Method for distributing stack series voltage and dc boost voltage based on energy consumption optimization

Abstract

The application discloses a kind of based on energy consumption optimization's electric pile series voltage and distribution method of direct current voltage, and the topology structure of energy storage subsystem in power station is connected with PCS after being connected in parallel by multiple electric pile groups, which comprises the following steps: determining direct current voltage grade according to power station parameters;Establish electric pile group energy consumption optimization model, which includes objective function and constraint condition constructed with the minimum electric pile string loss and DC / DC converter loss as target, electric pile string loss is a function about electric pile string voltage grade, DC / DC converter loss is a function about DC / DC converter boost grade, and the sum of electric pile string voltage grade and DC / DC converter boost grade is the direct current voltage grade;Solve electric pile group energy consumption optimization model, and set the number of single electric pile in series of electric pile string and DC / DC converter selection according to the solving result.The application can effectively improve the energy efficiency and reliability of flow battery power storage station.

Description

Technical Field

[0001] This invention belongs to the field of flow battery energy storage power station technology, and more specifically, relates to a method for allocating the series voltage of the battery stack and the DC boost voltage based on energy consumption optimization. Background Technology

[0002] To achieve dual-carbon goals, the installed capacity of new energy sources is increasing year by year, while the reliability of the power system needs to be enhanced, and the demand for backup power is increasing. Flow batteries have advantages such as safety, environmental friendliness, long service life, and the ability to design power and capacity units independently, leading to their growing development scale. However, single flow batteries have low voltage. In practical engineering applications, the DC-side voltage needs to be met by connecting multiple stacks in series to meet the converter requirements. Connecting multiple stacks in series increases the external common channel, reduces system energy efficiency, and increases the system reliability issues caused by single stack failures. Therefore, the DC-side voltage boosting method needs improvement.

[0003] Flow battery energy storage power stations suffer from low efficiency and poor reliability in long-term, large-scale applications, leading to high operation and maintenance costs and limiting their economic viability. Existing research indicates that because the stacks share an electrolyte and have common conduits, leakage current is increased while ensuring consistency within each stack, reducing the system's coulombic efficiency. As the number of flow battery stacks connected in series increases, the terminal voltage rises, resulting in a larger leakage current in the common conduit and a lower stack energy efficiency. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for allocating the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization, which can effectively improve the energy efficiency and reliability of the flow battery power station.

[0005] To achieve the above objectives, this invention provides a method for allocating the series voltage and DC boost voltage of a fuel cell stack based on energy consumption optimization, applicable to a flow battery energy storage power station. The energy storage subsystem in the flow battery energy storage power station adopts a topology of multiple fuel cell stacks connected in parallel and then connected to a power supply system (PCS). Each fuel cell stack includes a stack string and a DC / DC converter. The stack string is composed of n individual fuel cell stacks connected in series. The method includes the following steps:

[0006] (1) Determine the DC voltage level U based on the parameters of the flow battery energy storage power station. dc ;

[0007] (2) Establish a stack energy consumption optimization model based on the characteristics of flow batteries. The stack energy consumption optimization model includes the stack series loss P. RB Add DC / DC converter loss P DC / DC The objective function and constraints are constructed with the goal of minimizing; wherein, the stack string loss P RBThe DC / DC converter loss P is a function of the stack series voltage level U1. DC / DC The constraint is that the sum of the stack voltage level U1 and the DC / DC converter boost level U2 is equal to the DC voltage level U. dc ;

[0008] (3) Solve the energy consumption optimization model of the fuel cell stack to obtain the fuel cell string voltage level U1 and DC / DC converter boost level U2 with the minimum loss. Then, based on the solution results, set the number of single fuel cells connected in series and the selection of DC / DC converter accordingly.

