An energy management method based on degradation degree of energy storage system

Abstract

The application belongs to the technical field of energy storage, and particularly relates to an energy management method based on the degradation degree of an energy storage system, comprising the following steps: constructing a degradation model of a hydrogen energy storage device and an electric energy storage device in advance; wherein the degradation model of the hydrogen energy storage device is constructed by at least related parameters of the hydrogen energy storage device about start / stop state; based on power balance of the energy storage system, a target function of the energy storage system about the degradation degree is established according to the degradation models of the hydrogen energy storage device and the electric energy storage device; when the net load electric power of the energy storage system at the current time is obtained, 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 are optimized by taking the minimization of the degradation degree of the energy storage system as the target and substituting the net load electric power into the target function. The application optimizes 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 in the system by minimizing the degradation degree of the energy storage system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and particularly relates to an energy management method based on the degradation degree of an energy storage system. BACKGROUND

[0002] With the increasing development of renewable energy, energy storage has become an important component in power systems. Moreover, as one of the most promising solutions to adapt to the intermittency and uncertainty of renewable energy, energy storage is widely used to improve the stability and economy of the system. Electrical energy storage is suitable for short-term (i.e. hours to days) and small-to-medium-sized energy storage applications. Among them, supercapacitors and batteries are usually used as short-term electrical energy storage devices to store energy, supercapacitors mainly include double-layer capacitors, lithium ion capacitors, sodium ion capacitors and other types, and batteries mainly include lithium ion batteries, sodium ion batteries, lithium metal batteries, semi-solid state batteries, solid state batteries and other types. Electrical energy storage devices such as batteries and supercapacitors have a significant advantage in power density. For long-term (i.e. weeks, months, seasons) and large-scale applications, hydrogen energy storage technology may be a better choice. Hydrogen energy storage technology usually includes electrolytic cells, fuel cells, and hydrogen storage tanks and other devices to convert electrical energy into hydrogen energy storage and convert hydrogen energy into electrical energy for use. Hydrogen energy storage has a significant advantage in energy density. Considering the differences in physical properties such as energy density, power density, cycle life and energy efficiency between electrical energy storage and hydrogen energy storage technologies, hybrid energy storage systems combining the two technologies are being studied.

[0003] Therefore, in order to fully utilize the complementary characteristics of electrical energy storage and hydrogen energy storage technologies, it is necessary to design appropriate energy management strategies to ensure stable and efficient operation of the energy storage system. At present, although a series of progress has been made in the study of degradation of energy management strategies for energy storage systems, the impact of device start-stop state on degradation needs to be considered in the energy management process, especially under the condition of severe fluctuations in net load, which may cause hydrogen energy storage devices to start or stop frequently, thereby accelerating the degradation of hydrogen energy storage devices. How to optimize the start-stop state of the device in the design of the degradation-optimized energy management strategy has become a challenge. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to propose an energy management strategy, which optimizes the start / stop state of the hydrogen component to maximize the reduction of the degradation degree of the hybrid energy storage system, so that it can continue to operate stably.

[0005] To achieve the above object and other related objects, the present application provides an energy management method based on degradation degree of energy storage system, wherein the energy storage system is composed of electric energy storage device and hydrogen energy storage device; the electric energy storage device comprises super capacitor and / or battery; the hydrogen energy storage device comprises electrolytic tank, fuel cell and hydrogen storage tank; the energy management method comprises: constructing degradation model of the hydrogen energy storage device and the electric energy storage device in advance; the degradation model of the hydrogen energy storage device is constructed by at least related parameters of start / stop state thereof; based on power balance of the energy storage system, target function of the energy storage system about degradation degree is established according to the degradation model of the hydrogen energy storage device and the electric energy storage device; when net load electric power of the energy storage system at current time is obtained, the start / stop state of the hydrogen energy storage device and power distribution between the hydrogen energy storage device and the electric energy storage device are optimized by taking minimization of degradation degree of the energy storage system as target and substituting the net load electric power into the target function.

[0006] According to a specific embodiment of the present application, the step of constructing degradation model of the hydrogen energy storage device and the electric energy storage device in advance comprises: constructing corresponding degradation model of the hydrogen energy storage device according to its voltage drop characterization function; wherein the voltage drop characterization function of the hydrogen energy storage device comprises voltage drop caused by start / stop state thereof; constructing corresponding degradation model of the electric energy storage device according to its health state characterization function.

[0007] According to a specific embodiment of the present application, the step of constructing corresponding degradation model of the hydrogen energy storage device according to its voltage drop characterization function comprises: constructing voltage drop characterization function of the fuel cell as corresponding degradation model of the fuel cell according to voltage drop caused by start / stop state thereof, voltage drop caused by high power operation and voltage drop caused by power transient change; constructing voltage drop characterization function of the electrolytic tank as corresponding degradation model of the electrolytic tank according to voltage drop caused by start / stop state thereof, voltage drop caused by operation and voltage drop caused by power transient change.

[0008] According to a specific embodiment of the present application, the step of constructing corresponding degradation model of the electric energy storage device according to its health state characterization function comprises: constructing health state characterization function of the electric energy storage device as corresponding degradation model of the electric energy storage device according to cycle number of use thereof.

[0009] According to an embodiment of the present application, the step of establishing a target function of the energy storage system with respect to degradation degree based on power balance of the energy storage system according to degradation models of the hydrogen energy storage device and the electric energy storage device comprises: constructing the target function according to a degradation model of the fuel cell and its corresponding purchase cost, a degradation model of the electrolyzer and its corresponding purchase cost, and a degradation model of the electric energy storage device and its corresponding purchase cost.

