SCR-IGCT type current converter and direct current transmission commutation failure suppression method

Abstract

The invention discloses an SCR-IGCT type current converter, each bridge arm on the current converter comprises a thyristor and an IGCT, the thyristor and the IGCT are connected in series in a mixed mode, and the proportion of the IGCT is 10%-100%. The invention further discloses a direct-current transmission commutation failure suppression method which is used for the direct-current transmission system adopting the SCR-IGCT type converter. And monitoring the current on the bridge arm of the SCR-IGCT type current converter in the commutation process, and when judging that the valve group which should quit the conduction still works with the current, disconnecting the corresponding bridge arm by utilizing the active turn-off capability of the IGCT on the bridge arm of the SCR-IGCT type current converter. According to the technical scheme, the problem of direct-current commutation failure caused by complex and changeable structures of the direct-current power transmission system is solved, reliable and safe operation of the high-voltage direct-current power transmission system is effectively guaranteed, and wide popularization and application prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage direct current transmission, and in particular relates to a method for suppressing commutation failure of a current-type high-voltage direct current transmission system (LCC-HVDC) based on series voltage injection. Background Art

[0002] High-voltage direct current transmission systems play an important role in solving cross-regional power transmission problems. Since the advent of the world's first direct current transmission project, high-voltage direct current transmission technology has continued to develop, and more than 100 high-voltage direct current transmission projects have been built and put into operation around the world, covering different levels of transmission capacity and direct current voltage distribution. With the advancement of power electronics technology, the converter valves of high-voltage direct current projects have also undergone three generations of evolution, from mercury arc valves to thyristors to turn-off devices.

[0003] Among many types of DC projects, the line commutated converter based high voltage direct current (LCC-HVDC) system based on thyristor technology has been relatively mature after years of actual engineering construction and application. However, the LCC-HVDC transmission system has a series of technical challenges and defects. First, this system has high requirements for the connected AC power grid and is prone to inverter side commutation failure. Secondly, the LCC-HVDC system cannot achieve passive operation, which means that a large amount of reactive power is consumed during operation, which has a certain adverse effect on grid operation and energy efficiency. In particular, DC commutation failure will cause power shortages, reduced voltage stability, and chain commutation failures at the receiving end of the grid, which seriously affects the operation analysis method and corresponding regulation method of modern power systems. At present, there are roughly two methods to suppress DC commutation failure. One is to optimize the control method of the traditional LCC type high voltage direct current transmission system, and the other is to upgrade and transform the existing converter. However, the complete transformation of the converter equipment of the existing converter station faces typical problems such as high cost, long transformation cycle time, and waste of existing devices.

[0004] In summary, due to the complex and changeable structure of the AC system at the receiving end of the DC transmission system, the problem of DC commutation failure will always exist. Therefore, how to balance the economy and efficiency in the process of converter station transformation is one of the current difficulties. Summary of the invention

[0005] The purpose of the present invention is to provide a SCR-IGCT type converter and a method for suppressing DC power transmission commutation failure, which overcomes the problem of DC commutation failure caused by the complex and changeable structure of the DC power transmission system, effectively ensures the reliable and safe operation of the high-voltage DC power transmission system, and has broad promotion and application prospects.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A SCR-IGCT type converter, wherein each bridge arm of the converter comprises a thyristor and an IGCT connected in mixed series, and the proportion of the IGCT is 10% to 100%.

[0008] The above-mentioned thyristor is formed by connecting a balancing resistor and a dynamic buffer in parallel, and the IGCT is formed by connecting a balancing resistor, a dynamic buffer and a discrete lightning arrester in parallel.

[0009] A method for suppressing commutation failure in direct current transmission, for use in a direct current transmission system using the SCR-IGCT type converter as described above;

[0010] The current on the bridge arm of the SCR-IGCT converter is monitored during the commutation process. When it is determined that the valve group that should have been turned off still has current working, the active shutdown capability of the IGCT on the bridge arm of the SCR-IGCT converter is used to disconnect the corresponding bridge arm.

[0011] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor; when the processor executes the computer program, the steps of the method for suppressing commutation failure of direct current transmission as described above are implemented.

[0012] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, the steps of the method for suppressing direct current transmission commutation failure as described above are implemented.