[0009] The energy consumption optimization-based method for allocating the series voltage of the fuel cell stack and the DC boost voltage provided by this invention has the following effects: (1) The energy storage subsystem in the power station adopts a topology structure in which multiple fuel cell stacks are connected in parallel and then connected to the PCS, which can reduce the number of single fuel cell stacks in series, thereby reducing the leakage current of the common pipeline and improving the energy efficiency of the power station. At the same time, it reduces the impact of single fuel cell stack failure on the fuel cell stack series and improves the overall reliability of the power station. In addition, the power allocation space based on energy consumption optimization is increased, and the power station pump consumption can be further reduced according to the allocation strategy, thereby improving the overall energy efficiency of the power station. (2) The energy consumption distribution inside the liquid flow fuel cell stack is clearly defined, and a fuel cell stack energy consumption optimization model is established. This can realize the coordinated optimization of fuel cell stack boost energy consumption and DC / DC ratio loss, and increase the DC side voltage range to 1000~1200V, which can adapt to high inverter efficiency converters.

[0010] In one embodiment, in step (2), the stack string loss P RB The method for establishing the functional relationship between the stack voltage level U1 and the battery pack is as follows:

[0011] Based on the number of individual fuel cells connected in series n in the fuel cell string, the relationship between the voltage level U1 of the fuel cell string and n is determined, where U1 = n·a, and a is the voltage level of a single fuel cell string.

[0012] Calculate the normal operating current loss P of the stack string based on the normal operating current loss of a single stack and the number of stacks connected in series in the stack string, n. nc Simultaneously, the leakage current loss P of the fuel cell string is calculated based on the leakage current loss of a single fuel cell in the string and the number of fuel cell stacks connected in series n. sc Then, based on the normal operating current loss P of the fuel cell stack, nc and the leakage current loss P of the fuel cell series sc Calculate the battery stack string loss P RB P RB =P nc +P sc ;

[0013] Based on the relationship between the voltage level U1 and n of the fuel cell string and the fuel cell string loss PRB The relationship between P and n is established through data fitting to determine the stack string loss P. RB The functional relationship between the stack voltage level U1 and the stack voltage level U1.

[0014] In one embodiment, the normal operating current loss P of the fuel cell stack string nc The internal resistance of a single fuel cell stack in the fuel cell stack string is affected by the internal resistance of the single fuel cell stack, which includes ohmic internal resistance and polarization internal resistance. The internal resistance value changes with the operating state of the power plant.

[0015] The normal operating current loss P of the fuel cell string nc The calculation formula is:

[0016] P nc =n×P nc 0

[0017] P nc0 =(R0+f1(C oi )×I DC 2 +α0)

[0018] In the formula, P nc0 R0 is the normal operating current loss of a single fuel cell stack; f1(C) is the internal resistance of a single fuel cell stack in ohms; oi The polarization internal resistance of a single fuel cell stack is affected by the charge / discharge rate; I DC α is the operating current; α0 is the single-pile operating current loss correction amount, the value of which is obtained from actual measurement.

[0019] In one embodiment, the leakage current loss P of the fuel cell stack is... sc The leakage current loss of the fuel cell stack is affected by the resistance of the conduit and the number of fuel cell stacks connected in series. The calculation formula is as follows:

[0020]

[0021] P sc0,i =R plo ×(I dt,i 2 +I com,i 2 )

[0022] In the formula, P sc0,i α represents the leakage current loss of the i-th single stack in the stack string; sc This is the correction factor for leakage current loss in the fuel cell series, and its value is obtained from actual measurements; R plo I represents the internal resistance of the pipe corresponding to a single fuel cell stack. dt,i Assign the pipe leakage current I to the i-th single stack. com,iLet be the leakage current in the common conduit of the i-th single stack. The magnitude of both currents is related to the number of single stacks connected in series. According to the leakage current distribution characteristics, it is symmetrically distributed. Therefore, it is only necessary to calculate the leakage current loss of the 1-n / 2 or n / 2-n single stack, as follows:

[0023] When n / 2≤i≤n, I com,i =β com -α com ·(in / 2) 2 I dt,i =α dt ·(in / 2) 2 ;

[0024] In the formula, α com β com α is the leakage current coefficient for public pipelines. dt The coefficients for the calculation function of the leakage current in the pipeline are all affected by the length and shape of the liquid flow single stack pipeline.

