Energy management method based on equivalent hydrogen consumption of energy storage system

Abstract

The invention belongs to the technical field of energy storage, and particularly relates to an energy management method based on equivalent hydrogen consumption of an energy storage system, which comprises the following steps of: pre-constructing a hydrogen consumption model of a hydrogen energy storage device and an equivalent hydrogen consumption model of an electric energy storage device; wherein the hydrogen consumption model and the equivalent hydrogen consumption model are respectively constrained according to the hydrogen charge state and the charge state; based on the power balance of the energy storage system, establishing an objective function of the energy storage system about equivalent hydrogen consumption according to the hydrogen consumption model and the equivalent hydrogen consumption model; and when the net load electric power of the energy storage system at the current moment is obtained, taking the minimum equivalent hydrogen consumption of the energy storage system as a target, and substituting the target function into the net load electric power to analyze the target function so as to optimize the power distribution between the hydrogen energy storage device and the electric energy storage device. According to the method, the equivalent hydrogen consumption of the energy storage system can be reduced to the maximum extent, the hydrogen charge state of the hydrogen energy storage device and the charge state of the electric energy storage device are properly controlled, and sustainable and stable operation of the energy storage system is maintained.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and in particular relates to an energy management method based on equivalent hydrogen consumption of an energy storage system. Background Art

[0002] With the increasing development of renewable energy, energy storage has become an important component of the power system. Moreover, as one of the most promising solutions to adapt to the intermittent and uncertain nature of renewable energy, energy storage is widely used to improve the stability and economy of the system. Electric energy storage is suitable for short-term (i.e., a few hours to a few days) and small and medium-sized energy storage applications. Among them, supercapacitors and batteries are usually used as short-term electric energy storage devices to store energy. Supercapacitors mainly include double-layer capacitors, lithium-ion capacitors, sodium-ion capacitors and other types. Batteries mainly include lithium-ion batteries, sodium-ion batteries, lithium metal batteries, semi-solid batteries, solid-state batteries and other types. Electric energy storage devices such as batteries and supercapacitors have significant advantages 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 devices such as electrolyzers, fuel cells, and hydrogen storage tanks to convert electrical energy into hydrogen energy storage, and convert hydrogen energy into electrical energy utilization. Hydrogen energy storage has significant advantages in energy density. Considering the differences between electric 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 study.

[0003] Therefore, in order to fully utilize the complementary characteristics of electric energy storage and hydrogen energy storage technologies, it is urgent to design appropriate energy management strategies to ensure the stable and efficient operation of the energy storage system. At present, although a series of progress has been made in the research on equivalent hydrogen consumption in the energy management strategy of energy storage systems, in the energy management process, it is also necessary to properly control the state of charge of electric energy storage and the hydrogen state of charge of hydrogen energy storage to maintain the stability of the system. How to maintain the stability of the state of charge of electric energy storage and the hydrogen state of charge of hydrogen energy storage in the design of an energy management strategy for equivalent hydrogen consumption optimization has become a challenge. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to propose an equivalent hydrogen consumption minimization strategy to improve the economy of the system by minimizing the equivalent hydrogen consumption of the hybrid energy storage system and maintaining the hydrogen state of charge and charge state stability of the energy storage system.

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention provides an energy management method based on equivalent hydrogen consumption of an energy storage system, wherein 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 energy management method comprises: 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, constraining the hydrogen consumption model of the hydrogen energy storage device according to the hydrogen state of charge of the hydrogen energy storage device, and constraining the equivalent hydrogen consumption model of the electric energy storage device according to the state of charge of the electric energy storage device; based on the power balance of the energy storage system, establishing the objective function of the energy storage system regarding equivalent hydrogen consumption according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device; when obtaining the net load electric power of the energy storage system at the current moment, minimizing the equivalent hydrogen consumption of the energy storage system is taken as the goal, and substituting the net load electric power into the objective function to analyze the objective function, so as to optimize the power distribution between the hydrogen energy storage device and the electric energy storage device.

[0006] According to a specific embodiment of the present invention, the step of pre-constructing the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electrical energy storage device includes: 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.

