A frequency support method and device based on MMC-MTDC system

Abstract

The present application relates to the technical field of power system, disclose a kind of frequency support method and device based on MMC-MTDC system.The method comprises: based on the frequency variation information of detected inland receiving terminal power grid, adjust inland receiving terminal converter station DC voltage;In the variation process of inland receiving terminal converter station DC voltage, based on the DC voltage of sending terminal converter station collected back to obtain the frequency deviation estimation data of inland receiving terminal power grid;Based on the frequency support model of minimum frequency support cost construction, and according to the frequency deviation estimation data of inland receiving terminal power grid according to the constraint condition of pre-construction frequency support model is solved to obtain the frequency support strategy containing offshore wind power optimal support power and multi-energy integrated optimal support power;Based on the output adjustment of sending terminal system according to frequency support strategy, to provide frequency support for inland receiving terminal power grid.The present application improves the frequency support reliability and flexibility of MMC-MTDC system to inland receiving terminal power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to a frequency support method and device based on an MMC-MTDC system. BACKGROUND

[0002] With the continuous rise of new energy power generation in the power system, the power grid faces many challenges such as insufficient inertia and weakened frequency regulation capacity. Especially under the background of high proportion of offshore wind power access, due to the inherent uncertainty and isolation of offshore wind power system, it is difficult for it to quickly perceive and respond in time and effectively when the power grid is disturbed in frequency, not only can it not provide frequency support for the power grid, but the fluctuation of its own output may even become a new frequency disturbance source, affecting the safe and stable operation of the power grid.

[0003] At present, the modular multilevel converter type multi-terminal direct current transmission system (MMC-MTDC) is widely used in high-power long-distance new energy power transmission scenarios as the mainstream implementation of multi-terminal flexible direct current transmission system, because it has the advantages of flexible power regulation, high transmission efficiency, and can realize multi-source and multi-load interconnection. However, the application of the existing MMC-MTDC system focuses on the optimization of energy transmission function, such as improving transmission capacity, reducing loss, and improving power flow distribution, and few studies focus on its potential role in grid frequency support, and its control ability in maintaining system frequency stability is not fully tapped. SUMMARY

[0004] The purpose of the present application is to break through the functional limitations of the existing MMC-MTDC system and fully exert its active response capability to power grid frequency disturbance. In order to achieve the above purpose, the present application provides a frequency support method and device based on an MMC-MTDC system.

[0005] In a first aspect, the present application provides a frequency support method based on an MMC-MTDC system, wherein the MMC-MTDC system includes a receiving end system and a sending end system.

[0006] The receiving end system includes an inland receiving end power grid and an inland receiving end converter station, and the sending end system includes an offshore wind power sending system and a land multi-energy integrated system, and the offshore wind power sending system and the land multi-energy integrated system each include a corresponding sending end converter station.

[0007] The frequency support method based on the MMC-MTDC system includes:

[0008] Based on the detected frequency change information of the inland receiving end power grid, the DC voltage of the inland receiving end converter station is adjusted.

[0009] In the process of the change of the DC voltage of the inland receiving end converter station, the frequency deviation estimation data of the inland receiving end power grid is obtained based on the collected DC voltage of the sending end converter station.

[0010] The frequency support model is constructed with the lowest frequency support cost of the sending end system as an objective function, the constraint conditions of the frequency support model are determined based on the safety boundary of the MMC-MTDC system and the frequency support demand of the inland receiving end power grid, and the frequency support model is solved according to the frequency deviation estimation data of the inland receiving end power grid and the constraint conditions to obtain a frequency support strategy including optimal support power of offshore wind power and optimal support power of multi-energy integration.

[0011] The output of the sending end system is adjusted based on the frequency support strategy to provide frequency support for the inland receiving end power grid.

[0012] Preferably, the adjustment of the DC voltage of the inland receiving end converter station based on the detected frequency change information of the inland receiving end power grid comprises:

[0013] The DC voltage of the inland receiving end converter station is adjusted according to the droop characteristic based on the detected frequency change information of the inland receiving end power grid.

[0014] Preferably, the obtaining of the frequency deviation estimation data of the inland receiving end power grid based on the collected DC voltage of the sending end converter station in the process of the change of the DC voltage of the inland receiving end converter station comprises:

[0015] In the process of the change of the DC voltage of the inland receiving end converter station, the frequency deviation estimation value of the inland receiving end power grid is obtained based on the collected DC voltage of the sending end converter station, the initial value of the DC voltage of the inland receiving end converter station and the predefined droop coefficient, wherein the DC voltage of the sending end converter station is the DC voltage of the offshore sending end converter station or the DC voltage of the onshore sending end converter station.

