CN117117886A - Offshore large-scale wind power transmission system and control method thereof - Google Patents
Offshore large-scale wind power transmission system and control method thereof Download PDFInfo
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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
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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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
- H02J3/01—Arrangements for reducing harmonics or ripples
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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
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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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
Abstract
The invention discloses an offshore large-scale wind power transmission system and a control method thereof. The wind power generator of the offshore large-scale wind power transmission system adopts a grid-formation control strategy to form a grid for the offshore wind power alternating current bus, DRU uncontrolled rectification is adopted at an offshore station to collect wind power for transmission, meanwhile, a static reactive power compensator with corresponding capacity is configured, the static reactive power compensator realizes active/reactive power control and compensates harmonic current, wind power is transmitted to an onshore MMC inversion station through a high-voltage sea cable channel, onshore MMC controls the amplitude and reactive power exchange of an onshore alternating current network, and when faults occur, a DC side energy consumption device and a static reactive power compensator converter valve locking strategy are adopted to realize protection control on system faults, so that the reliable transmission and grid connection requirements of large-scale offshore wind power are realized.
Description
Technical Field
The invention belongs to the technical field of power transmission systems, and particularly relates to an offshore large-scale wind power transmission system, a control method and a medium.
Background
The offshore wind power is taken as one of important directions of renewable clean energy development and utilization, has the advantages of high wind speed, high power generation efficiency, large installed capacity of a single machine, small occupied space, close to a load center and the like, has rich offshore wind energy resources in a middle and far sea area, and is a main battlefield for future wind power generation. How to extend wind power generation to the middle and open sea and realize reliable grid connection of large-scale remote offshore wind power is a core technical problem in the field of middle and open sea wind power at present. In recent years, the conventional power frequency alternating current transmission technology and the flexible direct current transmission technology are basically adopted by the offshore wind farm, wherein the conventional power frequency alternating current transmission technology is limited by the transmission technology, and the flexible direct current transmission technology is economically limited by high investment cost and high operation and maintenance cost.
For improving the economy of the offshore wind power direct current transmission system, a technical route adopting a current converter based on a diode uncontrolled rectifying unit becomes a research hot spot of a novel low-cost offshore wind power direct current transmission technology in recent years, and is widely paid attention to the industry. Compared with MMC, DRU (diode rectification unit) has the advantages of small power loss, low investment cost, high reliability and the like, and has obvious economic advantages and development prospects in the middle and open sea wind power grid-connected transmission system.
Diodes belong to uncontrollable devices, when a diode unit is adopted in an offshore wind power rectifying and sending-out system, a DRU is used as an active commutation converter, an offshore wind power plant is required to provide alternating current commutation voltage, and at present, scholars have proposed numerous grid-structured control strategies which are mainly classified into the following 3 types: ding Ming et al propose a virtual synchronous machine control strategy in the "virtual synchronous generator concept based microgrid inverter power supply control strategy" in "power system Automation"; li Rui, loujie et al in IEEE Journal of Emerging and Selected Topics in Power Electronics, "Coordinated control of parallel DR-HVDC and MMC-HVDC systems for offshore wind energy transmission" propose a network formation control based on a communication system; li Rui, loujie et al in IEEE Transactions on Power Delivery, "Distributed PLL-based control of offshore wind turbines connected with diode-receiver-based HVDC systems" propose a Distributed phase-locked loop (PLL) based control of the network architecture. However, no grid-structured wind turbine is put into operation at present, and the control strategy of the grid-structured wind turbine is still in a research stage.
In addition, the diode rectifier cannot provide reactive power for the wind farm when power transmission is performed, and certain reactive power needs to be absorbed from the system. In order to solve the above problem, meng Pei et al propose a hybrid delivery scheme of performing serial and parallel connection on DRUs and MMCs in a "large-scale offshore wind power multi-voltage-level hybrid cascade direct current delivery system" in "power system automation", in which DRUs and MMCs need to be placed on an offshore wind power platform, but as voltage levels are increased, the number of MMC submodules is greatly increased, the volume and weight of the offshore platform are increased, and construction cost is correspondingly increased. The mixed converter consisting of the DRU and the MMC auxiliary converter with high transformation ratio is researched in a low-cost mixed type offshore wind field direct current converter in China engineering and motor school report, so that the number of the MMC sub-modules can be reduced, but the introduced high-voltage direct current capacitor can increase the volume and the weight of the system.
Jin Yanqiu et al in the "high-voltage technology," two offshore wind power delivery schemes based on a grid-structured fan and a diode rectification unit "research a delivery system of the grid-structured fan and a DRU, and an alternating voltage is established by the grid-structured fan, so that offshore wind power can be stably delivered, but reactive power provided by the fan is limited, and reactive power required by large-capacity transmission cannot be met. PRIGNITZ Cord et al in "FixRef: acontrolstrategyforoffshorewindfarmswithdifferentwindturbinetypesand dioderectifierHVDC transmission" studied the introduction of a low-power AC auxiliary line into the wind power plant to provide energy support for the start-up of the wind farm and stable AC voltage for grid-connection of the wind turbines, and currently, there are few documents on the research of this scheme, and the topology and control strategy thereof are yet to be further studied.
At present, the topological structure and the system control strategy of the medium and open sea wind power plant access alternating current system are realistic problems of the sea wind power plant delivery project, and aiming at the network control strategy and the reactive power compensation scheme of the large-scale offshore wind power delivery system through the diode rectifying unit, a system topology and a control method aiming at the large-scale offshore wind power delivery are urgently needed.
Disclosure of Invention
In view of the above problems, the invention provides an SDRU-MMC system suitable for offshore large-scale wind power delivery, which utilizes a static reactive compensator to compensate reactive power consumption and harmonic current of a diode rectifying unit in the operation process at the high-voltage side of a transformer of an offshore booster station, improves waveform quality, eliminates potential safety hazards of breaking capacitive current of an alternating current filter breaker, and greatly improves safety performance of equipment; in addition, an alternating current filter bank/parallel capacitor of an offshore booster station can be omitted, the noise level of equipment is reduced, and the engineering occupied area is saved.
