CN111509754A - Fault ride-through control method for offshore wind power direct current collecting and conveying system - Google Patents
Fault ride-through control method for offshore wind power direct current collecting and conveying system Download PDFInfo
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
- Y02B70/3225—Demand response systems, e.g. load shedding, peak shaving
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
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- Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
- Y04S20/20—End-user application control systems
- Y04S20/222—Demand response systems, e.g. load shedding, peak shaving
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Abstract
The invention discloses a fault ride-through control method of an offshore wind power direct current collection and transmission system, which comprises the following steps: a concentrated unloading circuit is configured at a DC collection bus of an offshore wind farm; acquiring a first direct current bus voltage of a wind turbine generator, a second bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current transmission system; respectively subtracting the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage from the corresponding starting threshold values, multiplying the maximum output value by a proportionality coefficient through an amplitude limiting link, and generating a duty ratio through a pulse modulation link to control the concentrated unloading circuit to consume energy; when the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are all recovered to be below the corresponding starting threshold values, the concentrated unloading circuit is quitted to operate, and the system is recovered to be normal. The invention can realize the fault ride-through of the onshore alternating current system and can also realize the fault ride-through of the direct current transmission system.
Description
Technical Field
The invention relates to the technical field of offshore wind power operation control, in particular to a fault ride-through control method of an offshore wind power direct current collecting and conveying system.
Background
Along with the continuous and rapid development of economy in China, the contradiction between environmental protection and economic development is increasingly prominent, and low-carbon economy based on energy conservation and emission reduction becomes a strategic measure for maintaining the sustainable development of society. Offshore wind power has the characteristics of abundant resources, relatively high electricity generation utilization hours and relatively high technology, and is the leading-edge field of new energy development.
A large-scale offshore wind power collection and transmission system is the key for realizing grid-connected consumption of offshore wind power. When the large-scale offshore wind power direct current collecting and conveying system normally operates, energy generated by the wind turbine generator and energy consumed by the receiving end alternating current power grid are always kept balanced. When a receiving end power grid fails, the energy consumption capacity of the receiving end power grid is reduced, the offshore wind power transmitting end is not affected, energy is accumulated on a direct current circuit, direct current voltage continuously and rapidly rises, the direct current circuit and a direct current converter trip in severe cases, the offshore wind power transmission system quits operation, and alternating current fault ride-through cannot be achieved.
At present, a centralized unloading circuit is usually added at a direct current receiving end converter station to consume redundant energy of a flexible direct current transmission system, a distributed unloading circuit is added at a direct current bus of a converter of a full-power wind turbine generator to consume redundant energy of the converter to realize fault ride-through of the wind turbine generator, and safe and reliable operation of an offshore wind turbine generator and a transmission system of the offshore wind turbine generator is ensured through the comprehensive configuration scheme. However, the scheme is directed to a power transmission mode of offshore wind power "alternating current collection + direct current sending", and if the scheme is applied to a system of "direct current collection + direct current sending", the number of the whole unloading devices is large, the investment is large, and the plurality of unloading devices are lack of coordination, so that the fault ride-through control efficiency of the offshore wind power collection and transmission system is low.
Disclosure of Invention
The embodiment of the invention aims to provide a fault ride-through control method for an offshore wind power direct current collection and transmission system.
In order to achieve the above object, an embodiment of the present invention provides a fault ride-through control method for an offshore wind power direct current collection and transmission system, including the following steps:
a concentrated unloading circuit is configured at a direct current collection bus of an offshore wind farm to replace a first unloading device of each wind turbine generator and a second unloading device of a flexible direct current receiving end converter station;
acquiring a first direct current bus voltage of the wind turbine generator, a second direct current bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current transmission system;
respectively subtracting the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage from corresponding starting threshold values, multiplying the maximum output value by a proportionality coefficient through an amplitude limiting link, and generating a duty ratio through a pulse modulation link so as to control the centralized unloading circuit to consume energy;
when the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are all restored to be below the corresponding starting threshold values, the concentrated unloading circuit is quitted to operate, and the offshore wind power collecting and conveying system restores to transmit direct current power.
