Alternating current filter replacement control method for hybrid cascade extra-high voltage direct current system

Abstract

The invention discloses a hybrid cascade extra-high voltage direct current system alternating current filter replacement control method. A power grid commutation current converter and a voltage source current converter of a system converter station are connected to the same alternating current bus; comprising the following steps: when a certain type of AC filter needs to be put into use, judging whether the type of AC filter can be put into use; if the alternating current filter can be switched on, the alternating current filter of the type is switched on, otherwise, a parallel capacitor is switched on, and the harmonic suppression function of the voltage source converter is started until the alternating current filter can be switched on or the alternating current filter of the type needs to be cut off; wherein the reactive capacity of the parallel capacitor is 1-1.2 times of the reactive capacity of the alternating current filter needing to be put into use, and the voltage source converter is used for inhibiting characteristic harmonic waves of the corresponding frequency of the power grid commutation converter. The method can effectively solve the problems that the harmonic distortion rate exceeds the standard, the direct current power drops back or is limited and the like due to the fact that hybrid cascade extra-high voltage direct current cannot be input due to alternating current filter faults, overhaul and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC transmission systems, and particularly relates to a control method for replacing AC filters in a hybrid cascaded UHV DC system. Background Art

[0002] High-voltage DC transmission systems can be divided into two types. One is the conventional DC transmission system (LCC-HVDC) based on thyristor technology, and the other is the flexible DC transmission system (VSC-HVDC) based on fully controlled voltage source converters.

[0003] Among them, the conventional DC transmission system (LCC-HVDC) has the advantages of low cost, low loss, and mature operation technology. Its disadvantages are that commutation failures are likely to occur on the inverter side, it has a strong dependence on the AC system, absorbs a large amount of reactive power, and the converter station occupies a large area. The new generation of flexible DC transmission system has the advantages of being able to achieve decoupled control of active power and reactive power, being able to supply power to passive networks, having a compact structure and a small floor area, and having no commutation failure problem on the inverter side. However, it has defects such as high cost and large loss. In recent years, the hybrid DC transmission technology integrating LCC-HVDC and VSC-HVDC technologies has good engineering application prospects. By adopting a cascaded structure of LCC converters and VSC converters at the receiving end, the commutation failure problem on the inverter side can be alleviated or avoided. By adopting a cascaded structure of LCC converters and VSC converters at the sending end, active support for voltage transients and steady states of extremely weak sending-end systems can be achieved. At the same time, the above solutions can ensure the advantages in terms of project land occupation and cost to a certain extent.

[0004] Since the LCC converter generates characteristic harmonics with specific frequencies on the AC side during operation, in order to prevent the harmonics from affecting the power grid, several passive AC filters are equipped in the converter station to suppress the harmonics. When the DC system is operating normally, if some types of AC filters cannot be put into operation due to faults, maintenance, etc., it may lead to problems such as excessive harmonic distortion rate on the AC side, and it may also lead to problems such as power reduction or power limitation of the DC system. Summary of the Invention

[0005] The purpose of the present invention is to provide a control method for replacing AC filters in a hybrid cascaded UHV DC system, which can effectively solve problems such as excessive harmonic distortion rate, DC power reduction or limitation caused by the inability to put into operation of AC filters in the hybrid cascaded UHV DC due to faults, maintenance, etc.

[0006] To achieve the above object, the solution of the present invention is:

[0007] A control method for replacing AC filters in a hybrid cascaded UHVDC system. In the converter station of the hybrid cascaded UHVDC system, the line-commutated converter and the voltage-source converter are connected in series, and the line-commutated converter and the voltage-source converter are connected to the same AC bus. The method includes:

[0008] When a certain type of AC filter needs to be put into operation, determine whether this type of AC filter can be put into operation.