[0025] In one embodiment, in step (2), the DC / DC converter loss P DC / DC The method for establishing the relationship between the DC / DC converter boost level U2 function and the DC / DC converter boost level is as follows:

[0026] Calculate the DC / DC converter loss P based on the DC / DC converter's duty cycle D. DC / DC ;

[0027] Based on the working principle of the DC / DC converter, the relationship between the DC / DC converter step-up level U2 and the DC / DC converter duty cycle D is determined as follows: U2 = D × V O V O This is the high-voltage side voltage of the DC / DC converter, which is equal to the rated low-voltage side voltage of the PCS (Power Storage System).

[0028] Based on the DC / DC converter loss P DC / DC The relationship between the duty cycle D and the step-up voltage U2 of the DC / DC converter and the duty cycle D of the DC / DC converter is established through data fitting to establish the DC / DC converter loss P. DC / DC Functional relationship with the boost level U2 of the DC / DC converter.

[0029] In one embodiment, the DC / DC converter loss P DC / DC The calculation formula is:

[0030] P DC / DC =P on +P oth

[0031] P on=α on ·(D)+β on

[0032] P oth =α oth ·I DC 2 +β oth ·I DC +γ oth

[0033] In the formula, P on α represents the conduction loss of power electronic devices in a DC / DC converter. on β on This is a correction for conduction losses. This correction is significantly affected by the DC / DC converter model and can be fitted and assigned a value through actual testing of the DC / DC converter; P oth To exclude P on The sum of external losses unrelated to the turns ratio is considered to be the sum of losses affected by the operating current I. DC The quantity affected is the low-voltage side input current of the DC / DC converter; α oth β oth γ oth This is for other loss corrections.

[0034] In one embodiment, the energy storage subsystem adopts a topology of 3 to 5 stacks connected in parallel and then connected to the PCS. Attached Figure Description

[0035] Figure 1 This is a topology diagram of the liquid flow current energy storage power station provided by the present invention;

[0036] Figure 2 This is a topology diagram of a traditional liquid flow current energy storage power station;

[0037] Figure 3 This is a flowchart of a method for improving the energy efficiency of a liquid flow current energy storage power station according to an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] It should be noted that a flow battery consists of a stack and an electrolyte. Internally, it has a common electrolyte channel. The electrolyte enters each stack through a main pipe and branch pipes, creating ion channels between different stacks. Because the stacks are connected in series, electron channels also exist between them. When the electron and ion channels form a closed loop, the electrolyte in the branch pipes acts as a conductor, allowing current to flow. This current is defined as leakage current. During battery discharge, the leakage current consumes some energy, reducing battery efficiency. Furthermore, as the scale of the energy storage power station increases and the voltage level rises, the leakage current also increases.

[0040] To address the aforementioned problems, the flow battery energy storage power station provided by this invention adopts a topology that combines a fuel cell stack and power electronics for voltage boosting, specifically as follows: Figure 1 As shown, the topology of a traditional flow battery energy storage power station is as follows: Figure 2 .Depend on Figure 1 and Figure 2 As can be seen, this invention improves the topology of the energy storage subsystem in a flow battery energy storage power station, changing the traditional energy storage subsystem topology (N battery stacks connected in series and directly connected to the power conversion system (PCS)) to the following: Figure 1 K fuel cell stacks are connected in parallel and then connected to the PCS. Each fuel cell stack consists of a fuel cell stack string and one DC / DC converter. The fuel cell stack string is composed of n individual fuel cell stacks connected in series. Since the current carrying capacity of existing PCS is generally within 2000A, and the current carrying capacity of a single DC / DC converter is generally within 500A, the value of K is generally 3 to 5 due to current limitations.

