Multi-scale voltage support method suitable for new energy transmission of Saggode weak end

Abstract

The invention discloses a multi-scale voltage support method suitable for new energy transmission of a Saggode weak end. And establishing a life cycle evaluation method and environmental pollution evaluation for the Sagomean new energy base engineering construction. A three-terminal hybrid direct current sending-out scheme suitable for Sagomean scene characteristics is provided, a control strategy and a steady-state operation boundary of a converter station are analyzed, and a converter station fault ride-through method is provided. Aiming at the problem of unbalanced system power caused by voltage drop of a direct current bus when a new energy base has a fault, different energy storage forms such as a super capacitor and a hydrogen fuel cell are used for realizing voltage support functions of different scales, so that the Saggowski new energy base can operate safely and stably.

Description

Technical Field

[0001] The present invention relates to the field of ultra-high voltage flexible direct current power transmission technology, and in particular to a multi-scale voltage support method suitable for extremely weak end new energy transmission in Shagohuang. Background Art

[0002] Hydrogen energy not only has the advantages of high energy density and long storage time, but also can use the existing chemical industry's hydrogen transportation pipelines and hydrogen transportation vehicles to achieve cross-space distribution scheduling of hydrogen resources. In view of the extremely weak system strength and low short-circuit ratio characteristics of the new energy base in the current Shagohuang area, two complementary energy storage methods, supercapacitors and hydrogen fuel cells, are used to improve the system strength and stability of new energy DC transmission. Supercapacitors are connected to the bus through DC transformers to provide transient voltage support for the entire system, while high-energy-density hydrogen fuel cells can achieve the auxiliary function of primary frequency modulation. Through the cooperation of the two, the new energy base can achieve voltage support functions of different scales, maximize the transmission of electricity, and increase the utilization hours of the channel. Summary of the invention

[0003] The purpose of the present invention is to provide a multi-scale voltage support method suitable for the extremely weak end renewable energy transmission of Shagohuang. The method is simple and effective, easy to modularize, can significantly improve the simulation speed of the converter station, save computer resources, and effectively improve the simulation speed of the large-capacity supercapacitor energy storage type modular multi-level converter, providing a basis for real-time simulation of the converter.

[0004] The object of the present invention is achieved through the following technical solution: a multi-scale voltage support method suitable for the extremely weak end new energy transmission of Shagohuang, the method comprising:

[0005] Step 1: Explore the development potential of wind and solar energy in Ulanqab, Inner Mongolia Autonomous Region, conduct a life cycle assessment of wind power and photovoltaic energy, and compare the economic efficiency of different new energy power generation methods;

[0006] Step 2: Analyze the pros and cons of various transmission schemes, and select the final transmission scheme, and establish the system topology structure for large-scale new energy transmission in Shagohuang;

[0007] Step 3: Propose a system control strategy based on different operating conditions and electrical characteristics of the converter station, calculate the system steady-state operating boundary, and propose a fault ride-through method for the fault state;

[0008] Step 4: Propose a transient multi-scale voltage support method for the entire system, analyze the transient support capability of high-power-density supercapacitors and the cross-temporal and spatial regulation capability of high-energy-density hydrogen fuel cells, and propose a renewable energy consumption method based on the electricity-hydrogen system.

[0009] It can be seen from the technical solution provided by the present invention that the above method is simple and effective, can significantly improve the stability of the extremely weak-end new energy base, and can achieve cross-domain integration, which is convenient for carrying out relevant research on the stability mechanism and optimized scheduling of the electricity-hydrogen coupling system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0011] Figure 1 A schematic flow chart of a multi-scale voltage support method for extremely weak-end renewable energy transmission in Shagohuang provided in an embodiment of the present invention;

[0012] Figure 2 The distribution of new energy resources in the Shagohuang area;

[0013] Figure 3 This is a schematic diagram of wind resource distribution in Ulanqab, Inner Mongolia Autonomous Region;

[0014] Figure 4 Topological diagram of AC and DC transmission scheme;

[0015] Figure 5 Schematic diagram of the power grid structure of the Jinzhong DC project;

[0016] Figure 6 LCC-MMC hybrid DC transmission scheme topology diagram;

