energy absorption occurs.

The three-phase fault detection module of the near-area AC system is used to calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage on the grid side of the flexible-DC converter transformer of the flexible-DC converter station in the hybrid cascade DC system. value and detect three-phase faults in the near-area AC system of flexible-to-DC converter transformers.

The AC fault recovery module is used to shift the phase of the sending end of the hybrid cascade DC system and maintain the set phase shift time before releasing the phase shift and entering the AC fault after detecting a three-phase fault of the near-area AC system in the flex-DC converter transformer. recovery process.

The power limit recovery module is used during the AC fault recovery process. According to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascade DC system, the sending end of the hybrid cascade DC system adopts square wave power limiting mode or The slope-type power limiting mode ensures stable frequency, stable voltage and stable power angle at the sending and receiving ends of the hybrid cascade DC system.

The system provided by this embodiment is used to execute each of the above method embodiments. Please refer to the above embodiments for specific processes and details, which will not be described again here.

Example 3

This embodiment provides a processing device corresponding to the continuous low-voltage three-phase fault ride-through method of the hybrid cascade DC system provided in Embodiment 1. The processing device can be suitable for client processing devices, such as mobile phones, laptops, and tablets. Computer, desktop computer, etc., to perform the method of Embodiment 1.

The processing device includes a processor, a memory, a communication interface, and a bus. The processor, the memory, and the communication interface are connected through the bus to complete communication with each other. The memory stores a computer program that can be run on the processing device. When the processing device runs the computer program, it executes the three-phase fault ride-through method for hybrid cascaded DC system with continuous low voltage provided in Embodiment 1.

In some implementations, the memory may be high-speed random access memory (RAM: Random Access Memory), and may also include non-volatile memory (non-volatile memory), such as at least one disk memory.

In other implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP), and other types of general-purpose processors, which are not limited here.

In addition, the above-mentioned logical instructions in the memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention essentially or the part that contributes to the existing technology or the part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including Several instructions are used to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage media include: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk and other media that can store program code. .

Those skilled in the art can understand that the structure of the above computing device is only a part of the structure related to the solution of the present application, and does not constitute a limitation on the computing device to which the solution of the present application is applied. The specific computing device may include more or Have fewer parts, or combine certain parts, or have different parts arrangements.

Example 4

This embodiment provides a computer program product corresponding to the continuous low-voltage three-phase fault ride-through method for hybrid cascaded DC systems provided in Embodiment 1. The computer program product may include a computer-readable storage medium on which is uploaded a program for executing Computer-readable program instructions for the hybrid cascaded DC system's continuous low-voltage three-phase fault ride-through method described in Embodiment 1.

Computer-readable storage media may be tangible devices that retain and store instructions for use by an instruction execution device. The computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the above.

The implementation principles and technical effects of the computer-readable storage medium provided by the above embodiments are similar to those of the above method embodiments, and will not be described again here.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each process and/or block in the flowchart illustrations and/or block diagrams, and combinations of processes and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions executed by the processor of the computer or other programmable data processing device produce a use A device for realizing the functions specified in a process or processes in a flowchart and/or a block or blocks in a block diagram.

These computer program instructions may also be stored in a computer-readable memory that causes a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction means, the instructions The device implements the functions specified in a process or processes in the flowchart and/or in a block or blocks in the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device, causing a series of operating steps to be performed on the computer or other programmable device to produce computer-implemented processing, thereby executing on the computer or other programmable device. Instructions provide steps for implementing the functions specified in a process or processes of a flowchart diagram and/or a block or blocks of a block diagram.

The above-mentioned embodiments are only used to illustrate the present invention. The structure, connection method and manufacturing process of each component can be changed. Any equivalent transformations and improvements based on the technical solution of the present invention should not be changed. excluded from the protection scope of the present invention.

Claims (10)

