Hybrid energy storage system and operating method applied to stand-alone photovoltaic microgrid

Abstract

The present invention belongs to the technical field of energy storage. Disclosed are a hybrid energy storage system and operating method applied to a stand-alone photovoltaic microgrid, which system and method can give full play to the advantages of the large-power charging and discharging of a supercapacitor, the rapid high-rate charging and discharging of a sodium-ion battery, and the long cycle performance, high safety and relatively large depth of discharging of an iron-chromium flow battery. The supercapacitor, the sodium-ion battery and the iron-chromium flow battery complement each other's advantages, improving the safety and the charging and discharging performance of a hybrid energy storage system, thus constructing the hybrid energy storage system. The hybrid energy storage system and operating method applied to a stand-alone photovoltaic microgrid involve a photovoltaic power generation module, a sodium-ion battery module, a supercapacitor module, an iron-chromium flow battery module, a DC-DC module, a DC-AC module, an electric load module and a hybrid battery management system, wherein a sodium-ion battery, a supercapacitor and an iron-chromium flow battery are each connected in parallel to the hybrid battery management system by means of the DC-DC module, and the photovoltaic power generation module is connected to the electric load module by means of the DC-DC module, a direct-current bus, the DC-AC module and an alternating-current bus.

Description

A hybrid energy storage system applied to an independent photovoltaic micro-grid and a working method thereof TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and particularly relates to a hybrid energy storage system applied to an independent photovoltaic micro-grid, and also particularly relates to a working method applied to an independent photovoltaic micro-grid. BACKGROUND

[0002] The independent photovoltaic micro-grid is not dependent on a large power grid, and can not only provide power for remote areas which cannot be considered by the large power grid, but also continue to supply power for loads when the large power grid fails, thereby reducing economic losses. However, the independent photovoltaic power generation system is greatly affected by environmental factors, resulting in instability and low efficiency of the micro-grid. In order to ensure the power quality and stable operation of the independent photovoltaic micro-grid, energy storage devices need to be configured in the independent photovoltaic micro-grid to balance the random fluctuations of renewable energy power.

[0003] At present, the energy storage devices applied to the micro-grid system mainly include lead-acid batteries, sodium ion batteries, iron-chromium flow batteries, and super capacitors. The lead-acid battery technology is mature and cheap, but the short cycle life and environmental pollution limit its subsequent development. The sodium ion battery has no over-discharge feature, can be discharged to zero volts, has an energy density greater than 100Wh / kg, is comparable to the lithium iron phosphate battery, has obvious cost advantages, and can be applied to large-scale energy storage. However, most sodium ion batteries contain liquid electrolytes, which have a risk of flammability. The iron-chromium flow battery is the latest liquid flow battery energy storage device, has flexible power and capacity configuration, long battery cycle life, low cost, low self-discharge rate, safety and stability, and deep discharge capability, and has high application value in medium and large-scale energy storage power stations and long-time energy storage fields. The main disadvantage of the iron-chromium flow battery is the low discharge rate.

[0004] The electrochemical battery has high energy density and can be used as an energy-type energy storage device. However, the electrochemical battery has a limited number of charge and discharge cycles. If the electrochemical battery is used as a high-frequency power section energy storage unit, the service life of the electrochemical battery will be reduced. In addition, the response time and output power characteristics of the electrochemical battery also cause it difficult to completely suppress the minute-level high-frequency component. Compared with the electrochemical battery, the electromagnetic energy storage device has high power density and long service life, and is a power-type energy storage device with excellent performance. The super capacitor is a typical electromagnetic energy storage device, and has a power density of more than 15kW / kg. The super capacitor applied to the micro-grid can effectively alleviate the impact of power mutation on the micro-grid and improve the dynamic response capability of the system.

