Inertia support control method, device and equipment of flexible direct current power transmission system and medium

Abstract

The invention discloses an inertia support control method, device and equipment of a flexible direct current power transmission system and a medium, which are used for solving the technical problem of delay of inertia support calling of current new energy. The receiving end of the flexible DC power transmission system adopts an MMC converter topological structure, and a single MMC converter in the MMC converter topological structure comprises a plurality of sub-module capacitors. The method comprises the following steps: acquiring the output power of the AC side of an MMC converter and the capacitor voltage of each sub-module capacitor; calculating a capacitance average voltage according to each capacitor voltage, and calculating a direct current voltage deviation value based on the capacitance average voltage; calculating a three-phase AC voltage reference value based on the output power, and calculating an input voltage reference value in combination with the DC voltage deviation value and the three-phase AC voltage reference value; according to the input voltage reference value and the average capacitance voltage, the number of sub-modules needing to be input is calculated, and the MMC converter is controlled by controlling the number of the input sub-modules.

Description

Technical Field

[0001] The present invention relates to the technical field of new power systems, and in particular to an inertia support control method, device, equipment and medium for a flexible direct current transmission system. Background Art

[0002] With the development of new power systems, a large number of power electronic equipment are connected to the power grid, which has changed the operating characteristics of the power grid. Under traditional control strategies, power electronic equipment basically does not provide inertia. Therefore, scholars at home and abroad have proposed a grid-type control strategy to enable power electronic equipment to have inertia support capabilities. Inertia support refers to the ability to maintain system frequency stability through the rotational inertia of rotating machinery (such as generators) in a power system. When load changes or power generation fluctuates in the power system, the frequency of the system will be affected. Inertia support can provide a buffer mechanism to help the system maintain frequency stability in a short period of time until other control measures (such as frequency regulation services) take effect.

[0003] At present, the inertia support energy of new energy sources mainly comes from power reserve or additional energy storage. However, with this method, once the power system changes or fluctuates, it is difficult to obtain inertia support in time due to the call delay, and the system frequency stability cannot be well maintained, which is likely to have an adverse impact on system operation. Summary of the invention

[0004] The present invention provides an inertia support control method, device, equipment and medium for a flexible direct current transmission system, which are used to solve or partially solve the technical problem of delay in calling the inertia support of current new energy sources.

[0005] The present invention provides an inertia support control method for a flexible direct current transmission system, wherein a receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure includes multiple submodule capacitors; the inertia support control method comprises:

[0006] Obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor;

[0007] Calculating a capacitor average voltage according to each of the capacitor voltages, and calculating a DC voltage deviation based on the capacitor average voltage;

[0008] Based on the output power, a three-phase AC voltage reference value is calculated, and an input voltage reference value is calculated by combining the DC voltage deviation and the three-phase AC voltage reference value;

[0009] The number of submodules that need to be put into operation is calculated according to the input voltage reference value and the capacitor average voltage, and the control of the MMC converter is completed by controlling the number of submodules put into operation.

[0010] Optionally, the MMC converter is composed of three-phase units A, B, and C connected in parallel, a single phase unit is composed of an upper bridge arm and a lower bridge arm, and a single bridge arm is composed of N submodules connected in series; the average capacitor voltage is calculated by the following formula:

[0011]

[0012] in, Represents the average capacitor voltage; , Respectively represent the capacitor voltages of the upper bridge arm of phase A and the lower bridge arm of phase A submodule; , Respectively represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B; , They represent the capacitor voltages of the C-phase upper bridge arm and the C-phase lower bridge arm submodules respectively.

[0013] Optionally, the calculating the DC voltage deviation based on the capacitor average voltage includes:

[0014] Based on the capacitor average voltage, a DC voltage deviation is obtained through a submodule average voltage control link.

[0015] Optionally, obtaining a DC voltage deviation through a submodule average voltage control link based on the capacitor average voltage includes:

[0016] Obtaining a measured frequency value and a rated frequency value of the AC power grid, and an average rated voltage value of a submodule of the MMC converter;

[0017] The frequency measured value is subtracted from the frequency rated value, and then multiplied by a preset voltage-frequency correlation coefficient, and after passing through a voltage limiting link, a voltage after limiting is obtained;

[0018] The sum of the voltage after limiting and the average voltage rating of the submodule is used, and the average voltage of the capacitor is subtracted, and after passing through the PI control link, a DC current reference value is obtained;

[0019] The actual value of the DC current is obtained, and the actual value of the DC current is subtracted from the DC current reference value. After the PI control link is passed, a DC voltage deviation is output.

