CN113708409A - Offshore wind power conversion method and system based on modular solid-state transformer - Google Patents
Offshore wind power conversion method and system based on modular solid-state transformer 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
- H02J3/38—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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
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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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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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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Abstract
The invention discloses an offshore wind power conversion method and system based on a modular solid-state transformer, which comprises the following steps: utilizing the machine side converters to transmit wind power to the low-voltage direct-current ports, and connecting the direct-current ports of the machine side converters in parallel for convergence to form a low-voltage direct-current bus; based on DAB active power control, uniformly transmitting the wind power of a low-voltage direct-current bus to each submodule of an MMC; through the direct current capacitor voltage and active/reactive current control of the MMC, wind power is transmitted to a medium-voltage alternating current end of the MMC, and medium-voltage alternating current convergence of output power of each wind turbine generator is achieved. The invention has the advantages of less cables, low cost and no current stress and cable distortion problems; the problems of size, weight and platform construction cost of the power frequency transformer are solved, and the high-capacity offshore wind turbine power conversion system is compact, integrated and light; the low-frequency fluctuation of the capacitance and voltage of the MMC sub-module can be greatly reduced, the power density of the device is optimized, and the light and compact design of the engine room is realized.
Description
Technical Field
The invention relates to the technical fields of offshore wind power generation conversion technology, power electronic technology, control technology and the like in a power system, in particular to an offshore wind power conversion method and system based on a modular solid-state transformer.
Background
Wind power generation is one of the most mature and scale-developed power generation modes in new energy power generation, and the scale of a wind power plant is gradually increased along with the development and application of the wind power generation technology. Offshore wind power has the advantages of stable resource conditions, closer distance to a load center and the like, and becomes an important direction for the development of wind power of various countries in the world in recent years.
In order to reduce the power generation cost, the offshore wind turbine generator is developed towards ultra-large scale, the generation time of 10MW level is entered, when the large-capacity offshore wind turbine generator is connected to the grid, a transformer needs to be configured to boost the voltage, and the large-capacity power frequency transformer has large volume, large occupied area and large weight, so that the construction cost and the operation and maintenance difficulty of the fan grid-connected platform can be further improved.
A conventional large capacity offshore wind power generation system is shown in fig. 1. In fig. 1, a multi-winding generator of an offshore wind turbine is connected to a 1.1kV low-voltage DC port through a plurality of machine side AC-DC converters, and then forms a 690V low-voltage AC port at an engine room outlet through a grid side DC-AC converter, and after passing through a low-voltage AC cable inside a tower drum of hundreds of meters, the wind turbine is boosted through a 690V/35kV power frequency transformer of an offshore boosting platform, thereby realizing 35kV medium-voltage AC convergence of the offshore wind turbine.
The offshore wind power generation system shown in fig. 1 is simple in structure and stable in operation. However, with the trend of increasing the capacity of offshore wind turbines, the system has the following problems: the 690V alternating current cable voltage is too low, and for a large-capacity wind turbine generator system, a large number of alternating current cables need to be configured to meet cable current stress during wind power transmission, so that the cable cost is high; when the wind turbine generator normally operates, the engine room rotates according to the wind direction to obtain the maximum generating power, so that the problems of distortion and uneven stress among low-voltage alternating-current cables in the tower can be easily caused, and potential safety hazards of a system are caused; the large-capacity power frequency transformer is too high in size and weight, and the construction cost of the offshore boosting platform is greatly increased.
Therefore, in order to realize the design of the high-capacity offshore wind power generation system with compactness, integration and light weight, the problems of the quantity and the distortion of low-voltage alternating current cables and the problems of the size and the weight of a high-capacity industrial frequency transformer need to be solved.
Disclosure of Invention
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the above-mentioned conventional problems.
Therefore, the technical problem solved by the invention is as follows: the 690V alternating current cable voltage is too low, and for a large-capacity wind turbine generator system, a large number of alternating current cables need to be configured to meet cable current stress during wind power transmission, so that the cable cost is high; when the wind turbine generator normally operates, the engine room rotates according to the wind direction to obtain the maximum generating power, so that the problems of distortion and uneven stress among low-voltage alternating-current cables in the tower can be easily caused, and potential safety hazards of a system are caused; the large-capacity power frequency transformer is too high in size and weight, and the construction cost of the offshore boosting platform is greatly increased.