[0009] If this type of AC filter can be put into operation, put it into operation; otherwise, put into operation the shunt capacitor and start the harmonic suppression function of the voltage-source converter until this type of AC filter can be put into operation or this type of AC filter needs to be removed. Wherein, the reactive power capacity of the shunt capacitor is 1 - 1.2 times the reactive power capacity of the AC filter to be put into operation, and the voltage-source converter is used to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0010] Among them, when a certain type of AC filter needs to be put into operation, it includes:

[0011] Obtain the harmonic data on the AC side of the hybrid cascaded UHVDC system.

[0012] If it is determined that the harmonic data meets the input condition, it is considered that the corresponding type of AC filter needs to be put into operation. Wherein, the harmonic data meets the input condition, including that the harmonic current of the AC filter is overloaded, or the total harmonic distortion rate of the AC side voltage of the DC system exceeds 1.75%.

[0013] Among them, starting the harmonic suppression function of the voltage-source converter includes:

[0014] If the voltage-source converter only includes one converter, start the harmonic suppression function of this converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0015] If the voltage-source converter includes multiple converters, start the harmonic suppression function of one or more converters to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0016] Among them, the voltage-source converter is used to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter, including:

[0017] Obtain the three-phase AC voltage of the AC bus of the hybrid cascaded UHVDC system or the three-phase AC current flowing into the DC system.

[0018] Extract the harmonic voltage or current of the corresponding frequency of the AC filter to be put into operation from the three-phase AC voltage or the three-phase AC current.

[0019] Control the voltage-source converter to generate a harmonic voltage or current that cancels it out.

[0020] Among them, the voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, a modular multi-level converter, or a combination of at least two of them.

[0021] A control device for replacing AC filters in a hybrid cascaded UHV DC system. The converter station of the hybrid cascaded UHV DC system adopts a series connection mode of a line-commutated converter and a voltage source converter, and the line-commutated converter and the voltage source converter are connected to the same AC bus; the device includes,

[0022] A harmonic suppression control module configured to determine whether to switch on the AC filter;

[0023] An AC filter switching-on control module configured to, when it is necessary to switch on a certain type of AC filter, determine whether the certain type of AC filter can be switched on, and control to switch on the certain type of AC filter when it can be switched on;

[0024] A shunt capacitor switching-on control module configured to, when it is necessary to switch on a certain type of AC filter and the certain type of AC filter cannot be switched on, control to switch on shunt capacitors with a reactive power capacity 1 - 1.2 times that of the AC filter to be switched on, and control to switch off the shunt capacitors when the AC filter to be switched on can be switched on or needs to be switched off; and,

[0025] A voltage source converter function control module configured to, when it is necessary to switch on a certain type of AC filter and the certain type of AC filter cannot be switched on, start the harmonic suppression function of the voltage source converter to suppress the characteristic harmonics of the corresponding frequencies of the line-commutated converter, and withdraw the harmonic suppression function of the voltage source converter when the AC filter to be switched on can be switched on or needs to be switched off.

[0026] Among them, the harmonic suppression control module determines that it is necessary to switch on the AC filter, including,

[0027] Obtaining the harmonic data on the AC side of the hybrid cascaded UHV DC system;

[0028] If it is determined that the harmonic data meets the switching-on conditions, it is considered that it is necessary to switch on the corresponding type of AC filter; among them, the harmonic data meets the switching-on conditions, including that the harmonic current of the AC filter is overloaded, or the total harmonic distortion rate of the voltage on the AC side of the DC system exceeds 1.75%.

[0029] Among them, the voltage source converter function control module starts the harmonic suppression function of the voltage source converter, including,

[0030] If the voltage source converter only includes one converter, start the harmonic suppression function of the converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter in the power grid;

[0031] If the voltage source converter includes multiple converters, start the harmonic suppression function of one or more converters to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter in the power grid.

[0032] Among them, the function control module of the voltage source converter starts the harmonic suppression function of the voltage source converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter in the power grid, including,

[0033] Obtain the three-phase AC voltage of the AC bus of the hybrid cascaded UHVDC system or the three-phase AC current flowing into the DC system;

[0034] Extract the harmonic voltage or current of the corresponding frequency of the AC filter to be put into operation from the three-phase AC voltage or three-phase AC current;

[0035] Control the voltage source converter to generate a harmonic voltage or current that cancels it out.