[0020] Optionally, the output power includes active power and reactive power; and the calculating the three-phase AC voltage reference value based on the output power includes:

[0021] According to the active power and the reactive power, a three-phase AC voltage reference value is obtained through double closed-loop vector control.

[0022] Optionally, the calculating the input voltage reference value by combining the DC voltage deviation and the three-phase AC voltage reference value includes:

[0023] According to the DC voltage deviation and the three-phase AC voltage reference value, the upper bridge arm voltage reference value and the lower bridge arm voltage reference value are calculated by the following formula:

[0024]

[0025] in, Indicates the upper bridge arm voltage reference value; Indicates the voltage reference value of the lower bridge arm; j=A, B, C; Indicates the DC voltage rating; Indicates the DC voltage deviation; Indicates the three-phase AC voltage reference value;

[0026] The upper bridge arm voltage reference value and the lower bridge arm voltage reference value are used as input voltage reference values ​​that the MMC converter needs to control input.

[0027] Optionally, the calculating the number of submodules to be put into operation according to the input voltage reference value and the capacitor average voltage, and completing the control of the MMC converter by controlling the number of submodules put into operation, includes:

[0028] For each phase of the MMC converter, the number of upper bridge arm submodules required for the upper bridge arm is calculated according to the upper bridge arm voltage reference value and the capacitor average voltage through nearest level approximation modulation, and the number of lower bridge arm submodules required for the lower bridge arm is calculated according to the lower bridge arm voltage reference value and the capacitor average voltage;

[0029] The control of the MMC converter is completed by controlling the submodule switches of the upper and lower bridge arms to input the number of each upper bridge arm submodule and the number of each lower bridge arm submodule.

[0030] The present invention also provides an inertia support control device for a flexible direct current transmission system, wherein the receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure includes multiple submodule capacitors; the inertia support control device comprises:

[0031] A data acquisition unit, used to acquire the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor;

[0032] a DC voltage deviation calculation unit, configured to calculate an average capacitor voltage according to each of the capacitor voltages, and calculate a DC voltage deviation based on the capacitor average voltage;

[0033] A voltage reference value calculation unit, configured to calculate a three-phase AC voltage reference value based on the output power, and calculate an input voltage reference value in combination with the DC voltage deviation and the three-phase AC voltage reference value;

[0034] The submodule input control unit is used to calculate the number of submodules that need to be put into operation according to the input voltage reference value and the capacitor average voltage, and complete the control of the MMC converter by controlling the number of submodules put into operation.

[0035] The present invention also provides an electronic device, the device comprising a processor and a memory:

[0036] The memory is used to store program code and transmit the program code to the processor;

[0037] The processor is used to execute the inertia support control method of the flexible direct current transmission system as described in any one of the above items according to the instructions in the program code.

[0038] The present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the inertia support control method of the flexible direct current transmission system as described in any one of the above items.

[0039] It can be seen from the above technical solutions that the present invention has the following advantages:

[0040] A method for controlling inertia support of a flexible direct current transmission system is provided. The receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure contains multiple submodule capacitors; the method comprises: obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor; calculating the average capacitor voltage according to each capacitor voltage, and calculating the DC voltage deviation based on the average capacitor voltage; calculating the three-phase AC voltage reference value based on the output power, and calculating the input voltage reference value in combination with the DC voltage deviation and the three-phase AC voltage reference value; calculating the number of submodules to be invested according to the input voltage reference value and the average capacitor voltage, and completing the control of the MMC converter by controlling the number of submodules invested. Therefore, by directly calling the capacitor energy of the receiving terminal module of the flexible direct current transmission system, the inertia support of the power grid can be performed without affecting the normal control function of the flexible direct current transmission system. Compared with the energy calling method at the sending end, the calling delay can be greatly reduced and the response is faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 A flow chart of the steps of an inertia support control method for a flexible direct current transmission system;

[0043] Figure 2 It is a circuit principle structure block diagram of a submodule average voltage control;

[0044] Figure 3 It is a circuit principle structure block diagram of a double closed-loop vector control;

[0045] Figure 4 It is a schematic diagram of the overall flow of an inertia support control method for a flexible direct current transmission system;

[0046] Figure 5 The figure is a structural block diagram of an inertia support control device for a flexible DC power transmission system. DETAILED DESCRIPTION

[0047] The embodiments of the present invention provide an inertia support control method, device, equipment and medium for a flexible direct current transmission system, which are used to solve or partially solve the technical problem of delay in calling the inertia support of current renewable energy sources.