[0007] According to a specific embodiment of the present invention, the formula of the fuel cell hydrogen consumption function is as follows:

[0008]

[0009] Among them, M H represents the molar mass of hydrogen, n c represents the number of monomers of the fuel cell, P fc (t) represents the electric power outputted by the fuel cell at the current moment, z represents the number of electrons moving in the fuel cell, F represents the Faraday constant, v fc (t) represents the voltage of the fuel cell at the current moment.

[0010] According to a specific embodiment of the present invention, the formula of the electrolyzer hydrogen production function is as follows:

[0011] The formula for the number is as follows:

[0012]

[0013] Among them, η F (t) represents the Faraday efficiency, n s represents the number of cells in the electrolytic cell, P el (t) represents the electric power input to 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.

[0014] According to a specific embodiment of the present invention, the step 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 includes: constructing the corresponding equivalent hydrogen consumption model according to the electric power input / output of the electric energy storage device.

[0015] According to a specific embodiment of the present invention, the formula of the equivalent hydrogen consumption model of the electric energy storage device is as follows:

[0016] H bt =P bt (t) / LHV,

[0017] Among them, P bt (t) represents the electric power input / output of the electric energy storage device at the current moment, and LHV represents the lower heating value of hydrogen.

[0018] According to a specific embodiment of the present invention, based on the power balance of the energy storage system, the step of establishing the objective function of the energy storage system regarding equivalent hydrogen consumption according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device includes: using an artificial potential field to determine the virtual force of the hydrogen energy storage device regarding the hydrogen state of charge, and the virtual force of the electric energy storage device regarding the state of charge, and use them as weight parameters of the hydrogen consumption model and the equivalent hydrogen consumption model, respectively; constructing the objective function according to the hydrogen consumption model of the hydrogen energy storage device and its corresponding weight parameters, and the equivalent hydrogen consumption model of the electric energy storage device and its corresponding weight parameters.

[0019] According to a specific embodiment of the present invention, the formula of the objective function is as follows:

[0020] J hy (t) = ω bt (t)H bt (t)Δt+ω hy (t)[H fc (t)-H el (t)]Δt,

[0021] ω bt (t) = 1-F bt (t),

[0022] ω hy (t) = 1-F hy (t),

[0023]

[0024] Among them, J hy (t) represents the objective function, ω bt(t) represents the weight parameter of the hydrogen consumption contribution of the electric energy storage device, H bt (t) represents the equivalent hydrogen consumption model of the electric energy storage device, ω hy (t) represents the weight parameter of the hydrogen consumption contribution of the hydrogen 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, and F bt (t) represents a virtual force related to the state of charge of the electric energy storage device, x1(t) = SOC(t) - SOC mid , and SOC mid It is a minimum SOC between the state of charge of the energy storage device min and maximum SOC max A set value between , in order to expect the state of charge of the electric energy storage device to be maintained at this value, u1 is the coefficient used to shape the virtual force curve of the electric energy storage device, F hy (t) represents a virtual force related to the hydrogen charge state of the hydrogen energy storage device, x2(t)=SOHC(t)-SOHC mid , and SOHC mid It is a minimum SOHC value between the hydrogen state of charge of the hydrogen energy storage device min and maximum SOHC max u2 is a set value between , in the expectation that the hydrogen state of charge of the hydrogen energy storage device is maintained at this value, and u2 is a coefficient used to shape the virtual force curve of the hydrogen energy storage device.

[0025] According to a specific embodiment of the present invention, 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] 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 outputted by the fuel cell at the current moment, P el (t) represents the electric power input to the electrolytic cell at the current moment.

[0028] According to a specific embodiment of the present invention, 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 as the goal, 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. The steps include: minimizing the objective function based on the net load electric power of the energy storage system at the current moment; obtaining the input power of the fuel cell at the current moment, the output power of the electrolyzer at the current moment, and the input / output power of the electric energy storage device at the current moment according to the calculation result of the objective function; according to the corresponding input / output power, by calculating the duty cycle of the converter of the fuel cell, the electrolyzer, and the electric energy storage device, and controlling the converter to work according to the corresponding duty cycle, so as to optimize the power distribution between the fuel cell, the electrolyzer, and the electric energy storage device.

[0029] 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 the electrolyzer, thereby minimizing system degradation.

[0030] 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 state of charge of the system.

[0031] 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

[0032] Figure 1 A structural block diagram of a specific embodiment of an energy storage system provided by the present invention;

[0033] 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;

[0034] Figure 3 A schematic 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;

[0035] Figure 4 A schematic 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

[0036] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0037] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being 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 complicated.

