MPC predictive control and electricity purchase cost optimization method of photovoltaic hydrogen production system

Abstract

The application discloses a kind of MPC prediction control and electricity purchase cost optimization method of photovoltaic hydrogen production system, belong to photovoltaic hydrogen production technical field, in system, the output direct current of photovoltaic system through booster converter and full bridge circuit, first excitation inductance is connected with first winding;The output direct current of grid after rectifier and full bridge circuit, second excitation inductance is connected with second winding;The output direct current of fuel cell through booster converter and full bridge circuit, third excitation inductance is connected with third winding;The output direct current of electrolytic tank through step-down converter and full bridge circuit, fourth excitation inductance is connected with fourth winding;Hydrogen storage tank connects electrolytic tank and fuel cell;Based on system, in electrolytic tank converter, join MPC prediction control algorithm and carry out Z-score function calculation optimal electricity purchase time when system purchases electricity from power grid.The application realizes the optimization of system hydrogen production efficiency, hydrogen production amount and system cost.

Description

TECHNICAL FIELD

[0001] The application relates to the field of photovoltaic hydrogen production technology, and particularly relates to MPC prediction control and electricity purchase cost optimization strategy of a photovoltaic hydrogen production system. BACKGROUND

[0002] With the development of green energy and hydrogen energy industry, photovoltaic hydrogen production gradually becomes an important clean energy conversion and energy storage technology. However, the volatility of photovoltaic power generation, the volatility of power grid price, and the uncertainty of hydrogen demand make the design of the optimization control strategy particularly important. The electrolytic cell requires that the input power and the output power of the photovoltaic system achieve minimum error, so as to improve the energy utilization rate of the photovoltaic hydrogen production system, maximize hydrogen production, and improve the hydrogen production efficiency. For the photovoltaic hydrogen production system, the error between the output power of the photovoltaic system and the input power of the electrolytic cell is required to be as small as possible, so as to maximize the energy utilization rate of the photovoltaic hydrogen production system and improve the hydrogen production efficiency. At the same time, the photovoltaic hydrogen production system is usually connected with a power grid, and the photovoltaic generated power can be used, and the power grid can be purchased when the photovoltaic generated power is insufficient. Since there is a difference between peak and valley prices of the power grid purchase, the power grid needs to be purchased when the purchase cost is optimized. SUMMARY

[0003] The application needs to solve the technical problem of providing the MPC prediction control and electricity purchase cost optimization strategy of the photovoltaic hydrogen production system, which can realize the synchronous tracking of the input power of the electrolytic cell and the output power of the photovoltaic system, and has the optimal electricity purchase cost.

[0004] To solve the above technical problems, the technical scheme adopted by the application is as follows:

[0005] An MPC prediction control and electricity purchase cost optimization method of a photovoltaic hydrogen production system, the photovoltaic hydrogen production system comprising a photovoltaic system, a power grid, an electrolytic cell, a hydrogen storage tank and a fuel cell; the photovoltaic system is connected with the power grid, supplies power to the power grid side through a boost converter, and the remaining power is used as input power of the electrolytic cell converter through a transformer, hydrogen produced by the electrolytic cell is delivered to the hydrogen storage tank, when the photovoltaic system is insufficient to supply power to the power grid, hydrogen in the hydrogen storage tank is delivered to the fuel cell, the fuel cell generates power, and the boost converter makes up for the power supply of the photovoltaic system, so that the overall photovoltaic hydrogen production system is stable.