Preferably, the centralized unloading circuit comprises an insulated gate bipolar transistor and an energy consumption resistor; wherein, the energy consumption calculation formula of the energy consumption resistor is
RchopperIs the energy-consuming resistance, PmaxIs the rated transmission power value, U, of the offshore wind power collecting and transmitting systemratedThe rated voltage of the access point of the centralized unloading circuit.
Preferably, the step of subtracting the first dc bus voltage, the second dc bus voltage, and the third dc bus voltage from the corresponding start threshold values, the step of performing a limiting link to multiply the maximum output value by a proportionality coefficient, and the step of performing a pulse modulation link to produce a duty ratio so as to control the centralized unloading circuit to perform energy consumption includes:
the first direct current bus voltage is differed from a corresponding first starting threshold value, and a first output value of 0 is obtained through an amplitude limiting link if the first direct current bus voltage is lower than the first starting threshold value; if the voltage of the first direct current bus is higher than the first starting threshold value, the absolute value of the difference value of the first output value and the second output value is obtained;
making a difference between the second direct-current bus voltage and a corresponding second starting threshold value, and obtaining a second output value of 0 if the second direct-current bus voltage is lower than the second starting threshold value through an amplitude limiting link; if the voltage of the second direct current bus is higher than the second starting threshold value, the second output value is obtained and is the absolute value of the difference value of the second output value and the second starting threshold value;
the third direct current bus voltage is differed from a corresponding third starting threshold value, and a third output value of 0 is obtained through an amplitude limiting link if the third direct current bus voltage is lower than the third starting threshold value; if the voltage of the third direct current bus is higher than the third starting threshold value, the third output value is obtained and is the absolute value of the difference value of the third output value and the third starting threshold value;
and comparing the first output value, the second output value and the third output value, multiplying the maximum output value by a proportionality coefficient, and producing a duty ratio through a pulse modulation link so as to control the insulated gate bipolar transistor of the centralized unloading circuit to consume energy.
Preferably, the method further comprises:
the onshore converter station of the offshore wind power collecting and conveying system maintains the voltage stability of a third direct current bus of the flexible direct current transmission system in a droop control mode; wherein the calculation formula of the reference value of the third direct current bus voltage is UDC_refi＝US+ki(PS-PDCi)，UDC_refiThe control reference value is the ith control reference value of the third direct current bus voltage; u shapesAnd PsRespectively a DC voltage set-point and a power set-point, P, of said onshore converter stationDCiAnd kiAnd respectively representing the actual injection of the land grid power and the droop coefficient of the ith landing point converter station, wherein the actual injection of the land grid power takes the injection of the third direct current bus as a positive direction.
Preferably, the method further comprises:
and the offshore booster station of the offshore wind power collecting and conveying system controls the voltage of the second bus of the direct current collecting system to be stable, and simultaneously performs direct current voltage boosting control.
Preferably, the method further comprises:
and the offshore wind power plant of the offshore wind power collecting and conveying system controls the voltage stability of a first direct current bus of the wind turbine generator in the wind power plant by using a direct current transformer.
Preferably, the method further comprises:
the offshore wind power plant of the offshore wind power collecting and conveying system utilizes the machine side converter to carry out maximum wind energy tracking control so that the wind turbine generator outputs maximum active power at a specific wind speed, and further utilizes the machine side converter to control machine side alternating voltage.
Compared with the prior art, the fault ride-through control method for the offshore wind power direct current collection and transmission system provided by the embodiment of the invention has the advantages that the unloading circuit is centrally configured at the bus of the direct current collection system, and the direct current bus voltages of the offshore wind power generation set, the direct current collection system and the flexible direct current transmission system are collected as the measurement signals for starting and controlling the unloading circuit, so that the fault ride-through of the onshore alternating current system can be realized, the fault ride-through of the direct current transmission system can also be realized, the cost is low, and the efficiency is high.