[0016] Preferably, the construction of the frequency support model with the lowest frequency support cost of the sending end system as an objective function, the determination of the constraint conditions of the frequency support model based on the safety boundary of the MMC-MTDC system and the frequency support demand of the inland receiving end power grid, and the solving of the frequency support model according to the frequency deviation estimation data of the inland receiving end power grid and the constraint conditions to obtain a frequency support strategy including optimal support power of offshore wind power and optimal support power of multi-energy integration, comprise:

[0017] The objective cost function is constructed based on the minimization of the frequency support cost, and the frequency support model is obtained by constraining the objective cost function;

[0018] Based on the inland receiving-end power grid frequency deviation estimation data updated in each time step, the frequency support model is solved to obtain the frequency support strategy containing the optimal offshore wind power support power and the optimal multi-energy integration support power in the time step.

[0019] Preferably, the target cost function is constructed based on the minimum frequency support cost, and the frequency support model is obtained by constraining the target cost function, including:

[0020] The frequency support cost is obtained based on the sending-end support cost and the sending-end support reward, and the target cost function is constructed by minimizing the frequency support cost;

[0021] The target cost function is constrained based on the pre-constructed safe operation constraint condition and support efficiency constraint condition to obtain the frequency support model.

[0022] Preferably, the frequency support cost is obtained based on the sending-end support cost and the sending-end support reward, and the target cost function is constructed by minimizing the frequency support cost, including:

[0023] The frequency support cost is obtained by differentiating the sending-end support cost and the sending-end support reward, and the target cost function is constructed by minimizing the frequency support cost;

[0024] The sending-end support cost includes offshore wind power support cost and multi-energy integration support cost, the offshore wind power support cost is constructed based on rotor kinetic energy loss, mechanical wear and tear, and wind turbine power generation loss, the multi-energy integration support cost is constructed based on energy storage cycle loss and unit regulation cost, and the sending-end support reward is constructed based on support power deviation and reward weight coefficient.

[0025] Preferably, the safe operation constraint condition includes sending-end power output constraint condition, sending-end energy change constraint condition, and sending-end power change rate constraint condition, and the support efficiency constraint condition includes minimum virtual inertia constraint condition.

[0026] Preferably, the sending-end system is adjusted based on the frequency support strategy to provide frequency support for the inland receiving-end power grid, including:

[0027] During the output adjustment, the state of the sending-end system is detected, and if the sending-end system is detected to have an abnormality, the frequency support for the inland receiving-end power grid is stopped.

[0028] Preferably, during the output adjustment, the state of the sending-end system is detected, and if the sending-end system is detected to have an abnormality, the frequency support for the inland receiving-end power grid is stopped, including:

[0029] In the process of performing the state detection, if it is detected that the sending end system is in an abnormal condition, it is determined that the sending end system has an abnormality, wherein the abnormal condition includes that the sending end power grid frequency fluctuation is lower than a protection threshold, the sending end system is in a start-stop or fault isolation stage.

[0030] In a second aspect, an embodiment of the present application provides a frequency support device based on an MMC-MTDC system, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and when the processor executes the computer program, the frequency support method based on the MMC-MTDC system is implemented.

[0031] Compared with the prior art, the frequency support method and device based on the MMC-MTDC system has the beneficial effects that when the frequency of the inland receiving end power grid is disturbed, the frequency information is transmitted through the adjustment of the DC voltage of the inland receiving end converter station, the frequency deviation is inversely deduced according to the voltage of the sending end converter station, and the power collaborative distribution of the offshore wind power sending out system and the land multi-energy integrated system is realized by combining the frequency support model of the minimum support cost. The frequency information is directly transmitted through the DC voltage signal, the time delay problem of the traditional frequency data transmission depending on the communication link is reduced, the optimal distribution of the support power is realized by accurately constructing the frequency support model including the support cost and the dynamic constraint, the frequency regulation economy and the response efficiency are taken into account, meanwhile, the frequency stability margin of the inland receiving end power grid in the high proportion of new energy access scenario is effectively improved by means of the multi-resource collaboration and the dynamic adjustment mechanism of the sending end system, and the frequency support reliability and flexibility of the MMC-MTDC system to the inland receiving end power grid are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a flowchart of the frequency support method based on the MMC-MTDC system;

