Reactive power control method and device for offshore wind power low-frequency AC transmission system

Abstract

This invention relates to the field of new energy power generation dispatch automation technology, and discloses a reactive power control method and device for a low-frequency AC transmission system for offshore wind power. The invention determines the required reactive power reference value for a wind farm by combining the power transfer characteristics of diode rectifiers, and calculates the actual power margin of wind turbine units in each area. Based on this actual power margin and the total reactive power reference value, reactive power commands for different wind farm areas are calculated. The reactive power commands are optimized and adjusted according to the allowable reactive power threshold range of the wind turbine converters in each area, and the adjusted reactive power commands are sent to the corresponding wind turbine units in the area, enabling the wind turbine units in each area to perform reactive power control based on the received reactive power commands. This invention can reduce the frequency offset of grid-connected wind turbine converters and effectively reduce the heavy-load operation time of wind turbine units.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation dispatch automation technology, and in particular to a reactive power control method and device for offshore wind power low-frequency AC transmission systems. Background Technology

[0002] Wind power is one of the main energy sources for building new power systems. With the continuous development of wind power technology, wind farms are expanding in scale and gradually extending into deep-sea areas. Currently, offshore wind power mainly uses flexible DC transmission systems, with wind turbine converters employing grid-fed control strategies, relying on offshore converter stations to provide AC voltage sources for phase-locking and power exchange. Offshore converter stations are heavy and bulky, making DC transmission technology costly.

[0003] To address the issue of high costs, existing technologies offer a solution for low-frequency AC transmission from offshore wind farms. This solution employs a grid-based control strategy for the wind turbine converters to construct low-frequency AC voltage, increasing the length of the AC submarine cable and placing the offshore converter station on land, thus significantly reducing construction costs. The grid-based wind turbine converter possesses the capabilities to establish AC voltage, self-synchronize, and provide inertial support, demonstrating high research value and promising application prospects.

[0004] Utilizing the inherent reactive power regulation capabilities of offshore wind turbines can reduce the installation costs of reactive power compensation devices. However, in this scheme, the reactive power control method for grid-type wind farms mainly involves proportional or direct-proportional allocation of reactive power based on capacity. Wind turbines operating at high wind speeds may be under heavy load for extended periods, failing to fully utilize the coordinated control capabilities between turbines. Furthermore, due to the Qf droop characteristic of grid-type control, if there is a deviation between the reference reactive power value of the wind farm and the actual required reactive power value, the frequency of the wind farm's structure will deviate from its rated value. Summary of the Invention

[0005] This invention provides a reactive power control method and device for offshore wind power low-frequency AC transmission systems, which solves the technical problems of existing offshore wind farm low-frequency AC transmission solutions, such as the wind turbine units being in heavy-load operation for a long time and the frequency of the wind farm structure deviating from the rated value.

[0006] The first aspect of this invention provides a reactive power control method for an offshore wind power low-frequency AC transmission system. The offshore wind power low-frequency AC transmission system includes, in sequence, an offshore AC bus, a step-up transformer, an onshore AC bus, a converter transformer, an onshore converter station, and an onshore AC system. The offshore AC bus connects wind farms in various areas. The voltage amplitude and frequency at the offshore AC bus are collectively controlled by grid-type wind turbine converters. The onshore AC bus connects a reactive power compensation device and an AC filter. The onshore converter station converts non-power frequency voltage to power frequency voltage using diode rectifiers and modular multilevel converters. The method includes:

[0007] The reactive power consumed by the diode rectifier is determined based on the power transfer characteristics of the diode rectifier, and the measured value of reactive power provided by the reactive power compensation device and AC filter, as well as the difference between the measured values ​​of reactive power between the offshore AC bus and the onshore AC bus, are determined.

[0008] The total reactive power reference value of the wind farm is calculated based on the reactive power consumed, the measured reactive power value, and the difference between the measured reactive power value.

[0009] Determine the rated capacity and active power output of wind turbine units in different wind farm areas. Calculate the actual power margin of wind turbine units in each area based on the rated capacity and active power output. Calculate the reactive power command for wind farms in different areas based on the actual power margin and the total reactive power reference value.

[0010] The reactive power commands are optimized and adjusted according to the allowable reactive power threshold range of the wind turbine converters in each region, so that each adjusted reactive power command is within the allowable reactive power threshold range of the corresponding wind turbine converters in the region.

[0011] The adjusted reactive power command is sent to the wind turbines in the corresponding areas so that the wind turbines in each area can perform reactive power control according to the received reactive power command.

[0012] According to a method achievable according to a first aspect of the present invention, determining the reactive power consumed by the diode rectifier based on the power transfer characteristics of the diode rectifier includes:

[0013] The reactive power consumed by the diode rectifier is determined according to the following formula:

[0014]

[0015] In the formula, Q dc P represents the reactive power consumed by the diode rectifier. dc U is the active power transmitted by the diode rectifier. dciX is the DC voltage on the inverter side of the diode rectifier, and X is the leakage reactance of the transformer.

