A control method suitable for a flexible direct current transmission module

Abstract

The application discloses a control method suitable for a flexible direct-current transmission sub-module, and is applied to a flexible direct-current transmission system, and the control method comprises the following steps: when a local fault occurs in a sub-module, the throwability of the sub-module is judged according to the capacitance value and the voltage increment of the sub-module; the local fault is a fault of a first all-controllable device or a second all-controllable device; when the throwability of the sub-module is no, a bypass instruction is executed; when the throwability of the sub-module is yes, the use is maintained; and when the local fault occurs in the sub-module, the throw-in and throw-out instructions of each sub-module are determined according to the bridge arm current direction and a preset rule. By using the application, the bypass switch does not need to be triggered when the local fault occurs in the flexible direct-current sub-module, and the overall bypass rate is reduced. The application can be widely applied to the field of circuit control.

Description

Technical Field

[0001] This invention relates to the field of circuit control, and more particularly to a control method applicable to flexible DC power transmission modules. Background Technology

[0002] With the increasing maturity of flexible DC transmission technology, the reliability of engineering operation has become a focus of industry attention, and the bypass rate of a flexible DC transmission system is an important indicator for measuring its reliability. The bypass switch is the only mechanical bypass component in a flexible DC transmission submodule. Currently, measures to reduce the bypass rate involve increasing the redundancy of submodules, such as adding redundant power supplies and redundant communications. The essence of this is to prevent failures of fully controlled devices in the submodules. However, existing methods do not consider adding corresponding control measures after a failure of a fully controlled device to reduce the triggering of the bypass switch, making it difficult to further reduce the bypass rate. Summary of the Invention

[0003] In view of this, in order to address the technical problem that most existing methods for reducing bypass ratio do not consider active control after a fault occurs, thus making it difficult to achieve an overall reduction in bypass ratio, this invention proposes a control method suitable for flexible DC transmission modules:

[0004] This control method is applied to the following flexible DC transmission systems:

[0005] The flexible DC transmission system includes three phase units, each of which includes a bridge arm unit and a bridge arm reactor. The bridge arm unit is composed of multiple sub-modules connected in series. The sub-modules include a first fully controlled device, a second fully controlled device, a first diode, a second diode, a DC capacitor, a bypass switch, and an overvoltage breakdown device.

[0006] The first terminal of the first fully controllable device, the second terminal of the first diode, and the first terminal of the DC capacitor are connected together;

[0007] The second terminal of the first fully controlled device, the first terminal of the first diode, the first terminal of the second fully controlled device, the second terminal of the second diode, the first terminal of the bypass switch, and the second terminal of the overvoltage breakdown device are connected together;

[0008] The second terminal of the second fully controlled device, the first terminal of the second diode, the second terminal of the DC capacitor, the second terminal of the bypass switch, and the first terminal of the overvoltage breakdown device are connected.

[0009] The control method includes the following steps:

[0010] When a submodule experiences a partial fault, its operational availability is determined based on the submodule's capacitance value and voltage increment.

[0011] A partial fault is defined as a failure of either the first fully controlled device or the second fully controlled device.

[0012] When the availability of a submodule is not specified, execute the bypass instruction;

[0013] If the submodule is available, continue using it;

[0014] When no submodule experiences a partial fault, all submodules are sorted according to voltage magnitude, and the switching command for each submodule is determined according to the direction of the bridge arm current.

[0015] When a submodule experiences a partial fault, the switching command for each submodule is determined based on the direction of the bridge arm current and preset rules.

[0016] Based on the above scheme, the present invention provides a control method applicable to flexible DC transmission modules. It takes into account that the submodule with a local fault does not affect normal operation under certain conditions. Through judgment rules and control settings, the submodule continues to operate in the system when a local fault occurs, without triggering a bypass, reducing the system bypass rate, providing a higher margin for continuous system operation, and greatly benefiting the continuity of energy supply and the reliability of engineering operation. Attached Figure Description

[0017] Figure 1 This is a topology diagram of the flexible DC transmission system of the present invention;

[0018] Figure 2 This is a schematic diagram of the structure of a submodule in the flexible DC transmission system of the present invention;

[0019] Figure 3 This is a schematic diagram of the current flow direction in state 1 of the submodule of the present invention;

[0020] Figure 4 This is a schematic diagram of the current flow direction in state 2 of the submodule of the present invention;

[0021] Figure 5 This is a schematic diagram of the current flow direction in state 3 of the submodule of the present invention;

[0022] Figure 6 This is a schematic diagram of the current flow direction in state 4 of the submodule of the present invention;

[0023] Figure 7 This is a schematic diagram of the working logic of a submodule of the present invention;

[0024] Reference numerals: K, bypass switch; Z, overvoltage protection device; T1, first fully controlled device; T2, second fully controlled device; D1, first diode; D2, second diode; C, DC capacitor. Detailed Implementation

[0025] Some existing solutions ensure that the IGCT-MMC submodule is switched out of the system within a controllable voltage range by setting up multi-level bypass methods, but do not mention reducing the bypass rate when a fully controllable device fails.