1. A three-phase fault ride-through method for sustained low voltage in hybrid cascaded DC systems, which is characterized by: According to the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer in the hybrid cascaded DC system, calculate the AC voltage amplitude at the receiving end of the hybrid cascaded DC system and detect the near-area AC of the flexible-to-DC converter transformer. System three-phase fault; When a three-phase fault in the near-area AC system of the flex-DC converter transformer is detected, the sending end of the hybrid cascade DC system shifts the phase and maintains the set phase shift time, then releases the phase shift and enters the AC fault recovery process; During the AC fault recovery process, according to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascaded DC system, the sending end of the hybrid cascaded DC system adopts the square wave power limiting mode or the slope power limiting mode to ensure The frequency, voltage and power angle of the sending and receiving ends of the hybrid cascade DC system are stable. 2. A three-phase fault ride-through method for sustained low voltage in a hybrid cascade DC system as claimed in claim 1, characterized in that the flexible-DC converter transformer of the flexible-DC converter station in the hybrid cascade DC system The three-phase AC voltage on the grid side, calculates the AC voltage amplitude at the receiving end of the hybrid cascade DC system, and detects the three-phase faults of the near-area AC system of the flexible DC converter transformer, including: Real-time collection of the three-phase AC voltage on the grid side of the flexible-to-DC converter transformer in the hybrid cascaded DC system; Calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer; Based on the three-phase AC voltage collected in real time on the grid side of the flex-to-dc converter transformer, the three-phase fault of the near-area AC system of the flex-to-dc converter transformer is detected. 3. A three-phase fault ride-through method for hybrid cascaded DC system with continuous low voltage as claimed in claim 2, characterized in that the calculation is based on the three-phase AC voltage collected in real time on the grid side of the flexible DC converter transformer. The AC voltage amplitude at the receiving end of the hybrid cascade DC system includes: Perform CLARK transformation on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer to obtain the two-phase components. and/> , then the AC voltage amplitude/> for: . 4. A three-phase fault ride-through method for continuous low voltage in a hybrid cascaded DC system as claimed in claim 2, characterized in that, based on the three-phase AC voltage collected in real time on the grid side of the flexible DC converter transformer, the detection Three-phase faults in the near-area AC system of flexible DC converter transformers include: Perform positive and negative sequence PARK transformation on the three-phase AC voltage collected in real time on the grid side of the flex-DC converter transformer to obtain the dq positive sequence voltage component. ,/> and dq negative sequence voltage component/> ,/> ; According to the dq positive sequence voltage component ,/> and dq negative sequence voltage component/> ,/> , respectively calculate the positive sequence voltage component amplitude/> and negative sequence voltage component amplitude/> : ; when satisfied and/> When , it is determined that the flex-DC converter transformer has a three-phase fault in the near-area AC system, where, /> is the positive sequence voltage component amplitude judgment threshold,/> It is the negative sequence voltage component amplitude judgment threshold. 5. A three-phase fault ride-through method for sustained low voltage in a hybrid cascade DC system as claimed in claim 1, characterized in that, during the AC fault recovery process, according to the sustained low voltage at the receiving end of the hybrid cascade DC system voltage status and AC voltage amplitude, the sending end of the hybrid cascaded DC system adopts the square wave power limiting mode or the slope power limiting mode to ensure the frequency stability, voltage stability and power of the sending and receiving ends of the hybrid cascaded DC system. Angular stabilization, including: During the AC fault recovery process, according to the continuous low voltage state of the receiving end of the hybrid cascaded DC system, the sending end of the hybrid cascaded DC system enters the power limit recovery mode, including square wave power limit mode and slope power limit mode; The transmitting end of the hybrid cascaded DC system preferentially adopts the square wave power limiting mode. Based on the AC voltage amplitude at the receiving end of the hybrid cascaded DC system, this mode is used to detect when a three-phase fault of the near-area AC system occurs in the hybrid cascaded DC system. Electromechanical-electromagnetic transient joint simulation to determine whether the square wave power limitation mode can ensure the frequency stability, voltage stability and power angle stability of the sending and receiving end AC systems; When the square wave power limiting mode cannot ensure the stability of the sending and receiving end AC systems, the slope power limiting mode is adopted based on the AC voltage amplitude of the receiving end of the hybrid cascade DC system to ensure the frequency stability of the sending and receiving ends. Voltage stability and power angle stability. 6. A three-phase fault ride-through method for sustained low voltage in a hybrid cascade DC system as claimed in claim 5, characterized in that the square wave power limiting mode is: shifting at the sending end of the hybrid cascade DC system. When the power is restored after the phase, set the maximum restored power limit value , limiting the maximum recovery power of the sending end of the hybrid cascade DC system to/> and maintain time/> Afterwards, it returns to the pre-fault level; The slope-type power limiting mode is: the AC voltage amplitude at the receiving end of the hybrid cascade DC system is Communicates to the sending end in real time, and the sending end performs low-voltage current limiting for the station based on the AC bus voltage of the receiving end, and sets the low-voltage current limiting curve of the hybrid cascade DC system/> , where,/> is the rated power of the hybrid cascade DC system under the current operating mode,/> is the margin coefficient. 7. A three-phase fault ride-through method for sustained low voltage in a hybrid cascaded DC system as claimed in claim 1, characterized in that the method further includes: Scan the three-phase fault of the near-area AC system of the flexible-DC converter station in the hybrid cascade DC system to obtain the sustained low voltage that maximizes the energy absorption of the energy dissipation device during the recovery process of the three-phase fault of the near-area AC system for more than several milliseconds. AC low voltage amplitude and low voltage duration under voltage operating conditions. The obtained AC low voltage amplitude and low voltage duration are used to determine the maximum recovery power limit value and maintenance time in the square wave power limit mode. 8. A three-phase fault ride-through method for sustained low voltage in hybrid cascaded DC systems, which is characterized by: The three-phase fault detection module of the near-area AC system is used to calculate the AC voltage amplitude at the receiving end of the hybrid cascade DC system based on the three-phase AC voltage on the grid side of the flexible-DC converter transformer of the flexible-DC converter station in the hybrid cascade DC system. value and detect the three-phase fault of the near-area AC system of the flexible DC converter transformer; The AC fault recovery module is used to shift the phase of the sending end of the hybrid cascade DC system and maintain the set phase shift time before releasing the phase shift and entering the AC fault after detecting a three-phase fault of the near-area AC system in the flex-DC converter transformer. recovery process; The power limit recovery module is used during the AC fault recovery process. According to the continuous low voltage state and AC voltage amplitude of the receiving end of the hybrid cascade DC system, the sending end of the hybrid cascade DC system adopts square wave power limiting mode or The slope-type power limiting mode ensures stable frequency, stable voltage and stable power angle at the sending and receiving ends of the hybrid cascade DC system. 9. A processing device, characterized by comprising computer program instructions, wherein the computer program instructions, when executed by the processing device, are used to implement the hybrid cascaded DC system according to any one of claims 1-7 with continuous low Corresponding steps for the three-phase fault ride-through method of voltage. 10. A computer-readable storage medium, characterized in that computer program instructions are stored on the computer-readable storage medium, wherein the computer program instructions are used to implement any of claims 1-7 when executed by a processor. Steps corresponding to the three-phase fault ride-through method for sustained low voltage in hybrid cascaded DC systems described in one item.