[0010] According to an embodiment of the present application, the formula of the characterization function of the fuel cell voltage drop is as follows:

[0011] Total voltage drop: D fc (t) = D fccycle (t) + D fchigh (t) + D fcshift (t),

[0012] Voltage drop caused by start / stop state: D fccycle (t) = a fccycle | y fc (t) - y fc (t - Δt) |,

[0013] Voltage drop caused by high power operation: D

[0014] Voltage drop caused by power transient change: D fcshift (t) = a fcshift | P fc (t) - P fc (t - Δt) |,

[0015] wherein D fc (t) represents the total voltage drop of the fuel cell at the current moment, D fccycle (t) represents the voltage drop caused by the start / stop state of the fuel cell at the current moment, D fchigh (t) represents the voltage drop caused by the high power operation of the fuel cell at the current moment, D fcshift (t) represents the voltage drop caused by the power transient change of the fuel cell at the current moment, a fccycle , a fchigh , and a fcshift are the correlation coefficients of the voltage degradation of the fuel cell, y fc represents the logic variable of the start / stop state of the fuel cell, y fc is 1 if starting, and y fc is 0 if stopping, and Δt represents the time interval between the last moment and the current moment, represents the logic variable of whether the operating power of the fuel cell at the current moment is in the high power interval, and if yes, then = 1 if not = 0, P fc (t) represents the output power of the fuel cell at the current time.

[0016] According to an embodiment of the present application, the formula of the characterization function of the electrolyzer voltage drop is as follows:

[0017] Total voltage drop: D el (t) = D elcycle (t) + D elop (t) + D elshift (t),

[0018] Voltage drop caused by start / stop state: D elcycle (t) = a elcycle | y el (t) - y el (t - At) |,

[0019] Voltage drop caused by operation: D elop (t) = a elop y el (t) At,

[0020] Voltage drop caused by power transient change: D elshift (t) = a elshift | P el (t) - P el (t - At) |,

[0021] wherein D el (t) represents the total voltage drop of the electrolyzer at the current time, D elcycle (t) represents the voltage drop caused by the start / stop state of the electrolyzer at the current time, D elop (t) represents the voltage drop caused by the operation of the electrolyzer at the current time, D elshift (t) represents the voltage drop caused by the power transient change of the electrolyzer at the current time, a elcycle , a elop , a elshift are the correlation coefficients of the voltage degradation of the electrolyzer, y el represents the logic variable of the start / stop state of the electrolyzer, y el = 1 if starting, y el = 0 if stopping, At represents the time interval between the last time and the current time, P el (t) represents the input power of the electrolyzer at the current time.

[0022] According to an embodiment of the present application, the formula of the characterization function of the health state of the energy storage device is as follows:

[0023]

[0024] wherein d soh (t) represents the change of the state of health of the electrical energy storage device, SOH(t) represents the state of health of the electrical energy storage device at the current time, P bt (t) represents the input / output power of the electrical energy storage device at the current time, Δt represents the time interval between the previous time and the current time, E bt represents the capacity of the electrical energy storage device, N C represents the number of cycles of the electrical energy storage device before reaching its lifetime.

[0025] According to an embodiment of the present application, the power balance of the energy storage system is shown in the following formula:

[0026] P load (t) - P pv (t) = P bt (t) + P fc (t) - P el (t),

[0027] wherein P load (t) represents the electrical power consumed by the load at the current time, P pv (t) represents the electrical power output by the renewable energy source and input to the system, P bt (t) represents the input / output power of the electrical energy storage device at the current time, P fc (t) represents the output power of the fuel cell at the current time, P el (t) represents the input power of the electrolyzer at the current time.

[0028] According to an embodiment of the present application, the formula of the objective function is as follows:

[0029]

[0030] wherein J deg (t) represents the objective function, C fcin represents the purchase cost of the fuel cell, C elin represents the purchase cost of the electrolyzer, C btin represents the purchase cost of the electrical energy storage device, D fc (t) represents the degradation model of the fuel cell, v fceol represents the maximum voltage drop of the fuel cell before reaching its lifetime, D el (t) represents the degradation model of the electrolyzer, v eleol represents the maximum voltage drop of the electrolyzer before reaching its lifetime, d soh(t) represents a degradation model of the electrical energy storage device.

[0031] According to an embodiment of the present application, at most one of the fuel cell and the electrolyzer is in normal operation at the same time, so as to constrain the objective function.

[0032] According to an embodiment of the present application, when the net load power of the energy storage system at the current time is obtained, the step of minimizing the degradation of the energy storage system and substituting the net load power to solve the objective function so as to optimize the start / stop state of the hydrogen energy storage device and the power distribution between the hydrogen energy storage device and the electrical energy storage device comprises: minimizing the objective function based on the net load power of the energy storage system at the current time; obtaining the start / stop state of the fuel cell / electrolyzer and the corresponding input / output power of the fuel cell / electrolyzer and the input / output power of the electrical energy storage device according to the calculation result of the objective function; and optimizing the power distribution between the fuel cell / electrolyzer and the electrical energy storage device by calculating the duty cycle of the converter of the fuel cell / electrolyzer and the electrical energy storage device according to the corresponding input / output power and controlling the converter to work according to the corresponding duty cycle.

[0033] The energy management strategy provided by the present application can not only reduce the degradation of the energy storage system, but also optimize the start / stop state of the fuel cell and the electrolyzer, and maximize the reduction of the system degradation.

[0034] Meanwhile, the present application also provides another energy management strategy which can not only maximize the reduction of the equivalent hydrogen consumption of the energy storage system in the island micro-grid, but also properly control the hydrogen state of charge and the state of charge of the system.

[0035] In addition, the present application also builds a complete energy management architecture based on the two energy management strategies of the degradation of the energy storage system and the equivalent hydrogen consumption, which can not only reduce the degradation of the system, but also reduce the equivalent hydrogen consumption of the system, so as to maintain the stable and reliable operation of the system and improve the economy of the system. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 a structural block diagram of an embodiment of the energy storage system provided by the present application;

[0037] Figure 2 a flowchart of an embodiment of the energy management method based on the degradation of the energy storage system provided by the present application;

[0038] Figure 3 a flowchart of an embodiment of the energy management method based on the equivalent hydrogen consumption of the energy storage system provided by the present application;

[0039] Figure 4 A flowchart of a two-stage energy management method of an energy storage system according to an embodiment of the present application. DETAILED DESCRIPTION

[0040] Other advantages and effects of the present application can be easily understood by those skilled in the art from the description of the present application. The present application can also be implemented or applied in other different embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be understood that the preferred embodiments are only for illustrating the present application, but not for limiting the protection scope of the present application.

