Offshore wind power twelve-pulse diode rectification sending-out system and construction method

Abstract

The invention discloses an offshore wind power twelve-pulse diode rectification sending-out system and a construction method. The offshore wind power twelve-pulse diode rectification sending-out system comprises a gas insulation switch device, M alternating current filters, a converter transformer, a twelve-pulse wave uncontrolled rectification valve and a smoothing reactor. The gas insulated switchgear is used for receiving an initial alternating current power supply output by the offshore wind power generator set; the converter transformer is used for carrying out voltage conversion on an initial alternating-current power supply and outputting the alternating-current power supply; the twelve-pulse-wave uncontrolled rectifying valve is used for rectifying an alternating current power supply to obtain an initial direct current power supply; the alternating current filter is used for filtering voltage harmonics and current harmonics generated by the twelve-pulse wave uncontrolled rectifying valve; the smoothing reactor is used for suppressing current harmonics generated by the direct current side voltage harmonics in the initial direct current power supply so as to output the direct current power supply. According to the offshore wind power twelve-pulse diode rectification sending-out system, the size and weight of an offshore converter station can be greatly reduced, and then the manufacturing cost of a power transmission project is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation, and in particular to an offshore wind power twelve-pulse diode rectification and transmission system and a construction method thereof. Background Art

[0002] Among many renewable energy sources, wind power generation has become a new energy source with the potential for large-scale commercial development due to its advantages such as low cost, large reserves, and mature technology. Currently, the wind power resources that can be developed mainly include onshore and offshore. Compared with onshore wind power, offshore wind power has the advantages of abundant resources, high wind speed, good quality, and small impact on the environment, and is a new growth point for wind power generation.

[0003] At present, the cost of offshore converter stations is mainly affected by the volume and weight of the platform. In the Rudong project, the weight of the 1100MW offshore platform reached 22,000 tons, and the preliminary design of the 2000MW offshore platform of the Qingzhou project was about 27,000 tons. The heavier the weight, the more limited the transportation resources and the higher the cost. According to the data provided by CNOOC, the current domestic platform transportation weight limit is about 30,000 tons. Grid parity is the future trend of offshore wind power resource development, and it is also a difficult problem that the industry must face. Therefore, the main breakthrough in the current industry on how to reduce the cost of deep-sea flexible direct transmission projects is how to reduce the volume and weight of offshore converter station platforms. Summary of the invention

[0004] The present invention provides an offshore wind power twelve-pulse diode rectification and transmission system and a construction method to solve the above-mentioned technical problems and effectively reduce the volume and weight of the offshore converter station platform.

[0005] In order to solve the above technical problems, the present invention provides an offshore wind power twelve-pulse diode rectification and transmission system, comprising:

[0006] Gas insulated switchgear, M AC filters, converter transformers, twelve-pulse uncontrolled rectifier valves and smoothing reactors, where M is a preset positive integer;

[0007] The gas insulated switchgear is electrically connected to M AC filters and the grid side of the converter transformer respectively;

[0008] The valve side of the converter transformer is electrically connected to the twelve-pulse uncontrolled rectifier valve;

[0009] The twelve-pulse uncontrolled rectifier valve is electrically connected to the smoothing reactor;

[0010] Wherein, the gas insulated switchgear is used to receive the initial AC power output by the offshore wind power generator set;

[0011] The converter transformer is used to convert the voltage of the initial AC power supply and output AC power supply;

[0012] The twelve-pulse uncontrolled rectifier valve is used to rectify the AC power supply to obtain an initial DC power supply;

[0013] The AC filter is used to filter out the 11th, 13th, 23rd and 25th voltage harmonics and current harmonics generated when the twelve-pulse uncontrolled rectifier valve performs rectification;

[0014] The smoothing reactor is used to suppress current harmonics generated by voltage harmonics on the DC side in the initial DC power supply to output DC power supply.

[0015] The beneficial effects of the present invention are:

[0016] The offshore wind power twelve-pulse diode rectification and transmission system of the present invention adopts a twelve-pulse uncontrolled rectifier valve for rectification at the transmission end based on the hybrid flexible direct current transmission technology of high-power diodes. As a diode rectifier valve, the twelve-pulse uncontrolled rectifier valve has more advantages in volume and weight than the modular multi-level topology. Their sizes are basically not in the same order of magnitude. In addition, each diode constituting the twelve-pulse uncontrolled rectifier valve has no trigger circuit, which is equivalent to a passive component and can be installed in a closed structure, so that the reliability of the twelve-pulse uncontrolled rectifier valve is higher than that of the modular multi-level topology, and it is very suitable for complex offshore environments and does not require year-round maintenance. Therefore, the offshore wind power twelve-pulse diode rectification and transmission system of the present invention adopts a twelve-pulse uncontrolled rectifier valve for rectification, which can greatly reduce the volume and weight of the offshore converter station, thereby reducing the cost of the transmission project.

[0017] The present invention filters out 11th, 13th, 23rd and 25th voltage harmonics and current harmonics generated when the twelve-pulse uncontrolled rectifier valve performs rectification through the AC filter, and suppresses the current harmonics generated by the DC side voltage harmonics of the initial DC power supply through the smoothing reactor, thereby avoiding excessive harmonic current of the system and making the output DC close to the ideal DC, thereby improving the power quality of the offshore wind power output power supply and the safety and reliability of the offshore wind power supply.

[0018] As a preferred solution, the converter transformer includes several groups of three-winding transformers;

[0019] The twelve-pulse uncontrolled rectifier valve includes four groups of six-pulse uncontrolled rectifiers with a 30-degree difference between them;

[0020] Four groups of six-pulse uncontrolled rectifiers with a mutual difference of 30 degrees are connected in series or electrically connected to the smoothing reactor on the DC side, and the four groups of six-pulse uncontrolled rectifiers are connected in parallel to the AC bus through four groups of three-winding transformers on the AC side.

[0021] As a preferred solution, the AC filter is a passive double-tuned filter.

[0022] In order to solve the above technical problems, the present invention also provides a method for constructing an offshore wind power twelve-pulse diode rectifier transmission system, which is applied to an offshore wind power twelve-pulse diode rectifier transmission system as described above. The method for constructing an offshore wind power twelve-pulse diode rectifier transmission system comprises:

[0023] Obtaining the system structure of an offshore wind power twelve-pulse diode rectification and transmission system as described above;

[0024] Determine the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system according to the scale of offshore wind power;

[0025] Based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system and the harmonic problem of the twelve-pulse uncontrolled rectifier valve, the AC filter parameters, smoothing reactor parameters, transformer ratio of the converter transformer, transformer capacity of the converter transformer, rated current of the twelve-pulse uncontrolled rectifier valve and rated voltage of the twelve-pulse uncontrolled rectifier valve are designed and obtained respectively, so as to obtain the parameter design scheme of the offshore wind power twelve-pulse diode rectifier transmission system;

[0026] An offshore wind power twelve-pulse diode rectification transmission system is constructed based on parameter design scheme and system structure.