Drawings
Fig. 1 is a schematic flow chart of a fault ride-through control method of an offshore wind power direct current collection and delivery system according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an offshore wind power direct current collection and transportation system according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a concentrated unloading circuit according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a control structure of a centralized unloading circuit according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a control architecture of an offshore wind power direct current collection and transmission system according to an embodiment of the present invention;
fig. 6 is a graph of a third dc bus voltage versus active power of a flexible dc transmission system controlled by a land converter station according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a schematic flow chart of a fault-ride-through control method of an offshore wind power direct current collection and transmission system according to an embodiment of the present invention is shown, where the method includes steps S1 to S5:
s1, configuring a concentrated unloading circuit at an offshore wind farm direct current collection bus to replace a first unloading device of each wind turbine generator and a second unloading device of a flexible direct current receiving end converter station;
s2, acquiring a first direct current bus voltage of the wind turbine generator, a second direct current bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current transmission system;
s3, respectively subtracting the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage from corresponding starting threshold values, multiplying the maximum output value by a proportionality coefficient through an amplitude limiting link, and generating a duty ratio through a pulse modulation link to control the centralized unloading circuit to consume energy;
and S4, when the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are all restored to be below the corresponding starting threshold values, the concentrated unloading circuit stops running, and the offshore wind power collecting and conveying system restores to transmit direct current power.
In order to more conveniently understand the implementation process of the present invention, an offshore wind power transmission system with "direct current collection + direct current output" is first described, and referring to fig. 2, the offshore wind power transmission system is a schematic structural diagram of an offshore wind power direct current collection and transmission system provided in an embodiment of the present invention. As shown in fig. 2, the full-power permanent-magnet direct-drive wind turbine generator system includes a wind turbine generator and a machine-side converter. Direct current generated by the wind power generation systems is collected and then boosted by the direct current transformer, and then is connected to a collection bus of the wind power plants through the direct current submarine cables. The offshore booster station further boosts the direct current voltage and then is connected to a plurality of onshore converter stations through a submarine direct current cable. The land converter station converts electric energy transmitted by the direct current cable into 50Hz alternating current, and then the alternating current is merged into different sites of a land alternating current main network through an alternating current transformer and an overhead line for consumption. After the structure of the offshore wind power collection and transportation system is clarified, the implementation process of the fault control method is described in detail below.
Specifically, a concentrated unloading circuit is configured at a direct current collection bus of an offshore wind farm to replace a first unloading device of each wind turbine generator and a second unloading device of a flexible direct current receiving end converter station. In the prior art, fault ride-through is realized by independently arranging a distributed unloading device on each wind turbine generator and arranging a centralized unloading device on a flexible direct current receiving end converter station. The method in the prior art is cancelled, and the concentrated unloading circuit is configured at the bus of the direct current collection system of the offshore wind farm, so that the grade of direct current voltage accessed by the concentrated unloading circuit is lower, and the manufacturing cost and difficulty of the device are lower.
The concentrated unloading circuit is quickly controlled by adopting a voltage comparator, an amplitude limiter, a maximum link and a proportional controller, and the detailed process is as follows:
the method comprises the steps of obtaining a first direct current bus voltage of a wind turbine generator, a second direct current bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current transmission system, wherein the direct current bus voltages are collected through a controller of a centralized unloading circuit and serve as input quantities of the controller.
Respectively subtracting the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage from the corresponding starting threshold values, multiplying the maximum output value by a proportionality coefficient through an amplitude limiting link, and producing a duty ratio through a pulse modulation link to control the concentrated unloading circuit to consume energy. Preferably, the starting threshold value is 1.05-1.25 p.u.; the lower limit of the amplitude limiting link is generally 0, and the upper limit is Uchopper_uplim。
When the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are all restored to be below the corresponding starting threshold values, namely the output value of the concentrated unloading circuit is 0, the concentrated unloading circuit quits operation, and the offshore wind power collecting and conveying system restores to transmit direct current power.
In summary, when a line ground fault occurs in the onshore ac system, the concentrated unloading circuit can reduce the voltage of the third dc bus by reducing the power injected into the dc bus of the grid-connected power transmission system, thereby preventing the third dc bus from tripping due to overvoltage, and realizing ac fault ride-through; when the direct current transmission cable has a ground fault, the offshore booster station can still consume redundant energy due to the fact that the fault isolation unloading device is achieved, and therefore fault ride-through of a direct current transmission system can be achieved.