[0006] The MPC prediction control and electricity purchase cost optimization method of the photovoltaic hydrogen production system comprises the following steps:

[0007] Step 1, setting an initial iteration cycle number t = 1; input current i E of the electrolytic cell, output current i s of the photovoltaic system, input current i of the fuel cell, output current i of the fuel cell, input voltage u and output voltage Sampling is performed, and the input power P of the electrolytic tank is calculated after sampling E , the output power P of the photovoltaic system S , the charging power p of the fuel cell BS,Chg (t) and the discharging power p BS,Dhg (t);

[0008] Step 2, judge whether the output power of the photovoltaic system can meet the power demand P of the power grid G ; if the demand can be met, the remaining power is input into the electrolytic tank converter, the input current i E of the electrolytic tank is optimized by MPC predictive control on the electrolytic tank converter; the generated hydrogen is stored in the hydrogen storage tank, and the remaining power is sold to the power grid; if it cannot be met, step 3 is performed;

[0009] Step 3, judge whether the discharging power p BS,Dhg (t) of the fuel cell can meet the remaining demand P G -P S ; if it can be met, the hydrogen in the hydrogen storage tank is used as raw material for the fuel cell; if it cannot be met, step 4 is performed;

[0010] Step 4, purchase power from the power grid, and sample the historical electricity price, obtain the optimal purchase time by calculating the Z-score function, and reduce the purchase cost;

[0011] Step 5, judge whether the cycle time t is equal to 8760, to meet the cycle within one year.

[0012] The further improvement of the technical scheme of the application is that the photovoltaic hydrogen production system realizes photovoltaic hydrogen production based on five modules, which are:

[0013] Photovoltaic system module: the photovoltaic system is connected at both ends of the full-bridge circuit through a DC-DC booster converter, and the output direct current is connected with the first winding N1 through the first excitation inductance L1;

[0014] Grid module: the grid outputs direct current through a rectifier and is connected at both ends of the full-bridge circuit, and the output direct current is connected with the second winding N2 through the second excitation inductance L2;

[0015] Fuel cell module: the fuel cell is connected at both ends of the full-bridge circuit through a DC-DC booster converter, and the output direct current is connected with the third winding N3 through the third excitation inductance L3;

[0016] Electrolytic tank module: the electrolytic tank is connected at both ends of the full-bridge circuit through a DC-DC step-down converter, and the output direct current is connected with the fourth winding N4 through the fourth excitation inductance L4;

[0017] The hydrogen storage tank module is connected with the electrolytic cell and the fuel cell module; wherein the full-bridge circuit of each module is composed of four groups of switch tubes S a1 -S a4 、S b1 -S b4 、S c1 -S c4 、S d1 -S d4 .

[0018] The further improvement of the technical scheme of the present application is that in step 2, the MPC predictive control specifically comprises the following contents:

[0019] The target function of the MPC predictive control is constructed:

[0020]

[0021] In the formula, N p is the prediction step, N p = 30; P E (k+l) is the input power of the electrolytic cell at k+l; i E (k+l) is the input current of the electrolytic cell at k+l; P S (k+l) is the output power of the photovoltaic system;

[0022] The optimal input current of the electrolytic cell at the optimal state is obtained by minimizing and optimizing the target function J through the iterative Newton method;

[0023] The error E G (t) between the input power of the electrolytic cell and the output power of the photovoltaic system is defined as E E (t) = P s (t)-P G (t), the first-order Taylor approximation of E G (t) is obtained, and the linearized expression of E Similarly, the input current i of the electrolytic cell and the output power P of the photovoltaic system are obtained G Further, the error E (t), the input current i of the electrolytic cell and the output power P of the photovoltaic system are discretized, and the Newton iterative cycle of the error is obtained:

[0024]

[0025] In the target function, P E (k+l)-P s (k+l) is essentially the error between the input power of the electrolytic cell converter and the maximum output power of the photovoltaic system, so the optimization of E is directly performed.