[0033] Figure 2 is a structural schematic diagram of the MMC-MTDC system;

[0034] Figure 3 is a flowchart of the frequency support strategy;

[0035] Figure 4 is a structural schematic diagram of the device;

[0036] REFERENCE NUMERALS:

[0037] 1, receiving end system; 2, offshore wind power sending-out system; 3, onshore multi-energy integration system; 4, DC overhead line; 5, DC submarine cable; 11, inland receiving end power grid; 12, inland receiving end converter station; 13, inland receiving end bus; 21, offshore sending end converter station; 22, offshore sending end converter station; 23, offshore wind farm; 24, offshore wind farm; 31, onshore sending end AC power grid; 32, multi-source energy cluster; 33, onshore sending end bus; 34, onshore sending end converter station; 35, collection line; 5000, device; 5001, processor; 5002, bus; 5003, memory; 5004, transceiver. DETAILED DESCRIPTION

[0038] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not intended to limit the scope of the present application.

[0039] In the description of the present application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as those commonly understood by those skilled in the art. The terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0040] As shown in Figure 1 , it is a flowchart of a frequency support method based on an MMC-MTDC system according to an embodiment of the present application. The flowchart shows in detail the key steps of realizing frequency support based on the MMC-MTDC system, which corresponds to the functional division in the MMC-MTDC system.

[0041] As shown in Figure 2 , it is a structural schematic diagram of an MMC-MTDC system according to an embodiment of the present application. Referring to Figure 2 , the MMC-MTDC system according to an embodiment of the present application includes a receiving end system 1 and a sending end system.

[0042] Specifically, the receiving end system includes an inland receiving end power grid 11 and an inland receiving end converter station 12, the sending end system includes an offshore wind power sending-out system 2 and an onshore multi-energy integration system 3, and the offshore wind power sending-out system and the onshore multi-energy integration system each include a corresponding sending end converter station.

[0043] The topological structure of the MMC-MTDC system according to an embodiment of the present application will be described below: Figure 2

[0044] The receiving end system includes an inland receiving end power grid 11, an inland receiving end converter station 12 and an inland receiving end bus 13, and the inland receiving end power grid is connected with the inland receiving end converter station through the inland receiving end bus.​

[0045] The offshore wind power transmission system comprises an offshore sending-end converter station 21, an offshore sending-end converter station 22, an offshore wind farm 23 and an offshore wind farm 24. The offshore wind farm 23 is connected with the offshore sending-end converter station 21, and the offshore wind farm 24 is connected with the offshore sending-end converter station 22.

[0046] The onshore multi-energy integrated system comprises an onshore sending-end AC power grid 31, a multi-source energy cluster 32, an onshore sending-end collection bus 33, an onshore sending-end converter station 34 and a collection line 35. The onshore sending-end AC power grid and the multi-source energy cluster are connected with the onshore sending-end converter station through the onshore sending-end collection bus, the onshore sending-end converter station is connected with the inland receiving-end converter station through the DC overhead line 4, and the onshore sending-end converter station is connected with the DC submarine cable 5 through the collection line.

[0047] With reference to Figure 1 , the frequency support method based on the MMC-MTDC system comprises the following steps:

[0048] S1, based on the detected inland receiving-end power grid frequency change information, adjusting the DC voltage of the inland receiving-end converter station;

[0049] Based on the detected inland receiving-end power grid frequency change information, adjusting the DC voltage of the inland receiving-end converter station according to the droop characteristic.

[0050] Specifically, the inland receiving-end converter station adopts fixed DC voltage control, and the fixed DC voltage control includes frequency disturbance detection and DC voltage adjustment. When active power sudden surge disturbance occurs in the inland receiving-end power grid, the frequency will drop. At this time, the inland receiving-end converter station will first detect the frequency change information, and change the DC voltage in proportion by using the frequency-DC voltage droop control. That is, based on the inland receiving-end power grid frequency change information, the DC voltage of the inland receiving-end converter station is adjusted according to the droop characteristic.

[0051] The frequency-DC voltage droop control process will be described below in combination with an embodiment:

[0052] When the inland receiving-end converter station detects that the inland receiving-end power grid has frequency deviation, the DC voltage of the inland receiving-end converter station will be adjusted according to the following formula:

[0053]

[0054] Wherein, indicates the DC voltage reference value of the inland receiving-end converter station, indicates the initial value of the DC voltage of the inland receiving-end converter station, indicates the pre-defined droop coefficient, indicates the frequency deviation value of the inland receiving-end power grid.