According to the fault ride-through control method for the offshore wind power direct current collection and transmission system provided by the embodiment 1 of the invention, the unloading circuit is centrally configured at the bus of the direct current collection system, and the direct current bus voltages of the offshore wind power generation set, the direct current collection system and the flexible direct current transmission system are collected as the measurement signals for starting and controlling the unloading circuit.
As an improvement of the scheme, the centralized unloading circuit comprises an insulated gate bipolar transistor and an energy consumption resistor; wherein, the energy consumption calculation formula of the energy consumption resistor is
RchopperIs the energy-consuming resistance, PmaxIs the rated transmission power value, U, of the offshore wind power collecting and transmitting systemratedThe rated voltage of the access point of the centralized unloading circuit.
Specifically, referring to fig. 3, a schematic structural diagram of a concentrated unloading circuit according to an embodiment of the present invention is shown. As can be seen from the figure 3 of the drawings,the centralized unloading circuit comprises an insulated gate bipolar transistor and an energy consumption resistor; wherein, the Insulated Gate Bipolar Transistor (IGBT) is called IGBT valve for short. When the voltage level of the direct current side is higher, the voltage withstanding level of the unloading circuit can be improved by adopting a method of connecting IGBT valves in series. The energy consumption calculation formula of the energy consumption resistor is
RchopperAs a dissipative resistance, PmaxFor the rated value of the power delivered by the offshore wind power collection and delivery system, in practice, PmaxIn order to obtain the difference value between the transmission power after the voltage drop and the rated transmission power of the system in the most serious alternating current side fault, the theoretical value that the voltage drop is zero can be considered in the invention, so that PmaxThe rated power transmission value of the offshore wind power collecting and transmitting system is obtained. U shaperatedIs the rated voltage of the access point of the centralized unloading circuit.
As an improvement of the above scheme, the step of respectively subtracting the first dc bus voltage, the second dc bus voltage, and the third dc bus voltage from corresponding start threshold values, the step of performing a limiting link to multiply the maximum output value by a proportionality coefficient, and the step of performing a pulse modulation link to produce a duty ratio so as to control the centralized unloading circuit to perform energy consumption specifically includes:
the first direct current bus voltage is differed from a corresponding first starting threshold value, and a first output value of 0 is obtained through an amplitude limiting link if the first direct current bus voltage is lower than the first starting threshold value; if the voltage of the first direct current bus is higher than the first starting threshold value, the absolute value of the difference value of the first output value and the second output value is obtained;
making a difference between the second direct-current bus voltage and a corresponding second starting threshold value, and obtaining a second output value of 0 if the second direct-current bus voltage is lower than the second starting threshold value through an amplitude limiting link; if the voltage of the second direct current bus is higher than the second starting threshold value, the second output value is obtained and is the absolute value of the difference value of the second output value and the second starting threshold value;
the third direct current bus voltage is differed from a corresponding third starting threshold value, and a third output value of 0 is obtained through an amplitude limiting link if the third direct current bus voltage is lower than the third starting threshold value; if the voltage of the third direct current bus is higher than the third starting threshold value, the third output value is obtained and is the absolute value of the difference value of the third output value and the third starting threshold value;
and comparing the first output value, the second output value and the third output value, multiplying the maximum output value by a proportionality coefficient, and producing a duty ratio through a pulse modulation link so as to control the insulated gate bipolar transistor of the centralized unloading circuit to consume energy.
Fig. 4 is a schematic diagram of a control structure of a centralized unloading circuit according to an embodiment of the present invention. Because there is more than one wind turbine generator in the system, the corresponding first dc bus voltage has more than one data, fig. 4 illustrates the first dc bus voltages of two wind turbine generators, in the figure, Udcbus1i、Udcbus1j、Udcbus2And Udcbus3The voltage of the first direct current bus of the ith wind power plant, the voltage of the first direct current bus of the jth wind power plant, the voltage of the second bus of the direct current collecting system and the voltage of the third bus of the direct current transmission system are respectively. U shapedcbus1i_ref、Udcbus1j_ref、Udcbus2_refAnd Udcbus3_refAre respectively Udcbus1i、Udcbus1j、Udcbus2And Udcbus3The start threshold value of (2).