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] It should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0028] It should be understood that the terms "system," "unit," and / or "module" used in this application are a method of distinguishing different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they may be replaced by other expressions.

[0029] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "a," and / or "the" are not specifically singular and may include the plural. Generally, the terms "comprising" and "including" only indicate the inclusion of expressly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements. An element defined by the phrase "comprising an..." does not exclude the presence of other identical elements in the process, method, product, or apparatus that includes the element.

[0030] In the description of the embodiments of this application, "a plurality of" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0031] Furthermore, flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, the steps can be processed in reverse order or simultaneously. Additionally, other operations can be added to these processes, or one or more steps can be removed from them.

[0032] The control method of this invention is applied to the following flexible DC transmission systems:

[0033] Reference Figure 1 The flexible DC transmission system includes three phase units, each of which includes a bridge arm unit and a bridge arm reactor. The bridge arm unit is composed of multiple sub-modules connected in series.

[0034] Refer to the connection diagram of the submodule. Figure 2 , specifically:

[0035] The submodule includes a first fully controlled device T1, a second fully controlled device T2, a first diode D1, a second diode D2, a DC capacitor C, a bypass switch K, and an overvoltage breakdown device Z;

[0036] The first terminal of the first fully controlled device T1, the second terminal of the first diode D1, and the first terminal of the DC capacitor C are connected together.

[0037] The second terminal of the first fully controlled device T1, the first terminal of the first diode D1, the first terminal of the second fully controlled device T2, the second terminal of the second diode D2, the first terminal of the bypass switch K, and the second terminal of the overvoltage breakdown device Z are connected.

[0038] The second terminal of the second fully controlled device T2, the first terminal of the second diode D2, the second terminal of the DC capacitor C, the second terminal of the bypass switch K, and the first terminal of the overvoltage breakdown device Z are connected.

[0039] The first fully controlled device T1, the second fully controlled device T2, and the bypass switch K are also connected to the main control board, which is also connected to the valve control.

[0040] Among them, the bypass switch K has a bypass triggering function, and the overvoltage breakdown device Z can be a surge arrester or a breakdown diode; the main control board can control the opening and closing of the first fully controlled device T1 and the second fully controlled device T2, and at the same time, the first fully controlled device T1 and the second fully controlled device T2 feed back their own status to the main control board; the main control board can trigger the bypass switch K to perform a closing action, and at the same time, the bypass switch K feeds back its own status to the main control board; the valve control can issue switching commands to the main control board, the main control board parses and executes them, and at the same time, the main control board feeds back the status of the submodule to the valve control, which makes the control decision.

[0041] The control method for flexible DC transmission modules proposed in this invention may include, but is not limited to, the following steps:

[0042] If a submodule experiences a partial fault, its operational availability is determined based on the submodule's capacitance value and voltage increment.

[0043] A partial fault is defined as a failure of either the first fully controlled device T1 or the second fully controlled device T2. In current flexible DC transmission projects, a "partial fault" can also directly trigger the bypass switch to operate.

[0044] When the availability of a submodule is not specified, execute the bypass instruction;

[0045] If the submodule is available, continue using it;

[0046] When no submodule experiences a partial fault, all submodules are sorted according to voltage magnitude, and the switching command for each submodule is determined according to the direction of the bridge arm current.

[0047] When a submodule experiences a partial fault, the switching command for each submodule is determined based on the direction of the bridge arm current and preset rules.

[0048] The control principle of the flexible DC transmission system is to stabilize the sum of the port output voltages of the control submodules. The submodule activation command is defined as S; when S=1, the submodule is activated, meaning the port output voltage is... When S=0, the submodule is switched off, meaning the port output voltage is 0. Therefore, once the system design is determined—that is, the DC side voltage, the submodule port output voltage, and the number of bridge arm submodules connected in series are all fixed—the number of submodules in operation at any given time is also fixed, and must satisfy the following:

[0049]

[0050] Indicates intermediate calculation parameters. n Indicates the number of the submodules. Indicates the DC side voltage. This indicates the output voltage of the port.

