Direct-current feed-out wind power generation hydrogen production method and system

Abstract

The invention provides a direct-current feed-out wind power generation hydrogen production method and system, and the method comprises the steps: 1, enabling blades of a wind turbine to rotate under the action of wind power, enabling a hub to be connected with a main shaft, outputting mechanical energy to a power generator in a torque form, and then driving the power generator to convert the mechanical energy into electric energy; 2, balancing power fluctuation in a system operation process through intervention of an energy storage device; 3, the wind power generation system uses an electrolytic cell to electrolyze water to obtain hydrogen and hydrogen, and a fitting method is used to obtain output characteristics; 4, obtaining the output power characteristics of the wind turbine under different wind speed conditions according to the mathematical model of the wind turbine; and 5, realizing wind power maximum power point tracking (MPPT) control by using an optimal tip speed ratio method. According to the direct-current feed-out wind power generation hydrogen production system, the grid connection link of a wind power generation system can be omitted, the hydrogen production system is directly connected to the direct-current bus, the system structure is simplified, the operation cost and energy loss are reduced, and the energy utilization efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a method and system for producing hydrogen by direct current-fed wind power generation. Background Art

[0002] As an important secondary clean energy, hydrogen energy has attracted much attention for its cleanliness, high efficiency, environmental protection, easy production, easy utilization, and flexible storage. At the same time, the combination of hydrogen production system and new energy power generation system can improve the utilization efficiency of renewable energy and the stability of the power generation system.

[0003] When the wind power generation system is combined with the hydrogen production system, the wind energy can be peak-shifted and valley-filled in the form of hydrogen energy storage. When there is a surplus of electricity, the excess electricity can be fully utilized to produce hydrogen through water electrolysis, and the electricity can be converted into hydrogen energy for storage; when there is a shortage of electricity, the stored hydrogen energy can be used to generate electricity in the form of fuel cells, and the hydrogen energy can be converted into electricity to maintain the power supply. The application of this combination of electricity and hydrogen in the wind power generation system can not only reduce the waste of wind energy, but also provide a flexible energy regulation method, increasing the reliability, stability, flexibility and resilience of the wind power generation system.

[0004] At present, there are two main technical routes for wind power generation and hydrogen production. One is the grid-connected offshore hydrogen production technology that uses electricity from the grid to produce hydrogen after the wind turbine is connected to the grid. The other is the off-grid hydrogen production technology that directly uses electricity to electrolyze hydrogen after the wind turbine generates electricity. In the wind power generation system, the off-grid hydrogen production technology reduces the dependence on the power grid and reduces the cost of hydrogen production. At the same time, it can realize the local consumption of new energy and improve the energy conversion rate. At the same time, the DC-fed wind power generation system has excellent stability and controllability compared to the traditional wind power generation system, which is crucial to dealing with the volatility and intermittency problems in wind power grid connection. Therefore, the DC-fed wind power generation system has become a hot topic in the field of new energy research. At present, the traditional wind power hydrogen production system is relatively mature, but the principle and control of the DC-fed wind power generation hydrogen production system still need to be studied and improved.

[0005] The wind power generation system proposed in patent application document CN109004665A utilizes excess electrical energy to produce hydrogen, and uses an energy storage device to release electrical energy to the system to stabilize the power fluctuation of the system and achieve stable production of hydrogen. However, the maximum power output of the system cannot be achieved under wind speed fluctuations, the utilization efficiency of wind energy is low, the cost of hydrogen production by the system is high, and no simulation verification has been carried out.

[0006] Patent application document CN117039875A proposes to directly connect the hydrogen production device to the DC bus after AC rectification of the wind turbine to perform hydrogen production operations, eliminating the grid-connected link of the wind power generation system and reducing the grid-connected topology construction to reduce system complexity. However, when the wind speed changes, the output power fluctuation of the system will cause the DC bus voltage to be unable to remain stable, seriously reducing the operating efficiency of the hydrogen production system and increasing the system cost.