[0038] 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, structures and devices known to the public are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0039] First of all, it should be explained that in order to enable people in this technical field to better understand the present application scheme, the technical background of this application is explained accordingly.

[0040] 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. Renewable energy sources 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, photovoltaic power sources are specifically used as an example in this application 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.

[0041] Usually, in the energy storage system, the photovoltaic generator, i.e., the photovoltaic power source, operates in the maximum power point tracking mode, and provides energy to the system and the load through the 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, and the electrolyzer obtains energy from the system through the Buck converter to prepare hydrogen, and the fuel cell consumes hydrogen and provides energy to the system through the Boost converter. The electrical energy storage device can be composed of one or more mixed energy storage devices such as supercapacitors and / or batteries whose power characteristics are better than hydrogen energy storage, and provide energy to the system or obtain energy from the system through a bidirectional Buck-Boost converter, and there are no excessive restrictions on this.

[0042] Furthermore, the net load power of the system is composed of two parts: photovoltaic power generation and load power consumption. When the photovoltaic power generation exceeds the load power consumption, 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 prepare hydrogen to store hydrogen energy or sell it. When the load power consumption exceeds the photovoltaic power generation, 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 releasing energy together, such as battery discharge to supply energy and fuel cell consumption of hydrogen to discharge to supply energy, so as to maintain the balance and stability of the system, and repeat the cycle.

[0043] Based on the above energy storage system, the present application provides a variety of energy management strategies to assist its sustainable operation, thereby improving the reliability and economy of the energy storage system.

[0044] Example 1

[0045] See also Figure 2 An energy management method based on the degradation degree of an energy storage system is shown, comprising:

[0046] 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.

[0047] 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.

[0048] Step S130, when obtaining the net load electric power of the energy storage system at the current moment, the goal is to minimize the degree of degradation of the energy storage system, and the net load electric power is substituted into the objective 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.

[0049] First of all, the hydrogen energy storage device is composed of a fuel cell, an electrolyzer, and a hydrogen storage tank, and the corresponding degradation models need to be constructed separately. It can be understood here that the hydrogen storage tank is only used to store hydrogen, and the degree of degradation is only affected by aging, so it does not participate in the subsequent degradation degree analysis and the construction of the degradation model.

[0050] In this regard, the degradation of a fuel cell (FC) can be characterized by the drop in its voltage, which can be further decomposed into the voltage drop (D) caused by high power operation and the voltage drop (V) caused by high power operation. fchigh (t)) and the voltage drop caused by power transient changes (D fcshift (t)), and after ignoring the coupling between the voltage drops, the characterization function of FC with respect to the voltage drop is as follows:

[0051] D fc (t) = D fchigh (t)+D fcshift (t),

[0052] And this is used as the degradation model of FC. However, in this embodiment, considering that the instability of the photovoltaic power source will cause the FC to start and stop frequently, thereby aggravating the degradation degree of FC. Therefore, in the above D fchigh (t) and D fcshift (t) is added with the voltage drop caused by the start / stop state (D fccycle (t)) to jointly characterize the voltage drop of FC. The corresponding characterization function of FC with respect to the voltage drop can be adjusted as follows:

[0053] D fc (t) = D fccycle (t)+D fchigh (t)+D fcshift (t),

[0054] It can be understood here that the instability of photovoltaic power sources will cause the net load electric power of the system to frequently switch between surplus and deficit, and the net load electric power surplus will use the electrolyzer to prepare hydrogen, and the net load electric power deficit 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, which will cause the FC to continuously switch between starting and stopping. Specifically, when there is an energy surplus in the net load of the system, the electrolyzer starts to operate to consume the surplus energy. When there is an energy shortage, the fuel cell is started to make up for the missing energy. When the net load of the system changes frequently, the hydrogen energy storage device may start or stop frequently, resulting in accelerated degradation.

[0055] 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.

[0056] Among them, the voltage drop (D fccycle (t)) characterization function:

[0057] D fccycle (t) = α fccycle |y fc (t)-y fc (t-Δt)|,

[0058] The voltage drop (D fchigh (t)) characterization function:

[0059]

[0060] FC voltage drop caused by power transient change (D fcshift (t)) characterization function:

[0061] D fcshift (t) = α fcshift |P fc (t)-P fc (t-Δt)|,

[0062] In the above formula, α fccycle , α fchigh , α fchigh is the correlation coefficient of FC voltage degradation.