[0051] In a flexible DC transmission system, valve-controlled switching commands are issued based on the arm current and submodule voltage. To ensure voltage balance among series-connected submodules, the valve controls the voltage of all submodules in the arm unit, prioritizing them by magnitude and determining the switching command for each submodule based on the direction of the arm current. The direction of the arm current flowing into the submodule port is defined as positive. Therefore, as follows... Figures 3-6 As shown, Iarm represents the bridge arm current. Figure 3 State 1 indicates the submodule's status when the bridge arm current is greater than 0 and an activation command needs to be executed; Figure 4 State 2 shows the submodule's state when the bridge arm current is greater than 0 and a cut-out command needs to be executed; Figure 5 State 3 illustrates the submodule's state when the bridge arm current is less than 0 and an activation command needs to be executed; Figure 6 State 4 illustrates the submodule's state when the bridge arm current is less than 0 and a cut-out command needs to be executed, where:

[0052] , Indicates the first pre-investment quantity;

[0053] When the bridge arm current is greater than 0, it is in a lower priority position. Each submodule executes the input command, the rest... Each submodule executes the cut-out instruction.

[0054] When the bridge arm current is less than 0, it is in the high-order position. Each submodule executes the input command, the rest... Each submodule executes the cut-out instruction.

[0055] In addition, from Figure 3 and Figure 6 It can be seen that when a "partial fault" occurs, even if the bypass switch is not triggered, the execution of "state 1" and "state 4" will not be affected.

[0056] For "State 3", the current flow direction in this state is referenced. Figure 5 When a submodule experiences a "partial fault" caused by the first fully controlled device T1, a "start command" needs to be executed when the bridge arm current is less than 0. The specific action logic at the submodule level is to turn on the first fully controlled device T1. If the first fully controlled device T1 fails to turn on at this time, current will flow out through the second diode D2, affecting the DC-side voltage. To ensure that the DC side voltage is Therefore, valve control needs to be activated at this time. Sub-modules.

[0057] For "State 2", the current flow direction in this state is referenced. Figure 4 When a submodule experiences a "partial fault" caused by the second fully controlled device T2, a "cut-out command" needs to be executed when the bridge arm current is greater than 0. The specific action logic at the submodule level is to turn on the second fully controlled device T2. If the second fully controlled device T2 fails to turn on at this time, the current will charge the DC capacitor through the first diode D1, affecting the DC side voltage. To ensure that the DC side voltage is Therefore, valve control needs to be activated at this time. Each submodule; the input rule judgment for each submodule refers to... Figure 5 .

[0058] In summary, the logic for determining the submodule deployment rules after a partial failure refers to... Figure 7 .

[0059] To ensure that the DC capacitor voltage of the submodule experiencing a "partial fault" does not become excessively high, the breakdown voltage value Uz of the overvoltage breakdown device Z configured at the port can be configured according to the actual operating conditions, generally not exceeding 1.35V. That is, when the capacitor voltage is higher than 1.35 Afterwards, the overvoltage breakdown device Z can short-circuit the bridge arm current.

[0060] The availability of a partially faulty submodule is determined primarily by checking whether its capacitance value and voltage increment are normal. The submodule's capacitance value is fixed during the design and finalization process. C rate If the capacitor value is less than 0.9 during use... C rate This is considered an anomaly. In some feasible embodiments, the capacitance value is estimated using a Bayesian ridge regression algorithm, including the following steps:

[0061] Step 1: Collect bridge arm current and submodule voltage;

[0062] The parameters obtained in this step are all instantaneous values. The Bayesian Ridge algorithm is used later to obtain a more accurate capacitance value.

[0063] Step 2: Set the decision duration to 20ms, with a calculation step size of 10μs;

[0064] Step 3, every 10 μs Calculating the capacitance value once yields 20 results. When the bridge arm current is greater than 0, the submodule capacitor voltage increment satisfies the following:

[0065]

[0066] In the above formula, Indicates the voltage increment of the submodule. I This indicates the value of the bridge arm current. C This refers to the capacitance value of the submodule.

[0067] Step 4: Use the 20 results as target variables. y At the same time, a feature matrix is ​​constructed. X ,Right now:

[0068]

[0069] The goal of Bayesian ridge regression is to find a linear model:

[0070]

[0071] in It is the regression coefficient. It is noise that follows a normal distribution. Bayesian ridge review estimates it by introducing priors. The variance of noise.

[0072] Assumption Follows a normal distribution ,noise Follows a normal distribution ,in and Let these represent different hyperparameters. Then, according to Bayes' theorem, the posterior distribution... It can be represented as:

[0073]

[0074] By maximizing the posterior score, we can obtain... The estimated value ,and The calculation formula is:

[0075]

[0076] Regression coefficients obtained through Bayesian Ridge regression algorithm This refers to the capacitance value of the submodule.

[0077] Step 5: Calculate the voltage increment based on the calculated capacitance value.

[0078] A storage medium storing processor-executable instructions, which, when executed by a processor, are used to implement a control method applicable to a flexible DC power transmission module as described above.

