MMC type high-voltage cascade hybrid energy storage coupling water electrolysis hydrogen production comprehensive energy system

Abstract

The invention provides an MMC type high-voltage cascade hybrid energy storage coupled water electrolysis hydrogen production comprehensive energy system. The comprehensive energy system comprises an MMC variable flow subsystem, a hybrid energy storage subsystem and a water electrolysis hydrogen production subsystem. The hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected to the direct current side of the MMC converter subsystem in parallel. The hybrid energy storage subsystem comprises an electrochemical energy storage branch and a supercapacitor energy storage branch which are arranged in parallel. According to the comprehensive energy system, the reverse frequency modulation capacity of the thermal power generating unit is improved, the investment of a water electrolysis hydrogen production subsystem is saved, the hydrogen production efficiency is improved, and the produced high-purity hydrogen is used for generator cooling or external sales; the efficiency and safety of the hybrid energy storage system are improved, the energy utilization efficiency of the whole system is improved, and meanwhile the service life and economical efficiency are both considered.

Description

Technical Field

[0001] The present invention belongs to the field of frequency modulation and hydrogen production, and relates to an MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen. Background Art

[0002] With the continuous development of the new power system based on new energy sources in China, the volatility of new energy sources has led to increasing difficulty in grid regulation, and the grid's requirements for power frequency regulation capabilities have become increasingly higher. However, thermal power units, which are the main force of frequency regulation in my country, have problems such as long response lag, poor regulation accuracy, reverse regulation, and insufficient automatic generation control (AGC) capabilities, making it difficult to meet the grid frequency regulation requirements and are therefore subject to grid assessment. At the same time, when thermal power units participate in frequency regulation, constantly responding to the frequently changing AGC frequency regulation instructions of the grid will cause the thermal power units to frequently increase and decrease loads, thereby increasing coal consumption and equipment wear of the thermal power units.

[0003] Using lithium battery energy storage systems to assist thermal power units in participating in frequency regulation can effectively improve the frequency regulation capability of the units and alleviate the pressure of grid frequency regulation assessment. However, when assisting thermal power units in participating in grid frequency regulation, lithium battery energy storage systems need to be frequently charged and discharged, resulting in rapid attenuation of lithium batteries, which requires the replacement of batteries after 3-4 years. Supercapacitors have the advantages of long cycle life, fast response and high power density, and can also be used to assist thermal power units in frequency regulation. However, the price of supercapacitors is much higher than that of lithium batteries, so there are very few engineering projects that only use supercapacitor systems to assist thermal power units in frequency regulation. Usually, a hybrid energy storage system of lithium battery energy storage systems and supercapacitor energy storage systems is used to assist frequency regulation. In the existing hybrid energy storage auxiliary frequency regulation systems that use lithium battery energy storage systems and supercapacitor energy storage systems, lithium battery energy storage systems and supercapacitor energy storage systems usually adopt a topological structure of converging and boosting, and the two different types of energy storage systems are controlled and converted by their own BMS and PCS systems. The two are not compatible, resulting in low efficiency, more system components, high control difficulty and poor compatibility of the current hybrid energy storage system.

[0004] For thermal power plants, especially medium and large thermal power plants, their generator sets are usually cooled by hydrogen. Therefore, it is necessary to build a water electrolysis hydrogen production device in the plant, or to purchase hydrogen regularly for cooling the generator. The construction of a conventional water electrolysis hydrogen production subsystem in a power plant requires a rectifier system that converts AC power into DC power, which increases the equipment investment and system complexity of the entire water electrolysis hydrogen production subsystem and reduces the efficiency of the hydrogen production system. Regularly purchasing hydrogen for generator cooling also faces the problem of high daily hydrogen purchase costs. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides an MMC (modular multi-level converter) type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen comprehensive energy system, the comprehensive energy system increases the reverse frequency modulation capability of the thermal power unit, saves the investment in the water electrolysis hydrogen production subsystem, and improves the hydrogen production efficiency; improves the efficiency and safety of the hybrid energy storage system, as well as the energy utilization efficiency of the entire system, while taking into account the service life and economy.