[0055] It should be noted that the predefined droop coefficient is actually the proportional coefficient of the direct current voltage change and the frequency change. If the allowed operating frequency deviation of the inland receiving end power grid is , the maximum deviation of the DC voltage from the rated value that the DC voltage can withstand during the operation of the MMC-MTDC system is defined as the maximum allowed deviation of the DC voltage of the MMC-MTDC system, denoted as , and then The value range of may be represented as . That is, needs to be predefined in the value range. In this way, the frequency change information of the inland receiving end power grid can be effectively reflected to the sending end system through the DC voltage, reducing the delay caused by the communication process.

[0056] S2, during the change of the DC voltage of the inland receiving end converter station, the frequency deviation estimation data of the inland receiving end power grid is obtained based on the collected DC voltage of the sending end converter station.

[0057] During the change of the DC voltage of the inland receiving end converter station, the frequency deviation estimation value of the inland receiving end power grid is obtained based on the collected DC voltage of the sending end converter station, the initial value of the DC voltage of the inland receiving end converter station and the predefined droop coefficient. The DC voltage of the sending end converter station is the DC voltage of the offshore sending end converter station or the DC voltage of the onshore sending end converter station.

[0058] Specifically, when the offshore sending end converter station and the onshore sending end converter station perceive the change of the DC voltage, the DC voltage of the sending end converter station (the DC voltage of the offshore sending end converter station or the DC voltage of the onshore sending end converter station) is obtained, the initial value of the DC voltage of the inland receiving end converter station and the predefined droop coefficient are combined, the DC voltage change information is reversely deduced and converted by reading the bus voltage in real time, the frequency deviation estimation value of the inland receiving end power grid is obtained, and the correlation mapping between the DC voltage change and the frequency deviation of the receiving end power grid is realized. The frequency state basis is provided for subsequent sending end system response control.

[0059] In this embodiment, the reverse deduction and conversion is represented by the following formula:

[0060]

[0061] , wherein represents the frequency deviation estimation value of the inland receiving end power grid, represents the DC voltage of the sending end converter station. It should be noted that the offshore sending end converter station and the onshore sending end converter station perceive the same DC voltage change (because they are in the same MMC-MTDC system), and the same frequency deviation estimation value of the inland receiving end power grid is reversely deduced by reading the bus voltage in real time.

[0062] S3. Using the lowest frequency support cost of the sending-end system as the objective function, a frequency support model is constructed. The constraints of the frequency support model are determined based on the safety boundary of the MMC-MTDC system and the frequency support requirements of the inland receiving-end power grid. The frequency support model is then solved according to the constraints based on the frequency deviation estimation data of the inland receiving-end power grid, resulting in a frequency support strategy that includes the optimal support power for offshore wind power and the optimal support power for multi-energy integration.

[0063] Frequency support requires coordinating the energy of offshore wind power transmission systems and onshore multi-energy integrated systems. To balance support effectiveness and cost, this invention models the coordination process as a constrained optimization problem, sequentially allocating energy between offshore wind farms and multi-source energy clusters by minimizing support costs.

[0064] like Figure 3 The diagram shown is a flowchart illustrating step S3 of an embodiment of the present invention. (Refer to...) Figure 3 Step S3 includes:

[0065] S301. Construct a target cost function based on minimizing the frequency support cost, and constrain the target cost function to obtain the frequency support model;

[0066] Specifically, step S301 includes:

[0067] 1) Obtain the frequency support cost based on the sending end support cost and the sending end support reward, and construct the target cost function by minimizing the frequency support cost;

[0068] The frequency support cost is obtained by performing differential operations on the sending end support cost and the sending end support reward, and the objective cost function is constructed with the goal of minimizing the frequency support cost.

[0069] The sending-end support cost includes the offshore wind power support cost and the multi-energy integration support cost. The offshore wind power support cost is constructed based on rotor kinetic energy loss, mechanical wear degree and wind turbine power generation loss. The multi-energy integration support cost is constructed based on energy storage cycle loss and unit regulation cost. The sending-end support reward is constructed based on support power deviation and reward weight coefficient.

[0070] Given that the objective cost function is in mathematical form, the following explanation of its construction process is provided from a mathematical perspective:

[0071] Specifically, this embodiment uses the following formula to characterize the target cost function:

[0072]

[0073] in, This indicates that the cost is supported by minimizing the frequency. To optimize the objective, represents the offshore wind power support cost, represents the offshore wind power support power at time t, represents the multi-energy integration support cost, represents the multi-energy integration support power at time t, represents the sending end support reward.

