Hybrid sodium ion battery energy storage system for power grid frequency modulation and frequency modulation method

Abstract

The invention discloses a mixed sodium ion battery energy storage system for power grid frequency modulation and a frequency modulation method. The system comprises a power type sodium ion battery energy storage unit which is used for primary frequency modulation and has the capacity accounting for 20-30% of the total capacity of the system, and an energy type sodium ion battery energy storage unit which is used for secondary frequency modulation and has the capacity accounting for 70-80% of the total capacity of the system. The battery energy storage system realizes automatic switching between primary frequency modulation and secondary frequency modulation through the battery management system based on the frequency change rate dF / dt of the power grid. The hybrid sodium ion battery energy storage system is provided with a power type sodium ion battery energy storage unit for primary frequency modulation and an energy type sodium ion battery energy storage unit for secondary frequency modulation, and based on the frequency change rate dF / dt of a power grid, the corresponding energy storage unit is started through a battery management system to realize automatic switching between the primary frequency modulation and the secondary frequency modulation; and the batteries of the same system are designed into energy type and power type units, so that the development cost and the production cost are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid frequency modulation, and particularly relates to a hybrid sodium-ion battery energy storage system and a frequency modulation method for power grid frequency modulation. Background Art

[0002] Power grid frequency modulation is divided into primary frequency modulation, secondary frequency modulation and tertiary frequency modulation. Among them, primary frequency modulation is a real-time response to frequency fluctuations, which is automatically completed by the governor of the generator set, and the response time is in the order of seconds; the response time of secondary frequency modulation is in the order of minutes, and the output of the unit is adjusted through automatic generation control (AGC) to restore the frequency to the target value; tertiary frequency modulation belongs to economic dispatch, which takes longer, generally in the range of 15 minutes to hours, and the power generation plan is adjusted manually.

[0003] In the prior art, for the characteristics of different frequency modulations, a hybrid energy storage system of "flywheel + lithium battery" or "supercapacitor + lithium battery" is commonly used to achieve power grid frequency modulation. The cooperation between different energy storage technologies has caused great obstacles to the construction and dispatch of the energy storage system. Therefore, it is of great significance to research and develop a hybrid sodium-ion battery energy storage system based on different performances for power grid frequency modulation. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a hybrid sodium-ion battery energy storage system and a frequency modulation method for power grid frequency modulation. According to the characteristics of power grid frequency modulation, a power-type sodium-ion battery energy storage unit is set in the hybrid sodium-ion battery energy storage system for primary frequency modulation, and an energy-type sodium-ion battery energy storage unit is set for secondary frequency modulation. Based on the frequency change rate dF / dt of the power grid, the corresponding energy storage unit is started through the battery management system to realize the automatic switching between primary frequency modulation and secondary frequency modulation, avoiding the cooperation between different energy storage systems; at the same time, using the same system of batteries to design two types of battery products, namely energy type and power type, can largely solve the development cost and production cost.

[0005] To solve the above technical problems, the present invention provides a hybrid sodium-ion battery energy storage system for power grid frequency modulation, including a power-type sodium-ion battery energy storage unit (NP) for primary frequency modulation, with a capacity accounting for 20-30% of the total system capacity, and an energy-type sodium-ion battery energy storage unit (NE) for secondary frequency modulation, with a capacity accounting for 70-80% of the total system capacity; the battery energy storage system realizes the automatic switching between primary frequency modulation and secondary frequency modulation through the battery management system based on the frequency change rate dF / dt of the power grid.

[0006] In view of the characteristics of power grid frequency regulation, primary frequency regulation requires rapid charge and discharge, which demands that the battery has a high rate capability, such as 2C to 5C, or even higher. Secondary frequency regulation, on the other hand, requires a long-term continuous output, and the rate requirement may be between 0.5C and 2C. In the hybrid sodium-ion battery energy storage system, a power-type sodium-ion battery energy storage unit and an energy-type sodium-ion battery energy storage unit are set up, which are respectively applied to primary frequency regulation and secondary frequency regulation to meet the requirements of rapid response for primary frequency regulation and long-term continuous output for secondary frequency regulation.