In order to solve the technical problems, the invention provides the following technical scheme: utilizing the machine side converters to transmit wind power to the low-voltage direct-current ports, and connecting the direct-current ports of the machine side converters in parallel for convergence to form a low-voltage direct-current bus; based on DAB active power control, uniformly transmitting the wind power of a low-voltage direct-current bus to each submodule of an MMC; through the direct current capacitor voltage and the active/reactive current control of the MMC, wind power is transmitted to the medium-voltage alternating current end of the MMC, and medium-voltage alternating current convergence of output power of each wind turbine generator is achieved.
As a preferable scheme of the offshore wind power conversion method based on the modular solid-state transformer, the method comprises the following steps: the input side of DAB is low voltage direct current bus, the output side with each submodule interconnection of MMC.
As a preferable scheme of the offshore wind power conversion method based on the modular solid-state transformer, the method comprises the following steps: the DAB control strategy comprises low-voltage direct-current voltage common duty ratio control and RPD control.
As a preferable scheme of the offshore wind power conversion method based on the modular solid-state transformer, the method comprises the following steps: the low-voltage direct-current voltage common duty cycle control is realized by closed-loop PI control, the input of the PI controller is the deviation of a voltage reference value and an actual value, and the output is the common phase shift angle of each DAB module; the RPD control comprises the steps of realizing through open loop calculation, wherein the RPD control input is instantaneous power of each bridge arm of the MMC obtained through online calculation, and the RPD control output is a fluctuation phase shift angle of DAB of each bridge arm; and superposing the fluctuation phase shift angle and the public phase shift angle to obtain phase shift angle reference values required by all the DAB modules of the three-phase six-bridge arm.
As a preferable scheme of the offshore wind power conversion method based on the modular solid-state transformer, the method comprises the following steps: the MMC control strategy comprises voltage current control and capacitance voltage balance control.
As a preferable scheme of the offshore wind power conversion method based on the modular solid-state transformer, the method comprises the following steps: the voltage and current control is realized through closed-loop PI control, the input of an external voltage loop PI controller is the deviation of a capacitor voltage reference value and the average value of the actual voltage of each capacitor, and the output is an active current reference value; defining a reactive current reference value as 0, or configuring a reactive power control loop to realize output; and the active/reactive current is controlled by a decoupling PI to output a three-phase voltage reference value, a superposed direct current voltage reference value and the output of module capacitor voltage balance control, so that a modulation voltage reference value required by each MMC submodule of the three-phase six-bridge arm is obtained.
In order to solve the technical problems, the invention provides the following technical scheme: offshore wind power conversion system based on modularization solid state transformer includes: the machine side converter is used for transmitting wind power to the low-voltage direct-current port, and the direct-current ports of the machine side converters are connected in parallel and converged to form a low-voltage direct-current bus; and the modularized solid-state transformer is connected with the machine side converter and is used for realizing medium-voltage alternating current convergence of the output power of each wind turbine generator.
As a preferred solution of the offshore wind power conversion system based on the modular solid-state transformer, the present invention further comprises: modularization solid state transformer includes two active bridge converter units DAB and the many level of modularization transverter MMC, the input side of two active bridge converter units DAB is low pressure direct current bus, the output side with each submodule piece interconnection of the many level of modularization transverter MMC, through the active power control of two active bridge converter units DAB will the wind-powered electricity generation power of low pressure direct current bus divides equally and transmits to in each submodule piece of the many level of modularization transverter MMC, through the many level of modularization transverter MMC's direct current capacitor voltage and active/reactive current control, finally transmit wind-powered electricity generation power to the middling pressure AC end of the many level of modularization MMC transverter realizes that the middling pressure of each wind turbine generator output exchanges and assembles.