[0074] Further, the offshore wind power support cost reflects the unit power cost of frequency support participated by wind power, and is modeled as a quadratic function of due to the comprehensive consideration of multiple factors (rotor kinetic energy loss, mechanical wear and tear, and wind turbine power generation loss). Specifically, the offshore wind power support cost is calculated by the following formula:

[0075]

[0076] wherein, , , are offshore wind power active output cost coefficients.

[0077] It should be noted that the above coefficients are affected by the following factors: first, rotor kinetic energy loss: the wind turbine provides support by releasing rotor kinetic energy, which leads to a decrease in rotational speed and affects subsequent power generation efficiency. The cost function includes the energy cost required for speed recovery; second, mechanical wear and tear: frequent power adjustment will increase the mechanical wear and tear of devices such as gearboxes and bearings, and this factor is quantified by historical failure data; third, wind power generation loss: the power generation loss caused by the deviation of wind turbine output from the maximum power point tracking, which is related to wind speed and adjustment time.

[0078] Further, the multi-energy integration support cost reflects the unit power cost of frequency support participated by multi-source energy, and is modeled as a quadratic function of due to the comprehensive consideration of multiple factors (energy storage cycle loss and unit adjustment cost). Specifically, the multi-energy integration support cost is calculated by the following formula:

[0079]

[0080] wherein, , , are multi-source energy active output cost coefficients.

[0081] It should be noted that for the energy storage system, the cost mainly comes from the cycle life loss of charging and discharging, which is related to the state of charge change; for the thermal power / nuclear power unit, the cost coefficient depends on the fuel cost, start-stop loss and climbing rate limit penalty.

[0082] Further, the design of the sending-end support reward needs to encourage the sending-end support source to provide more frequency support within a suitable range. The sending-end support reward is used to encourage the sending-end system to provide sufficient frequency support while avoiding excessive punishment, in the form of a saturation function, as follows:

[0083]

[0084] wherein, represents a reward weight coefficient, represents the expected support power.

[0085] It should be noted that the reward weight coefficient can be flexibly set according to the frequency regulation demand of the receiving-end system. Specifically, when the drop amplitude of the inland receiving-end grid frequency exceeds a certain critical value (such as 0.2 Hz), the value of the reward weight coefficient can be appropriately increased to encourage the sending-end system to provide more support. In general, the design of the sending-end support reward is as follows: when the sending-end support power greatly deviates from the expected support power, the reward is relatively large; when the sending-end support power is close to the expected support power, the reward tends to be saturated, avoiding blind increase of power. The introduction of the tanh function can improve the smoothness of the design of the sending-end support reward, facilitating optimization solution.

[0086] 2) The target cost function is constrained based on the pre-constructed safe operation constraint condition and support efficiency constraint condition, to obtain a frequency support model.

[0087] The safe operation constraint condition includes a sending-end power output constraint condition, a sending-end energy change constraint condition, and a sending-end power change rate constraint condition, and the support efficiency constraint condition includes a minimum virtual inertia constraint condition.

[0088] Specifically, the following formula is used to represent each constraint condition:

[0089] 1) The sending-end power output constraint condition;

[0090]

[0091] wherein, represents the offshore wind power support power at time t or the multi-energy integrated support power at time t, represents the upper limit of the offshore wind power output or the upper limit of the multi-energy integrated active power output.

[0092] 2) The sending-end energy change constraint condition;

[0093]

[0094] wherein, represents the cumulative energy change of the power adjustment amount of the offshore wind power sending-out system or the onshore multi-energy integrated system within a continuous time period, represents the upper limit of the energy variation of the offshore wind power transmission system or the onshore multi-energy integrated system. For the offshore wind power transmission system, it is related to the wind speed, the rotor speed of the wind turbine, etc. For the onshore multi-energy integrated system, it is related to the state of charge of the energy storage, the installed capacity and the on-line capacity of the thermal power and nuclear power, etc.

[0095] 3) the power variation rate constraint condition of the sending end;

[0096]

[0097] wherein, represents the upper limit of the power variation rate of the offshore wind power transmission system or the onshore multi-energy integrated system.

[0098] 4) the minimum virtual inertia constraint condition.