[0007] Based on the rate of change of the power grid frequency dF / dt, the energy storage system of the present invention starts the corresponding energy storage unit through the battery management system to realize the automatic switching between primary frequency regulation and secondary frequency regulation, avoiding the obstacles to the construction and dispatching of the energy storage system caused by the cooperation between different energy storage technologies in the "flywheel + lithium battery" or "supercapacitor + lithium battery" hybrid energy storage system in power grid frequency regulation; using the same system of battery to design two battery products of energy type and power type can largely solve the problems of development cost and production cost.

[0008] Furthermore, the 10C / 1C discharge capacity retention rate of the power-type sodium-ion battery energy storage unit > 95%, the 10C discharge energy efficiency > 85%, and the 10C operating tab temperature rise < 8°C.

[0009] Furthermore, the thickness of the positive electrode of the power-type sodium-ion battery energy storage unit is 80 - 100μm, and the loading amount is 1.7 - 2.0g / cm 3 ; the thickness of the negative electrode is 90 - 110μm, and the loading amount is 1.5 - 1.8g / cm 3 .

[0010] Furthermore, the positive and negative electrode material formula of the power-type sodium-ion battery energy storage unit is active material: conductive agent: binder = (92 - 95):(3 - 5):(1 - 2).

[0011] The power-type sodium-ion battery energy storage unit of the present invention can achieve a 20C rate, and the battery system has low heat dissipation and does not require a specific cooling design.

[0012] Furthermore, the cycle life of the energy-type sodium-ion battery energy storage unit > 20000 times, and it can achieve 100% DOD operation.

[0013] Furthermore, the thickness of the positive electrode of the energy-type sodium-ion battery energy storage unit is 150 - 200μm, and the loading amount is 1.8 - 2.1g / cm 3 ; the thickness of the negative electrode is 170 - 220μm, and the loading amount is 1.6 - 1.9g / cm 3 .

[0014] Further, the positive and negative electrode material formula of the energy-type sodium-ion battery energy storage unit is active material: conductive agent: binder = (95-97):(1-3):(1-2).

[0015] Further, the positive active material of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit is selected from one or more of Na4Fe3(PO4)2(P2O7), Na4Fe 2.5 Ti 0.5 (PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7), Na3MnTi(PO4)3, where 0 < x < 3.

[0016] Further, the negative active material of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit is selected from one or more of NaTi2(PO4)3, Na3Fe2(PO4)3, Na3MnTi(PO4)3.

[0017] In the second aspect of the present invention, a grid frequency modulation method for the hybrid sodium-ion battery energy storage system described in the first aspect is provided. When dF / dt > 0.5 Hz / s, the power-type sodium-ion battery energy storage unit is started for primary frequency modulation and outputs at full power; when 0.2 Hz / s < dF / dt ≤ 0.5 Hz / s, the energy-type sodium-ion battery energy storage unit is started for secondary frequency modulation and outputs in a linear proportion.

[0018] Further, when dF / dt < 0.2 Hz / s, the thermal power unit dominates the frequency modulation.

[0019] Advantages of the present invention:

[0020] In view of the characteristics of grid frequency modulation, the present invention sets a power-type sodium-ion battery energy storage unit and an energy-type sodium-ion battery energy storage unit in the hybrid sodium-ion battery energy storage system, which are respectively applied to primary frequency modulation and secondary frequency modulation to meet the requirements of fast response for primary frequency modulation and long-term continuous output for secondary frequency modulation.

[0021] Based on the frequency change rate dF / dt of the power grid, the energy storage system of the present invention starts the corresponding energy storage unit through the battery management system to realize the automatic switching between primary frequency modulation and secondary frequency modulation, avoiding the obstacles to the construction and scheduling of the energy storage system caused by the cooperation between different energy storage technologies in the "flywheel + lithium battery" or "supercapacitor + lithium battery" hybrid energy storage system in grid frequency modulation in the prior art.

[0022] The present invention uses the same system of batteries to design two types of battery energy storage units, namely energy type and power type, which can largely solve the problems of development cost and production cost.