[0006] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] The present invention provides an MMC type high-voltage cascade hybrid energy storage coupled water electrolysis hydrogen production integrated energy system, the integrated energy system comprises an MMC converter subsystem, a hybrid energy storage subsystem and a water electrolysis hydrogen production subsystem;

[0008] The hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected in parallel to the DC side of the MMC converter subsystem;

[0009] The hybrid energy storage subsystem includes an electrochemical energy storage branch and a supercapacitor energy storage branch arranged in parallel;

[0010] A DC / DC step-down component is provided on the circuit connecting the water electrolysis hydrogen production device and the hybrid energy storage subsystem; a DC / DC chopper component is provided on the circuit connecting the water electrolysis hydrogen production device and the DC / DC step-down component.

[0011] As a preferred technical solution of the present invention, the MMC converter system includes at least two three-phase bridges, and the three-phase bridges are composed of cascaded single-phase full-bridge power units.

[0012] As a preferred technical solution of the present invention, the electrochemical energy storage branch is a lithium battery energy storage branch.

[0013] As a preferred technical solution of the present invention, the lithium battery energy storage branch is composed of a cascade of standard links, and the standard links include PCS units and lithium battery clusters.

[0014] As a preferred technical solution of the present invention, the lithium battery cluster includes battery packs connected in series, and the battery packs include lithium battery cells connected in series.

[0015] As a preferred technical solution of the present invention, the supercapacitor energy storage branch is composed of a cascade of standard links, and the standard links include a PCS (energy storage converter) unit and a supercapacitor cabinet.

[0016] As a preferred technical solution of the present invention, the supercapacitor cabinet includes supercapacitor modules connected in series, the supercapacitor modules include supercapacitor string groups connected in parallel, and the supercapacitor string groups include supercapacitor cells connected in series.

[0017] As a preferred technical solution of the present invention, the water electrolysis hydrogen production subsystem includes at least one set of water electrolysis hydrogen production equipment, such as 1 set, 2 sets, 3 sets, 5 sets, 8 sets or 10 sets, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] As a preferred technical solution of the present invention, when the water electrolysis hydrogen production subsystem includes no less than two water electrolysis hydrogen production devices, the water electrolysis hydrogen production devices are connected in parallel.

[0019] As a preferred technical solution of the present invention, a DC / DC chopper component is independently arranged in front of each of the water electrolysis hydrogen production devices.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) The present invention provides an MMC type high-voltage cascade hybrid energy storage coupled water electrolysis hydrogen production integrated energy system, which utilizes the water electrolysis hydrogen production subsystem on the DC bus side of the MMC converter system to produce high-purity hydrogen while further improving the reverse frequency regulation capability of the thermal power unit;

[0022] (2) The present invention provides an MMC-type high-voltage cascade hybrid energy storage coupled water electrolysis hydrogen production integrated energy system, the integrated energy system uses a DC / DC transformer assembly, the water electrolysis hydrogen production subsystem can be directly connected in parallel to the 20kV DC bus side of the MMC converter subsystem, without the need to set up an AC / DC rectification system, saving the investment in the water electrolysis hydrogen production subsystem and improving the hydrogen production efficiency;

[0023] (3) The present invention provides an MMC type high-voltage cascade hybrid energy storage coupled water electrolysis hydrogen production integrated energy system, in which the electrochemical energy storage branch of the hybrid energy storage subsystem, the supercapacitor energy storage branch and the water electrolysis hydrogen production subsystem can achieve internal distribution and balance of electricity, thereby increasing the operational flexibility among the electrochemical energy storage branch, the supercapacitor energy storage branch and the water electrolysis hydrogen production subsystem;

[0024] (4) The present invention provides an MMC-type high-voltage cascade hybrid energy storage coupled with water electrolysis for hydrogen production. The comprehensive energy system couples the hybrid energy storage system and the water electrolysis for hydrogen production subsystem, which can not only improve the frequency regulation capability of thermal power units and avoid grid assessment, but also produce high-purity hydrogen for use in thermal power plant generator cooling or external sales. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic structural diagram of the MMC-type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen comprehensive energy system provided in Example 1 of the present invention.

