Inertia support control method and system for flexible DC power transmission system

Abstract

The invention belongs to the technical field of grid-connected power electronic equipment, and particularly discloses a flexible direct current power transmission system inertia support control method and system. According to the invention, based on a frequency signal of an AC power grid connected with a receiving end converter station, an energy instruction signal of the receiving end converter station is obtained, and based on the energy instruction signal and a difference signal of an energy measurement value of the receiving end converter station, a first control signal corresponding to a bridge arm voltage DC component is generated. According to the method, an invariant direct-current component in a bridge arm voltage calculation mode in a traditional receiving-end converter station is converted into a controllable quantity, so that control over the direct-current component is introduced, active and accurate control over energy of the receiving-end converter station is achieved, control over the receiving-end converter station is more flexible, independent decoupling of the energy and direct-current voltage of the receiving-end converter station is achieved, and the energy efficiency of the receiving-end converter station is improved. The problem that an existing flexible direct-current power transmission system inertia supporting method can sacrifice direct-current voltage stability is solved, and the active inertia supporting capacity of the flexible direct-current power transmission system is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of grid-connected power electronic equipment, and more specifically, to an inertia support control method and system for a flexible direct current transmission system. Background Art

[0002] Modular Multilevel Converter-based High Voltage Direct Current Transmission (MMC-HVDC) has become the main technical means for the centralized transmission of new energy and the interconnection of asynchronous power grids. However, under the traditional vector control strategy, MMC-HVDC completely decouples the active-frequency dynamics of the AC systems at both ends and cannot actively participate in the inertia support of the system. With the rapid development of new energy, a large number of converter-type power sources are gradually replacing synchronous generators, and the power system is facing the severe challenge of inertia reduction. In order to cope with the above problems, the power system hopes that the flexible DC transmission system has the ability to actively support inertia.

[0003] For grid-following MMC, the existing inertia support method mainly considers introducing measured frequency information for additional control, so that the DC voltage of the MMC is associated with the system frequency or frequency change rate, and the DC voltage reference is adjusted when the frequency fluctuates, forcing the MMC to release or absorb more energy during the disturbance for support. Most of the above methods control energy by controlling the DC voltage under the condition of strong coupling between energy and DC voltage, which has a great impact on the normal operation of the system. When the parameter design is inappropriate or the disturbance is large, it may cause DC voltage instability.

[0004] Some methods start with MMC valve-level control, measure the capacitor voltage in real time and introduce it into the nearest level approximation modulation, and use the characteristics of MMC with redundant sub-modules to dynamically adjust the number of sub-modules according to the change of capacitor voltage, release more capacitor energy, and keep the DC voltage within the rated or allowed range. However, these methods can only passively control the DC voltage near the rated value, and cannot achieve active and precise control of the DC voltage. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present application is to provide an inertia support control method and system for a flexible DC transmission system, aiming to solve the problem that the inertia support method of the existing flexible DC transmission system sacrifices the stability of the DC voltage and can only passively control the DC voltage of the receiving end converter station near the rated value.

[0006] To achieve the above objectives, in a first aspect, the present application provides an inertia support control method for a flexible direct current transmission system, comprising: Based on the frequency signal of the AC power grid connected to the receiving-end converter station in the flexible DC power transmission system, an energy command signal of the receiving-end converter station is obtained, and the receiving-end converter station is a modular multi-level converter; Generate a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; According to the first control signal, the switching devices in each submodule in the receiving-end converter station are controlled to be turned on and off.

[0007] In some embodiments, obtaining the energy command signal of the receiving-end converter station based on the frequency signal of the AC power grid connected to the receiving-end converter station in the flexible DC power transmission system includes: Based on the frequency signal, the energy error value of the receiving-end converter station is obtained; An energy command signal is obtained based on the energy error value and the energy rating of the receiving-end converter station.

[0008] In some embodiments, according to the first control signal, controlling the on and off of the switch devices in each submodule in the receiving-end converter station includes: Based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station, a second control signal corresponding to the differential-mode d-axis voltage is obtained; Based on the grid connection point AC voltage command signal and the grid connection point AC voltage measurement value, a third control signal corresponding to the differential mode q-axis voltage is obtained; Performing an inverse Park transform on the second control signal and the third control signal to obtain a fourth control signal; Based on the circulating current between different bridge arms in the receiving-end converter station, a fifth control signal is obtained; The switching devices in each submodule are controlled to be turned on and off according to the fourth control signal, the fifth control signal and the first control signal.