[0041] It should be noted that the diagrams provided in the following embodiments only schematically illustrate the basic concept of the present application, and only the components related to the present application are shown in the diagrams, but not the number, shape and size of the components when actually implemented. The actual implementation of each component can be randomly changed, and the component layout pattern can be more complex.

[0042] In the following description, a large number of details are discussed to provide a more thorough explanation of the embodiments of the present application, however, it is obvious to those skilled in the art that the embodiments of the present application can be implemented without these specific details, and in other embodiments, the structures and devices known to the public are shown in the form of block diagrams rather than in the form of details, to avoid making the embodiments of the present application difficult to understand.

[0043] First of all, it should be noted that in order for those skilled in the art to better understand the scheme of the present application, the technical background of the present application is explained accordingly.

[0044] As shown in Figure 1 The energy storage system is an important component in the island microgrid, maintaining the stable operation of the microgrid, and developing hydrogen energy to build a hybrid energy storage system. Among them, the energy storage system is composed of hydrogen energy storage devices and electric energy storage devices. In order to promote the development of green energy and fully meet the goal of "carbon peak and carbon neutral", renewable energy such as photovoltaic power generation, hydroelectric power 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 scheme provided, photovoltaic power is taken as an example in the present application as the power input of the energy storage system, but the type of renewable energy is not limited, and other renewable energy can be used as the power input in actual application.

[0045] Generally, in the energy storage system, the photovoltaic generator, i.e., the photovoltaic power supply, operates in a maximum power point tracking mode to provide energy for the system and the load through a Boost converter. Meanwhile, the hydrogen energy storage device needs to have the ability to produce, store 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 for producing, storing and consuming hydrogen respectively, and the electrolyzer obtains energy from the system through a Buck converter to produce hydrogen, and the fuel cell consumes hydrogen and provides energy for the system through a Boost converter. The electric energy storage device can be composed of one or more of the energy storage devices with better power characteristics than hydrogen energy storage, such as supercapacitors and / or batteries, and provides energy for the system or obtains energy from the system through a bidirectional Buck-Boost converter, which is not limited.

[0046] Further, the net load power of the system is composed of 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 to charge, and the electrolyzer starts to work to produce hydrogen to reserve hydrogen energy or for sale. When the load consumption power exceeds the photovoltaic power generation power, the net load power of the system is in a deficiency state, which can be compensated by the hydrogen energy storage device and the electric energy storage device, for example, battery discharge power supply and fuel cell hydrogen consumption discharge power supply, so as to maintain the balance and stability of the system.

[0047] Based on the above energy storage system, the present application provides various energy management strategies to assist the sustainable operation of the system, thereby improving the reliability and economy of the energy storage system.

[0048] Embodiment 1

[0049] Please refer to Figure 2 An energy management method based on the degradation degree of the energy storage system is shown, which comprises:

[0050] Step S110, a degradation model of the hydrogen energy storage device and the electric energy storage device is constructed in advance; wherein the degradation model of the hydrogen energy storage device is constructed by at least related parameters thereof about start / stop state.

[0051] Step S120, based on the power balance of the energy storage system, a target function of the energy storage system about degradation degree is established according to the degradation model of the hydrogen energy storage device and the electric energy storage device.

[0052] Step S130, when the net load electric power of the energy storage system at the current time is obtained, the degradation degree of the energy storage system is minimized as the target, and the net load electric power is substituted into the target function 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.

[0053] Firstly, the hydrogen energy storage device is composed of fuel cell, electrolyzer, and hydrogen storage tank, which requires to build the degradation model respectively. It can be understood that the hydrogen storage tank is only used to store hydrogen, and the degradation degree is only affected by aging, so it does not participate in the subsequent degradation degree analysis and the construction of the degradation model.

[0054] For this, the degradation of fuel cell (FC) can be characterized by the decline of its voltage, and the decline of voltage can be further decomposed into voltage drop (D fchigh (t)) caused by high-power operation and voltage drop (D fcshift (t)) caused by power transient change, and after ignoring the coupling between voltage drops, the characterization function of FC about voltage drop is as follows:

[0055] D fc (t) = D fchigh (t) + D fcshift (t),

[0056] and this is used as the degradation model of FC. However, in this embodiment, considering that the instability of photovoltaic power supply will cause the FC to start and stop frequently, thereby accelerating the degradation degree of FC. Therefore, on the basis of D fchigh (t) and D fcshift (t), the voltage drop (D fccycle (t)) caused by start / stop state is also added to characterize the voltage drop of FC, and the characterization function of FC about voltage drop can be adjusted as follows:

[0057] D fc (t) = D fccycle (t) + D fchigh (t) + D fcshift (t),

[0058] It can be understood here that the instability of photovoltaic power supply will cause the net load power of the system to frequently switch between surplus and deficiency, and the surplus of net load power will use the electrolyzer to prepare hydrogen, and the deficiency of net load power will use the fuel cell to consume hydrogen to release energy. And in order to ensure the stability and balance of the system, the electrolyzer and the fuel cell try not to work at the same time, so that the FC will continue to switch between start and stop. Specifically, when there is energy surplus in the net load of the system, the electrolyzer starts to run to consume the surplus energy. When there is energy shortage, the fuel cell is started to make up the shortage of energy. When the net load of the system changes frequently, the hydrogen energy storage device may start or stop frequently, thereby accelerating the degradation.

[0059] Therefore, in order to optimize the start-stop state of the FC to minimize its degradation, the characterization function of the FC with respect to the voltage drop preferably adopts the latter.