[0026] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0027] The technical solution of the present application is further described below through specific implementation methods.

[0028] The specific embodiment of the present invention provides an MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production integrated energy system, the integrated energy system includes an MMC converter subsystem, a hybrid energy storage subsystem and a water electrolysis hydrogen production subsystem;

[0029] The hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected in parallel to the DC side of the MMC converter subsystem;

[0030] The hybrid energy storage subsystem includes an electrochemical energy storage branch and a supercapacitor energy storage branch arranged in parallel.

[0031] A DC / DC step-down component is provided on the circuit connecting the water electrolysis hydrogen production device and the hybrid energy storage subsystem; a DC / DC chopper component is provided on the circuit connecting the water electrolysis hydrogen production device and the DC / DC step-down component.

[0032] In the present invention, the water electrolysis hydrogen production subsystem can be used to produce hydrogen by electrolysis of water in a thermal power plant using the power generated by the generator. While obtaining high-purity hydrogen, it can also further increase the reverse frequency modulation capability of the thermal power unit; it can also avoid the power loss (usually between 10-15%) during the charging and discharging process of the hybrid energy storage subsystem when responding to the AGC frequency modulation of the power grid, thereby improving the energy utilization efficiency of the entire system. The hybrid energy storage subsystem is composed of a supercapacitor with a higher price but a longer cycle life and a lithium battery with a lower price but a shorter cycle life, which avoids the circulation problem caused by the series-parallel grouping of the conventional lithium battery energy storage system and the supercapacitor energy storage system, thereby improving the efficiency and safety of the hybrid energy storage system.

[0033] In the present invention, the DC / DC step-down component in the water electrolysis hydrogen production subsystem is used to step down the 20kV DC voltage on the DC side of the MMC converter subsystem to the working voltage (about 600V) of the water electrolysis hydrogen production subsystem. The water electrolysis hydrogen production subsystem can be directly connected in parallel to the 20kV DC bus side of the MMC converter subsystem, eliminating the AC power supply rectification system required for the conventional water electrolysis hydrogen production subsystem, saving investment, and improving the efficiency of the water electrolysis hydrogen production subsystem.

[0034] In a specific implementation of the present invention, the AC side of the MMC converter subsystem is connected to the 10kV plant power bus of the thermal power plant, and the power on the AC side is adjusted by controlling the AC power output of the MMC converter subsystem.

[0035] In a specific embodiment of the present invention, the MMC converter system may be composed of two three-phase bridges, each of which may be composed of 16 to 48 single-phase full-bridge power units in cascade, and the output may be a 10 kV, 50 Hz three-phase AC power supply.

[0036] In a specific embodiment of the present invention, the hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected in parallel to the DC side of the MMC converter subsystem, such as a 20kV DC bus; the MMC converter subsystem realizes power exchange between the hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem by controlling the DC voltage and DC current.

[0037] In a specific embodiment of the present invention, the hybrid energy storage subsystem includes a lithium battery energy storage branch and a supercapacitor energy storage branch. For low-power and frequent grid AGC frequency modulation instructions, the supercapacitor energy storage branch is preferentially called, and the long cycle life of the supercapacitor energy storage branch is utilized to significantly reduce the number of actions of the lithium battery energy storage branch, and correspondingly extend the service life of the lithium battery. For relatively high-power AGC frequency modulation instructions, the lithium battery energy storage branch and the supercapacitor energy storage branch are called to jointly assist the thermal power plant in carrying out frequency modulation services. This allows the entire hybrid energy storage to significantly improve the frequency modulation capability of the thermal power unit while taking into account both service life and economy.

[0038] In a specific embodiment of the present invention, the lithium battery energy storage branch may be composed of 15 to 30 cascaded standard chain links.

