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

Abstract

The present invention discloses an inertia support control method, device, equipment and medium for a flexible direct current transmission system, which is used to solve the technical problem of delay in the inertia support call of current renewable energy. 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 sub-module capacitors; the method includes: obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each sub-module capacitor; calculating the average capacitor voltage based on each capacitor voltage, and calculating the DC voltage deviation based on the capacitor average voltage; calculating the three-phase AC voltage reference value based on the output power, and calculating the input voltage reference value by combining the DC voltage deviation and the three-phase AC voltage reference value; calculating the number of sub-modules that need to be put into use based on the input voltage reference value and the average capacitor voltage, and completing the control of the MMC converter by controlling the number of sub-modules put into use.

Description

Technical Field

[0001] The present invention relates to the technical field of novel 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 have been connected to the grid, changing the grid's operating characteristics. Under traditional control strategies, power electronic equipment provides little inertia. Therefore, scholars at home and abroad have proposed grid-based control strategies to provide power electronic equipment with inertia support capabilities. Inertia support refers to the ability to maintain system frequency stability in a power system through the rotational inertia of rotating machinery (such as generators). When load changes or power generation fluctuates in the power system, the system frequency is affected. Inertia support can provide a buffer mechanism, helping the system maintain frequency stability for a short period of time until other control measures (such as frequency regulation services) take effect.

[0003] Currently, inertia support for renewable energy sources primarily comes from power backup or additional energy storage. However, with this approach, once the power system changes or fluctuates, inertia support is difficult to obtain in a timely manner due to call delays. This makes it difficult to maintain system frequency stability, potentially adversely affecting 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 inertia support of current new energy.

[0005] The present invention provides an inertia support control method 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 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 an average capacitor voltage according to each of the capacitor voltages, and calculating a DC voltage deviation based on the average capacitor 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 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 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 and a lower bridge arm combined, 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; 、 Represent the capacitor voltages of the upper bridge arm and lower bridge arm submodules of phase A respectively; 、 Represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B respectively; 、 Represent the capacitor voltages of the C-phase upper bridge arm and C-phase lower bridge arm sub-modules respectively.

[0013] Optionally, 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 voltage rated value of the submodules 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 limited voltage is obtained;

[0018] The DC current reference value is obtained by subtracting the average capacitor voltage from the sum of the voltage after limiting and the average voltage rating of the submodule, and then passing the sum through a PI control link.

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

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

[0021] A three-phase AC voltage reference value is obtained according to the active power and the reactive power 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 lower bridge arm voltage reference value; 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 need to be controlled for inputting of the MMC converter.

[0027] Optionally, the calculating the number of submodules required 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, includes:

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

[0030] The present invention further 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, configured 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 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 average capacitor voltage, and complete the control of the MMC converter by controlling the number of submodules put into operation.

[0035] The present invention further provides an electronic 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, 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 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, and a single MMC converter in the MMC converter topology contains multiple submodule capacitors. The method includes: 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 based on the voltages of each capacitor, 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 that need to be put into operation based on 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. Thus, by directly calling the energy of the capacitor 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

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

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

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

[0045] Figure 4 The figure is a schematic diagram of the overall flow of an inertia support control method for a flexible DC transmission system;

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

[0047] 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 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 making creative work are within the scope of protection of the present invention.

[0049] As an example, current renewable energy inertia support energy primarily comes from power reserve or additional energy storage. More specifically, inertia support is provided to the receiving grid by mobilizing energy from the sending end or additional energy storage at the sending end. Flexible direct current (FDC) transmission systems (FDCs) are generally used for long-distance power transmission, and it takes time for the receiving grid's status to be transmitted to the sending end. This inertia support provided by mobilizing energy from the sending end is subject to a time delay. This means that if the power system changes or fluctuates, timely inertia support will be difficult to obtain due to the latency, making it difficult to maintain system frequency stability, potentially adversely impacting system operation.

[0050] Further analysis reveals that, unlike new energy converters, flexible DC transmission systems typically employ a modular multilevel topology. Submodule capacitors store a significant amount of energy, and the number of submodules is large. Therefore, submodule energy can be utilized for inertia support by switching them on and off.