[0048] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] As an example, the inertia support energy of current new energy sources mainly comes from power reserve or additional energy storage. More specifically, for example, the inertia support of the receiving-end power grid is provided by calling the energy at the sending end or the additional energy storage at the sending end. Flexible direct current transmission systems (i.e. flexible direct current transmission systems) are generally used for long-distance power transmission, and it takes a certain amount of time for the state of the receiving-end power grid to be transmitted to the sending end. There is a delay in providing inertia support to the receiving-end power grid by calling the energy at the sending end. In other words, using this method, once the power system changes or fluctuates, it is difficult to obtain inertia support in time due to the call delay, and the system frequency stability cannot be well maintained, which is likely to have an adverse effect on the system operation.

[0050] After further analysis, the present invention finds that, unlike new energy converters, flexible direct current transmission systems generally adopt modular multi-level topology. Submodule capacitors store a large amount of energy, and there are many submodules. Therefore, the submodule energy can be used for inertia support by switching.

[0051] Therefore, one of the core inventive points of the embodiment of the present invention is: in view of the shortcomings of the current technology, an inertia support control method based on the capacitor energy of the sub-module of the flexible direct current transmission system is proposed. The average voltage value of the capacitor of the terminal module of the flexible direct current transmission system is independently adjusted through an additional control strategy, and the capacitor energy of the sub-module is directly called to achieve inertia support for the power grid without affecting the normal control function of the flexible direct current transmission system. Compared with the sending-end energy calling method, the calling delay can be greatly reduced and the response is faster. In addition, compared with the method of calling the sending-end energy or additionally configuring energy storage for inertia support, the method provided by the present invention can save additional configuration costs and has better economy.

[0052] In practical applications, the receiving end of the high-voltage flexible direct current transmission system usually adopts a modular multilevel converter (MMC) topology. N sub-modules are connected in series to form a single bridge arm. The upper and lower bridge arms are combined to form a phase unit. The three-phase units A, B, and C are connected in parallel to form a single MMC converter. A single MMC converter can contain 6N sub-module capacitors. In other words, the MMC converter is composed of three-phase units A, B, and C in parallel, a single phase unit is composed of the upper and lower bridge arms combined, and a single bridge arm is composed of N sub-modules in series. This structural feature enables the MMC converter to store a large amount of capacitor energy. In an embodiment of the present invention, by calling the sub-module capacitor energy, active support is achieved for the inertia of the AC power grid.

[0053] Reference Figure 1 , shows a flowchart of the steps of an inertia support control method of a flexible direct current transmission system provided by an embodiment of the present invention, which may specifically include the following steps:

[0054] Step 101, obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor;

[0055] The output power of the AC side of the MMC converter specifically refers to the active power and reactive power output by the AC side of the MMC converter. When the flexible direct current transmission system operates normally, the active power and reactive power will be controlled to be set values.

[0056] Step 102, calculating an average capacitor voltage according to each of the capacitor voltages, and calculating a DC voltage deviation based on the average capacitor voltage;

[0057] Specifically, the average capacitor voltage is calculated by the following formula:

[0058] (1)

[0059] in, Represents the average capacitor voltage; , Respectively represent the capacitor voltages of the upper bridge arm of phase A and the lower bridge arm of phase A submodule; , Respectively represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B; , They represent the capacitor voltages of the C-phase upper bridge arm and the C-phase lower bridge arm submodules respectively.

[0060] Combined with the previous discussion, a single MMC converter contains six bridge arms, each bridge arm has N submodules. Assuming that the capacitance value of a single submodule is C, the energy stored in the capacitors of all submodules is for:

[0061] (2)

[0062] In traditional power systems, the inertia response comes from rotating equipment. The inertia response characteristics of synchronous machines can be described by the following equation (3):

[0063] (3)

[0064] in, is the inertia response power; is the inertia constant of the synchronous machine; is the rated capacity; is the frequency rating; is the frequency change rate.

[0065] The flexible direct current transmission system simulates the inertia response characteristics of the synchronous machine by controlling the inertia response power. The inertia response power is shown in the following formula (4):

[0066] (4)

[0067] in, is the inertia response power of the flexible DC transmission system; The inertia constant simulated for the flexible DC transmission system; is the rated capacity of the flexible DC transmission system.