In order to achieve the above purpose, the invention adopts the following technical scheme: an offshore large-scale wind power transmission system comprises a net-structured fan for providing offshore alternating voltage, an offshore booster station, a high-voltage alternating current transmission sea cable, an onshore MMC inverter station and an onshore alternating current system;
The net-structured fan is connected with an alternating current bus of the offshore booster station, and the alternating current bus of the offshore booster station is connected with the offshore booster station;
active power sent out by an offshore wind farm is sent out by a high-voltage alternating-current transmission sea cable through a diode rectifying unit of an offshore booster station, and the offshore booster station is provided with a static reactive compensator for providing reactive power required by the diode rectifying unit and filtering corresponding harmonic waves;
the land MMC inversion station controls the constant direct current voltage and the reactive power interaction of the land MMC inversion station and a land alternating current system.
The invention also provides a control method of the offshore large-scale wind power transmission system, which is used for controlling the offshore large-scale wind power transmission system and comprises the following steps:
performing net forming control on the net forming fan to obtain a net forming fan characteristic control result;
performing cooperative control on the static var compensator to obtain a cooperative control result of the static var compensator;
controlling the land MMC inversion station to obtain a land MMC inversion station characteristic control result;
the strategy for controlling and protecting faults of the offshore large-scale wind power transmission system comprises a direct current energy consumption device and a static reactive compensator converter valve locking strategy which are arranged on the direct current side of a back-to-back converter of a fan and the direct current side of a land MMC inverter station, and a system fault ride-through protection control result is obtained;
And controlling the offshore large-scale wind power transmission system according to the characteristic control result of the net-structured fan, the cooperative control result of the static reactive compensator, the characteristic control result of the land MMC inversion station and the system fault ride-through protection control result.
According to the invention, when faults occur, protection control on system faults is realized by adopting a direct-current side energy consumption device and a static var compensator (STATCOM) converter valve locking strategy, and the requirements of reliable delivery and grid connection of large-scale offshore wind power are met.
Further, the method for carrying out the net construction control on the net construction type fan comprises the following steps:
the net-structured fan adopts a full-power converter type offshore wind turbine generator set based on a permanent magnet synchronous motor;
the machine side converter of the net-structured fan adopts zero d-axis current control, and the d-axis current reference value is set to be 0; the machine side converter of the fan works in a constant direct current voltage control mode, and a direct current voltage control loop inputs direct current voltage deviation and outputs the direct current voltage deviation as a q-axis current reference value;
the grid-side converter of the grid-formed fan performs coordinate transformation in a control system based on a globally uniform reference coordinate system, and the reference coordinate system position signal theta 0 Given by a broadcast signal or generated by a GPS time signal;
According to the rotating speed (positively related to wind speed) of the fans, combining a maximum power tracking algorithm to obtain active power instruction values of all fans, and combining actual measured values of the active power of the fans to generate a fan output voltage reference amplitude;
obtaining reactive power instruction values of all fans according to reactive power distribution algorithms (related to rated capacity of all fans), and generating fan output voltage reference phase angle values by combining actual measurement values of the reactive power of the fans;
according to the fan output voltage reference amplitude and the phase angle value, a valve side voltage reference value of a fan transformer is generated, a valve side voltage actual value of the fan transformer is combined, a voltage control loop is input, an alternating current side current reference value of a fan network side converter is obtained, a current control loop is input, and meanwhile, an alternating current side output voltage reference signal of the converter is obtained by combining the valve side voltage actual value of the fan transformer, so that a target voltage is generated through a network side converter PWM modulation strategy.
Further, the method for cooperatively controlling the static var compensator comprises the following steps:
controlling the fundamental current;
controlling harmonic current;
and combining the fundamental current and harmonic current control results, and simultaneously fusing a voltage feedforward result to obtain a control voltage of the converter valve of the static var compensator, and controlling the converter valve.
Further, the specific control of the fundamental current is as follows:
inputting a reactive power instruction of a system into a reactive current regulator for regulation, wherein the reactive power instruction value of the system is reactive power required by steady-state operation of a compensation diode rectifying unit;
inputting a system active command into an active current regulator for regulation, wherein the system active command value is set to 0, namely, the power of the offshore wind farm is ensured to be completely sent out through a diode rectifying unit;
inputting an alternating current system voltage into a phase-locked loop to generate a system voltage phase;
and combining the reactive current target value with the active current target value, inputting the combined result into a fundamental frequency current controller, and generating a fundamental current control result according to the system voltage phase and the static reactive compensator valve side current.
Further, the specific control of the harmonic current is as follows:
inputting the current at the valve side of the diode rectifying unit into a harmonic current control unit to output a harmonic current target value;
and inputting the harmonic current target value and the current at the valve side of the static var compensator into a harmonic current control unit to generate a harmonic current control result.
Further, the control method for the land MMC inversion station of the offshore large-scale wind power transmission system comprises the following steps:
The method comprises the steps of adopting constant direct current voltage control and constant alternating current side reactive power/alternating current side voltage amplitude control, controlling constant direct current voltage at the direct current side, and controlling constant alternating current bus voltage amplitude at the connection part of the land MMC inversion station and the land alternating current system or controlling reactive power exchange of the land MMC inversion station and the land alternating current system at the alternating current side.
Further, the dc energy-consuming device locking strategy is as follows:
when a short circuit fault occurs in the land alternating current system, the voltage of an alternating current bus of the land MMC inversion station is rapidly reduced, the transmission of direct current power is blocked, the direct current voltage of the offshore large-scale wind power transmission system is rapidly increased, the direct current is reduced to 0, the diode of the diode rectifying unit is blocked, and the active power output by a fan can induce power frequency overvoltage in a wind power plant; when a short circuit fault occurs to an alternating current bus of the offshore booster station, a net-structured fan net side converter cannot output active power captured by a fan, and a direct current link of a back-to-back fan converter generates direct current overvoltage; when the power transmission of the fan network side converter is blocked, the direct current energy consumption device is used for maintaining the voltage stability of the direct current capacitor;
meanwhile, a direct current energy consumption device is also arranged on the direct current side of the land MMC inversion station, so that the direct current system is helped to complete alternating current fault ride-through on the inversion side; in a normal running state, the direct current energy consumption device is in a locking state, and when the direct current voltage exceeds the upper limit of the threshold value, the direct current energy consumption device is triggered to be conducted, and redundant energy is dissipated by using a resistor in the direct current energy consumption device; when the dc voltage is below the lower threshold, the dc energy consuming device will latch or bypass.