[0017] Figure 7 Hybrid cascaded DC system topology;

[0018] Figure 8 Schematic diagram of the location of the inverter station of the hybrid cascade DC system;

[0019] Fig. 9 Pure MMC DC transmission solution;

[0020] Fig.10 Zhangbei Engineering Topology;

[0021] Fig.11 Schematic diagram of the topology of the transmission system of Shagohuang New Energy Base;

[0022] Fig.12 Schematic diagram of basic control strategy of LCC at the sending and receiving ends;

[0023] Fig.13 Schematic diagram of basic control strategy of MMC at sending and receiving ends;

[0024] Fig.14 The steady-state operation area of ​​MMC under the transmission scenario with a 1:1 capacity ratio between LCC and MMC;

[0025] Fig.15 Schematic diagram of energy storage unit access method;

[0026] Fig.16 Cascaded H-bridge power converter control block diagram; DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings 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, which does not constitute a limitation of the present invention. 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.

[0028] like Figure 2 The figure shows a schematic diagram of the distribution of new energy resources in the Shagohuang area. The method comprises:

[0029] Step 1: Explore the development potential of wind and solar energy in Ulanqab, Inner Mongolia Autonomous Region, and conduct a life cycle assessment of new energy using wind power generation as an example:

[0030] my country has a vast territory and rich land wind energy resources. The actual exploitable amount is as high as 800 million kilowatts, ranking first in the world. Figure 2 As shown. Among them, the wind resources in Inner Mongolia Autonomous Region rank first in the country, with exploitable wind energy reserves of 101 million kilowatts. In 2009, China's newly installed capacity exceeded that of the United States, ranking first in the world. There are already 8 cities in Inner Mongolia Autonomous Region with a cumulative installed capacity of wind turbines exceeding one million kilowatts, and Ulanqab is one of them. The effective wind farm area in Ulanqab is 6,828 square kilometers, and the technically exploitable capacity is 68 million kilowatts, accounting for one-third of the Inner Mongolia Autonomous Region and one-tenth of the country respectively. The installed wind power capacity is 4.85 million kilowatts. It is known as the "Three Gorges in the Sky and the Capital of Wind Power". The schematic diagram of the distribution of wind resources in Ulanqab is shown below Figure 3 shown.

[0031] The Three Gorges Ulanqab new generation grid-friendly green power station demonstration project is used as an example for analysis. The total installed capacity of the project is 2000MW, the total installed capacity of wind power is 1700MW, the total installed capacity of photovoltaic power is 300MW, and the energy storage is 550MW·2h, which are: 450MW·2h lithium battery energy storage on the AC side of power generation, 50MW·2h new digital energy storage on the AC side of power generation, and 50MW·2h statcom energy storage system. In terms of "energy storage scale configuration", the project has built an energy storage system of about 30% of the total wind and solar installed capacity.

[0032] Life Cycle Assessment (LCA), also known as life cycle analysis, is a technique used to evaluate environmental factors and their potential impacts related to a product. LCA studies the environmental factors and potential impacts throughout the entire life cycle of a product - from obtaining raw materials, production, use to final disposal.

[0033] Since the wind turbine capacity of the project accounts for a large proportion, this step takes the Gamesa G8X-2MW wind turbine as an example to conduct a life cycle assessment. Considering redundancy, 920 wind turbines are required. The total energy consumption and emissions of the materials required for the production of a Gamesa G8X-2MW wind turbine are shown in Table 1 below.

[0034] Table 1 Total energy consumption and emissions of each material in the production of a single 2MW wind turbine

[0035]

[0036] The main modes of transportation in the transportation stage are trucks and trains, and the fuel consumed is diesel. Assume that the unit load unit mileage fuel consumption of trucks and trains is 0.0267 and 0.0072 kg / (t·km) respectively. Gamesa series wind turbines are produced in Tianjin, which is 500 km away from Ulanqab City, Inner Mongolia Autonomous Region. Assume that 30% of them are transported by train and 70% by truck during transportation, and the total transportation mass is 250 tons. Trucks consume diesel and trains consume gasoline.

[0037] During the operation and maintenance phase, the main energy consumption and environmental impact comes from the replacement of parts. However, since the energy consumption and environmental emissions at this stage are difficult to calculate, it is assumed that the energy consumption during the entire operation of the fan is 15% of the initial energy consumption.