[0060] Among them, the characterization function of the voltage drop (D fccycle (t)) of the FC caused by the start-stop state is:

[0061] D fccycle (t) = a fccycle |y fc (t) - y fc (t - Δt)|,

[0062] The characterization function of the voltage drop (D fchigh (t)) of the FC caused by high-power operation is:

[0063]

[0064] The characterization function of the voltage drop (D fcshift (t)) of the FC caused by power transient change is:

[0065] D fcshift (t) = a fcshift |P fc (t) - P fc (t - Δt)|,

[0066] In the above formula, a fccycle , a fchigh , a fcshift are the correlation coefficients of the voltage degradation of the FC.

[0067] And, in order to represent the start-stop state of the FC, a logical variable y fc is defined (when the net load electric power of the system is missing, that is, corresponding to the start of the FC, y fc is 1, otherwise 0, that is, corresponding to the stop of the FC).

[0068] At the same time, in order to represent whether the FC is located in the high-power interval, a logical variable is defined (when the operating power of the FC at the current moment is located in the high-power interval, y is 1, otherwise y is 0).

[0069] Δt represents the time interval between the last moment and the current moment. It should be noted that energy management can be performed at any moment according to the net load electric power of the system, and continues to the next moment when energy management is performed again. The interval between the two moments is the time interval Δt mentioned above.

[0070] P fc(t) represents the operating power of FC, i.e. the output power at the current time, and the upper and lower limits of the operating power of FC are as follows:

[0071] y fc (t) P fcmin ≤ P fc (t) ≤ y fc (t) P fcmax ,

[0072] and P fcmin and P fcmax correspond to the minimum and maximum power of FC, respectively.

[0073] The degradation of the electrolyzer (EL) can also be characterized by the decrease of its voltage, and the decrease of voltage can be decomposed into the voltage drop (D elop (t)) caused by operation and the voltage drop (D elshift (t)) caused by power transient change, and after ignoring the coupling between the voltage drops, the characterization function of EL with respect to voltage drop is as follows:

[0074] D el (t) = D elop (t) + D elshift (t),

[0075] which can be used as a degradation model of EL. Similarly, considering the start-stop state of EL, the voltage drop D elop (t) caused by the start-stop state is added to the above D elshift (t) and D elcycle (t) to jointly characterize the voltage drop of EL, and the corresponding characterization function of EL with respect to voltage drop can be adjusted as follows:

[0076] D el (t) = D elcycle (t) + D elop (t) + D elshift (t),

[0077] Among them, the characterization function of the voltage drop D elcycle (t) of EL caused by the start-stop state is:

[0078] D elcycle (t) = a elcycle |y el (t) - y el (t - At) |,

[0079] The characterization function of the voltage drop D elop (t) of EL caused by operation is:

[0080] D elop (t) = aelop y el (t)Δt,

[0081] EL voltage drop D caused by power transient elshift (t) is a function of:

[0082] D elshift (t) = a elshift |P el (t) - P el (t - At) |,

[0083] In the above formula, a elcycle , a elop , a elshift are the correlation coefficients of EL voltage degradation.

[0084] Similarly, to represent the start-stop state of the EL, a logic variable y el is defined (when the net load power of the system is surplus, i.e. corresponding to the start of the EL y el is 1, otherwise 0, i.e. corresponding to the stop of the EL).

[0085] P el (t) represents the operating power of the EL, i.e. the input power at the current time, and the upper and lower limits of the operating power of the EL are as follows:

[0086] y el (t) P elmin ≤ P el (t) ≤ y el (t) P elmax ,

[0087] and P elmin and P elmax correspond to the minimum and maximum power of the EL respectively.

[0088] In this embodiment, the electrical energy storage device is taken as an example of a battery to illustrate the technical solutions. The degradation of the battery (BT) can be represented by its state of health (SOH). The SOH of the battery can be represented as:

[0089]

[0090] where d soh (t) represents the change in SOH, SOH(t) represents the state of health of the battery at the current time, P bt (t) represents the input / output power of the battery at the current time, E bt represents the capacity of the battery, and N C represents the number of cycles before the battery reaches its service life.

[0091] In addition, the energy storage system also needs to meet the law of conservation of energy, that is, to maintain energy balance. For this, the fuel cell, electrolyzer, and battery need to meet the following power balance:

[0092] P load (t)-P pv (t) = P bt (t) + P fc (t)-P el (t),

[0093] where P load (t) represents the electric power required by the load at the current time, that is, the load consumption power, P pv (t) represents the electric power output by the renewable energy source and input to the system, that is, the electric power output by the photovoltaic power source at the current time (photovoltaic power generation power).

[0094] Based on the power balance of the above system and the degradation model of each component, the objective function J deg (t) can be constructed as follows:

[0095]

[0096] In the above formula, C fcin , C elin , and C btin represent the purchase costs of FC, EL, and BT, respectively, v fceol represents the maximum voltage drop of FC before reaching its service life, and v eleol represents the maximum voltage drop of EL before reaching its service life.

[0097] Therefore, the three terms in the above formula represent the degradation costs of FC, EL, and BT within a certain time, respectively. Considering the economy of the energy storage system, the degradation cost of the system should be minimized, that is, the degradation degree of the system should be minimized.

[0098] At the same time, in order to ensure the stable operation of the system, it is assumed that only one of FC and EL operates at any time, that is, it satisfies:

[0099] y fc (t) + y el (t) ≤ 1,

[0100] For this, based on the net load electric power at the current time of the system, the objective function J deg(t) the input / output power of FC, EL and BT at the current time can be calculated accordingly. Finally, the Boost converter of FC or the Buck converter of EL and the bidirectional Buck-Boost converter of BT can be controlled according to the corresponding input / output power, i.e. the duty cycle of the converter is calculated according to the input / output power, so as to realize the power distribution of the system. At this point, since at most one of the fuel cell and the electrolyzer is running, the excess electric power can be distributed to the electrolyzer to prepare hydrogen and / or the battery to charge and store energy when the net load electric power is in surplus, or the fuel cell can be controlled to consume hydrogen to release energy and / or the battery can be controlled to discharge to supply energy to make up for the part of the net load electric power when the net load electric power is in shortage.