Further, the static var compensator converter valve latching strategy is as follows:
detecting that the current instantaneous value of a bridge arm of the converter valve exceeds a preset value, and temporarily blocking overcurrent;
when permanent faults occur, locking the converter valve of the static var compensator when the number of times of continuous triggering temporary locking actions exceeds a threshold value within preset time;
when the average value of the capacitance voltage of any bridge arm exceeds a threshold value, carrying out overvoltage protection on the average value of the capacitance of a bridge arm submodule of the converter valve, and locking the converter valve;
in the operation process of the converter valve, when a power module fails, a power module control board sends a bypass request, a valve control controller counts whether the sum of the number of the submodules which are bypassed by any bridge arm and the number of the submodules which are currently requested to bypass is larger than a set value or not, and if so, the converter valve is locked;
the fault ride-through control strategy of the converter valve of the static var compensator is as follows: after the converter valve detects that the voltage of the alternating current bus of the offshore booster station drops, the harmonic compensation function is closed, the maximum current is output according to the rated capacity, and after the voltage of the alternating current bus of the offshore booster station is recovered, the harmonic compensation function and the reactive power instruction are recovered again.
The present invention also provides a computer-readable storage medium having stored thereon a computer program that is executed by a processor to implement a control method of the offshore large-scale wind power delivery system.
Based on the technical scheme, the invention has the following beneficial technical effects:
1. according to the invention, the STATCOM static reactive compensator is configured at the offshore booster station, reactive power consumption and harmonic current of the DRU unit in the operation process are compensated by the static reactive compensator at the high-voltage side of the offshore booster station transformer, the waveform quality is improved, the potential safety hazard of switching on and off the capacitive current of the alternating current filter circuit breaker is eliminated, the safety performance of equipment is greatly improved, the alternating current filter bank/parallel capacitor of the offshore booster station is eliminated, the noise level of the equipment is reduced, and the engineering floor area is saved.
2. The invention can adopt intermediate frequency collection at the offshore alternating current network side, compared with power frequency (50 Hz) power transmission, the rated operating frequency of the offshore wind turbine generator and the current collecting system adopts intermediate frequency (100-400 Hz), thereby greatly reducing the volume and weight of the offshore DRU station converter transformer and improving the economical efficiency of the system.
3. The invention adopts the net-structured fan to construct the offshore alternating current network, and the built-in phase-locked loop PLL is cancelled in fan control, thereby avoiding the system stability problem caused by the self-synchronization and mutual synchronization of the PLL and the grid-connected inverter and other parallel inverters under the weak current network condition; and the offshore STATCOM device is added, a certain reactive margin can be reserved, and the stability of an offshore alternating current system is enhanced.
Drawings
FIG. 1 is a schematic diagram of a large-scale offshore wind turbine delivery system of the present invention;
fig. 2 is a schematic structural diagram of an SDRU unit (STATCOM device and DRU unit) of the present invention;
FIG. 3 is an equivalent diagram of the steady-state circuit of the SDRU unit of the present invention;
fig. 4 is a diagram showing power characteristics of an offshore DRU according to the present invention, wherein in fig. 4, (a) is a reactive power characteristic of a DRU unit, and (b) is a reactive/active power characteristic of the DRU unit;
FIG. 5 is a schematic diagram of a full power grid-tied fan apparatus control strategy of the present invention;
FIG. 6 is a STATCOM package displacement flow valve control block diagram of the present invention;
FIG. 7 is a block diagram of the STATCOM device fundamental current control of the present invention;
FIG. 8 is a schematic diagram of a DC side energy dissipation device of a fan and a DC side energy dissipation device of an MMC inverter station according to the present invention;
FIG. 9 shows waveforms of parameters of wind speed change in the embodiment of the invention, (a) is an outlet voltage amplitude waveform of a fan grid-side converter, (b) is an outlet voltage phase angle waveform of the fan grid-side converter, (c) is an outlet active reactive waveform of the fan grid-side converter, (d) is a fan DC link voltage waveform, (e) is a DC voltage waveform of an offshore wind power transmission system, (f) is a DC waveform of the offshore wind power transmission system, (g) is an active reactive waveform of the offshore wind power transmission system converter, and (h) is a DC power waveform of the offshore wind power transmission system converter;
FIG. 10 shows waveforms of parameters of a land AC bus fault in an embodiment of the present invention, (a) is an outlet voltage amplitude waveform of a fan grid-side converter, (b) is an outlet voltage phase angle waveform of a fan grid-side converter, (c) is an outlet active reactive waveform of a fan grid-side converter, (d) is a fan DC link voltage waveform, (e) is a DC voltage waveform of an offshore wind power transmission system, (f) is a DC current waveform of an offshore wind power transmission system, (g) is an active reactive waveform of an offshore wind power transmission system converter, and (h) is a DC power waveform of an offshore wind power transmission system converter;
FIG. 11 shows waveforms of parameters of an offshore AC bus fault in an embodiment of the invention, (a) shows a waveform of an amplitude of an outlet voltage of a fan grid-side converter, (b) shows a waveform of an outlet voltage phase angle of the fan grid-side converter, (c) shows an outlet active reactive waveform of the fan grid-side converter, (d) shows a waveform of a fan DC link voltage, (e) shows a waveform of a DC voltage of an offshore wind power transmission system, (f) shows a waveform of a DC voltage of the offshore wind power transmission system, (g) shows an active reactive waveform of the offshore wind power transmission system converter, and (h) shows a waveform of a DC power of the offshore wind power transmission system converter;
FIG. 12 is an enlarged view at C of FIG. 5;
FIG. 13 is an enlarged view at B of FIG. 5;
fig. 14 is an enlarged view at a of fig. 5.