[0051] Therefore, one of the core invention points of the embodiment of the present invention is: in response to the shortcomings of the current technology, a method for controlling inertia support 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 of 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 a high-voltage flexible direct current transmission system usually adopts a modular multilevel converter (MMC) topology. N submodules 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 submodule capacitors. In other words, the MMC converter is composed of three-phase units A, B, and C connected 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 submodules connected in series. This structural feature enables the MMC converter to store a large amount of capacitive energy. In an embodiment of the present invention, active support is achieved for the inertia of the AC power grid by calling on the submodule capacitor energy.

[0053] Reference Figure 1 , shows a flowchart of the steps of an inertia support control method for 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 on 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. During normal operation of the flexible direct current transmission system, the active power and reactive power are controlled to set values.

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

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

[0058] (1)

[0059] in, Represents the average capacitor voltage; 、 Represent the capacitor voltages of the upper bridge arm and lower bridge arm submodules of phase A respectively; 、 Represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B respectively; 、 Represent the capacitor voltages of the C-phase upper bridge arm and C-phase lower bridge arm sub-modules 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 capacitance 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 DC transmission system simulates the inertia response characteristics of the synchronous machine through control. 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 in the 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; 、 are the voltage upper and lower limits of the limiting link respectively; PI (Proportional-Integral Controller) is the 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 average capacitor voltage. This can be achieved by obtaining the DC voltage deviation through a sub-module average voltage control link based on the average capacitor voltage.

[0077] More specifically, combined 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 multiplied by the preset voltage-frequency correlation coefficient , after the voltage limiting link ( ~ ) to obtain the voltage after clipping; the voltage after clipping 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 made zero, as shown in the following formula (7):

[0079] (7)

[0080] By taking the derivative of equation (7), we can get equation (6). 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 values Stay consistent.

[0081] Step 103: Calculate a three-phase AC voltage reference value based on the output power, and calculate an input voltage reference value 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 by double closed-loop vector control based on the active power and reactive power output from 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 lower bridge arm voltage reference value; 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.

[0089] Step 104 : Calculate the number of submodules that need to be put into operation according to the input voltage reference value and the average capacitor voltage, and complete 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 precisely controls the output voltage of the MMC converter by selecting the voltage level combination that is closest to the desired output voltage. Output voltage regulation is achieved by controlling the activation and deactivation 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. It can be as follows: for each phase of the MMC converter, the nearest level approximation modulation is used to adjust the upper arm voltage reference value. and the average capacitor voltage , calculate the number of upper arm submodules required for the upper 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 the following formula (9):

[0092] (9)

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

[0094] Then, the MMC converter can be controlled by controlling 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.

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

[0096] In an embodiment of the present invention, an additional control strategy is employed to independently adjust the average voltage value of the terminal module capacitors of the flexible direct current transmission system and directly call upon the energy of the submodule capacitors to achieve inertia support for the power grid without affecting the normal control functions of the flexible direct current transmission system. Compared to the sending-end energy call method, this method can significantly reduce call latency and achieve faster response. Furthermore, compared to methods that call upon sending-end energy or configure additional energy storage for inertia support, the method provided by the present invention can save additional configuration costs and achieve better economic efficiency.

[0097] For better explanation, refer to Figure 4 , which shows a schematic diagram of the overall flow of an inertia support control method for a flexible DC transmission system provided by an embodiment of the present invention. It should be noted that this embodiment only briefly describes the general flow of inertia support control for a flexible DC transmission system. The specific implementation of each step can be understood by referring to the relevant content in the aforementioned embodiments and will not be elaborated here. It should be understood that the present invention is not limited to this.

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

[0099] Step 402: Calculate the average capacitor voltage based on the voltages of the individual capacitors, and obtain a DC voltage deviation through a 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 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, the number of upper arm submodules required for the upper arm is calculated based on the upper arm voltage reference value and the average capacitor voltage through nearest level approximation modulation, and the number of lower arm submodules required for the lower arm is calculated based on the lower arm voltage reference value and the average capacitor voltage.

[0103] Step 406: Control the MMC converter by controlling the submodule switches of the upper and lower bridge arms to switch on the number of upper bridge arm submodules and the number of lower bridge arm submodules.