[0039] In a specific embodiment of the present invention, one battery cluster may be composed of 2 to 10 battery packs connected in series, and each battery pack is composed of 1 to 30 to 150 lithium battery cells connected in series.

[0040] In a specific embodiment of the present invention, the number of standard links, battery clusters, battery packs and lithium battery cells in the lithium battery energy storage branch can be selected according to the AGC frequency modulation requirements, lithium battery model and capacity and other conditions, and is not further limited here.

[0041] In a specific embodiment of the present invention, the final voltage level of the lithium battery energy storage branch entering the DC side of the MMC converter system can be calculated by V=3.2*M, where M is the number of cells entering the DC side.

[0042] In a specific embodiment of the present invention, a circuit breaker and an inductor are provided on the circuit connecting the first-level standard link in the lithium battery energy storage branch and the MMC converter subsystem.

[0043] In a specific embodiment of the present invention, the supercapacitor energy storage branch is composed of 15 to 30 standard chain links in cascade.

[0044] In the present invention, the lithium battery energy storage branch and the supercapacitor energy storage branch are combined and boosted to a high voltage of 20kV in a cascade manner, and then connected to the DC side of the MMC converter subsystem, thereby eliminating the PCS converter of the conventional energy storage system, improving the efficiency of the hybrid energy storage system described in this patent, reducing the control difficulty, and increasing the response speed.

[0045] In a specific embodiment of the present invention, one supercapacitor cabinet is composed of 10 to 30 supercapacitor modules connected in series, and each supercapacitor module is composed of 1 to 2 and 10 to 30 supercapacitor cells connected in series.

[0046] In a specific embodiment of the present invention, the number of standard links, supercapacitor cabinets, supercapacitor modules and supercapacitor cells in the supercapacitor energy storage branch can be selected according to the AGC frequency modulation requirements, supercapacitor cell model and capacity and other conditions, and no further limitation is made here.

[0047] In a specific embodiment of the present invention, the final voltage level of the supercapacitor energy storage branch entering the DC side of the MMC converter system can be calculated by V=4.0*N / L, where N is the number of supercapacitor cells entering the DC, and L is the number of parallel strings of supercapacitor modules.

[0048] In a specific embodiment of the present invention, a circuit breaker and an inductor are provided on the circuit connecting the first-level standard link in the supercapacitor energy storage branch and the lithium battery energy storage branch.

[0049] In a specific embodiment of the present invention, the PCS unit is preferably a half-bridge structure PCS unit, which is composed of IGBTs (insulated gate bipolar transistors), capacitors, inductors, filter units and DC interfaces arranged in sequence along the current propagation direction.

[0050] In a specific embodiment of the present invention, a circuit breaker is provided on the circuit connecting the DC / DC step-down component to the hybrid energy storage subsystem.

[0051] In a specific embodiment of the present invention, a circuit breaker is provided on the circuit connecting each DC / DC chopper component and the DC / DC step-down component.

[0052] In a specific embodiment of the present invention, the operation strategy of the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen comprehensive energy system includes:

[0053] (1) The operation strategy of the grid forward AGC frequency modulation command is as follows:

[0054] a. A small positive frequency modulation command (the grid positive AGC command requires that the power output of the hybrid energy storage subsystem is less than the power of the supercapacitor energy storage branch):

[0055] For small-amplitude forward frequency modulation commands from the power grid, only supercapacitor energy storage systems with high power density and high cycle times are used to discharge to the power grid (cut off the lithium battery energy storage system to avoid frequent operation of the lithium battery energy storage system, increase the service life of the lithium battery energy storage system, and thus increase the service life of the entire hybrid energy storage system);

[0056] b. Medium amplitude forward frequency modulation command (the grid forward AGC command requires that the power output of the hybrid energy storage subsystem is greater than the power of the supercapacitor energy storage branch, but less than the sum of the powers of the lithium battery energy storage branch and the supercapacitor energy storage branch):