[0099]

[0100] wherein, represents the minimum virtual inertia that the MMC-MTDC system should provide to the inland receiving end during frequency disturbance, represents the frequency variation rate calculated by the sending end according to the variation of the outlet DC voltage.

[0101] S302, based on the updated inland receiving end power grid frequency deviation estimation data in each time step, the frequency support model is solved to obtain the frequency support strategy in the corresponding time step, which includes the optimal support power of offshore wind power and the optimal support power of multi-energy integration.

[0102] In each time step, the updated inland receiving end power grid frequency deviation estimation data is obtained based on the real-time collected DC voltage signal of the sending end converter station, which is used as the input to solve the frequency support model. Specifically, the frequency deviation estimation data is substituted into the frequency support model, and the safety operation constraint condition and the support efficiency constraint condition are included in the solving process to ensure that the solving result meets the system safety and support efficiency requirements. Finally, the optimal support power of the offshore wind power system and the optimal support power of the onshore multi-energy integrated system in the corresponding time step are obtained by solving the mathematical programming algorithm, which together constitute the frequency support strategy in the time step to provide accurate instructions for the output adjustment of the sending end system.

[0103] It should be noted that the design of time step needs to comprehensively consider the frequency response characteristics of power grid, the execution efficiency of calculation and the constraints of device hardware. After frequency disturbance, the inertia support of power grid acts on the first swing period (0.1s~5s), and the primary frequency modulation covers 10s~30s. If the step is too long, the instruction will lag, and it is difficult to suppress frequency oscillation. If the step is too short, the central dispatch optimization calculation may not be completed, and the risk of communication delay and packet loss will increase. Therefore, the step selection needs to meet multiple conditions: first, it should not be lower than the lower limit determined by the communication delay and the central dispatch calculation time (usually about 200ms through offline testing), to ensure the effective output of calculation instruction; second, it should not exceed the duration of system inertia response, which is generally designed to be within 1000ms, to maintain the support effect; third, it should be adapted to the characteristics of hardware facilities. If the multi-source energy cluster is mainly composed of power electronic devices such as energy storage, the step can be appropriately reduced due to fast response. If the main synchronous units are thermal power and nuclear power, the step should be extended to 500ms~1000ms to avoid frequent adjustment of devices. By balancing the support response speed and the calculation burden, a reasonable time reference is provided for the rolling solution process, ensuring that the frequency support strategy is accurate, real-time and feasible. The central dispatch can be understood as the core link for solving the frequency support model and generating output adjustment instructions.

[0104] S4, adjusting the output of the sending-end system based on the frequency support strategy to provide frequency support for the inland receiving-end power grid.

[0105] After obtaining the frequency support strategy in each time step, the corresponding power adjustment instructions are sent to the offshore sending-end converter station and the land sending-end converter station of the sending-end system. After receiving the instructions, the offshore sending-end converter station transmits the signals to the directly connected offshore wind turbine converter through the communication link. The wind turbine adjusts the active reference value of the maximum power point tracking control for a short time to release or recover the rotor kinetic energy to achieve optimal support power output. The land sending-end converter station directly adjusts the active power reference value of the land multi-energy integrated system based on the instructions. The energy storage system adjusts the charging and discharging power, and the thermal power / nuclear power unit adjusts the power demand through the climbing rate control to make the land multi-energy integrated system output matched optimal support power.

[0106] Through the above coordinated output adjustment, the offshore wind power sending-out system and the land multi-energy integrated system will transmit the total support power to the inland receiving-end converter station through the DC overhead line, and finally convert it into active support for the inland receiving-end power grid, quickly suppressing frequency deviation and achieving dynamic frequency stability control.

[0107] Specifically, during the output adjustment process, the state of the sending-end system is detected. If an abnormality is detected in the sending-end system, the frequency support for the inland receiving-end power grid is stopped.

[0108] Further, in the process of state detection, if it is detected that the sending end system is in an abnormal condition, it is determined that the sending end system is abnormal.

[0109] It should be noted that the abnormal condition includes but is not limited to that the frequency fluctuation of the sending end power grid is lower than a protection threshold, the sending end system is in a start-stop or fault isolation stage, the device is overloaded or has an abnormal temperature rise, the state of charge of the energy storage is lower than a running threshold, and the rotating speed of the fan is lower than a minimum inertia support rotating speed.