[0038] In the final disposal stage, when the wind turbine is scrapped, it is assumed that 98% of the blades, 90% of the nacelle and 90% of the tower will be recycled, while the foundation will remain in place. Therefore, it is assumed that the energy consumption and emissions of the entire scrapping and recycling stage are 10% of the production stage. Therefore, the energy consumption and environmental emissions of the Gamesa G8X-2MW wind turbine during its life cycle are shown in Table 2 below.

[0039] Table 2 Energy consumption and environmental emissions of a single 2MW wind turbine

[0040]

[0041] According to the wind resources in Ulanqab, assuming that the wind turbine generates electricity at full load for about 2,000 hours a year, it can be calculated that a single wind turbine can repay the energy consumed in its entire life cycle by working for 0.8 years. Therefore, this type of wind turbine will save an equivalent amount of non-renewable energy of 76.743 GW·h in its entire life cycle. The comparison of the environmental load of wind power generation and coal-fired power generation is shown in Table 3 below.

[0042] Table 3 Comparison of environmental loads between wind power generation and coal-fired power generation

[0043]

[0044] Based on the above analysis, if the new energy base built in Ulanqab City, Inner Mongolia Autonomous Region adopts Gamesa G8X-2MW wind turbine, it can reduce the consumption of 1.46×10 7 tons of standard coal, reducing emissions to the atmosphere by 3.66×10 7 tCO2, 1.84×10 5 NO x , 2.9×10 5 t SO2. As can be seen from Table 3, the energy consumption, global warming potential (GWP) and acidification potential (AP) of wind power generation are only 0.925%, 0.395% and 0.683% of those of coal-fired power generation, respectively. Therefore, large-scale new energy bases not only have the advantage of short specific energy payback time.

[0045] Step 2: Analyze the pros and cons of various transmission schemes, and select the final transmission scheme, and establish the system topology structure for large-scale new energy transmission in Shagohuang:

[0046] The characteristics of my country's energy resource distribution and electricity load conditions determine the basic pattern and development strategy of my country's "West-to-East Power Transmission". However, there are few studies on the energy transmission scheme of the Shagohuang large-scale new energy base. This step compares the three typical DC transmission schemes: AC / DC transmission scheme, new energy via LCC (Line Commutated Converter Based High Voltage Direct Current, LCC-HVDC) and MMC (Modular Multilevel Converter Based High Voltage Direct Current, MMC-HVDC) hybrid DC transmission scheme, and new energy via MMC transmission scheme.

[0047] Large-scale transmission of new energy requires the establishment of a stable AC voltage at the grid connection point. By using a flexible DC converter (Voltage Source Converter HVDC, VSC-HVDC) based on fully controlled devices to establish an AC voltage on the AC bus side, stable transmission of new energy can be achieved. Since there are AC lines in my country's large power grid structure, in order to achieve the transmission of new energy, a high-voltage DC transmission line based on a voltage source converter can be connected to the grid in parallel with the original AC transmission line, which not only realizes the transmission of new energy, but also increases the transmission capacity without increasing the short-circuit current capacity of the original power system. The topological structure diagram of the AC / DC transmission scheme is shown in the figure below. Figure 4 shown.

[0048] The Jinzhong DC Project is the first ±500kV DC transmission project in Guangxi Zhuang Autonomous Region. Figure 5 The project line is 1,105 km long and has a transmission capacity of 3,200 MW. It was completed and put into operation on May 28, 2016, marking the formation of 17 west-to-east power transmission channels for the Southern Power Grid, including eight cross-connections and nine direct-connections.

[0049] The starting point of the Jinzhong DC project is located at the Jinguan Converter Station in Lijiang, Yunnan Province, and the landing point is located at the ±500kV Guizhong Converter Station in Liuzhou, Guangxi Zhuang Autonomous Region. The supporting power sources of the project are the Ahai and Liyuan power stations, including the Liyuan Power Plant (4×600MW) and the Ahai Power Plant (5×400MW), with a total installed capacity of 4400MW. The 500kV AC field of the receiving end converter station is connected to the 500kV Shalai line, forming 1 500kV Shazhongjia line and 1 500kV Laibinzhongjia line. A new 500kV Liuzhongjia line was put into operation in conjunction with the converter station, and the two 1000MW main transformers of the new Guizhong station were connected to the Guangxi Zhuang Autonomous Region power grid.

