A two-level energy management method for energy storage system

Abstract

The present invention belongs to the field of energy storage technology, and specifically relates to a two-level energy management method for an energy storage system, comprising: pre-constructing a degradation model of an electric / hydrogen energy storage device and establishing a first objective function based thereon; pre-constructing an equivalent hydrogen consumption model and a hydrogen consumption model of the electric / hydrogen energy storage device and establishing a second objective function based thereon; obtaining the net load electric power at the current moment; analyzing the first objective function with the goal of minimizing the degree of degradation of the system to obtain a reference power of the electric / hydrogen energy storage device; minimizing the equivalent hydrogen consumption of the system, and analyzing the second objective function based on the reference power of the electric / hydrogen energy storage device to obtain the input / output power of the electric / hydrogen energy storage device; and adjusting the power distribution between the electric / hydrogen energy storage devices according to the corresponding input / output power. The present invention can not only reduce the degree of degradation of the energy storage system, but also reduce its equivalent hydrogen consumption, which is beneficial to the sustainable operation of the energy storage system.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and in particular relates to a two-level energy management method for an energy storage system. Background Art

[0002] With the growing development of renewable energy, energy storage has become a vital component of power systems. Furthermore, as one of the most promising solutions for adapting to the intermittent and uncertain nature of renewable energy, energy storage is widely used to improve system stability and economic efficiency. Electrical energy storage is suitable for short-term (i.e., hours to days) and small- to medium-sized energy storage applications. Supercapacitors and batteries are commonly used as short-term energy storage devices. Supercapacitors primarily include double-layer capacitors, lithium-ion capacitors, and sodium-ion capacitors, while batteries primarily include lithium-ion batteries, sodium-ion batteries, lithium metal batteries, semi-solid-state batteries, and solid-state batteries. Energy storage devices such as batteries and supercapacitors offer significant advantages in power density. For long-term (i.e., weekly, monthly, and seasonal) and large-scale applications, hydrogen energy storage technology may be a better choice. Hydrogen energy storage technology typically includes devices such as electrolyzers, fuel cells, and hydrogen storage tanks, used to convert electrical energy into hydrogen energy for storage and hydrogen energy for utilization. Hydrogen energy storage offers significant advantages in energy density. Considering the differences between electric energy storage and hydrogen energy storage technologies in physical properties such as energy density, power density, cycle life and energy efficiency, hybrid energy storage systems combining the two technologies are under research.

[0003] Therefore, to fully leverage the complementary nature of electric and hydrogen energy storage technologies, it is imperative to design appropriate energy management strategies to ensure stable and efficient operation of energy storage systems. While research on equivalent hydrogen consumption has made significant progress in energy storage system energy management strategies, the energy management process also requires consideration of the coordinated optimization of energy storage device degradation, which is crucial to the long-term economic viability of the system. Designing energy management strategies that optimize equivalent hydrogen consumption presents a significant challenge. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to propose an energy management framework to minimize the degradation degree and equivalent hydrogen consumption of the energy storage system in an island microgrid.

[0005] To achieve the above-mentioned and other related purposes, the present invention provides an energy management method for an energy storage system, comprising: the energy storage system is composed of an electric energy storage device and a hydrogen energy storage device; wherein the electric energy storage device includes a supercapacitor and / or a battery; the hydrogen energy storage device includes at least an electrolyzer, a fuel cell and a hydrogen storage tank; the two-level energy management method comprises: pre-constructing degradation models of the hydrogen energy storage device and the electric energy storage device; based on the power balance of the energy storage system, establishing a first objective function according to the degradation models of the hydrogen energy storage device and the electric energy storage device; pre-constructing a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device; based on the power balance of the energy storage system, establishing a first objective function according to the degradation models of the hydrogen energy storage device and the electric energy storage device; The equivalent hydrogen consumption model of the electric energy storage device and the second objective function of the energy storage system with respect to the preset weight between the degree of degradation and the equivalent hydrogen consumption are established; the net load electric power of the energy storage system at the current moment is obtained; the first objective function is parsed with the goal of minimizing the degree of degradation of the energy storage system, and the net load electric power is substituted into the first objective function to calculate the reference power of the hydrogen energy storage device and the electric energy storage device; the equivalent hydrogen consumption of the energy storage system is minimized, and the second objective function is parsed based on the reference power of the hydrogen energy storage device and the electric energy storage device to calculate the input / output power of the hydrogen energy storage device and the electric energy storage device; and the power distribution between the hydrogen energy storage device and the electric energy storage device is adjusted according to the corresponding input / output power.

[0006] According to a specific embodiment of the present invention, the step of pre-constructing degradation models of the hydrogen energy storage device and the electric energy storage device includes: constructing a characterization function of the voltage drop of the fuel cell based on the voltage drop caused by high-power operation and the voltage drop caused by power transient changes, as the degradation model corresponding to the fuel cell; constructing a characterization function of the voltage drop of the electrolyzer based on the voltage drop caused by operation and the voltage drop caused by power transient changes, as the degradation model corresponding to the electrolyzer; and constructing a characterization function of the health status of the electric energy storage device based on the number of cycles used, as the degradation model corresponding to the electric energy storage device.

[0007] According to a specific embodiment of the present invention, the formula for the characterization function of the fuel cell voltage drop is as follows:

[0008] Total voltage drop: D fc (t) = D fchigh (t)+D fcshift (t),

[0009] Regarding the voltage drop caused by high power operation:

[0010] Regarding the voltage drop caused by transient power changes: D fcshift (t) = αfcshift |P fc (t)-P fc (t-Δt)|,

[0011] The formula for the characterization function of the electrolytic cell voltage drop is as follows:

[0012] Total voltage drop: D el (t) = D elop (t)+D elshift (t),

[0013] Regarding the voltage drop caused by operation: D elop (t) = α elop y el (t)Δt,

[0014] Regarding the voltage drop caused by transient power changes: D elshift (t) = α elshift |P el (t)-P el (t-Δt)|,

[0015] The formula for the characterization function of the health status of the electric energy storage device is as follows:

[0016]