[0041] It should be noted that, Figure 1 The intermediate storage tank is only used for connection illustration. In practice, each battery stack string can be connected to a set of positive and negative electrolyte tanks, or several battery stack strings can share a set of positive and negative electrolyte tanks as needed. Figure 2 The intermediate storage tank is only used for connection illustration. In practice, each subsystem can be connected to a set of positive and negative electrolyte tanks, or several subsystems can share a set of positive and negative electrolyte tanks as needed.

[0042] Existing research indicates that the more fuel cell stacks connected in series, the greater the leakage current in the common pipe. Furthermore, the closer the common pipe and branch channels are to the positive and negative inlet / outlet ports within each fuel cell stack string, the greater the leakage current. This invention reduces the number of fuel cell stacks connected in series to 1 / K of the number in traditional topology fuel cell stacks. Theoretical research shows that this invention's topology can effectively reduce the leakage current in the common pipe, thereby reducing energy loss in this area.

[0043] Furthermore, compared to existing [measures] Figure 1The power allocation command is applied to stacks 1#-m# in the PCS. The topology proposed in this invention can further allocate power to stacks 1-K# under the PCS. Especially when the flow battery energy storage power station is in a non-rated output condition, power allocation can be carried out according to the energy consumption distribution law of the stacks and energy storage subsystems, avoiding leakage current loss of non-output stacks.

[0044] Figure 1 The positive and negative electrode circulating pumps shown are key devices for transporting electrolyte. According to actual engineering experience, their losses account for about 5%, which is a relatively large proportion. By adopting the topology proposed in this invention, the pump consumption of non-output stacks can be reduced, thereby improving the overall energy efficiency of the power plant.

[0045] For example, a 20MW·4h flow battery energy storage power station only needs to operate 3 / 4 of the energy storage subsystems when it needs to output a constant power of 15MW. At the same time, the number of active stacks in each energy storage subsystem can be reduced as much as possible according to the allocated power value, thereby reducing leakage current and pump consumption of non-working stacks.

[0046] In addition, the present invention also provides a method for improving energy efficiency based on the above-mentioned flow battery energy storage power station topology, namely, a voltage distribution method for single-stack series boost and DC boost, including steps S10 to S30, which are detailed below:

[0047] S10, Determine the DC voltage level U based on the parameters of the flow battery energy storage power station. dc .

[0048] S20, establish a stack energy consumption optimization model based on the characteristics of flow batteries. The stack energy consumption optimization model includes the stack series loss P. RB Add DC / DC converter loss P DC / DC The objective function and constraints are constructed with the goal of minimizing; wherein, the stack string loss P RB The DC / DC converter loss P is a function of the stack series voltage level U1. DC / DC The constraint is that the sum of the stack voltage level U1 and the DC / DC converter boost level U2 is equal to the DC voltage level U. dc .

[0049] In this embodiment, the stack string loss P in step S20 RB The principle for establishing the functional relationship between the voltage level U1 of the fuel cell stack string can be as follows: (1) Determine the relationship between the voltage level U1 of the fuel cell stack string and n based on the number of single fuel cell stacks connected in series in the fuel cell stack string, U1 = n·a, where a is the voltage level of a single fuel cell stack; (2) Calculate the normal operating current loss P of the fuel cell stack string based on the normal operating current loss of a single fuel cell stack and the number of single fuel cell stacks connected in series in the fuel cell stack string n. ncSimultaneously, the leakage current loss P of the fuel cell string is calculated based on the leakage current loss of a single fuel cell in the string and the number of fuel cell stacks connected in series n. sc Then, based on the normal operating current loss P of the fuel cell stack, nc and the leakage current loss P of the fuel cell series sc Calculate the battery stack string loss P RB P RB =P nc +P sc (3) Based on the relationship between the voltage level U1 and n of the fuel cell string and the fuel cell string loss P RB The relationship between P and n is established through data fitting to determine the stack string loss P. RB The functional relationship between the stack voltage level U1 and the stack voltage level U1.