[0013] After adopting the above scheme, the beneficial effects of the present invention are as follows: the present invention is based on the analysis of the operating characteristics of the SCR-IGCT type converter. When a fault occurs in the AC system to which the high-voltage direct current transmission system is connected, resulting in insufficient commutation margin, the IGCT can use its ability to actively shut down under large currents to complete forced commutation, thereby avoiding the occurrence of DC commutation failure; during steady-state operation, the SCR-IGCT converter operates in the same manner as the traditional LCC type high-voltage direct current transmission system, and the existing control system can be retained, saving corresponding research and development investment; the topological structure of the thyristor series IGCT is modified and upgraded, and some thyristor devices in the operating converter can be retained, which has higher economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the present invention;

[0015] Figure 2 It is a topological structure diagram of the SCR-IGCT type converter provided by the present invention;

[0016] Figure 3It is a schematic diagram of the forced phase shift process of the SCR-IGCT system;

[0017] Figure 4 This is the main wiring diagram of unit I of a converter station;

[0018] Figure 5 It is a schematic diagram of commutation failure suppression simulation results. DETAILED DESCRIPTION

[0019] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0020] In the work, the present invention analyzes the commutation failure mechanism and influencing factors of the traditional line commutated converter based high voltage direct current (LCC) type high voltage direct current transmission system, explains the working characteristics of high power IGCT, and derives the expressions of IGCT tolerance and shutdown capability; proposes a new converter structure of thyristor series IGCT, and analyzes the steady-state working principle of the structure and the fault ride-through characteristics during commutation failure.

[0021] The present invention provides a method for suppressing commutation failure of direct current transmission based on SCR-IGCT type converter, which overcomes the problem of direct current commutation failure caused by the structural complexity and variability faced by the high voltage direct current transmission system, thereby ensuring that the system can operate stably and reliably. Figure 1 As shown, the following steps are included:

[0022] S1. Based on the working principle of conventional LCC type DC transmission system and the working characteristics of core components, the process of DC commutation failure and its influencing factors are analyzed, including the following steps:

[0023] After applying a forward voltage and giving a certain gate current trigger signal, the thyristor will be turned on, losing its forward blocking ability, and the current flowing through it will increase rapidly. H To maintain the current, U B0 is the forward critical transition voltage, i.e., the gate current I g When the gate current I g If the value is large, the corresponding forward transition voltage will be reduced, and the thyristor can also be forward-conducted.

[0024] To restore the blocking capability of the thyristor, a reverse voltage needs to be applied to the thyristor so that the current flowing through it is lower than the holding current I H, and withstand reverse voltage for a period of time. It should be noted that once the reverse voltage is too large and exceeds its reverse breakdown voltage threshold U R0 , the leakage current on the thyristor increases sharply, and it faces a serious risk of permanent damage due to device overheating.

[0025] Most commutation failures occur on the inverter side. During the rectification process, the forward voltage that the conduction valve bears is relatively long, so commutation failure due to short triggering time is less likely to occur. However, during the inverter process, the lead trigger angle is closer to the natural commutation point. Once the trigger lead angle is small, commutation failure will occur.

[0026] The fundamental reason for the commutation failure is that the arc extinction angle γ of the exit valve is less than its limit arc extinction angle γ min , the valve that should have exited conduction did not exit in time and turned on again under the action of the forward voltage. Therefore, the types of factors affecting commutation failure can be analyzed based on the mathematical expression of the arc extinction angle (SVC Optimization Design under Ground Fault and Its Control Strategy for Subsequent Commutation Failure, Automation of Electric Power Systems, Vol.43No.20,2019)

[24] .

[0027] The expression of the arc extinction angle γ is:

[0028]

[0029] Where γ is the arc extinction angle of the inverter side converter station, U L is the effective value of the voltage on the commutation bus, X C is the commutation reactance, I d is the DC current, β is the leading trigger angle, is the zero-crossing offset angle of the commutation voltage.

[0030] Due to the commutation reactance X C , leading trigger angle β and commutation voltage zero-crossing offset angle The arc extinction angle γ is relatively fixed and is generally affected by the inverter side AC system voltage U L and the DC current I of the DC transmission system d During the fault at the receiving end, the AC voltage recovery process is prone to improper reactive interaction with the DC transmission system, resulting in continuous commutation failure. In severe cases, it will cause the converter station to lock, resulting in a large-scale power shortage in the AC system.