[0017] Among them, D fc (t) represents the voltage drop of the fuel cell at the current moment, D fchigh (t) represents the voltage drop of the fuel cell caused by high power operation at the current moment, D fcshift (t) represents the voltage drop of the fuel cell caused by the transient change of power at the current moment, α fchigh , α fchigh is the correlation coefficient of the fuel cell voltage degradation, A logical variable indicating whether the current operating power of the fuel cell is in the high power range. If so, 1, if otherwise is 0, P fc (t) represents the output power of the fuel cell at the current moment; D el (t) represents the voltage drop of the electrolytic cell at the current moment, D elop (t) represents the voltage drop of the electrolytic cell caused by operation at the current moment, D elshift (t) represents the voltage drop of the electrolytic cell caused by the transient change of power at the current moment, α elop , α elop is the correlation coefficient of the electrolytic cell voltage degradation, y el A logical variable indicating the start / stop state of the electrolytic cell. If it is started, y el If it is 1, then yel is 0, P el (t) represents the input power of the electrolytic cell at the current moment; d soh (t) represents the change of the health status of the electric energy storage device, SOH(t) represents the health status of the electric energy storage device at the current moment, P bt (t) represents the input / output power of the electric energy storage device at the current moment, Δt represents the time interval between the previous moment and the current moment, and E bt Represents the capacity of the electrical energy storage device, N C Indicates the number of cycles before the electrical energy storage device reaches the end of its service life.

[0018] According to a specific embodiment of the present invention, the formula of the first objective function is as follows:

[0019]

[0020] Among them, J deg (t) represents the first objective function, C fcin represents the purchase cost of the fuel cell, C elin represents the purchase cost of the electrolytic cell, C btin represents the purchase cost of the electric energy storage device, D fc (t) represents the degradation model of the fuel cell, v fceol Denotes the maximum voltage drop of the fuel cell before reaching the end of its service life, D el (t) represents the degradation model of the electrolytic cell, v eleol represents the maximum voltage drop of the electrolytic cell before reaching the end of its service life, d soh (t) represents the degradation model of the electric energy storage device.

[0021] According to a specific embodiment of the present invention, the steps of pre-constructing the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device include: constructing the hydrogen consumption model of the hydrogen energy storage device according to the hydrogen consumption function of the fuel cell and the hydrogen production function of the electrolyzer; constructing the corresponding equivalent hydrogen consumption model according to the electric power input / output of the electric energy storage device; wherein, the hydrogen consumption model of the hydrogen energy storage device is constrained according to the hydrogen state of charge of the hydrogen storage tank, and the equivalent hydrogen consumption model of the electric energy storage device is constrained according to the state of charge of the electric energy storage device, so as to maintain the stability of the hydrogen state of charge of the hydrogen energy storage device and the state of charge of the electric energy storage device.

[0022] According to a specific embodiment of the present invention, the formula of the fuel cell hydrogen consumption function is as follows:

[0023]

[0024] The formula of the electrolyzer hydrogen production function is as follows:

[0025]

[0026] The formula of the equivalent hydrogen consumption model of the electric energy storage device is as follows:

[0027] H bt =P bt (t) / LHV,

[0028] Among them, M H represents the molar mass of hydrogen, n c represents the number of cells in the fuel cell, P fc (t) represents the output power of the fuel cell at the current moment, z represents the number of electrons moving in the fuel cell, v fc (t) represents the voltage of the fuel cell at the current moment; η F (t) represents the Faraday efficiency, n s represents the number of cells in the electrolytic cell, P el (t) represents the input power of the electrolytic cell at the current moment, F represents the Faraday constant, v el (t) represents the voltage of the electrolytic cell at the current moment; P bt (t) represents the input / output power of the electric energy storage device at the current moment, and LHV represents the lower heating value of hydrogen.

[0029] According to a specific embodiment of the present invention, the formula of the second objective function is as follows:

[0030] J hy (t) = H bt (t)Δt+[H fc (t)-H el (t)]Δt+β[(P fc (t)-P fcr (t)) 2 +(P el (t)-P elr (t)) 2 ],

[0031] Among them, J hy (t) represents the second objective function, H bt (t) represents the equivalent hydrogen consumption model of the electric energy storage device, H fc (t) represents the hydrogen consumption function of the fuel cell, H fc (t) represents the hydrogen production function of the electrolyzer, Δt represents the time interval between the previous moment and the current moment, β is used as a penalty factor to coordinate the weight between the degradation degree of the energy storage system and the equivalent hydrogen consumption, P fc(t) represents the output power of the fuel cell at the current moment, P fcr (t) represents the reference power of the fuel cell, P el (t) represents the input power of the electrolytic cell at the current moment, P elr (t) represents the reference power of the electrolytic cell.

[0032] According to a specific embodiment of the present invention, the steps of minimizing the equivalent hydrogen consumption of the energy storage system, analyzing the second objective function based on the reference power of the hydrogen energy storage device and the electric energy storage device, and calculating the input / output power of the hydrogen energy storage device and the electric energy storage device include: minimizing the equivalent hydrogen consumption of the energy storage system by minimizing the second objective function, and minimizing the deviation between the input / output power of the hydrogen energy storage device and the electric energy storage device and the corresponding reference power.

[0033] According to a specific embodiment of the present invention, the step of adjusting the power distribution between the hydrogen energy storage device and the electrical energy storage device according to the corresponding input / output power includes: according to the corresponding input / output power, calculating the duty cycle of the converters of the fuel cell, the electrolyzer, and the electrical energy storage device, and controlling the operation of the converters according to the corresponding duty cycle to optimize the power distribution between the fuel cell, the electrolyzer, and the electrical energy storage device.

[0034] According to a specific embodiment of the present invention, the power balance of the energy storage system is expressed as follows:

[0035] P load (t)-P pv (t) = P bt (t)+P fc (t)-P el (t),

[0036] Among them, P load (t) represents the electric power that the load needs to consume at the current moment, P pv (t) represents the electric power generated by renewable energy and input into the system, P bt (t) represents the electric power input / output of the electric energy storage device at the current moment, P fc (t) represents the electric power output by the fuel cell at the current moment, P el (t) represents the electric power input to the electrolytic cell at the current moment.

[0037] The present invention provides an energy management strategy that can not only reduce the degradation of the energy storage system, but also optimize the start and stop states of the fuel cell and electrolyzer to minimize system degradation.

[0038] At the same time, the present invention also provides another energy management strategy that can not only minimize the equivalent hydrogen consumption of the energy storage system in the isolated microgrid, but also properly control the hydrogen state of charge and charge state of the system.