Detailed Description
In order to enable those skilled in the art to better understand the technical scheme of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood, however, that the detailed description is presented only to provide a better understanding of the invention, and should not be taken to limit the invention. In the description of the present invention, it is to be understood that the terminology used is for the purpose of description only and is not to be interpreted as indicating or implying relative importance.
Example 1
The embodiment is an offshore large-scale wind power transmission system (abbreviated as an SDRU-MMC system), as shown in FIG. 1, comprising an offshore grid-structured fan and a current collecting system, an offshore booster station static reactive compensator (STATCOM), an offshore booster station Diode Rectifier Unit (DRU), a high-voltage alternating current transmission sea cable, an onshore MMC inverter station and an onshore alternating current system.
As shown in fig. 2 and 3, the equivalent model of the SDRU unit converter valve structure and the steady-state circuit comprises an offshore wind farm equivalent loop and a static reactive compensator, the offshore wind farm equivalent loop comprises an alternating current signal source and a converter transformer equivalent impedance, the alternating current signal source is connected in series with the converter transformer equivalent impedance, and an output end of the converter transformer equivalent impedance is connected with an uncontrolled rectifier diode DR valve; the static reactive compensator comprises a second alternating current signal source and a connecting reactor inductor, wherein the second alternating current signal source is connected with the connecting reactor inductor in series, and the output end of the connecting reactor inductor is connected with an equivalent loop of the offshore wind farm. Us is the converter transformer voltage, ig is the converter transformer outlet line current, lr is the converter transformer equivalent impedance; ps and Qs deliver active and reactive power, respectively, for an offshore wind farm; u (U) L For grid-connected point alternating voltage, pg and Qg are grid-connected points for transmitting active power and reactive power; is the side line current of the outlet valve of the converter transformer, P L And Q L Active power and reactive power transmitted by the valve side of the DRU unit respectively; lapf is a static var compensator connecting reactor, it is static var compensator current, ut is a static var compensator equivalent voltage source, and Qt is reactive power emitted by the static var compensator.
The operation mode of the SDRU-MMC system is as follows: the grid-structured fan realizes the power grid support of the offshore wind farm; the DRU unit of the offshore booster station bears the transmission of active power; the static reactive compensator provides reactive power, adopts compensation DRU reactive power as a control target and filters corresponding harmonic waves; the MMC inversion station adopts a constant direct current voltage and a constant alternating current side reactive power/bus voltage as control targets.
Example two
The embodiment provides a control method of an offshore large-scale wind power transmission system, which is used for controlling the SDRU-MMC system in embodiment 1, and comprises the following steps:
(1) Carrying out network formation control on fans in the system to obtain a fan characteristic control result;
(2) Performing cooperative control on the STATCOM in the system to obtain a STATCOM cooperative control result;
(3) Controlling an onshore MMC inversion station in the system to obtain MMC characteristic control results;
(4) Performing fault ride-through strategy control on a system fault, wherein the fault ride-through strategy control comprises a direct current energy consumption device and a STATCOM converter valve locking strategy, and obtaining a system fault ride-through protection control result;
(5) And controlling the SDRU-MMC system according to the control result of the network-structured fan, the cooperative control result of the offshore STATCOM, the control result of the land MMC and the system fault ride-through protection control result.
First, considering that the external characteristics of the DRU diode rectifying unit offshore station are the same as LCCs with a firing angle of 0 °, a 12-pulse rectifying bridge is adopted as a basic converting unit. The DC voltage of the DRU diode rectifying unit is controlled by the constant DC voltage of the land MMC inversion station to be constant. From the quasi-steady state model of LCC, the DRU external characteristic equation can be obtained as follows:
P dr ＝U dcr I dcr (2)
wherein U is r And U dcr The DC voltage of the DRU and the effective value of the no-load AC voltage of the converter transformer are respectively obtained; i dcr And X r1 The direct current of the DRU and the leakage reactance of the converter transformer are respectively; p (P) dr And Q dr Active power and reactive power at the alternating current system side of the converter transformer respectively; mu is the phase change angle of the DRU;power for DRU unitFactor angle.
According to formula (1), the DC current of the DRU is obtained as follows:
in U const The DC side voltage of the DRU unit is kept constant.
The active power of the DRU is obtained by combining formulas (2) to (3) as follows:
P dr ＝U dcr I dcr ＝C 1 U r -C 2 (6)
wherein,
the power factor of a DRU can be expressed approximately as:
wherein,subscript "N" represents the nominal operating condition; u (U) dN 、U d0N And respectively representing the direct current voltage of the DRU unit under the rated working condition and the direct current voltage of the DRU unit in no-load.
According to formula (3), the reactive power required to be absorbed by the DRU is obtained as follows:
wherein,
as can be seen from the above, the power characteristic curve of the DRU diode rectifying unit is shown in fig. 4. Thus, when the active power of the DRU diode rectifying unit is 1.0p.u., the reactive power required to be consumed is about 0.4p.u., and the reactive power and the active power are in positive correlation. In order to improve the utilization rate of the long-distance high-voltage alternating-current transmission submarine cable and compensate reactive power required by the normal operation of the DRU, a STATCOM static reactive power compensation device is additionally arranged in an offshore booster station, and reactive power required by a DRU diode rectifying unit is balanced.
As shown in fig. 5 and fig. 12-14, the offshore rectifier station uses DRU units to achieve power transmission, and cannot provide offshore voltage support, so that the offshore wind turbine converter adopts network control. Net construction type control of a full-power converter type offshore wind turbine based on a permanent magnet synchronous motor: the machine side converter of the fan adopts a control strategy of zero d-axis current control, the d-axis current reference value is set to be 0, and at the moment, the electromagnetic torque of the generator and the q-axis current are in linear relation. Considering that the fan network side converter needs to control the alternating voltage amplitude and phase angle of the offshore alternating current bus, the side converter of the fan works in a constant direct current voltage control mode. The DC voltage control loop inputs the DC voltage deviation, outputs a q-axis current reference value, and the d-axis current reference value is set to 0. The control model of the direct current voltage control loop and the zero d-axis current control loop of the fan side converter is as follows:
In the psi- r Representing rotor flux linkage; u (U) dcwt The direct-current voltage of the back-to-back converter of the wind turbine generator is represented; l (L) d Representing the self inductance of the generator stator winding; u and i represent the ac side voltage and ac side current of the fan side converter, respectively; omega m Indicating the rotational speed of the generator rotor. The variable subscripts d and q represent the d-axis component and q-axis component of the variable, respectively; variable superscript indicates the reference value of the variable; k (k) dp And k di The proportional coefficient and the integral coefficient of the voltage loop PI controller are respectively; k (k) ip And k ii The proportional coefficient and the integral coefficient of the current loop PI controller of the fan side converter are respectively.