[0007] In summary, the existing wind power generation and hydrogen production system with energy storage devices involved has problems such as low wind energy utilization efficiency and no simulation verification, while the wind power generation and hydrogen production system directly involved in the DC bus does not consider the impact of wind speed fluctuations on the operation of the hydrogen production system. Summary of the invention

[0008] In view of the defects in the prior art, an object of the present invention is to provide a method and system for producing hydrogen by direct current-fed wind power generation.

[0009] The method for producing hydrogen by direct current-fed wind power generation provided by the present invention comprises:

[0010] Step 1: Analyze the wind turbine operation mechanism of the DC-fed wind power generation system: The blades of the wind turbine rotate under the action of wind, connected to the main shaft through the hub, and output mechanical energy in the form of torque to the generator, which then drives the generator to convert mechanical energy into electrical energy;

[0011] Step 2: Analyze the operating mechanism of the energy storage device in the DC-fed wind power generation hydrogen production system: balance the power fluctuations during system operation through the intervention of the energy storage device;

[0012] Step 3: Analyze the operating mechanism of the hydrogen production device of the DC-fed wind power generation hydrogen production system: The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen, and uses the fitting method to obtain its output characteristics;

[0013] Step 4: According to the mathematical model of the wind turbine, the output power characteristics of the wind turbine under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the output power of the wind turbine; under the same wind speed conditions, the wind turbine outputs the maximum power at a certain wind turbine speed;

[0014] Step 5: Use the optimal tip speed ratio method to achieve wind maximum power MPPT control.

[0015] Preferably, based on the relevant principles of aerodynamics, the mathematical model of the wind turbine is as follows:

[0016] P m =k p C p (β,λ)v 3

[0017]

[0018]

[0019]

[0020]

[0021] Where R is the radius of the wind turbine, P m is the mechanical power generated, β is the blade tip pitch angle, λ is the blade tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind wheel speed, ρ is the air density; k p is the proportional constant in the wind turbine calculation formula, which is related to the air density ρ and the radius R of the wind turbine rotor; v is the wind speed; c1, c2, c3, c4, c5, c6 are the empirical parameters in the wind energy utilization coefficient formula; λ i Represents the intermediate variable related to the blade speed ratio λ, used for the wind energy utilization coefficient C p Calculation of mechanical torque T of wind turbine m satisfy:

[0022] Preferably, the bidirectional Buck-Boost circuit structure of the energy storage device is: an input voltage source V1 is connected in parallel with a capacitor C1, one end of the capacitor C1 is connected to an inductor L, the other end of the capacitor C1 is connected to an output capacitor C2, the other end of the inductor L is connected to switch tubes S1 and S2 respectively, the switch tubes S1 and S2 are respectively connected in reverse parallel with diodes D1 and D2, the common node of the switch tubes S1 and S2 is connected to the output capacitor C2, and the two ends of the output capacitor C2 are respectively the positive and negative electrodes of the output voltage V2;

[0023] There are two working modes of energy storage devices:

[0024] Charging mode: When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit works in Buck mode, the switch tube S1 is always off, and the switch tube S2 is turned on or off under the control of the drive signal of the control system; when the switch tube S2 is turned on, the DC bus provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the charging time. When the switch tube S2 is turned off, the inductor current I L The current flows through diode D1 and continues to charge the battery, but I L It decreases with the increase of charging time;

[0025] Discharge mode: When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit works in the Boost mode, the switch tube S2 is always off, and the switch tube S1 is turned on or off under the control of the drive signal of the control system; when the switch tube S1 is turned on, the energy storage system battery provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the discharge time. When the switch tube S1 is turned off, the inductor current I L The current flows through diode D2 and continues to charge the DC bus, but I L It decreases with the increase of discharge time.

[0026] Preferably, using a fitting method to obtain its output characteristics comprises:

[0027]

[0028] Among them, U el Represents the output voltage, I el Represents the working current, n c Represents the number of serial slots, U r represents the reversible voltage, r1 and r2 represent the resistance, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 With k el represents the overvoltage parameter of the electrolytic cell, and A represents the electrode surface area;

[0029] The reversible voltage calculation equation of the electrolytic cell is:

[0030]

[0031] in, Represents the reversible voltage under standard conditions, k r represents the empirical temperature coefficient;

[0032] At the same time, according to the relevant principles of hydrogen production by electrolysis in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as:

[0033]

[0034]

[0035] Among them, q H2 represents the hydrogen production rate, F represents the Faraday constant, η F represents the current efficiency, k f1 , k f2 Represents the empirical parameter in the current efficiency calculation formula.