[0039] In addition, the present invention also builds a complete energy management architecture based on two energy management strategies: the degree of degradation of the energy storage system and the equivalent hydrogen consumption. This can not only reduce the degree of degradation of the system, but also reduce the equivalent hydrogen consumption of the system to maintain stable and reliable operation of the system, thereby correspondingly improving the economy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A structural block diagram of a specific embodiment of an energy storage system provided by the present invention;

[0041] Figure 2 A flowchart of a specific embodiment of an energy management method based on the degradation degree of an energy storage system provided by the present invention;

[0042] Figure 3 A flow chart of a specific embodiment of an energy management method based on equivalent hydrogen consumption of an energy storage system provided by the present invention;

[0043] Figure 4 This is a flow chart of a specific embodiment of a two-level energy management method for an energy storage system provided by the present invention. DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0045] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0046] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, publicly known structures and devices are shown in block diagram form rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0047] First of all, it should be noted that in order to enable people in this technical field to better understand the solution of this application, the technical background of this application is explained accordingly.

[0048] like Figure 1 As shown, in the isolated microgrid, the energy storage system is an important component, maintaining the cyclic and stable operation of the microgrid, and at the same time, building a hybrid energy storage system for the development of hydrogen energy. Among them, the energy storage system is composed of a hydrogen energy storage device and an electric energy storage device. In addition, in order to promote the development of green energy, renewable energy such as photovoltaic power generation, hydropower generation, and wind power generation can be used as the power input of the energy storage system to develop, prepare, and store hydrogen energy, and promote the green, low-carbon, safe and efficient transformation of energy. In order to better illustrate the technical solution provided, in this application, photovoltaic power is specifically used as an example as the power input of the energy storage system, but there is no restriction on the type of renewable energy. In actual applications, other renewable energy sources can be used as power input.

[0049] Typically, in an energy storage system, a photovoltaic generator, i.e., a photovoltaic power source, operates in maximum power point tracking mode, and provides energy to the system and the load through a Boost converter. At the same time, the hydrogen energy storage device needs to have the ability to produce hydrogen, store hydrogen, and convert hydrogen into energy to maintain the balance of the system. Therefore, the hydrogen energy storage device is composed of at least an electrolyzer, a hydrogen storage tank, and a fuel cell, which are used for hydrogen production, hydrogen storage, and hydrogen consumption, respectively. The electrolyzer obtains energy from the system through a Buck converter to produce hydrogen, and the fuel cell consumes hydrogen and provides energy to the system through a Boost converter. The electrical energy storage device can be composed of a mixture of one or more energy storage devices such as supercapacitors and / or batteries whose power characteristics are better than those of hydrogen energy storage, and provide energy to the system or obtain energy from the system through a bidirectional Buck-Boost converter. There are no excessive restrictions on this.

[0050] Furthermore, the net load power of the system is composed of two parts: photovoltaic power generation power and load consumption power. When the photovoltaic power generation power exceeds the load consumption power, the net load power of the system is in a surplus state, the electric energy storage device starts charging, and the electrolyzer starts working to produce hydrogen to store hydrogen energy or sell it. When the load consumption power exceeds the photovoltaic power generation power, the net load power of the system is in a missing state, which can be compensated by the hydrogen energy storage device and the electric energy storage device jointly releasing energy, such as battery discharge to supply energy and fuel cell consumption of hydrogen discharge to supply energy, so as to maintain the balance and stability of the system, and the cycle repeats.

[0051] Based on the above-mentioned energy storage system, this application provides a variety of energy management strategies to assist its sustainable operation, thereby improving the reliability and economy of the energy storage system.

[0052] Example 1

[0053] See Figure 2 An energy management method based on the degradation degree of an energy storage system is shown, comprising:

[0054] Step S110 , pre-constructing degradation models of the hydrogen energy storage device and the electric energy storage device; wherein the degradation model of the hydrogen energy storage device is constructed at least by parameters related to the start / stop state thereof.

[0055] Step S120 : Based on the power balance of the energy storage system and according to the degradation models of the hydrogen energy storage device and the electric energy storage device, an objective function of the energy storage system regarding the degree of degradation is established.

[0056] In step S130, when the net load electric power of the energy storage system at the current moment is obtained, the objective function is analyzed by substituting the net load electric power into the objective function with the goal of minimizing the degree of degradation of the energy storage system to optimize the start / stop state of the hydrogen energy storage device and the power distribution between the hydrogen energy storage device and the electric energy storage device.

[0057] First, a hydrogen energy storage device consists of a fuel cell, an electrolyzer, and a hydrogen storage tank, each requiring its own degradation model. It should be understood that the hydrogen storage tank is only used to store hydrogen, and its degradation is affected only by aging. Therefore, it is not involved in the subsequent degradation analysis or degradation model construction.

[0058] In this regard, the degradation of a fuel cell (FC) can be characterized by its voltage drop, which can be further decomposed into the voltage drop caused by high power operation (D fchigh (t)) and the voltage drop caused by power transient changes (D fcshift (t)), and after ignoring the coupling between voltage drops, the characterization function of FC with respect to voltage drop is as follows:

[0059] D fc (t) = D fchigh (t)+D fcshift (t),

[0060] And this is used as the degradation model of FC. However, in this embodiment, considering that the instability of photovoltaic power supply will cause FC to start and stop frequently, thus aggravating the degradation degree of FC. Therefore, in the above D fchigh (t) and D fcshift (t) is based on the voltage drop caused by the start / stop state (D fccycle (t)) to jointly characterize the voltage drop of FC. The corresponding FC characterization function of voltage drop can be adjusted as follows:

[0061] D fc (t) = D fccycle (t)+D fchigh (t)+D fcshift (t),

[0062] It is understandable that the instability of photovoltaic power sources causes the system's net load power to frequently switch between surplus and deficit. A net load power surplus utilizes the electrolyzer to produce hydrogen, while a net load power deficit utilizes the fuel cell to consume hydrogen and release energy. Furthermore, to ensure system stability and balance, the electrolyzer and fuel cell are designed to operate as close to each other as possible, causing the FC to continuously switch between starting and stopping. Specifically, when the system's net load has an energy surplus, the electrolyzer begins operating to consume the surplus energy. When there is an energy shortage, the fuel cell is activated to supplement the energy shortage. When the system's net load fluctuates frequently, the hydrogen energy storage device may frequently start and stop, leading to accelerated degradation.

[0063] Therefore, in order to optimize the start-stop state of FC and minimize its degradation, the characterization function of FC with respect to voltage drop preferably adopts the latter.