[0026] Where the Newton method iterative equation is:

[0027]

[0028] Therefore, the problem of solving the minimum value of the objective function J is transformed into the solution of the Newton method iteration of the error;

[0029] Where the relationship between the input voltage and current of the electrolytic cell is as follows:

[0030]

[0031] In the formula, V rev is the reversible voltage of the electrolytic cell, which is 1.299v; r e is the resistance of the electrolytic cell, which is 6.89×10 -5 Ω·m 2 ; s e is the overvoltage coefficient of the electrolytic cell, which is 0.185v, t e is the coefficient of the relationship between the overvoltage of the electrolytic cell and the current, which is 0.2596m 2 / A; A is the electrode area, which is A=0.013m 2 ; the input voltage v E (i E ) of the electrolytic cell is expressed in the above formula to perform the Newton method iteration of the error function;

[0032] Define the constraint condition of the control variable: in the ideal state, without considering the constraint of the hydrogen storage capacity of the hydrogen storage tank, when (P E (i E )-P s (t)) 2 takes the minimum value, the maximum value of the input current i E of the electrolytic cell can be obtained;

[0033] Define the function g(i E )=(P E (i E )-P s (t)) 2 , and take the derivative of g(i E ) to obtain:

[0034]

[0035] Note that the input power P E (i E ) of the electrolytic cell is an increasing function of the input current of the electrolytic cell, so solving the maximum value of the input current i E of the electrolytic cell is to make P E (i E )=Ps P s is the maximum output power of the photovoltaic system;

[0036] The iteration process is stopped when the iteration result reaches the constraint condition, and the optimal input current i of the electrolyzer converter at this time is obtained E out The sampled output voltage v of the photovoltaic system is input to the input current of the electrolyzer converter through the transformer s The sampled output voltage v of the photovoltaic system is input to the input current of the electrolyzer converter through the transformer is:

[0037]

[0038] Because the electrolyzer converter is a step-down converter, the duty cycle of the electrolyzer converter at this time is calculated as:

[0039]

[0040] The further improvement of the technical scheme of the present application is that in step 4, the power purchase cost function of the power grid is as follows:

[0041]

[0042] In the formula, is the electricity price at time t; is the average value of the historical electricity price; is the standard deviation of the historical electricity price;

[0043] For the grid-side rectifier, the SPWM three-phase circuit control strategy is used to change the current reference value of the current loop PI controller to adjust the grid power purchase power;

[0044] The grid power has the following constraints:

[0045]

[0046] In the formula, is the grid power purchase power, and are the minimum and maximum grid power purchase powers, respectively; and are determined according to the power supply capacity of the grid and the equipment demand;

[0047] When the Z-score is less than 0, it indicates that the electricity price is lower than the historical minimum value, at which time the grid power purchase power should be increased That is, the photovoltaic hydrogen production system should increase the grid power purchase power, at which time the current reference value of the current loop PI control of the grid rectifier is increased and the grid output power is controlled within the constraint condition;

[0048] When Z-score>0, it indicates that the electricity price is higher than the historical minimum value, at this time the photovoltaic hydrogen production system should reduce the electricity purchase from the grid That is, the photovoltaic hydrogen production system should reduce the electricity purchase from the grid; at this time, the current reference value of the grid rectifier current loop PI control is reduced and the grid output power is controlled within the constraint condition.

[0049] Thanks to the above technical solutions, the present application has achieved the following technical progress:

[0050] In the present application, after the photovoltaic system passes through the DC-DC booster converter and the full-bridge circuit, the output DC current is connected with the winding N1 through the excitation inductance L1; after the grid passes through the rectifier and the full-bridge circuit, the output DC current is connected with the winding N2 through the excitation inductance L2; after the fuel cell passes through the DC-DC booster converter and the full-bridge circuit, the output DC current is connected with the winding N3 through the excitation inductance L3; after the electrolytic tank passes through the DC-DC booster converter and the full-bridge circuit, the output DC current is connected with the winding N4 through the excitation inductance L4; the hydrogen storage tank is connected with the electrolytic tank and the fuel cell; based on this structure, the MPC predictive control algorithm is added in the electrolytic tank converter and the Z-score function is calculated to obtain the optimal electricity purchase time when the system purchases electricity from the grid, so as to realize the optimization of the hydrogen production efficiency, hydrogen production amount and system cost of the system. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative labor on the basis of these drawings;

[0052] Figure 1 is the circuit diagram of the photovoltaic hydrogen production system provided in the embodiments of the present application;