Specifically, the difference is made between the first direct current bus voltage and the corresponding first starting threshold value, and after the amplitude limiting link, if the first direct current bus voltage is lower than the first starting threshold value, the difference is Udcbus1i＜Udcbus1i_refIf so, obtaining a first output value of 0; if the first DC bus voltage is higher than the first start threshold, Udcbus1i＞Udcbus1i_refThen the absolute value of the difference between the two is obtained, i.e. the first output value is | Udcbus1i-Udcbus1i_ref|。
The second direct current bus voltage and the corresponding second starting thresholdThe difference is made, and after the amplitude limiting link, if the voltage of the second direct current bus is lower than a second starting threshold value, namely U is obtaineddcbus12＜Udcbus12_refIf so, obtaining a second output value of 0; if the voltage of the second DC bus is higher than the second start threshold, Udcbus12＞Udcbus12_refThen the absolute value of the difference between the second output value and the first output value is obtained, i.e. the second output value is | Udcbus12-Udcbus12_ref|。
And (4) making a difference between the voltage of the third direct current bus and the corresponding third starting threshold value, and passing through an amplitude limiting link, wherein if the voltage of the third direct current bus is lower than the third starting threshold value, namely U is obtaineddcbus13＜Udcbus13_refIf so, obtaining a third output value of 0; if the third DC bus voltage is higher than the third start threshold, Udcbus13＞Udcbus13_refThen the absolute value of the difference between the third output value and the second output value is obtained, i.e. the third output value is | Udcbus13-Udcbus13_ref|。
And comparing the first output value, the second output value and the third output value, multiplying the maximum output value by a proportionality coefficient, and producing a duty ratio through a pulse modulation link (PWM) so as to control the insulated gate bipolar transistor of the centralized unloading circuit to consume energy. The scaling factor is denoted by P.
As an improvement of the above, the method further comprises:
the onshore converter station of the offshore wind power collecting and conveying system maintains the voltage stability of a third direct current bus of the flexible direct current transmission system in a droop control mode; wherein the calculation formula of the reference value of the third direct current bus voltage is UDC_refi＝US+ki(PS-PDCi)，UDC_refiThe control reference value is the ith control reference value of the third direct current bus voltage; u shapesAnd PsRespectively a DC voltage set-point and a power set-point, P, of said onshore converter stationDCiAnd kiAnd respectively representing the actual injection of the land grid power and the droop coefficient of the ith landing point converter station, wherein the actual injection of the land grid power takes the injection of the third direct current bus as a positive direction.
Referring to fig. 5, a schematic diagram of a control architecture of an offshore wind power direct current collection and transmission system according to an embodiment of the present invention is shown.
Specifically, a droop control mode is adopted by a land converter station of the offshore wind power collecting and conveying system to maintain the voltage stability of a third direct current bus of the flexible direct current transmission system; wherein, the calculation formula of the reference value of the third direct current bus voltage is UDC_refi＝US+ki(PS-PDCi)，UDC_refiThe control reference value is the ith third direct current bus voltage; u shapesAnd PsDC voltage set-point and power set-point, P, respectively, for a land-based converter stationDCiAnd kiAnd respectively showing the actual injection of the land grid power and the droop coefficient of the ith landing point converter station, wherein the actual injection of the land grid power takes the injection of the third direct current bus as a positive direction. In addition, the onshore converter station also controls the reactive power exchanged with the ac system, but usually the reference value for the reactive power is zero. That is to say, the reference value of the third dc bus voltage and the active power are in a linear relationship, and when the active power changes, the dc voltage also changes linearly, so as to ensure the stability of the dc voltage, and make the system in a stable operation state. Referring to fig. 6, a graph of a third dc bus voltage versus active power of a flexible dc transmission system controlled by a land converter station is provided according to an embodiment of the present invention. As can be seen from fig. 6, the reference value of the third dc bus voltage of the flexible dc power transmission system is related to the actual injection of the on-ground grid power corresponding to different droop coefficients. If it is desired that the actual output power of each converter station is inversely proportional to its rated capacity, the droop factor of each converter station should satisfy the following relation
Wherein, PDCjAnd kjRespectively representing the actual injection of the land grid power and the droop coefficient of the jth landing point converter station.
