A flexible HVDC power transmission control system and method

Abstract

The application discloses a flexible direct current transmission control system and method, which comprises a master control module and at least one slave control module connected with the master control module; the master control module is used for sampling alternating current from an alternating current side connected with the master control module; the master control module comprises a first phase-locked unit, a first voltage control unit and a first current control unit; the slave control module comprises a second phase-locked unit, a second voltage control unit and a second current control unit; the first phase-locked unit is connected with the second phase-locked unit; the first voltage control unit and the first current control unit are connected, the second voltage control unit and the second current control unit are connected, and the first voltage control unit is connected with the second voltage control unit; the slave control module keeps consistent with the master control module in transmission parameters by tracking the first control reference value of the master control module in real time, so that the automatic power balance and system stability of the flexible direct current transmission control system are kept.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, and in particular to a flexible DC transmission control system and method. Background Technology

[0002] Flexible DC transmission refers to high-voltage direct current (HVDC) transmission based on voltage source converters (VSCs). It has outstanding advantages such as flexible operation, strong controllability, good economy and good interconnectivity, and is one of the representative key technologies of smart grids.

[0003] In a flexible DC transmission system, when a grid fault occurs, the flexible DC transmission system can supply power to the passive network as a black start power source without the need for an external power source, quickly restoring control capabilities and enabling the grid to achieve a black start in a short time.

[0004] In black-start mode, flexible DC transmission can only use one side as an AC power source, while the other side still needs to operate in HVDC (High Voltage Direct Current) mode to transmit power. For single-ended flexible DC transmission systems, since only one AC side is connected, black start only requires controlling the AC voltage to the set value. However, with the increase in transmission capacity, most current flexible DC transmission systems are configured with double-ended or multi-ended structures, thus connecting multiple AC sides. If both units control AC voltage, although the total power exchanged with the AC system remains unchanged, the power distribution among units will be uneven or even oscillating, easily leading to instability. If one unit controls AC voltage and the other unit controls active power in HVDC mode, there is a mode switching problem, and the capacity of a single unit is limited and insufficient to maintain the stability of the AC voltage. Furthermore, the external characteristics of the two units are inconsistent during transients. Summary of the Invention

[0005] This invention provides a flexible DC transmission control system and method, which enables the slave control module to track the first control reference value of the master control module in real time, thereby ensuring that the slave control module and the master control module maintain consistent transmission parameters. This allows the flexible DC transmission control system with a dual-terminal or multi-terminal structure to maintain automatic power balance and system stability during the black start of the power grid.

[0006] According to one aspect of the present invention, a flexible DC transmission control system is provided, comprising:

[0007] The system comprises at least two control modules, including a master control module and at least one slave control module connected to the master control module; each control module is connected to a converter on the black-start side of the flexible DC transmission system; characterized in that the master control module includes a first phase-locked loop (PLL) unit, a first voltage control unit, and a first current control unit, and the slave control module includes a second PLL unit, a second voltage control unit, and a second current control unit; the first PLL unit is connected to the second PLL unit; the first voltage control unit is connected to the first current control unit, the second voltage control unit is connected to the second current control unit, and the first voltage control unit is connected to the second voltage control unit.

[0008] The main control module is used to acquire a first AC sampling signal from the AC grid side of the connected first converter; determine a first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal; generate a first modulation signal based on the first control reference value and the first AC sampling signal to control the connected first converter to output a first AC voltage; and send the first control reference value to each of the slave control modules.

[0009] The slave control module is used to acquire a second AC sampling signal from the AC grid side of the connected second converter, and receive the first control reference value sent by the master control module, determine a second control reference value based on the first control reference value, and generate a second modulation signal based on the second control reference value and the second AC sampling signal to control the connected second converter to output a second AC voltage.