[0036] Among them, the voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, and a modular multilevel converter, or a combination of at least two of them.

[0037] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor; when the processor executes the computer program, it implements the steps of the AC filter replacement control method for the hybrid cascaded UHVDC system as described above.

[0038] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, it implements the steps of the AC filter replacement control method for the hybrid cascaded UHVDC system as described above.

[0039] After adopting the above solution, the present invention adopts the method of connecting the line-commutated converter and the voltage source converter in series. When a certain type of AC filter in the converter station is unavailable, it may lead to the filtering performance of the converter station not meeting the requirements, and even lead to power reduction and power loss. By putting into parallel capacitors with the same or similar reactive power capacity and allowing the voltage source converter to suppress the characteristic harmonics of the corresponding frequency of the AC filter to be put into operation, the replacement of the unavailable AC filter is realized. The present invention does not need to modify the current hardware configuration of the converter station, has a low implementation difficulty, can effectively avoid the problems of filtering performance degradation and power reduction caused by the unavailability of the AC filter in the DC system, and ensure the safe and stable operation level of the converter station. Description of the Drawings

[0040] Figure 1 It is a schematic diagram of the topology of a single converter station of a hybrid cascaded UHVDC system targeted by the present invention;

[0041] Figure 2 It is a schematic diagram of the topology of another single converter station of a hybrid cascaded UHVDC system targeted by the present invention;

[0042] Figure 3 It is a schematic diagram of the configuration of an AC filter field in an embodiment of the present invention;

[0043] Figure 4 It is a schematic diagram of the principle of harmonic current extraction and suppression control of a hybrid cascaded UHVDC system provided by the present invention;

[0044] Figure 5 It is a flowchart of a method for replacing an AC filter in a hybrid cascaded UHVDC system provided by the present invention;

[0045] Figure 6 It is the AC side current and voltage waveforms of the DC system before replacing the AC filter in an embodiment of the present invention;

[0046] Among them, (a) is the voltage waveform diagram, and (b) is the current waveform diagram;

[0047] Figure 7 It is the AC side current and voltage waveforms of the DC system after replacing the AC filter in an embodiment of the present invention;

[0048] Among them, (a) is the voltage waveform diagram, and (b) is the current waveform diagram. Detailed implementation manner

[0049] The present invention provides a control method for replacing an AC filter in a hybrid cascaded UHVDC system. The converter station of the hybrid cascaded UHVDC system adopts a series connection mode of a line-commutated converter and a voltage-source converter, and the line-commutated converter and the voltage-source converter are connected to the same AC bus. The method includes,

[0050] When a certain type of AC filter needs to be put into operation, it is judged whether the certain type of AC filter can be put into operation;

[0051] If the certain type of AC filter can be put into operation, the certain type of AC filter is put into operation. Otherwise, a shunt capacitor is put into operation, and the harmonic suppression function of the voltage-source converter is started until the certain type of AC filter can be put into operation, or the certain type of AC filter needs to be removed. Among them, the reactive power capacity of the shunt capacitor is 1 - 1.2 times the reactive power capacity of the AC filter to be put into operation, and the voltage-source converter is used to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0052] Among them, a certain type of AC filter needs to be invested, including,

[0053] Obtain the harmonic data on the AC side of the hybrid cascaded UHVDC system;

[0054] If it is determined that the harmonic data meets the investment conditions, it is considered that the corresponding type of AC filter needs to be invested; among them, the harmonic data meeting the investment conditions includes that the harmonic current of the AC filter is overloaded, or the total harmonic distortion rate of the AC side voltage of the DC system exceeds 1.75%.