[0050] The MMC-based high-voltage direct current transmission system has the advantages of being able to independently control active and reactive power, and being able to supply power to weak AC systems and even passive systems, making it suitable for direct connection to wind farms. However, its high cost, small capacity, and inability to effectively handle DC-side faults limit its application in large-scale wind power transmission scenarios. The hybrid cascading of LCC and MMC can achieve the fusion of their respective advantages, so that the system has the advantages of large capacity, low loss, low cost, and strong short-term overcurrent tolerance of LCC, as well as the strong adaptability to weak networks and flexible control of MMC. The topology diagram of the LCC-MMC hybrid direct current transmission scheme is shown below. Figure 6 shown.

[0051] The rated transmission power of the Baihetan-Jiangsu ±800kV hybrid cascade DC project is 8000MW, and the line length is 2087km. Its topology is as follows: Figure 7 As shown in the figure, the sending end uses dual 12-pulse conventional DC, the receiving end uses conventional DC converters at the high voltage end, and three flexible DC converters are connected in parallel at the low voltage end. The eight converters at the receiving end are connected to four different busbars of the Suzhou power grid. Figure 8 As shown, the inverter-side LCC is connected to Dousan via 2 loops and to Changshu South via 3 loops. The 2 outgoing lines of MMC1 are connected to Zhangjiagang and Changshu North respectively; MMC2 and MMC3 are connected to Mudu and Yushan via 2 loops respectively. In steady state, half of the DC power is sent by LCC and the other half by 3 MMCs.

[0052] The DC transmission mode in which all new energy is transmitted through MMC converters is simple to control, and there is no AC line stability limit problem in AC / DC transmission. It can realize asynchronous networking of the sending and receiving ends, and does not need to start and stop LCC and MMC in sequence like the LCC-MMC hybrid DC transmission mode. The control is simpler and the reliability is high. The topological structure diagram of pure MMC DC transmission mode is as follows: Fig. 9 shown.

[0053] The Zhangbei flexible DC power grid is a "mouth" shaped structure, consisting of four DC transmission lines from Kangbao to Zhangbei, Zhangbei to Beijing, Beijing to Fengning, and Fengning to Kangbao, forming an interconnected power grid. Among them, Kangbao Station and Zhangbei Station are new energy feed-in stations, connected to the 220kV AC power grid or AC isolated grid, Fengning Station is a pumped storage station, and Beijing Station is the receiving end. Both stations are connected to the 500kV AC power grid. The balancing node of the entire DC power grid is set at Fengning Station, and its output power is controlled by the power changes of other stations to ensure the stability of the DC voltage.

[0054] The Zhangbei project converter station adopts a symmetrical bipolar topology structure, and the converter valve adopts modular multi-level technology based on half-bridge topology. A 150mH reactor is configured on the DC line and a 300mH reactor is configured on the neutral line. Fig.10This is the topology diagram of the Zhangbei project. When any pole converter fails, the non-faulty pole converter can still transmit at most half of the rated power, thereby improving the reliability of DC power supply.

[0055] According to the above analysis, LCC-MMC hybrid three-terminal DC is finally adopted as the DC transmission solution of Shagohuang New Energy. LCC is used at the sending end of DC transmission, and MMC is used at the two receiving ends. The topological structure diagram of the system is as follows Fig.11 This solution not only gives full play to the advantages of large capacity and low cost of LCC, but also the four-quadrant operation capability of MMC can solve the problem of conventional DC commutation failure, reduce reactive compensation capacity, reduce the floor space of equipment, and effectively improve the economy of the entire solution.