The net side converter of the fan adopts net-structured control to control the voltage amplitude and the offshore phase angle of the offshore alternating current system, the setting of a phase-locked loop is canceled, and the side converters of the fan are all arranged according to the uniformly-arranged fixed frequency omega 0 The rotating reference coordinate system performs coordinate transformation, and the reference coordinate system position signal theta 0 Given by a broadcast signal or generated by a GPS time signal, i.e. the grid-side inverter of the wind turbine performs a coordinate transformation in a control system based on a globally uniform reference coordinate system. The network side converter of the offshore net-structured fan adopts a three-ring control structure with V-f control overlapped with active-reactive control. Specifically, the 1 st layer is adopted as an active power controller and a reactive power controller, and a reference signal of alternating voltage amplitude and phase angle of a fan network side converter is generated; the 2 nd layer and the 3 rd layer are respectively a voltage controller and a current controller.
For the active power controller at the outermost layer, as can be seen from the formula (6), the active power absorbed by the DRU unit and the ac bus voltage of the marine rectifying station have positive correlation. Therefore, the output voltage amplitude of the fan network side converter can be adjusted according to the active power deviation, namely:
in the method, in the process of the invention,representing an output voltage amplitude reference value of the wind power grid converter; />Representing the wind turbine generator according to the current generator rotor speed omega m Calculating a wind power reference value by adopting a maximum power tracking control algorithm; k (k) pp And k pi The proportional and integral coefficients of the active control loop, respectively.
In order to make the grid-side converter of each wind turbine set bear reactive load proportionally according to capacity without single machine overload, the phase angle of the output voltage of the fan grid-side converter can be adjusted according to the deviation of reactive power, namely:
in the method, in the process of the invention,the reactive power reference value is the reactive power reference value of the fan; k (k) qp And k qi The proportional coefficient and the integral coefficient of the reactive control loop are respectively.
Reference value of current reactive powerAnd the total reactive power of the grid-side converters of all the wind turbines measured at the previous moment is distributed in each wind turbine in proportion to the capacity.
The relationship of the voltage controller of layer 2 and the current controller of layer 3 can be expressed as:
Wherein L is f And C f Respectively representing the inductance and the capacitance of the intermediate frequency filter; u (u) w And u f Respectively representing the alternating current side voltage and the fan transformer valve side voltage of the fan network side converter; i.e w And i s Respectively representing alternating-current side current of a fan network side converter and valve side current of a fan transformer; the variable subscripts d and q represent the d-axis component and q-axis component of the variable, respectively; the variable superscript indicates the reference value of the variable.
k vp And k vi Respectively are provided withThe proportional coefficient and the integral coefficient of the voltage control loop; k (k) ipg And k iig The proportional coefficient and the integral coefficient of the current control loop of the fan network side converter are respectively.
The current control loop will give a reference signal for the output voltage of the ac side of the converter. At DC voltage U dcwt0 While remaining stable, the grid-side inverter can generate a target voltage with a suitable PWM modulation strategy, wherein intermediate frequency components will be filtered out by the LC filter.
As shown in fig. 6, the method for cooperatively controlling the STATCOM device of the SDRU-MMC system includes: controlling the fundamental current; controlling harmonic current; and combining the fundamental current and harmonic current control results, and simultaneously fusing a voltage feedforward result to obtain a STATCOM converter valve control voltage to control the converter valve.
The method for controlling the fundamental frequency current comprises the following steps: inputting a reactive power instruction of the system into a reactive power current regulator for regulation, and outputting a reactive power current target value; inputting a system active command into an active current regulator for regulation, wherein the system active command value is set to 0, namely, the power of the offshore wind farm is all sent out through a DRU unit, and an active current target value is output; inputting an alternating current system voltage into a phase-locked loop to generate a system voltage phase; and combining the reactive current target value with the active current target value, inputting the combined result into a fundamental frequency current controller, and generating a fundamental frequency current control result according to the system voltage phase and the valve side current of the static reactive compensator.
As shown in fig. 7, the control of the fundamental current of the offshore STATCOM device is supplemented with an active power controller and a reactive power controller. In order to utilize the reactive power capacity of the STATCOM device as much as possible, active power is not transmitted on the rectification side STATCOM in a normal state, and the fixed value of the STATCOM active power is set to be 0, namely, all active power sent out by the offshore wind farm is sent out through the DRU unit; because the DRU needs to consume a large amount of reactive power in normal operation, a reactive power controller is added to the STATCOM, so that the offshore STATCOM device can correspondingly output the reactive power of the compensation DRU unit in a normal operation state of the system, and the alternating current filter device of the offshore booster station is omitted. The external power control loop of the marine STATCOM device fundamental current is shown as (15), (16):
In the method, in the process of the invention,and->Active and reactive power reference values, P, respectively transmitted by offshore STATCOM devices sta And Q sta Active and reactive power, Q, respectively, transmitted by offshore STATCOM devices DRU The reactive power k required to be absorbed for running the offshore DRU unit at the current moment spp 、k spi And k sqp 、k sqi Proportional and integral coefficients of the active/reactive power control loop, respectively, the active/reactive power control loop outputs +.>And->And will serve as a reference input to the inner loop current control loop.
The internal control loop of the offshore STATCOM device adopts a DDSRF-PLL control strategy, adopts double synchronous rotation coordinate transformation to eliminate negative sequence fundamental wave components, and adopts a low-pass filtering method to remove harmonic wave components, which is not described herein.
The method for controlling the harmonic current comprises the following steps: inputting the current of the converter valve into a harmonic current detection unit to output a harmonic current target value; and inputting the harmonic current target value and the valve side current of the static var compensator into a harmonic current control unit to generate a harmonic current control result.