[0016] According to one achievable method of the first aspect of the present invention, the step of calculating a reference value for the total reactive power of the wind farm based on the consumed reactive power, the measured value of the reactive power, and the difference between the measured reactive power values ​​includes:

[0017] The reference value for the total reactive power of the wind farm is calculated using the following formula:

[0018]

[0019] In the formula, Q represents the reference value of the total reactive power of a wind farm. dc Q represents the reactive power consumed by the diode rectifier. C The measured reactive power value provided by the reactive power compensation device and AC filter, Q L This represents the difference in reactive power measurements between the offshore AC bus and the onshore AC bus.

[0020] According to one aspect of the present invention, the calculation of the actual power margin of wind turbine units in each area based on the rated capacity and the output active power includes:

[0021] The actual power margin of wind turbines in each area is calculated using the following formula:

[0022]

[0023] In the formula, ΔS i S represents the actual power margin of the wind turbines in the i-th region. Ni Let P be the rated capacity of the wind turbine in the i-th area. gi This represents the active power output of the wind turbine in the i-th area.

[0024] According to a method achievable according to a first aspect of the present invention, the step of calculating the reactive power command for wind farms in different areas based on the actual power margin and the total reactive power reference value includes:

[0025] The reactive power command for wind farms in different areas is calculated using the following formula:

[0026]

[0027] In the formula, ΔS represents the reactive power command of the i-th wind farm area. i Let n be the actual power margin of the wind turbines in the i-th region, and n be the number of regions. This is the reference value for the total reactive power.

[0028] According to one achievable method of the first aspect of the present invention, the reactive power threshold range includes a maximum reactive power value and a minimum reactive power value, and the optimization adjustment of each of the reactive power commands based on the allowable reactive power threshold range of each area's wind turbine converter includes:

[0029] Step S10: Determine whether each of the reactive power commands exceeds the reactive power threshold range allowed by the corresponding area wind turbine converter;

[0030] Step S20: If there is a reactive power command that exceeds the reactive power threshold range allowed by the corresponding wind turbine converter, adjust the reactive power command that is greater than the corresponding maximum reactive power value to the corresponding maximum reactive power value, and adjust the reactive power command that is less than the corresponding minimum reactive power value to the corresponding minimum reactive power value, and redistribute the reactive power commands for the remaining wind farms.

[0031] Step S30: Repeat steps S10-S20 until all current reactive power commands are within the reactive power threshold range allowed by the corresponding wind turbine converter.

[0032] According to one feasible method of the first aspect of the present invention, the redistribution of reactive power commands for the remaining wind farm areas includes:

[0033] Suppose that the reactive power commands of k wind farm areas exceed the reactive power threshold allowed by the corresponding wind turbine converters, the reactive power commands of the remaining wind farm areas are redistributed according to the following formula:

[0034]

[0035] In the formula, ΔS represents the reactive power redistribution command for the j-th wind farm in the remaining wind farm areas. i The actual power margin of the wind farm in the j-th region, where n is the number of regions. The total reactive power reference value is... This refers to the reactive power command of the xth wind farm in a wind farm area where the reactive power command exceeds the allowable reactive power threshold range of the corresponding wind turbine converter.

[0036] A second aspect of this invention provides a reactive power control device for an offshore wind power low-frequency AC transmission system. The offshore wind power low-frequency AC transmission system includes, in sequence, an offshore AC bus, a step-up transformer, an onshore AC bus, a converter transformer, an onshore converter station, and an onshore AC system. The offshore AC bus connects to wind farms in various areas. The voltage amplitude and frequency at the offshore AC bus are collectively controlled by grid-type wind turbine converters. The onshore AC bus connects to a reactive power compensation device and an AC filter. The onshore converter station converts non-power frequency voltage to power frequency voltage using diode rectifiers and modular multilevel converters. The device includes:

[0037] The determination module is used to determine the reactive power consumed by the diode rectifier based on the power transmission characteristics of the diode rectifier, determine the measured value of reactive power provided by the reactive power compensation device and the AC filter, and the difference between the measured values ​​of reactive power between the offshore AC bus and the onshore AC bus.

[0038] The first calculation module is used to calculate the reference value of the total reactive power of the wind farm based on the consumed reactive power, the measured value of reactive power and the difference between the measured value of reactive power.

[0039] The second calculation module is used to determine the rated capacity and active power output of wind turbine units in different wind farm areas, calculate the actual power margin of wind turbine units in each area based on the rated capacity and active power output, and calculate the reactive power command of wind farms in different areas based on the actual power margin and the total reactive power reference value.

[0040] The instruction adjustment module is used to optimize and adjust each reactive power instruction according to the reactive power threshold range allowed by the wind turbine converter in each area, so that each adjusted reactive power instruction is within the reactive power threshold range allowed by the corresponding wind turbine converter in the area.