[0031] The commutation failure of the thyristor-based converter is determined by its own working characteristics. It is impossible to completely suppress the DC commutation failure, especially the first commutation failure, from the perspective of control strategy. Therefore, only from the perspective of device upgrade, by transforming the type of converter valve in the converter station, can the occurrence of DC commutation failure be completely avoided, and the efficient and stable operation of the DC transmission system be achieved.

[0032] S2. Combining the working principle of IGCT and the important indicators in the process of suppressing commutation failure, the expressions of IGCT tolerance and shutdown capability are derived, including:

[0033] IGCT devices used in high-voltage DC transmission systems need to withstand extremely large voltage and current changes during transient operations. Therefore, the du / dt and di / dt tolerance capabilities of IGCTs are one of the important indicators that need to be paid attention to.

[0034] Especially in the process of IGCT active shutdown, when the gate K applies a reverse polarization voltage to the gate (cathode) of the IGCT, the corresponding anode current of the IGCT begins to gradually commutate to the gate K. The speed of current transfer determines the time response of the IGCT entering the shutdown state. Generally, the commutation time is required to be less than 1μs. Therefore, whether the IGCT is successfully shut down needs to satisfy the following formula:

[0035]

[0036] Where I Gmax is the maximum cut-off current, I G is the transfer current of gate K. When dI G The larger the value of / dt is, the stronger the shutdown capability of the IGCT is, and the faster the response speed and action time of the IGCT are during emergency control, thus ensuring efficient operation of the transient process of the control object containing the IGCT.

[0037] S3. Taking advantage of the IGCT's ability to shut down autonomously, a new type of SCR-IGCT topology structure is designed, which is formed by mixing thyristors and IGCTs in series in corresponding proportions (IGCT accounts for 10% to 100%), including:

[0038] The present invention combines the advantages of IGCT's autonomous shutdown and designs a novel SCR-IGCT topology structure formed by mixing thyristors and IGCTs in a corresponding proportion in series, wherein the thyristor device is internally formed by a balancing resistor and a dynamic buffer connected in parallel, and the IGCT device is internally formed by a balancing resistor, a dynamic buffer and a discrete lightning arrester connected in parallel. The corresponding internal topology is as follows: Figure 2As shown, six bridge arms V1 to V6 are symmetrical in pairs, each bridge arm is composed of m IGCTs and n thyristors connected in series, and satisfies m / (m+n)=10% to 100%, wherein the IGCTs and thyristors can be arranged sequentially or at intervals, without being limited by the diagram.

[0039] The topology of the new SCR-IGCT has the following three typical features:

[0040] (1) Because the basic structure and design of IGCT are similar to those of thyristor, the device has the same response speed and operating characteristics as thyristor. Therefore, it can be completely equivalent to thyristor when the system is in steady-state operation. That is, the bridge arm combination system of SCR-IGCT is consistent with the operation mode of traditional LCC type HVDC transmission system, and the mature and widely used steady-state control link of LCC type HVDC transmission system can be retained.

[0041] (2) Based on the analysis in Section 2, it can be seen that IGCT can actively control the opening or closing of IGCT by controlling whether the gate current is injected. For the common problem of loss of commutation synchronization in LCC type high-voltage DC transmission systems, the IGCT is actively shut down to force the valve group to commutate, thereby avoiding the occurrence of commutation failure.

[0042] (3) The proposed topology is convenient for the transformation of existing converter stations. At present, the core components of the mainstream converters in DC transmission projects are series-connected thyristors. If flexible DC transformation is to be carried out, all converters must be replaced. However, the SCR-IGCT bridge arm combination system only needs to replace some thyristors in the original bridge arm, and retain some existing thyristors, which is convenient for transformation and also has certain economical efficiency.

[0043] S4. The steady-state working principle of the structure and the fault ride-through characteristics during commutation failure are analyzed to avoid the occurrence of DC commutation failure, including:

[0044] During steady-state operation, the inverter side of the conventional LCC type HVDC transmission system adopts fixed arc extinction angle control. The schematic diagram of the forced phase shift process of the SCR-IGCT system is as follows: Figure 3 When a fault occurs at the receiving end, the commutation voltage support capacity is weak, and the initial commutation time t β and the commutation end time t γ The resulting commutation area is small, and the commutation between valves needs to be achieved by reducing the arc extinction angle γ. However, the reduction in the arc extinction angle means that the reverse voltage time borne by the valve group that has exited conduction is shorter, which may trigger conduction again.