[0055] Among them, starting the harmonic suppression function of the voltage source converter includes,

[0056] If the voltage source converter only includes one converter, start the harmonic suppression function of this converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter;

[0057] If the voltage source converter includes multiple converters, start the harmonic suppression function of one or more converters to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0058] Among them, the voltage source converter is used to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter, including,

[0059] Obtain the three-phase AC voltage of the AC bus of the hybrid cascaded UHVDC system or the three-phase AC current flowing into the DC system;

[0060] Extract the harmonic voltage or current of the corresponding frequency of the AC filter to be invested from the three-phase AC voltage or three-phase AC current;

[0061] Control the voltage source converter to generate a harmonic voltage or current that cancels it out.

[0062] Among them, the voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, a modular multilevel converter, or a combination of at least two of them.

[0063] The present invention also provides a control device for replacing the AC filter of a hybrid cascaded UHVDC system. The converter station of the hybrid cascaded UHVDC system adopts a series connection method of a line-commutated converter and a voltage source converter, and the line-commutated converter and the voltage source converter are connected to the same AC bus; the device includes,

[0064] A harmonic suppression control module configured to determine whether an AC filter needs to be invested;

[0065] An AC filter investment control module configured to determine whether a certain type of AC filter can be invested when a certain type of AC filter needs to be invested, and control the investment of this type of AC filter when it can be invested;

[0066] The shunt capacitor input control module is configured to, when it is necessary to input a certain type of AC filter and the said type of AC filter cannot be input, control the input of shunt capacitors with a reactive power capacity 1 - 1.2 times that of the AC filter to be input, and control the cut-off of the shunt capacitors when the AC filter to be input can be input or needs to be cut off; and,

[0067] The voltage source converter function control module is configured to, when it is necessary to input a certain type of AC filter and the said type of AC filter cannot be input, start the harmonic suppression function of the voltage source converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter, and withdraw the harmonic suppression function of the voltage source converter when the AC filter to be input can be input or needs to be cut off.

[0068] Among them, the harmonic suppression control module determines that an AC filter needs to be input, including,

[0069] Obtaining the harmonic data on the AC side of the hybrid cascaded UHVDC system;

[0070] If it is determined that the harmonic data meets the input conditions, it is considered that the corresponding type of AC filter needs to be input; among them, the harmonic data meeting the input conditions includes that the harmonic current of the AC filter is overloaded, or the total harmonic distortion rate of the AC side voltage of the DC system exceeds 1.75%.

[0071] Among them, the voltage source converter function control module starts the harmonic suppression function of the voltage source converter, including,

[0072] If the voltage source converter only includes one converter, start the harmonic suppression function of this converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter;

[0073] If the voltage source converter includes multiple converters, start the harmonic suppression function of one or more converters to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter.

[0074] Among them, the voltage source converter function control module starts the harmonic suppression function of the voltage source converter to suppress the characteristic harmonics of the corresponding frequency of the line-commutated converter, including,

[0075] Obtaining the three-phase AC voltage of the AC bus of the hybrid cascaded UHVDC system or the three-phase AC current flowing into the DC system;

[0076] Extracting the harmonic voltage or current of the corresponding frequency of the AC filter to be input from the said three-phase AC voltage or three-phase AC current;

[0077] Controlling the voltage source converter to generate a harmonic voltage or current that cancels it out.

[0078] Among them, the voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, and a modular multi-level converter, or a combination of at least two of them.

[0079] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0080] As Figure 1 A schematic diagram of the topology of a single converter station of a hybrid cascaded UHV DC system, in which the positive and negative poles of the DC side of the converter station are both composed of a line-commutated converter 1 and a voltage source converter 2 connected in series. The line-commutated converter 1 is the high-end converter, and the voltage source converter 2 is the low-end converter. The AC sides of the converters are connected to the AC bus 4, the AC filter field 3 is connected to the AC bus 4, and the AC bus 4 is connected to the power grid.