[0027] In order to solve the problems existing in the prior art, the present invention designs an offshore wind power twelve-pulse diode rectifier transmission system. Different from the existing offshore wind power transmission system adopting a modular multi-level topology structure, the present invention adopts a twelve-pulse uncontrolled rectifier valve to form an offshore wind power twelve-pulse diode rectifier transmission system. However, since the circuit topology structure, operating state, and operating mode of the modular multi-level topology and the twelve-pulse uncontrolled rectifier valve are different, the parameter design and implementation methods of the two offshore wind power transmission systems are completely different. In addition, due to the problem that the parameters in the offshore wind power twelve-pulse diode rectifier transmission system of the present invention are difficult to design, the offshore wind power twelve-pulse diode rectifier transmission system proposed by the present invention is The twelve-pulse diode rectifier transmission system is difficult to be directly applied to the actual power transmission project. Therefore, the present invention proposes a construction method of an offshore wind power twelve-pulse diode rectifier transmission system. Based on the system structure of the offshore wind power twelve-pulse diode rectifier transmission system and considering the harmonic problem of the twelve-pulse uncontrolled rectifier valve, a parameter design scheme is obtained by matching and designing various parameters of the AC filter, smoothing reactor, converter transformer and the twelve-pulse uncontrolled rectifier valve. Finally, a twelve-pulse diode rectifier transmission system for offshore wind power is constructed by combining the parameter design scheme and the system structure, so that it can be actually applied to realize the efficient and safe transmission of the electric energy generated by the offshore wind farm.

[0028] As a preferred solution, the method for designing the parameters of the AC filter includes:

[0029] Considering the minimum requirement of fundamental wave reactive power, a first calculation formula of the filter capacitance of the single tuned filter is obtained; the first calculation formula is specifically:

[0030]

[0031] Among them, C f is the filter capacitance of the single tuned filter, ω s is the fundamental frequency, n is the harmonic order, Ifn is the nth order filter capacitor current, and U1 is the filter capacitor voltage;

[0032] Based on the wind farm frequency deviation condition, a second calculation formula for the series resistance of the single tuned filter is obtained; the second calculation formula is specifically:

[0033]

[0034] Among them, R f is the single tuned filter series resistance, Q opt is the optimal tuning sharpness of a single tuned filter, is the impedance angle of the offshore wind power twelve-pulse diode rectifier transmission system, δ m is the relative frequency offset of the offshore wind power twelve-pulse diode rectifier transmission system;

[0035] Obtaining the single tuned filter parameters for filtering out 11th, 13th, 23rd and 25th harmonics respectively through the first calculation formula and the second calculation formula;

[0036] The AC filter parameters are obtained based on the single tuned filter parameters.

[0037] As a preferred solution, the method for designing the parameters of the smoothing reactor includes:

[0038] Under the rated voltage condition of offshore wind farm, the no-load voltage of the DC side of k-pulse uncontrolled rectifier is calculated;

[0039] Based on the no-load voltage of the k-pulse uncontrolled rectifier DC side, the harmonic voltage amplitude when only the twelfth current harmonic is considered is calculated:

[0040]

[0041] In the above formula, U nk is the harmonic voltage amplitude when only the twelfth current harmonic is considered, U dc0 is the no-load voltage of the DC side of the k-pulse uncontrolled rectifier, n is a positive integer; U A is the phase voltage amplitude on the AC side of the six-pulse uncontrolled rectifier;

[0042] The number of smoothing reactors and the inductance of the smoothing reactors are determined according to the harmonic voltage amplitude when only the twelfth current harmonic is considered, so that the twelfth current harmonic meets the preset constraint conditions, and the design of the smoothing reactor parameters is completed.

[0043] As a preferred solution, the design method of the transformer ratio of the converter transformer includes:

[0044] Determine the voltage level on the offshore AC side based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system;

[0045] Obtaining a mapping relationship between the AC side voltage and the DC side voltage of a six-pulse uncontrolled rectifier;

[0046] According to the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier, the corresponding AC side no-load phase voltage amplitude of a single six-pulse uncontrolled rectifier when the DC side voltage is a first preset proportion of the DC side rated voltage is calculated;

[0047] Divide the no-load phase voltage amplitude of the AC side by a preset value to calculate the AC phase voltage amplitude and the line voltage amplitude;

[0048] Determine common transformer voltage levels based on line voltage amplitude;

[0049] According to the commonly used transformer voltage level and the offshore AC side voltage level, the transformer ratio of the converter transformer is obtained.

[0050] As a preferred solution, the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier is expressed by the following formula:

[0051]

[0052] In the above formula, v a is the phase A voltage, v c is the phase C voltage, i a is the input current of phase A, U dc is the DC side voltage of the six-pulse uncontrolled rectifier valve, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, ω is the system power frequency, L t is the leakage reactance of the converter transformer, I dc It is the DC side current of the six-pulse uncontrolled rectifier.

[0053] As a preferred solution, the method for designing the transformer capacity of the converter transformer includes:

[0054] Obtain the system capacity and number of three-winding transformers for the offshore wind power twelve-pulse diode rectifier transmission system;

[0055] Obtain the angle-voltage-current relationship between the commutation angle and the AC side voltage and the DC side current; the angle-voltage-current relationship is expressed by the following formula:

[0056]

[0057] In the above formula, μ is the commutation angle, I dc is the DC side current, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, L t is the leakage reactance of the converter transformer;

[0058] Considering the commutation angle of the six-pulse uncontrolled rectifier, the power factor calculation formula is obtained;

[0059] Calculate the apparent power of a single three-winding transformer based on the system capacity and the number of three-winding transformers;

[0060] Determining a first preset load rate based on the apparent power; the first preset load rate is used to provide an apparent power transfer margin;

[0061] According to the angle-voltage-current relationship, the power factor calculation formula, and in combination with the first preset load rate, the leakage reactance of the converter transformer is set to a preset leakage reactance value, and the transformer capacity of the converter transformer is calculated.

[0062] As a preferred solution, the method for obtaining the rated current and the rated voltage of the twelve-pulse uncontrolled rectifier valve includes:

[0063] The maximum phase current amplitude of a single six-pulse uncontrolled rectifier is calculated;

[0064] Based on the maximum amplitude of the phase current of a single six-pulse uncontrolled rectifier, the rated current of the twelve-pulse uncontrolled rectifier valve is obtained;

[0065] Get the maximum reverse voltage that a single six-pulse uncontrolled rectifier can withstand;

[0066] Under the condition that the maximum reverse pressure borne by a single six-pulse uncontrolled rectifier is ensured to be a second preset ratio of the rated voltage, the rated voltage of the twelve-pulse uncontrolled rectifier valve is calculated according to the maximum reverse pressure borne by the single six-pulse uncontrolled rectifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 : A structural schematic diagram of an embodiment of an offshore wind power twelve-pulse diode rectification and transmission system provided by the present invention;

[0068] Figure 2 : A topological diagram of the AC side feeder collection of an offshore converter station provided by an embodiment of the present invention;

[0069] Figure 3: A schematic diagram of a double busbar non-segmented wiring provided by an embodiment of the present invention;

[0070] Figure 4 : A schematic diagram of electrical wiring in an offshore converter station provided by an embodiment of the present invention;

[0071] Figure 5 : A wiring diagram of a converter transformer and a twelve-pulse uncontrolled rectifier valve provided in an embodiment of the present invention;

[0072] Figure 6 : A schematic diagram of the topological structure of a passive double-tuned filter provided in an embodiment of the present invention;

[0073] Figure 7 : A schematic diagram of the arrangement of a lightning arrester provided in an embodiment of the present invention;

[0074] Figure 8 : A schematic diagram of the arrangement of diode area protection measurement points for an offshore converter station provided by an embodiment of the present invention;

[0075] Fig. 9 : A flow chart of an embodiment of a method for constructing an offshore wind power twelve-pulse diode rectification and transmission system provided by the present invention;

[0076] Fig.10 : Schematic diagram of a DRU withstanding back pressure provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0077] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0078] Embodiment 1

[0079] In order to solve the problems in the prior art, the present invention proposes an offshore wind power twelve-pulse diode rectification and transmission system.