[0101] Therefore, the above energy management strategy not only can reduce the degradation degree of the energy storage system, but also can optimize the start-stop state of the fuel cell and the electrolyzer, maximize the reduction of system degradation, ensure the sustainable operation of the system, and accordingly improve the economy of the system.

[0102] Embodiment 2

[0103] Please refer to Figure 3 The energy management method of the energy storage system comprises the following steps:

[0104] In step S210, a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device are constructed in advance; wherein the hydrogen consumption model of the hydrogen energy storage device is constrained according to the hydrogen state of charge of the hydrogen energy storage device, 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.

[0105] In step S220, based on the power balance of the energy storage system, a target function of the energy storage system about 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.

[0106] In step S230, when the net load electric power of the energy storage system at the current time is obtained, the power distribution between the hydrogen energy storage device and the electric energy storage device is optimized by taking the minimization of the equivalent hydrogen consumption of the energy storage system as the target and substituting the net load electric power into the target function.

[0107] Firstly, the hydrogen consumption models of the fuel cell and the electrolyzer, and the equivalent hydrogen consumption model of the battery are constructed, and the hydrogen storage tank does not generate actual hydrogen consumption or equivalent hydrogen consumption, but only stores hydrogen, and accordingly does not participate in the subsequent equivalent hydrogen consumption analysis and model construction.

[0108] For this purpose, FC needs to consume hydrogen to release energy, and accordingly the hydrogen consumption function H fc (t) as follows:

[0109]

[0110] In the above formula, M H represents the molar mass of hydrogen, n c represents the number of monomers of FC, z represents the number of electrons moving in FC, and F represents the Faraday constant.

[0111] P fc (t) represents the operating power of FC, i.e. the output power at the current moment, and the upper and lower limits of the operating power of FC are as follows:

[0112] P fcmin ≤P fc (t)≤P fcmax , and P fcmin and P fcmax correspond to the minimum and maximum power of FC, respectively.

[0113] v fc (t) represents the voltage of FC at the current moment.

[0114] It can be seen that the hydrogen consumption of fuel cell, i.e. the degree of hydrogen consumption, is closely related to the output electric power and voltage.

[0115] Further, EL needs to use energy production to prepare hydrogen, and the hydrogen production function H el of EL can be constructed accordingly as follows:

[0116]

[0117] In the above formula, η F (t) represents the Faraday efficiency, n s represents the number of monomers of EL, and F represents the Faraday constant.

[0118] P el (t) represents the operating power of EL, i.e. the input power at the current moment, and the upper and lower limits of the operating power of EL are as follows:

[0119] P elmin ≤P el (t)≤P elmax , and P elmin and P elmax correspond to the minimum and maximum power of EL, respectively.

[0120] v el (t) represents the voltage of EL at the current moment.

[0121] It can be seen that the hydrogen production of electrolytic cell, i.e. the equivalent degree of hydrogen consumption, is closely related to the input electric power and voltage.

[0122] Based on this, the hydrogen production function H elAnd the hydrogen production function H of EL el A hydrogen consumption model for a hydrogen energy storage device is constructed. Furthermore, although the hydrogen storage tank is not included in the equivalent hydrogen consumption analysis, the hydrogen produced by the electrolyzer needs to be stored in the storage tank, and the storage capacity and internal pressure that the tank can withstand have certain upper limits. Therefore, to reflect the level of hydrogen stored in the hydrogen storage tank (HST), a state of hydrogen charge (SOHC) is defined to constrain the aforementioned hydrogen consumption model, preventing the storage tank from failing to store enough hydrogen and thus becoming unusable.

[0123] The HST SOHC real-time mapping function is as follows:

[0124] and

[0125]

[0126] Where, n int This refers to the amount of hydrogen initially stored in HST, while n hst (t) reflects the real-time hydrogen quantity at HST, p hst (t) represents the pressure of HST, while p max R represents the maximum pressure that HST can withstand. hst T hst V hst These are the gas constant, temperature, and volume, respectively.

[0127] Therefore, it can be seen that constraining the hydrogen consumption model through the SOHC of the hydrogen storage tank corresponds to constraining the hydrogen consumption function H. fc (t) and hydrogen production function H el This avoids excessive hydrogen production by the EL and insufficient hydrogen consumption by the FC.

[0128] While batteries do not actually produce or consume hydrogen, they can provide or consume energy. Therefore, the electrical power output or input of a battery can be considered as equivalent hydrogen consumption, and the corresponding formula for the equivalent hydrogen consumption model is as follows:

[0129] H bt =P bt (t) / LHV,

[0130] Where LHV represents the lower heating value of hydrogen, and P bt (t) represents the input / output power of BT at the current moment, and its upper and lower limits are as follows: -P btmaxc ≤P bt (t)≤P btmaxd When the battery discharges, P bt (t)>0, P btmaxd For maximum discharge power, P during chargingbt (t) < 0, P btmaxc is the maximum charging power.

[0131] In addition, in order to maintain the stability and balance of the battery state of charge (SOC), the corresponding equivalent hydrogen consumption model of the battery is also constrained by the SOC of the battery to avoid excessive discharge or excessive charge of the battery and affect the service life of the battery.

[0132] For this purpose, the real-time mapping function of the SOC of the BT is as follows:

[0133]

[0134] wherein, SOC init is the initial SOC of the battery, i.e. the electric quantity, Q bt represents the charge quantity of the battery, i bt represents the input / output current of the battery.

[0135] Therefore, based on the charge quantity of the battery and the size of the input / output current at the current time, and the initial electric quantity, the real-time SOC can be calculated accordingly to constrain the SOC of the battery within a predetermined range interval, 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 SOC of the battery remains stable at all times.