[0005] In summary, combined with the characteristics of each energy storage device, a hybrid energy storage system is constructed to give full play to the advantages of energy storage devices, which will be conducive to the economic and stable operation of independent photovoltaic micro-grid, and therefore a hybrid energy storage system and its working method applied to independent photovoltaic micro-grid are needed to assist in solving this problem. SUMMARY

[0006] (1) Technical problems to be solved

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a hybrid energy storage system and its working method applied to independent photovoltaic micro-grid, which can give full play to the advantages of supercapacitors, sodium ion batteries and iron-chromium flow batteries, such as large power charge and discharge, fast and large rate charge and discharge, long cycle performance, high safety and large discharge depth, complement each other among the three, improve the safety and charge and discharge performance of the hybrid energy storage system, combine sodium ion batteries, iron-chromium flow batteries and supercapacitors to construct a hybrid energy storage system, which can well suppress the minute and hour components in the daily micro-grid, and improve the safety and stability of the energy storage system.

[0008] (2) Technical solutions

[0009] In order to solve the above technical problems, the present application provides a hybrid energy storage system applied to independent photovoltaic micro-grid, which comprises a photovoltaic power generation module, a sodium ion battery module, a supercapacitor module, an iron-chromium flow battery module, a DC-DC module, a DC-AC module, a power load module and a hybrid battery management system.

[0010] The sodium ion battery, supercapacitor and iron-chromium flow battery are connected in parallel to the hybrid battery management system through the DC-DC module, and the hybrid battery management system is connected with a DC bus; the photovoltaic power generation module is connected to the power load module through the DC-DC module, the DC bus, the DC-AC module and an AC bus.

[0011] As a further preferred scheme, each DC / DC module in the hybrid energy storage system is connected with a BMS module, and a plurality of BMS modules are connected to the hybrid battery management system. By connecting each DC-DC module with a BMS module, the data of the supercapacitor, iron-chromium flow battery and sodium ion battery can be collected in real time, and the hybrid battery management module can timely allocate and manage the entire system according to these data, thereby improving the comprehensive efficiency and stability of the system.

[0012] As a further preferred solution, the DC / DC module in the hybrid energy storage system is a bidirectional DC / DC module, and several DC / DC modules are connected with fast cut-off switches, which can be individually withdrawn in case of failure without affecting the operation of other battery modules.

[0013] As a further preferred solution, the sodium-ion battery module is composed of several sodium-ion battery cells in series or in parallel, and the sodium-ion battery cell is one or more of vanadate sodium-ion battery, lithium iron phosphate sodium-ion battery, sulfide sodium-ion battery, oxide sodium-ion battery, and Prussian blue sodium-ion battery, preferably Prussian blue sodium-ion battery.

[0014] As a further preferred solution, the iron-chromium flow battery module is composed of several iron-chromium flow battery cells in series or in parallel, and the supercapacitor module is composed of several supercapacitor cells in series or in parallel. The supercapacitor is a power-type energy storage device, which can suppress the high-frequency power fluctuation of the system. The iron-chromium flow battery has both power-type and energy-type energy storage functions, which can suppress the medium-frequency power fluctuation. The sodium-ion battery is an energy-type energy storage device, which can suppress the low-frequency power fluctuation.

[0015] As a further preferred solution, the power of the hybrid energy storage system is calculated as follows: HESS = P load - P PV (1) P HESS = P FC + P BAT + P SC (2)

[0016] Where: P HESS is the output / input power of the hybrid energy storage system; P load is the power of the load power system; P PV is the output power of the photovoltaic power generation system; P FC is the charging and discharging power of the iron-chromium flow battery; P BAT is the charging and discharging power of the sodium-ion battery; and P SC is the charging and discharging power of the supercapacitor.

[0017] As a further preferred solution, the power P HESS of the hybrid energy storage system is filtered by a second-order low-pass filter, and the power PSC of the supercapacitor energy storage device is calculated as follows:

[0018] The power PFC of the iron-chromium flow battery energy storage device is calculated as follows:

[0019] Wherein: T1 is a filter time constant for distinguishing low-frequency components in a second-order low-pass filter, T2 is a filter time constant for distinguishing high-frequency components in a second-order low-pass filter, and s is a complex variable.

[0020] As a further preferred scheme, the super capacitor is a power-type energy storage device, which smoothes high-frequency power fluctuations of the system; the iron-chromium flow battery has both power-type and energy-type energy storage functions, which smoothes medium-frequency power fluctuations; and the sodium-ion battery is an energy-type energy storage device, which smoothes low-frequency power fluctuations, and the demarcation frequency between the low frequency and the medium frequency is 0.0001 Hz to 0.0004 Hz, and the demarcation frequency between the high frequency and the medium frequency is 0.003 Hz to 0.005 Hz.