And combining the fundamental frequency current and the harmonic current to output a combination result. And fusing the combination result and the voltage feedforward result to obtain the control voltage of the converter valve to control the converter valve.
The control method for the MMC inversion station of the SDRU-MMC system comprises the following steps: the method comprises the steps of adopting constant direct current voltage control and constant alternating current side reactive power/alternating current side voltage amplitude control, controlling constant direct current voltage on the direct current side, and controlling constant alternating current bus voltage amplitude at the junction of the reactive power exchange of the SDRU-MMC system and the land alternating current system or the control system on the alternating current side.
The fault ride-through protection control strategy method for the SDRU-MMC system comprises the following steps: a direct current energy consumption device is arranged on the direct current side of the fan back-to-back converter and the direct current side of the land MMC inversion station; and setting a control protection converter valve locking strategy on the STATCOM device.
As shown in fig. 8, the working principle of the dc power dissipation device (DCchopper) installed on the dc side is that the dc power dissipation device is in a locked state in a normal operation state; when the DC voltage exceeds the upper threshold limit U H When the direct current energy consumption device is triggered to be conducted, the resistor in the direct current energy consumption device is used for dissipating redundant energy; when the DC voltage is lower than the threshold lower limit U L The dc consumer will be locked or bypassed.
Setting a control protection converter valve locking strategy for the STATCOM device, and temporarily locking overcurrent when detecting that the current instantaneous value of a bridge arm of the converter valve exceeds a preset value; when permanent faults occur, when the number of times of continuous triggering temporary locking actions exceeds a threshold value within preset time, locking the converter valve; when the average value of the capacitance voltage of any bridge arm exceeds a threshold value, carrying out overvoltage protection on the average value of the capacitance of a bridge arm submodule of the converter valve, and locking the converter valve; in the operation process of the converter valve, when a power module fails, the power module control board sends a bypass request, the valve control controller counts whether the sum of the number of the sub-modules which are bypassed by any bridge arm and the number of the sub-modules which are currently requested to bypass is larger than a set value or not, and if so, the converter valve is locked; the STATCOM dress displacement flow valve fault ride-through protection control strategy is: after the converter valve detects that the voltage of the offshore alternating current bus drops, the harmonic compensation function is closed, the maximum current is output according to the rated capacity, and after the voltage of the alternating current bus is recovered, the harmonic compensation function and the reactive power instruction are recovered again.
In the embodiment, simulation verification is carried out by taking a 1000MW offshore wind farm alternating current sending-out project as an example, and a test system structure simulation model shown in figure 1 is built. In the simulation model, the wind farm is equivalent to 3 equivalent wind turbines, each equivalent wind turbine is directly connected to a low-voltage side winding of a corresponding offshore boosting platform transformer, a high-voltage side winding of the transformer is connected with an intermediate-frequency uncontrolled rectifying station, and an offshore STATCOM device is connected in parallel to an offshore alternating current bus. The parameters of the main loop of the simulation system are shown in tables 1 to 5.
Table 1 equivalent fan set parameters
Table 2 offshore booster station parameters
| Parameters (parameters) | Actual value | Per unit value |
| Transformer transformation ratio | 35kV/220kV | ------ |
| Rated capacity of transformer | 400MVA(#1)300MVA(#2，#3) | 1.0 |
| Leakage reactance of transformer | ------ | 0.1 |
TABLE 3 offshore STATCOM charge displacement flow valve parameters
| Parameters (parameters) | Actual value | Per unit value |
| Converter power | 400MVA | 1.00 |
| Rated inter-electrode DC voltage | 200kV | 1.00 |
| Shan Qiaobei number of submodules (with redundancy) | 100 | ------ |
| Sub-module capacitor | 6.667mF | ------ |
| Bridge arm reactor | 9.498mH | ------ |
| Rated ac frequency | 100Hz | ------ |
TABLE 4 submarine cable parameters
| Parameters (parameters) | Actual value |
| Length/km | 100 |
| Resistance per unit length/(Ω·km) -1 ) | 0.079 |
| Resistance per unit length/(Ω·km) -1 ) | 0.85 |
| Resistance per unit length/(Ω·km) -1 ) | 0.188 |
Table 5 land MMC inversion station parameters
| Parameters (parameters) | Actual value | Per unit value |
| Converter transformer transformation ratio | 220kV/250kV | ------ |
| Rated capacity of converter transformer | 1200MVA | 1.20 |
| Leakage reactance of converter transformer | ------ | 0.18 |
| Rated inter-electrode DC voltage | 500kV | 1.00 |
| Rated DC power | 1000MW | 1.00 |
| Shan Qiaobei number of sub-modules | 250 | ------ |
| Bridge arm reactor | 47.49mH | ------ |
| Sub-module capacitor | 13.333mF | ------ |
| Upper threshold limit of energy consumption device | 550kV | 1.10 |
| Lower threshold of energy consumption device | 450kV | 0.90 |
As shown in fig. 9, response characteristics of the offshore wind power delivery SDRU-MMC system at the time of wind speed change: assuming that the system is already operating steadily at nominal conditions, at t=2.0 s the wind speed changes from 12m/s step to 11m/s, and the wind speed drops causing the mechanical power of the fan to drop, and the fan speed to drop. Because the fan adopts maximum power tracking control, the fan rotating speed is reduced to directly lead to the reduction of the active power instruction value at the fan network side, thereby reducing the active power of the wind turbine generator, the voltage amplitude at the alternating current side controlled by the network side converter is also reduced, the active power of the static reactive compensator is controlled to be zero, the reactive power required by the reactive power compensation DRU is compensated, the whole system is stably transited to a stable running state after the wind speed is reduced, and the alternating current voltage amplitude at the outlet of the fan network side converter, the alternating current and the direct current of the converter station are gradually and stably reduced.