[0064] Among them, the voltage drop (D fccycle (t)) characterization function:

[0065] D fccycle (t) = α fccycle |y fc (t)-y fc (t-Δt)|,

[0066] The voltage drop (D fchigh (t)) characterization function:

[0067]

[0068] FC voltage drop caused by power transient change (D fcshift (t)) characterization function:

[0069] D fcshift (t) = α fcshift |P fc (t)-P fc (t-Δt)|,

[0070] In the above formula, α fccycle , α fchigh , α fchigh is the correlation coefficient of FC voltage degradation.

[0071] In addition, in order to indicate the start and stop status of FC, a logical variable y is defined fc (When the net load power of the system is lost, the corresponding FC starts fc is 1, otherwise it is 0, which means the corresponding FC stops).

[0072] At the same time, in order to indicate whether FC is in the high power range, a logical variable is defined (When the current operating power of FC is in the high power range, is 1, otherwise is 0).

[0073] Δt represents the time interval between the previous moment and the current moment. It should be noted here that energy management can be performed at any moment based on the net load electric power of the system, and will continue until the next moment when energy management is performed again. The interval between these two moments is the above-mentioned time interval Δt.

[0074] P fc (t) represents the operating power of FC, that is, the output power at the current moment, and the upper and lower limits of FC operating power are as follows:

[0075] y fc (t)P fcmin ≤P fc (t)≤y fc (t)P fcmax ,

[0076] And P fcmin and P fcmax Corresponding to the minimum and maximum power of FC respectively.

[0077] The degradation of an electrolyzer (EL) can also be characterized by a drop in its voltage, which can be decomposed into the voltage drop caused by operation (D elop (t)) and the voltage drop caused by power transient changes (D elshift(t)), and after ignoring the coupling between the voltage drops, the characterization function of EL with respect to the voltage drop is as follows:

[0078] D el (t) = D elop (t)+D elshift (t),

[0079] This can be used as the degradation model of EL. Similarly, considering the start and stop state of EL, in the above D elop (t) and D elshift (t) is based on the voltage drop D caused by the start / stop state. elcycle (t), to jointly characterize the voltage drop of EL, the corresponding EL characterization function of voltage drop can be adjusted as follows:

[0080] D el (t) = D elcycle (t)+D elop (t)+D elshift (t),

[0081] Among them, EL is caused by the voltage drop D caused by the start / stop state. elcycle Characterization function of (t):

[0082] D elcycle (t) = α elcycle |y el (t)-y el (t-Δt)|,

[0083] EL voltage drop caused by operation D elop Characterization function of (t):

[0084] D elop (t) = α elop y el (t)Δt,

[0085] EL voltage drop caused by power transient change D elshift Characterization function of (t):

[0086] D elshift (t) = α elshift |P el (t)-P el (t-Δt)|,

[0087] In the above formula, α elcycle , α elop , α elop is the correlation coefficient of EL voltage degradation.

[0088] Similarly, to indicate the start and stop status of EL, a logical variable y is defined el(When the net load power of the system is in surplus, the corresponding EL starts el is 1, otherwise it is 0, that is, the corresponding EL stops).

[0089] P el (t) represents the operating power of EL, that is, the input power at the current moment, and the upper and lower limits of the operating power of EL are as follows:

[0090] y el (t)P elmin ≤P el (t)≤y el (t)P elmax ,

[0091] And P elmin and P elmax Corresponding to the minimum and maximum power of EL respectively.

[0092] In this embodiment, the battery is used as an example of an electrical energy storage device to illustrate the technical solution. The degradation of the battery (BT) can be characterized by its state of health (SOH). The SOH of the battery can be expressed as:

[0093]

[0094] Among them, d soh (t) represents the change of SOH, SOH(t) represents the health status of the battery at the current moment, P bt (t) represents the input / output power of the battery at the current moment, E bt Indicates the capacity of the battery, N C Indicates the number of cycles before the battery reaches the end of its service life.

[0095] In addition, the energy storage system must also comply with the law of conservation of energy, that is, maintain energy balance. To this end, the fuel cell, electrolyzer, and battery must meet the following power balance:

[0096] P load (t)-P pv (t) = P bt (t)+P fc (t)-P el (t),

[0097] Among them, P load (t) represents the electric power that the load needs to consume at the current moment, that is, the load consumption power, P pv (t) represents the electric power generated by renewable energy and input into the system, that is, the electric power generated by the photovoltaic power source at the current moment (photovoltaic power generation power).

[0098] Based on the power balance of the above system and the degradation models of each system, the objective function J can be constructed accordingly. deg (t) are as follows:

[0099]

[0100] In the above formula, C fcin 、C elin 、C btin Represent the purchase cost of FC, EL, and BT respectively, v fceol It represents the maximum voltage drop of FC before reaching the end of its service life, v eleol Indicates the maximum voltage drop of an EL before reaching the end of its service life.

[0101] It can be seen that the three items in the above formula represent the degradation costs of FC, EL, and BT over a certain period of time. Considering the economic efficiency of the energy storage system, the degradation cost of the system should be minimized, that is, the degree of degradation of the system should be minimized.

[0102] At the same time, in order to ensure the stable operation of the system, it is assumed that there is at most one operation between FC and EL at any time, that is, it satisfies:

[0103] y fc (t)+y el (t)≤1,

[0104] In this regard, based on the net load power of the system at the current moment, in minimizing the objective function J deg After (t), the current input / output power of FC, EL, and BT can be calculated accordingly. Finally, the FC's Boost converter or the EL's Buck converter, as well as the BT's bidirectional Buck-Boost converter, can be controlled according to the corresponding input / output power. That is, the corresponding duty cycle of the converter is calculated based on the input / output power, thereby achieving system power distribution. Since at most only one of the fuel cell and the electrolyzer is operating, when the net load power is in surplus, the excess power can be allocated to the electrolyzer to produce hydrogen and / or the battery to charge and store energy. Alternatively, when the net load power is missing, the fuel cell can be controlled to consume hydrogen to release energy and / or the battery can be controlled to discharge energy to compensate for the missing net load power.

[0105] It can be seen that the above energy management strategy can not only reduce the degree of degradation of the energy storage system, but also optimize the start and stop status of the fuel cell and electrolyzer, minimize system degradation, ensure the sustainable operation of the system, and correspondingly improve the economy of the system.

[0106] Example 2

[0107] See Figure 3An energy management method for an energy storage system is shown, comprising:

[0108] Step S210, pre-constructing a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device; wherein the hydrogen consumption model of the hydrogen energy storage device is constrained according to the hydrogen state of charge, and the equivalent hydrogen consumption model of the electric energy storage device is constrained according to the state of charge.