[0081] As Figure 2 Another schematic diagram of the topology of a single converter station of a hybrid cascaded UHV DC system, in which the positive and negative poles of the DC side of the converter station are both composed of a line-commutated converter 1 and a voltage source converter group 5 connected in series. The voltage source converter group 5 is composed of several voltage source converters connected in parallel. The line-commutated converter 1 is the high-end converter, and the voltage source converter group 5 is the low-end converter. The AC sides of the converters are connected to the AC bus 4, the AC filter field 3 is connected to the AC bus 4, and the AC bus 4 is connected to the power grid.

[0082] As Figure 3 It is a schematic diagram of the configuration of an AC filter field in an embodiment of the present invention. The AC filter field includes HP12 / 24, HP3, and SC type AC filters or shunt capacitors. The HP12 / 24 AC filter is used to filter out the 11 / 13 / 23 / 25th characteristic harmonics, the HP3 is used to filter out the 3rd harmonic, and the SC is a shunt capacitor. The reactive power capacities of the AC filters and the shunt capacitors are equal. Each AC filter is connected to the large group bus 6 and then to the AC bus 4 of the converter station.

[0083] As Figure 4 It is a schematic diagram of the principle of harmonic current extraction and suppression control of a hybrid cascaded UHV DC system provided by the present invention. By extracting the three-phase AC current IS flowing into the converter station, it is converted into a DC component after synchronous rotating coordinate transformation of the corresponding harmonics, compared with the reference value 0 after passing through a low-pass filter, and the final harmonic suppression voltage reference wave is obtained through closed-loop PI control and superimposed on the original voltage reference wave of the voltage source converter to achieve the suppression of the corresponding frequency harmonics.

[0084] As Figure 5This is a flowchart of the AC filter replacement control method for a hybrid cascaded UHV DC system provided by the present invention. When the DC system determines that a group of AC filters need to be put into operation according to the operating conditions, if there is an available AC filter of this type at this time, a group of AC filters of this type will be put into operation. If there is no available AC filter of this type, a group of shunt capacitors will be put into operation, and the voltage source converter will be used to suppress the corresponding frequency harmonics.

[0085] The following will introduce Embodiment 1, Embodiment 2, and Embodiment 3 in conjunction with Figures 1 to 5 ,.

[0086] Embodiment 1: For the Figure 1 shown topological structure, when the power of the DC system rises to a certain power point, the DC control system requires a group of HP12 / 24 AC filters to be put into operation. However, if all the remaining unoperated HP12 / 24 AC filters cannot be put into operation at this time, a group of shunt capacitors will be put into operation, and the voltage source converter 2 will be used to suppress the 11th / 13th / 23rd / 25th harmonics. After that, if there is an available AC filter among the remaining HP12 / 24 AC filters, this AC filter will be put into operation, the shunt capacitors will be removed, and the harmonic suppression function of the voltage source converter 2 will be exited.

[0087] Embodiment 2: For the Figure 2 shown topological structure, when the power of the DC system rises to a certain power point, the DC control system requires a group of HP12 / 24 AC filters to be put into operation. However, if all the remaining unoperated HP12 / 24 AC filters cannot be put into operation at this time, a group of shunt capacitors will be put into operation, and the voltage source converter group 5 will be used to suppress the 11th / 13th / 23rd / 25th harmonics. If the voltage source converter group 5 consists of two converters in parallel, the first converter can be used to suppress the 11th / 13th harmonics, and the second converter can be used to suppress the 23rd / 25th harmonics. After that, if there is an available AC filter among the remaining HP12 / 24 AC filters, this AC filter will be put into operation, the shunt capacitors will be removed, and the harmonic suppression function of the voltage source converter group 5 will be exited.

[0088] Embodiment 3: Taking the Figure 1 hybrid cascaded UHV DC as an example, the rated power of the DC bipolar is 8000 MW, the rated power of a single pole is 4000 MW, and the DC voltage is ±800 kV. Unlock DC pole 1 and operate at the minimum power of 400 MW. At this time, a group of HP12 / 24 AC filters need to be put into operation. Let all HP12 / 24 AC filters be in the maintenance state and cannot be put into operation. At this time, the harmonic content in the AC system is relatively large, and the waveforms of the grid-side current and grid-side voltage are as shown in Figure 6 . The total harmonic distortion rate of the grid-side current is 6.91%, and the total harmonic distortion rate of the grid-side voltage is 4.34%.