[0057] For the medium-amplitude forward frequency modulation command of the power grid, the supercapacitor energy storage branch is first put into use to discharge to the power grid; the remaining power demand for power grid frequency modulation is discharged by the lithium battery energy storage branch; that is, all supercapacitor energy storage branches and some lithium battery energy storage branches jointly participate in frequency modulation;

[0058] c. Large positive frequency modulation instructions (the grid positive AGC instructions require that the power output of the hybrid energy storage system is greater than the total power of the lithium battery energy storage branch and the supercapacitor energy storage branch):

[0059] For large-scale forward frequency modulation commands from the power grid, both the lithium battery energy storage branch and the supercapacitor energy storage branch are put into use to jointly transmit power to the power grid to participate in frequency modulation.

[0060] (2) The operation strategy of the grid reverse AGC frequency modulation command is as follows:

[0061] a. Small amplitude reverse frequency modulation command (the grid reverse AGC command requires that the power absorbed by the frequency modulation system is less than the power of the supercapacitor energy storage branch):

[0062] For small-amplitude reverse frequency modulation commands from the power grid, only supercapacitor energy storage systems with high power density and high cycle times are charged to absorb excess power from the power grid.

[0063] b. Medium-amplitude reverse frequency modulation command (the grid reverse AGC command requires that the power absorbed by the frequency modulation system is greater than the power of the supercapacitor energy storage branch, but less than the sum of the powers of the lithium battery energy storage system (or water electrolysis hydrogen production subsystem) and the supercapacitor energy storage branch):

[0064] For the reverse frequency modulation command of medium amplitude in the power grid, the supercapacitor energy storage branch is first put into charging to absorb the excess power of the power grid; for the remaining power demand of the power grid frequency modulation, the lithium battery energy storage branch can be used for charging to absorb the excess power. At this time, all the supercapacitor energy storage branches and some lithium battery energy storage branches participate in the frequency modulation together; or when there is a demand for high-purity hydrogen from the outside world, the water electrolysis hydrogen production subsystem is selected to absorb the remaining power demand of the power grid frequency modulation. At this time, all the supercapacitor energy storage systems and the water electrolysis hydrogen production subsystem participate in the frequency modulation together;

[0065] c. Large reverse frequency modulation instructions (the grid reverse AGC instructions require that the power absorbed by the frequency modulation system is greater than the total power of the lithium battery energy storage branch, the supercapacitor energy storage branch and the water electrolysis hydrogen production subsystem):

[0066] In response to the grid's large-scale reverse frequency modulation commands, the lithium battery energy storage branch, supercapacitor energy storage branch and water electrolysis hydrogen production subsystem are all put into use. The lithium battery energy storage branch and supercapacitor energy storage branch are used for charging, and the water electrolysis hydrogen production subsystem is used to produce hydrogen, so as to jointly absorb the excess power of the grid.

[0067] (3) The operation strategy when the power grid does not send AGC frequency modulation commands is as follows:

[0068] a. When there is no external demand for high-purity hydrogen:

[0069] By releasing power to the plant power bus, the power of the lithium battery energy storage branch and the supercapacitor energy storage branch is maintained at about 50% of the rated current of their respective systems;

[0070] The water electrolysis hydrogen production subsystem is not used;

[0071] b. When there is a demand for high-purity hydrogen from the outside:

[0072] The water electrolysis hydrogen production subsystem is put into use, and the power of the lithium battery energy storage branch and the supercapacitor energy storage branch is transmitted to the water electrolysis hydrogen production subsystem, so that the lithium battery energy storage branch and the supercapacitor energy storage branch are respectively at a level of about 50% of the rated current of the system.