[0110] The frequency support method based on the MMC-MTDC system according to the embodiment of the application can directly transmit frequency information through a DC voltage signal, reduce the time delay problem of the conventional frequency data transmission depending on a communication link, accurately construct a frequency support model containing a support cost and a dynamic constraint, realize optimal distribution of support power, take into account frequency modulation economy and response efficiency, effectively improve the frequency stability margin of the inland receiving end power grid in a high proportion of new energy access scenario, and significantly improve the frequency support reliability and flexibility of the MMC-MTDC system to the inland receiving end power grid.

[0111] The embodiment of the application further provides a frequency support device based on the MMC-MTDC system, which comprises:

[0112] a processor, a memory and a bus;

[0113] the bus is used to connect the processor and the memory;

[0114] the memory is used to store operation instructions;

[0115] the processor is used to execute the operation corresponding to the frequency support method based on the MMC-MTDC system according to the application by calling the operation instructions.

[0116] In an optional embodiment, an apparatus is provided, as shown in Figure 4 the apparatus 5000 shown in Figure 4 The apparatus 5000 shown in comprises a processor 5001 and a memory 5003. The processor 5001 and the memory 5003 are connected, for example, through a bus 5002. Optionally, the apparatus 5000 can further comprise a transceiver 5004. It should be noted that in actual application, the transceiver 5004 is not limited to one, and the structure of the apparatus 5000 does not constitute a limitation on the embodiments of the application.

[0117] The processor 5001 can be a CPU, a general-purpose processor, a DSP, an ASIC, an FPGA, or other programmable logic device, a transistor logic device, a hardware component, or any combination thereof. It can implement or execute various exemplary logical blocks, modules, and circuits described in conjunction with the present disclosure. The processor 5001 can also be a combination that implements a computing function, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, and the like.

[0118] The bus 5002 can include a path for transmitting information between the above-mentioned components. The bus 5002 can be a PCI bus, an EISA bus, or the like. The bus 5002 can be divided into an address bus, a data bus, a control bus, and the like. For convenience of representation, Figure 4 In the figure, only one thick line is used, but it does not mean that there is only one bus or one type of bus.

[0119] The memory 5003 can be a ROM or other type of static storage device that can store static information and instructions, a RAM or other type of dynamic storage device that can store information and instructions, an EEPROM, a CD-ROM or other optical disk storage, an optical disk storage (including a compact disk, a laser disk, an optical disk, a digital versatile disk, a Blu-ray disk, and the like), a magnetic disk storage medium or other magnetic storage device, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and capable of being accessed by a computer, but is not limited thereto.

[0120] The memory 5003 is used to store application program codes for implementing the scheme of the present application, and is controlled by the processor 5001 for execution. The processor 5001 is used to execute the application program codes stored in the memory 5003 to implement the content shown in any of the foregoing method embodiments.

[0121] In summary, the frequency support method and device based on the MMC-MTDC system according to the embodiments of the present application, when the frequency disturbance occurs in the inland receiving end power grid, the frequency information is transmitted through adjusting the DC voltage of the inland receiving end converter station, the frequency deviation is inversely deduced according to the voltage of the sending end converter station, and the power collaborative distribution of the offshore wind power sending system and the onshore multi-energy integrated system is realized by combining the frequency support model of the minimum support cost. The present application directly transmits the frequency information through the DC voltage signal, reduces the time delay problem of the conventional frequency data transmission relying on the communication link; by accurately constructing the frequency support model containing the support cost and the dynamic constraint, the optimal distribution of the support power is realized, and the frequency regulation economy and the response efficiency are taken into account; at the same time, by means of the multi-resource collaboration and the dynamic adjustment mechanism of the sending end system, the frequency stability margin of the inland receiving end power grid in the high proportion of new energy access scenario is effectively improved, and the frequency support reliability and flexibility of the MMC-MTDC system to the inland receiving end power grid are significantly improved.

[0122] Various embodiments are described herein with reference to the drawings. Each example is described in sufficient detail to provide structural details, manufacturing processes and application information. Obviously, various modifications and changes can be made in view of these implementations. It is intended that the implementations be construed as examples only. It is intended that all such modifications and changes be included in the scope of the implementations and the scope of the claims.

[0123] The above only is the preferred implementation of the present application, it should be pointed out that, for the ordinary skilled in the art, without departing from the technical principles of the present application, can make a number of improvements and replacement, these improvements and replacement also should be considered as the protection scope of the present application.