[0053] Figure 2 is the control flow chart of the MPC predictive control and electricity purchase cost optimization method of the photovoltaic hydrogen production system provided in the embodiments of the present application. DETAILED DESCRIPTION

[0054] It should be noted that the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device containing a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0055] The present application will be further described in detail below in combination with the drawings and embodiments:

[0056] As Figure 1 shown, a MPC predictive control and electricity purchase cost optimization method of a photovoltaic hydrogen production system, specifically includes the following contents:

[0057] The photovoltaic hydrogen production system includes a photovoltaic system, a power grid, an electrolytic tank, a hydrogen storage tank and a fuel cell, and the specific connection mode is: the photovoltaic system is connected with the power grid, supplies power to the power grid side through a boost converter, and the remaining power is used as input power to the electrolytic tank converter through a transformer. The hydrogen produced by the electrolytic tank is delivered to the hydrogen storage tank. When the photovoltaic system is insufficient to supply power to the power grid, the hydrogen in the hydrogen storage tank is delivered to the fuel cell, the fuel cell generates electricity, and the boost converter makes up for the power supply of the photovoltaic system, so that the overall photovoltaic hydrogen production system is stable.

[0058] The constructed photovoltaic hydrogen production system model realizes photovoltaic hydrogen production based on five modules, including a photovoltaic system module, a power grid module, a fuel cell module, an electrolytic tank module and a hydrogen storage tank module. Respectively:

[0059] Photovoltaic system module: the photovoltaic system is connected at both ends of the full-bridge circuit through a DC-DC boost converter, and the output direct current is connected with the first winding N1 through the first excitation inductance L1;

[0060] Power grid module: the power grid outputs direct current through a rectifier and is connected to both ends of the full-bridge circuit. The output direct current is connected with the second winding N2 through the second excitation inductance L2;

[0061] Fuel cell module: the fuel cell is connected at both ends of the full-bridge circuit through a DC-DC boost converter, and the output direct current is connected with the third winding N3 through the third excitation inductance L3;

[0062] Electrolytic tank module: the electrolytic tank is connected at both ends of the full-bridge circuit through a DC-DC step-down converter, and the output direct current is connected with the fourth winding N4 through the fourth excitation inductance L4;

[0063] Hydrogen storage tank module: connected with the electrolytic tank and fuel cell module; wherein the full-bridge circuit of each module is composed of four groups of switching tubes S a1 -S a4 、S b1 -S b4 、S c1 -S c4 、S d1 -S d4 .

[0064] As Figure 2 shown, the MPC predictive control and electricity purchase cost optimization method of the photovoltaic hydrogen production system includes the following steps:

[0065] Step 1: Set the initial iteration number t = 1; sample the electrolytic cell input current to obtain i E , the output current of the photovoltaic system is sampled and i s , the fuel cell input current and output current are sampled and Input voltage and output voltage sampling and After sampling, the input power P of the electrolytic cell is calculated E , the output power P of the photovoltaic system S , the charging power and discharging power p of the fuel cell BS,Chg (t) and p BS,Dhg (t);

[0066] Step 2: Determine the output power P of the photovoltaic system S Whether it can meet the power demand P of the power grid G If the demand can be met, the remaining power is input to the electrolyzer converter, and the current i of the electrolyzer input is optimized by performing MPC predictive control on the electrolyzer converter. E The generated hydrogen is stored in a hydrogen storage tank, and the remaining electricity is sold to the grid; if it cannot be met, proceed to step 3;

[0067] MPC predictive control specifically includes the following:

[0068] Construct the objective function of MPC predictive control:

[0069]

[0070] Among them, N p is the prediction step length. In this photovoltaic hydrogen production system, the prediction step length N p =30;P E (k+1) is the input power of the electrolyzer at time k+1; i E (k+l) is the input current of the electrolytic cell; P S (k+l) is the output power of the photovoltaic system.