[0010] Furthermore, the first control reference value includes: a first phase reference value and a first current reference value; the first phase-locked unit is used to generate the first phase reference value according to a preset frequency and send the first phase reference value to the second phase-locked unit; the first phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system;

[0011] The first voltage control unit is configured to acquire a first AC sampling voltage signal, determine a first current reference value based on the voltage sampling value of the first AC sampling voltage signal and a preset voltage value, and send the first current reference value to the first current control unit and the second voltage control unit.

[0012] The first current control unit is used to acquire a first AC sampling current signal and generate a first modulation signal based on the first current reference value and the first AC sampling current signal.

[0013] Furthermore, the first voltage control unit is specifically used for:

[0014] Determine the difference between the voltage sample value and the preset voltage value of the first AC sampling voltage signal;

[0015] The first current reference value is determined by proportional-integral adjustment of the difference.

[0016] Furthermore, the second control parameter value includes: a second phase reference value and a second current reference value.

[0017] The second phase-locked unit is used to receive the first phase reference value sent by the first phase-locked unit, and determine the second phase reference value according to the first phase reference value and the preset phase compensation value; the second phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system.

[0018] The second voltage control unit is configured to receive the first current reference value sent by the first voltage control unit, determine the second current reference value based on the first current reference value and a preset allocation coefficient, and send the second current reference value to the second current control unit.

[0019] The second current control unit is used to acquire the second AC sampling current signal and generate a second modulation signal based on the second current reference value and the second AC sampling current signal.

[0020] Furthermore, the preset allocation coefficient is determined based on the ratio of the power transmission capacity of the master control module to the power transmission capacity of the slave control module.

[0021] According to another aspect of the present invention, a flexible direct current transmission control method is provided, applied to the main control module in a control system for flexible direct current transmission, the method comprising:

[0022] Acquire the first AC sampling signal;

[0023] The first control reference value for flexible DC transmission is determined based on the parameters of the first AC sampling signal;

[0024] A first modulation signal is generated based on the first control reference value and the first AC sampling signal to control the first converter connected to output a first AC voltage;

[0025] The first control reference value is sent to each slave control module.

[0026] Furthermore, the first AC sampling signal includes: a first AC sampling voltage signal, and the first control reference value includes: a first phase reference value and a first current reference value; determining the first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal includes:

[0027] A first phase reference value is generated based on a preset frequency;

[0028] The first current reference value is determined based on the voltage sampling value of the first AC sampling voltage signal and the preset voltage value.

[0029] Furthermore, determining the first current reference value based on the voltage sample value of the first AC sampling voltage signal and a preset voltage value includes:

[0030] Determine the difference between the voltage sample value and the preset voltage value of the first AC sampling voltage signal;

[0031] The first current reference value is determined by proportional-integral adjustment of the difference.

[0032] According to another aspect of the present invention, a flexible direct current (DC) transmission control method is provided, applied to a slave control module in a control system for flexible DC transmission, the method comprising:

[0033] Acquire the second AC sampling signal and receive the first control reference value sent by the main control module;

[0034] Determine the second control reference value based on the first control reference value;

[0035] A second modulation signal is generated based on the second control reference value and the second AC sampling signal to control the connected second converter to output a second AC voltage.

[0036] Furthermore, the first control reference value includes a first phase reference value and a first current reference value, and the second control parameter value includes a second phase reference value and a second current reference value. Determining the second control reference value based on the first control reference value includes:

[0037] The second phase reference value is determined based on the first phase reference value and the preset phase compensation value;

[0038] The second current reference value is determined based on the first current reference value and the preset allocation coefficient.