[0056] Step 3: Based on the different operating conditions and electrical characteristics of the converter station, propose a system control strategy, calculate the system steady-state operating boundary, and propose a fault ride-through method for the fault state:

[0057] When the large-scale new energy base in Shagohuang is connected to the LCC-MMC DC transmission system and operates in a steady state, the MMC converter station at the sending end usually adopts constant AC voltage / constant frequency control to provide a stable grid-connected voltage for the wind farm. In order to reasonably distribute the DC voltage at the sending and receiving ends, the LCC at the sending end adopts constant DC voltage control, while the LCC at the receiving end adopts a combination of constant DC voltage and constant γ angle control to prevent commutation failure, and the MMC at the receiving end adopts constant DC voltage and constant reactive power control to maintain the balance of active and reactive power in the system. Its control strategies are listed below.

[0058] The schematic diagram of the basic control strategy of LCC at the sending and receiving ends is as follows: Fig.12 As shown, the sending-end LCC adopts constant DC voltage control, the receiving-end LCC adopts constant DC voltage and constant γ angle control, and the reference values ​​of the trigger angles of the sending and receiving converter valves are obtained respectively. The method of combining constant DC voltage and constant γ angle control on the inverter side can also reduce the probability of commutation failure of LCC and ensure the reasonable distribution of DC voltage on the inverter side.

[0059] The basic control strategy diagram of MMC at the sending and receiving end is as follows: Fig.13 For the new energy grid access system at the sending end, the MMC at the sending end needs to adopt a fixed AC voltage / fixed AC frequency control strategy to establish a stable AC bus voltage to ensure that new energy can be sent out stably; the MMC at the receiving end adopts a fixed DC voltage and fixed reactive power control to ensure the reasonable distribution of DC voltage on LCC and MMC and the reasonable distribution of reactive power.

[0060] Although MMC has the ability to operate in four quadrants, its flexible operation is also subject to some regulatory constraints. The operating boundary index can be measured by the active and reactive operating range of MMC. Comparing different DC transmission schemes, the active power values ​​are not much different, but the reactive power values ​​are quite different. MMC can achieve four-quadrant operation, which can not only absorb reactive power, but also generate reactive power.

[0061] Constraint 1: Converter capacity constraint

[0062] The bridge arm of the MMC converter consists of a series submodule and a series bridge arm reactor. The submodule contains IGBT, anti-parallel diode and submodule capacitor. These devices themselves have certain capacity constraints, which leads to the limitation of the overall capacity of the converter. Therefore, the steady-state power operation range of MMC-HVDC must be obtained within this capacity range. The converter capacity constraints that affect the steady-state operation range of MMC-HVDC can be summarized as follows:

[0063]

[0064] Where P v and Q v represents the active and reactive power measured at point v, S vN Indicates the rated apparent power value of the inverter.

[0065] Constraint 2: Voltage stability constraint

[0066] Assuming that the system voltage on the AC side remains unchanged and known, the voltage Upcc obtained after converting the AC side voltage to the transformer valve side also remains unchanged and known. The power of the MMC converter AC outlet observation point v is given in advance as the research object. By detecting whether the given power operating point meets the constraints, it is determined whether it is within the stable operating range.

[0067] Constraint 3: Maximum capacity constraint of the connecting transformer

[0068] Similar to the capacity constraints of the converter itself, the connection transformer also has capacity constraints. The constraints can be expressed as:

[0069]

[0070] Where S pccN State the rated apparent power of the connecting transformer.

[0071] Constraint 4: Modulation ratio constraint

[0072] When the modulation ratio exceeds the maximum allowable value, the number of bridge arm sub-modules is insufficient to support the required bridge arm voltage, resulting in distortion of the AC outlet voltage waveform, with a flat top instead of a sine wave; when the modulation ratio is too low, the number of sub-modules put into the bridge arm is greatly reduced as the modulation ratio decreases, resulting in an increase in the harmonic content of the MMC output voltage.

[0073] Constraint 5: Submodule capacitor voltage fluctuation rate constraint

[0074] When the converter is operating normally, since each submodule is put into operation at different times and the bridge arm current is different at the time of input, the energy absorbed or released by each submodule is also different. The capacitor voltage of each submodule fluctuates around the rated value. The voltage fluctuation of each submodule needs to be within the allowable range of the project.

[0075] According to the above five constraints, the operation boundary diagram of the converter station when the final MMC-LCC hybrid DC capacity ratio is 1:1 can be obtained as shown in the figure: Fig.14 shown.