[0021] As a further preferred scheme, the sodium-ion battery smoothes power fluctuations below (1 / T1) Hz, the iron-chromium flow battery smoothes power fluctuations of (1 / T1 to 1 / T2) Hz, and the super capacitor smoothes power fluctuations above (1 / T2) Hz.

[0022] A working method applied to an independent photovoltaic micro-grid, comprising the following steps:

[0023] S1, a hybrid battery management system acquires running parameters of a sodium-ion battery module, an iron-chromium flow battery module, and a super capacitor module in real time;

[0024] S2, the hybrid battery management system analyzes residual capacities of sodium-ion batteries, iron-chromium flow batteries, and super capacitors in the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module according to voltages and currents of the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module;

[0025] S3, the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module are respectively matched through corresponding DC-DC modules, and a power load is discharged through a DC-AC module;

[0026] S4, high-frequency power instructions are completed by the super capacitor module first, medium-frequency power instructions are completed by the iron-chromium flow battery module first, and low-frequency power instructions are completed by the sodium-ion battery module first;

[0027] S5, when a single battery module cannot complete a charge-discharge instruction, the super capacitor module, the sodium-ion battery module, and the iron-chromium flow battery module are cooperatively used to complete the charge-discharge instruction.

[0028] (3) Beneficial effects

[0029] Compared with the prior art, the beneficial effects of the present application are as follows:

[0030] The sodium ion battery will reduce the service life due to frequent charging, and when overcharging, overdischarging or poor consistency occurs, combustion or even explosion is prone to occur, while the iron-chromium flow battery has a charge-discharge depth of 100%, and can prepare a large-capacity battery, and has low comprehensive cost, wide operation temperature of-20 to 70 DEG C, long cycle life (> 10000 times), high safety, low battery cost per unit capacity, low self-discharge, and the super capacitor as a power type energy storage has high reliability in different environments, short reaction time, low operation cost, and can suppress the power component of the minute level, and the combination of the sodium ion battery, the iron-chromium flow battery and the super capacitor can well suppress the minute component and the hour component in the daily microgrid, and improve the operation safety and stability of the energy storage system.

[0031] The super capacitor has high power characteristics, the flow battery has long cycle life, the sodium ion battery has rate performance advantage, the cycle service life of the energy storage system is prolonged, the hybrid energy storage system controls the charge and discharge of the super capacitor, the iron-chromium flow battery and the sodium ion battery through the hybrid battery management module and the respective independent DC-DC module, can improve the operation efficiency of the system and is convenient to expand, and has the characteristics of easy maintenance;

[0032] The application can fully exert the advantages of the super capacitor, the sodium ion battery and the iron-chromium flow battery, such as large power charge and discharge, fast and large rate charge and discharge, long cycle performance, high safety and large discharge depth, the advantages of the three are complementary, the safety and charge and discharge performance of the hybrid energy storage system are improved, the super capacitor is an electromagnetic energy storage device and can be charged and discharged at high power, the sodium ion battery can quickly respond to instructions and has medium rate discharge performance, but is not suitable for frequent charge and discharge, and the capacity of the iron-chromium flow battery is flexible and has long cycle life, therefore, the high-frequency power instruction is preferentially completed by the super capacitor module, the medium-frequency power instruction is preferentially completed by the iron-chromium flow battery module, and the low-frequency power instruction is preferentially completed by the sodium ion battery module. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0034] Fig. 1 is a system block diagram of the application;

[0035] Fig. 2 is a system connection relationship diagram of the application;

[0036] Fig. 3 is a method flowchart of the application. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0038] The specific embodiment is a hybrid energy storage system applied to an independent photovoltaic micro-grid and a working method thereof, as shown in FIG. 1 and FIG. 2. The hybrid energy storage system applied to the independent photovoltaic micro-grid comprises a photovoltaic power generation module, a sodium ion battery module, a super capacitor module, a iron-chromium flow battery module, a DC-DC module, a DC-AC module, a power consumption load module and a hybrid battery management system.