[0045] The SCR-IGCT series topology proposed in the present invention can monitor the abnormal current on the bridge arm during the commutation process based on the current detection device configured on the converter bridge arm. If the valve group that should be turned off still has current working, the active shutdown ability of the IGCT on the SCR-IGCT series bridge arm is used to disconnect the corresponding bridge arm to achieve forced commutation.

[0046] Based on a specific embodiment of the present invention, a back-to-back converter station unit I has a DC voltage of 120kV, a current of 3kA, and an exchange power of 360,000 kilowatts. The main wiring diagram of a back-to-back converter station unit I is as follows: Figure 4 shown.

[0047] The specific fault setting is that the AC system of the inverter side converter station has a bus single-phase temporary grounding fault at 0.4s, the fault duration is 100ms, and the fluctuation form of the AC system bus voltage is as follows: Figure 5 As shown in Figure 2, when a fault occurs in the receiving grid, the DC current rises sharply from 2880A to 2970A, and the maximum power transmitted by the DC system drops to 190MW. The DC current and the DC system transmission power are shown in Figure 2. Figure 5 shown.

[0048] After a fault occurs in the receiving-end AC system, the arc extinction angle on the inverter side drops to 0 instantaneously. At this time, the trigger angle is adjusted in real time. The DC commutation failure only occurs during the transient process of the fault. There is no continuous commutation failure caused by improper reactive interaction with the receiving-end AC system during the DC commutation failure, or the inability of the semi-controlled thyristor device to shut down. This effectively ensures the reliable and safe operation of the high-voltage DC transmission system.

[0049] An embodiment of the present invention further provides another computer device, including a processor and a memory configured to store a computer program that can be run on the processor; wherein, when the processor is configured to run the computer program, the method steps in the aforementioned embodiment are executed.

[0050] In practical applications, the processor includes a field programmable gate array (FPGA), and the processor may be a central processing unit (CPU) or a digital signal processor (DSP). It is understandable that for different devices, the electronic device used to implement the function of the processor may be other, and the embodiment of the present invention does not specifically limit it.

[0051] The above-mentioned memory can be a volatile memory (volatile memory), such as a random access memory (RAM); or a non-volatile memory (non-volatile memory), such as a read-only memory (ROM), a flash memory, a hard disk (HDD) or a solid-state drive (SSD); or a combination of the above-mentioned types of memory, and provide instructions and data to the processor.

[0052] In an exemplary embodiment, an embodiment of the present invention further provides a computer-readable storage medium for storing a computer program.

[0053] Optionally, the computer-readable storage medium can be applied to any one of the methods in the embodiments of the present invention, and the computer program enables the computer to execute the corresponding processes implemented by the processor in each method in the embodiments of the present invention. For the sake of brevity, they are not described here.

[0054] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as: multiple units or components can be combined, or can be integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the components shown or discussed can be through some interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0055] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0056] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0057] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0058] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0059] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0060] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A SCR-IGCT type converter, characterized in that: Each bridge arm of the converter includes a thyristor and an IGCT connected in series, and the proportion of the IGCT is 10% to 100%.

2. The SCR-IGCT converter according to claim 1, characterized in that: The thyristor is formed by connecting a balancing resistor and a dynamic buffer in parallel, and the IGCT is formed by connecting a balancing resistor, a dynamic buffer and a discrete lightning arrester in parallel.

3. A method for suppressing commutation failure in direct current transmission, used in a direct current transmission system using the SCR-IGCT converter according to claim 1; characterized in that: The current on the bridge arm of the SCR-IGCT converter is monitored during the commutation process. When it is determined that the valve group that should have been turned off still has current working, the active shutdown capability of the IGCT on the bridge arm of the SCR-IGCT converter is used to disconnect the corresponding bridge arm.

4. A computer 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 computer program, the steps of the method for suppressing direct current transmission commutation failure as claimed in claim 3 are implemented.

5. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, the steps of the method for suppressing direct current transmission commutation failure as claimed in claim 3 are implemented.

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