The invention has the beneficial effects that: the outlet of the engine room is a medium-voltage alternating-current cable, the power of the fan can be transmitted to a convergence point only by 1-2 medium-voltage cables in the tower, the number of the cables is small, the cost is low, and the problems of current stress and cable distortion do not exist; the high-frequency transformer is adopted, electrical isolation and high-frequency voltage transformation are completed inside the wind turbine cabin, the configuration of an external power frequency transformer is cancelled, the problems of size, weight and platform construction cost of the power frequency transformer are solved, and the high-capacity offshore wind turbine power conversion system is compact, integrated and light; through adding the fluctuation power control in the control loop of each DAB module, the low-frequency fluctuation of the capacitance voltage of the MMC sub-module can be greatly reduced, the power density of the device is optimized, and the light and compact design of the engine room is realized.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:
fig. 1 is a schematic diagram of a conventional offshore wind power generation system of an offshore wind power conversion method and system based on a modular solid-state transformer according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a control strategy of a modular solid-state transformer of the offshore wind power conversion method and system based on the modular solid-state transformer according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a set wind speed curve of the offshore wind power conversion method and system based on the modular solid-state transformer according to an embodiment of the present invention;
fig. 4 is a schematic diagram of active power and reactive power curves of a wind turbine grid-connected point of an offshore wind power conversion method and system based on a modular solid-state transformer according to an embodiment of the present invention;
fig. 5 is a schematic diagram of low-voltage dc voltage and low-voltage dc current curves of an offshore wind power conversion method and system based on a modular solid-state transformer according to an embodiment of the present invention;
fig. 6 is a schematic view of a sub-module capacitance-voltage curve of the offshore wind power conversion method and system based on the modular solid-state transformer according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a modular solid-state transformer topology of an offshore wind power conversion method and system based on the modular solid-state transformer according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a modular solid-state transformer module unit topology of the offshore wind power conversion method and system based on the modular solid-state transformer according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of a high-capacity offshore wind power generation system for an offshore wind power conversion method and system based on modular solid-state transformers according to an embodiment of the present invention;
fig. 10 is a schematic block structure diagram of an offshore wind power conversion method and system based on a modular solid-state transformer according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below, and it is apparent that the described embodiments are a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, shall fall within the protection scope of the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
The present invention will be described in detail with reference to the drawings, wherein the cross-sectional views illustrating the structure of the device are not enlarged partially in general scale for convenience of illustration, and the drawings are only exemplary and should not be construed as limiting the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
Meanwhile, in the description of the present invention, it should be noted that the terms "upper, lower, inner and outer" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation and operate, and thus, cannot be construed as limiting the present invention. Furthermore, the terms first, second, or third are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The terms "mounted, connected and connected" in the present invention are to be understood broadly, unless otherwise explicitly specified or limited, for example: can be fixedly connected, detachably connected or integrally connected; they may be mechanically, electrically, or directly connected, or indirectly connected through intervening media, or may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example 1
Referring to fig. 1 to 6, an embodiment of the present invention provides an offshore wind power conversion method based on a modular solid-state transformer, including:
s1: wind power is transmitted to a low-voltage direct-current port by utilizing the machine side converters 100, and the direct-current ports of the machine side converters 100 are connected in parallel and converged to form a low-voltage direct-current bus;
s2: based on the active power control of DAB201, uniformly transmitting the wind power of a low-voltage direct-current bus to each submodule of an MMC 202;
s3: through the direct current capacitor voltage and the active/reactive current control of the MMC202, the wind power is transmitted to the medium-voltage alternating current end of the MMC202, and medium-voltage alternating current convergence of the output power of each wind turbine generator is achieved.
The steps S1 to S3 specifically include:
the input side of the DAB201 is a low-voltage direct current bus, and the output side of the DAB is interconnected with all the submodules of the MMC 202.
The control strategy of the high-capacity offshore wind power generation system based on the modular solid-state transformer is shown in FIG. 2; the machine side AC-DC converter transmits the wind power of each winding to a low-voltage direct current side through active power control; the MMC-SST is formed by cascading a plurality of DAB201 units and MMC202, wherein the low-voltage direct-current voltage of each DAB201 unit is controlled to realize the stabilization of the low-voltage direct-current voltage at the input side, and the wind power is transmitted to the side of an MMC202 sub-module; the MMC202 controls the voltage of the direct current capacitor of the submodule to realize the stabilization of the voltage of the output side of the DAB201 and transmits the wind power to the medium-voltage alternating current port; in addition, the DAB201 unit also transmits the instantaneous fluctuation power in the MMC202 to the low-voltage direct current side by an additional fluctuation power control strategy, and the three-phase instantaneous fluctuation power is self-balanced, so that the fluctuation of the sub-module capacitor voltage is greatly reduced while the stable transmission power of each winding of the fan is not influenced, the capacitor selection is optimized, and the compact and light design of the cabin is realized.