[0009] In some embodiments, obtaining a second control signal corresponding to the differential-mode d-axis voltage based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station includes: Generate a d-axis current command signal based on a difference signal between the DC voltage command signal and the DC voltage measurement value; A second control signal is generated based on a difference signal between the d-axis current command signal and the d-axis current measurement value.

[0010] In some embodiments, based on the grid connection point AC voltage command signal and the grid connection point AC voltage measurement value, obtaining a third control signal corresponding to the differential mode q-axis voltage includes: Generate a q-axis current command signal based on a grid-connected point AC voltage command signal and a difference signal of a grid-connected point AC voltage measurement value; A third control signal is generated based on a difference signal between the q-axis current command signal and the q-axis current measurement value.

[0011] In some embodiments, obtaining the fifth control signal based on the circulating current between different bridge arms in the receiving-end converter station includes: Performing Park transformation on the circulating current to obtain the measured value of the circulating current d-axis current component and the measured value of the circulating current q-axis current component; generating a sixth control signal corresponding to the common-mode d-axis voltage based on a difference signal between a circulating d-axis current component measurement value and a circulating d-axis current component command signal; generating a seventh control signal corresponding to the common-mode q-axis voltage based on a difference signal between a circulating q-axis current component measurement value and a circulating q-axis current component command signal; Performing inverse Park transformation on the sixth control signal and the seventh control signal to obtain a fifth control signal.

[0012] In a second aspect, the present application provides an inertia support control method system for a flexible direct current transmission system, comprising: A first acquisition module is used to obtain an energy command signal of a receiving-end converter station based on a frequency signal of an AC power grid connected to the receiving-end converter station in the flexible DC power transmission system, where the receiving-end converter station is a modular multi-level converter; A second acquisition module is used to generate a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; The control module is used to control the on and off of the switch devices in each submodule in the receiving-end converter station according to the first control signal.

[0013] In a third aspect, the present application provides an electronic device comprising: at least one memory for storing programs; and at least one processor for executing the programs stored in the memory. When the programs stored in the memory are executed, the processor is used to execute the method described in the first aspect or any embodiments of the first aspect.

[0014] In a fourth aspect, the present application provides a computer-readable storage medium, which stores a computer program. When the computer program runs on a processor, the processor executes the method described in the first aspect or any embodiments of the first aspect.

[0015] In a fifth aspect, the present application provides a computer program product. When the computer program product runs on a processor, the processor executes the method described in the first aspect or any embodiments of the first aspect.

[0016] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art: The inertia support control method and system of the flexible direct current transmission system provided in the present application obtain an energy command signal of the receiving-end converter station based on a frequency signal of an alternating current grid connected to the receiving-end converter station, and generate a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station, convert the unchanged DC component in the traditional bridge arm voltage calculation method in the receiving-end converter station into a controllable quantity, thereby introducing control of the DC component, realizing active and precise control of the energy of the receiving-end converter station, making the control of the receiving-end converter station more flexible, realizing independent decoupling of the energy and DC voltage of the receiving-end converter station, solving the problem that the inertia support method of the existing flexible direct current transmission system sacrifices the stability of the DC voltage, and improving the active inertia support capability of the flexible direct current transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of an inertia support control method for a flexible direct current transmission system provided in an embodiment of the present application; Figure 2 is a schematic structural diagram of a flexible direct current transmission system provided in an embodiment of the present application; Figure 3 is a schematic diagram of the structure of a modular multi-level converter provided in an embodiment of the present application; Figure 4 A structural schematic diagram of virtual inertia control of an inertia support control method for a flexible direct current transmission system provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of the station-level control structure of the receiving-end converter station provided in an embodiment of the present application; Figure 6 It is a schematic diagram of the control effect of the inertia support control method of the flexible direct current transmission system provided in the embodiment of the present application when the system frequency decreases; Figure 7 It is a simulation effect diagram of the embodiment of the present invention provided in the embodiment of the present application, which illustrates that the MMC energy and the DC voltage have a strong coupling relationship under the traditional control; Figure 8 This is a simulation effect diagram of MMC energy-DC voltage decoupling control after adopting the method proposed in this application, provided in an embodiment of this application; Fig. 9 It is a simulation effect diagram of active power output of a flexible direct current transmission system provided by an embodiment of the present application, when the load of the receiving-end power grid is suddenly increased and when the method proposed in the present application is not adopted; Fig.10 It is a frequency simulation effect diagram of a receiving-end power grid without using the method proposed in the present application and using the method proposed in the present application after a sudden increase in the load of the receiving-end power grid provided by an embodiment of the present application; Fig.11It is a structural schematic diagram of an inertia support control system of a flexible direct current transmission system provided in an embodiment of the present application; Fig.12 It is a schematic diagram of the structure of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0019] The term "and / or" in this article is a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The symbol " / " in this article indicates that the associated objects are in an or relationship, for example, A / B means A or B.