[0109] Step S220 , based on the power balance of the energy storage system, an objective function of the energy storage system regarding equivalent hydrogen consumption is established according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device.

[0110] In step S230, when the net load electric power of the energy storage system at the current moment is obtained, the equivalent hydrogen consumption of the energy storage system is minimized, and the net load electric power is substituted into the objective function to optimize the power distribution between the hydrogen energy storage device and the electric energy storage device.

[0111] First, we should build the hydrogen consumption model of the fuel cell and electrolyzer, as well as the equivalent hydrogen consumption model of the battery. The hydrogen storage tank does not generate actual hydrogen consumption or equivalent hydrogen consumption. It is only used to store hydrogen and does not participate in the subsequent equivalent hydrogen consumption analysis and model construction.

[0112] Therefore, FC needs to consume hydrogen to release energy, and the hydrogen consumption function H of FC can be constructed accordingly. fc (t) are as follows:

[0113]

[0114] In the above formula, M H represents the molar mass of hydrogen, n c represents the number of monomers in FC, z represents the number of mobile electrons in FC, and F represents the Faraday constant.

[0115] P fc (t) represents the operating power of FC, that is, the output power at the current moment, and the upper and lower limits of FC operating power are as follows:

[0116] P fcmin ≤P fc (t)≤P fcmax , and P fcmin and P fcmax Corresponding to the minimum and maximum power of FC respectively.

[0117] v fc (t) represents the voltage of FC at the current moment.

[0118] It can be seen from this that the hydrogen consumption of a fuel cell, that is, the degree of hydrogen consumption, is closely related to the electrical power and voltage it outputs.

[0119] Furthermore, EL needs to use energy to produce hydrogen, and the hydrogen production function H of EL can be constructed accordingly. el as follows:

[0120]

[0121] In the above formula, η F (t) represents the Faraday efficiency, n s represents the number of EL monomers, and F represents the Faraday constant.

[0122] P el (t) represents the operating power of EL, that is, the input power at the current moment, and the upper and lower limits of the operating power of EL are as follows:

[0123] P elmin ≤P el (t)≤P elmax , and P elmin and P elmax Corresponding to the minimum and maximum power of EL respectively.

[0124] v el (t) represents the voltage of EL at the current moment.

[0125] It can be seen from this that the hydrogen production of the electrolyzer, that is, the equivalent negative hydrogen consumption, is closely related to its input electrical power and voltage.

[0126] Based on this, the hydrogen production function H of FC can be used el and EL's hydrogen production function H el Construct a hydrogen consumption model for hydrogen energy storage devices. Furthermore, although hydrogen storage tanks are not included in the equivalent hydrogen consumption analysis, hydrogen produced by the electrolyzer needs to be stored in hydrogen storage tanks. However, both the hydrogen storage capacity and the internal pressure that a hydrogen storage tank can withstand have certain upper limits. Therefore, to reflect the level of hydrogen stored in a hydrogen storage tank (HST), a hydrogen state of charge (SOHC) is defined to constrain the aforementioned hydrogen consumption model, preventing the hydrogen storage tank from being damaged due to its inability to store more hydrogen.

[0127] In this regard, HST's SOHC real-time mapping function is as follows:

[0128] and

[0129]

[0130] Among them, n int is the amount of hydrogen initially stored in the HST, and n hst (t) reflects the real-time hydrogen amount of HST, phst (t) represents the pressure of HST, and p max Indicates the maximum pressure that HST can withstand, R hst 、T hst 、V hst are the gas constant, temperature, and volume, respectively.

[0131] It can be seen that the hydrogen consumption model is constrained by the SOHC of the hydrogen storage tank, that is, the corresponding constrained hydrogen consumption function H fc (t) and hydrogen production function H el , to avoid EL producing more hydrogen and FC consuming less hydrogen.

[0132] For batteries, although they do not actually produce or consume hydrogen, they can provide or consume energy. Therefore, the electric power output or input of the battery can be regarded as equivalent hydrogen consumption. The corresponding equivalent hydrogen consumption model formula is as follows:

[0133] H bt =P bt (t) / LHV,

[0134] Among them, LHV represents the lower heating value of hydrogen, P bt (t) is the input / output power of BT at the current moment, and the upper and lower limits are as follows: btmaxc ≤P bt (t)≤P btmaxd , when the battery is discharged P bt (t)>0,P btmaxd is the maximum discharge power, when charging P bt (t)<0,P btmaxc is the maximum charging power.

[0135] In addition, in order to maintain the stability and balance of the battery's State of Charge (SOC), the battery's SOC is also used to constrain its corresponding equivalent hydrogen consumption model to avoid over-discharge or over-charge of the battery, thereby affecting its service life.

[0136] In this regard, the real-time mapping function of BT's SOC is as follows:

[0137]

[0138] Among them, SOC init is the initial SOC of the battery, i.e., the charge, Q bt Indicates the charge of the battery, i bt Indicates the current input / output of the battery.

[0139] It can be seen from this that the real-time SOC can be calculated based on the battery charge, the current input / output current at the current moment, and the initial power, so as to constrain the battery SOC within a preset range. For example, when the SOC exceeds the upper limit, the battery can be controlled to discharge, and when the SOC exceeds the lower limit, the battery can be controlled to charge, so that the battery SOC always remains stable.

[0140] Similarly, fuel cells, electrolyzers, and batteries must meet the following power balance:

[0141] P load (t)-P pv (t) = P bt (t)+P fc (t)-P el (t),

[0142] Based on the power balance of the above system, the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device, the objective function J can be constructed accordingly. hy (t) are as follows:

[0143] J hy (t) = ω bt (t)H bt (t)Δt+ω hy (t)[H fc (t)-H el (t)]Δt,

[0144] Among them, the hydrogen consumption model constructed based on the hydrogen consumption function of FC and the hydrogen production function of EL is H fc (t)-H el (t),ω bt (t) and ω hy (t) are two weight parameters introduced to characterize the contribution of the electric energy storage device and the hydrogen energy storage device to the equivalent hydrogen consumption of the system. Specifically, the virtual forces of the electric energy storage device and the hydrogen energy storage device are determined by the artificial potential field and calculated accordingly, as follows:

[0145] ω bt (t)=1-F bt (t),

[0146] ω hy (t)=1-F hy (t),

[0147] Among them, F bt (t) is the virtual force on the SOC of the energy storage device, F hy (t) is the virtual force of the hydrogen energy storage device SOHC.