[0063] 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).

[0064] 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).

[0065] 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 continue until the next moment when energy management is performed again. The interval between these two moments is the above-mentioned time interval Δt.

[0066] 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 the operating power of FC are as follows:

[0067] y fc (t)P fcmin ≤P fc (t)≤y fc (t)P fcmax ,

[0068] And P fcmin and P fcmax Corresponding to the minimum and maximum power of FC respectively.

[0069] 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:

[0070] D el (t) = D elop (t)+D elshift (t),

[0071] 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 characterization function of EL with respect to voltage drop can be adjusted as follows:

[0072] D el (t) = D elcycle (t)+D elop (t)+D elshift (t),

[0073] Among them, EL is caused by the voltage drop D caused by the start / stop state. elcycle Characterization function of (t):

[0074] D elcycle (t) = α elcycle |y el (t)-y el (t-Δt)|,

[0075] EL voltage drop caused by operation D elop Characterization function of (t):

[0076] D elop (t) = αelop y el (t)Δt,

[0077] EL voltage drop caused by power transient change D elshift Characterization function of (t):

[0078] D elshift (t) = α elshift |P el (t)-P el (t-Δt)|,

[0079] In the above formula, α elcycle , α elop , α elop is the correlation coefficient of EL voltage degradation.

[0080] 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).

[0081] 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:

[0082] y el (t)P elmin ≤P el (t)≤y el (t)P elmax ,

[0083] And P elmin and P elmax Corresponding to the minimum and maximum power of EL respectively.

[0084] In this embodiment, the electric energy storage device takes a battery as an example to illustrate the technical solution. The degradation of the battery (Battery, BT) can be characterized by its state of health (State of Health, SOH). The SOH of the battery can be expressed as:

[0085]

[0086] 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.

[0087] In addition, the energy storage system also needs to satisfy the law of conservation of energy, that is, maintain energy balance. To this end, fuel cells, electrolyzers, and batteries need to satisfy the following power balance:

[0088] P load (t)-P pv (t) = P bt (t)+P fc (t)-P el (t),

[0089] 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).

[0090] 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:

[0091]

[0092] In the above formula, C fcin , C elin , C btin Respectively represent the purchase cost of FC, EL, and BT, 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.

[0093] It can be seen that the three items in the above formula represent the degradation costs of FC, EL, and BT within a certain period of time. Considering the economy 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.

[0094] 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:

[0095] y fc (t)+y el (t)≤1,

[0096] In this regard, based on the net load power of the system at the current moment, in minimizing the objective function J deg(t) can be calculated accordingly to obtain the input / output power of FC, EL, and BT at the current moment. Finally, the Boost converter of FC or the Buck converter of EL, as well as the bidirectional Buck-Boost converter of BT can be controlled to work according to the corresponding input / output power, that is, the duty cycle corresponding to the converter is calculated according to the input / output power, thereby realizing the power distribution of the system. Among them, since at most only one of the fuel cell and the electrolyzer is running, when the net load electric power is surplus, the excess electric power can be allocated to the electrolyzer to prepare hydrogen and / or the battery to charge and store energy, or when the net load electric power is missing, the fuel cell can be controlled to consume hydrogen to release energy and / or the battery to discharge and supply energy to make up for the missing part of the net load electric power.

[0097] It can be seen that the above energy management strategy can not only reduce the 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.

[0098] Example 2

[0099] See also Figure 3 An energy management method based on equivalent hydrogen consumption of an energy storage system is shown, comprising:

[0100] 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.

[0101] Step S220, based on the power balance of the energy storage system, according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device, establish the objective function of the energy storage system regarding equivalent hydrogen consumption.

[0102] Step S230, when obtaining the net load electric power of the energy storage system at the current moment, 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.

[0103] First of all, we should build the hydrogen consumption model of fuel cells and electrolyzers, as well as the equivalent hydrogen consumption model of batteries. 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.

[0104] In this regard, 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:

[0105]

[0106] 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 mobile electrons in FC, and F represents the Faraday constant.