[0080] Please refer to the following Figure 1 , Figure 1 A schematic structural diagram of an embodiment of an offshore wind power twelve-pulse diode rectification and transmission system provided by the present invention.

[0081] like Figure 1 As shown, the offshore wind power twelve-pulse diode rectification and transmission system comprises:

[0082] Gas insulated switchgear, M AC filters, converter transformers, twelve-pulse uncontrolled rectifier valves and smoothing reactors, where M is a preset positive integer;

[0083] The gas insulated switchgear is electrically connected to M AC filters and the grid side of the converter transformer respectively;

[0084] The valve side of the converter transformer is electrically connected to the twelve-pulse uncontrolled rectifier valve;

[0085] The twelve-pulse uncontrolled rectifier valve is electrically connected to the smoothing reactor;

[0086] Wherein, the gas insulated switchgear is used to receive the initial AC power output by the offshore wind power generator set;

[0087] The converter transformer is used to convert the voltage of the initial AC power supply and output AC power supply;

[0088] The twelve-pulse uncontrolled rectifier valve is used to rectify the AC power supply to obtain an initial DC power supply;

[0089] The AC filter is used to filter out the 11th, 13th, 23rd and 25th voltage harmonics and current harmonics generated when the twelve-pulse uncontrolled rectifier valve performs rectification;

[0090] The smoothing reactor is used to suppress current harmonics generated by voltage harmonics on the DC side in the initial DC power supply to output DC power supply.

[0091] In this embodiment, the gas insulated switchgear is electrically connected to the offshore wind turbine generator set through an AC busbar, the gas insulated switchgear is connected to the grid side of the converter transformer through the derived branch busbar, and the smoothing reactor is connected to the DC line through a DC cable.

[0092] Further, the converter transformer includes several groups of three-winding transformers;

[0093] The twelve-pulse uncontrolled rectifier valve includes four groups of six-pulse uncontrolled rectifiers with a 30-degree difference between them;

[0094] Four groups of six-pulse uncontrolled rectifiers with a mutual difference of 30 degrees are connected in series or electrically connected to the smoothing reactor on the DC side, and the four groups of six-pulse uncontrolled rectifiers are connected in parallel to the AC bus through four groups of three-winding transformers on the AC side.

[0095] Furthermore, the transformation groups of the three-winding transformer are Y / Y / Y and Y / Y / Δ.

[0096] In this embodiment, considering the number of times required for the phase shift of the AC voltage by the twelve-pulse uncontrolled rectifier valve, the transformer groups of the three-winding transformer are designed to be Y / Y / Y and Y / Y / Δ.

[0097] In this embodiment, the converter transformer is formed by a plurality of groups of three-winding transformers, so that the converter transformer can be small in size, light in weight, high in efficiency, and save manufacturing costs, thereby reducing the size of the offshore converter platform.

[0098] In this embodiment, compared with the six-pulse uncontrolled rectifier with high DC 6k and AC 6k±1 harmonic content, in order to meet the harmonic requirements of offshore wind farms, more passive filters need to be additionally equipped, and the economic benefits are poor. The diode rectifier device in the offshore wind power twelve-pulse diode rectifier transmission system of the present invention adopts a twelve-pulse uncontrolled rectifier valve.

[0099] Furthermore, the AC filter is a passive double-tuned filter.

[0100] Since the twelve-pulse uncontrolled rectifier valve will generate voltage and current harmonics, in order to improve the voltage / current power quality of the offshore wind farm, it is necessary to connect an active or passive filter in parallel to the twelve-pulse uncontrolled rectifier valve. Since the reactive power required by the twelve-pulse uncontrolled rectifier valve can be automatically compensated by the reactive self-synchronous control of the generator set, the AC filter only needs to meet the harmonic capacity requirements; compared with the active filter, which will generate negative resistance in the frequency domain, it is not conducive to the stable operation of the system under small disturbances. The passive filter used in the present invention can ensure the stable operation of the system under small disturbances. In addition, the AC filter in the present invention adopts a double-tuned form to achieve 11 / 13 tuning filtering and 23 / 25 tuning filtering. Therefore, the present invention uses a passive double-tuned filter, and the passive double-tuned filter is configured on the grid side of the converter transformer to reduce the 11, 13 and 23, 25 voltage and current harmonics generated by the twelve-pulse uncontrolled rectifier valve, thereby avoiding excessive harmonic current in the system.

[0101] In this embodiment, the gas insulated switchgear, M AC filters, converter transformers, twelve-pulse uncontrolled rectifier valves and smoothing reactors are used as offshore converter stations and are located on the offshore side of the offshore wind power twelve-pulse diode rectifier transmission system; the offshore wind power twelve-pulse diode rectifier transmission system also includes an onshore side, and the onshore side adopts an MMC flexible direct current valve for inversion; according to engineering experience, in order to minimize costs and ensure benefits, a symmetrical single-pole wiring method is adopted on the offshore side.

[0102] To facilitate the description of the offshore wind power twelve-pulse diode rectifier transmission system and the construction method thereof of the present invention, this embodiment takes a 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system as an example for description; wherein, the boundary conditions of the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system include system capacity, DC system voltage level, DC system wiring mode, offshore AC side voltage level, offshore AC side wiring mode, onshore AC side voltage level, onshore AC side wiring mode, onshore converter valve structure and transmission submarine cable length, see Table 1 for details:

[0103] Table 1

[0104]

[0105] Furthermore, this embodiment determines the AC side wiring method of the offshore converter station, the DC side wiring method of the offshore converter station, the in-station wiring method of the offshore converter station, the lightning arrester wiring method, the measuring device wiring method and the converter station power wiring method based on the structure and connection relationship of the offshore converter station.

[0106] In this embodiment, the AC side connection mode of the offshore converter station may be a feeder collection mode or an AC bus connection mode on the grid side of the converter transformer.

[0107] For the feeder collection method on the AC side of the converter station, it is necessary to design the feeder output power type and the number of feeders of each type. The feeder output power type is determined according to the unit capacity type and number of the generator sets, and the number of feeders of each type is determined according to the total number of feeders in the offshore wind farm.

[0108] Please refer to Figure 2 , Figure 2 A topological diagram of feeder aggregation at the AC side of an offshore converter station provided in an embodiment of the present invention.

[0109] Based on the above 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system, since the offshore wind farm transmission power is 2GW, there are 36 feeders, including two types of unit capacity of 8MW and 11MW. Therefore, the feeders are classified into two transmission power types of 8MW*7 and 11MW*5, including 16 feeders of 55MW and 20 feeders of 56MW.

[0110] Taking into account the constraint of the maximum current of the wind farm busbar incoming line, the offshore wind farm is equipped with 8 66kV collecting transformer windings. Taking into account the reactive power consumption of the twelve-pulse uncontrolled rectifier valve during the diode uncontrolled rectification process, the active power of the wind farm busbar at full load is 2000MW and the power factor is 0.9.