[0071] The objective function J is minimized by iterative Newton method to obtain the optimal input current of the electrolytic cell in the optimal state.

[0072] Define the error between the electrolyzer input power and the photovoltaic system output power as E G (t) = P E (t)-P s (t), E G (t) Perform first-order Taylor approximation and obtain E G (t) The linearized expression is: Similarly, the electrolytic cell input current is obtained and the output power of the photovoltaic system Further, the error E G (t), electrolytic tank input current and photovoltaic system output power Discretization processing, and Newton method iteration cycle for error:

[0073]

[0074] In the objective function, P E (k+l)-P s (k+l) is the error of electrolytic tank converter input power and photovoltaic system maximum output power, so we can directly optimize .

[0075] Where the Newton method iteration equation is:

[0076]

[0077] Therefore, the problem of solving the minimum value of the objective function J is transformed into the solution of the error by Newton method iteration.

[0078] Where the relationship between the input voltage and the input current of the electrolytic tank is as follows:

[0079]

[0080] In the formula, V rev is the reversible voltage of the electrolytic tank, usually 1.299v; r e is the resistance of the electrolytic tank, taking 6.89×10 -5 Ω·m 2 , s e is the overvoltage coefficient of the electrolytic tank, taking 0.185v, t e is the coefficient of the electrolytic tank overvoltage and current relationship, which is 0.2596m 2 / A; A is the electrode area, taking A=0.013m 2 .

[0081] The expression of the input voltage v E (i E ) of the electrolytic tank is brought into the above formula to perform Newton method iteration of the error function.

[0082] Define the constraint condition of the control variable:

[0083] Under ideal conditions, without considering the constraint of the hydrogen storage capacity of the hydrogen storage tank, when (P E (i E )-P s (t)) 2 takes the minimum value, the maximum value of the current i E is obtained.

[0084] Define the function g(i E )=(P E (i E )-P s (t)) 2 , for g(i E ) Take the derivative and get:

[0085]

[0086] Note that the electrolytic cell input power P E (i E ) is an increasing function of the electrolytic cell input current, so the electrolytic cell input current i E The maximum value, that is, when P E (i E )=P s At this time P s is the maximum output power of the photovoltaic system.

[0087] When the iteration result reaches the constraint condition, the iteration process is stopped and the optimal input current i of the electrolyzer converter is obtained. E out , according to the sampled photovoltaic system output voltage v s , the input current to the electrolyzer converter through the transformer for:

[0088]

[0089] Because the electrolyzer converter is a step-down converter, the duty cycle of the electrolyzer converter is calculated as:

[0090]

[0091] Step 3: Determine the fuel cell output power p BS,Dhg (t) Whether the remaining demand of the power grid can be met P G -P S If the conditions are met, the hydrogen in the hydrogen storage tank is used to provide raw materials for the fuel cell; if not, proceed to step 4;

[0092] Step 4: Purchase electricity from the power grid, sample historical electricity prices, and calculate the Z-score function to obtain the optimal purchase time to reduce the purchase cost.

[0093] Specifically, the power purchase cost from the power grid is compared with the lowest power purchase cost at the previous moment, and the optimal power purchase time and cost are selected through logical judgment, including:

[0094] The power purchase cost function of the power grid is as follows:

[0095]

[0096] wherein: is the electricity price at time t; is the average value of historical electricity price; is the standard deviation of historical electricity price. For grid-side rectifier, we use SPWM three-phase circuit control strategy to adjust the grid purchase power by changing the current reference value of the current loop PI controller.

[0097] The grid power has the following constraints:

[0098]

[0099] wherein, is the grid purchase power, and are the minimum and maximum grid purchase power, respectively, which are determined according to the grid power supply capacity and equipment demand.

[0100] When Z-score < 0, it indicates that the electricity price is lower than the historical minimum value, at which time the grid purchase power should be increased i.e. the photovoltaic hydrogen system should increase the purchase of electricity from the grid, at which time the current reference value of the grid rectifier current loop PI control is increased and the grid output power is controlled within the constraint condition.