[0036] Preferably, when the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the real-time wind speed and the fan speed of the system, and compared with the theoretical optimal tip speed ratio. If the actual tip speed ratio matches the optimal tip speed ratio or the difference is within a preset range, the system is operating at the optimal power point; otherwise, the controller automatically adjusts according to the difference, and controls the fan speed of the wind power system according to the analysis result to reduce the deviation between the actual tip speed ratio and the optimal tip speed ratio;

[0037] After the ideal speed signal is obtained through the optimal tip speed ratio control method, the speed signal is responded to by using the double closed-loop control method of speed outer loop and current inner loop on the rectifier side of the permanent magnet synchronous generator;

[0038] The dual closed-loop control method of the speed outer loop and the current inner loop includes: the speed outer loop calculates the ideal speed of the wind turbine output by the optimal tip speed ratio method as the input of the outer loop, and compares it with the motor speed of the permanent magnet synchronous generator during actual operation; then the reference size of the d-axis current and the q-axis current is obtained by the action of the zero d-axis current control and the PI regulator, and the q-axis current iq is adjusted to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed is close to the ideal speed of the wind turbine, thereby realizing speed regulation control; then the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, the voltage signal is coordinate-transformed, and finally a suitable PWM drive signal is output through the SVPWM space vector modulation method to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed-out function of the wind power generation system.

[0039] The DC-fed wind power generation hydrogen production system provided by the present invention comprises:

[0040] Module M1: Analysis of the wind turbine operating mechanism of the DC-fed wind power generation system: The blades of the wind turbine rotate under the action of wind, connected to the main shaft through the hub, and output mechanical energy to the generator in the form of torque, which in turn drives the generator to convert mechanical energy into electrical energy;

[0041] Module M2: Analysis of the operating mechanism of the energy storage device in the DC-fed wind power generation hydrogen production system: balancing the power fluctuations during system operation through the intervention of the energy storage device;

[0042] Module M3: Analysis of the operating mechanism of the hydrogen production device of the DC-fed wind power generation hydrogen production system: The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen, and the fitting method is used to obtain its output characteristics;

[0043] Module M4: Based on the mathematical model of the wind turbine, the output power characteristics of the wind turbine under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the output power of the wind turbine; under the same wind speed conditions, the wind turbine outputs the maximum power at a certain wind turbine speed;

[0044] Module M5: Use the optimal tip speed ratio method to achieve wind maximum power MPPT control.

[0045] Preferably, based on the relevant principles of aerodynamics, the mathematical model of the wind turbine is as follows:

[0046] P m =k p C p (β,λ)v 3

[0047]

[0048]

[0049]

[0050]

[0051] Where R is the radius of the wind turbine, P m is the mechanical power generated, β is the blade tip pitch angle, λ is the blade tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind wheel speed, ρ is the air density; k p is the proportional constant in the wind turbine calculation formula, which is related to the air density ρ and the radius R of the wind turbine rotor; v is the wind speed; c1, c2, c3, c4, c5, c6 are the empirical parameters in the wind energy utilization coefficient formula; λ i Represents the intermediate variable related to the blade speed ratio λ, used for the wind energy utilization coefficient C p Calculation of mechanical torque T of wind turbine m satisfy:

[0052] Preferably, the bidirectional Buck-Boost circuit structure of the energy storage device is: an input voltage source V1 is connected in parallel with a capacitor C1, one end of the capacitor C1 is connected to an inductor L, the other end of the capacitor C1 is connected to an output capacitor C2, the other end of the inductor L is connected to switch tubes S1 and S2 respectively, the switch tubes S1 and S2 are respectively connected in reverse parallel with diodes D1 and D2, the common node of the switch tubes S1 and S2 is connected to the output capacitor C2, and the two ends of the output capacitor C2 are respectively the positive and negative electrodes of the output voltage V2;