[0136] Similarly, the fuel cell, the electrolytic tank, and the battery need to satisfy the following power balance:

[0137] P load (t) - P pv (t) = P bt (t) + P fc (t) - P el (t),

[0138] Based on the power balance of the above system, and 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 hy (t) can be constructed as follows:

[0139] J hy (t) = ω bt (t) H bt (t) Δt + ω hy (t) [H fc (t) - H el (t)] Δt,

[0140] wherein, the hydrogen consumption model constructed based on the hydrogen consumption function of the FC and the hydrogen production function of the EL is H fc (t) - H el (t), ω bt (t) and ωhy (t) are two weight parameters introduced to represent the contribution of the electric energy storage device and the hydrogen energy storage device to the equivalent hydrogen consumption of the system, which are determined by the artificial potential field to calculate the virtual force of the electric energy storage device and the hydrogen energy storage device, respectively, as follows:

[0141] ω bt (t) = 1 - F bt (t),

[0142] ω hy (t) = 1 - F hy (t),

[0143] where F bt (t) is the virtual force related to the SOC of the electric energy storage device, and F hy (t) is the virtual force related to the SOHC of the hydrogen energy storage device.

[0144] It should be noted that the virtual force is defined in the context of the "artificial potential field", which was originally proposed for robot applications and recently applied to renewable energy systems. The artificial potential field is widely used in multi-agent formation control, in which multiple agents must maintain a reference distance to form a stable formation. By this method, an artificial potential field can be constructed, and the force function between any two agents in the artificial potential field, also known as the action function. When the distance between two agents is equal to the reference value, no force is generated between them, i.e. the potential energy is zero. When they are close to each other, there is a large repulsive force; while when they are far away from each other, there is a large attractive force. This high potential energy (i.e. repulsive or attractive force) can ensure that their distance quickly converges to the reference value. For example, when the SOC of the electric energy storage device is high, there is an attractive force to reduce the SOC, and when the SOC is low, there is an attractive force to increase the SOC, and when the SOC is close to or equal to the reference value, the above phenomenon can be effectively reduced, i.e. the virtual force corresponding to the battery SOC, to maintain the SOC of the electric energy storage device in a stable state. Similarly, the same applies to the SOHC of the hydrogen energy storage device.

[0145] Therefore, the virtual force related to the SOC of the electric energy storage device is defined as follows:

[0146]

[0147] where x1(t) = SOC(t) - SOC mid , and SOC mid is a set value between the minimum value SOC min and the maximum value SOC max of the SOC of the electric energy storage device, so as to expect the SOC of the electric energy storage device to run at this value, and u1 is a coefficient for shaping the virtual force curve of the electric energy storage device.

[0148] Similarly, the virtual force related to the hydrogen storage device, i.e. HST, is defined as follows:

[0149]

[0150] where x2(t) = SOHC(t) - SOHC mid , and SOHC mid is a set value between the minimum value SOHC min and the maximum value SOHC max of the SOHC of the hydrogen storage device, so as to expect the SOHC of the hydrogen storage device to operate at the value, and u2 is a coefficient for shaping the virtual force curve of the hydrogen storage device.

[0151] In a specific embodiment, SOC min and SOHC min may be set to 30%, SOC max and SOHC max may be set to 90%, and SOC mid and SOHC mid may be set to 60% for calculation. Correspondingly, based on the net load electric power of the system at the current time, and the objective function is minimized, the input power of the FC at the current time and the output power of the EL at the current time, and the input / output power of the BT at the current time can be calculated. Finally, the Boost converter of the FC or the Buck converter of the EL, and the bidirectional Buck-Boost converter of the BT can be controlled according to the corresponding input / output power, that is, the duty cycle of the converter is calculated according to the input / output power, so as to realize the power distribution of the system.

[0152] As can be seen, the above energy management strategy not only can minimize the equivalent hydrogen consumption of the energy storage system in the island micro-grid, but also can properly control the SOHC and SOC of the system, so as to maintain the stable and reliable operation of the system.

[0153] Embodiment 3

[0154] In summary, the above two embodiments respectively adopt different energy management strategies for assisting the energy storage system to coordinate the fuel cell, the electrolyzer, and the battery. Of course, a complete energy management framework can also be built by combining the above two strategies, so as to further improve the reliability of the strategy.

[0155] For this purpose, please refer to a two-stage energy management method of an energy storage system shown in Figure 4 , which comprises:

[0156] Step S311, a degradation model of the hydrogen storage device and the electric energy storage device is constructed in advance.

[0157] Step S312, based on the power balance of the energy storage system, a first objective function of the energy storage system about the degradation degree is established according to the degradation models of the hydrogen energy storage device and the electric energy storage device.

[0158] Step S321, a hydrogen consumption model of the hydrogen energy storage device and an equivalent hydrogen consumption model of the electric energy storage device are pre-constructed.

[0159] 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, and a preset weight between the degradation degree and the equivalent hydrogen consumption of the energy storage system.

[0160] Step S330, the net load electric power of the energy storage system at the current time is obtained.

[0161] Step S340, the first objective function is solved by substituting the net load electric power, with the goal of minimizing the degradation degree of the energy storage system, to calculate the reference power of the hydrogen energy storage device and the electric energy storage device.

[0162] Step S350, the second objective function is solved based on the reference power of the hydrogen energy storage device and the electric energy storage device, with the goal of minimizing the equivalent hydrogen consumption of the energy storage system, to calculate the input / output power of the hydrogen energy storage device and the electric energy storage device.

[0163] Step S360, the power distribution between the hydrogen energy storage device and the electric energy storage device is adjusted according to the corresponding input / output power.

[0164] Firstly, based on the degradation models of the fuel cell, the electrolyzer and the battery provided in Embodiment 1, a first objective function J deg (t) is constructed to achieve first-level energy management, i.e., to minimize the degradation degree of the system.