As shown in table 6, the STATCOM device effects harmonic compensation characteristics of the SDRU-MMC system: the current of the converter valve is compensated by adopting a current source control mode by the converter valve of the STATCOM device, the compensation effect depends on the current measurement precision of the converter valve, and the compensation effect of the converter valve is slightly reduced due to the measurement error of harmonic current at the valve side and the uncertainty of time delay. The static var compensator model compensates 6k + -1 th order harmonic to 49 th order. The harmonic current content of the power grid compensated by the static reactive compensator is reduced, the compensation degree is more than 98%, and the harmonic voltage meets the standard requirement. Loss, temperature rise and vibration of the transformer of the offshore booster station are effectively reduced, and fault risks are reduced.
TABLE 6 harmonic compensation effects table
As shown in fig. 10, response characteristics of the offshore wind power output SDRU-MMC system at the time of land grid short-circuit fault: assuming that the system is already operating stably at rated conditions, at t=2.0 s, the three-phase metallic short-circuit fault occurs in the ac bus of the inverter station, and after 100ms the fault is removed. After the fault occurs, the active power of the inversion station is blocked, and the surplus active power can directly cause the voltage rise of the direct current system; when the direct-current voltage rises to 1.1p.u., the inverter station direct-current side energy consumption device is put in, and surplus power injected into the direct-current system by the DRU is absorbed by the direct-current side energy consumption device, so that the direct-current voltage can be effectively limited to 1.1p.u.. The running state of the 3 equivalent wind turbines is changed due to slight rising of the direct current voltage during the fault, and the reactive power of the converter at the fan network side is fluctuated although the active power of the 3 equivalent wind turbines is basically unchanged during the fault. When the fault disappears, the active power transmission capability of the inverter station is recovered, and the delivery system can be quickly recovered to a stable operation state.
As shown in fig. 11, response characteristics of the offshore wind power delivery SDRU-MMC system at the time of a short-circuit failure of the offshore wind farm: assuming that the system is already operating stably at rated conditions, at t=2.0 s, the three-phase metallic short-circuit fault occurs in the ac bus of the rectifier station, and after 100ms the fault is removed. After the fault occurs, the active power of the wind turbine generator is blocked, and the power transmission of the whole direct current system is interrupted. Due to the effects of the equivalent inductance on the DC side and the equivalent capacitance to ground, the DC voltage and the DC current can oscillate with larger amplitude during the fault. During the fault period, the voltage of the equivalent fan DC link can rise due to the blocking of the active power; when the voltage of the equivalent fan direct current ring rises to 1.1p.u., the fan direct current side energy dissipation device is put in, surplus power injected into the back-to-back converter by the fan side converter can be absorbed, and therefore the voltage of the equivalent fan direct current ring can be effectively limited to 1.1p.u. When the fault disappears, the active power transmission capacity of the equivalent fan is recovered, and the delivery system can be quickly recovered to a stable running state.
As shown in table 7, the STATCOM device performs ac fault ride-through control strategy on the SDRU-MMC system: according to the foregoing, the dc energy dissipation devices on the dc side of the back-to-back converter and the dc side of the inverted MMC station of the fan can absorb the redundant energy in the system, and the STATCOM device replacement flow valve locking strategy is:
detecting that the bridge arm current of the converter valve is temporarily blocked after the delay of 10us when the bridge arm current instantaneous value exceeds 5kA, detecting that the bridge arm current is instantaneously reduced to be lower than 3kA, delaying for 5ms, and unlocking the converter valve;
when the system has permanent faults, the temporary locking can generate multiple actions, so that the equipment is damaged due to continuous frequent switching, and when the temporary locking actions are continuously triggered for three times in 1s, the converter valve is locked;
when the average value of the capacitance voltage of any bridge arm is detected to be larger than 3100V, delaying for 200us, performing overvoltage protection on the average value of the capacitance of a bridge arm submodule of the converter valve, and locking the converter valve;
in the operation process of the converter valve, when the power module fails, the power module control board sends a bypass request to the valve control controller, the valve control controller counts whether the sum of the number of the sub-modules which are bypassed by any bridge arm and the number of the sub-modules which are required to bypass at present is larger than a set value or not, and if so, the converter valve is blocked;
The fault ride-through control strategy of the converter valve is as follows: after the converter valve detects that the voltage of the 220kV alternating current bus drops, the harmonic compensation function is closed, the maximum current is output according to the rated capacity, and after the voltage of the alternating current bus is recovered, the harmonic compensation function and the reactive power instruction are recovered again.
TABLE 7 Experimental items of communication faults
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those having ordinary skill in the art that various modifications to the above-described embodiments may be readily made and the generic principles described herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications within the scope of the present invention.
Claims (10)
1. The offshore large-scale wind power transmission system is characterized by comprising a net-structured fan for providing offshore alternating voltage, an offshore booster station, a high-voltage alternating current transmission sea cable, an onshore MMC inversion station and an onshore alternating current system;
the net-structured fan is connected with an alternating current bus of the offshore booster station, and the alternating current bus of the offshore booster station is connected with the offshore booster station;
Active power sent out by an offshore wind farm is sent out by a high-voltage alternating-current transmission sea cable through a diode rectifying unit of an offshore booster station, and the offshore booster station is provided with a static reactive compensator for providing reactive power required by the diode rectifying unit and filtering corresponding harmonic waves;
the land MMC inversion station controls the constant direct current voltage and the reactive power interaction of the land MMC inversion station and a land alternating current system.
2. A method for controlling the offshore large-scale wind power generation system according to claim 1, comprising:
performing net forming control on the net forming fan to obtain a net forming fan characteristic control result;
performing cooperative control on the static var compensator to obtain a cooperative control result of the static var compensator;
controlling the land MMC inversion station to obtain a land MMC inversion station characteristic control result;
the strategy for controlling and protecting faults of the offshore large-scale wind power transmission system comprises a direct current energy consumption device and a static reactive compensator converter valve locking strategy which are arranged on the direct current side of a back-to-back converter of a fan and the direct current side of a land MMC inverter station, and a system fault ride-through protection control result is obtained;
And controlling the offshore large-scale wind power transmission system according to the characteristic control result of the net-structured fan, the cooperative control result of the static reactive compensator, the characteristic control result of the land MMC inversion station and the system fault ride-through protection control result.