[0101] When Z-score > 0, it indicates that the electricity price is higher than the historical minimum value, at which time the grid purchase power should be reduced i.e. the photovoltaic hydrogen system should reduce the purchase of electricity from the grid. At this time, the current reference value of the grid rectifier current loop PI control is reduced and the grid output power is controlled within the constraint condition.

[0102] Step 5, judge whether the cycle time t is equal to 8760, to meet the cycle within one year.

[0103] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for MPC predictive control and electricity purchase cost optimization of a photovoltaic hydrogen production system, characterized by: The photovoltaic hydrogen production system includes a photovoltaic system, power grid, electrolyzer, hydrogen storage tank, and fuel cell. The photovoltaic system is connected to the power grid and supplies power to the grid via a boost converter. The remaining power is applied to the electrolyzer converter as input power via a transformer. The hydrogen produced by the electrolyzer is then delivered to the hydrogen storage tank. When the photovoltaic system's power supply to the grid is insufficient, the hydrogen in the hydrogen storage tank is delivered to the fuel cell. The fuel cell generates electricity, which is then supplemented by the boost converter to stabilize the overall photovoltaic hydrogen production system. The MPC predictive control and electricity purchase cost optimization method for the photovoltaic hydrogen production system includes the following steps: Step 1, set the initial iteration cycle number t = 1; the input current i of the electrolytic cell E , the output current i of the photovoltaic system s , fuel cell input current Output current Input voltage and output voltage Sampling is performed and the input power P of the electrolytic cell is calculated after sampling. E , the output power P of the photovoltaic system S , fuel cell charging power p BS,Chg (t) and discharge power p BS,Dhg (t); Step 2: Determine whether the output power of the photovoltaic system can meet the power demand of the grid P G If the demand can be met, the remaining power is input to the electrolyzer converter, and the input current i of the electrolyzer is optimized by performing MPC predictive control on the electrolyzer converter. E The generated hydrogen is stored in a hydrogen storage tank, and the remaining electricity is sold to the grid; if it cannot be met, proceed to step 3; Step 3: Determine the discharge power p of the fuel cell BS,Dhg (t) Whether the remaining demand of the power grid can be met P G -P S If the conditions are met, the hydrogen in the hydrogen storage tank is used to provide raw materials for the fuel cell; if not, proceed to step 4; Step 4: Purchase electricity from the power grid, sample historical electricity prices, and calculate the Z-score function to obtain the optimal electricity purchase time to reduce electricity purchase costs; Step 5: Determine whether the cycle time t is equal to 8760, so as to meet the cycle time of one year.

2. The MPC predictive control and electricity purchase cost optimization method for a photovoltaic hydrogen production system according to claim 1, characterized in that: The photovoltaic hydrogen production system is based on five modules to achieve photovoltaic hydrogen production, namely: Photovoltaic system module: The photovoltaic system is connected to both ends of the full-bridge circuit through a DC-DC boost converter, and the output DC current is connected to the first winding N1 through the first excitation inductor L1; Grid module: The grid outputs DC power through the rectifier and is connected to both ends of the full-bridge circuit. The output DC current is connected to the second winding N2 through the second excitation inductor L2; Fuel cell module: The fuel cell is connected to both ends of the full-bridge circuit through a DC-DC boost converter, and the output DC current is connected to the third winding N3 through the third excitation inductor L3; Electrolyzer module: The electrolyzer is connected to both ends of the full-bridge circuit through a DC-DC step-down converter, and the output DC current is connected to the fourth winding N4 through the fourth excitation inductor L4; Hydrogen storage tank module: connects the electrolyzer and fuel cell module; the full bridge circuit of each module consists of four sets of switch tubes S a1 -S a4 、S b1 -S b4 、S c1 -S c4 、S d1 -S d4 constitute.