[0073] In a specific embodiment of the present invention, the DC side voltage fluctuation control strategy of the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production integrated energy system includes:

[0074] (1) MMC DC side voltage fluctuation control when the water electrolysis hydrogen production subsystem is not in operation:

[0075] When the frequency regulation command of the power grid changes, the energy management system of the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production integrated energy system is used to adjust the PCS unit in a single standard link in the lithium battery energy storage branch and the supercapacitor energy storage branch, change the energy storage unit voltage in a single standard link, and then adjust the voltage fluctuation on the DC side of the MMC converter subsystem;

[0076] (2) Control of DC voltage fluctuation when the water electrolysis hydrogen production subsystem is put into operation;

[0077] When the water electrolysis hydrogen production subsystem is put into operation, the voltage fluctuation on the DC side of the MMC converter subsystem can be adjusted by adjusting the load rate of the water electrolysis hydrogen production subsystem, together with adjusting the PCS unit in a single standard link in the lithium battery energy storage branch and the supercapacitor energy storage branch, and changing the energy storage unit voltage in a single standard link.

[0078] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0079] Example 1

[0080] This embodiment provides a comprehensive energy system of MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen, and its structure is as follows: Figure 1 As shown, the integrated energy system is configured in a 600MW thermal power plant;

[0081] The integrated energy system includes an MMC converter subsystem, a hybrid energy storage subsystem, and a water electrolysis hydrogen production subsystem;

[0082] The hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected in parallel to the DC side of the MMC converter subsystem;

[0083] The hybrid energy storage subsystem includes a lithium battery energy storage branch and a supercapacitor energy storage branch arranged in parallel;

[0084] The AC side of the MMC converter system is connected to the 10kV power busbar of the thermal power plant. It consists of two upper and lower three-phase bridges. One arm of each three-phase bridge is composed of 24 single-phase full-bridge power units in cascade, and the output is a 10kV, 50Hz three-phase AC power supply.

[0085] The lithium battery energy storage branch is equipped with a commutation chain consisting of 24 standard links. Each link consists of a half-bridge PCS unit and a battery cluster. A battery cluster consists of 6 battery packs in series. A single battery pack consists of 1 parallel and 52 series lithium battery cells. A total of 7488 lithium battery cells are connected in series. According to the calculation of 280Ah, 3.2V cells, the lithium battery system branch finally converges to form a 23.9kV DC high voltage, which is selected to converge and connect to a 20kV DC high voltage line. The total capacity of the lithium battery energy storage system is 6.7MW / 6.7MWh.

[0086] The supercapacitor energy storage branch is equipped with a commutation chain consisting of 24 standard links. Each link consists of a half-bridge PCS unit and a supercapacitor cabinet. Every 16 supercapacitor modules are connected in series to form a single supercapacitor cabinet. The internal structure of a single supercapacitor module is designed as 2 parallel 18 series supercapacitor cells, and a total of 13824 supercapacitor cells are connected in series. According to the calculation of 4.0V, 30000F supercapacitor monomers, the supercapacitor energy storage branch finally converges to form a 27.6kV DC high voltage, which is selected to converge and access a 20kV DC high voltage line. The total capacity of the supercapacitor system is 1.7MW / 0.31MWh.

[0087] The water electrolysis hydrogen production subsystem is equipped with 3 sets of alkaline water electrolysis hydrogen production devices and their auxiliary components. The capacity of a single alkaline water electrolysis hydrogen production subsystem is 500m 3 / h, a DC / DC step-down device is provided on the circuit connecting the water electrolysis hydrogen production device and the hybrid energy storage subsystem, and a DC / DC chopper is provided on the circuit connecting the water electrolysis hydrogen production device and the DC / DC step-down device;

[0088] The DC / DC step-down device is used to reduce the 20kV DC voltage on the DC bus side of the MMC converter system to the operating voltage of the hydrogen production electrolyzer (about 600V). After passing through the DC / DC chopper, it is transmitted to three 500m 3 / h alkaline electrolyzer to produce high-purity hydrogen.