[0050] Specifically, the battery stack string loss P RB The analysis process for establishing the functional relationship between the fuel cell stack series voltage level U1 and the fuel cell stack voltage level U1 is as follows:

[0051] Existing research indicates that the number of fuel cell stacks connected in series significantly affects the leakage current of flow batteries. Specifically, the leakage current in the common conduit increases non-linearly with the number of stacks connected in series. Since leakage current losses are a major component of fuel cell stack losses, the total series loss P in this invention is considered... RB The main consideration is the normal operating current loss P. nc and leakage current loss P sc The approximate calculation is as follows:

[0052] P RB =P nc +P sc

[0053] In the formula, the normal operating current loss P nc The main influence is the internal resistance of each individual cell in the battery stack string. The internal resistance of a single cell includes ohmic internal resistance and polarization internal resistance, and the internal resistance value changes with the operating state; leakage current loss P sc It is mainly affected by the resistance of the pipe and the number of fuel cells connected in series.

[0054] In this embodiment, regarding the normal operating current loss P nc Calculation: First, calculate the normal operating current loss P of a single fuel cell stack. nc0 Then, the normal operating current loss P is calculated based on the number of individual fuel cells connected in series, n. nc The calculation formula is as follows:

[0055] P nc =n×P nc0

[0056] P nc0 =(R0+f1(C oi )×I DC2 +α0)

[0057] In the formula, R0 is the ohmic internal resistance of a single fuel cell stack; f1(C oi ) represents the polarization internal resistance of a single fuel cell stack (which is affected by the charge / discharge rate); I DC α0 is the operating current; α0 is the correction amount for the operating current loss of a single fuel cell stack (which is generally the fixed loss generated in the non-operating state, and its value is obtained by actual measurement); n is the number of fuel cell stacks connected in series.

[0058] Leakage current loss P sc Calculation: First, calculate the leakage current loss P of a single fuel cell stack. sc0,i The leakage current loss P of the fuel cell string is calculated by the number of fuel cells connected in series (n) in the fuel cell string. sc .

[0059]

[0060] In the formula, P sc0,i α represents the leakage current loss of the i-th single stack in the stack string; sc This is the correction for leakage current loss in the fuel cell stack (which is a fixed loss generated in non-operating conditions, and its value can be obtained by actual measurement).

[0061] Specifically, P sc0,i The calculation formula is:

[0062] P sc0,i =R plo ×(I dt,i 2 +I com,i 2 )

[0063] In the formula, R plo I represents the internal resistance of the pipe corresponding to a single fuel cell stack. dt,i Assign the pipe leakage current I to the i-th single stack. com,i Let P be the leakage current in the common conduit of the i-th single stack. The magnitude of both currents depends on the number of single stacks connected in series. Based on the leakage current distribution characteristics, it is symmetrically distributed. Therefore, we only need to calculate the leakage current loss of the 1-n / 2 or n / 2-n single stack to obtain the total leakage current loss P of the stack series. sc .

[0064] Specifically, I dt,i and I com,i The calculation formula is as follows:

[0065] When n / 2≤i≤n:

[0066] I com,i =β com -α com ·(in / 2)2

[0067] I dt,i =α dt ·(in / 2) 2

[0068] I com,i-n / 2 =I com,i

[0069] I dt,i-n / 2 =I dt,i

[0070] In the formula, α com β com α is the leakage current coefficient for public pipelines. dt The coefficients for the calculation function of the leakage current in the pipeline are all affected by the length and shape of the liquid flow charge pipeline.

[0071] Therefore, it can be seen that the corresponding stack string loss P can be calculated for different values ​​of n. RB The series voltage level U1 of the fuel cell stack is a function of n; that is, when the voltage level of a single fuel cell stack is aV, the series voltage level U1 of the fuel cell stack can be obtained as (n·a)V. From this, a set of voltage levels U1 and fuel cell stack series losses P can be obtained. RB One-to-one corresponding data, and then P can be established through data fitting. RB The relationship between P and the stack series voltage level U1 RB =f2(U1).