The DAB201 control strategy is formed by low-voltage direct-current voltage common duty ratio control and RPD control; the low-voltage direct-current voltage control is realized through closed-loop PI control, the input of a PI controller is the deviation of a voltage reference value and an actual value, and the output is the common phase shift angle of each DAB201 module; the RPD control is realized by open-loop calculation, the control input of the RPD control is instantaneous power of each bridge arm of the MMC202 obtained by online calculation, and the control output of the RPD control is a fluctuation phase shift angle of DAB201 of each bridge arm. And superposing the fluctuation phase shift angle and the public phase shift angle to obtain the phase shift angle reference value required by each DAB201 module of the three-phase six-bridge arm.
The MMC202 control strategy is formed by voltage current control and capacitance voltage balance control; the voltage and current control is realized by closed-loop PI control, the input of an external voltage loop PI controller is the deviation of a capacitor voltage reference value and the average value of the actual capacitor voltage, and the output is an active current reference value; setting a reactive current reference value to be 0, or configuring a reactive power control loop to realize output; the active reactive current is controlled by a decoupling PI, a three-phase voltage reference value is output, a direct current voltage reference value is superposed, and the output of module capacitor voltage balance control is output, so that the modulation voltage reference value required by each MMC202 sub-module of the three-phase six-bridge arm can be obtained.
In order to verify the theoretical feasibility of the scheme provided by the section, a 10MVA type MMC-SST is built in a Matlab/Simulink simulation model, a high-capacity fan is equivalent to a power source connected to a low-voltage direct-current bus side, a medium-voltage direct-current side is in no-load, and simulation parameters are shown in the following table.
Table 1: and (4) a simulation parameter table.
The simulation timing settings are as follows:
when t is 0s, starting the MMC-SST, and not starting the fan;
when t is 0.8s, setting the wind speed to be 10m/s, transmitting 4MW power by the equivalent power source of the fan, and adopting a control strategy shown in fig. 2 by the MMC-SST;
t is 1.5s, the set wind speed is 15m/s, and the equivalent power source of the fan transmits 10MW power;
t is 2.2s, and the simulation ends.
In the simulation example, the modular solid-state transformer consists of a medium-voltage side MMC and a plurality of DABs; different converters need to adopt different modulation modes to realize the steady-state operation of the converters. For the MMC at the medium-voltage side, a carrier phase-shifting modulation mode is adopted; for DAB, a square wave phase-shifting modulation mode is adopted; the simulation results are shown in FIGS. 3 to 6.
Fig. 3 shows a wind speed waveform set in the simulation, in which the initial wind speed is set at 10m/s, and the wind speed increases to 15m/s after t is 0.8 s.
FIG. 4 shows the active power and reactive power waveforms of the wind turbine grid-connected point; through the reactive current control in fig. 2, under different working conditions, the reactive power of the fan grid-connected point can be controlled to be 0; before the fan is started, the active power of a grid-connected point is 0; after the fan is started, when the wind speed is 10m/s, the output power of the fan is 5MW, and the active power of a fan grid-connected point is stabilized at 5MW after 3-4 cycles through the active current control in FIG. 2; when the wind speed is 15m/s, the output power of the fan is 10MW, and the active power of a fan grid-connected point is stabilized at 10MW after 3-4 cycles through the active current control in the graph 2. Therefore, the control strategy shown in fig. 2 can realize independent control of active power and reactive power of the fan, stable transmission of fan power and reliable grid connection.
FIG. 5 is a low voltage DC bus voltage and current waveform; after the MMC-SST is started, a stable 1.1kV bus voltage can be established; after the fan is started, the direct current is increased to 4.55kA from 0A, and after the power of the fan is increased to 10MW, the direct current is increased to 9.1 kA; the low-voltage side current and the low-voltage side have no low-frequency ripple, which shows that the three-phase fluctuation power can realize self-balance on the low-voltage direct current side under the control of the fluctuation power, and the transmission of the power of the fan is not influenced.
FIG. 6 is a MMC sub-module capacitance voltage waveform; after the MMC-SST is started, stable 2kV capacitor voltage can be established through the capacitor voltage average value control in the figure 2, but the fan is not started, and the MMC-SST does not transmit power, so that the capacitor voltage has no fluctuation; after the fan is started, the low-frequency fluctuation of the capacitor voltage can be greatly inhibited through the fluctuation power control, so that the ripple amplitude of the capacitor voltage is within 0.85%; and after the power of the fan is changed from 5MW to 10MW, the capacitor voltage is still stabilized at 2kV through 3-4 cycles, and the ripple amplitude is within 0.85%. The result verifies the effectiveness and feasibility of the fluctuating power control under the power transmission working condition of the low-voltage side of the fan.