[0023] The power-type sodium-ion battery energy storage unit of the present invention can achieve a rate of 20C, and the battery system has low heat dissipation, does not require a specific cooling design, has a simple structure, and reduces costs. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is the rate discharge energy efficiency diagram of the power-type sodium-ion battery energy storage unit of Embodiment 1 of the present invention;

[0026] Figure 2 It is the rate discharge capacity utilization rate of the power-type sodium-ion battery energy storage unit of Embodiment 1 of the present invention;

[0027] Figure 3 It is the rate discharge tab temperature rise curve of the power-type sodium-ion battery energy storage unit of Embodiment 1 of the present invention;

[0028] Figure 4 It is the cycle test data of the energy-type sodium-ion battery energy storage unit of Embodiment 1 of the present invention;

[0029] Figure 5 It is the flow chart of the power grid frequency modulation method of the hybrid sodium-ion battery energy storage system of the present invention. Detailed Embodiments

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] This embodiment relates to a hybrid sodium-ion battery energy storage system for power grid frequency regulation, including a power-type sodium-ion battery energy storage unit for primary frequency regulation, with a capacity accounting for 20-30% of the total system capacity, and an energy-type sodium-ion battery energy storage unit for secondary frequency regulation, with a capacity accounting for 70-80% of the total system capacity; the battery energy storage system realizes automatic switching between primary frequency regulation and secondary frequency regulation based on the rate of change of the power grid frequency dF / dt through a battery management system. In this embodiment, in view of the characteristics of power grid frequency regulation, primary frequency regulation requires fast charge and discharge, and the battery is required to have a high rate capability, such as 2C to 5C, or even higher, while secondary frequency regulation requires continuous output for a long time, and the rate requirement may be between 0.5C and 2C. A power-type sodium-ion battery energy storage unit and an energy-type sodium-ion battery energy storage unit are set in the hybrid sodium-ion battery energy storage system, which are respectively applied to primary frequency regulation and secondary frequency regulation to meet the requirements of fast response for primary frequency regulation and long-time continuous output for secondary frequency regulation.

[0032] The energy storage system of the present invention realizes automatic switching between primary frequency regulation and secondary frequency regulation by starting the corresponding energy storage unit based on the rate of change of the power grid frequency dF / dt through a battery management system, avoiding the obstacles to the construction and dispatching of the energy storage system caused by the cooperation between different energy storage technologies in the "flywheel + lithium battery" or "supercapacitor + lithium battery" hybrid energy storage system in power grid frequency regulation; using the same system of batteries to design two battery products of energy type and power type can largely solve the problems of development cost and production cost.

[0033] As a preferred embodiment, the thickness of the positive electrode of the power-type sodium-ion battery energy storage unit is 80-100 μm, and the loading amount is 1.7-2.0 g / cm 3 ; the thickness of the negative electrode is 90-110 μm, and the loading amount is 1.5-1.8 g / cm 3 . The positive and negative electrode material formula of the power-type sodium-ion battery energy storage unit is active material: conductive agent: binder = (92-95):(3-5):(1-2). The 10C / 1C discharge capacity retention rate of the power-type sodium-ion battery energy storage unit > 95%, the 10C discharge energy efficiency > 85%, and the 10C operating tab temperature rise < 8°C. The power-type sodium-ion battery energy storage unit of the present invention can achieve a 20C rate, and the battery system has low heat dissipation and does not require a specific cooling design.

[0034] As a preferred embodiment, the thickness of the positive electrode of the energy-type sodium-ion battery energy storage unit is 150-200 μm, and the loading amount is 1.8-2.1 g / cm 3 ; the thickness of the negative electrode is 170-220 μm, and the loading amount is 1.6-1.9 g / cm 3The positive and negative electrode material formulations of the energy-type sodium-ion battery energy storage unit are active material: conductive agent: binder = (95-97): (1-3): (1-2). The cycle life of the energy-type sodium-ion battery energy storage unit > 20,000 times, and 100% DOD operation can be achieved.

[0035] As a preferred embodiment, the positive active materials of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit are selected from Na4Fe3(PO4)2(P2O7), Na4Fe 2.5 Ti 0.5 (PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7), Na3MnTi(PO4)3, where 0 < x < 3.

[0036] As a preferred embodiment, the negative active materials of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit are selected from one or more of NaTi2(PO4)3, Na3Fe2(PO4)3, and Na3MnTi(PO4)3.