[0039] The sodium ion battery, the super capacitor and the iron-chromium flow battery are connected in parallel to the hybrid battery management system through the DC-DC module. The unbalanced power distribution method of the sodium ion battery-iron-chromium flow battery-super capacitor hybrid energy storage system is a Hilbert-Huang transform power distribution method, a wavelet packet decomposition method, a second-order low-pass filtering method and the like, and the second-order low-pass filtering method is preferably selected. The hybrid battery management system is connected with a direct current bus. The photovoltaic power generation module is connected to the power consumption load module through the DC-DC module, the direct current bus, the DC-AC module and an alternating current bus.

[0040] As a further embodiment, each DC / DC module in the hybrid energy storage system is connected with a BMS module, and a plurality of BMS modules are connected to the hybrid battery management system. By connecting each DC-DC module with a BMS module, the data of the super capacitor, the iron-chromium flow battery and the sodium ion battery can be collected in real time. The hybrid battery management module can timely allocate and manage the entire system according to these data, thereby improving the comprehensive efficiency and stability of the system.

[0041] Specifically, the DC / DC module in the hybrid energy storage system is a bidirectional DC / DC module, and a plurality of DC / DC modules are connected with quick cut-off switches, which can be individually withdrawn in case of failure without affecting the operation of other battery modules.

[0042] Specifically, the sodium ion battery module is composed of a plurality of sodium ion battery monomers connected in series or in parallel. The sodium ion battery monomer is one or more of a vanadate sodium ion battery, a lithium sodium phosphate ion battery, a sulfide sodium ion battery, an oxide sodium ion battery and a Prussian blue sodium ion battery.

[0043] As a further embodiment, the iron-chromium flow battery module is composed of a plurality of iron-chromium flow battery cells in series or parallel, the supercapacitor module is composed of a plurality of supercapacitor cells in series or parallel, the supercapacitor is a power type energy storage device, and the power fluctuation of the system at high frequency is smoothed, the iron-chromium flow battery has both power type and energy type energy storage functions, and the power fluctuation at medium frequency is smoothed; the sodium ion battery is an energy type energy storage device, and the power fluctuation at low frequency is smoothed. Taking an independent photovoltaic microgrid with a installed capacity of 200 kW, an average power of 42.4 kW, and a typical daily power generation of 1021 kW·h as an example, the electrical load is a general industrial high-power pulsating load. A 40kW / 80kWh supercapacitor energy storage system, a 50kW / 400kWh sodium ion battery energy storage system, and a 60kW / 400kWh iron-chromium flow battery energy storage system are configured. Among them, the sodium ion battery is a Prussian blue sodium ion battery. In the supercapacitor system, every 10kWh is a module connected in series with a DC-DC module; in the sodium ion battery system, every 50kWh is a module connected in series with a DC-DC module; in the iron-chromium flow battery system, every 50kWh is a module connected in series with a DC-DC module. After being boosted by the DC-DC module, the supercapacitor system, the sodium ion battery system, and the iron-chromium flow battery system are uniformly output, connected with the hybrid battery management system, and finally converted to AC by the DC-AC module and connected to the electrical load.

[0044] Specifically, the power of the hybrid energy storage system is calculated as follows: HESS load PV (1) P HESS FC +P BAT +P SC (2)

[0045] Among them: P HESS is the output / input power of the hybrid energy storage system; P load is the power of the load power system; P PV is the output power of the photovoltaic power generation system; P FC is the charging and discharging power of the iron-chromium flow battery; P BAT is the charging and discharging power of the sodium ion battery; and P SC is the charging and discharging power of the supercapacitor.

[0046] Specifically, the power P HESS of the hybrid energy storage system is filtered by a second-order low-pass filter, and the power PSC of the supercapacitor energy storage device is calculated as follows:

[0047] ​​​The power PFC of the iron-chromium flow battery energy storage device is calculated as follows:

[0048] Wherein: T1 is a filter time constant distinguishing low-frequency components in a second-order low-pass filter, T2 is a filter time constant distinguishing high-frequency components in a second-order low-pass filter, and s is a complex variable.