[0072] In this embodiment, the DC / DC converter loss P in step S20 DC / DC The principle for establishing the relationship between the DC / DC converter boost level U2 function can be: (1) Calculate the DC / DC converter loss P based on the DC / DC converter duty cycle D. DC / DC (2) Based on the working principle of the DC / DC converter, determine the relationship between the DC / DC converter step-up level U2 and the DC / DC converter duty cycle D: U2(1+1 / D)=V O V O (2) The high-voltage side voltage of the DC / DC converter is determined according to the sharing instruction obtained by the power station; (3) According to the DC / DC converter loss P DC / DC The relationship between the duty cycle D and the step-up voltage U2 of the DC / DC converter and the duty cycle D of the DC / DC converter is established through data fitting to establish the DC / DC converter loss P. DC / DC Functional relationship with the boost level U2 of the DC / DC converter.

[0073] Specifically, the DC / DC converter loss P DC / DCThe analysis process for establishing the functional relationship between the DC / DC converter's boost level U2 and the DC / DC converter is as follows:

[0074] There is also a corresponding relationship between the turns ratio and the losses of a DC / DC converter. Research has found that its turns ratio 1 / β DC / DC The relationship with duty cycle D is as follows:

[0075] β DC / DC =1-D

[0076] 1-D=V in / V O

[0077] In the formula, β DC / DC V is the turns ratio coefficient of the DC / DC converter. in V O These are the low-voltage side and high-voltage side voltages at both ends of the DC / DC converter, respectively.

[0078] In this embodiment, the high-voltage side voltage is a constant (equal to the rated low-voltage side voltage of the PCS in the energy storage power station), meaning the DC / DC output voltage is constant, while the input voltage varies with the voltage distribution provided in this embodiment; that is, D increases as the input voltage decreases. Furthermore, through research and analysis, DC / DC losses include power device losses, inductor losses, capacitor losses, sampling control drive losses, etc., among which power device losses are closely related to the turns ratio. Therefore, this invention establishes a DC / DC loss P... DC / DC The relationship with duty cycle D is as follows:

[0079] P DC / DC =P on +P oth

[0080] In the formula, P on P represents the conduction loss of power devices (power electronic devices in DC / DC converters). oth To exclude P on The sum of external losses unrelated to the turns ratio is considered to be the sum of losses affected by the operating current I. DC The quantity affected is the DC / DC low-voltage side input current value.

[0081] The specific calculation formulas for both are as follows:

[0082] P on =α on ·(D)+β on

[0083] P oth =α oth ·I DC 2 +β oth ·I DC +γ oth

[0084] In the formula, α on β on As the correction factor for conduction loss, α oth β oth γ oth For other loss corrections, the aforementioned corrections are greatly affected by the DC / DC model and can be fitted and assigned values ​​by conducting actual tests on the DC / DC.

[0085] According to the working principle of DC / DC converter, U2 = V O -V in V in = (1-D)×V O That is, U2 = D × V O .

[0086] The DC / DC converter loss P was established through data fitting. DC / DC Functional relationship between P and the step-up stage U2 of the DC / DC converter DC / DC =f3(U2).

[0087] Among them, the voltage level must meet the following conditions: U dc =U1 + U2. Where U dc The input parameter is known, and its value is constant for a specific power station.

[0088] S30, solve the energy consumption optimization model of the fuel cell stack to obtain the fuel cell string voltage level U1 and the DC / DC converter boost level U2 with the minimum loss. Then, based on the solution results, set the number of individual fuel cells connected in series and the selection of DC / DC converter accordingly.