[0111] For AC busbar wiring, a double busbar non-segmented structure is selected.

[0112] Please refer to Figure 3 , Figure 3 A schematic diagram of a double busbar non-segmented wiring arrangement provided in an embodiment of the present invention.

[0113] By adopting a double busbar non-segmented structure, the voltage phases of different busbars can be kept the same, and the uncontrolled rectifier valve can provide precise phase shift angles through the rectifier transformer winding to achieve staggered phase cancellation of harmonics, avoiding affecting the harmonic power quality of the wind farm network. At the same time, it can also effectively prevent power outages caused by busbar failures or maintenance. When one busbar fails, normal operation can be achieved through the other busbar.

[0114] In this embodiment, the DC side wiring method of the offshore converter station adopts a symmetrical single-stage wiring method. By adopting the symmetrical single-stage wiring method, the present invention can maximize land saving, reduce the weight and size of the offshore platform, and the AC side of the converter transformer does not need to bear the DC bias voltage. The equipment requirements are relatively simple and there is no need to set up a special grounding electrode.

[0115] Please refer to the following Figure 4 , Figure 4 A schematic diagram of electrical wiring within an offshore converter station provided by an embodiment of the present invention.

[0116] In this embodiment, the offshore converter station includes a converter transformer, an AC filter, a twelve-pulse uncontrolled rectifier valve and a smoothing reactor. Figure 4 As shown, the input end of the AC filter is connected to the branch busbar led out from the gas insulated switchgear, the AC filter is connected to the grid side of the converter transformer, the valve side of the converter transformer is electrically connected to the twelve-pulse uncontrolled rectifier valve, the twelve-pulse uncontrolled rectifier valve is electrically connected to the smoothing reactor, and the smoothing reactor is connected to the DC line through a DC cable;

[0117] The converter transformer is designed as a three-winding transformer with four groups of 8 windings on the wind farm side and 4 windings on the rectifier side; the twelve-pulse uncontrolled rectifier valve is composed of four groups of six-pulse uncontrolled rectifiers with a difference of 30 degrees to achieve harmonic cancellation, so the number of six-pulse uncontrolled rectifiers must be an integer multiple of 2. The number of windings of the converter transformer needs to match the twelve-pulse uncontrolled rectifier valve, and also needs to match the incoming line current of the gas-insulated switchgear. Therefore, the twelve-pulse uncontrolled rectifier can use four groups of six-pulse uncontrolled rectifiers in series on the DC side and four groups of three-winding transformers in parallel on the AC bus on the AC side.

[0118] Please refer to the following Figure 5 , Figure 5 A schematic diagram of the connection between a converter transformer and a twelve-pulse uncontrolled rectifier valve provided in an embodiment of the present invention.

[0119] In this embodiment, Figure 5 As shown, the three-winding transformer (rectifier transformer winding) adopts two types of groups, yn / yn / Y and yn / yn / Δ. The grounding method is small resistance grounding of the AC side winding, and the phase shift angle is 30 degrees. At the same time, in order to ensure the requirements of the gas insulated switchgear for the incoming current, the number of windings on the wind farm side of the converter transformer is 8 groups.

[0120] In this embodiment, the AC filter is a passive double-tuned filter.

[0121] Please refer to the following Figure 6 , Figure 6 A schematic diagram of the topological structure of a passive double-tuned filter provided in an embodiment of the present invention.

[0122] In this embodiment, in consideration of reliability, to prevent any group of AC filters from exiting operation due to a fault, a total of 4 groups of AC filters are provided in this embodiment, and both the 11 / 13th tuning filter and the 23 / 25th tuning filter are provided as two groups for mutual backup.

[0123] Please refer to the following Figure 7 , Figure 7 A schematic diagram of the arrangement of a lightning arrester provided in an embodiment of the present invention.

[0124] In this embodiment, the lightning arrester wiring method is as follows Figure 7 It is implemented by the arrangement of lightning arresters.

[0125] The main protection device for equipment in offshore converter stations is the metal zinc oxide arrester. The overvoltage generated on the AC side is limited by the arrester on the AC side, and the overvoltage generated on the DC side is limited by the arrester on the DC side. The key protection equipment is directly protected by the arrester close to it; generally, several types of arresters that protect other equipment are connected in series to achieve the protection of the valve side winding of the converter transformer, and the valve side winding of the converter transformer with the highest potential is directly protected by the arrester close to it.

[0126] exist Figure 7 Among them, the "A" type AC bus arrester is used to protect the converter transformer and AC bus; the "A1" type arrester is used to protect the valve side of the converter transformer; the "D" type arrester is used to protect the smoothing reactor and DC line equipment; the "BR" type arrester is used to protect the bridge arm reactor; the "DR" type arrester is used to protect the smoothing reactor; the "VD" type arrester is used to protect the diode of the twelve-pulse uncontrolled rectifier valve. The positive and negative high-voltage side diode valves are equipped with two-column VD1 arresters.

[0127] Please refer to the following Figure 8 , Figure 8 A schematic diagram of the arrangement of diode area protection measurement points for an offshore converter station provided in an embodiment of the present invention.

[0128] In this embodiment, in order to realize the control and protection of the offshore wind power twelve-pulse diode rectifier transmission system, a control and protection strategy needs to be integrated in the main wiring mode, and a measuring device is configured at the corresponding measuring point. In this embodiment, the wiring mode of the measuring device is as follows: Figure 8 It is implemented according to the arrangement of diode area protection measurement points in offshore converter stations.

[0129] exist Figure 8 The specific information of the diode area protection measurement points in the offshore converter station is shown in the following table:

[0130] Table 2

[0131]

[0132] In this embodiment, for the station power wiring mode of the converter station, the offshore converter station power is generally equipped with three high-voltage station power supplies, one of which is drawn from the diesel generator, and the other two can be drawn from the fourth winding of the rectifier transformer or the 66kV dedicated step-down transformer. In order to ensure the balance of the rectifier transformer and facilitate maintenance and inspection, it is preferably configured with a dedicated step-down transformer at the 66kV bus.

[0133] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0134] The offshore wind power twelve-pulse diode rectification and transmission system of the present invention adopts a twelve-pulse uncontrolled rectifier valve for rectification at the transmission end based on the hybrid flexible direct current transmission technology of high-power diodes. As a diode rectifier valve, the twelve-pulse uncontrolled rectifier valve has more advantages in volume and weight than the modular multi-level topology. Their sizes are basically not in the same order of magnitude. In addition, each diode constituting the twelve-pulse uncontrolled rectifier valve has no trigger circuit, which is equivalent to a passive component and can be installed in a closed structure, so that the reliability of the twelve-pulse uncontrolled rectifier valve is higher than that of the modular multi-level topology, and it is very suitable for complex offshore environments and does not require year-round maintenance. Therefore, the offshore wind power twelve-pulse diode rectification and transmission system of the present invention adopts a twelve-pulse uncontrolled rectifier valve for rectification, which can greatly reduce the volume and weight of the offshore converter station, thereby reducing the cost of the transmission project.

[0135] The present invention filters out 11th, 13th, 23rd and 25th voltage harmonics and current harmonics generated when the twelve-pulse uncontrolled rectifier valve performs rectification through the AC filter, and suppresses the current harmonics generated by the DC side voltage harmonics of the initial DC power supply through the smoothing reactor, thereby avoiding excessive harmonic current of the system and making the output DC close to the ideal DC, thereby improving the power quality of the offshore wind power output power supply and the safety and reliability of the offshore wind power supply.