[0148] It should be noted that virtual forces are defined in the context of "artificial potential fields," initially proposed for robotics applications and more recently applied to renewable energy systems. Artificial potential fields are widely used in multi-agent formation control. In these formation problems, multiple agents must maintain a reference distance to form a stable formation. This method constructs an artificial potential field, and the force function between any two agents in the artificial potential field, also known as the action function, is defined. When the distance between two agents is equal to the reference value, no force is generated between them, meaning the potential energy is zero. When the two agents are close, a strong repulsive force acts; when they are far apart, a strong attractive force acts. This high potential energy (i.e., repulsive or attractive force) ensures that their distance quickly converges to the reference value. For example, when the SOC of an energy storage device is high, it experiences an attractive force that lowers the SOC, while when the SOC is low, it experiences an attractive force that raises the SOC. When the SOC approaches or equals the reference value, this phenomenon can be effectively reduced, effectively creating a virtual force corresponding to the battery SOC, thereby maintaining the SOC of the energy storage device at a stable state. Similarly, the SOHC (solar-octane hydrogen storage system) is similarly effective.

[0149] Therefore, the virtual force related to the SOC of the electric energy storage device is defined as follows:

[0150]

[0151] Where x1(t) = SOC(t) - SOC mid , and SOC mid It is a minimum SOC between the SOC of the energy storage device min and maximum SOC max A set value between , in which it is expected that the SOC of the electric energy storage device will be maintained at this value, and u1 is a coefficient used to shape the virtual force curve of the electric energy storage device.

[0152] Similarly, the virtual force associated with the hydrogen storage device, i.e., HST, is defined as follows:

[0153]

[0154] Where x2(t)=SOHC(t)-SOHC mid , and SOHC mid It is a minimum SOHC between the hydrogen energy storage device SOHC min and maximum SOHC max A set value between , in which it is expected that the SOHC of the hydrogen energy storage device maintains operation at this value, and u2 is a coefficient used to shape the virtual force curve of the hydrogen energy storage device.

[0155] In one embodiment, the SOC min and SOHC min Set to 30%, SOCmax and SOHC max Set to 90%, SOC mid and SOHC mid Set to 60% for calculation purposes. Accordingly, based on the system's current net load power and minimizing the objective function to minimize the system's equivalent hydrogen consumption, the current FC input power, the current EL output power, and the current BT input / output power can be calculated. Finally, the FC's Boost converter, the EL's Buck converter, and the BT's bidirectional Buck-Boost converter can be controlled based on the corresponding input / output power. This means that the converter's duty cycle is calculated based on the input / output power, thereby achieving system power distribution.

[0156] It can be seen that the above energy management strategy can not only minimize the equivalent hydrogen consumption of the energy storage system in the isolated microgrid, but also properly control the SOHC and SOC of the system to maintain stable and reliable operation of the system.

[0157] Example 3

[0158] In summary, the above two embodiments respectively adopt different energy management strategies to assist the energy storage system in coordinating the operation of fuel cells, electrolyzers, and batteries. Of course, the above two strategies can also be combined to build a complete energy management framework to further improve the reliability of the strategy.

[0159] For this, see Figure 4 A two-level energy management method for an energy storage system is shown, comprising:

[0160] Step S311 : Pre-constructing degradation models of the hydrogen energy storage device and the electric energy storage device.

[0161] Step S312 : Based on the power balance of the energy storage system and according to the degradation models of the hydrogen energy storage device and the electric energy storage device, a first objective function of the energy storage system regarding the degree of degradation is established.

[0162] Step S321 : pre-constructing a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device.

[0163] Step S322: Based on the power balance of the energy storage system, a second objective function is established according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device, as well as a preset weight between the degree of degradation and the equivalent hydrogen consumption of the energy storage system.

[0164] Step S330: Obtain the net load electric power of the energy storage system at the current moment.

[0165] Step S340 , with the goal of minimizing the degree of degradation of the energy storage system, substituting the net load electric power into the first objective function, and calculating the reference power of the hydrogen energy storage device and the electric energy storage device.

[0166] Step S350: Minimize the equivalent hydrogen consumption of the energy storage system, and analyze the second objective function based on the reference power of the hydrogen energy storage device and the electric energy storage device to calculate the input / output power of the hydrogen energy storage device and the electric energy storage device.

[0167] Step S360: Adjust the power distribution between the hydrogen energy storage device and the electric energy storage device according to the corresponding input / output power.

[0168] First, based on the degradation model of the fuel cell, electrolyzer, and battery provided in Example 1, a first objective function J can be constructed. deg (t), in order to achieve the first-level energy management, i.e., to minimize the degradation of the system.

[0169] It should be noted that in Example 1, two degradation models are provided for the fuel cell and the electrolyzer, respectively, one of which does not include the voltage drop caused by the start / stop state, and the other includes the voltage drop caused by the start / stop state.

[0170] Therefore, the first objective function constructed can be divided into the following two categories:

[0171] Category 1: and

[0172] D fc (t) = D fchigh (t)+D fcshift (t), D el (t) = D elop (t)+D elshift (t),

[0173] Category 2: and

[0174] D fc (t) = D fccycle (t)+D fchigh (t)+D fcshift (t), D el (t) = D elcycle (t)+D elop (t)+D elshift (t)

[0175] Both of the above first objective functions can be used to optimize the degree of degradation of the system. For example, without considering the optimization of the start and stop states of the fuel cell and the electrolyzer, the first objective function of the first type can be used to reduce the degree of degradation of the system. Alternatively, in order to minimize the degree of degradation of the system, the first objective function of the second type can be used for energy management. Specific choices and trade-offs can be made according to actual conditions. There are no excessive restrictions on this, and only two options are provided.

[0176] Furthermore, based on the net load power of the system at the current moment, in minimizing the first objective function J deg (t) can be used to calculate the reference power of FC, EL and BT at the current moment.

[0177] Secondly, based on the hydrogen consumption model of the hydrogen energy storage device provided in Example 2 and the equivalent hydrogen consumption model of the electric energy storage device, a second objective function J can be constructed. hy (t) to achieve secondary energy management, that is, to minimize the equivalent hydrogen consumption of the system, to further optimize the reference power of the hydrogen energy storage device and the electric energy storage device obtained above, and obtain the final input / output power of the hydrogen energy storage device and the electric energy storage device.