[0089] The energy consumption optimization-based distribution method for the series voltage of the fuel cell stack and the DC boost voltage provided in this embodiment has the following effects: (1) The energy storage subsystem in the power station adopts a topology structure in which multiple fuel cell stacks are connected in parallel and then connected to the PCS, which can reduce the number of single fuel cell stacks in series, thereby reducing the leakage current of the common pipeline and improving the energy efficiency of the power station. At the same time, it reduces the impact of single fuel cell stack failure on the fuel cell stack series and improves the overall reliability of the power station. In addition, the power allocation space based on energy consumption optimization is increased, and the power station pump consumption can be further reduced according to the allocation strategy, thereby improving the overall energy efficiency of the power station. (2) The energy consumption distribution inside the liquid flow fuel cell stack is clearly defined, and a fuel cell stack energy consumption optimization model is established. This can realize the coordinated optimization of fuel cell stack boost energy consumption and DC / DC ratio loss, and increase the DC side voltage range to 1000~1200V, which can adapt to high inverter efficiency converters.

[0090] The present invention will be described in detail below with reference to specific embodiments:

[0091] A specific implementation example is as follows: A 35kV flow battery energy storage power station has a transformer ratio of 35kV / 690V and a PCS ratio of 690V(AC) / 1500V(DC). The DC voltage level U can be determined through the power station parameters. dc The value is 1500V.

[0092] According to the method proposed in this invention, an optimization solution is obtained:

[0093] min P RB +P DC / DC

[0094] st U1+U2=1500

[0095] P DC / DC =f3(U2) and P RB =f2(U1) The specific calculation is as described above. By solving the above, we can obtain: the stack voltage level U1 and the power electronic boost level U2.

[0096] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for allocating series voltage and DC boost voltage of a fuel cell stack based on energy consumption optimization, applied to a flow battery energy storage power station, characterized in that, The energy storage subsystem in the flow battery energy storage power station adopts a topology of multiple battery stacks connected in parallel and then connected to the PCS. Each battery stack includes a battery stack string and a DC / DC converter. The battery stack string is composed of n individual battery stacks connected in series. The method includes the following steps: (1) Determine the DC voltage level U based on the parameters of the flow battery energy storage power station. dc ; (2) Establish a stack energy consumption optimization model based on the characteristics of flow batteries. The stack energy consumption optimization model includes the stack series loss P. RB Add DC / DC converter loss P DC / DC The objective function and constraints are constructed with the goal of minimizing; wherein, the stack string loss P RB The DC / DC converter loss P is a function of the stack series voltage level U1. DC / DC The constraint is that the sum of the stack voltage level U1 and the DC / DC converter boost level U2 is equal to the DC voltage level U. dc ; (3) Solve the energy consumption optimization model of the fuel cell stack to obtain the fuel cell string voltage level U1 and DC / DC converter boost level U2 with the minimum loss. Then, based on the solution results, set the number of single fuel cells connected in series and the selection of DC / DC converter accordingly.

2. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 1, characterized in that, In step (2), the stack string loss P RB The method for establishing the functional relationship between the stack voltage level U1 and the battery pack is as follows: Based on the number of individual fuel cells connected in series n in the fuel cell string, the relationship between the voltage level U1 of the fuel cell string and n is determined, where U1 = n·a, and a is the voltage level of a single fuel cell string. Calculate the normal operating current loss P of the stack string based on the normal operating current loss of a single stack and the number of stacks connected in series in the stack string, n. nc Simultaneously, the leakage current loss P of the fuel cell string is calculated based on the leakage current loss of a single fuel cell in the string and the number of fuel cell stacks connected in series n. sc Then, based on the normal operating current loss P of the fuel cell stack, nc And the leakage current loss P of the fuel cell series sc Calculate the battery stack string loss P RB P RB =P nc +P sc ; Based on the relationship between the voltage level U1 and n of the fuel cell string and the fuel cell string loss P RB The relationship between the stack loss P and n is established through data fitting. RB The functional relationship between the stack voltage level U1 and the stack voltage level U1.

3. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 2, characterized in that, The normal operating current loss P of the fuel cell string nc The internal resistance of a single fuel cell stack in the fuel cell stack string is affected by the internal resistance of the single fuel cell stack, which includes ohmic internal resistance and polarization internal resistance. The internal resistance value changes with the operating state of the power plant. The normal operating current loss P of the fuel cell string nc The calculation formula is: P nc =n×P nc0 P nc0 =(R0+f1(C oi )×I DC 2 +α0) In the formula, P nc0 R0 is the normal operating current loss of a single fuel cell stack; f1(C) is the internal resistance of a single fuel cell stack in ohms; oi The polarization internal resistance of a single fuel cell stack is affected by the charge / discharge rate; I DC α is the operating current; α0 is the single-pile operating current loss correction amount, the value of which is obtained from actual measurement.

4. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 2 or 3, characterized in that, The leakage current loss P of the fuel cell series sc The leakage current loss of the fuel cell stack is affected by the resistance of the conduit and the number of fuel cell stacks connected in series. The calculation formula is as follows: P sc0,i =R plo ×(I dt,i 2 +I com,i 2 ) In the formula, P sc0,i α represents the leakage current loss of the i-th single stack in the stack string; sc This is the correction amount for leakage current loss in the fuel cell series, and its value is obtained from actual measurement; R plo I represents the internal resistance of the pipe corresponding to a single fuel cell stack. dt,i Assign the pipe leakage current I to the i-th single stack. com,i Let be the leakage current in the common conduit of the i-th single stack. The magnitude of both currents is related to the number of single stacks connected in series. According to the leakage current distribution characteristics, it is symmetrically distributed. Therefore, it is only necessary to calculate the leakage current loss of the 1-n / 2 or n / 2-n single stack, as follows: When n / 2≤i≤n, I com,i = β com -α com (in / 2) 2 , I dt,i = α dt (in / 2) 2 ; In the formula, α com β com α is the leakage current coefficient for public pipelines. dt The coefficients for the calculation function of the leakage current in the pipeline are all affected by the length and shape of the liquid flow single stack pipeline.

5. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 1, characterized in that, In step (2), the DC / DC converter loss P DC / DC The method for establishing the relationship between the DC / DC converter boost level U2 function and the DC / DC converter boost level is as follows: Calculate the DC / DC converter loss P based on the DC / DC converter's duty cycle D. DC / DC ; Based on the working principle of the DC / DC converter, the relationship between the DC / DC converter step-up level U2 and the DC / DC converter duty cycle D is determined as follows: U2 = D × V O V O This is the high-voltage side voltage of the DC / DC converter, which is equal to the rated low-voltage side voltage of the PCS (Power Storage System). Based on the DC / DC converter loss P DC / DC The relationship between the duty cycle D and the step-up voltage U2 of the DC / DC converter and the duty cycle D of the DC / DC converter is established through data fitting to establish the DC / DC converter loss P. DC / DC Functional relationship with the boost level U2 of the DC / DC converter.

6. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 1, characterized in that, The DC / DC converter loss P DC / DC The calculation formula is: P DC / DC =P on +P oth P on =a on ·(D)+β on P oth =a oth ·I DC 2 +b oth ·I DC +g oth In the formula, P on α represents the conduction loss of power electronic devices in a DC / DC converter. on β on This is a correction for conduction losses. This correction is significantly affected by the DC / DC converter model and can be fitted and assigned a value through actual testing of the DC / DC converter; P oth To exclude P on The sum of external losses unrelated to the turns ratio is considered to be the sum of losses affected by the operating current I. DC The quantity affected is the low-voltage side input current of the DC / DC converter; α oth β oth γ oth This is for other loss corrections.

7. The method for distributing the series voltage and DC boost voltage of the fuel cell stack based on energy consumption optimization according to claim 1, characterized in that, The energy storage subsystem adopts a topology of 3 to 5 stacks connected in parallel and then connected to the PCS.

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