[0068] The technical solution provided by the embodiment of the present invention provides inertia support through the submodule capacitor energy. The inertia response power satisfies the following formula (5):

[0069] (5)

[0070] in, for ~ (Right now ) The change of submodule capacitance energy within the time; is the rated value of the average voltage of the submodule; is the average voltage change rate of the submodule capacitor.

[0071] By combining equations (4) and (5), we can get the relationship between the average voltage and frequency of the submodule as shown in equation (6):

[0072] (6)

[0073] Among them, the coefficient is the correlation coefficient between the average voltage of the submodule capacitor and the frequency. Through this coefficient, the flexible direct current transmission system can provide the same inertia response characteristics as the synchronous machine.

[0074] In order to realize the control characteristics of the above formula (6), the embodiment of the present invention proposes a submodule average voltage control link. The DC voltage deviation can be obtained through the submodule average voltage control link. The control block diagram of its circuit principle structure is as follows Figure 2 shown.

[0075] exist Figure 2 middle, is the measured value of the frequency of the AC power grid; , They are the upper and lower voltage limits of the limiting link respectively; PI (Proportional-Integral Controller) is a proportional-integral controller; is the DC current reference value; is the actual value of DC current.

[0076] In a specific implementation, the DC voltage deviation is calculated based on the capacitor average voltage, which can be: based on the capacitor average voltage, the DC voltage deviation is obtained through a sub-module average voltage control link.

[0077] More specifically, combined with Figure 2 Based on the average capacitor voltage, the DC voltage deviation is obtained through the submodule average voltage control link, which can be used to obtain the actual frequency value of the AC power grid: , frequency rating , and the average voltage rating of the submodules of the MMC converter ; Using the measured frequency value Subtract frequency rating , then multiply it by the preset voltage-frequency correlation coefficient , after the voltage limiting link ( ~ ) to obtain the voltage after limiting; the voltage after limiting and the average voltage rating of the submodule are used The sum of the capacitors minus the average voltage After the PI control link, the DC current reference value is obtained ; Get the actual value of DC current , using DC current reference value Subtract the actual value of DC current After the PI control link, the output DC voltage deviation .

[0078] Among them, the PI controller can achieve zero-error control. Figure 2 By adjusting the output DC current reference value of the first PI controller , the input deviation can be achieved to be zero, as shown in the following formula (7):

[0079] (7)

[0080] By taking the derivative of equation (7), we can get equation (6). Therefore, Figure 2 The control block diagram can realize the control characteristics of formula (6). Figure 2 The second PI controller is used to adjust the output voltage (i.e. the DC voltage deviation) ), so that the actual value of DC current and reference value Be consistent.

[0081] Step 103, based on the output power, a three-phase AC voltage reference value is calculated, and an input voltage reference value is calculated by combining the DC voltage deviation and the three-phase AC voltage reference value;

[0082] Based on the output power, the three-phase AC voltage reference value is calculated. Specifically, the three-phase AC voltage reference value is obtained through double closed-loop vector control according to the active power and reactive power output on the AC side of the MMC converter. (j=A, B, C).

[0083] The circuit principle structure block diagram of the dual closed-loop vector control is shown in Figure (3). Among them, the voltage outer loop and current inner loop are commonly used control methods and will not be described here.

[0084] In a specific implementation, the input voltage reference value is calculated by combining the DC voltage deviation and the three-phase AC voltage reference value, which can be:

[0085] According to the DC voltage deviation and the three-phase AC voltage reference value, the upper bridge arm voltage reference value and the lower bridge arm voltage reference value are calculated by the following formula:

[0086] (8)

[0087] in, Indicates the upper bridge arm voltage reference value; Indicates the voltage reference value of the lower bridge arm; j=A, B, C; Indicates the DC voltage rating; Indicates the DC voltage deviation; Indicates the three-phase AC voltage reference value.

[0088] The upper bridge arm voltage reference value and the lower bridge arm voltage reference value may be used as input voltage reference values ​​that the MMC converter needs to control input.

[0089] Step 104, calculating the number of submodules that need to be put into operation according to the input voltage reference value and the average capacitor voltage, and completing the control of the MMC converter by controlling the number of submodules put into operation.

[0090] Nearest Level Modulation (NLM) is a modulation strategy that can be applied to MMC converters. NLM achieves precise control of the output voltage of the MMC converter by selecting the level combination closest to the desired output voltage. The output voltage can be adjusted by controlling the input and removal of submodules.