[0020] The terms "first" and "second" in the specification and claims herein are used to distinguish different objects rather than to describe a specific order of the objects. For example, a first control signal and a second control signal are used to distinguish different control signals rather than to describe a specific order of the control signals.

[0021] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0022] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more than two.

[0023] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0024] See also Figure 1 An embodiment of the present application provides an inertia support control method for a flexible direct current transmission system, which may include: step 110, step 120 and step 130.

[0025] Step 110 obtains an energy command signal of a receiving-end converter station based on a frequency signal of an AC power grid connected to the receiving-end converter station in the flexible DC power transmission system, where the receiving-end converter station is a modular multilevel converter. Step 120 generates a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; Step 130 controls the on and off of the switch devices in each submodule in the receiving-end converter station according to the first control signal.

[0026] Please see further Figure 2 The flexible DC transmission system provided in the embodiment of the present application includes a sending-end converter station, a sending-end power grid connected to the sending-end converter station, a receiving-end converter station connected to the sending-end converter station through a DC line, and a converter station transformer reactor. X t , Grid Reactance X s The sending-end converter station can convert the AC power transmitted by the sending-end power grid into DC power and transmit it to the receiving-end converter station through the DC line. The receiving-end converter station converts the DC power into AC power and supplies power to the receiving-end power grid.

[0027] like Figure 2 As shown, the receiving-end converter station is directly connected to the AC power grid (i.e., the receiving-end power grid), and can directly detect the frequency signal of the receiving-end power grid and use its own energy for support, which is achieved by implementing virtual inertia control at the energy control front end of the receiving-end converter station.

[0028] Specifically, the receiving-end converter station of the flexible DC transmission system acquires the frequency signal of the receiving-end power grid connected thereto through phase-locked loop detection, and sends the frequency signal to the virtual inertia controller to obtain the energy command signal of the receiving-end converter station.

[0029] In the embodiment of the present application, the receiving-end converter station and the sending-end converter station are both configured as follows: Figure 3 The Modular Multilevel Converter (MMC) shown in FIG. 1 may specifically include submodules, submodule capacitance C 0 , bridge arm resistance R 0 , bridge arm inductance L 0 and grid reactance X s .in, Design redundancy for MMC, is the rated number of sub-modules in the bridge arm, and each sub-module includes 2 switching devices.

[0030] The energy command signal and the energy measurement value of the receiving-end converter station are input into a first proportional integral (PI) controller, which outputs a DC current command signal of the receiving-end converter station, and a difference signal obtained by subtracting the DC current command signal from the DC current measurement value of the receiving-end converter station is input into a second PI controller, which outputs a control signal corresponding to the DC component of the bridge arm voltage of the receiving-end converter station, i.e., a first control signal.

[0031] In the embodiment of the present application, the adjustable proportional coefficient and the adjustable integral time constant in the first PI controller and the second PI controller can be set according to actual needs, and the embodiment of the present application does not specifically limit this.

[0032] According to the first control signal obtained above, a control signal is generated for controlling the switching of the switch devices in each submodule in the receiving end converter station, so that only one of the two switch devices in each submodule is turned on at the same time. In the embodiment of the present application, the switch device adopts an insulated gate bipolar transistor (IGBT).

[0033] The inertia support control method of the flexible direct current transmission system provided in the embodiment of the present application obtains an energy command signal of the receiving-end converter station based on a frequency signal of an alternating current power grid connected to the receiving-end converter station, and generates a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station, converts the unchanged DC component in the traditional bridge arm voltage calculation method in the receiving-end converter station into a controllable quantity, thereby introducing control of the DC component, realizing active and precise control of the energy of the receiving-end converter station, making the control of the receiving-end converter station more flexible, realizing independent decoupling of the energy and DC voltage of the receiving-end converter station, solving the problem that the existing inertia support method of the flexible direct current transmission system sacrifices the stability of the DC voltage, and improving the active inertia support capability of the flexible direct current transmission system.

[0034] Further, in some embodiments, in step 110, obtaining the energy command signal of the receiving-end converter station based on the frequency signal of the AC power grid connected to the receiving-end converter station in the flexible DC power transmission system includes: Based on the frequency signal, the energy error value of the receiving-end converter station is obtained; An energy command signal is obtained based on the energy error value and the energy rating of the receiving-end converter station.