[0104] Reference Figure 5 , shows a structural block diagram of an inertia support control device for a flexible direct current transmission system provided by an embodiment of the present invention. 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 sub-module capacitors; the inertia support control device may specifically include:

[0105] The data acquisition unit 501 is configured 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 an average capacitor voltage according to the capacitor voltages, and calculate a DC voltage deviation based on the average capacitor voltage;

[0107] A voltage reference value calculation unit 503 is configured to calculate a three-phase AC voltage reference value based on the output power, and calculate an input voltage reference value by combining 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 average capacitor 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 lower bridge arm combined, and a single bridge arm is composed of N submodules connected in series; the average capacitor voltage is calculated using the following formula:

[0110]

[0111] in, Represents the average capacitor voltage; 、 Represent the capacitor voltages of the upper bridge arm and lower bridge arm submodules of phase A respectively; 、 Represent the capacitor voltages of the upper bridge arm of phase B and the lower bridge arm of phase B respectively; 、 Represent the capacitor voltages of the C-phase upper bridge arm and C-phase lower bridge arm sub-modules respectively.

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

[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, configured to acquire a measured frequency value and a rated frequency value of the AC power grid, and an average voltage rated value of the submodules of the MMC converter;

[0116] a voltage limiting unit, configured to obtain a limited voltage by subtracting the rated frequency value from the measured frequency 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 subtracting the average capacitor voltage from the sum of the clipped voltage and the average voltage rating of the submodule, and performing a PI control step therethrough;

[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 configured to:

[0120] A three-phase AC voltage reference value is obtained according to the active power and the reactive power 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 lower bridge arm voltage reference value; 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 need to be controlled for inputting of the MMC converter.

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

[0127] a nearest level approximation modulation unit, configured to calculate, for each phase of the MMC converter, the number of upper bridge arm submodules required for the upper bridge arm according to the upper bridge arm voltage reference value and the average capacitor voltage, and the number of lower bridge arm submodules required for the lower bridge arm according to the lower bridge arm voltage reference value and the average capacitor voltage, through nearest level approximation modulation;

[0128] The input control subunit is used to control the number of upper bridge arm submodules and the number of lower bridge arm submodules 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 including a processor and a memory:

[0131] The memory is used to store program codes and transmit the program codes 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 according to any embodiment of the present invention.

[0134] Those skilled in the art will 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 merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interface, device or unit, which can be electrical, mechanical or other forms.

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

[0137] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0138] If the integrated unit is implemented as 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, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[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 above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can 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. A method for controlling inertia support of a flexible DC 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 sub-module capacitors; The inertia support control method includes: Obtaining the output power of the AC side of the MMC converter and the capacitor voltage of each submodule capacitor; Calculating an average capacitor voltage according to each of the capacitor voltages, and calculating a DC voltage deviation based on the average capacitor 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 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 submodules put into operation.

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

3. The inertia support control method according to claim 1, characterized in that: The calculating of 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 voltage rated value of the submodules 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 limited voltage is obtained; The DC current reference value is obtained by subtracting the average capacitor voltage from the sum of the voltage after limiting and the average voltage rating of the submodule, and then passing the sum through a PI control link. The actual value of the DC current is obtained, the actual value of the DC current is subtracted from the DC current reference value, and after passing through a PI control link, 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: A three-phase AC voltage reference value is obtained according to the active power and the reactive power 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 calculating the input voltage reference value by combining the DC voltage deviation and the three-phase AC voltage reference value includes: 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 lower bridge arm voltage reference value; 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 need to be controlled for inputting of the MMC converter.

7. The inertia support control method according to claim 6, characterized in that: The step of calculating the number of submodules required 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 includes: For each phase of the MMC converter, calculating, by nearest level approximation modulation, the number of upper arm submodules required for the upper arm according to the upper arm voltage reference value and the average capacitor voltage, and calculating the number of lower arm submodules required for the lower arm according to the lower arm voltage reference value and the average capacitor 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 the upper bridge arm submodules and the number of the lower bridge arm submodules.

8. An inertia support control device for a flexible DC 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 sub-module capacitors; The inertia support control device includes: A data acquisition unit, configured 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 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 average capacitor 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 includes a processor and a memory: The memory is used to store program code and transmit the program code 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 to 7.

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