[0165] It should be noted that in Embodiment 1, the fuel cell and the electrolyzer are respectively provided with two kinds of degradation models, one of which does not contain the voltage drop caused by the start / stop state, and the other of which contains the voltage drop caused by the start / stop state. Therefore, the first objective function constructed can be divided into the following two categories:

[0166] First category: and

[0167] D fc (t) = D fchigh (t) + D fcshift (t), D el (t) = D elop (t) + Delshift (t),

[0168] The second type is: and

[0169] D fc (t) = D fccycle (t) + D fchigh (t) + D fcshift (t), D el (t) = D elcycle (t) + D elop (t) + D elshift (t)

[0170] The above two first objective functions can be used to optimize the degradation of the system. For example, the first objective function of the first type can be used to reduce the degradation of the system without considering the optimization of the start-stop state of the fuel cell and the electrolytic cell, or the first objective function of the second type can be used for energy management to maximize the reduction of the degradation of the system. The specific selection and trade-off can be made according to the actual situation, and no more limitation is made, and only two selection schemes are provided.

[0171] Further, based on the net load electric power of the system at the current time, the reference power of FC, EL and BT at the current time can be calculated correspondingly after minimizing the first objective function J deg (t).

[0172] Secondly, based on the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device provided in embodiment 2, a second objective function J hy (t) can be constructed to realize 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 to obtain the final input / output power of the hydrogen energy storage device and the electric energy storage device.

[0173] For this purpose, in order to integrate the two strategies to reduce the equivalent hydrogen consumption while reducing the degradation of the system, the weight between the degradation and the equivalent hydrogen consumption can be adjusted accordingly, and then the second objective function J hy (t) can be constructed based on different weights of the degradation and the equivalent hydrogen consumption.

[0174] It should be further pointed out that in embodiment 2, in order to synchronously maintain the SOHC of the hydrogen energy storage device and the SOC of the electric energy storage device stable, two weight parameters ω bt (t) and ω hy (t) are introduced to represent the contribution of the electric energy storage device and the hydrogen energy storage device to the equivalent hydrogen consumption of the system, so that the SOHC and SOC of the system can be properly controlled while the equivalent hydrogen consumption of the system is maximized. Therefore, when constructing the second objective function, it can also be divided into the following two types, and the specific formula is as follows:

[0175] The first type:

[0176] 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 ],

[0177] The second type:

[0178] 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 ],

[0179] wherein 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 time, P fcr (t) represents the reference power of the fuel cell, P el (t) represents the input power of the electrolyzer at the current time, P elr (t) represents the reference power of the electrolyzer.

[0180] Similarly, the above two second target functions represent the equivalent hydrogen consumption of the system, in order to reduce the equivalent hydrogen consumption of the system as much as possible, it is also necessary to minimize the hydrogen consumption parameter of the hydrogen storage energy device and the equivalent hydrogen consumption parameter of the electric storage energy device. At the same time, on the basis of the above, it is also necessary to minimize the deviation between the input / output power of the hydrogen storage energy device and the corresponding reference power, that is, minimize the deviation between the output power calculated by the second target function and the reference power calculated by the first target function of the FC, and the deviation between the input power calculated by the second target function and the reference power calculated by the first target function of the EL, so as to optimize the input / output power of the FC and the EL by calculating the reference power by the first target function. Therefore, by minimizing the second target function, the above-mentioned target can be achieved, and the input / output power of the FC and the EL at the current time can be calculated. It can also be understood that based on the power balance of the system, when the input / output power of the FC and the EL is determined, the input / output power of the BT is also determined.

[0181] Finally, the Boost converter of the FC, the Buck converter of the EL and the bidirectional Buck-Boost converter of the BT can be controlled according to the corresponding input / output power, that is, the duty ratio of the converter is calculated according to the input / output power, so as to complete the power distribution of the system, and realize the two-stage energy management based on the degradation degree and the equivalent hydrogen consumption.

[0182] It should be noted that the step division of the above methods is only for clear description, and can be combined into one step or split into multiple steps in implementation, as long as the same logical relationship is included, and all are within the protection scope of the patent. Adding irrelevant modifications or introducing irrelevant designs in the algorithm or process, but not changing the core design of the algorithm and process, are within the protection scope of the patent.

[0183] In summary, the energy management strategy provided by the application not only reduces the degradation degree of the energy storage system, but also optimizes the start-stop state of the fuel cell and the electrolytic tank, and maximizes the reduction of system degradation.

[0184] Meanwhile, the application also provides another energy management strategy which can maximize the reduction of the equivalent hydrogen consumption of the energy storage system in the island micro-grid, and also properly controls the hydrogen state of charge and the state of charge of the system.

[0185] In addition, the application also builds a complete energy management architecture based on the two energy management strategies of the degradation degree and the equivalent hydrogen consumption of the energy storage system, which not only reduces the degradation degree of the system, but also reduces the equivalent hydrogen consumption of the system, so as to maintain the stable and reliable operation of the system, and accordingly improves the economy of the system.

[0186] The above embodiments merely illustrate the principles of the present application and its effects, and are not intended to limit the present application. Any modification or change made by any person skilled in the art without departing from the spirit and scope of the present application shall be covered by the claims of the present application.

Claims

1. An energy management method based on the degradation level of an energy storage system, characterized in that, The energy storage system comprises an electrical energy storage device and a hydrogen energy storage device; wherein the electrical 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 energy management method includes: A degradation model for the hydrogen energy storage device and the electrical energy storage device is pre-constructed; wherein, the degradation model for the hydrogen energy storage device is constructed at least by its relevant parameters with respect to start / stop states; Based on the power balance of the energy storage system, an objective function of the energy storage system with respect to the degree of degradation is established according to the degradation models of the hydrogen energy storage device and the electric energy storage device. When the net load power of the energy storage system at the current moment is obtained, the objective function is analyzed by substituting the net load power with the goal of minimizing the degradation of the energy storage system, so as 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. The objective function is formulated as follows: And J deg (t) represents the objective function, C fcin C represents the purchase cost of the fuel cell. elin C represents the purchase cost of the electrolytic cell. btin D represents the purchase cost of the energy storage device. fc (t) represents the degradation model of the fuel cell, v fceol D represents the maximum voltage drop of the fuel cell before it reaches the end of its service life. el (t) represents the degradation model of the electrolytic cell, v eleol d represents the maximum voltage drop of the electrolytic cell before it reaches the end of its service life. soh (t) represents the degradation model of the energy storage device.