[0107] 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 the operating power of FC are as follows:

[0108] P fcmin ≤P fc (t)≤P fcmax , and P fcmin and P fcmax Corresponding to the minimum and maximum power of FC respectively.

[0109] v fc (t) represents the voltage of FC at the current moment.

[0110] It can be seen 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.

[0111] Furthermore, EL needs to use energy to produce hydrogen, and the hydrogen production function H of EL can be constructed accordingly. el as follows:

[0112]

[0113] 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.

[0114] 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:

[0115] P elmin ≤P el (t)≤P elmax , and P elmin and P elmax Corresponding to the minimum and maximum power of EL respectively.

[0116] v el (t) represents the voltage of EL at the current moment.

[0117] 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.

[0118] Based on this, the hydrogen production function H of FC can be used eland EL's hydrogen production function H el Construct a hydrogen consumption model for hydrogen energy storage devices. In addition, although hydrogen storage tanks do not participate in the equivalent hydrogen consumption analysis, the hydrogen produced by the electrolyzer needs to be stored in hydrogen storage tanks, and the hydrogen storage capacity and the internal pressure of hydrogen storage tanks have certain upper limits. Therefore, in order to reflect the level of hydrogen storage in hydrogen storage tanks (HST), a hydrogen state of charge (SOHC) is defined to constrain the above hydrogen consumption model to avoid damage to the hydrogen storage tank due to its inability to store more hydrogen.

[0119] In this regard, HST's SOHC real-time mapping function is as follows:

[0120] and

[0121]

[0122] 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, p hst (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.

[0123] 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 excessive hydrogen production by EL and less hydrogen consumption by FC.

[0124] 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, and the corresponding equivalent hydrogen consumption model formula is as follows:

[0125] H bt =P bt (t) / LHV,

[0126] Wherein, 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, P during chargingbt (t)<0,P btmaxc is the maximum charging power.

[0127] In addition, in order to maintain the stability and balance of the battery state of charge (SOC), the battery 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.

[0128] In this regard, the real-time mapping function of BT's SOC is as follows:

[0129]

[0130] 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.

[0131] It can be seen that the real-time SOC can be calculated based on the battery charge, the current input / output current, and the initial power 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.

[0132] Similarly, fuel cells, electrolyzers, and batteries need to meet the following power balance:

[0133] P load (t)-P pv (t) = P bt (t)+P fc (t)-P el (t),

[0134] 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:

[0135] J hy (t) = ω bt (t)H bt (t)Δt+ω hy (t)[H fc (t)-H el (t)]Δt,

[0136] 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 ωhy (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 to calculate accordingly, as follows:

[0137] ω bt (t) = 1-F bt (t),

[0138] ω hy (t) = 1-F hy (t),

[0139] 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.

[0140] It should be noted that virtual force is defined in the context of "artificial potential field", which was originally proposed for robotic applications and recently applied to renewable energy systems. Artificial potential field is widely used in the formation control of multiple agents. In the formation problem, multiple agents must maintain a reference distance to form a stable formation. This method can construct an artificial potential field, and the force function between any two agents in the artificial potential field is also called the action function. When the distance between two agents is equal to the reference value, no force is generated between them, that is, the potential energy is zero. When the two are close, there will be a large repulsive force; 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 converges quickly to the reference value. For example, when the SOC of the electric energy storage device is high, there will be an attractive force to reduce the SOC, and when the SOC is low, there will be an attractive force to increase the SOC. When the SOC is close to or equal to the reference value, the above phenomenon can be effectively reduced, that is, the virtual force corresponding to the battery SOC, so as to maintain the SOC of the electric energy storage device in a stable state. Similarly, the same is true for the SOHC of the hydrogen energy storage device.

[0141] Therefore, the virtual force related to the SOC of the electric energy storage device is defined as follows:

[0142]

[0143] 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 , with the expectation that the SOC of the electric energy storage device is maintained at this value, and u1 is a coefficient used to shape the virtual force curve of the electric energy storage device.

[0144] Likewise, the virtual force associated with the hydrogen storage device, i.e., HST, is defined as follows:

[0145]

[0146] Where x2(t)=SOHC(t)-SOHC mid , and SOHC mid It is a minimum value SOHC between hydrogen energy storage device SOHC min and maximum SOHC max A set value between , with the expectation 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.