[0039] This invention provides a flexible DC transmission control system and method. The system includes at least two control modules, each comprising a master control module and at least one slave control module connected to the master control module. Each control module is connected to a converter on the black-start side of the flexible DC transmission system. The master control module includes a first phase-locked loop (PLL) unit, a first voltage control unit, and a first current control unit; the slave control module includes a second PLL unit, a second voltage control unit, and a second current control unit. The first PLL unit is connected to the second PLL unit; the first voltage control unit and the first current control unit are connected; the second voltage control unit and the second current control unit are connected; and the first voltage control unit is connected to the second voltage control unit. The master control module is used to acquire a first AC sampling signal from the AC grid side of the connected first converter; and to determine a first control reference value for the flexible DC transmission based on the parameters of the first AC sampling signal. The first control reference value includes a first phase reference value and a first current reference value. A first modulation signal is generated based on the first control reference value and the first AC sampling signal to control the first converter connected to the system to output a first AC voltage. The first control reference value is then sent to each slave control module. The slave control module is used to obtain a second AC sampling signal from the AC grid side of the connected second converter and receive the first control reference value sent by the master control module. Based on the first control reference value, it determines a second control reference value, the second control parameter values ​​including a second phase reference value and a second current reference value. Based on the second control reference value and the second AC sampling signal, a second modulation signal is generated to control the second converter connected to the system to output a second AC voltage. By tracking the first control reference value of the master control module in real time, the slave control module maintains consistent transmission parameters with the master control module, thereby maintaining automatic power balance and system stability of the flexible DC transmission control system during the black start process of the power grid.

[0040] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of a flexible DC transmission control system according to Embodiment 1 of the present invention;

[0043] Figure 2This is a flowchart of a flexible DC transmission control method provided in Embodiment 3 of the present invention;

[0044] Figure 3 This is a flowchart of another flexible DC transmission control method provided in Embodiment 4 of the present invention. Detailed Implementation

[0045] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] Example 1

[0048] Figure 1 This is a schematic diagram of a flexible DC transmission control system provided in Embodiment 1 of the present invention. This embodiment is applicable to the control of flexible DC transmission under the black start mode of the power grid. Figure 1As shown, the flexible DC transmission control system 1 includes at least two control modules, each including a master control module 10 and at least one slave control module 20 connected to the master control module; each control module is connected to a converter on the black start side of the flexible DC transmission system; the master control module 10 includes a first phase-locked loop unit 11, a first voltage control unit 12, and a first current control unit 13; the slave control module 20 includes a second phase-locked loop unit 21, a second voltage control unit 22, and a second current control unit 23; the first phase-locked loop unit 11 is connected to the second phase-locked loop unit 21; the first voltage control unit 22 is connected to the second current control unit 23 ... The control unit 12 is connected to the first current control unit 13, the second voltage control unit 22 is connected to the second current control unit 23, and the first voltage control unit 12 is connected to the second voltage control unit 22; the main control module 10 is used to obtain a first AC sampling signal from the AC grid side of the connected first converter 31; determine a first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal; generate a first modulation signal based on the first control reference value and the first AC sampling signal to control the connected first converter 31 to output a first AC voltage; and send the first control reference value to each slave control module;

[0049] The slave control module 20 is used to acquire a second AC sampling signal from the AC grid side of the connected second converter 32, and receive a first control reference value sent by the master control module 10, determine a second control reference value based on the first control reference value, and generate a second modulation signal based on the second control reference value and the second AC sampling signal to control the connected second converter 32 to output a second AC voltage.

[0050] In the event of a grid fault, the flexible DC transmission system transforms from an active network to a passive network, acting as a black-start power source to supply AC power to the passive network. The control module of the flexible DC transmission control system modulates the sampled AC signal and outputs AC voltage to the converter of the flexible DC transmission system.

[0051] Specifically, for a flexible DC transmission control system with a dual-end or multi-end structure, it includes at least two control modules, one of which is a master control module 10, and the other at least one is a slave control module 20. The master control module 10 is connected to at least one slave control module 20, and each control module is connected to each converter on the black start side of the flexible DC transmission system.

[0052] The main control module 10 acquires a first AC sampling signal from the AC grid side of the connected first converter 31, determines a first control reference value for flexible DC transmission based on parameters such as the frequency and voltage of the first AC sampling signal, and modulates the first AC sampling signal according to the first control reference value to control the connected first converter 31 to output a first AC voltage. Simultaneously, the main control module 10 sends the first control reference value to each slave control module 20, so that each slave control module 20 determines a second control reference value based on the first control reference value, modulates the second AC sampling signal acquired from the AC grid side of the connected second converter 32 according to the second control reference value, and controls the connected second converter 32 to output a second AC voltage. This achieves consistent transmission parameters between the slave control modules and the main control module, maintaining automatic power balancing and system stability in the flexible DC transmission control system with a dual-terminal or multi-terminal structure.