Example 2
Referring to fig. 7 to 10, according to another embodiment of the present invention, which is different from the first embodiment, there is provided an offshore wind power conversion system based on a modular solid-state transformer, including:
the generator side converter 100 is used for transmitting wind power to a low-voltage direct-current port, the direct-current ports of the generator side converters 100 are connected in parallel and converged to form a low-voltage direct-current bus, and the generator side converter 100 is a generator side AC/DC converter;
the modularized solid-state transformer 200 is connected to the machine-side converter 100, and is used for realizing medium-voltage alternating current convergence of output power of each wind turbine.
The Modular Solid-State Transformer 200(Modular Multilevel Converter based Solid State Converter, MMC-SST) comprises a plurality of double-Active-Bridge Converter units DAB201(Dual Active Bridge, DAB) and a Modular Multilevel Converter MMC202(Modular Multilevel Converter, MMC), wherein the input side of the double-Active-Bridge Converter units DAB201 is a low-voltage direct-current bus, the output side is interconnected with each sub-module of the Modular Multilevel Converter MMC201, wind power of the low-voltage direct-current bus is evenly transmitted to each sub-module of the Modular Multilevel Converter MMC202 through Active power control of the double-Active-Bridge Converter units DAB201, and the wind power is finally transmitted to a medium-voltage alternating-current end of the Modular Multilevel Converter MMC202 through direct-current capacitor voltage and Active/reactive current control of the Modular Multilevel Converter MMC202, so that medium-voltage alternating-current convergence of output power of each wind turbine generator set is realized.
Specifically, the topological architecture of the modular solid-state transformer 200(MMC-SST) is shown in fig. 7; the MMC-SST topology is formed by an MMC202 and a plurality of DAB201 units together, the MMC202 can provide medium-voltage alternating current (MVAC) and medium-voltage direct current (MVDC) ports, the input sides of all the DAB201 units are connected in parallel and converged to form a low-voltage direct current (LVDC) port, the direct current side of each Submodule (Submodule, SM) of the MMC202 is connected with the output side of the DAB201 unit in an interconnecting mode to form a module unit of the MMC-SST, the specific topology of the module unit is shown in figure 8, and power transmission among the low-voltage ports in the MMC-SST can be achieved through the module unit.
The large-capacity offshore wind power generation system proposed by the invention is shown in fig. 9 by combining the MMC-SST, the machine side AC-DC converter and the offshore wind power generation unit. In fig. 9, the multi-winding generator of the large-capacity offshore wind turbine generator system is connected in parallel to the low-voltage direct current side through AC-DC machine side converters, the direct current bus is interconnected to the MMC202 submodule side through the DAB201 unit of the upper and lower bridge arms of the MMC-SST topology, and is connected in series to boost through the MMC202 submodule, an output voltage of medium-voltage alternating current is formed at the outlet side of the wind turbine generator room, and is transmitted to the medium-voltage aggregation network through a medium-voltage alternating current cable, so that the power conversion of the large-capacity offshore wind turbine generator system is realized.
It should be recognized that embodiments of the present invention can be realized and implemented by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer readable memory. The methods may be implemented in a computer program using standard programming techniques, including a non-transitory computer-readable storage medium configured with the computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner, according to the methods and figures described in the detailed description. Each program may be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the program(s) can be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language. Furthermore, the program can be run on a programmed application specific integrated circuit for this purpose.
Further, the operations of processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The processes described herein (or variations and/or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions, and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) collectively executed on one or more processors, by hardware, or combinations thereof. The computer program includes a plurality of instructions executable by one or more processors.
Further, the method may be implemented in any type of computing platform operatively connected to a suitable interface, including but not limited to a personal computer, mini computer, mainframe, workstation, networked or distributed computing environment, separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, and the like. Aspects of the invention may be embodied in machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optically read and/or write storage medium, RAM, ROM, or the like, such that it may be read by a programmable computer, which when read by the storage medium or device, is operative to configure and operate the computer to perform the procedures described herein. Further, the machine-readable code, or portions thereof, may be transmitted over a wired or wireless network. The invention described herein includes these and other different types of non-transitory computer-readable storage media when such media include instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor. The invention also includes the computer itself when programmed according to the methods and techniques described herein. A computer program can be applied to input data to perform the functions described herein to transform the input data to generate output data that is stored to non-volatile memory. The output information may also be applied to one or more output devices, such as a display. In a preferred embodiment of the invention, the transformed data represents physical and tangible objects, including particular visual depictions of physical and tangible objects produced on a display.