[0089] After a set of shunt capacitors are put into operation and the harmonic suppression function of the voltage source converter is started, the harmonic content in the AC system drops significantly at this time, and the waveforms of the grid-side current and grid-side voltage are as Figure 7 shown. The total harmonic distortion rate of the grid-side current is 1.2%, and the total harmonic distortion rate of the grid-side voltage is 0.5%.

[0090] An embodiment of the present invention also provides another computer device, including a processor and a memory configured to store a computer program that can run on the processor; wherein, when the processor is configured to run the computer program, it executes the method steps in the foregoing embodiments.

[0091] In practical applications, the foregoing processor includes a Field-Programmable Gate Array (FPGA), and the processor can be a Central Processing Unit (CPU) or a Digital Signal Processor (DSP). It can be understood that for different devices, the electronic devices used to implement the functions of the foregoing processor can also be others, and the embodiments of the present invention do not make specific limitations.

[0092] The foregoing memory can be a volatile memory, such as a Random-Access Memory (RAM); or a non-volatile memory, such as a Read-Only Memory (ROM), a flash memory, a Hard Disk Drive (HDD), or a Solid-State Drive (SSD); or a combination of the foregoing types of memories, and provides instructions and data to the processor.

[0093] In an exemplary embodiment, an embodiment of the present invention also provides a computer-readable storage medium for storing a computer program.

[0094] 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 causes the computer to execute the corresponding processes implemented by the processor in each of the methods of the embodiments of the present invention. For the sake of brevity, it will not be elaborated here.

[0095] In 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 merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, 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 with each other can be through some interfaces. The indirect coupling or communication connection of devices or units can be electrical, mechanical, or other forms.

[0096] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can be implemented in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can be implemented in 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 code. The solutions in the embodiments of the present invention can be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0097] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0098] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0099] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operational steps are performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions for implementing the functions specified in one process or multiple processes and / or blocks Figure 1 one process or multiple processes and / or blocks Figure 1 steps for implementing the functions specified in one block or multiple blocks.

[0100] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to cover the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0101] 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 equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A hybrid cascaded UHV DC system AC filter replacement control method, wherein the converter station of the hybrid cascaded UHV DC system adopts a grid-commutated converter and a voltage source converter connected in series, and the grid-commutated converter and the voltage source converter are connected to the same AC bus; characterized in that: include, When a certain type of AC filter needs to be put into use, determine whether this type of AC filter can be put into use; If this type of AC filter can be put into operation, then this type of AC filter is put into operation; otherwise, a parallel capacitor is put into operation, and the harmonic suppression function of the voltage source converter is started until this type of AC filter can be put into operation, or this type of AC filter needs to be removed; wherein the reactive capacity of the parallel capacitor is 1-1.2 times the reactive capacity of the AC filter to be put into operation, and the voltage source converter is used to suppress the characteristic harmonics of the corresponding frequency of the grid commutation converter.

2. The method according to claim 1, characterized in that: Some type of AC filter is required, including: Obtain AC side harmonic data of hybrid cascaded UHV DC system; If it is determined that the harmonic data meets the input conditions, it is considered that the corresponding type of AC filter needs to be put into use; wherein the harmonic data meets the input conditions, including AC filter harmonic current overload, or the total harmonic distortion rate of the AC side voltage of the DC system exceeds 1.75%.

3. The method according to claim 1, characterized in that: Starting the harmonic suppression function of the voltage source converter comprises: If the voltage source converter includes only one converter, the harmonic suppression function of the converter is activated to suppress characteristic harmonics of the corresponding frequency of the grid commutation converter; If the voltage source converter includes multiple converters, the harmonic suppression function of one or more converters is started to suppress characteristic harmonics of corresponding frequencies of the grid commutation converter.