[0053] For example, the first control reference value includes a first phase reference value and a first current reference value, and the second control reference value includes a second phase reference value and a second current reference value.

[0054] Based on the above embodiments, the main control module 10 includes: a first phase-locked unit 11, a first voltage control unit 12, and a first current control unit 13; the slave control module 20 includes: a second phase-locked unit 21, a second voltage control unit 22, and a second current control unit 23; the first phase-locked unit 11 is connected to the second phase-locked unit 21; the first voltage control unit 12 is connected to the first current control unit 13, the second voltage control unit 22 is connected to the second current control unit 23, and the first voltage control unit 12 is connected to the second voltage control unit 22.

[0055] The first phase-locked unit 11 generates a first phase reference value according to a preset frequency and sends the first phase reference value to the second phase-locked unit 21; wherein, the first phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system; the first voltage control unit 12 acquires a first AC sampling voltage signal, determines a first current reference value according to the voltage sampling value of the first AC sampling voltage signal and a preset voltage value; and sends the first current reference value to the first current control unit 13 and the second voltage control unit 22; the first current control unit 13 acquires a first AC sampling current signal from the AC grid side of the connected first converter 31, and generates a first modulation signal according to the first current reference value and the first AC sampling current signal.

[0056] The second phase-locked unit 21 receives the first phase reference value sent by the first phase-locked unit 11, and determines the second phase reference value according to the first phase reference value and the preset phase compensation value; the second phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system; the second voltage control unit 22 receives the first current reference value sent by the first voltage control unit 12, determines the second current reference value according to the first current reference value and the preset allocation coefficient, and sends the second current reference value to the second current control unit 23; the second current control unit 23 obtains the second AC sampling current signal from the AC grid of the connected second converter 32, and generates a second modulation signal according to the second current reference value and the second AC sampling current signal.

[0057] For example, the first phase-locked unit 11 determines a first phase reference value of the AC voltage based on a preset frequency. The preset frequency refers to the number of times the AC current changes periodically per unit time; this frequency is a fixed value and is inversely related to the period. The AC frequency varies in different countries' power systems, typically 50 Hz or 60 Hz. A phase-locked unit is a negative feedback control system that uses voltage generated by phase synchronization to tune a voltage-controlled oscillator to generate a target frequency. The first phase-locked unit 11 sends the determined first phase reference value to the second phase-locked unit 21, which determines a second phase reference value based on the first phase reference value and a preset phase compensation value. The preset phase compensation value can be set according to actual needs. The first and second phase reference values ​​provide coordinate transformation references for the AC quantities of the flexible DC transmission control system. For example, if the preset frequency is 50 Hz, the first phase-locked unit 11 determines the first phase reference value of the AC voltage to be 2π. 50Hz If the delay in communication and processing of the inter-unit phase reference signal is Tphase, then the compensated phase angle can be Tphase. 50Hz The second phase reference value determined by the second phase-locked unit 21 can be 2π. 50Hz t+Tphase 50Hz 2π.

[0058] The flexible DC transmission control system provided in this embodiment of the invention includes at least two control modules, each including a master control module and at least one slave control module connected to the master control module. Each control module is connected to a converter on the black start side of the flexible DC transmission system. By having the slave control module track the first control reference value of the master control module in real time, the slave control module and the master control module maintain consistent transmission parameters, thereby maintaining automatic power balance and system stability of the flexible DC transmission control system with a dual-terminal or multi-terminal structure during the black start of the power grid.

[0059] Optionally, the first voltage control unit 12 is specifically used for:

[0060] Determine the difference between the voltage sample value and the preset voltage value of the first AC sampling voltage signal;

[0061] The first current reference value is determined by proportional-integral adjustment of the difference.