[0076] When a serious AC fault occurs on the rectifier side of the LCC-MMC hybrid DC transmission system, the drop in AC bus voltage will cause the DC voltage on the rectifier side to decrease, and the system DC operating voltage should also decrease to ensure the transmission of active power. The low DC voltage operation capability of the inverter side MMC characterizes the fault ride-through capability of the LCC-MMC hybrid DC transmission system under the fault on the rectifier side. Its strong low DC voltage operation capability is the prerequisite for the system to achieve fault ride-through under the condition of the rectifier side fault. However, the half-bridge MMC based on the half-bridge sub-module (HBSM) is difficult to operate under the state of greatly reduced DC voltage; at the same time, the half-bridge MMC does not have the ability to self-clear DC faults. When a DC short-circuit fault occurs, the fault current has the characteristics of fast rise and large peak value, which seriously threatens the safety of the converter valve. The full-bridge MMC based on the full-bridge sub-module (FBSM) and the hybrid MMC based on HBSM and FBSM overcome the shortcomings of the half-bridge MMC. In comparison, the full-bridge MMC requires more components, has high cost and large losses; while the hybrid MMC combines the advantages of both HBSM and FBSM and has great application prospects.

[0077] Step 4: Propose a transient multi-scale voltage support method for the entire system, analyze the transient support capability of high-power-density supercapacitors and the cross-temporal capacity of high-energy-density hydrogen fuel cells, and propose a renewable energy consumption method based on the electricity-hydrogen system. :

[0078] Due to the low short-circuit ratio characteristics of the Shagohuang extremely weak new energy base, it is difficult to achieve multi-scale voltage support for access to large-capacity load converter stations. To address this problem, a method is proposed to use supercapacitors and to achieve voltage support functions of different scales. The high power density characteristics of supercapacitors are used to achieve millisecond-level, low-power, and low-energy voltage support, while the high energy density characteristics of hydrogen fuel cells are used to achieve second-level, high-power, and high-energy voltage support. The combination of the two achieves multi-scale voltage support capabilities. The schematic diagram of supercapacitors and hydrogen fuel cells connected to the DC bus is shown in the figure. Fig.15 shown.

[0079] Depend on Fig.15 It can be seen that supercapacitors are connected to the DC bus in cascade after an isolated DC / DC converter. They have the advantages of modularity and easy expansion. They can be directly connected to medium and high voltage distribution networks and transmission networks without a transformer to compensate for reactive current and negative sequence current, effectively improving power quality and voltage stability. However, since there is no common DC bus, the DC voltage of each phase is prone to imbalance under transient conditions, which increases the voltage stress of the device. In order to better support the grid voltage, the cascaded H-bridge needs to be equipped with a certain amount of energy storage to maintain the stability of the sub-module capacitor voltage under transient conditions. Considering the low withstand voltage level of the energy storage unit, the energy storage unit uses a coupling method in which it is connected in parallel through an isolated DC / DC converter.

[0080] Among them, the power converter adopts constant power control, and the DC / DC converter adopts constant DC voltage control. The cascaded H-bridge power converter adopts network control, which is mainly composed of power / voltage control loop, internal potential and current internal loop. Its control block diagram is as follows Fig.16 shown.

[0081] For hydrogen energy systems, hydrogen is added to hydrogen storage tanks through transportation or pipelines, and hydrogen storage tanks deliver hydrogen to fuel cells. The low-voltage DC output of the fuel cell will change greatly with changes in load or temperature, so a boost converter is required in the back stage to meet the DC bus voltage required for stable operation of the inverter, and then an isolated DC / DC converter is used to isolate the chemical part and the electrical part to ensure safe and stable operation of the system. The hydrogen energy storage system can adapt to the random, intermittent and fluctuating characteristics of wind power within the range of 0 to 100% rated power.

[0082] When the output of the new energy base drops sharply, causing the DC bus voltage to drop. First, the supercapacitor adjusts its own power to achieve millisecond-level, low-power, and small-energy-scale voltage support, slowing down the drop in the DC bus voltage. Secondly, the hydrogen storage tank delivers hydrogen to the hydrogen fuel cell, and the fuel cell starts working, achieving second-level, high-power, and high-energy-scale voltage support, balancing the power of the entire Shagohuang new energy delivery system.