[0035] In the embodiment of the present application, the energy command signal of the receiving-end converter station is obtained by inputting the measured frequency signal of the receiving-end power grid into the virtual inertia controller, which is specifically implemented as follows: Inertia is the property of an object to maintain its own state of motion unchanged, and inertia is a physical quantity that measures the size of inertia. Because the frequency of the power system is determined by the speed of the synchronous generator, and the rotor mass of the synchronous generator is large and has a large inertia, the traditional power system dominated by synchronous generators can more calmly deal with power disturbances, and the frequency change rate is not easy to exceed the limit. As the penetration rate of new energy power generation using power electronics connected to the grid gradually increases and gradually replaces synchronous generators, the inertia of the system will gradually decrease, and the power system faces severe challenges in frequency stability. As the main technical means for the centralized transmission of new energy, flexible direct current transmission is expected to have the ability to actively support the power grid and provide an inertia response similar to that of a synchronous generator. The existing virtual inertia control is to associate the DC voltage of the MMC with the system frequency or the frequency change rate, adjust the DC voltage command signal when the frequency fluctuates, and force the MMC to release or absorb more energy during the disturbance for support. The above methods only control energy by controlling the DC voltage under the condition of strong coupling between energy and DC voltage, which has a great impact on the stability of the DC voltage of the system.

[0036] The embodiment of the present application cooperates with the improvement of station-level control to realize the decoupling control of MMC energy and realize the transformation of inertia support from "indirect voltage support" to "direct energy support". The following is an energy-based virtual inertia control of a flexible DC transmission system designed by analogy with a synchronous generator.

[0037] For synchronous generators, when there is unbalanced power When acting on the rotor, the rotor speed will change to satisfy the following relationship:

[0038] in, is the inertia time constant, is the base capacity, is the rated angular velocity. For MMC, after the energy and DC voltage are decoupled and controlled, the effect of unbalanced power will be directly manifested as the change of MMC energy, that is:

[0039] in, and are the energy measurement value and energy rating of the MMC respectively. If the output of the MMC during frequency fluctuation is the same as that of the synchronous generator, we can get:

[0040] Since the synchronous generator rotor speed Frequency signal of the receiving power grid The energy reference value (i.e., energy command signal) of MMC virtual inertia control based on energy can be obtained from the above formula:

[0041]

[0042] in, is the energy error value of the receiving converter station, is the energy command signal of MMC, is the rated frequency of the power grid. In the embodiment of the present application, Take 50HZ.

[0043] Please see further Figure 4 , the frequency signal of the receiving power grid Send it to the virtual inertia controller and output the energy error value of the receiving converter station , and the energy error value and energy rating Perform cumulative summation to obtain the above energy command signal .

[0044] The inertia support control method of the flexible direct current transmission system provided in the embodiment of the present application directly utilizes energy for inertia support to force the DC voltage to change in a direct and simple manner, and does not occupy the control dimension of the DC voltage, thereby realizing independent and rapid control of energy, and transforming the inertia support from "indirect voltage support" to "direct energy support", thereby improving the DC voltage stability and inertia coordinated control capability of the MMC-HVDC system.

[0045] Further, in some embodiments, in step 130, controlling the on and off of the switch devices in each submodule in the receiving-end converter station according to the first control signal includes: Based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station, a second control signal corresponding to the differential-mode d-axis voltage is obtained; Based on the grid connection point AC voltage command signal and the grid connection point AC voltage measurement value, a third control signal corresponding to the differential mode q-axis voltage is obtained; Performing an inverse Park transform on the second control signal and the third control signal to obtain a fourth control signal; Based on the circulating current between different bridge arms in the receiving-end converter station, a fifth control signal is obtained; The switching devices in each submodule are controlled to be turned on and off according to the fourth control signal, the fifth control signal and the first control signal.

[0046] In the embodiment of the present application, the station-level control of the receiving end converter station consists of four aspects: DC voltage control, AC voltage control, circulating current simulation control and energy control. DC voltage control and AC voltage control belong to the AC side control link of MMC, and circulating current suppression control and energy control belong to the DC side control link of MMC.

[0047] Specifically, the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station are used as inputs of the DC voltage control, and the output of the DC voltage control is a control signal corresponding to the differential-mode d-axis voltage, ie, the second control signal.

[0048] The grid-connected point AC voltage command signal and the grid-connected point AC voltage measurement value are used as inputs of the AC voltage control, and the output of the AC voltage control is a control signal corresponding to the differential-mode q-axis voltage, ie, a third control signal.

[0049] After the second control signal and the third control signal obtained above are subjected to inverse Park transformation, a fourth control signal is obtained, and the fourth control signal is a control signal corresponding to the differential-mode voltage of the bridge arm voltage of the three phases abc.