[0089] Application Example 1

[0090] In this application example, the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production comprehensive energy system provided in Example 1 is used, and its operation mode includes:

[0091] (1) The operation strategy of the grid forward AGC frequency modulation command is as follows:

[0092] a. A small positive frequency modulation command (the grid positive AGC command requires that the power output of the hybrid energy storage subsystem is less than the power of the supercapacitor energy storage branch):

[0093] For small-amplitude forward frequency modulation commands from the power grid, only supercapacitor energy storage systems with high power density and high cycle times are used to discharge to the power grid (cut off the lithium battery energy storage system to avoid frequent operation of the lithium battery energy storage system, increase the service life of the lithium battery energy storage system, and thus increase the service life of the entire hybrid energy storage system);

[0094] b. Medium amplitude forward frequency modulation command (the grid forward AGC command requires that the power output of the hybrid energy storage subsystem is greater than the power of the supercapacitor energy storage branch, but less than the sum of the powers of the lithium battery energy storage branch and the supercapacitor energy storage branch):

[0095] For the medium-amplitude forward frequency modulation command of the power grid, the supercapacitor energy storage branch is first put into use to discharge to the power grid; the remaining power demand for power grid frequency modulation is discharged by the lithium battery energy storage branch; that is, all supercapacitor energy storage branches and some lithium battery energy storage branches jointly participate in frequency modulation;

[0096] c. Large positive frequency modulation instructions (the grid positive AGC instructions require that the power output of the hybrid energy storage system is greater than the total power of the lithium battery energy storage branch and the supercapacitor energy storage branch):

[0097] For large-scale forward frequency modulation commands from the power grid, both the lithium battery energy storage branch and the supercapacitor energy storage branch are put into use to jointly transmit power to the power grid to participate in frequency modulation.

[0098] (2) The operation strategy of the grid reverse AGC frequency modulation command is as follows:

[0099] a. Small amplitude reverse frequency modulation command (the grid reverse AGC command requires that the power absorbed by the frequency modulation system is less than the power of the supercapacitor energy storage branch):

[0100] For small-amplitude reverse frequency modulation commands from the power grid, only supercapacitor energy storage systems with high power density and high cycle times are charged to absorb excess power from the power grid.

[0101] b. Medium-amplitude reverse frequency modulation command (the grid reverse AGC command requires that the power absorbed by the frequency modulation system is greater than the power of the supercapacitor energy storage branch, but less than the sum of the powers of the lithium battery energy storage system (or water electrolysis hydrogen production subsystem) and the supercapacitor energy storage branch):

[0102] For the reverse frequency modulation command of medium amplitude in the power grid, the supercapacitor energy storage branch is first put into charging to absorb the excess power of the power grid; for the remaining power demand of the power grid frequency modulation, the lithium battery energy storage branch can be used for charging to absorb the excess power. At this time, all the supercapacitor energy storage branches and some lithium battery energy storage branches participate in the frequency modulation together; or when there is a demand for high-purity hydrogen from the outside world, the water electrolysis hydrogen production subsystem is selected to absorb the remaining power demand of the power grid frequency modulation. At this time, all the supercapacitor energy storage systems and the water electrolysis hydrogen production subsystem participate in the frequency modulation together;

[0103] c. Large reverse frequency modulation instructions (the grid reverse AGC instructions require that the power absorbed by the frequency modulation system is greater than the total power of the lithium battery energy storage branch, the supercapacitor energy storage branch and the water electrolysis hydrogen production subsystem):

[0104] In response to the grid's large-scale reverse frequency modulation commands, the lithium battery energy storage branch, supercapacitor energy storage branch and water electrolysis hydrogen production subsystem are all put into use. The lithium battery energy storage branch and supercapacitor energy storage branch are used for charging, and the water electrolysis hydrogen production subsystem is used to produce hydrogen, so as to jointly absorb the excess power of the grid.