[0041] The instruction issuing module is used to issue the adjusted reactive power instruction to the wind turbine units in the corresponding area, so that the wind turbine units in each area can perform reactive power control according to the received reactive power instruction.

[0042] According to one achievable embodiment of the second aspect of the present invention, the determining module comprises:

[0043] The determining unit is used to determine the reactive power consumed by the diode rectifier according to the following formula:

[0044]

[0045] In the formula, Q dc P represents the reactive power consumed by the diode rectifier. dc U is the active power transmitted by the diode rectifier.dci X is the DC voltage on the inverter side of the diode rectifier, and X is the leakage reactance of the transformer.

[0046] According to one achievable embodiment of the second aspect of the present invention, the first computing module includes:

[0047] The first calculation unit is used to calculate the reference value of the total reactive power of the wind farm according to the following formula:

[0048]

[0049] In the formula, Q represents the reference value of the total reactive power of a wind farm. dc Q represents the reactive power consumed by the diode rectifier. C The measured reactive power value provided by the reactive power compensation device and AC filter, Q L This represents the difference in reactive power measurements between the offshore AC bus and the onshore AC bus.

[0050] According to one achievable embodiment of the second aspect of the present invention, the second computing module includes:

[0051] The second calculation unit is used to calculate the actual power margin of wind turbines in each area according to the following formula:

[0052]

[0053] In the formula, ΔS i S represents the actual power margin of the wind turbines in the i-th region. Ni Let P be the rated capacity of the wind turbine in the i-th area. gi This represents the active power output of the wind turbine in the i-th area.

[0054] According to one achievable embodiment of the second aspect of the present invention, the second computing module includes:

[0055] The third calculation unit is used to calculate the reactive power command for wind farms in different areas according to the following formula:

[0056]

[0057] In the formula, ΔS represents the reactive power command of the i-th wind farm area. i Let n be the actual power margin of the wind turbines in the i-th region, and n be the number of regions. This is the reference value for the total reactive power.

[0058] According to one achievable embodiment of the second aspect of the present invention, the instruction adjustment module includes:

[0059] The judgment unit is used to determine whether each of the reactive power commands exceeds the reactive power threshold range allowed by the corresponding area wind turbine converter;

[0060] The adjustment unit is used to adjust reactive power commands that exceed the reactive power threshold range allowed by the corresponding wind turbine converter to the corresponding maximum reactive power value, and to adjust reactive power commands that are less than the corresponding minimum reactive power value to the corresponding minimum reactive power value, and to redistribute reactive power commands to the remaining wind farm areas if there are reactive power commands that exceed the threshold range allowed by the corresponding wind turbine converter.

[0061] The iterative control unit repeatedly executes the judgment unit and the adjustment unit until all current reactive power commands are within the reactive power threshold range allowed by the corresponding wind turbine converter.

[0062] According to one achievable method of the second aspect of the invention, the adjustment unit is specifically used for:

[0063] Suppose that the reactive power commands of k wind farm areas exceed the reactive power threshold allowed by the corresponding wind turbine converters, the reactive power commands of the remaining wind farm areas are redistributed according to the following formula:

[0064]

[0065] In the formula, ΔS represents the reactive power redistribution command for the j-th wind farm in the remaining wind farm areas. i The actual power margin of the wind farm in the j-th region, where n is the number of regions. The total reactive power reference value is... This refers to the reactive power command of the xth wind farm in a wind farm area where the reactive power command exceeds the allowable reactive power threshold range of the corresponding wind turbine converter.

[0066] A third aspect of the present invention provides a reactive power control device for a low-frequency AC transmission system of offshore wind power, comprising:

[0067] A memory for storing instructions; wherein the instructions are used to implement the reactive power control method for the offshore wind power low-frequency AC transmission system as described in any of the above-mentioned ways;

[0068] A processor for executing instructions in the memory.

[0069] The fourth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the reactive power control method for a low-frequency AC transmission system of offshore wind power as described in any of the above embodiments.

[0070] As can be seen from the above technical solutions, the present invention has the following advantages:

[0071] This invention determines the reactive power consumed by the diode rectifier based on its power transfer characteristics, and determines the measured reactive power provided by the reactive power compensation device and AC filter, as well as the difference between the measured reactive power values ​​between the offshore AC bus and the onshore AC bus. It calculates a reference value for the total reactive power of the wind farm based on the consumed reactive power, the measured reactive power value, and the difference between the measured reactive power values. It determines the rated capacity and active power output of wind turbines in different wind farm areas, calculates the actual power margin of wind turbines in each area based on the rated capacity and active power output, and calculates the reactive power command for wind farms in different areas based on the actual power margin and the reference value for total reactive power. Finally, it adjusts the reactive power command for each wind turbine converter according to the allowable reactive power threshold range for each area. The reactive power command is optimized and adjusted so that each adjusted reactive power command is within the reactive power threshold range allowed by the corresponding wind turbine converter in the corresponding area. The adjusted reactive power command is then sent to the wind turbine units in the corresponding area so that the wind turbine units in each area can perform reactive power control according to the received reactive power command. This invention combines the power transmission characteristics of diode rectifiers to determine the reference value of reactive power that the wind farm needs to provide, so as to reduce the frequency deviation of grid-type wind turbine converters, and optimize the reactive power allocation according to the actual power margin of wind turbine units in different areas, thereby reducing the heavy load operation time of wind turbine units. It can effectively solve the technical problems of existing offshore wind farm low-frequency AC transmission technology, which has the defects of wind turbine units being in heavy load operation for a long time and the frequency of wind farm structure deviating from the rated value. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 A schematic diagram of the existing offshore wind power low-frequency AC transmission system;