[0050] The circulating current between different bridge arms in the receiving-end converter station is used as the input of the circulating current suppression control, and the output of the circulating current suppression control is the control signal corresponding to the common-mode voltage of the bridge arm voltages of the three phases abc, that is, the fifth control signal.

[0051] According to the fourth control signal, the fifth control signal and the first control signal obtained above, the command signal of the voltage of each bridge arm (specifically the upper and lower bridge arms) in the receiving-end converter station can be obtained.

[0052] After further processing by voltage balancing and modulation algorithm, the command signals of the upper and lower bridge arm voltages obtained above can obtain switching signals, which can be used to control the on and off of switching devices in each submodule in the receiving-end converter station.

[0053] Furthermore, in some embodiments, in the above steps, obtaining the second control signal corresponding to the differential-mode d-axis voltage based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station includes: Generate a d-axis current command signal based on a difference signal between the DC voltage command signal and the DC voltage measurement value; A second control signal is generated based on a difference signal between the d-axis current command signal and the d-axis current measurement value.

[0054] Please see further Figure 5 At the receiving-end converter station, the phase-locked loop is used to synchronize the output voltage of the converter station with the voltage at the grid connection point and obtain the frequency signal of the receiving-end grid. Figure 5As shown, the station-level control of the receiving-end converter station consists of four aspects: DC voltage control, AC voltage control, circulating current suppression control and energy control.

[0055] Specifically, the DC voltage control consists of a DC voltage outer loop and a d-axis current inner loop: , They are the DC voltage command signal and the DC voltage measurement value of the receiving converter station. The difference signal obtained by subtracting the two is sent to the third PI controller (such as Figure 5 shown ), generates the d-axis current command signal , and the d-axis current measurement value After the difference is made, the difference signal is sent to the fourth PI controller (such as Figure 5 shown ), generates a control signal corresponding to the differential mode d-axis voltage , that is, the second control signal.

[0056] In the embodiment of the present application, the adjustable proportional coefficient and the adjustable integral time constant in the third PI controller and the fourth PI controller can be set according to actual needs, and the embodiment of the present application does not specifically limit this.

[0057] Further, in some embodiments, in the above steps, obtaining the third control signal corresponding to the differential-mode q-axis voltage based on the grid-connected point AC voltage command signal and the grid-connected point AC voltage measurement value includes: Generate a q-axis current command signal based on a grid-connected point AC voltage command signal and a difference signal of a grid-connected point AC voltage measurement value; A third control signal is generated based on a difference signal between the q-axis current command signal and the q-axis current measurement value.

[0058] Please continue to see Figure 5 , the AC voltage control consists of an AC voltage outer loop and a q-axis current inner loop. , They are the grid-connected point AC voltage command signal and the grid-connected point AC voltage measurement value, and the difference signal obtained by subtracting the two is sent to the fifth PI controller (such as Figure 5 shown ), generates the q-axis current command signal , and the q-axis current measurement value After the difference is made, the difference signal is sent to the sixth PI controller (such as Figure 5 shown ), generates a control signal corresponding to the differential mode q-axis voltage , i.e. the third control signal; the control signal generated above , After the inverse Park transformation, the bridge arm voltage differential mode voltage control signal of the abc three-phase is obtained. ( ), that is, the fourth control signal. Figure 5 middle, The grid phase angle locked by the phase-locked loop.

[0059] In the embodiment of the present application, the adjustable proportional coefficient and the adjustable integral time constant in the fifth PI controller and the sixth PI controller can be set according to actual needs, and the embodiment of the present application does not specifically limit this.

[0060] Further, in some embodiments, in the above steps, obtaining the fifth control signal based on the circulating current between different bridge arms in the receiving-end converter station includes: Performing Park transformation on the circulating current to obtain the measured value of the circulating current d-axis current component and the measured value of the circulating current q-axis current component; generating a sixth control signal corresponding to the common-mode d-axis voltage based on a difference signal between a circulating d-axis current component measurement value and a circulating d-axis current component command signal; generating a seventh control signal corresponding to the common-mode q-axis voltage based on a difference signal between a circulating q-axis current component measurement value and a circulating q-axis current component command signal; Performing inverse Park transformation on the sixth control signal and the seventh control signal to obtain a fifth control signal.