[0091] In the specific implementation, the number of sub-modules required to be put into operation is calculated according to the input voltage reference value and the average capacitor voltage, and the control of the MMC converter is completed by controlling the number of sub-modules put into operation. For each phase of the MMC converter, the nearest level approximation modulation is used to adjust the upper bridge arm voltage reference value. And the average capacitor voltage , calculate the number of upper bridge arm submodules required for the upper bridge arm , and according to the lower bridge arm voltage reference value And the average capacitor voltage , calculate the number of lower bridge arm submodules required for the lower bridge arm . Number of upper bridge arm submodules And the number of lower bridge arm submodules The calculation formula is shown in formula (9):

[0092] (9)

[0093] Among them, round means to take the nearest integer.

[0094] Then, the number of upper bridge arm submodules and the number of lower bridge arm submodules can be put into operation by controlling the submodule switches of the upper and lower bridge arms to complete the control of the MMC converter.

[0095] By combining the submodule average voltage control link and the upper and lower bridge arm voltage reference value calculation, the independent control of the submodule average voltage is achieved. Without affecting the normal operation of the system, the submodule energy can be called for inertia support.

[0096] In an embodiment of the present invention, the average voltage value of the terminal module capacitor of the flexible direct current transmission system is independently adjusted through an additional control strategy, and the energy of the sub-module capacitor is directly called to achieve inertia support for the power grid without affecting the normal control function of the flexible direct current transmission system. Compared with the energy calling method at the sending end, the calling delay can be greatly reduced and the response is faster. In addition, compared with the method of calling the sending end energy or additionally configuring energy storage for inertia support, the method provided by the present invention can save additional configuration costs and has better economy.

[0097] For better explanation, refer to Figure 4 , showing an overall flow chart of an inertia support control method for a flexible direct current transmission system provided by an embodiment of the present invention. It should be pointed out that this embodiment only briefly describes the general process of inertia support control of a flexible direct current transmission system, and the specific implementation process of each step can be understood by referring to the relevant content in the aforementioned embodiment, which will not be described here. It can be understood that the present invention does not limit this.

[0098] Step 401: obtaining the active power and reactive power outputted by the AC side of the MMC converter, and the capacitor voltage of each submodule capacitor;

[0099] Step 402: Calculate the average capacitor voltage according to the voltages of the capacitors, and obtain the DC voltage deviation through the submodule average voltage control link based on the average capacitor voltage;

[0100] Step 403: Obtain a three-phase AC voltage reference value through double closed-loop vector control according to the active power and the reactive power;

[0101] Step 404: Calculate an upper bridge arm voltage reference value and a lower bridge arm voltage reference value according to the DC voltage deviation and the three-phase AC voltage reference value;

[0102] Step 405: for each phase of the MMC converter, by nearest level approximation modulation, according to the upper bridge arm voltage reference value and the average capacitor voltage, the number of upper bridge arm submodules required for the upper bridge arm is calculated, according to the lower bridge arm voltage reference value and the average capacitor voltage, the number of lower bridge arm submodules required for the lower bridge arm is calculated;

[0103] Step 406: Control the submodule switches of the upper and lower bridge arms to input the number of submodules of each upper bridge arm and the number of submodules of each lower bridge arm, thereby completing the control of the MMC converter.

[0104] Reference Figure 5 , shows a structural block diagram of an inertia support control device of a flexible direct current transmission system provided by an embodiment of the present invention, wherein the receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure includes multiple submodule capacitors; the inertia support control device may specifically include:

[0105] The data acquisition unit 501 is used to acquire the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor;

[0106] A DC voltage deviation calculation unit 502, configured to calculate a capacitor average voltage according to each of the capacitor voltages, and calculate a DC voltage deviation based on the capacitor average voltage;

[0107] A voltage reference value calculation unit 503 is used to calculate a three-phase AC voltage reference value based on the output power, and calculate an input voltage reference value in combination with the DC voltage deviation and the three-phase AC voltage reference value;

[0108] The submodule input control unit 504 is used to calculate the number of submodules that need to be put into operation according to the input voltage reference value and the capacitor average voltage, and complete the control of the MMC converter by controlling the number of submodules put into operation.