2. The energy management method based on the degradation level of the energy storage system according to claim 1, characterized in that, The steps of pre-constructing degradation models for the hydrogen energy storage device and the electrical energy storage device include: A degradation model is constructed based on the characterization function of the voltage drop of the hydrogen energy storage device; wherein, the characterization function of the hydrogen energy storage device includes the voltage drop caused by the start / stop state; A degradation model is constructed based on the health status representation function of the energy storage device.

3. The energy management method based on the degradation level of the energy storage system according to claim 2, characterized in that, The steps for constructing the corresponding degradation model based on the characterization function of the voltage drop of the hydrogen energy storage device include: A voltage drop characterization function is constructed based on the voltage drop caused by the start / stop state, the voltage drop caused by high power operation, and the voltage drop caused by power transient changes, which serves as the corresponding degradation model for the fuel cell; A voltage drop characterization function is constructed based on the voltage drop caused by the start / stop state, the voltage drop caused by operation, and the voltage drop caused by power transient changes in the electrolytic cell, which serves as the degradation model corresponding to the electrolytic cell.

4. The energy management method based on the degradation level of the energy storage system according to claim 3, 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 fccycle (t)+D fchigh (t)+D fcshift (t), Regarding the voltage drop caused by start / stop states: D fccycle (t)=α fccycle |y fc (t)-y fc (t-Δt)|, Regarding voltage drop caused by high-power operation: Regarding the voltage drop caused by power transients: D fcshift (t)=α fcshift |P fc (t)-P fc (t-Δt)|, Among them, D fc (t) represents the total voltage drop of the fuel cell at the current moment, D fccycle (t) represents the voltage drop of the fuel cell caused by the start / stop state at the current moment, D fchigh (t) represents the voltage drop caused by the fuel cell operating at high power at the current moment, D fcshift (t) represents the voltage drop of the fuel cell caused by the power transient change at the current moment, α fccycle α fchigh α fcshift y is the correlation coefficient for the voltage degradation of the fuel cell. fc A logical variable representing the start / stop state of the fuel cell; if it is started, then y fc If y is 1, then if it stops, then y fc The value is 0, where Δt represents the time interval between the previous moment and the current moment. A logical variable indicating whether the current operating power of the fuel cell is in the high-power range; if so, then... =1, otherwise P is 0 fc (t) represents the output power of the fuel cell at the current moment.

5. The energy management method based on the degradation level of the energy storage system according to claim 3, characterized in that, The formula for the characterization function of the voltage drop in the electrolytic cell is as follows: Total voltage drop: D el (t)=D elcycle (t)+D elop (t)+D elshift (t), Regarding the voltage drop caused by start / stop states: D elcycle (t)=α elcycle |y el (t)-y el (t-Δt)|, Regarding the voltage drop caused by operation: D elop (t)=α elop y el (t)Δt, Regarding the voltage drop caused by power transients: D elshift (t)=α elshift |P el (t)-P el (t-Δt)|, Among them, D el (t) represents the total voltage drop of the electrolytic cell at the current moment, D elcycle (t) represents the voltage drop of the electrolytic cell caused by the start / stop state 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 in the electrolytic cell caused by the transient power change at the current moment, α elcycle α elop α elshift y is the correlation coefficient for the voltage degradation of the electrolytic cell. el A logical variable representing the start / stop state of the electrolytic cell; if started, then y el If y is 1, then if it stops, then y el P is 0, where Δt represents the time interval between the previous moment and the current moment. el (t) represents the input power of the electrolytic cell at the current moment.

6. The energy management method based on the degradation level of the energy storage system according to claim 2, characterized in that, The formula for the health status characteristic function of the energy storage device is as follows: Where, d soh (t) represents the change in the health status of the energy storage device, SOH(t) represents the current health status of the energy storage device, and P bt (t) represents the current input / output power of the energy storage device, Δt represents the time interval between the previous moment and the current moment, and E bt N represents the capacity of the energy storage device. C This indicates the number of cycles before the energy storage device reaches its service life.

7. The energy management method based on the degradation level of the 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 electrical power that the load needs to consume at the current moment, P pv (t) represents the electrical power generated from renewable energy sources and input into the system, P bt (t) represents the current input / output power of the energy storage device, P fc (t) represents the current output power of the fuel cell, P. el (t) represents the input power of the electrolytic cell at the current moment.

8. The energy management method based on the degradation level of the energy storage system according to claim 1, characterized in that, At any given time, at most one of the fuel cell and the electrolyzer is operating normally, in order to constrain the objective function.

9. The energy management method based on the degradation level of the energy storage system according to claim 1, characterized in that, When the net load power of the energy storage system at the current moment is obtained, the steps of optimizing the start / stop state of the hydrogen energy storage device and the power distribution between the hydrogen energy storage device and the electrical energy storage device, with the goal of minimizing the degradation of the energy storage system and substituting the net load power into the objective function, include: Minimize the objective function based on the current net load power of the energy storage system; Based on the calculation results of the objective function, the start-up and shutdown states of the fuel cell / electrolyzer and their corresponding input / output power, as well as the input / output power of the energy storage device, are obtained; Based on the corresponding input / output power, the duty cycle of the converters of the fuel cell / electrolyzer and the energy storage device is calculated, and the converters are controlled to operate according to the corresponding duty cycle, so as to optimize the power distribution between the fuel cell / electrolyzer and the energy storage device.

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