[0061] Please continue to see Figure 5 The circulating current of MMC is the negative sequence double frequency component, and the circulating current between different bridge arms in the receiving end converter station is ( )After Park transformation, we get the dq component in the dq-2 coordinate system (including d-axis current component measurement value and q-axis current component measurement value ), in order to suppress it to 0, the d-axis current component command signal , q-axis current component command signal are set to 0, and the d-axis current component command signal The measured value of the d-axis current component The difference signal obtained after the difference is sent to the seventh PI controller (such as Figure 5 shown ), and obtain the control signal corresponding to the common-mode d-axis voltage , i.e. the sixth control signal, which combines the q-axis current component command signal with the q-axis current component measurement value The difference signal obtained after the difference is sent to the seventh PI controller, which outputs the control signal corresponding to the common-mode q-axis voltage ; For the sixth control signal and the seventh control signal After the inverse Park transformation, the common-mode voltage control signal of the bridge arm voltage of the abc three-phase is obtained. , ( ), which is the fifth control signal.

[0062] It should be noted that the embodiment of the present application also introduces energy control, which is achieved by controlling the DC component of the bridge arm voltage. and The difference signal obtained by subtracting the energy command signal and the energy measurement value of the receiving converter station is sent to the first PI controller (such as Figure 5 shown ), output DC current command signal , and measure the actual DC current signal After the difference is made, the difference signal is sent to the second PI controller (such as Figure 5 shown ), the control signal corresponding to the DC component of the output bridge arm voltage , i.e. the first control signal. According to the fourth control signal, the fifth control signal and the first control signal obtained in the above process, the command signal of the upper and lower bridge arm voltages can be obtained. , , follow these rules:

[0063] The command signal of the upper and lower bridge arm voltage is generated , After voltage balancing and modulation algorithms, it can be converted into a switching signal to control the switching of the sub-modules and realize the on and off control of each switching device in the sub-module.

[0064] Please see further Figure 6 , which is the control effect of a flexible DC transmission system inertia support control method provided in this application when the system frequency decreases. Take the case where the frequency decreases and energy needs to be released for support as an example: the system originally operates normally and maintains the rated DC voltage , the system frequency decreases, the energy reference value output by the virtual inertia controller decreases, and the DC component of the bridge arm voltage output by the energy control The redundant submodule is put into operation, and the DC voltage rises , and the DC voltage loop will control the DC voltage tracking instruction, so that the voltage of the sub-modules that are put into operation will drop , releasing sub-energy. In traditional control methods, only the The energy of the block submodule can be utilized, and the present application enables the redundant submodule to be put into use during the support period, and all submodules (total The energy of all blocks is utilized, that is, the energy of the MMC-HVDC system is fully utilized, and the frequency support potential of the MMC-HVDC system is deeply excavated.

[0065] To further illustrate the control effect of the inertia support control method of the flexible DC transmission system proposed in this application, a specific implementation example is described below: This implementation method takes a 1100MW flexible DC transmission system connecting two AC power grid systems as an example to conduct simulation research. Since the focus is on the supporting capacity of the flexible DC transmission system for the receiving system, the sending system is simplified to an infinite system. The parameters of the flexible DC transmission system and the receiving system are shown in Table 1. The schematic diagram of the system is shown in Figure 2 shown.

[0066] Table 1

[0067] Verification Aspect 1: MMC energy-DC voltage decoupling capability of the proposed solution: Scenario I: Traditional control where energy and DC voltage are not decoupled; Scenario II: The energy and DC voltage decoupling control proposed in this application.

[0068] Figure 7 It is a simulation effect diagram that illustrates the strong coupling relationship between MMC energy and DC voltage under traditional control. Figure 7 It is shown that under the traditional control without decoupling, the energy of MMC is coupled with the DC voltage, and only the voltage of MMC can be controlled, and the energy of MMC changes accordingly.

[0069] Figure 8 This is a simulation effect diagram of the decoupling control of MMC energy and DC voltage after adopting the method proposed in this application, wherein (a) controls the energy to change while the DC voltage remains unchanged, and (b) controls the DC voltage to change while the energy remains unchanged. Figure 8 It is shown that under the decoupling control proposed in the present application, the energy and DC voltage of the MMC are decoupled. Within a certain range, the energy or DC voltage can be controlled separately, and the other can still be controlled at the original value.

[0070] Verification aspect 2: Supporting effect of the method proposed in this application: In the simulation, there was originally 1000MW of active load in the receiving grid. At 20s, the active load suddenly increased by 100MW (10%) to verify the inertia support capacity of the flexible DC transmission system using the proposed strategy. Specifically, the scenarios in the embodiment are set as follows: Scenario I: No inertia support strategy is used; Scenario II: Using the traditional non-decoupled inertia control strategy; Scenario III: Using the method proposed in this application.