[0037] Another embodiment provides a method for grid frequency modulation of the hybrid sodium-ion battery energy storage system described in the above embodiment. When dF / dt > 0.5 Hz / s, the power-type sodium-ion battery energy storage unit is started for primary frequency modulation and outputs at full power; when 0.2 Hz / s < dF / dt ≤ 0.5 Hz / s, the energy-type sodium-ion battery energy storage unit is started for secondary frequency modulation and outputs in a linear proportion. In addition, when dF / dt < 0.2 Hz / s, the thermal power unit dominates the frequency modulation.

[0038] Example 1

[0039] This embodiment relates to a hybrid sodium-ion battery energy storage system for grid frequency modulation. It is designed according to the capacity of the hybrid sodium-ion energy storage battery system being 100 KWh, including a power-type sodium-ion battery energy storage unit with a capacity of 25 KWh for primary frequency modulation and an energy-type sodium-ion battery energy storage unit with a capacity of 75 KWh for secondary frequency modulation.

[0040] The preparation method of the power-type sodium-ion battery energy storage unit includes the following steps:

[0041] (1) Preparation of positive and negative electrode slurries: Weigh 93.0 Kg of positive and negative electrode active materials respectively (the positive electrode active material is sodium iron pyrophosphate Na4Fe3(PO4)2(P2O7), and the negative electrode active material is sodium titanium phosphate NaTi2(PO4)3), 3.0 Kg of conductive agent conductive carbon black, 2.0 Kg of conductive agent carbon nanotube dry powder, and 2.0 Kg of binder polyvinylidene fluoride dry powder. Add 150 Kg of solvent N-methyl-2-pyrrolidone and put it into a ball mill tank to ball mill at a speed of 40 rpm for 180 min to obtain positive and negative electrode slurries respectively;

[0042] (2) Preparation of positive and negative electrode sheets: Pour the positive and negative electrode slurries into the trough of a transfer coater, control the transfer die head to coat on carbon-coated aluminum foil with a thickness of 14 μm, and dry it in an oven at 130 °C. Coat the front side first and then the back side to obtain positive and negative electrode rolls respectively; Pass the positive and negative electrode rolls through a roll press with a roll pressure of 4.0 MPa to obtain compacted positive and negative electrode rolls. The thicknesses of the positive and negative electrodes are 90 μm and 100 μm respectively, and the tap densities of the positive and negative electrodes are 1.8 g / cm 3 and 1.6 g / cm 3 ;

[0043] (3) Battery assembly: Stack the sheets in a Z-shape in the order of "positive electrode sheet, separator, negative electrode sheet, separator" to make a battery cell with a capacity of 20 Ah. After making and welding the electrode tabs, encapsulate the top and bottom edges with a pre-punched aluminum-plastic film, and put the dry battery cell into a vacuum oven with a vacuum degree of -0.095 MPa and a temperature of 120 °C for baking for 12 h to obtain a dry battery cell; Take out the dry battery cell and put it into a glove box, inject the electrolyte with a concentration of 1 mol / L, and then complete the side encapsulation to obtain a power-type sodium-ion battery energy storage unit to be formed; Among them, the electrolyte is sodium perchlorate dissolved in ethylene carbonate.

[0044] (4) System assembly: For the battery cells obtained above, after strictly screening battery cells with similar performance, form a battery cell group in series and parallel, install it in a customized module frame, lay insulating buffer materials, install monitoring and protection components, and complete the construction of a single battery module. According to the system requirements, connect the required number of modules in series and parallel and install a heat dissipation system. Subsequently, integrate the battery management system and electrical protection device to obtain a 25 KWh power-type sodium-ion battery energy storage unit

[0045] Perform a discharge performance test on this power-type sodium-ion battery energy storage unit, Figure 1 which is the rate discharge energy efficiency diagram of the power-type sodium-ion battery energy storage unit. It can be seen that the power-type sodium-ion battery energy storage unit prepared in this example has good rate discharge performance, where the 10C discharge energy efficiency > 85%, and the 20C discharge energy efficiency is still greater than 70%. Figure 2It is the rate discharge capacity utilization rate of the power-type sodium-ion battery energy storage unit. It can be seen that the 10C / 1C discharge capacity retention rate of this power-type sodium-ion battery energy storage unit > 97%. Figure 3 It is the rate discharge tab temperature rise curve of the power-type sodium-ion battery energy storage unit. It can be seen that it has excellent heat dissipation performance, and the tab temperature rise at 10C operation is as low as 6.8°C.