As an improvement of the above, the method further comprises:
and the offshore booster station of the offshore wind power collecting and conveying system controls the voltage of the second bus of the direct current collecting system to be stable, and simultaneously performs direct current voltage boosting control.
Specifically, the offshore booster station of the offshore wind power collecting and conveying system controls the voltage of the second bus of the direct current collecting system to be stable, and meanwhile, the direct current voltage boosting control is carried out. The voltage of the second bus of the direct current collection system is kept stable, and the operation stability of the offshore wind power collection and transmission system is ensured so as to avoid faults.
As an improvement of the above, the method further comprises:
and the offshore wind power plant of the offshore wind power collecting and conveying system controls the voltage stability of a first direct current bus of the wind turbine generator in the wind power plant by using a direct current transformer.
Specifically, an offshore wind farm of the offshore wind power collection and delivery system controls the voltage stabilization of a first direct current bus of a wind turbine in the wind farm by using a direct current transformer. The method is used for maintaining the voltage stability of the first direct current bus of the wind turbine generator in the wind power plant, and also is used for ensuring the operation stability of an offshore wind power collecting and conveying system so as to avoid faults.
As an improvement of the above, the method further comprises:
the offshore wind power plant of the offshore wind power collecting and conveying system utilizes the machine side converter to carry out maximum wind energy tracking control so that the wind turbine generator outputs maximum active power at a specific wind speed, and further utilizes the machine side converter to control machine side alternating voltage.
Specifically, the offshore wind farm of the offshore wind power collection and transmission system utilizes the machine side converter to perform maximum wind energy tracking control so that the wind turbine generator outputs maximum active power at a specific wind speed, and also utilizes the machine side converter to control machine end alternating voltage so as to prevent the machine end voltage of the wind turbine generator from generating large fluctuation. The measures are all used for ensuring the operation stability of the offshore wind power collecting and conveying system so as to avoid faults.
To sum up, the fault ride-through control method for the offshore wind power direct current collection and transmission system provided by the embodiment of the invention has the following advantages: firstly, an unloading circuit is centrally configured at a direct-current collection bus of a large-scale offshore wind farm, and an independent unloading device of each wind turbine generator and an unloading device of a flexible direct-current receiving end converter station are replaced, so that the number of the unloading devices is greatly reduced, the use efficiency of the unloading devices is improved, the cost is saved, and the efficiency is improved; secondly, the direct-current bus voltage of the offshore wind turbine generator, the direct-current collecting system and the flexible direct-current transmission system is simultaneously acquired as a measurement signal for starting and controlling the unloading circuit, so that not only can onshore alternating-current system fault ride-through be realized, but also direct-current transmission system fault ride-through can be realized, the protection range of the unloading device is expanded, the sensitivity of the unloading device is improved, and direct-current side overvoltage is effectively prevented; and thirdly, the unloading circuit is quickly controlled by adopting a voltage comparator, an amplitude limiter and a proportional controller, the structure is clear, the response speed is high, the quick consumption of redundant energy on the direct current side can be realized, and meanwhile, after the direct current voltage is recovered, the control strategy can enable the unloading device to be quickly withdrawn, so that the quick recovery of the offshore wind power collecting and conveying system is facilitated.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (7)
1. A fault ride-through control method for an offshore wind power direct current collection and transmission system is characterized by comprising the following steps:
a concentrated unloading circuit is configured at a direct current collection bus of an offshore wind farm to replace a first unloading device of each wind turbine generator and a second unloading device of a flexible direct current receiving end converter station;
acquiring a first direct current bus voltage of the wind turbine generator, a second direct current bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current transmission system;
respectively subtracting the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage from corresponding starting threshold values, multiplying the maximum output value by a proportionality coefficient through an amplitude limiting link, and generating a duty ratio through a pulse modulation link so as to control the centralized unloading circuit to consume energy;
when the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are all restored to be below the corresponding starting threshold values, the concentrated unloading circuit is quitted to operate, and the offshore wind power collecting and conveying system restores to transmit direct current power.