[0074] Figure 2 A flowchart of a reactive power control method for a low-frequency AC transmission system for offshore wind power, provided as an optional embodiment of the present invention;

[0075] Figure 3A flowchart for optimizing and adjusting each reactive power command according to the allowable reactive power threshold range of each wind turbine converter in each region, as provided in an optional embodiment of the present invention;

[0076] Figure 4 The diagram below shows the structural connection of a reactive power control device for a low-frequency AC power transmission system for offshore wind power, provided as an optional embodiment of the present invention.

[0077] Figure label:

[0078] L1 - Offshore AC busbar; T1 - Step-up transformer; L2 - Onshore AC busbar; T2 - Converter transformer; A1 - Onshore converter station; A2 - Onshore AC system; SVC1 - Reactive power compensation device; F1 - AC filter; D1 - Diode rectifier; M1 - Converter; CL1 - Collector line; SC1 - AC submarine cable line; 1 - Determining module; 2 - First calculation module; 3 - Second calculation module; 4 - Instruction adjustment module; 5 - Instruction issuance module. Detailed Implementation

[0079] This invention provides a reactive power control method and apparatus for a low-frequency AC transmission system for offshore wind power, which addresses the technical problems of existing offshore wind farm low-frequency AC transmission solutions, such as the possibility that wind turbines may be in heavy-load operation for extended periods and that the frequency of the wind farm structure may deviate from the rated value.

[0080] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0081] Figure 1 A schematic diagram of an existing offshore wind power low-frequency AC transmission system is shown. The method and apparatus of this invention are used to solve, for example... Figure 1 The existing offshore wind farm low-frequency AC transmission system shown has technical problems such as the wind turbine units being in a heavy-load operation state for a long time and the frequency of the wind farm structure deviating from the rated value.

[0082] like Figure 1As shown, the offshore wind power low-frequency AC transmission system includes an offshore AC bus L1, a step-up transformer T1, an onshore AC bus L2, a converter transformer T2, an onshore converter station A1, and an onshore AC system A2 connected in sequence. The offshore AC bus L1 connects to the wind farms in each area. The voltage amplitude and frequency at the offshore AC bus L1 are collectively controlled by the grid-type wind turbine converters. The onshore AC bus L2 connects to the reactive power compensation device SVC1 and the AC filter F1. The onshore converter station A1 converts the non-power frequency voltage to the power frequency voltage through diode rectifier D1 and converter M1.

[0083] Each wind farm in the designated area is connected to the offshore AC bus L1 via collector line CL1. The frequency of the offshore AC bus L1 can be selected according to requirements, generally less than 50Hz. After passing through step-up transformer T1, the offshore AC bus L1 is connected to the onshore AC bus L2 via submarine AC cable line SC1.

[0084] In a specific implementation, the diode rectifier D1 is a 12-pulse diode valve (DRU), and the converter M1 is a modular multilevel converter (MMC). Thus, the onshore converter station A1 uses a 12-pulse diode valve (DRU) for rectification and a modular multilevel converter (MMC) for inversion to convert non-power frequency voltage into power frequency voltage, which is then connected to the onshore AC system A2.

[0085] Please see Figure 2 , Figure 2 A flowchart of a reactive power control method for a low-frequency AC transmission system for offshore wind power provided by an embodiment of the present invention is shown.

[0086] The present invention provides a reactive power control method for a low-frequency AC transmission system for offshore wind power, comprising steps S1-S5.

[0087] Step S1: Determine the reactive power consumed by the diode rectifier D1 based on the power transmission characteristics of the diode rectifier D1, and determine the measured value of reactive power provided by the reactive power compensation device SVC1 and the AC filter F1, as well as the difference between the measured values ​​of reactive power between the offshore AC bus L1 and the onshore AC bus L2.

[0088] The diode rectifier D1 is an uncontrolled rectifier, and its characteristics are equivalent to a special case of an LCC converter M1 with a zero firing angle. To reduce AC and DC side harmonics, a 12-pulse rectifier bridge is generally used as the basic commutation unit. The external characteristic equation of the diode rectifier is:

[0089]

[0090] In the formula, U dcr U is the DC voltage on the rectifier side. rX is the unloaded line voltage on the transformer valve side, and I is the transformer leakage reactance. dc For direct current, U dci R is the DC voltage on the inverter side. dc For DC line resistance, For the power factor angle, P dc The active power transferred by diode rectifier D1, Q dc The reactive power consumed by diode rectifier D1.