3. The MPC predictive control and electricity purchase cost optimization method for a photovoltaic hydrogen production system according to claim 1, characterized in that: In step 2, MPC predictive control specifically includes the following: Construct the objective function of MPC predictive control: Where N p is the prediction step size, N p =30;P E (k+1) is the input power of the electrolyzer at time k+1; i E (k+1) is the input current of the electrolytic cell at time k+1; P S (k+l) is the output power of the photovoltaic system; The objective function J is minimized by iterative Newton method to obtain the optimal input current of the electrolytic cell in the optimal state; Define the error between the electrolyzer input power and the photovoltaic system output power as E G (t) = P E (t)-P s (t), E G (t) performs first-order Taylor approximation and obtains E G (t) The linearized expression is: Similarly, the electrolytic cell input current is obtained and the output power of the photovoltaic system Further, the error E G (t), electrolytic cell input current and photovoltaic system output power Discretization processing and Newton method iteration cycle are performed on the error to obtain: In the objective function, P E (k+l)-P s The essence of (k+l) is the error between the input power of the electrolyzer converter and the maximum output power of the photovoltaic system. Just search for the best result; The Newton method iteration equation is: Therefore, the problem of solving the minimum value of the objective function J is transformed into solving the error by Newton's method iteration; The relationship between the input voltage and current of the electrolytic cell is as follows: Where V rev is the reversible voltage of the electrolytic cell, which is 1.299V; r e The resistance of the electrolytic cell is 6.89×10 -5 Ω·m 2 ; s e Take 0.185v as the overvoltage coefficient of the electrolytic cell, t e is the coefficient of the relationship between the overvoltage and current of the electrolytic cell, which is 0.2596m 2 / A; A is the electrode area, A = 0.013m 2 ; Input voltage v to the electrolytic cell E (i E ) expression is brought into the above formula to perform Newton method iteration of the error function; Define the constraints of the control variables: Under ideal conditions, without considering the constraints of the hydrogen storage capacity of the hydrogen storage tank, when (P E (i E )-P s (t)) 2 When the minimum value is obtained, the input current i of the electrolytic cell can be obtained. E The maximum value of Define the function g(i E )=(P E (i E )-P s (t)) 2 , for g(i E ) Take the derivative and get: Note the input power P of the electrolyzer E (i E ) is an increasing function of the electrolytic cell input current, so the input current i of the electrolytic cell is solved E The maximum value, that is, when P E (i E )=P s When P s is the maximum output power of the photovoltaic system; When the iteration result reaches the constraint condition, the iteration process is stopped and the optimal input current i of the electrolyzer converter is obtained. E out , the sampled photovoltaic system output voltage v s , the input current to the electrolyzer converter through the transformer for: Because the electrolyzer converter is a step-down converter, the duty cycle of the electrolyzer converter is calculated as:

4. The MPC predictive control and electricity purchase cost optimization method for a photovoltaic hydrogen production system according to claim 1, characterized in that: In step 4, the power purchase cost function of the grid is as follows: Where, is the electricity price at time t; is the average of historical electricity prices; is the standard deviation of historical electricity prices; For the grid-side rectifier, the SPWM three-phase circuit control strategy is used to adjust the power purchased from the grid by changing the current reference value of the current loop PI controller; The following constraints apply to grid power: Where, The power purchased by the grid, and are the minimum and maximum purchased power of the power grid respectively; and Determined by the power supply capacity of the power grid and the equipment requirements; When Z-score is less than 0, it means that the electricity price is lower than the historical lowest value. That is, the photovoltaic hydrogen production system should increase the amount of electricity purchased from the grid. At this time, the current reference value of the grid rectifier current loop PI control should be increased and the grid output power should be controlled within the constraint conditions. When Z-score>0, it means that the electricity price is higher than the historical lowest value, and p should be reduced. t Grd , that is, the photovoltaic hydrogen production system should reduce the amount of electricity purchased from the grid; at this time, the current reference value of the grid rectifier current loop PI control is reduced and the grid output power is controlled within the constraint conditions.

Images