4. The method according to claim 1, characterized in that: The voltage source converter is used to suppress the characteristic harmonics of the corresponding frequency of the grid commutation converter, including: Obtaining the three-phase AC voltage of the AC busbar of the hybrid cascaded UHV DC system or the three-phase AC current flowing into the DC system; Extracting harmonic voltage or current of corresponding frequency to be put into AC filter from the three-phase AC voltage or three-phase AC current; The voltage source converter is controlled to generate a harmonic voltage or current that offsets the harmonic voltage or current.

5. The method according to claim 1, characterized in that: The voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, and a modular multi-level converter, or a combination of at least two of them.

6. A hybrid cascaded UHV DC system AC filter replacement control device, wherein the converter station of the hybrid cascaded UHV DC system adopts a grid-commutated converter and a voltage source converter connected in series, and the grid-commutated converter and the voltage source converter are connected to the same AC bus; characterized in that: include, A harmonic suppression control module is configured to determine whether an AC filter needs to be activated; The AC filter input control module is configured to determine whether a certain type of AC filter can be put into use when a certain type of AC filter needs to be put into use, and control the input of the AC filter of this type when it can be put into use; A parallel capacitor input control module is configured to control the input of a parallel capacitor of 1-1.2 times the reactive capacity of the AC filter to be put into operation when a certain type of AC filter needs to be put into operation and the AC filter of the type cannot be put into operation, and control the removal of the parallel capacitor when the AC filter to be put into operation can be put into operation or needs to be removed; as well as, The voltage source converter function control module is configured to start the harmonic suppression function of the voltage source converter when a certain type of AC filter needs to be put into use and this type of AC filter cannot be put into use, so as to suppress the characteristic harmonics of the corresponding frequency of the grid-commutated converter, and to exit the harmonic suppression function of the voltage source converter when the AC filter that needs to be put into use can be put into use or needs to be removed.

7. The device according to claim 6, characterized in that: The harmonic suppression control module determines whether an AC filter needs to be put into operation, including: Obtain AC side harmonic data of hybrid cascaded UHV DC system; If it is determined that the harmonic data meets the input conditions, it is considered that the corresponding type of AC filter needs to be put into use; wherein the harmonic data meets the input conditions, including AC filter harmonic current overload, or the total harmonic distortion rate of the AC side voltage of the DC system exceeds 1.75%.

8. The device according to claim 6, characterized in that: The voltage source converter function control module starts the harmonic suppression function of the voltage source converter, including: If the voltage source converter includes only one converter, the harmonic suppression function of the converter is activated to suppress characteristic harmonics of the corresponding frequency of the grid commutation converter; If the voltage source converter includes multiple converters, the harmonic suppression function of one or more converters is started to suppress characteristic harmonics of corresponding frequencies of the grid commutation converter.

9. The device according to claim 6, characterized in that: The voltage source converter function control module starts the harmonic suppression function of the voltage source converter to suppress the characteristic harmonics of the corresponding frequency of the grid commutation converter, including: Obtaining the three-phase AC voltage of the AC busbar of the hybrid cascaded UHV DC system or the three-phase AC current flowing into the DC system; Extracting harmonic voltage or current of corresponding frequency to be put into AC filter from the three-phase AC voltage or three-phase AC current; The voltage source converter is controlled to generate harmonic voltages or currents that counteract them.

10. The device according to claim 6, characterized in that: The voltage source converter includes at least one converter; the voltage source converter is one of a two-level converter, a three-level converter, and a modular multi-level converter, or a combination of at least two of them.

11. 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 hybrid cascaded ultra-high voltage direct current system AC filter replacement control method according to any one of claims 1 to 5 are implemented.

12. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by a processor, the steps of the hybrid cascaded UHV DC system AC filter replacement control method according to any one of claims 1 to 5 are implemented.

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