[0071] Fig. 9 It is a simulation effect diagram of the active power output of the flexible DC transmission system without using the method proposed in the present application and using the method proposed in the present application after a sudden increase in the load on the receiving-end power grid; it can be seen that the flexible DC transmission system without using the inertia support strategy has almost no active response; the use of the traditional non-decoupled collaborative control strategy has the ability to generate more active power for support during frequency disturbances; using the method proposed in the present application, the flexible DC transmission system provides a higher active power peak and a longer support time under the same disturbance, and the inertia support capability is improved.

[0072] Fig.10 The embodiment of the present application provides a frequency simulation effect diagram of the receiving-end power grid without using the method proposed in the present application and using the method proposed in the present application after a sudden increase in the load on the receiving-end power grid; it can be seen that under the same load disturbance, the frequency change rate is the largest and the lowest frequency point is the lowest when the inertia support strategy is not used; the traditional non-decoupling strategy has a certain improvement on the frequency response; and when the method proposed in the present application is used, the frequency change rate of the system is further reduced, and the lowest frequency point is further improved.

[0073] In summary, compared with the prior art, this application has the following advantages: The introduction of control over the DC component makes the control of the MMC more flexible, making independent decoupling control of its energy and DC voltage possible; the realization of independent and rapid control over energy enables the inertia support to shift from "indirect voltage support" to "direct energy support", further releasing the energy stored in the redundant sub-modules and improving the support capacity; the traditional vector control structure of the existing flexible DC transmission system is retained, and the original modulation algorithm does not require any changes, which has strong versatility.

[0074] The inertia support control method for the flexible DC transmission system provided in the embodiment of the present application only converts the DC component of the bridge arm voltage into a controllable quantity, introduces an energy controller therefor, retains the traditional vector control structure of the existing flexible DC transmission system, and does not require any changes to the original modulation algorithm, and has strong versatility.

[0075] The inertia support control system of the flexible direct current transmission system provided in the present application is described below. The inertia support control system of the flexible direct current transmission system described below and the inertia support control method of the flexible direct current transmission system described above can be referred to each other.

[0076] See also Fig.11 An embodiment of the present application provides an inertia support control system for a flexible direct current transmission system, which may include: a first acquisition module 1110 , a second acquisition module 1120 and a control module 1130 .

[0077] A first acquisition module 1110 is configured to obtain an energy command signal of a receiving-end converter station based on a frequency signal of an AC power grid connected to the receiving-end converter station in the flexible DC power transmission system, wherein the receiving-end converter station is a modular multilevel converter; The second acquisition module 1120 is used to generate a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; The control module 1130 is used to control the on and off of the switch devices in each submodule in the receiving-end converter station according to the first control signal.

[0078] The inertia support control system of the flexible direct current transmission system provided in the embodiment of the present application obtains an energy command signal of the receiving-end converter station based on a frequency signal of an alternating current grid connected to the receiving-end converter station, and generates a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station, converts the unchanged DC component in the traditional bridge arm voltage calculation method in the receiving-end converter station into a controllable quantity, thereby introducing control of the DC component, realizing active and precise control of the energy of the receiving-end converter station, making the control of the receiving-end converter station more flexible, realizing independent decoupling of the energy and DC voltage of the receiving-end converter station, solving the problem that the inertia support method of the existing flexible direct current transmission system sacrifices the stability of the DC voltage, and improving the active inertia support capability of the flexible direct current transmission system.

[0079] It can be understood that the detailed functional implementation of each of the above-mentioned units / modules can be found in the introduction of the aforementioned method embodiment, and will not be repeated here.

[0080] It should be understood that the above-mentioned device is used to execute the method in the above-mentioned embodiment. The implementation principle and technical effect of the corresponding program module in the device are similar to those described in the above-mentioned method. The working process of the device can refer to the corresponding process in the above-mentioned method, which will not be repeated here.

[0081] Based on the method in the above embodiment, the present application embodiment provides an electronic device, see Fig.12 The electronic device may include: a processor 1210, a communication interface 1220, a memory 1230 and a communication bus 1240, wherein the processor 1210, the communication interface 1220 and the memory 1230 communicate with each other via the communication bus 1240. The processor 1210 may call the logic instructions in the memory 1230 to execute the method in the above embodiment.

[0082] In addition, the logic instructions in the above-mentioned memory 1230 can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes a number of 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 application.

[0083] Based on the method in the above embodiment, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program runs on a processor, the processor executes the method in the above embodiment.

[0084] Based on the method in the above embodiment, an embodiment of the present application provides a computer program product. When the computer program product runs on a processor, the processor executes the method in the above embodiment.