[0109] In an optional embodiment, the MMC converter is composed of three-phase units A, B, and C connected in parallel, a single phase unit is composed of an upper and a lower bridge arm, and a single bridge arm is composed of N submodules connected in series; the average capacitor voltage is calculated by the following formula:

[0110]

[0111] in, Represents the average capacitor voltage; , Respectively represent the capacitor voltages of the upper bridge arm of phase A and the lower bridge arm of phase A submodule; , Respectively represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B; , They represent the capacitor voltages of the C-phase upper bridge arm and the C-phase lower bridge arm submodules respectively.

[0112] In an optional embodiment, the DC voltage deviation calculation unit 502 is specifically used for:

[0113] Based on the capacitor average voltage, a DC voltage deviation is obtained through a submodule average voltage control link.

[0114] In an optional embodiment, the DC voltage deviation calculation unit 502 includes:

[0115] A data acquisition subunit, used to acquire a measured frequency value and a rated frequency value of the AC power grid, and an average voltage rated value of a submodule of the MMC converter;

[0116] A voltage limiting unit, used to obtain a voltage after limiting by subtracting the frequency rated value from the frequency measured value and multiplying the result by a preset voltage-frequency correlation coefficient;

[0117] A DC current reference value calculation unit, configured to obtain a DC current reference value by taking the sum of the voltage after limiting and the average voltage rating of the submodule and subtracting the average voltage of the capacitor, and passing through a PI control link;

[0118] The DC voltage deviation calculation subunit is used to obtain the actual value of the DC current, subtract the actual value of the DC current from the DC current reference value, and output the DC voltage deviation after passing through the PI control link.

[0119] In an optional embodiment, the output power includes active power and reactive power; the voltage reference value calculation unit 503 is specifically used for:

[0120] According to the active power and the reactive power, a three-phase AC voltage reference value is obtained through double closed-loop vector control.

[0121] In an optional embodiment, the voltage reference value calculation unit 503 is further specifically configured to:

[0122] According to the DC voltage deviation and the three-phase AC voltage reference value, the upper bridge arm voltage reference value and the lower bridge arm voltage reference value are calculated by the following formula:

[0123]

[0124] in, Indicates the upper bridge arm voltage reference value; Indicates the voltage reference value of the lower bridge arm; j=A, B, C; Indicates the DC voltage rating; Indicates the DC voltage deviation; Indicates the three-phase AC voltage reference value;

[0125] The upper bridge arm voltage reference value and the lower bridge arm voltage reference value are used as input voltage reference values ​​that the MMC converter needs to control input.

[0126] In an optional embodiment, the submodule input control unit 504 includes:

[0127] A nearest level approximation modulation unit is used for calculating, for each phase of the MMC converter, the number of upper bridge arm submodules required to be invested in the upper bridge arm according to the upper bridge arm voltage reference value and the capacitor average voltage through nearest level approximation modulation, and the number of lower bridge arm submodules required to be invested in the lower bridge arm according to the lower bridge arm voltage reference value and the capacitor average voltage;

[0128] The input control subunit is used to input the number of each upper bridge arm submodule and the number of each lower bridge arm submodule by controlling the submodule switches of the upper and lower bridge arms to complete the control of the MMC converter.

[0129] As for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the aforementioned method embodiment.

[0130] An embodiment of the present invention further provides an electronic device, the device comprising a processor and a memory:

[0131] The memory is used to store the program code and transmit the program code to the processor;

[0132] The processor is used to execute the inertia support control method of the flexible direct current transmission system of any embodiment of the present invention according to the instructions in the program code.

[0133] An embodiment of the present invention further provides a computer-readable storage medium, which is used to store program code, and the program code is used to execute the inertia support control method of the flexible direct current transmission system of any embodiment of the present invention.

[0134] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0135] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0136] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0137] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0138] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0139] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An inertia support control method for a flexible direct current transmission system, characterized in that: The receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure includes multiple submodule capacitors; The inertia support control method comprises: Obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor; Calculating a capacitor average voltage according to each of the capacitor voltages, and calculating a DC voltage deviation based on the capacitor average voltage; Based on the output power, a three-phase AC voltage reference value is calculated, and an input voltage reference value is calculated by combining the DC voltage deviation and the three-phase AC voltage reference value; The number of submodules that need to be put into operation is calculated according to the input voltage reference value and the capacitor average voltage, and the control of the MMC converter is completed by controlling the number of submodules put into operation.