[0053] There are two working modes of energy storage devices:

[0054] Charging mode: When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit works in Buck mode, the switch tube S1 is always off, and the switch tube S2 is turned on or off under the control of the drive signal of the control system; when the switch tube S2 is turned on, the DC bus provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the charging time. When the switch tube S2 is turned off, the inductor current I L The current flows through diode D1 and continues to charge the battery, but I L It decreases with the increase of charging time;

[0055] Discharge mode: When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit works in the Boost mode, the switch tube S2 is always off, and the switch tube S1 is turned on or off under the control of the drive signal of the control system; when the switch tube S1 is turned on, the energy storage system battery provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the discharge time. When the switch tube S1 is turned off, the inductor current I L The current flows through diode D2 and continues to charge the DC bus, but I L It decreases with the increase of discharge time.

[0056] Preferably, using a fitting method to obtain its output characteristics comprises:

[0057]

[0058] Among them, U el Represents the output voltage, I el Represents the working current, n c Represents the number of serial slots, U r represents the reversible voltage, r1 and r2 represent the resistance, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 With k el represents the overvoltage parameter of the electrolytic cell, and A represents the electrode surface area;

[0059] The reversible voltage calculation equation of the electrolytic cell is:

[0060]

[0061] in, Represents the reversible voltage under standard conditions, k r represents the empirical temperature coefficient;

[0062] At the same time, according to the relevant principles of hydrogen production by electrolysis in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as:

[0063]

[0064]

[0065] Among them, q H2 represents the hydrogen production rate, F represents the Faraday constant, η F represents the current efficiency, k f1 , k f2 Represents the empirical parameter in the current efficiency calculation formula.

[0066] Preferably, when the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the real-time wind speed and the fan speed of the system, and compared with the theoretical optimal tip speed ratio. If the actual tip speed ratio matches the optimal tip speed ratio or the difference is within a preset range, the system is operating at the optimal power point; otherwise, the controller automatically adjusts according to the difference, and controls the fan speed of the wind power system according to the analysis result to reduce the deviation between the actual tip speed ratio and the optimal tip speed ratio;

[0067] After the ideal speed signal is obtained through the optimal tip speed ratio control method, the speed signal is responded to by using the double closed-loop control method of speed outer loop and current inner loop on the rectifier side of the permanent magnet synchronous generator;

[0068] The dual closed-loop control method of the speed outer loop and the current inner loop includes: the speed outer loop calculates the ideal speed of the wind turbine output by the optimal tip speed ratio method as the input of the outer loop, and compares it with the motor speed of the permanent magnet synchronous generator during actual operation; then the reference size of the d-axis current and the q-axis current is obtained by the action of the zero d-axis current control and the PI regulator, and the q-axis current iq is adjusted to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed is close to the ideal speed of the wind turbine, thereby realizing speed regulation control; then the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, the voltage signal is coordinate-transformed, and finally a suitable PWM drive signal is output through the SVPWM space vector modulation method to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed-out function of the wind power generation system.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] (1) The DC-fed wind power generation hydrogen production system proposed in the present invention can save the grid connection link of the wind power generation system, directly connect the hydrogen production system to the DC bus, simplify the system structure, reduce operating costs and energy loss, and improve energy utilization efficiency;

[0071] (2) The wind MPPT control method proposed in the present invention enables the DC-fed wind power generation hydrogen production system to achieve the best working state under wind speed fluctuation scenarios and maximize the capture of wind energy;

[0072] (3) The DC-fed wind power generation hydrogen production system proposed in the present invention connects the energy storage device to the system DC bus, responds to wind speed fluctuations to stabilize system power fluctuations, and enables the hydrogen production system to operate stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0074] Figure 1 This is the structural diagram of the DC-fed wind power generation hydrogen production system;

[0075] Figure 2 This is the operating principle diagram of the wind turbine of the DC-fed wind power generation and hydrogen production system;

[0076] Figure 3 This is the bidirectional Buck-Boost circuit topology diagram of the energy storage device of the DC-fed wind power generation hydrogen production system;