[0046] The preparation method of the energy-type sodium-ion battery energy storage unit includes the following steps:

[0047] (1) Preparation of the positive and negative electrode slurries: Weigh 95.0 Kg of the positive and negative electrode active materials (the positive electrode active material is sodium iron pyrophosphate, and the negative electrode active material is sodium titanium phosphate), 2.0 Kg of the conductive agent conductive carbon black, 1 Kg of the conductive agent carbon nanotube dry powder, and 2.0 Kg of the binder polyvinylidene fluoride dry powder. Add 150 Kg of the solvent N-methyl-2-pyrrolidone and put them into a ball mill tank to ball mill at a speed of 40 rpm for 180 min to obtain the positive and negative electrode slurries respectively;

[0048] (2) Preparation of the positive and negative electrode sheets: Pour the positive and negative electrode slurries into the trough of a transfer coater, control the transfer die head to coat on the carbon-coated aluminum foil with a thickness of 14 μm, and dry it in an oven at 130°C. Coat the front side first and then the back side to obtain the positive and negative electrode rolls respectively; Pass the positive and negative electrode rolls through a roll press with a roll pressure of 4.0 MPa to obtain the compacted positive and negative electrode rolls respectively. The thicknesses of the positive and negative electrodes are 160 μm and 170 μm respectively, and the compaction densities of the positive and negative electrodes are 2.0 g / cm 3 and 1.8 g / cm 3 ;

[0049] (3) Battery assembly: Stack the sheets in a Z-shaped pattern in the order of "positive electrode sheet, separator, negative electrode sheet, separator" to make an electric core with a capacity of about 50 Ah. After making and welding the tabs, encapsulate the top and bottom edges with a pre-punched aluminum-plastic film, put the dry electric core into a vacuum oven with a vacuum degree of -0.095 MPa and a temperature of 120°C to bake for 12 h to obtain the dry electric core; Take out the dry electric core and put it into a glove box, inject the electrolyte with a concentration of 1 mol / L, and then complete the side encapsulation to obtain the energy-type sodium-ion battery energy storage unit to be formed; Among them, the electrolyte is prepared by dissolving sodium perchlorate in ethylene carbonate.

[0050] (4) System assembly: Select the electric cores with similar performance from the above-obtained electric cores through strict screening, form an electric core group in series and parallel, install them in a customized module frame, lay insulating buffer materials, install monitoring and protection components, and complete the construction of a single battery module. According to the system requirements, connect the required number of modules in series and parallel and install a heat dissipation system. Subsequently, integrate the battery management system and the electrical protection device to obtain a 75 KWh energy-type sodium-ion battery energy storage unit

[0051] The energy-type sodium-ion battery energy storage unit is subjected to performance testing. Figure 4 The following are the cycle test data of the energy-type sodium-ion battery energy storage unit. It can be seen that the battery has no capacity decay after 9,000 cycles at a 1C test rate. It is expected that the cycle life can reach more than 100,000 cycles, which can meet the requirements of long-life energy storage. The charge and discharge performance of this energy-type sodium-ion battery is shown in Table 1.

[0052] Table 1

[0053]

[0054] It can be seen that the energy-type sodium-ion battery energy storage unit of this embodiment can stably achieve energy output in a wide rate range of 0.5C - 4C. Under the operating condition of 100% DOD, its energy efficiency always remains above 75%. This excellent performance provides an extremely high-quality and reliable energy storage solution for the power grid frequency modulation scenario, strongly supporting the efficient and stable operation of the power grid system.

[0055] The hybrid sodium-ion battery energy storage system prepared in this embodiment is applied to power grid frequency modulation. Referring to Figure 5 as shown, when dF / dt > 0.5Hz / s, the power-type sodium-ion battery energy storage unit is started for primary frequency modulation and outputs at full power; when 0.2Hz / s < dF / dt ≤ 0.5Hz / s, the energy-type sodium-ion battery energy storage unit is started for secondary frequency modulation and outputs in a linear proportion.