2. The inertia support control method according to claim 1, characterized in that: The MMC converter is composed of three-phase units A, B, and C connected in parallel, a single phase unit is composed of an upper and a lower bridge arm, and a single bridge arm is composed of N submodules connected in series; the average capacitor voltage is calculated by the following formula: in, Represents the average capacitor voltage; , Respectively represent the capacitor voltages of the upper bridge arm of phase A and the lower bridge arm of phase A submodule; , Respectively represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B; , They represent the capacitor voltages of the C-phase upper bridge arm and the C-phase lower bridge arm submodules respectively.

3. The inertia support control method according to claim 1, characterized in that: The step of calculating the DC voltage deviation based on the capacitor average voltage includes: Based on the capacitor average voltage, a DC voltage deviation is obtained through a submodule average voltage control link.

4. The inertia support control method according to claim 3, characterized in that: The method of obtaining a DC voltage deviation through a submodule average voltage control link based on the capacitor average voltage includes: Obtaining a measured frequency value and a rated frequency value of the AC power grid, and an average rated voltage value of a submodule of the MMC converter; The frequency measured value is subtracted from the frequency rated value, and then multiplied by a preset voltage-frequency correlation coefficient, and after passing through a voltage limiting link, a voltage after limiting is obtained; The sum of the voltage after limiting and the average voltage rating of the submodule is used, and the average voltage of the capacitor is subtracted, and after passing through the PI control link, a DC current reference value is obtained; The actual value of the DC current is obtained, and the actual value of the DC current is subtracted from the DC current reference value. After the PI control link is passed, a DC voltage deviation is output.

5. The inertia support control method according to claim 1, characterized in that: The output power includes active power and reactive power; and the calculating of the three-phase AC voltage reference value based on the output power includes: According to the active power and the reactive power, a three-phase AC voltage reference value is obtained through double closed-loop vector control.

6. The inertia support control method according to any one of claims 1 to 5, characterized in that: The step of calculating the input voltage reference value by combining the DC voltage deviation and the three-phase AC voltage reference value comprises: According to the DC voltage deviation and the three-phase AC voltage reference value, the upper bridge arm voltage reference value and the lower bridge arm voltage reference value are calculated by the following formula: in, Indicates the upper bridge arm voltage reference value; Indicates the voltage reference value of the lower bridge arm; j=A, B, C; Indicates the DC voltage rating; Indicates the DC voltage deviation; Indicates the three-phase AC voltage reference value; The upper bridge arm voltage reference value and the lower bridge arm voltage reference value are used as input voltage reference values ​​that the MMC converter needs to control input.

7. The inertia support control method according to claim 6, characterized in that: The method of calculating the number of submodules to be put into operation according to the input voltage reference value and the capacitor average voltage, and completing the control of the MMC converter by controlling the number of submodules put into operation includes: For each phase of the MMC converter, the number of upper bridge arm submodules required for the upper bridge arm is calculated according to the upper bridge arm voltage reference value and the capacitor average voltage through nearest level approximation modulation, and the number of lower bridge arm submodules required for the lower bridge arm is calculated according to the lower bridge arm voltage reference value and the capacitor average voltage; The control of the MMC converter is completed by controlling the submodule switches of the upper and lower bridge arms to input the number of each upper bridge arm submodule and the number of each lower bridge arm submodule.

8. An inertia support control device for a flexible direct current transmission system, characterized in that: The receiving end of the flexible direct current transmission system adopts an MMC converter topology structure, and a single MMC converter in the MMC converter topology structure includes multiple submodule capacitors; The inertia support control device comprises: A data acquisition unit, used to acquire the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor; a DC voltage deviation calculation unit, configured to calculate an average capacitor voltage according to each of the capacitor voltages, and calculate a DC voltage deviation based on the capacitor average voltage; A voltage reference value calculation unit, configured to calculate a three-phase AC voltage reference value based on the output power, and calculate an input voltage reference value in combination with the DC voltage deviation and the three-phase AC voltage reference value; The submodule input control unit is used to calculate the number of submodules that need to be put into operation according to the input voltage reference value and the capacitor average voltage, and complete the control of the MMC converter by controlling the number of submodules put into operation.

9. An electronic device, characterized in that: The device comprises a processor and a memory: The memory is used to store program codes and transmit the program codes to the processor; The processor is used to execute the inertia support control method of the flexible direct current transmission system according to any one of claims 1 to 7 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program code, and the program code is used to execute the inertia support control method of the flexible direct current transmission system according to any one of claims 1-7.

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