[0147] In one embodiment, the SOC min and SOHC min Set to 30%, SOC max and SOHC max Set to 90%, SOC mid and SOHC mid Set to 60% for calculation. Accordingly, based on the net load electric power of the system at the current moment, the objective function is minimized to minimize the equivalent hydrogen consumption of the system, and the input power of FC at the current moment and the output power of EL at the current moment, as well as the input / output power of BT at the current moment, can be calculated. Finally, the Boost converter of FC or the Buck converter of EL, as well as the bidirectional Buck-Boost converter of BT, can be controlled according to the corresponding input / output power, that is, the corresponding duty cycle of the converter is calculated according to the input / output power, thereby realizing the power distribution of the system.

[0148] 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.

[0149] Example 3

[0150] 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.

[0151] For this, see Figure 4 A two-level energy management method for an energy storage system is shown, comprising:

[0152] Step S311, pre-constructing degradation models of the hydrogen energy storage device and the electric energy storage device.

[0153] 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.

[0154] 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.

[0155] 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 degree of degradation and the equivalent hydrogen consumption of the energy storage system.

[0156] Step S330, obtaining the net load electric power of the energy storage system at the current moment.

[0157] 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 to calculate the reference power of the hydrogen energy storage device and the electric energy storage device.

[0158] Step S350, 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, and calculating the input / output power of the hydrogen energy storage device and the electric energy storage device.

[0159] Step S360: adjusting the power distribution between the hydrogen energy storage device and the electric energy storage device according to the corresponding input / output power.

[0160] 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) to achieve first-level energy management, i.e., to minimize the degradation of the system.

[0161] 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.

[0162] Therefore, the first objective function constructed can be divided into the following two categories:

[0163] Category 1: and

[0164] D fc (t) = D fchigh (t)+D fcshift (t), D el (t) = Delop (t)+D elshift (t),

[0165] Category 2: and

[0166] D fc (t) = D fccycle (t)+D fchigh (t)+D fcshift (t), D el (t) = D elcycle (t)+D elop (t)+D elshift (t)

[0167] Both of the above first objective functions can be used to optimize the degree of degradation of the system. For example, the first objective function of the first type can be used to reduce the degree of degradation of the system without considering the optimization of the start and stop states of the fuel cell and the electrolyzer. 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.

[0168] 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.

[0169] 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 to obtain the final input / output power of the hydrogen energy storage device and the electric energy storage device.

[0170] In order to integrate the two strategies and reduce the equivalent hydrogen consumption while reducing the system degradation degree, the weight between the degradation degree 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 degradation degree and the equivalent hydrogen consumption. hy (t).

[0171] 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 equivalent hydrogen consumption of the system, so that the SOHC and SOC of the system can be properly controlled while minimizing the equivalent hydrogen consumption of the system. Therefore, when constructing the second objective function, it can also be divided into the following two categories, and the specific formula is as follows:

[0172] Category 1:

[0173] 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 ],

[0174] Category 2:

[0175] 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 ],

[0176] 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.

[0177] Similarly, the above two second objective functions both 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 parameters of the hydrogen energy storage device and the equivalent hydrogen consumption parameters of the electric energy storage 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 energy storage device and its corresponding reference power, that is, minimize the deviation between the output power of FC calculated by the second objective function and the reference power calculated by the first objective function, and the deviation between the input power of EL calculated by the second objective function and the reference power calculated by the first objective function, so as to optimize the input / output power of FC and EL using the reference power calculated by the first objective function. Therefore, the above objectives can be achieved by minimizing the second objective function, and the input / output power of FC and EL at the current moment can be calculated. It can also be understood here that based on the power balance of the system, when the input / output power of FC and EL is determined, the input / output power of BT is also determined.

[0178] Finally, the Boost converter of FC, the Buck converter of EL, and the bidirectional Buck-Boost converter of BT can be controlled according to the corresponding input / output power. That is, the corresponding duty cycle of the converter is calculated according to 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.

[0179] It should be noted that the step division of the above methods is only for clear description. When implemented, 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.

[0180] 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 the electrolyzer, thereby minimizing system degradation.

[0181] 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 state of charge of the system.

[0182] 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.

[0183] 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 familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An energy management method based on equivalent hydrogen consumption of 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 energy management method includes: 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; 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; When the net load electric power of the energy storage system at the current moment is obtained, the goal is to minimize the equivalent hydrogen consumption of the energy storage system, 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.

2. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 1 is characterized in that: 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: A hydrogen consumption model of the hydrogen energy storage device is constructed according to the hydrogen consumption function of the fuel cell and the hydrogen production function of the electrolyzer.

3. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 2 is characterized in that: The formula of the fuel cell hydrogen consumption function is as follows: 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 electric power outputted by the fuel cell at the current moment, z represents the number of electrons moving in the fuel cell, F represents the Faraday constant, v fc (t) represents the voltage of the fuel cell at the current moment.

4. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 2 is characterized in that: The formula of the electrolyzer hydrogen production function is as follows: Among them, η F (t) represents the Faraday efficiency, n s represents the number of cells in the electrolytic cell, P el (t) represents the electric power input to 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.

5. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 1 is characterized in that: 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: An equivalent hydrogen consumption model corresponding to the electric energy storage device is constructed according to the electric power input / output of the electric energy storage device.

6. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 5 is characterized in that: 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, P bt (t) represents the electric power input / output of the electric energy storage device at the current moment, and LHV represents the lower heating value of hydrogen.

7. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 1 is characterized in that: Based on the power balance of the energy storage system, the step of establishing the objective function of the energy storage system regarding equivalent hydrogen consumption according to the hydrogen consumption model of the hydrogen energy storage device and the equivalent hydrogen consumption model of the electric energy storage device comprises: Using an artificial potential field to determine the virtual force of the hydrogen energy storage device on the hydrogen state of charge and the virtual force of the electric energy storage device on the state of charge, and use them as weight parameters of the hydrogen consumption model and the equivalent hydrogen consumption model respectively; The objective function is constructed according to the hydrogen consumption model of the hydrogen energy storage device and its corresponding weight parameters, and the equivalent hydrogen consumption model of the electric energy storage device and its corresponding weight parameters.

8. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 7 is characterized in that: The objective function formula is as follows: J hy (t)=ω bt (t)H bt (t)Δt+ω hy (t)[H fc (t)-H el (t)]Δt, ω bt (t)=1-F bt (t), ω hy (t)=1-F hy (t), Among them, J hy (t) represents the objective function, ω bt (t) represents the weight parameter of the hydrogen consumption contribution of the electric energy storage device, H bt (t) represents the equivalent hydrogen consumption model of the electric energy storage device, ω hy (t) represents the weight parameter of the hydrogen consumption contribution of the hydrogen 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, and F bt (t) represents a virtual force related to the state of charge of the electric energy storage device, x1(t) = SOC(t) - SOC mid , and SOC mid It is a minimum SOC between the state of charge of the energy storage device min and maximum SOC max A set value between , in order to expect the state of charge of the electric energy storage device to be maintained at this value, u1 is the coefficient used to shape the virtual force curve of the electric energy storage device, F hy (t) represents a virtual force related to the hydrogen charge state of the hydrogen energy storage device, x2(t)=SOHC(t)-SOHC mid , and SOHC mid It is a minimum SOHC value between the hydrogen state of charge of the hydrogen energy storage device min and maximum SOHC max u2 is a set value between , in the expectation that the hydrogen state of charge of the hydrogen energy storage device is maintained at this value, and u2 is a coefficient used to shape the virtual force curve of the hydrogen energy storage device.

9. The energy management method based on equivalent hydrogen consumption of 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 electric power input / output of the electric energy storage device at the current moment, P fc (t) represents the electric power outputted by the fuel cell at the current moment, P el (t) represents the electric power input to the electrolytic cell at the current moment.

10. The energy management method based on equivalent hydrogen consumption of energy storage system according to claim 1, characterized in that: When the net load electric power of the energy storage system at the current moment is obtained, the steps of minimizing the equivalent hydrogen consumption of the energy storage system and substituting the net load electric power into the objective function to optimize the power distribution between the hydrogen energy storage device and the electric energy storage device include: Minimizing the objective function based on the net load electric power of the energy storage system at the current moment; According to the calculation result of the objective function, the input power of the fuel cell at the current moment, the output power of the electrolyzer at the current moment, and the input / output power of the electric energy storage device at the current moment are obtained; According to the corresponding input / output power, the duty cycle of the converter of the fuel cell, the electrolyzer, and the electrical energy storage device is calculated, and the operation of the converter 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.

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