[0178] In order to integrate the two strategies and reduce the equivalent hydrogen consumption while reducing the degree of system degradation, the weight between the degree of degradation and the equivalent hydrogen consumption can be adjusted accordingly, and then the second objective function J is constructed based on the different weights of the degree of degradation and the equivalent hydrogen consumption. hy (t).

[0179] It should also be noted that in Example 2, in order to synchronously maintain the stability of the SOHC of the hydrogen energy storage device and the SOC of the electric energy storage device, two weight parameters ω are introduced. bt (t) and ω hy (t) is used to characterize the contribution of the electric energy storage device and the hydrogen energy storage device to the system equivalent hydrogen consumption, thereby minimizing the system equivalent hydrogen consumption while appropriately controlling the system's SOHC and SOC. Therefore, when constructing the second objective function, it can also be divided into the following two categories, with the specific formula as follows:

[0180] Category 1:

[0181] J hy (t) = H bt (t)Δt+[H fc (t)-H el (t)]Δt+β[(P fc (t)-P fcr (t)) 2 +(P el (t)-P elr (t)) 2 ],

[0182] Category 2:

[0183] J hy (t) = ω bt (t)H bt (t)Δt+ω hy (t)[H fc (t)-H el (t)]Δt+β[(P fc (t)-P fcr (t)) 2 +(P el (t)-P elr (t)) 2 ],

[0184] Among them, β is used as a penalty factor to coordinate the weight between the degradation degree of the energy storage system and the equivalent hydrogen consumption, P fc (t) represents the output power of the fuel cell at the current moment, P fcr (t) represents the reference power of the fuel cell, P el (t) represents the input power of the electrolytic cell at the current moment, P elr (t) represents the reference power of the electrolytic cell.

[0185] Similarly, both of the above second objective functions represent the equivalent hydrogen consumption of the system. To minimize the system's equivalent hydrogen consumption, it is also necessary to minimize the hydrogen consumption parameters of the hydrogen energy storage device and the equivalent hydrogen consumption parameters of the electric energy storage device. Furthermore, based on the above, it is also necessary to minimize the deviation between the input / output power of the hydrogen energy storage device and its corresponding reference power. Specifically, this means minimizing the deviation between the output power of FC calculated using the second objective function and the reference power calculated using the first objective function, as well as the deviation between the input power of EL calculated using the second objective function and the reference power calculated using the first objective function. This allows the reference power calculated using the first objective function to be used to optimize the input / output power of FC and EL. Therefore, minimizing the second objective function achieves the above objectives and allows the calculation of the current input / output power of FC and EL. It should also be understood that, based on the system's power balance, once the input / output power of FC and EL is determined, the input / output power of BT is also determined.

[0186] Finally, the operation of the FC's Boost converter, the EL's Buck converter, and the BT's bidirectional Buck-Boost converter can be controlled according to the corresponding input / output power. That is, the corresponding duty cycle of the converter is calculated based on the input / output power, thereby completing the power distribution of the system and realizing two-level energy management based on both degradation degree and equivalent hydrogen consumption strategies.

[0187] It should be noted that the step division of the various methods above is only for the purpose of clear description. During implementation, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they contain the same logical relationship, they are all within the scope of protection of this patent; adding insignificant modifications to the algorithm or process or introducing insignificant designs without changing the core design of the algorithm and process are all within the scope of protection of this patent.

[0188] In summary, the present invention provides an energy management strategy that can not only reduce the degradation of the energy storage system, but also optimize the start and stop states of the fuel cell and electrolyzer, thereby minimizing system degradation.

[0189] At the same time, the present invention also provides another energy management strategy that can not only minimize the equivalent hydrogen consumption of the energy storage system in the isolated microgrid, but also properly control the hydrogen state of charge and charge state of the system.

[0190] In addition, the present invention also builds a complete energy management architecture based on two energy management strategies: the degree of degradation of the energy storage system and the equivalent hydrogen consumption. This can not only reduce the degree of degradation of the system, but also reduce the equivalent hydrogen consumption of the system to maintain stable and reliable operation of the system, thereby correspondingly improving the economy of the system.

[0191] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, any equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A two-level energy management method for an energy storage system, characterized in that: The energy storage system is composed of an electric energy storage device and a hydrogen energy storage device; wherein the electric energy storage device includes a supercapacitor and / or a battery; the hydrogen energy storage device includes at least an electrolyzer, a fuel cell and a hydrogen storage tank; the two-level energy management method includes: Pre-building degradation models of the hydrogen energy storage device and the electric energy storage device; Based on the power balance of the energy storage system, establishing a first objective function according to degradation models of the hydrogen energy storage device and the electric energy storage device; Pre-constructing a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device; Based on the power balance of the energy storage system, a second objective function is established according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device, and a preset weight between the degree of degradation and the equivalent hydrogen consumption of the energy storage system; Obtaining the net load electric power of the energy storage system at a current moment; Minimizing the degree of degradation of the energy storage system is the goal. Substituting the net load electric power into the first objective function, the reference power of the hydrogen energy storage device and the electric energy storage device are calculated. Minimizing the equivalent hydrogen consumption of the energy storage system, and analyzing the second objective function based on the reference power of the hydrogen energy storage device and the electric energy storage device to calculate the input / output power of the hydrogen energy storage device and the electric energy storage device; adjusting the power distribution between the hydrogen energy storage device and the electrical energy storage device according to the corresponding input / output power; The formula of the second objective function is as follows: J hy (t)=H bt (t)Δt+[H fc (t)-H el (t)]Δt+β[(P fc (t)-P fcr (t)) 2 +(P el (t)-P elr (t)) 2 ], Among them, J hy (t) represents the second objective function, H bt (t) represents the equivalent hydrogen consumption model of the electric energy storage device, H fc (t) represents the hydrogen consumption function of the fuel cell, H fc (t) represents the hydrogen production function of the electrolyzer, Δt represents the time interval between the previous moment and the current moment, β is used as a penalty factor to coordinate the weight between the degradation degree of the energy storage system and the equivalent hydrogen consumption, P fc (t) represents the output power of the fuel cell at the current moment, P fcr (t) represents the reference power of the fuel cell, P el (t) represents the input power of the electrolytic cell at the current moment, P elr (t) represents the reference power of the electrolytic cell.