Claims

1. A frequency support method based on an MMC-MTDC system, characterized in that, The MMC-MTDC system comprises a receiving end system and a sending end system; The receiving end system comprises an inland receiving end power grid and an inland receiving end converter station, and the sending end system comprises an offshore wind power sending out system and a land multi-energy integrated system, both of which comprise corresponding sending end converter stations; The frequency support method based on the MMC-MTDC system comprises the following steps: S1, adjusting the DC voltage of the inland receiving end converter station based on the detected frequency change information of the inland receiving end power grid; S2, obtaining the frequency deviation estimation data of the inland receiving end power grid by backstepping based on the collected DC voltage of the sending end converter station during the change process of the DC voltage of the inland receiving end converter station; S3, taking the minimum cost of the frequency support of the sending end system as the objective function, constructing a frequency support model, determining the constraint conditions of the frequency support model based on the safety boundary of the MMC-MTDC system and the frequency support demand of the inland receiving end power grid, and solving the frequency support model according to the frequency deviation estimation data of the inland receiving end power grid and the constraint conditions to obtain a frequency support strategy comprising optimal support power of offshore wind power and optimal support power of multi-energy integration; Step S3 comprises: differential operation of the sending end support cost and the sending end support reward to obtain a frequency support cost, and construction of an objective cost function taking the minimization of the frequency support cost as the target, wherein the sending end support cost comprises offshore wind power support cost and multi-energy integration support cost, the offshore wind power support cost is constructed based on rotor kinetic energy loss, mechanical wear degree and wind turbine power generation loss, the multi-energy integration support cost is constructed based on energy storage cycle loss and unit adjustment cost, and the sending end support reward is constructed based on support power deviation and reward weight coefficient; constraint of the objective cost function based on the pre-constructed safety operation constraint condition and support efficiency constraint condition to obtain a frequency support model; rolling solution of the frequency support model based on the updated frequency deviation estimation data of the inland receiving end power grid in each time step to obtain a frequency support strategy comprising optimal support power of offshore wind power and optimal support power of multi-energy integration in the corresponding time step; S4, output adjustment of the sending end system based on the frequency support strategy to provide frequency support for the inland receiving end power grid.

2. The frequency support method based on the MMC-MTDC system according to claim 1, wherein, The adjustment of the DC voltage of the inland receiving end converter station based on the detected frequency change information of the inland receiving end power grid comprises: adjustment of the DC voltage of the inland receiving end converter station according to the droop characteristic based on the detected frequency change information of the inland receiving end power grid.

3. The frequency support method based on the MMC-MTDC system according to claim 1, wherein, The backstepping of the frequency deviation estimation data of the inland receiving end power grid based on the collected DC voltage of the sending end converter station during the change process of the DC voltage of the inland receiving end converter station comprises: obtaining the frequency deviation estimation value of the inland receiving end power grid based on the collected DC voltage of the sending end converter station, the initial value of the DC voltage of the inland receiving end converter station and the pre-defined droop coefficient during the change process of the DC voltage of the inland receiving end converter station, wherein the DC voltage of the sending end converter station is the DC voltage of the offshore sending end converter station or the DC voltage of the land sending end converter station.

4. The frequency support method based on the MMC-MTDC system according to claim 1, wherein, The safe operation constraint conditions comprise a sending end power output constraint condition, a sending end energy variation constraint condition and a sending end power variation rate constraint condition, and the support efficiency constraint condition comprises a minimum virtual inertia constraint condition.

5. The frequency support method based on the MMC-MTDC system according to claim 1, wherein, The output adjustment of the sending end system based on the frequency support strategy to provide frequency support for the inland receiving end power grid comprises: During the output adjustment, the state of the sending end system is detected, and if it is detected that the sending end system has an abnormality, the frequency support for the inland receiving end power grid is stopped.

6. The frequency support method based on the MMC-MTDC system according to claim 5, wherein, The state detection of the sending end system during the output adjustment, and if it is detected that the sending end system has an abnormality, the frequency support for the inland receiving end power grid is stopped, comprises: During the state detection, if it is detected that the sending end system has an abnormal condition, it is determined that the sending end system has an abnormality, wherein the abnormal condition comprises that the sending end power grid frequency fluctuation is lower than a protection threshold, or the sending end system is in a start-stop or fault isolation stage.

7. A frequency support device based on an MMC-MTDC system, characterized in that, The frequency support method based on the MMC-MTDC system comprises a processor, a memory and a computer program stored in the memory and configured to be executed by the processor, and the processor implements the frequency support method based on the MMC-MTDC system according to any one of claims 1 to 6 when executing the computer program.

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