[0091] This external characteristic equation can characterize the power transfer characteristics of the diode rectifier D1.

[0092] Since the onshore converter station A1 is co-located with the shore-based station, the DC line resistance can be ignored. Based on the power transfer characteristics of diode rectifier D1, the formula for calculating the reactive power consumed by diode rectifier D1 is as follows:

[0093]

[0094] In the formula, Q dc P represents the reactive power consumed by diode rectifier D1. dc The active power transmitted by diode rectifier D1, U dci X is the DC voltage on the inverter side of diode rectifier D1, and X is the leakage reactance of the transformer.

[0095] As can be seen from the above formula, the DC voltage on the inverter side is controlled by the converter M1, and the reactive power consumed by the diode rectifier D1 is positively correlated with the active power transmitted.

[0096] Step S2: Calculate the reference value of the total reactive power of the wind farm based on the consumed reactive power, the measured value of reactive power, and the difference between the measured reactive power value.

[0097] In one feasible approach, calculating the total reactive power reference value of the wind farm based on the consumed reactive power, the measured reactive power value, and the difference between the measured reactive power value includes:

[0098] The reference value for the total reactive power of the wind farm is calculated using the following formula:

[0099]

[0100] In the formula, Q represents the reference value of the total reactive power of a wind farm. dc Q is the reactive power consumed by diode rectifier D1. C The measured reactive power value, Q, provided by the reactive power compensation device SVC1 and the AC filter F1. L This is the difference in reactive power measurements between the offshore AC bus L1 and the onshore AC bus L2.

[0101] As another possible approach, Q can be pre-set based on historical data or other specific circumstances. C and Q L The correction factor is used to calculate the reference value of the total reactive power of the wind farm according to the following formula:

[0102]

[0103] In the formula, λ1 represents Q L The correction factor, λ2 represents Q. C The correction factor.

[0104] Step S3: Determine the rated capacity and active power output of the wind turbine units in different wind farm areas. Calculate the actual power margin of the wind turbine units in each area based on the rated capacity and active power output. Calculate the reactive power command for the wind farms in different areas based on the actual power margin and the total reactive power reference value.

[0105] In one feasible approach, the calculation of the actual power margin of wind turbine units in each area based on the rated capacity and output active power includes:

[0106] The actual power margin of wind turbines in each area is calculated using the following formula:

[0107]

[0108] In the formula, ΔS i S represents the actual power margin of the wind turbines in the i-th region. Ni Let P be the rated capacity of the wind turbine in the i-th area. gi This represents the active power output of the wind turbine in the i-th area.

[0109] It should be noted that the actual power margin of wind turbines in each area can also be calculated using other methods. For example, the difference or weighted difference between the rated capacity and the active power output of the wind turbines can be used as the actual power margin of the wind turbines in the corresponding area.

[0110] In one feasible approach, the calculation of reactive power commands for wind farms in different areas based on the actual power margin and the total reactive power reference value includes:

[0111] The reactive power command for wind farms in different areas is calculated using the following formula:

[0112]

[0113] In the formula, ΔS represents the reactive power command of the i-th wind farm area.i Let n be the actual power margin of the wind turbines in the i-th region, and n be the number of regions. This is the reference value for the total reactive power.

[0114] Step S4: Optimize and adjust each reactive power command according to the allowable reactive power threshold range of the wind turbine converter in each area, so that each adjusted reactive power command is within the allowable reactive power threshold range of the corresponding wind turbine converter.

[0115] In one feasible way, such as Figure 3 As shown, the reactive power threshold range includes a maximum reactive power value and a minimum reactive power value. The optimization and adjustment of each reactive power command based on the allowable reactive power threshold range of the wind turbine converters in each area includes:

[0116] Step S10: Determine whether each of the reactive power commands exceeds the reactive power threshold range allowed by the corresponding area wind turbine converter;

[0117] Step S20: If there is a reactive power command that exceeds the reactive power threshold range allowed by the corresponding wind turbine converter, adjust the reactive power command that is greater than the corresponding maximum reactive power value to the corresponding maximum reactive power value, and adjust the reactive power command that is less than the corresponding minimum reactive power value to the corresponding minimum reactive power value, and redistribute the reactive power commands for the remaining wind farms.

[0118] Step S30: Repeat steps S10-S20 until all current reactive power commands are within the reactive power threshold range allowed by the corresponding wind turbine converter.

[0119] Specifically, reactive power commands exceeding the permissible reactive power threshold range of the corresponding wind turbine converter are adjusted according to the following formula:

[0120]

[0121] In the formula, Q MAXi Q represents the maximum reactive power value within the allowable reactive power threshold range for the wind turbine converter in the i-th wind farm area. MINi This represents the minimum reactive power value within the allowable reactive power threshold range for the wind turbine converter in the i-th wind farm area.