[0079] The content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0080] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A control method suitable for a flexible DC power transmission sub-module, characterized in that, The application is applied to a flexible direct current transmission system, the flexible direct current transmission system comprises three phase units, the phase unit comprises a bridge arm unit and a bridge arm reactor, the bridge arm unit comprises at least two sub-modules, the sub-module comprises a first full-control device, a second full-control device, a first diode, a second diode, a direct current capacitor, a bypass switch and an overvoltage breakdown device, and the control method comprises the following steps: When the sub-module has a local fault, the throwability of the sub-module is judged according to the capacitance value and the voltage increment of the sub-module; The local fault is that the first full-control device or the second full-control device has a fault; When the throwability of the sub-module is no, a bypass instruction is executed; When the throwability of the sub-module is yes, the use is maintained; When the sub-module has a local fault, the throw-in and throw-out instructions of each sub-module are determined according to the bridge arm current direction and a preset rule; The step of determining the throw-in and throw-out instructions of each sub-module according to the bridge arm current direction and the preset rule when the sub-module has a local fault specifically comprises: When the sub-module has a local fault caused by the first full-control device, the throw-in instruction is executed on the second pre-throw number of sub-modules, and the throw-out instruction is executed on the remaining sub-modules, when the throwability of the sub-module is yes and the bridge arm current is less than 0; When the sub-module has a local fault caused by the second full-control device, the throw-in instruction is executed on the first pre-throw number of sub-modules, and the throw-out instruction is executed on the remaining sub-modules, when the throwability of the sub-module is yes and the bridge arm current is less than 0; When the sub-module has a local fault caused by the first full-control device, the throw-in instruction is executed on the first pre-throw number of sub-modules, and the throw-out instruction is executed on the remaining sub-modules, when the throwability of the sub-module is yes and the bridge arm current is greater than 0; When the sub-module has a local fault caused by the second full-control device, the throw-in instruction is executed on the third pre-throw number of sub-modules, and the throw-out instruction is executed on the remaining sub-modules, when the throwability of the sub-module is yes and the bridge arm current is greater than 0; The constraint of the first pre-throw number is as follows: wherein, represents a first pre-throw number, represents an intermediate calculation parameter, n represents the number of sub-modules, represents a direct current side voltage, represents a port output voltage; The constraint of the second pre-throw number and the third pre-throw number is as follows: In the above formula, represents the second pre-throw number, represents the third pre-throw number, represents an intermediate calculation parameter, n represents the number of sub-modules, represents the direct current side voltage, represents the port output voltage; The process of judging the throwability of the sub-module according to the capacitance value and the voltage increment of the sub-module specifically comprises: The bridge arm current and the sub-module voltage are collected; The capacitance value is calculated according to the bridge arm current and the sub-module voltage, and a calculation result is obtained; The capacitance value is calculated by taking the calculation result as a target variable and combining a Bayesian ridge regression algorithm; The voltage increment is solved according to the capacitance value; When the capacitance value and the voltage increment of the sub-module are both in corresponding preset intervals, it is determined that the throwability of the sub-module is yes.

2. The control method for a flexible HVDC electronic module according to claim 1, wherein, Further comprising: When no sub-module has a local fault, all the sub-modules are sorted according to the voltage, and the throw-in and throw-out instructions of each sub-module are determined according to the bridge arm current direction.

3. The control method for a flexible HVDC electronic module according to claim 2, wherein, The step of sorting all the sub-modules according to the voltage size and determining the switching instruction of each sub-module according to the bridge arm current direction when no local fault occurs in the sub-modules, specifically comprises: sorting all the sub-modules according to the order from large to small voltage; defining the direction of the bridge arm current flowing into the port of the sub-module as positive; when the bridge arm current is greater than 0, the first pre-throw number of sub-modules in the low order execute the input instruction, and the remaining sub-modules execute the cut-out instruction; when the bridge arm current is less than 0, the first pre-throw number of sub-modules in the high order execute the input instruction, and the remaining sub-modules execute the cut-out instruction.

4. The control method for the flexible DC power transmission electronic module according to claim 3, wherein The connection mode of the devices in the sub-module is as follows: the first end of the first full-control device, the second end of the first diode and the first end of the direct current capacitor are connected; the second end of the first full-control device, the first end of the first diode, the first end of the second full-control, the second end of the second diode, the first end of the bypass switch and the second end of the overvoltage breakdown device are connected; the second end of the second full-control device, the first end of the second diode, the second end of the direct current capacitor, the second end of the bypass switch and the first end of the overvoltage breakdown device are connected.

5. The control method for a flexible HVDC electronic module according to claim 4, wherein, The calculation formula of the voltage increment is represented as follows: In the above formulae, denotes the voltage increment, denotes the bridge arm current, C denotes the capacitance value, t denotes the calculation step.

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