As used in this application, the terms "component," "module," "system," and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, or software in execution. For example, a component may be, but is not limited to being: a process running on a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of example, both an application running on a computing device and the computing device can be a component. One or more components can reside within a process and/or thread of execution and a component can be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures thereon. The components may communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a network such as the internet with other systems by way of the signal).
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (8)
1. The offshore wind power conversion method based on the modularized solid-state transformer is characterized by comprising the following steps:
wind power is transmitted to a low-voltage direct-current port by utilizing a machine side converter (100), and the direct-current ports of the machine side converters (100) are connected in parallel and converged to form a low-voltage direct-current bus;
equally dividing and transmitting the wind power of a low-voltage direct-current bus to each submodule of an MMC (202) based on the active power control of the DAB (201);
through the direct current capacitor voltage and the active/reactive current control of MMC (202), transmit wind power to the middling pressure alternating current end of MMC (202), realize that the middling pressure of each wind turbine generator system output power exchanges and assembles.
2. An offshore wind power conversion method based on modular solid state transformers according to claim 1, characterized in that: the input side of DAB (201) is low pressure direct current bus, the output side with each submodule piece interconnection of MMC (202).
3. An offshore wind power conversion method based on modular solid state transformers according to claim 1 or 2, characterized in that: the control strategy of the DAB (201) comprises low-voltage direct-current voltage common duty ratio control and RPD control.
4. An offshore wind power conversion method based on modular solid state transformers according to claim 3, characterized in that: also comprises the following steps of (1) preparing,
the low-voltage direct-current voltage common duty cycle control comprises,
the method is realized through closed-loop PI control, the input of the PI controller is the deviation of a voltage reference value and an actual value, and the output is the common phase shift angle of each DAB (201) module;
the RPD control includes the steps of,
the method is realized through open loop calculation, the RPD control input is instantaneous power of each bridge arm of the MMC (202) obtained through online calculation, and the RPD control output is a fluctuation phase shift angle of DAB (201) of each bridge arm;
and superposing the fluctuation phase shift angle and the public phase shift angle to obtain phase shift angle reference values required by all DAB (201) modules of the three-phase six-bridge arm.
5. An offshore wind power conversion method based on modular solid state transformers according to claim 1 or 2, characterized in that: the control strategy of the MMC (202) comprises voltage current control and capacitance voltage balance control.
6. An offshore wind power conversion method based on modular solid state transformers according to claim 5, characterized in that: also comprises the following steps of (1) preparing,
the voltage and current control is realized through closed-loop PI control, the input of an external voltage loop PI controller is the deviation of a capacitor voltage reference value and the average value of the actual capacitor voltage, and the output is an active current reference value;
defining a reactive current reference value as 0, or configuring a reactive power control loop to realize output;
active/reactive current is controlled through a decoupling PI, three-phase voltage reference values are output, direct current voltage reference values are superposed, and output of module capacitor voltage balance control is achieved, so that modulation voltage reference values needed by all MMC (202) sub-modules of the six-bridge arm three-phase are obtained.
7. Offshore wind power conversion system based on modularization solid state transformer, its characterized in that includes:
the system comprises machine side converters (100), wherein the machine side converters (100) are used for transmitting wind power to low-voltage direct-current ports, and the direct-current ports of the machine side converters (100) are connected in parallel and converged to form a low-voltage direct-current bus;
and the modularized solid-state transformer (200) is connected with the machine side converter (100) and is used for realizing medium-voltage alternating current convergence of the output power of each wind turbine generator.
8. An offshore wind power conversion process based on modular solid state transformers according to claim 8, characterized in that: modularization solid state transformer (200) are including two active bridge converter units DAB (201) and modularization multilevel converter MMC (202), the input side of two active bridge converter units DAB (201) is low pressure direct current bus, the output side with each submodule piece interconnection of modularization multilevel converter MMC (201), through the active power control of two active bridge converter units DAB (201), will the wind-powered electricity generation power of low pressure direct current bus divides equally and transmits to in each submodule piece of modularization multilevel converter MMC (202), through the direct current capacitance voltage and the active/reactive current control of modularization multilevel converter MMC (202), with wind-powered electricity generation power final transmission arrive the middling pressure alternating current end of modularization multilevel converter MMC (202), realize that the middling pressure of each wind turbine generator group output power exchanges and assembles.
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