[0056] In summary, in view of the characteristics of power grid frequency modulation, the present invention sets a power-type sodium-ion battery energy storage unit and an energy-type sodium-ion battery energy storage unit in the hybrid sodium-ion battery energy storage system, which are respectively applied to primary frequency modulation and secondary frequency modulation to meet the requirements of fast response for primary frequency modulation and long-time continuous output for secondary frequency modulation; based on the frequency change rate dF / dt of the power grid, the corresponding energy storage unit is started through the battery management system to realize the automatic switching between primary frequency modulation and secondary frequency modulation, avoiding the obstacles caused by the cooperation between different energy storage technologies in the "flywheel + lithium battery" or "supercapacitor + lithium battery" hybrid energy storage system in power grid frequency modulation to the construction and dispatching of the energy storage system; using the same system of battery to design two types of battery energy storage units, namely energy type and power type, can largely solve the problems of development cost and production cost; the power-type sodium-ion battery energy storage unit can achieve a 20C rate, and the battery system has low heat dissipation, does not require a specific cooling design, has a simple structure, and reduces costs.

[0057] The present invention has been described in detail in connection with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A hybrid sodium-ion battery energy storage system for power grid frequency regulation, characterized in that, It includes a power-type sodium-ion battery energy storage unit for primary frequency regulation, with a capacity accounting for 20 - 30% of the total system capacity, and an energy-type sodium-ion battery energy storage unit for secondary frequency regulation, with a capacity accounting for 70 - 80% of the total system capacity; the battery energy storage system realizes automatic switching between primary frequency regulation and secondary frequency regulation through a battery management system based on the rate of change of the grid frequency dF / dt.

2. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, characterized in that, The 10C / 1C discharge capacity retention rate of the power-type sodium-ion battery energy storage unit > 95%, the 10C discharge energy efficiency > 85%, and the 10C operating tab temperature rise < 8°C.

3. The hybrid sodium-ion battery energy storage system for power grid frequency regulation according to claim 1, characterized in that, The thickness of the positive electrode of the power-type sodium-ion battery energy storage unit is 80-100 μm, and the loading amount is 1.7-2.0 g / cm 3 ; the thickness of the negative electrode is 90-110 μm, and the loading amount is 1.5-1.8 g / cm 3 .

4. The hybrid sodium-ion battery energy storage system for power grid frequency regulation according to claim 1, characterized in that The positive and negative electrode material formula of the power-type sodium-ion battery energy storage unit is active material: conductive agent: binder = (92 - 95):(3 - 5):(1 - 2).

5. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, characterized in that The cycle life of the energy-type sodium-ion battery energy storage unit > 20,000 times, and it can achieve 100% DOD operation.

6. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, characterized in that The thickness of the positive electrode of the energy-type sodium-ion battery energy storage unit is 150-200 μm, and the loading amount is 1.8-2.1 g / cm 3 ; the thickness of the negative electrode is 170-220 μm, and the loading amount is 1.6-1.9 g / cm 3 .

7. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, characterized in that The positive and negative electrode material formula of the energy-type sodium-ion battery energy storage unit is active material: conductive agent: binder = (95 - 97):(1 - 3):(1 - 2).

8. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, wherein, The positive electrode active materials of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit are selected from Na4Fe3(PO4)2(P2O7), Na4Fe 2.5 Ti 0.5 (PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7), Na3MnTi(PO4)3, or one or more of them, where 0 < x < 3.

9. The hybrid sodium-ion battery energy storage system for power grid frequency modulation according to claim 1, characterized in that, The negative electrode active materials of the power-type sodium-ion battery energy storage unit and the energy-type sodium-ion battery energy storage unit are selected from one or more of NaTi2(PO4)3, Na3Fe2(PO4)3, and Na3MnTi(PO4)3.

10. A method for grid frequency regulation of the hybrid sodium-ion battery energy storage system according to any one of claims 1-9, characterized in that, When dF / dt > 0.5Hz / s, the power-type sodium-ion battery energy storage unit is started for primary frequency regulation and outputs at full power; when 0.2Hz / s < dF / dt ≤ 0.5Hz / s, the energy-type sodium-ion battery energy storage unit is started for secondary frequency regulation and outputs in a linear proportion.

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