[0136] Embodiment 2

[0137] In order to solve the above technical problems, the present invention also provides a method for constructing an offshore wind power twelve-pulse diode rectifier transmission system, which is applied to an offshore wind power twelve-pulse diode rectifier transmission system as described in the above embodiment one.

[0138] Please refer to the following Fig. 9 , Fig. 9The present invention provides a flowchart of an embodiment of a method for constructing an offshore wind power twelve-pulse diode rectification and transmission system.

[0139] like Fig. 9 As shown, the method for constructing the offshore wind power twelve-pulse diode rectification and transmission system includes: steps 101 to 104, specifically:

[0140] Step 101: Obtain the system structure of an offshore wind power twelve-pulse diode rectification and transmission system as described above;

[0141] Step 102: Determine the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system according to the scale of the offshore wind power;

[0142] Step 103: Based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system and the harmonic problem of the twelve-pulse uncontrolled rectifier valve, the parameters of the AC filter, the parameters of the smoothing reactor, the transformer ratio of the converter transformer, the transformer capacity of the converter transformer, the rated current of the twelve-pulse uncontrolled rectifier valve, and the rated voltage of the twelve-pulse uncontrolled rectifier valve are respectively designed to obtain a parameter design scheme for the offshore wind power twelve-pulse diode rectifier transmission system;

[0143] Step 104: Construct an offshore wind power twelve-pulse diode rectification transmission system based on the parameter design scheme and system structure.

[0144] Furthermore, the design method of the AC filter parameters includes:

[0145] Considering the minimum requirement of fundamental wave reactive power, a first calculation formula of the filter capacitance of the single tuned filter is obtained; the first calculation formula is specifically:

[0146]

[0147] Among them, C f is the filter capacitance of the single tuned filter, ω s is the fundamental frequency, n is the harmonic order, Ifn is the nth order filter capacitor current, and U1 is the filter capacitor voltage;

[0148] Based on the wind farm frequency deviation condition, a second calculation formula for the series resistance of the single tuned filter is obtained; the second calculation formula is specifically:

[0149]

[0150] Among them, R f is the single tuned filter series resistance, Q opt is the optimal tuning sharpness of a single tuned filter, is the impedance angle of the offshore wind power twelve-pulse diode rectifier transmission system, δ mis the relative frequency offset of the offshore wind power twelve-pulse diode rectifier transmission system;

[0151] Obtaining the single tuned filter parameters for filtering out 11th, 13th, 23rd and 25th harmonics respectively by the first calculation formula and the second calculation formula;

[0152] The AC filter parameters are obtained based on the single tuned filter parameters.

[0153] The present invention designs the series resistance of the monotonic passive filter, which can improve the tuning sharpness of the monotonic passive filter and prevent the frequency of the output voltage of the offshore wind farm from shifting.

[0154] In this embodiment, the wind farm frequency deviation condition is to ensure that the wind farm frequency deviation is within 1%.

[0155] The effectiveness of the AC filter can be ensured by setting the wind farm frequency deviation condition.

[0156] In this embodiment, the impedance angle range is 80 to 85 degrees, and the optimal tuning sharpness range is 30 to 60 degrees; the larger the tuning filter resistance, the greater the filter loss, so the tuning sharpness Q opt The value is 60.

[0157] In this embodiment, the 11th order single tuned AC filter parameters, the 13th order single tuned AC filter parameters, the 23rd order single tuned AC filter parameters and the 25th order single tuned AC filter parameters are obtained by the first calculation formula and the second calculation formula, respectively, as shown in the following table:

[0158] Table 3

[0159]

[0160] The AC filter in the present invention adopts a double-tuned form, and is respectively designed with 11 / 13th-order tuned filters and 23 / 25th-order tuned filters. According to the principle of minimum capacity, a passive single-tuned filter is first designed, and then the single-tuned filter is aggregated. Specifically, the parameters of the two groups of single-tuned filters are fitted into a group of double-tuned filter parameters by parameter fitting, so that the two have the same frequency response characteristics, that is, the 11th and 23rd-order single-tuned filter parameters are fitted into a group of double-tuned filter parameters, and the 13th and 25th-order single-tuned filter parameters are fitted into another group of double-tuned filter parameters, and the parameters of the 11th and 13th-order double-tuned filters are obtained as shown in Table 4 below:

[0161] Table 4

[0162]

[0163] The parameters of the 23rd and 25th order double tuned filters are shown in Table 5 below:

[0164] Table 5

[0165]

[0166]

[0167] The present invention can effectively reduce the 11th, 13th, 23rd and 25th voltage and current harmonics generated by the twelve-pulse uncontrolled rectifier valve by configuring a passive double-tuned filter on the AC side, thereby avoiding excessive harmonic current in the system. The tuned filter is simple in design, and the fundamental reactive power compensation capacity of the system does not need to be considered during design. It only needs to be designed according to the minimum reactive power capacity, which can not only minimize the design and construction costs, but also reduce the volume and weight of the offshore converter station.

[0168] In this embodiment, in order to apply the offshore wind power twelve-pulse diode rectifier transmission system of the present invention to the industrial frequency DC collection project, it is necessary to design the parameters of the AC filter with the industrial frequency of 50 Hz as the base frequency; compared with the offshore wind power transmission scheme of low frequency such as 20 Hz, the present invention designs various parameters of the offshore wind power twelve-pulse diode rectifier transmission system based on the industrial frequency of 50 Hz, which can improve the transmission distance of the offshore wind power twelve-pulse diode rectifier transmission system of the present invention.

[0169] Furthermore, the design method of the transformer ratio of the converter transformer includes:

[0170] Determine the voltage level on the offshore AC side based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system;

[0171] Obtaining a mapping relationship between the AC side voltage and the DC side voltage of a six-pulse uncontrolled rectifier;

[0172] According to the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier, the corresponding AC side no-load phase voltage amplitude of a single six-pulse uncontrolled rectifier when the DC side voltage is a first preset proportion of the DC side rated voltage is calculated;

[0173] Divide the no-load phase voltage amplitude of the AC side by a preset value to calculate the AC phase voltage amplitude and the line voltage amplitude;

[0174] Determine common transformer voltage levels based on line voltage amplitude;

[0175] According to the commonly used transformer voltage level and the offshore AC side voltage level, the transformer ratio of the converter transformer is obtained.

[0176] In this embodiment, the commutation process of the six-pulse uncontrolled rectifier is not considered, and the DC side voltage of the six-pulse uncontrolled rectifier is equal to its maximum line voltage at any time. Therefore, when the commutation process is not considered, the DC voltage of a single six-pulse uncontrolled rectifier can be expressed as:

[0177]

[0178] Due to the commutation process, the DC voltage of the six-pulse uncontrolled rectifier will decrease due to the commutation process.

[0179] In this embodiment, the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier takes the commutation process of the six-pulse uncontrolled rectifier into consideration.