[0083] As for the hydrogen system, it not only integrates highly intermittent renewable energy on a large scale, but also decarbonizes transportation, heating and industrial production processes. An electrolyzer of a certain capacity is connected to the new energy power generation side, and the wind and light resources that were originally abandoned due to power balance considerations are stored through electrolysis to produce hydrogen. This not only solves the problem of absorbing renewable energy, but also increases the flexibility of grid dispatch to a certain extent. Hydrogen, as an electric load, can participate in medium- and long-term, day-ahead and spot market transactions as an independent entity or together with local wind and solar power generation, energy storage, etc. to form a virtual power plant. At the same time, due to the huge demand for hydrogen in the middle and lower reaches, the cross-integration of the power industry and the chemical industry has been achieved.

[0084] In summary, the complementary characteristics of different energy storage forms can effectively solve the transient voltage support problem of Shagohuang New Energy Base. For engineering practice, equipping with a variety of different energy storage forms such as lithium batteries, flywheel energy storage and gravity energy storage can fully utilize their different characteristics and enhance the capacity of energy storage power stations with reactive support.

Claims

1. A multi-scale voltage support method suitable for the extremely weak end renewable energy transmission of Shagohuang, the method include: Step 1: Explore the development potential of wind and solar energy in Ulanqab, Inner Mongolia, and conduct a life cycle assessment of new energy using wind power generation as an example; Step 2: Analyze the pros and cons of various transmission schemes, and select the final transmission scheme, and establish the system topology structure for large-scale new energy transmission in Shagohuang; Step 3: Propose a system control strategy based on different operating conditions and electrical characteristics of the converter station, calculate the system steady-state operating boundary, and propose a fault ride-through method for the fault state; Step 4: Propose a transient multi-scale voltage support method for the entire system, analyze the transient support capability of high-power-density supercapacitors and the cross-temporal and spatial regulation capability of high-energy-density hydrogen fuel cells, and propose a renewable energy consumption method based on the electricity-hydrogen system.

2. According to claim 1, the development potential of wind and solar energy in Ulanqab, Inner Mongolia, is explored, and the life cycle assessment of new energy is conducted by taking wind power generation as an example. By taking Gamesa G8X-2MW wind turbine as an example, the energy consumption and emission of environmental pollutants in its production, transportation, operation and maintenance, and final scrapping stages are calculated, and finally compared with the traditional 300MW coal-fired power unit, the energy repayment time of the wind farm construction is obtained to be 0.8 years, and the remaining years are all profitable stages.

3. According to the analysis of the advantages and disadvantages of multiple transmission schemes as described in claim 2, and the selection of the final transmission scheme, the system topology structure of large-scale new energy transmission in Shagohuang is established, and the system topology structure of large-scale new energy transmission in Shagohuang is established. In view of the characteristics of my country's energy resource distribution and power load conditions, a low-cost, large-capacity, safe and stable DC transmission scheme is needed to realize the "West-to-East Power Transmission" of energy. A LCC-MMC hybrid three-terminal DC scheme is proposed to effectively solve the commutation failure problem of traditional DC transmission, and can also introduce the use of fully controlled devices to reduce costs.

4. According to claim 2, a system control strategy is proposed based on different operating conditions and electrical characteristics of the converter station, the system steady-state operation boundary is calculated, and a fault ride-through method of the fault state is proposed. The basic control strategy of the sending and receiving converter stations is determined, and the MMC steady-state operation boundary is drawn according to five constraints. It is proposed to improve the fault ride-through capability of the flexible direct current converter station by using a semi-full hybrid MMC submodule.

5. According to the transient multi-scale voltage support method for the entire system described in claim 2, the transient support capability of high-power-density supercapacitors and the cross-temporal and spatial scheduling capability of high-energy-density hydrogen fuel cells are analyzed, and a renewable energy consumption method is proposed based on the electric-hydrogen system. Taking supercapacitor-hydrogen fuel cells as an example, the feasibility of cooperating with different energy storage methods is verified. According to the characteristics of hydrogen, hydrogen is used to solve the problem of renewable energy consumption and improve the flexibility of scheduling, realizing the cross-integration of the power industry and the chemical industry.

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