[0122] In one feasible approach, assuming that the reactive power commands of k wind farm areas exceed the reactive power threshold allowed by the corresponding wind turbine converters, the reactive power commands of the remaining wind farm areas are redistributed according to the following formula:

[0123]

[0124] In the formula, ΔS represents the reactive power redistribution command for the j-th wind farm in the remaining wind farm areas. i The actual power margin of the wind farm in the j-th region, where n is the number of regions. The total reactive power reference value is... This refers to the reactive power command of the xth wind farm in a wind farm area where the reactive power command exceeds the allowable reactive power threshold range of the corresponding wind turbine converter.

[0125] Step S5: The adjusted reactive power command is sent to the wind turbine units in the corresponding area so that the wind turbine units in each area can perform reactive power control according to the received reactive power command.

[0126] Since the operating conditions of wind turbines within the same area are similar, reactive power commands within the same area can be evenly distributed to each wind turbine for control. Specifically, the average value of the received reactive power command can be calculated based on the number of wind turbines in the area, and then each wind turbine can perform reactive power control according to the average value of the reactive power command.

[0127] It should be noted that control units can be set up in each area to receive and process the reactive power commands to obtain the actual reactive power commands for each wind turbine in the area. These actual reactive power commands can be obtained by evenly distributing the issued reactive power commands, or other methods can be used to allocate the issued reactive power commands according to actual conditions. This embodiment does not limit this approach.

[0128] The present invention also provides a reactive power control device for a low-frequency AC transmission system for offshore wind power.

[0129] Please see Figure 4 , Figure 4 The diagram shows a structural connection block diagram of a reactive power control device for a low-frequency AC power transmission system for offshore wind power provided in an embodiment of the present invention.

[0130] This invention provides a reactive power control device for a low-frequency AC transmission system of offshore wind power, comprising:

[0131] The determination module 1 is used to determine the reactive power consumed by the diode rectifier D1 based on the power transmission characteristics of the diode rectifier D1, and to determine the measured value of reactive power provided by the reactive power compensation device SVC1 and the AC filter F1, as well as the difference between the measured values ​​of reactive power between the offshore AC bus L1 and the onshore AC bus L2.

[0132] The first calculation module 2 is used to calculate the reference value of the total reactive power of the wind farm based on the consumed reactive power, the measured value of reactive power and the difference between the measured value of reactive power.

[0133] The second calculation module 3 is used to determine the rated capacity and output active power of wind turbine units in different wind farm areas, calculate the actual power margin of wind turbine units in each area based on the rated capacity and output active power, and calculate the reactive power command of wind farms in different areas based on the actual power margin and the total reactive power reference value.

[0134] The instruction adjustment module 4 is used to optimize and adjust each reactive power instruction according to the reactive power threshold range allowed by the wind turbine converter in each area, so that each adjusted reactive power instruction is within the reactive power threshold range allowed by the corresponding wind turbine converter in the area.

[0135] The instruction issuing module 5 is used to issue the adjusted reactive power instruction to the wind turbine units in the corresponding area, so that the wind turbine units in each area can perform reactive power control according to the received reactive power instruction.

[0136] In one feasible manner, the determining module 1 includes:

[0137] The determining unit is used to determine the reactive power consumed by the diode rectifier D1 according to the following formula:

[0138]

[0139] In the formula, Q dc P represents the reactive power consumed by diode rectifier D1. dc The active power transmitted by diode rectifier D1, U dci X is the DC voltage on the inverter side of diode rectifier D1, and X is the leakage reactance of the transformer.

[0140] In one feasible implementation, the first computing module 200 includes:

[0141] The first calculation unit is used to calculate the reference value of the total reactive power of the wind farm according to the following formula:

[0142]

[0143] In the formula, Q represents the reference value of the total reactive power of a wind farm. dc Q is the reactive power consumed by diode rectifier D1. C The measured reactive power value, Q, provided by the reactive power compensation device SVC1 and the AC filter F1. LThis is the difference in reactive power measurements between the offshore AC bus L1 and the onshore AC bus L2.

[0144] In one feasible implementation, the second computing module 3 includes:

[0145] The second calculation unit is used to calculate the actual power margin of wind turbines in each area according to the following formula:

[0146]

[0147] In the formula, ΔS i S represents the actual power margin of the wind turbines in the i-th region. Ni Let P be the rated capacity of the wind turbine in the i-th area. gi This represents the active power output of the wind turbine in the i-th area.

[0148] In one feasible implementation, the second computing module 3 includes:

[0149] The third calculation unit is used to calculate the reactive power command for wind farms in different areas according to the following formula:

[0150]

[0151] In the formula, ΔS represents the reactive power command of the i-th wind farm area. i Let n be the actual power margin of the wind turbines in the i-th region, and n be the number of regions. This is the reference value for the total reactive power.