[0062] The preset voltage value can be 110KV or other set values. For a bipolar flexible DC transmission control system, the first current reference values ​​output by the first voltage control unit 12 are IDREF and IQREF, respectively. The difference is adjusted proportionally and integrally to determine the first current reference value. Optionally, the preset allocation coefficient is determined based on the ratio of the transmission capacity of the master control module to the transmission capacity of the slave control module.

[0063] For example, if the transmission capacity of the master control module 10 of the flexible DC transmission control system is M and the transmission capacity of the slave control module 20 is N, then the preset allocation coefficient K = N / M is used to allocate the first current reference value of the master control module 10 and the second current reference value of the slave control module 20 in a ratio of M:N. For a bipolar flexible DC transmission control system, the second current reference values ​​output by the second voltage control unit 22 are IDREF. N / M and IQREF N / M. Since the voltage values ​​of the master control module 10 and the slave control module 20 are the same, the AC power of the two control modules will be automatically distributed in real time according to the M:N ratio, resulting in consistent external characteristics and automatic power balancing and system stability of the flexible DC transmission control system.

[0064] Example 2

[0065] Figure 2 This invention provides a flowchart of a flexible DC transmission control method according to Embodiment 2. This embodiment is applicable to the control of flexible DC transmission under grid black-start mode. The method is applied to the main control module in the flexible DC transmission control system of the embodiment. Figure 2 As shown, the method includes:

[0066] S210, Obtain the first AC sampling signal.

[0067] Specifically, the main control module is connected to the first converter on the black start side of the flexible DC transmission system; and obtains the first AC sampling signal from the AC grid side of the first converter.

[0068] S220. Determine the first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal.

[0069] Specifically, the flexible DC transmission system transforms from an active network to a passive network, acting as a black-start power source to supply AC power to the passive network. The main control module of the flexible DC transmission control system determines the first control reference value for the flexible DC transmission based on parameters such as the frequency and voltage of the first AC sampling signal.

[0070] Optionally, the first AC sampling signal includes: a first AC sampling voltage signal; the first control reference value includes: a first phase reference value and a first current reference value; determining the first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal includes:

[0071] A first phase reference value is generated based on a preset frequency;

[0072] The first current reference value is determined based on the voltage sampling value of the first AC sampling voltage signal and the preset voltage value.

[0073] The preset phase compensation value can be set according to actual needs. The first phase reference value provides a coordinate transformation reference for the AC quantities of the flexible DC transmission control system.

[0074] For example, a first phase reference value is determined by a phase-locked loop (PLL) unit based on a preset frequency. If the preset frequency is 50Hz, the first phase reference value for the AC voltage determined by the first PLL unit is 2π. 50Hz t. Based on the difference between the sampled voltage value of the alternating current and the preset voltage value, the first current reference value is determined by proportional-integral adjustment of the difference.

[0075] For example, determining a first current reference value based on a voltage sample value of a first AC sampling voltage signal and a preset voltage value may include: determining the difference between the voltage sample value of the first AC sampling voltage signal and the preset voltage value; and performing proportional-integral adjustment on the difference to determine the first current reference value. The preset voltage value may be 110KV or other set values.

[0076] S230. Generate a first modulation signal based on the first control reference value and the first AC sampling signal, and control the first converter connected to it to output a first AC voltage.

[0077] Specifically, the main control module modulates the first AC sampling signal according to the first control reference value to control the first converter connected to it to output the first AC voltage.

[0078] S240 sends the first control reference value to each slave control module.

[0079] Specifically, the master control module sends the first control reference value to each slave control module so that each slave control module can determine the second control reference value based on the first control reference value and modulate the second AC sampling signal obtained from the AC grid side of the connected second converter according to the second control reference value.