[0105] (3) The operation strategy when the power grid does not send AGC frequency modulation commands is as follows:

[0106] a. When there is no external demand for high-purity hydrogen:

[0107] By releasing power to the plant power bus, the power of the lithium battery energy storage branch and the supercapacitor energy storage branch is maintained at about 50% of the rated current of their respective systems;

[0108] The water electrolysis hydrogen production subsystem is not used;

[0109] b. When there is a demand for high-purity hydrogen from the outside:

[0110] The water electrolysis hydrogen production subsystem is put into use, and the power of the lithium battery energy storage branch and the supercapacitor energy storage branch is transmitted to the water electrolysis hydrogen production subsystem, so that the lithium battery energy storage branch and the supercapacitor energy storage branch are respectively at a level of about 50% of the rated current of the system.

[0111] Application Example 2

[0112] In this application example, the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production comprehensive energy system provided in Example 1 is used, and its DC side voltage fluctuation control method includes:

[0113] (1) MMC DC side voltage fluctuation control when the water electrolysis hydrogen production subsystem is not in operation:

[0114] When the frequency regulation command of the power grid changes, the energy management system of the MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis hydrogen production integrated energy system is used to adjust the PCS unit in a single standard link in the lithium battery energy storage branch and the supercapacitor energy storage branch, change the energy storage unit voltage in a single standard link, and then adjust the voltage fluctuation on the DC side of the MMC converter subsystem;

[0115] (2) Control of DC voltage fluctuation when the water electrolysis hydrogen production subsystem is put into operation;

[0116] When the water electrolysis hydrogen production subsystem is put into operation, the voltage fluctuation on the DC side of the MMC converter subsystem can be adjusted by adjusting the load rate of the water electrolysis hydrogen production subsystem, together with adjusting the PCS unit in a single standard link in the lithium battery energy storage branch and the supercapacitor energy storage branch, and changing the energy storage unit voltage in a single standard link.

[0117] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0118] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0119] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0120] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A comprehensive energy system of MMC type high-voltage cascade hybrid energy storage coupled with water electrolysis to produce hydrogen, characterized in that: The comprehensive energy system includes an MMC converter subsystem, a hybrid energy storage subsystem and a water electrolysis hydrogen production subsystem; The hybrid energy storage subsystem and the water electrolysis hydrogen production subsystem are independently connected in parallel to the DC side of the MMC converter subsystem; The hybrid energy storage subsystem includes an electrochemical energy storage branch and a supercapacitor energy storage branch arranged in parallel; A DC / DC step-down component is provided on the circuit connecting the water electrolysis hydrogen production device and the hybrid energy storage subsystem; a DC / DC chopper component is provided on the circuit connecting the water electrolysis hydrogen production device and the DC / DC step-down component.

2. The integrated energy system according to claim 1, characterized in that: The MMC converter subsystem includes at least two three-phase bridges, and the three-phase bridges are composed of cascaded single-phase full-bridge power units.

3. The integrated energy system according to claim 1, characterized in that: The electrochemical energy storage branch is a lithium battery energy storage branch.

4. The integrated energy system according to claim 3, characterized in that: The lithium battery energy storage branch is formed by cascading standard links, and the standard links include PCS units and lithium battery clusters.

5. The integrated energy system according to claim 4, characterized in that: The lithium battery cluster includes battery packs connected in series, and the battery packs include lithium battery cells connected in series.

6. The integrated energy system according to claim 1, characterized in that: The supercapacitor energy storage branch is formed by cascading standard links, and the standard links include PCS units and supercapacitor cabinets.

7. The integrated energy system according to claim 6, characterized in that: The supercapacitor cabinet includes supercapacitor modules connected in series, the supercapacitor modules include supercapacitor string groups connected in parallel, and the supercapacitor string groups include supercapacitor cells connected in series.

8. The integrated energy system according to claim 1, characterized in that: The water electrolysis hydrogen production subsystem includes at least one water electrolysis hydrogen production device.

9. The integrated energy system according to claim 8, characterized in that: When the water electrolysis hydrogen production subsystem includes no less than 2 water electrolysis hydrogen production devices, the water electrolysis hydrogen production devices are connected in parallel.

10. The integrated energy system according to claim 8, characterized in that: A DC / DC chopper component is independently arranged in front of each of the water electrolysis hydrogen production devices.

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