[0180] Furthermore, the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier is expressed by the following formula:

[0181]

[0182] This embodiment obtains a mapping relationship between the AC side voltage and the DC side voltage of the twelve-pulse uncontrolled rectifier valve based on the pulse number of the twelve-pulse uncontrolled rectifier valve and the DC side voltage of the six-pulse uncontrolled rectifier:

[0183]

[0184] In the above formula, v a is the phase A voltage, v c is the phase C voltage, i a is the input current of phase A, U dc is the DC side voltage of the six-pulse uncontrolled rectifier valve, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, ω is the system power frequency, L t is the leakage reactance of the converter transformer, I dc is the DC side current of the six-pulse uncontrolled rectifier, B is the number of six-pulse uncontrolled rectifiers included in the twelve-pulse uncontrolled rectifier valve, and U dc ' is the DC side voltage of the twelve-pulse uncontrolled rectifier valve.

[0185] In this embodiment, the DC side voltage of the six-pulse uncontrolled rectifier is equal to its maximum line voltage at any time.

[0186] In this embodiment, considering the large-scale wind farm, in order to prevent overvoltage of the feeder terminal unit when the wind farm is fully powered, the transformer ratio is designed so that when the wind farm voltage is 0.9pu, the twelve-pulse uncontrolled rectifier valve starts to conduct.

[0187] The following is a 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system in Example 1 to illustrate the design method of the transformer ratio of the converter transformer in the present invention: the offshore AC side voltage level of the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system is 66KV. Since the offshore wind farm transmission power is 2GW, it requires at least 6 sets of coils. If the converter transformer uses a three-winding transformer, it requires at least three secondary windings. For the twelve-pulse uncontrolled rectifier valve, the number of secondary windings of the converter transformer needs to be an even number. Therefore, in this embodiment, the converter transformer is designed as a four-set three-winding transformer with 8 windings on the wind farm side and 4 windings on the rectifier side.

[0188] In this embodiment, the first preset proportion is 1 / 4, and the preset value is 0.9.

[0189] By using the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier, it can be calculated that when the DC side voltage of a single six-pulse uncontrolled rectifier is 1 / 4 of the rated voltage of the DC side, the corresponding AC side no-load phase voltage amplitude is 151.1499 kV. Dividing the AC side no-load phase voltage amplitude by 0.9, the corresponding AC phase voltage amplitude is 167.9444 kV, and the corresponding line voltage is 205.6890 kV. Here, the commonly used transformer voltage level 200 kV that is closest to the line voltage is selected. Therefore, the transformer ratio of the converter transformer can be obtained as 66 kV / 66 kV / 200 kV.

[0190] Furthermore, the design method of the transformer capacity of the converter transformer includes:

[0191] Obtain the system capacity and number of three-winding transformers for the offshore wind power twelve-pulse diode rectifier transmission system;

[0192] Obtain the angle-voltage-current relationship between the commutation angle and the AC side voltage and the DC side current; the angle-voltage-current relationship is expressed by the following formula:

[0193]

[0194] In the above formula, μ is the commutation angle, I dc is the DC side current, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, L t is the leakage reactance of the converter transformer;

[0195] Considering the commutation angle of the six-pulse uncontrolled rectifier, the power factor calculation formula is obtained;

[0196] Calculate the apparent power of a single three-winding transformer based on the system capacity and the number of three-winding transformers;

[0197] Determining a first preset load rate based on the apparent power; the first preset load rate is used to provide an apparent power transfer margin;

[0198] According to the angle-voltage-current relationship, the power factor calculation formula, and in combination with the first preset load rate, the leakage reactance of the converter transformer is set to a preset leakage reactance value, and the transformer capacity of the converter transformer is calculated.

[0199] In this embodiment, the first preset load rate is 0.85; the preset value of leakage reactance is 16%.

[0200] In this embodiment, for a single six-pulse uncontrolled rectifier, its two-phase bridge arm is commutated once every 60°. During the commutation period, the line voltage is added to the interphase connection reactance. The voltage and current dynamic equations during the commutation period between phase A and phase C can be written as:

[0201]

[0202] Among them, v ac is the phase-to-phase voltage of AC, i a is the input current of phase A.

[0203] Furthermore, the power factor calculation formula is obtained by considering the commutation angle of the six-pulse uncontrolled rectifier, including:

[0204] The reactive power of the six-pulse uncontrolled rectifier is related to the commutation angle of the six-pulse uncontrolled rectifier. Due to the commutation process, the fundamental current will lag the fundamental voltage by μ / 2. When the commutation angle is very small, the formula for the load power factor angle is:

[0205]

[0206] Under the condition of very small commutation angle, the above formula can be further simplified as:

[0207]

[0208] Therefore, considering the commutation angle of the six-pulse uncontrolled rectifier, the power factor calculation formula is expressed as:

[0209]

[0210] Where μ is the commutation angle.

[0211] The following is a 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system in Example 1 to illustrate the design method of the transformer capacity of the converter transformer described in the present invention: the system capacity of the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system is 2GW, and the number of three-winding transformers is four groups. Therefore, the apparent power Pn of a single three-winding transformer is 500MW. According to the angle-voltage-current relationship, the power factor calculation formula, and the 0.85 load rate to provide an apparent power transmission margin, the design capacity of the four three-winding transformers can be calculated to be 650MVA. The power factor calculation formula can be used to calculate that the power factor at this time is 0.9240; thus, the transformer ratio and transformer capacity of the converter transformer have been designed, and the converter transformer parameters of the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system are shown in the following table:

[0212] Table 6

[0213]

[0214] Furthermore, the method for designing the parameters of the smoothing reactor includes:

[0215] Under the rated voltage condition of offshore wind farm, the no-load voltage of the DC side of k-pulse uncontrolled rectifier is calculated;

[0216] Based on the no-load voltage of the k-pulse uncontrolled rectifier DC side, the harmonic voltage amplitude when only the twelfth current harmonic is considered is calculated:

[0217]

[0218] In the above formula, U nk is the harmonic voltage amplitude when only the twelfth current harmonic is considered, U dc0 is the no-load voltage of the DC side of the k-pulse uncontrolled rectifier, n is a positive integer; U A is the phase voltage amplitude on the AC side of the six-pulse uncontrolled rectifier;

[0219] The number of smoothing reactors and the inductance of the smoothing reactors are determined according to the harmonic voltage amplitude when only the twelfth current harmonic is considered, so that the twelfth current harmonic meets the preset constraint conditions, and the design of the smoothing reactor parameters is completed.

[0220] In the present invention, the smoothing reactor is designed to suppress the current harmonics generated by the nk (n is a positive integer, k is the number of uncontrolled rectifier pulses) voltage harmonics appearing on the DC side. Since a DC submarine cable is used instead of an overhead line, the present invention does not consider constraining the short-circuit current of the DC system when designing the smoothing reactor.

[0221] In the present invention, under the no-load voltage of the k-pulse uncontrolled rectifier DC side, since the harmonic voltage and harmonic order of the system decay in square, the harmonic voltage amplitude U is calculated when only the twelfth current harmonic is considered. nk .

[0222] In this embodiment, under the rated voltage condition of the offshore wind farm, the no-load voltage of the k-pulse uncontrolled rectifier DC side is calculated by the above-mentioned voltage and current dynamic equation during the phase switching between phases A and C, the angle-voltage and current relationship, and the formula of the load power factor angle.

[0223] In this embodiment, the preset constraint condition is: the design requirement of the DC side current harmonic is less than 1% of the rated value, which is expressed by the following formula:

[0224]

[0225] The following is an implementation case to illustrate the design method of the smoothing reactor parameters described in the present invention: if the calculated harmonic voltage amplitude when only considering the 12th current harmonic is 15.1102kV, two 75mH reactors are selected as smoothing reactors. The rated current of the smoothing reactor is 2kA. At this time, the 12th current harmonic can be constrained to within 1%. Considering that the DC submarine cable has a large distributed capacitance to the ground, the actual value of the harmonic current of the DC system will be smaller.