2. The fault ride-through control method for the offshore wind power direct current collection and transmission system according to claim 1, wherein the concentration unloading circuit comprises an insulated gate bipolar transistor and an energy consumption resistor; wherein, the energy consumption calculation formula of the energy consumption resistor is
RchopperIs the energy-consuming resistance, PmaxIs the rated transmission power value, U, of the offshore wind power collecting and transmitting systemratedThe rated voltage of the access point of the centralized unloading circuit.
3. The method for controlling fault ride-through of an offshore wind power direct current collection and delivery system according to claim 2, wherein the first direct current bus voltage, the second direct current bus voltage and the third direct current bus voltage are respectively differentiated from corresponding start threshold values, a maximum output value is obtained by multiplying a proportionality coefficient through an amplitude limiting link, and a duty ratio is produced through a pulse modulation link to control the centralized unloading circuit to consume energy, specifically comprising:
the first direct current bus voltage is differed from a corresponding first starting threshold value, and a first output value of 0 is obtained through an amplitude limiting link if the first direct current bus voltage is lower than the first starting threshold value; if the voltage of the first direct current bus is higher than the first starting threshold value, the absolute value of the difference value of the first output value and the second output value is obtained;
making a difference between the second direct-current bus voltage and a corresponding second starting threshold value, and obtaining a second output value of 0 if the second direct-current bus voltage is lower than the second starting threshold value through an amplitude limiting link; if the voltage of the second direct current bus is higher than the second starting threshold value, the second output value is obtained and is the absolute value of the difference value of the second output value and the second starting threshold value;
the third direct current bus voltage is differed from a corresponding third starting threshold value, and a third output value of 0 is obtained through an amplitude limiting link if the third direct current bus voltage is lower than the third starting threshold value; if the voltage of the third direct current bus is higher than the third starting threshold value, the third output value is obtained and is the absolute value of the difference value of the third output value and the third starting threshold value;
and comparing the first output value, the second output value and the third output value, multiplying the maximum output value by a proportionality coefficient, and producing a duty ratio through a pulse modulation link so as to control the insulated gate bipolar transistor of the centralized unloading circuit to consume energy.
4. The method for fault-ride-through control of an offshore wind power direct current collection and transfer system of claim 1, further comprising:
the onshore converter station of the offshore wind power collecting and conveying system maintains the voltage stability of a third direct current bus of the flexible direct current transmission system in a droop control mode; wherein the calculation formula of the reference value of the third direct current bus voltage is UDC_refi＝US+ki(PS-PDCi)，UDC_refiThe control reference value is the ith control reference value of the third direct current bus voltage; u shapesAnd PsRespectively a DC voltage set-point and a power set-point, P, of said onshore converter stationDCiAnd kiAnd respectively representing the actual injection of the land grid power and the droop coefficient of the ith landing point converter station, wherein the actual injection of the land grid power takes the injection of the third direct current bus as a positive direction.
5. The method for fault-ride-through control of an offshore wind power direct current collection and transfer system of claim 1, further comprising:
and the offshore booster station of the offshore wind power collecting and conveying system controls the voltage of the second bus of the direct current collecting system to be stable, and simultaneously performs direct current voltage boosting control.
6. The method for fault-ride-through control of an offshore wind power direct current collection and transfer system of claim 1, further comprising:
and the offshore wind power plant of the offshore wind power collecting and conveying system controls the voltage stability of a first direct current bus of the wind turbine generator in the wind power plant by using a direct current transformer.
7. The method for fault-ride-through control of an offshore wind power direct current collection and transfer system of claim 6, further comprising:
the offshore wind power plant of the offshore wind power collecting and conveying system utilizes the machine side converter to carry out maximum wind energy tracking control so that the wind turbine generator outputs maximum active power at a specific wind speed, and further utilizes the machine side converter to control machine side alternating voltage.
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