3. The method for controlling a large-scale offshore wind turbine delivery system according to claim 2, wherein the method for controlling the grid-formation type wind turbine comprises the steps of:
the net-structured fan adopts a full-power converter type offshore wind turbine generator set based on a permanent magnet synchronous motor;
the machine side converter of the net-structured fan adopts zero d-axis current control, and the d-axis current reference value is set to be 0; the machine side converter of the fan works in a constant direct current voltage control mode, and a direct current voltage control loop inputs direct current voltage deviation and outputs the direct current voltage deviation as a q-axis current reference value;
the grid-side converter of the grid-formed fan performs coordinate transformation in a control system based on a globally uniform reference coordinate system, and the reference coordinate system position signal theta 0 Given by a broadcast signal or generated by a GPS time signal;
according to the rotating speed of the fans, combining a maximum power tracking algorithm to obtain active power instruction values of all fans, and combining actual measured values of the active power of the fans to generate a fan output voltage reference amplitude;
Obtaining reactive power instruction values of all fans according to a reactive power distribution algorithm, and generating a fan output voltage reference phase angle value by combining the actual measured value of the reactive power of the fans;
according to the fan output voltage reference amplitude and the phase angle value, a valve side voltage reference value of a fan transformer is generated, a valve side voltage actual value of the fan transformer is combined, a voltage control loop is input, an alternating current side current reference value of a fan network side converter is obtained, a current control loop is input, and a converter alternating current side output voltage reference signal is obtained by combining the valve side voltage actual value of the fan transformer, so that a target voltage is generated through a network side converter PWM modulation strategy.
4. The method for controlling a large-scale offshore wind power generation system according to claim 2, wherein the method for cooperatively controlling the static var compensator comprises the steps of:
controlling the fundamental current;
controlling harmonic current;
and combining the fundamental current and harmonic current control results, and simultaneously fusing a voltage feedforward result to obtain a control voltage of the converter valve of the static var compensator, and controlling the converter valve.
5. The method for controlling an offshore large scale wind power generation system according to claim 4, wherein the specific control of the fundamental wave current is:
Inputting a reactive power instruction of a system into a reactive current regulator for regulation, wherein the reactive power instruction value of the system is reactive power required by steady-state operation of a compensation diode rectifying unit;
inputting a system active command into an active current regulator for regulation, wherein the system active command value is set to 0, namely, the power of the offshore wind farm is ensured to be completely sent out through a diode rectifying unit;
inputting an alternating current system voltage into a phase-locked loop to generate a system voltage phase;
and combining the reactive current target value with the active current target value, inputting the combined result into a fundamental frequency current controller, and generating a fundamental current control result according to the system voltage phase and the static reactive compensator valve side current.
6. The method for controlling an offshore large scale wind power generation system according to claim 4, wherein the specific control of the harmonic current is:
inputting the current at the valve side of the diode rectifying unit into a harmonic current control unit to output a harmonic current target value;
and inputting the harmonic current target value and the current at the valve side of the static var compensator into a harmonic current control unit to generate a harmonic current control result.
7. The control method of an offshore large-scale wind power generation system according to claim 2, wherein the control method of an onshore MMC inverter station of the offshore large-scale wind power generation system is:
The method comprises the steps of adopting constant direct current voltage control and constant alternating current side reactive power/alternating current side voltage amplitude control, controlling constant direct current voltage at the direct current side, and controlling constant alternating current bus voltage amplitude at the connection part of the land MMC inversion station and the land alternating current system or controlling reactive power exchange of the land MMC inversion station and the land alternating current system at the alternating current side.
8. The method for controlling an offshore large scale wind power generation system according to claim 2, wherein the dc energy consuming device locking strategy is as follows:
when a short circuit fault occurs in the land alternating current system, the voltage of an alternating current bus of the land MMC inversion station is rapidly reduced, the transmission of direct current power is blocked, the direct current voltage of the offshore large-scale wind power transmission system is rapidly increased, the direct current is reduced to 0, the diode of the diode rectifying unit is blocked, and the active power output by a fan can induce power frequency overvoltage in a wind power plant; when a short circuit fault occurs to an alternating current bus of the offshore booster station, a net-structured fan net side converter cannot output active power captured by a fan, and a direct current link of a back-to-back fan converter generates direct current overvoltage; when the power transmission of the fan network side converter is blocked, the direct current energy consumption device is used for maintaining the voltage stability of the direct current capacitor;
meanwhile, a direct current energy consumption device is also arranged on the direct current side of the land MMC inversion station, so that the direct current system is helped to complete alternating current fault ride-through on the inversion side; in a normal running state, the direct current energy consumption device is in a locking state, and when the direct current voltage exceeds the upper limit of the threshold value, the direct current energy consumption device is triggered to be conducted, and redundant energy is dissipated by using a resistor in the direct current energy consumption device; when the dc voltage is below the lower threshold, the dc energy consuming device will latch or bypass.
9. The method for controlling an offshore large scale wind power generation system of claim 2, wherein the static var compensator converter valve locking strategy is as follows:
detecting that the current instantaneous value of a bridge arm of the converter valve exceeds a preset value, and temporarily blocking overcurrent;
when permanent faults occur, locking the converter valve of the static var compensator when the number of times of continuous triggering temporary locking actions exceeds a threshold value within preset time;
when the average value of the capacitance voltage of any bridge arm exceeds a threshold value, carrying out overvoltage protection on the average value of the capacitance of a bridge arm submodule of the converter valve, and locking the converter valve;
in the operation process of the converter valve, when a power module fails, a power module control board sends a bypass request, a valve control controller counts whether the sum of the number of the submodules which are bypassed by any bridge arm and the number of the submodules which are currently requested to bypass is larger than a set value or not, and if so, the converter valve is locked;
the fault ride-through control strategy of the converter valve of the static var compensator is as follows: after the converter valve detects that the voltage of the alternating current bus of the offshore booster station drops, the harmonic compensation function is closed, the maximum current is output according to the rated capacity, and after the voltage of the alternating current bus of the offshore booster station is recovered, the harmonic compensation function and the reactive power instruction are recovered again.
10. A computer-readable storage medium, characterized in that the computer-readable storage medium has stored thereon a computer program that is executed by a processor to realize the control method of the offshore large-scale wind power delivery system according to any one of claims 2 to 9.
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