2. The two-level energy management method of the energy storage system according to claim 1, characterized in that: The step of pre-building degradation models of the hydrogen energy storage device and the electric energy storage device includes: Constructing a characterization function of the voltage drop of the fuel cell according to the voltage drop caused by high power operation and the voltage drop caused by transient power change, as a degradation model corresponding to the fuel cell; Constructing a characterization function of the voltage drop of the electrolytic cell according to the voltage drop caused by operation and the voltage drop caused by transient power changes, as a degradation model corresponding to the electrolytic cell; A characterization function of the health state of the electric energy storage device is constructed according to the number of cycles of use of the electric energy storage device, as a degradation model corresponding to the electric energy storage device.

3. The two-level energy management method of the energy storage system according to claim 2, characterized in that: The formula for the characterization function of the fuel cell voltage drop is as follows: Total voltage drop: D fc (t) = D fchigh (t)+D fcshift (t), Regarding the voltage drop caused by high power operation: Regarding the voltage drop caused by transient power changes: D fcshift (t) = α fcshift |P fc (t)-P fc (t-Δt)|, The formula for the characterization function of the electrolytic cell voltage drop is as follows: Total voltage drop: D el (t) = D elop (t)+D elshift (t), Regarding the voltage drop caused by operation: D elop (t) = α elop y el (t)Δt, Regarding the voltage drop caused by transient power changes: D elshift (t) = α elshift |P el (t)-P el (t-Δt)|, The formula for the characterization function of the health status of the electric energy storage device is as follows: Among them, D fc (t) represents the voltage drop of the fuel cell at the current moment, D fchigh (t) represents the voltage drop of the fuel cell caused by high power operation at the current moment, D fcshift (t) represents the voltage drop of the fuel cell caused by the transient power change at the current moment, α fchigh , α fchigh is the correlation coefficient of the fuel cell voltage degradation, A logical variable indicating whether the current operating power of the fuel cell is in the high power range. If so, 1, if otherwise is 0, P fc (t) represents the output power of the fuel cell at the current moment; D el (t) represents the voltage drop of the electrolytic cell at the current moment, D elop (t) represents the voltage drop of the electrolytic cell caused by operation at the current moment, D elshift (t) represents the voltage drop of the electrolytic cell caused by the transient change of power at the current moment, α elop , α elop is the correlation coefficient of the electrolytic cell voltage degradation, y el A logical variable indicating the start / stop state of the electrolytic cell. If it is started, y el If it is 1, then y el is 0, P el (t) represents the input power of the electrolytic cell at the current moment; d soh (t) represents the change of the health status of the electric energy storage device, SOH(t) represents the health status of the electric energy storage device at the current moment, P bt (t) represents the input / output power of the electric energy storage device at the current moment, Δt represents the time interval between the previous moment and the current moment, and E bt Represents the capacity of the electrical energy storage device, N C Indicates the number of cycles before the electrical energy storage device reaches the end of its service life.

4. The two-level energy management method of the energy storage system according to claim 1, characterized in that: The formula of the first objective function is as follows: Among them, J deg (t) represents the first objective function, C fcin represents the purchase cost of the fuel cell, C elin represents the purchase cost of the electrolytic cell, C btin represents the purchase cost of the electric energy storage device, D fc (t) represents the degradation model of the fuel cell, v fceol Denotes the maximum voltage drop of the fuel cell before reaching the end of its service life, D el (t) represents the degradation model of the electrolytic cell, v eleol represents the maximum voltage drop of the electrolytic cell before reaching the end of its service life, d soh (t) represents the degradation model of the electric energy storage device.

5. The two-level energy management method of the energy storage system according to claim 1, characterized in that: The steps of pre-building the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device include: Constructing a hydrogen consumption model of the hydrogen energy storage device according to the hydrogen consumption function of the fuel cell and the hydrogen production function of the electrolyzer; Constructing a corresponding equivalent hydrogen consumption model according to the electric power input / output of the electric energy storage device; The hydrogen consumption model of the hydrogen energy storage device is constrained according to the hydrogen state of charge of the hydrogen storage tank, and the equivalent hydrogen consumption model of the electric energy storage device is constrained according to the state of charge of the electric energy storage device, so as to maintain the stability of the hydrogen state of charge of the hydrogen energy storage device and the state of charge of the electric energy storage device.

6. The two-level energy management method of the energy storage system according to claim 5, characterized in that: The formula of the fuel cell hydrogen consumption function is as follows: The formula of the electrolyzer hydrogen production function is as follows: The formula of the equivalent hydrogen consumption model of the electric energy storage device is as follows: H bt =P bt (t) / LHV, Among them, M H represents the molar mass of hydrogen, n c represents the number of cells in the fuel cell, P fc (t) represents the output power of the fuel cell at the current moment, z represents the number of electrons moving in the fuel cell, v fc (t) represents the voltage of the fuel cell at the current moment; η F (t) represents the Faraday efficiency, n s represents the number of cells in the electrolytic cell, P el (t) represents the input power of the electrolytic cell at the current moment, F represents the Faraday constant, v el (t) represents the voltage of the electrolytic cell at the current moment; P bt (t) represents the input / output power of the electric energy storage device at the current moment, and LHV represents the lower heating value of hydrogen.

7. The two-level energy management method for an energy storage system according to claim 1, characterized in that: The steps of minimizing the equivalent hydrogen consumption of the energy storage system, analyzing the second objective function based on the reference powers of the hydrogen energy storage device and the electric energy storage device, and calculating the input / output power of the hydrogen energy storage device and the electric energy storage device include: By minimizing the second objective function, the equivalent hydrogen consumption of the energy storage system is minimized, and the deviation between the input / output power of the hydrogen energy storage device and the electric energy storage device and the corresponding reference power is minimized.

8. The two-level energy management method for an energy storage system according to claim 1, characterized in that: The step of adjusting the power distribution between the hydrogen energy storage device and the electric energy storage device according to the corresponding input / output power includes: According to the corresponding input / output power, the duty cycle of the converters of the fuel cell, the electrolyzer, and the electrical energy storage device is calculated, and the operation of the converters is controlled according to the corresponding duty cycle to optimize the power distribution among the fuel cell, the electrolyzer, and the electrical energy storage device.

9. The two-level energy management method for an energy storage system according to claim 1, characterized in that: The power balance of the energy storage system is shown in the following formula: P load (t)-P pv (t)=P bt (t)+P fc (t)-P el (t), Among them, P load (t) represents the electric power that the load needs to consume at the current moment, P pv (t) represents the electric power generated by renewable energy and input into the system, P bt (t) represents the input / output power of the electric energy storage device at the current moment, P fc (t) represents the output power of the fuel cell at the current moment, P el (t) represents the input power of the electrolytic cell at the current moment.

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