[0226] Furthermore, the method for obtaining the rated current and the rated voltage of the twelve-pulse uncontrolled rectifier valve comprises:

[0227] The maximum phase current amplitude of a single six-pulse uncontrolled rectifier is calculated;

[0228] Based on the maximum amplitude of the phase current of a single six-pulse uncontrolled rectifier, the rated current of the twelve-pulse uncontrolled rectifier valve is obtained;

[0229] Get the maximum reverse voltage that a single six-pulse uncontrolled rectifier can withstand;

[0230] Under the condition that the maximum reverse pressure borne by a single six-pulse uncontrolled rectifier is ensured to be a second preset ratio of the rated voltage, the rated voltage of the twelve-pulse uncontrolled rectifier valve is calculated according to the maximum reverse pressure borne by the single six-pulse uncontrolled rectifier.

[0231] In this embodiment, the input current of the twelve-pulse uncontrolled rectifier valve includes active current and commutation reactive current, and the DC side output current satisfies the active power conservation. Considering the rated active power, the maximum amplitude of the phase current of a single six-pulse uncontrolled rectifier is:

[0232]

[0233] Since the rated current I of the six-pulse uncontrolled rectifier is the maximum phase current I of a single six-pulse uncontrolled rectifier, A Therefore, based on the maximum phase current amplitude of a single six-pulse uncontrolled rectifier, the rated current of the six-pulse uncontrolled rectifier can be obtained, and based on the rated current of the six-pulse uncontrolled rectifier, the rated current of the twelve-pulse uncontrolled rectifier valve can be obtained.

[0234] Please refer to Fig.10 , Fig.10 A schematic diagram of a DRU withstanding back pressure provided in an embodiment of the present invention.

[0235] In this embodiment, if Fig.10 As shown, for a single diode rectifier equivalent unit in the twelve-pulse uncontrolled rectifier valve, one end is connected to the offshore wind farm, and the other end is connected to the HVDC.

[0236] Ignore the voltage drop between the AC and DC neutral points. Fig.10 Taking the winning red DRU as an example, when a three-phase short circuit occurs in the onshore power grid, the HVDC voltage rises to 1.3pu. The offshore wind farm voltage is constrained by the unit AC voltage loop to 1.1pu. Therefore, when the AC voltage is the negative half-cycle peak, the maximum reverse pressure that a single six-pulse uncontrolled rectifier can withstand is:

[0237]

[0238] In this embodiment, the twelve-pulse uncontrolled rectifier valve and the six-pulse uncontrolled rectifier should ensure a withstand voltage margin. Under the condition that the maximum reverse pressure borne by a single six-pulse uncontrolled rectifier is 0.9 pu (a second preset proportion) of the rated withstand voltage, the rated voltage of the six-pulse uncontrolled rectifier can be calculated according to the maximum reverse pressure borne by the six-pulse uncontrolled rectifier; then, the rated voltage of the twelve-pulse uncontrolled rectifier valve is obtained according to the rated voltage of the six-pulse uncontrolled rectifier.

[0239] The following is a method for obtaining the rated current and rated voltage of the twelve-pulse uncontrolled rectifier valve in the present invention by using the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system in Example 1:

[0240] In the 2GW / ±500kV offshore wind power twelve-pulse diode rectifier transmission system, U LL For 200KV, the apparent power P of a single three-winding transformer is n For 500MW, the power factor is 0.9. Through the expression formula of the maximum phase current of a single six-pulse uncontrolled rectifier, the maximum phase current of a single six-pulse uncontrolled rectifier I can be calculated. Ais 2.2680KA, therefore, the rated current I of each group of six-pulse uncontrolled rectifiers is 3.4020KA;

[0241] Since the DRU uncontrolled rectifier unit is composed of four groups of six-pulse DRUs connected in series, and the DC voltage of each DRU is 250kV, the maximum reverse voltage that a single six-pulse uncontrolled rectifier can withstand can be calculated as:

[0242]

[0243] Therefore, according to the maximum reverse pressure that the six-pulse uncontrolled rectifier can withstand, it can be calculated that the rated voltage of the six-pulse uncontrolled rectifier is 380kV.

[0244] Compared with traditional grid-connected wind turbines, offshore converter stations all adopt modular multi-level topology, which is costly and difficult to maintain. The twelve-pulse uncontrolled rectifier valve is used in the present invention to realize diode rectification, which can greatly reduce the cost. Moreover, the present invention designs the converter transformer parameters and AC and DC rated voltages in detail through the above-mentioned offshore wind power twelve-pulse diode rectification transmission system construction method, which can avoid overvoltage and overcurrent problems caused by voltage mismatch.

[0245] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0246] In order to solve the problems existing in the prior art, the present invention designs an offshore wind power twelve-pulse diode rectifier transmission system. Different from the existing offshore wind power transmission system adopting a modular multi-level topology structure, the present invention adopts a twelve-pulse uncontrolled rectifier valve to form an offshore wind power twelve-pulse diode rectifier transmission system. However, since the circuit topology structure, operating state, and operating mode of the modular multi-level topology and the twelve-pulse uncontrolled rectifier valve are different, the parameter design and implementation methods of the two offshore wind power transmission systems are completely different. In addition, due to the problem that the parameters in the offshore wind power twelve-pulse diode rectifier transmission system of the present invention are difficult to design, the offshore wind power twelve-pulse diode rectifier transmission system proposed by the present invention is The twelve-pulse diode rectifier transmission system is difficult to be directly applied to the actual power transmission project. Therefore, the present invention proposes a construction method of an offshore wind power twelve-pulse diode rectifier transmission system. Based on the system structure of the offshore wind power twelve-pulse diode rectifier transmission system and considering the harmonic problem of the twelve-pulse uncontrolled rectifier valve, a parameter design scheme is obtained by matching and designing various parameters of the AC filter, smoothing reactor, converter transformer and the twelve-pulse uncontrolled rectifier valve. Finally, a twelve-pulse diode rectifier transmission system for offshore wind power is constructed by combining the parameter design scheme and the system structure, so that it can be actually applied to realize the efficient and safe transmission of the electric energy generated by the offshore wind farm.

[0247] The present invention is designed by the transformer ratio and transformer capacity of the converter transformer and the rated voltage / current of the twelve-pulse uncontrolled rectifier valve, so as to realize low-cost diode rectification and transmission for industrial frequency grid-type wind farms. In addition, the present invention can suppress DC current harmonics and meet the requirements of DC transmission through the design of smoothing reactors.

[0248] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. An offshore wind power twelve-pulse diode rectification and transmission system, characterized in that: include: Gas insulated switchgear, M AC filters, converter transformers, twelve-pulse uncontrolled rectifier valves and smoothing reactors, where M is a preset positive integer; The gas insulated switchgear is electrically connected to M AC filters and the grid side of the converter transformer respectively; The valve side of the converter transformer is electrically connected to the twelve-pulse uncontrolled rectifier valve; The twelve-pulse uncontrolled rectifier valve is electrically connected to the smoothing reactor; Wherein, the gas insulated switchgear is used to receive the initial AC power output by the offshore wind power generator set; The converter transformer is used to convert the voltage of the initial AC power supply and output AC power supply; The twelve-pulse uncontrolled rectifier valve is used to rectify the AC power supply to obtain an initial DC power supply; The AC filter is used to filter out the 11th, 13th, 23rd and 25th voltage harmonics and current harmonics generated when the twelve-pulse uncontrolled rectifier valve performs rectification; The smoothing reactor is used to suppress current harmonics generated by voltage harmonics on the DC side in the initial DC power supply to output DC power supply.