[0080] The technical solution of this invention obtains a first AC sampling signal from the master control module; determines a first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal; generates a first modulation signal based on the first control reference value and the first AC sampling signal; controls the first converter connected to the master control module to output a first AC voltage and send the first control reference value to each slave control module, so that the slave control modules and the master control module maintain consistent transmission parameters, thereby maintaining automatic power balance and system stability of the flexible DC transmission control system during the black start process of the power grid.

[0081] Example 3

[0082] Figure 3 This invention provides a flowchart of a flexible DC transmission control method in Embodiment 3. This embodiment is applicable to the control of flexible DC transmission under grid black-start mode. The method is applied to the slave control module in the flexible DC transmission control system of the embodiment. Figure 3 As shown, the method includes:

[0083] S310: Acquire the second AC sampling signal and receive the first control reference value sent by the main control module.

[0084] S320. Determine the second control reference value based on the first control reference value.

[0085] Optionally, the first control reference value includes: a first phase reference value and a first current reference value; the second control parameter value includes: a second phase reference value and a second current reference value; determining the second control reference value based on the first control reference value includes:

[0086] The second phase reference value is determined based on the first phase reference value and the preset phase compensation value;

[0087] The second current reference value is determined based on the first current reference value and the preset allocation coefficient.

[0088] The preset phase compensation value can be set according to actual needs. The preset allocation coefficient can be set according to actual needs or according to the attributes of the flexible DC transmission control system.

[0089] For example, if the preset frequency is 50Hz, the first phase reference value is 2π. 50Hz If the delay in communication and processing of the inter-unit phase reference signal is Tphase, then the compensated phase angle can be Tphase. 50Hz 2π; the second phase reference value can be 2π. 50Hz t+Tphase 50Hz 2π.

[0090] If the transmission capacity of the master control module of the flexible DC transmission control system is M, and the transmission capacity of the slave control module is N, then the preset allocation coefficient K = N / M is used to allocate the first current reference value of the master control module and the second current reference value of the slave control module in a ratio of M:N. For a bipolar flexible DC transmission control system, if the first current reference values ​​are IDREF and IQREF, then the second current reference values ​​are IDREF and IQREF respectively. N / M and IQREF N / M. Since the voltage values ​​of the master control module and the slave control module are the same, the AC power of the two control modules will be automatically distributed in real time according to the M:N ratio, resulting in consistent external characteristics and automatic power balancing and system stability of the flexible DC transmission control system.

[0091] S330: Generate a second modulation signal based on the second control reference value and the second AC sampling signal, and control the connected second converter to output a second AC voltage.

[0092] Specifically, when a grid fault occurs, the flexible DC transmission system transforms from an active network to a passive network, acting as a black-start power source to supply AC power to the passive network. The control module of the flexible DC transmission control system modulates the sampled AC signal and outputs AC voltage to the converter of the flexible DC transmission system.

[0093] The technical solution of this invention involves acquiring a second AC sampling signal and receiving a first control reference value sent by the main control module; determining a second control reference value based on the first control reference value; generating a second modulation signal based on the second control reference value and the second AC sampling signal; and controlling the connected second converter to output a second AC voltage, so that the slave control module and the main control module maintain consistent transmission parameters, thereby maintaining automatic power balance and system stability of the flexible DC transmission control system during the black start process of the power grid.

[0094] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and no limitation is imposed herein.