[0152] In one feasible implementation, the instruction adjustment module 4 includes:

[0153] The judgment unit is used to determine whether each of the reactive power commands exceeds the reactive power threshold range allowed by the corresponding area wind turbine converter;

[0154] The adjustment unit is used to adjust reactive power commands that exceed the reactive power threshold range allowed by the corresponding wind turbine converter to the corresponding maximum reactive power value, and to adjust reactive power commands that are less than the corresponding minimum reactive power value to the corresponding minimum reactive power value, and to redistribute reactive power commands to the remaining wind farm areas if there are reactive power commands that exceed the threshold range allowed by the corresponding wind turbine converter.

[0155] The iterative control unit repeatedly executes the judgment unit and the adjustment unit until all current reactive power commands are within the reactive power threshold range allowed by the corresponding wind turbine converter.

[0156] In one feasible implementation, the adjustment unit is specifically used for:

[0157] Suppose that the reactive power commands of k wind farm areas exceed the reactive power threshold allowed by the corresponding wind turbine converters, the reactive power commands of the remaining wind farm areas are redistributed according to the following formula:

[0158]

[0159] In the formula, ΔS represents the reactive power redistribution command for the j-th wind farm in the remaining wind farm areas. i The actual power margin of the wind farm in the j-th region, where n is the number of regions. The total reactive power reference value is... This refers to the reactive power command of the xth wind farm in a wind farm area where the reactive power command exceeds the allowable reactive power threshold range of the corresponding wind turbine converter.

[0160] The present invention also provides a reactive power control device for a low-frequency AC transmission system of offshore wind power, comprising:

[0161] A memory for storing instructions; wherein the instructions are used to implement the reactive power control method of the offshore wind power low-frequency AC transmission system as described in any of the above embodiments;

[0162] A processor for executing instructions in the memory.

[0163] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the reactive power control method for a low-frequency AC transmission system for offshore wind power as described in any of the above embodiments.

[0164] In the above embodiments of the present invention, the reactive power required by the wind farm is calculated considering the characteristics of the diode rectifier D1, which can reduce the frequency offset of the grid-type wind turbine converter. In addition, the reactive power allocation is optimized according to the actual power margin of the wind turbine units in different areas. The wind turbine with a larger actual power margin receives a higher reactive power command, which reduces the heavy-load operation time of the wind turbine units.

[0165] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the above-described device and module can be referred to the corresponding process in the foregoing method embodiments, and the specific beneficial effects of the above-described device and module can be referred to the corresponding beneficial effects in the foregoing method embodiments, and will not be repeated here.

[0166] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or modules may be electrical, mechanical, or other forms.

[0167] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0168] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated modules described above can be implemented in hardware or as software functional modules.

[0169] If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0170] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A reactive power control method for an offshore wind power low-frequency AC transmission system, wherein the offshore wind power low-frequency AC transmission system comprises, in sequence, an offshore AC bus, a step-up transformer, an onshore AC bus, a converter transformer, an onshore converter station, and an onshore AC system; the offshore AC bus connects wind farms in various areas; the voltage amplitude and frequency at the offshore AC bus are collectively controlled by grid-type wind turbine converters; the onshore AC bus connects a reactive power compensation device and an AC filter; and the onshore converter station converts non-power frequency voltage to power frequency voltage through diode rectifiers and converter inverters. The method is characterized in that... The method includes: The reactive power consumed by the diode rectifier is determined based on the power transfer characteristics of the diode rectifier, and the measured value of reactive power provided by the reactive power compensation device and AC filter, as well as the difference between the measured values ​​of reactive power between the offshore AC bus and the onshore AC bus, are determined. The total reactive power reference value of the wind farm is calculated based on the reactive power consumed, the measured reactive power value, and the difference between the measured reactive power value. Determine the rated capacity and active power output of wind turbine units in different wind farm areas. Calculate the actual power margin of wind turbine units in each area based on the rated capacity and active power output. Calculate the reactive power command for wind farms in different areas based on the actual power margin and the total reactive power reference value. The reactive power commands are optimized and adjusted according to the allowable reactive power threshold range of the wind turbine converters in each region, so that each adjusted reactive power command is within the allowable reactive power threshold range of the corresponding wind turbine converters in the region. The adjusted reactive power command is sent to the wind turbines in the corresponding areas so that the wind turbines in each area can perform reactive power control according to the received reactive power command.

2. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 1, characterized in that, The determination of the reactive power consumed by the diode rectifier based on its power transfer characteristics includes: The reactive power consumed by the diode rectifier is determined according to the following formula: In the formula, This indicates the reactive power consumed by the diode rectifier. The active power transmitted by the diode rectifier. This refers to the DC voltage on the inverter side of the diode rectifier. This refers to the transformer leakage reactance.

3. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 1, characterized in that, The step of calculating the total reactive power reference value of the wind farm based on the consumed reactive power, the measured reactive power value, and the difference between the measured reactive power value includes: The reference value for the total reactive power of the wind farm is calculated using the following formula: In the formula, This represents a reference value for the total reactive power of a wind farm. The reactive power consumed by the diode rectifier. The measured reactive power values ​​provided for reactive power compensation devices and AC filters. This represents the difference in reactive power measurements between the offshore AC bus and the onshore AC bus.

4. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 1, characterized in that, The calculation of the actual power margin of wind turbines in each area based on the rated capacity and output active power includes: The actual power margin of wind turbines in each area is calculated using the following formula: In the formula, Indicates the first The actual power margin of wind turbine units in each area For the first The rated capacity of wind turbine units in each area For the first The active power output of wind turbine units in each area.

5. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 1, characterized in that, The calculation of reactive power commands for wind farms in different areas based on the actual power margin and the total reactive power reference value includes: The reactive power command for wind farms in different areas is calculated using the following formula: In the formula, Indicates the first Reactive power instructions for wind farms in each area For the first The actual power margin of wind turbine units in each area For the number of districts, This is the reference value for the total reactive power.

6. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 1, characterized in that, The reactive power threshold range includes a maximum reactive power value and a minimum reactive power value. The optimization and adjustment of each reactive power command based on the allowable reactive power threshold range for each wind turbine converter in each region includes: Step S10: Determine whether each of the reactive power commands exceeds the reactive power threshold range allowed by the corresponding area wind turbine converter; Step S20: If there is a reactive power command that exceeds the reactive power threshold range allowed by the corresponding wind turbine converter, adjust the reactive power command that is greater than the corresponding maximum reactive power value to the corresponding maximum reactive power value, and adjust the reactive power command that is less than the corresponding minimum reactive power value to the corresponding minimum reactive power value, and redistribute the reactive power commands for the remaining wind farms. Step S30: Repeat steps S10-S20 until all current reactive power commands are within the reactive power threshold range allowed by the corresponding wind turbine converter.

7. The reactive power control method for a low-frequency AC transmission system for offshore wind power according to claim 6, characterized in that, The redistribution of reactive power commands to the remaining wind farm areas includes: Assume there is If the reactive power command of a wind farm in a certain area exceeds the reactive power threshold allowed by the corresponding wind turbine converter, the reactive power command will be redistributed to the remaining wind farms in the area according to the following formula: In the formula, Indicates the number of wind farms in the remaining area Reactive power redistribution instructions for wind farms in various regions For the first The actual power margin of wind farms in each area For the number of districts, The total reactive power reference value is... The first wind farm in the area whose reactive power command exceeds the allowable reactive power threshold range of the corresponding wind turbine converter. Reactive power instructions for wind farms in each area This indicates the number of wind farm areas where the reactive power command exceeds the reactive power threshold range allowed by the corresponding wind turbine converter.

8. A reactive power control device for an offshore wind power low-frequency AC transmission system, the offshore wind power low-frequency AC transmission system comprising, in sequence, an offshore AC bus, a step-up transformer, an onshore AC bus, a converter transformer, an onshore converter station, and an onshore AC system; the offshore AC bus connects wind farms in various areas; the voltage amplitude and frequency at the offshore AC bus are collectively controlled by grid-type wind turbine converters; the onshore AC bus connects a reactive power compensation device and an AC filter; the onshore converter station converts non-power frequency voltage to power frequency voltage through diode rectifiers and converter inverters; characterized in that... The device includes: The determination module is used to determine the reactive power consumed by the diode rectifier based on the power transmission characteristics of the diode rectifier, determine the measured value of reactive power provided by the reactive power compensation device and the AC filter, and the difference between the measured values ​​of reactive power between the offshore AC bus and the onshore AC bus. The first calculation module is used to calculate the reference value of the total reactive power of the wind farm based on the consumed reactive power, the measured value of reactive power and the difference between the measured value of reactive power. The second calculation module is used to determine the rated capacity and active power output of wind turbine units in different wind farm areas, calculate the actual power margin of wind turbine units in each area based on the rated capacity and active power output, and calculate the reactive power command of wind farms in different areas based on the actual power margin and the total reactive power reference value. The instruction adjustment module is used to optimize and adjust each reactive power instruction according to the reactive power threshold range allowed by the wind turbine converter in each area, so that each adjusted reactive power instruction is within the reactive power threshold range allowed by the corresponding wind turbine converter in the area. The instruction issuing module is used to issue the adjusted reactive power instruction to the wind turbine units in the corresponding area, so that the wind turbine units in each area can perform reactive power control according to the received reactive power instruction.

9. A reactive power control device for a low-frequency AC transmission system of offshore wind power, characterized in that, include: A memory for storing instructions; wherein the instructions are used to implement the reactive power control method of the offshore wind power low-frequency AC transmission system as described in any one of claims 1-7; A processor for executing instructions in the memory.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the reactive power control method for a low-frequency AC transmission system for offshore wind power as described in any one of claims 1-7.

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