2. An offshore wind power twelve-pulse diode rectification and transmission system as claimed in claim 1, characterized in that: The converter transformer includes several groups of three-winding transformers; The twelve-pulse uncontrolled rectifier valve includes four groups of six-pulse uncontrolled rectifiers with a 30-degree difference between them; Four groups of six-pulse uncontrolled rectifiers with a mutual difference of 30 degrees are connected in series or electrically connected to the smoothing reactor on the DC side, and the four groups of six-pulse uncontrolled rectifiers are connected in parallel to the AC bus through four groups of three-winding transformers on the AC side.

3. The offshore wind power twelve-pulse diode rectification and transmission system according to claim 1, characterized in that: The AC filter is a passive double-tuned filter.

4. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system, characterized in that: Applied to an offshore wind power twelve-pulse diode rectifier transmission system as claimed in any one of claims 1 to 3, the construction method of the offshore wind power twelve-pulse diode rectifier transmission system comprises: Obtain the system structure of an offshore wind power twelve-pulse diode rectification transmission system as described in any one of claims 1 to 3; Determine the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system according to the scale of offshore wind power; Based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system and the harmonic problem of the twelve-pulse uncontrolled rectifier valve, the AC filter parameters, smoothing reactor parameters, transformer ratio of the converter transformer, transformer capacity of the converter transformer, rated current of the twelve-pulse uncontrolled rectifier valve and rated voltage of the twelve-pulse uncontrolled rectifier valve are designed and obtained respectively, so as to obtain the parameter design scheme of the offshore wind power twelve-pulse diode rectifier transmission system; An offshore wind power twelve-pulse diode rectification transmission system is constructed based on parameter design scheme and system structure.

5. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 4, characterized in that: The design method of the AC filter parameters includes: Considering the minimum requirement of fundamental wave reactive power, a first calculation formula of the filter capacitance of the single tuned filter is obtained; the first calculation formula is specifically: Among them, C f is the filter capacitance of the single tuned filter, ω s is the fundamental frequency, n is the harmonic order, Ifn is the nth order filter capacitor current, and U1 is the filter capacitor voltage; Based on the wind farm frequency deviation condition, a second calculation formula for the series resistance of the single tuned filter is obtained; the second calculation formula is specifically: Among them, R f is the single tuned filter series resistance, Q opt is the optimal tuning sharpness of a single tuned filter, is the impedance angle of the offshore wind power twelve-pulse diode rectifier transmission system, δ m is the relative frequency offset of the offshore wind power twelve-pulse diode rectifier transmission system; Obtaining the single tuned filter parameters for filtering out 11th, 13th, 23rd and 25th harmonics respectively by the first calculation formula and the second calculation formula; The AC filter parameters are obtained based on the single tuned filter parameters.

6. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 4, characterized in that: The method for designing parameters of the smoothing reactor includes: Under the rated voltage condition of offshore wind farm, the no-load voltage of the DC side of k-pulse uncontrolled rectifier is calculated; Based on the no-load voltage of the k-pulse uncontrolled rectifier DC side, the harmonic voltage amplitude when only the twelfth current harmonic is considered is calculated: In the above formula, U nk is the harmonic voltage amplitude when only the twelfth current harmonic is considered, U dc0 is the no-load voltage of the DC side of the k-pulse uncontrolled rectifier, n is a positive integer; U A is the phase voltage amplitude on the AC side of the six-pulse uncontrolled rectifier; The number of smoothing reactors and the inductance of the smoothing reactors are determined according to the harmonic voltage amplitude when only the twelfth current harmonic is considered, so that the twelfth current harmonic meets the preset constraint conditions, and the design of the smoothing reactor parameters is completed.

7. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 4, characterized in that: The method for designing the transformer ratio of the converter transformer comprises: Determine the voltage level on the offshore AC side based on the system parameters of the offshore wind power twelve-pulse diode rectifier transmission system; Obtaining a mapping relationship between the AC side voltage and the DC side voltage of a six-pulse uncontrolled rectifier; According to the mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier, the corresponding AC side no-load phase voltage amplitude of a single six-pulse uncontrolled rectifier when the DC side voltage is a first preset proportion of the DC side rated voltage is calculated; Divide the no-load phase voltage amplitude of the AC side by a preset value to calculate the AC phase voltage amplitude and the line voltage amplitude; Determine common transformer voltage levels based on line voltage amplitude; According to the commonly used transformer voltage level and the offshore AC side voltage level, the transformer ratio of the converter transformer is obtained.

8. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 7, characterized in that: The mapping relationship between the AC side voltage and the DC side voltage of the six-pulse uncontrolled rectifier is expressed by the following formula: In the above formula, v a is the phase A voltage, v c is the phase C voltage, i a is the input current of phase A, U dc is the DC side voltage of the six-pulse uncontrolled rectifier valve, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, ω is the system power frequency, L t is the leakage reactance of the converter transformer, I dc It is the DC side current of the six-pulse uncontrolled rectifier.

9. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 4, characterized in that: The method for designing the transformer capacity of the converter transformer comprises: Obtain the system capacity and number of three-winding transformers for the offshore wind power twelve-pulse diode rectifier transmission system; Obtain the angle-voltage-current relationship between the commutation angle and the AC side voltage and the DC side current; the angle-voltage-current relationship is expressed by the following formula: In the above formula, μ is the commutation angle, I dc is the DC side current, U A is the phase voltage amplitude of the AC side of the six-pulse uncontrolled rectifier, L t is the leakage reactance of the converter transformer; Considering the commutation angle of the six-pulse uncontrolled rectifier, the power factor calculation formula is obtained; Calculate the apparent power of a single three-winding transformer based on the system capacity and the number of three-winding transformers; Determining a first preset load rate based on the apparent power; the first preset load rate is used to provide an apparent power transfer margin; According to the angle-voltage-current relationship, the power factor calculation formula, and in combination with the first preset load rate, the leakage reactance of the converter transformer is set to a preset leakage reactance value, and the transformer capacity of the converter transformer is calculated.

10. A method for constructing an offshore wind power twelve-pulse diode rectifier transmission system as claimed in claim 4, characterized in that: The method for obtaining the rated current and the rated voltage of the twelve-pulse uncontrolled rectifier valve comprises: The maximum phase current amplitude of a single six-pulse uncontrolled rectifier is calculated; Based on the maximum amplitude of the phase current of a single six-pulse uncontrolled rectifier, the rated current of the twelve-pulse uncontrolled rectifier valve is obtained; Get the maximum reverse voltage that a single six-pulse uncontrolled rectifier can withstand; Under the condition that the maximum reverse pressure borne by a single six-pulse uncontrolled rectifier is ensured to be a second preset ratio of the rated voltage, the rated voltage of the twelve-pulse uncontrolled rectifier valve is calculated according to the maximum reverse pressure borne by the single six-pulse uncontrolled rectifier.

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