[0049] Specifically, the super capacitor is a power-type energy storage device, which smoothes high-frequency power fluctuations of the system; the iron-chromium flow battery has both power-type and energy-type energy storage functions, which smoothes medium-frequency power fluctuations; the sodium-ion battery is an energy-type energy storage device, which smoothes low-frequency power fluctuations,

[0050] Specifically, the sodium-ion battery smoothes power fluctuations below (1 / T1) Hz, the iron-chromium flow battery smoothes power fluctuations between (1 / T1 and 1 / T2) Hz, and the super capacitor smoothes power fluctuations above (1 / T2) Hz.

[0051] Referring to FIG. 3, a working method applied to an independent photovoltaic micro-grid includes the following steps:

[0052] S1, the hybrid battery management system obtains the operating parameters of the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module in real time;

[0053] S2, the hybrid battery management system analyzes the residual capacity of the sodium-ion battery, the iron-chromium flow battery, and the super capacitor in the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module according to the voltage and current of the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module;

[0054] S3, the sodium-ion battery module, the iron-chromium flow battery module, and the super capacitor module are respectively matched through the corresponding DC-DC modules, and the DC-AC module is used to discharge the power load;

[0055] S4, high-frequency power instructions are completed by the super capacitor module first, medium-frequency power instructions are completed by the iron-chromium flow battery module first, and low-frequency power instructions are completed by the sodium-ion battery module first.

[0056] S5, when a single battery module cannot complete the charge and discharge instructions, the super capacitor module, the sodium-ion battery module, and the iron-chromium flow battery module are used to complete the instructions cooperatively.

[0057] Generally, the power fluctuation frequency greater than 0.005 Hz is high frequency power, the power fluctuation frequency greater than 0.0001 Hz to 0.005 Hz is medium frequency power, and the power fluctuation frequency less than 0.0001 Hz is low frequency power. For example, when the unbalanced power fluctuation frequency of the hybrid energy storage system of the independent photovoltaic micro-grid is 5 Hz, the hybrid battery management system instructs the super capacitor with high power to charge and discharge; when the unbalanced power fluctuation frequency of the hybrid energy storage system is 0.00001 Hz, the hybrid battery management system instructs the sodium ion battery with high capacity to charge and discharge; when the unbalanced power fluctuation frequency of the hybrid energy storage system is 0.001 Hz, the hybrid battery management system instructs the iron-chromium flow battery with long cycle life and large capacity to charge and discharge; when the unbalanced power fluctuation frequency of the hybrid energy storage system is 0.003 Hz and the iron-chromium flow battery cannot meet the charge and discharge requirements, the hybrid battery management system instructs the iron-chromium flow battery and the sodium ion battery to cooperatively charge and discharge.

[0058] The data of the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module are transmitted to the hybrid battery management module in real time, the hybrid battery management module independently controls the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module in real time, and the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module do not affect each other, which is helpful for the management and scheduling of the management system. The hybrid battery management module can perform basic information monitoring, power detection, system fault detection and maintenance, internal and external electric strategy control and data communication on the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module. The sodium ion battery module, the iron-chromium flow battery module and the super capacitor module are modularly managed, can be individually withdrawn when a fault occurs, do not affect the operation of other energy storage modules, and can be directly expanded to access the sodium ion battery module, the iron-chromium flow battery module or the super capacitor module.

[0059] All the technical features in the embodiment can be freely combined according to actual needs.

[0060] Finally, it should be noted that: the above only describes the preferred embodiments of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A hybrid energy storage system applied to an independent photovoltaic micro-grid, characterized in that: The mixed energy storage system comprises a photovoltaic power generation module, a sodium ion battery module, a super capacitor module, a iron-chromium flow battery module, a DC-DC module, a DC-AC module, a power load module and a hybrid battery management system. The sodium ion battery, the super capacitor and the iron-chromium flow battery are connected in parallel to the hybrid battery management system through the DC-DC module, and the hybrid battery management system is connected with a direct current bus; the photovoltaic power generation module is connected to the power load module through the DC-DC module, the direct current bus and the DC-AC module.