[0085] It is understandable that the processor in the embodiment of the present application may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0086] The method steps in the embodiments of the present application can be implemented by hardware or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, mobile hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC.

[0087] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions may be transmitted from a website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state drive (SSD)), etc.

[0088] It should be understood that the various numerical numbers involved in the embodiments of the present application are only used for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0089] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for controlling inertia support of a flexible direct current transmission system, characterized in that: include: Based on a frequency signal of an AC power grid connected to a receiving-end converter station in the flexible DC power transmission system, an energy command signal of the receiving-end converter station is obtained, wherein the receiving-end converter station is a modular multi-level converter; Generate a first control signal corresponding to the DC component of the bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; According to the first control signal, the switching devices in each submodule in the receiving-end converter station are controlled to be turned on and off.

2. The inertia support control method of a flexible DC transmission system according to claim 1, characterized in that: The step of obtaining the energy command signal of the receiving-end converter station based on the frequency signal of the AC power grid connected to the receiving-end converter station in the flexible DC power transmission system comprises: Based on the frequency signal, obtaining an energy error value of the receiving-end converter station; The energy command signal is obtained based on the energy error value and the energy rating of the receiving-end converter station.

3. The inertia support control method of a flexible DC transmission system according to claim 1, characterized in that: According to the first control signal, controlling the switching devices in each submodule in the receiving-end converter station to be turned on and off includes: Based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station, a second control signal corresponding to the differential-mode d-axis voltage is obtained; Based on the grid connection point AC voltage command signal and the grid connection point AC voltage measurement value, a third control signal corresponding to the differential mode q-axis voltage is obtained; Performing an inverse Park transform on the second control signal and the third control signal to obtain a fourth control signal; Based on the circulating current between different bridge arms in the receiving-end converter station, a fifth control signal is obtained; The switching devices in each submodule are controlled to be turned on and off according to the fourth control signal, the fifth control signal and the first control signal.

4. The inertia support control method of a flexible DC transmission system according to claim 3, characterized in that: The obtaining of the second control signal corresponding to the differential-mode d-axis voltage based on the DC voltage command signal and the DC voltage measurement value of the receiving-end converter station comprises: generating a d-axis current command signal based on the DC voltage command signal and a difference signal of the DC voltage measurement value; The second control signal is generated based on a difference signal between the d-axis current command signal and the d-axis current measurement value.

5. The inertia support control method of a flexible DC transmission system according to claim 3, characterized in that: The method of obtaining a third control signal corresponding to the differential-mode q-axis voltage based on the grid-connected point AC voltage command signal and the grid-connected point AC voltage measurement value comprises: Generate a q-axis current command signal based on the grid connection point AC voltage command signal and the difference signal of the grid connection point AC voltage measurement value; The third control signal is generated based on a difference signal between the q-axis current command signal and the q-axis current measurement value.

6. The inertia support control method of a flexible DC transmission system according to claim 3, characterized in that: The obtaining of the fifth control signal based on the circulating current between different bridge arms in the receiving-end converter station comprises: Performing Park transformation on the circulating current to obtain a measured value of a circulating current d-axis current component and a measured value of a circulating current q-axis current component; generating a sixth control signal corresponding to the common-mode d-axis voltage based on a difference signal between a circulating d-axis current component measurement value and a circulating d-axis current component command signal; generating a seventh control signal corresponding to the common-mode q-axis voltage based on a difference signal between a circulating q-axis current component measurement value and a circulating q-axis current component command signal; Performing inverse Park transformation on the sixth control signal and the seventh control signal to obtain the fifth control signal.

7. A method and system for controlling inertia support of a flexible direct current transmission system, characterized in that: include: A first acquisition module is used to obtain an energy command signal of a receiving-end converter station based on a frequency signal of an AC power grid connected to the receiving-end converter station in the flexible DC power transmission system, wherein the receiving-end converter station is a modular multi-level converter; A second acquisition module, configured to generate a first control signal corresponding to a DC component of a bridge arm voltage based on a difference signal between the energy command signal and the energy measurement value of the receiving-end converter station; A control module is used to control the on and off of the switch devices in each submodule in the receiving-end converter station according to the first control signal.

8. An electronic device, characterized in that: include: at least one memory for storing a computer program; At least one processor is used to execute the program stored in the memory. When the program stored in the memory is executed, the processor is used to execute the method according to any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program runs on a processor, the processor is caused to execute the method according to any one of claims 1 to 6.

10. A computer program product, characterized in that When the computer program product runs on a processor, the processor is caused to execute the method according to any one of claims 1 to 6.

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