[0095] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A flexible DC transmission control system, comprising: The system comprises at least two control modules, including a master control module and at least one slave control module connected to the master control module; each control module is connected to a converter on the black-start side of the flexible DC transmission system; characterized in that the master control module includes a first phase-locked loop (PLL) unit, a first voltage control unit, and a first current control unit, and the slave control module includes a second PLL unit, a second voltage control unit, and a second current control unit; the first PLL unit is connected to the second PLL unit; the first voltage control unit is connected to the first current control unit, the second voltage control unit is connected to the second current control unit, and the first voltage control unit is connected to the second voltage control unit. The main control module is used to acquire a first AC sampling signal from the AC grid side of the connected first converter; determine a first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal; generate a first modulation signal based on the first control reference value and the first AC sampling signal to control the connected first converter to output a first AC voltage; and send the first control reference value to each of the slave control modules. The slave control module is used to acquire a second AC sampling signal from the AC grid side of the connected second converter, and receive the first control reference value sent by the master control module, determine a second control reference value based on the first control reference value, and generate a second modulation signal based on the second control reference value and the second AC sampling signal to control the connected second converter to output a second AC voltage. The first control reference value includes: a first phase reference value and a first current reference value; the first phase-locked unit is used to generate the first phase reference value according to a preset frequency and send the first phase reference value to the second phase-locked unit; the first phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system; The first voltage control unit is configured to acquire a first AC sampling voltage signal, determine a first current reference value based on the voltage sampling value of the first AC sampling voltage signal and a preset voltage value, and send the first current reference value to the first current control unit and the second voltage control unit. The first current control unit is configured to acquire a first AC sampling current signal and generate a first modulation signal based on the first current reference value and the first AC sampling current signal; The second control parameter values ​​include: a second phase reference value and a second current reference value. The second phase-locked unit is used to receive the first phase reference value sent by the first phase-locked unit, and determine the second phase reference value according to the first phase reference value and the preset phase compensation value; the second phase reference value provides a coordinate transformation reference for the AC quantity of the flexible DC transmission control system. The second voltage control unit is configured to receive the first current reference value sent by the first voltage control unit, determine the second current reference value based on the first current reference value and a preset allocation coefficient, and send the second current reference value to the second current control unit. The second current control unit is used to acquire the second AC sampling current signal and generate a second modulation signal based on the second current reference value and the second AC sampling current signal.

2. The flexible DC transmission control system according to claim 1, characterized in that, The first voltage control unit is specifically used for: Determine the difference between the voltage sample value and the preset voltage value of the first AC sampling voltage signal; The first current reference value is determined by proportional-integral adjustment of the difference.

3. The flexible DC transmission control system according to claim 1, characterized in that, The preset allocation coefficient is determined based on the ratio of the power transmission capacity of the master control module to the power transmission capacity of the slave control module.

4. A flexible DC transmission control method, characterized in that, The method for controlling the main control module in the flexible DC transmission control system described in any one of claims 1 to 3 includes: Acquire the first AC sampling signal; The first control reference value for flexible DC transmission is determined based on the parameters of the first AC sampling signal; A first modulation signal is generated based on the first control reference value and the first AC sampling signal to control the first converter connected to output a first AC voltage; The first control reference value is sent to each slave control module.

5. The method according to claim 4, characterized in that, The first AC sampling signal includes: a first AC sampling voltage signal; the first control reference value includes: a first phase reference value and a first current reference value; determining the first control reference value for flexible DC transmission based on the parameters of the first AC sampling signal includes: A first phase reference value is generated based on a preset frequency; The first current reference value is determined based on the voltage sampling value of the first AC sampling voltage signal and the preset voltage value.

6. The method according to claim 5, characterized in that, Determining a first current reference value based on the voltage sample value of the first AC sampling voltage signal and a preset voltage value includes: Determine the difference between the voltage sample value and the preset voltage value of the first AC sampling voltage signal; The first current reference value is determined by proportional-integral adjustment of the difference.

7. A flexible DC transmission control method, characterized in that, The control method for the slave control module in the flexible DC transmission control system according to any one of claims 1 to 3 includes: Acquire the second AC sampling signal and receive the first control reference value sent by the main control module; Determine the second control reference value based on the first control reference value; A second modulation signal is generated based on the second control reference value and the second AC sampling signal to control the connected second converter to output a second AC voltage.

8. The method according to claim 7, characterized in that, The first control reference value includes a first phase reference value and a first current reference value; the second control parameter value includes a second phase reference value and a second current reference value; determining the second control reference value based on the first control reference value includes: The second phase reference value is determined based on the first phase reference value and the preset phase compensation value; The second current reference value is determined based on the first current reference value and the preset allocation coefficient.

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