2. The hybrid energy storage system of claim 1, applied to an independent photovoltaic micro-grid, characterized in that: Each DC / DC module in the mixed energy storage system is connected with a BMS module, and a plurality of BMS modules are connected to the hybrid battery management system.

3. The hybrid energy storage system of claim 2, applied to an independent photovoltaic microgrid, characterized in that: The DC / DC module in the mixed energy storage system is a bidirectional DC / DC module, and a plurality of DC / DC modules are connected with a quick cut-off switch.

4. The hybrid energy storage system of claim 1, applied to an independent photovoltaic micro-grid, characterized in that: The sodium ion battery module is composed of a plurality of sodium ion battery monomers connected in series or in parallel, and the sodium ion battery monomer is one or more of a vanadate sodium ion battery, a lithium iron phosphate sodium ion battery, a sulfide sodium ion battery, an oxide sodium ion battery and a prussian blue sodium ion battery.

5. The hybrid energy storage system of claim 1, applied to an independent photovoltaic micro-grid, characterized in that: The iron-chromium flow battery module is composed of a plurality of iron-chromium flow battery monomers connected in series or in parallel, and the super capacitor module is composed of a plurality of super capacitor monomers connected in series or in parallel.

6. The hybrid energy storage system of claim 1, applied to an independent photovoltaic micro-grid, characterized in that: The power calculation of the hybrid energy storage system is as follows: P HESS = P load - P PV (1) P HESS = P FC + P BAT + P SC (2) Wherein: P HESS is the output / input power of the hybrid energy storage system; P load is the power of the load power system; P PV is the output power of the photovoltaic power generation system; P FC is the charging and discharging power of the iron-chromium flow battery; P BAT is the charging and discharging power of the sodium ion battery; P SC is the charging and discharging power of the super capacitor.

7. The hybrid energy storage system of claim 1, applied to an independent photovoltaic micro-grid, characterized in that: The power P of the hybrid energy storage system HESS The power PSC of the supercapacitor energy storage device is calculated after a second order low pass filter as follows: The power PFC of the iron-chromium flow battery energy storage device is calculated as follows: Wherein: T1 is a filter time constant for distinguishing low-frequency components in a second-order low-pass filter, T2 is a filter time constant for distinguishing high-frequency components in a second-order low-pass filter, and s is a complex variable. 8.The hybrid energy storage system applied to an independent photovoltaic micro-grid according to claim 1, characterized in that: The super capacitor is a power-type energy storage device, which can suppress high-frequency power fluctuations; the iron-chromium flow battery has both power-type and energy-type energy storage functions, which can suppress medium-frequency power fluctuations; and the sodium ion battery is an energy-type energy storage device, which can suppress low-frequency power fluctuations. The dividing frequency between low frequency and medium frequency is 0.0001 Hz to 0.0004 Hz, and the dividing frequency between high frequency and medium frequency is 0.003 Hz to 0.005 Hz. 9.The hybrid energy storage system applied to an independent photovoltaic micro-grid according to claim 1, characterized in that: The sodium ion battery suppresses power fluctuations below (1 / T1) Hz, the iron-chromium flow battery suppresses power fluctuations between (1 / T1 and 1 / T2) Hz, and the super capacitor suppresses power fluctuations above (1 / T2) Hz.

10. A working method applied to an independent photovoltaic micro-grid, applied to a hybrid energy storage system applied to an independent photovoltaic micro-grid according to any one of claims 1-9, characterized in that, The method comprises the following steps: S1, the hybrid battery management system acquires the operating parameters of the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module in real time; S2, the hybrid battery management system analyzes the residual capacity of the sodium ion battery, the iron-chromium flow battery and the super capacitor in the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module according to the voltage and current of the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module; S3, the sodium ion battery module, the iron-chromium flow battery module and the super capacitor module are respectively adjusted through the corresponding DC-DC module, and the power load is discharged through the DC-AC module; S4, high-frequency power instructions are preferentially completed by the super capacitor module, medium-frequency power instructions are preferentially completed by the iron-chromium flow battery module, and low-frequency power instructions are preferentially completed by the sodium ion battery module. S5, when a single battery module cannot complete the charge and discharge instruction, the super capacitor module, the sodium ion battery module and the iron-chromium flow battery module cooperate to complete it.

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