[0077] Figure 4 This is the working mode 1 of the energy storage device of the DC-fed wind power generation hydrogen production system: the bidirectional Buck-Boost equivalent circuit diagram in the charging mode; Figure 4 (a) in the figure means S2 is turned on. Figure 4 (b) in the figure shows that S2 is turned off;

[0078] Figure 5 Working mode 1 of the energy storage device for the DC-fed wind power generation hydrogen production system: Bidirectional Buck-Boost inductor current variation diagram in charging mode;

[0079] Figure 6 This is the working mode 2 of the energy storage device of the DC-fed wind power generation hydrogen production system: the bidirectional Buck-Boost equivalent circuit diagram in the discharge mode; Figure 6 (a) in the figure means S1 is turned on. Figure 6 (b) in the figure shows S1 is turned off;

[0080] Figure 7 This is the working mode 2 of the energy storage device of the DC-fed wind power generation hydrogen production system: the bidirectional Buck-Boost inductor current variation diagram in the discharge mode;

[0081] Figure 8 This is the operating principle diagram of the energy storage device of the DC-fed wind power generation hydrogen production system;

[0082] Fig. 9 This is the operating principle diagram of the hydrogen production device of the DC-fed wind power generation hydrogen production system;

[0083] Fig.10 This is the optimal tip speed ratio control strategy diagram for the wind turbine of the DC-fed wind power generation hydrogen production system;

[0084] Fig.11 This is a control strategy diagram for the permanent magnet synchronous generator side rectifier of the DC-fed wind power generation hydrogen production system;

[0085] Fig.12 It is the simulation model block diagram of the DC-fed wind power generation system;

[0086] Fig.13 The simulation results of wind maximum power point tracking control under the step wind speed model are shown;

[0087] Fig.14 The simulation results of the state change of the energy storage device under the step wind speed model;

[0088] Fig.15 The simulation results of DC bus voltage change under step wind speed model are shown;

[0089] Fig.16 These are the simulation results of the DC-fed wind power generation hydrogen production system under the step wind speed model. DETAILED DESCRIPTION

[0090] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0091] Example 1

[0092] The present invention proposes a novel DC-fed wind power generation and hydrogen production system. The wind power generation and hydrogen production system omits the grid connection link, has a simple system structure, and has lower energy loss and cost during system operation. It uses an energy storage device to stabilize system power fluctuations, and at the same time uses a wind MPPT control method to regulate the system wind energy to maximize the utilization of wind energy. It is applicable to scenarios such as wind speed fluctuations, and the system solution is more feasible.

[0093] A. Structural description of the DC-fed wind power generation hydrogen production system

[0094] The main structure of the DC-fed wind power generation hydrogen production system is as follows: Figure 1 As shown, the wind turbine senses wind speed input, the DC bus outputs electrical energy to the hydrogen production system for hydrogen production, and the DC bus is connected to an energy storage device.

[0095] The structure can be specifically described as follows: the DC-fed wind power generation system is mainly composed of wind turbines, permanent magnet synchronous generators, rectifiers, DC energy storage devices, wind power hydrogen production devices, wind MPPT control and other parts, among which the wind turbines and permanent magnet synchronous generators constitute the core of the system. The wind turbine senses the change in wind speed and generates mechanical energy, driving the permanent magnet synchronous generator to rotate and generate electricity. Under the control of the wind MPPT control strategy, it responds to the fluctuation of wind speed and adjusts the system's power output. After being processed by the rectifier, the electric energy is input to the hydrogen production system on the DC bus to participate in hydrogen production. At the same time, the DC bus is connected to the energy storage device, and the charging and discharging actions are performed under the action of the energy storage control system to maintain the stability of the DC bus voltage, so that the hydrogen production system operates in a stable working state.

[0096] The specific application background of this structure has been explained in the technical background.

[0097] B. Operational mechanism of DC-fed wind power generation hydrogen production system

[0098] First, the operation mechanism of the wind turbine in the DC-fed wind power generation system is analyzed:

[0099] The basic principle of a wind turbine involves the conversion and utilization of wind energy. The blades of a wind turbine rotate under the action of wind power, and are connected to the main shaft through the hub, outputting mechanical energy to the generator in the form of torque, which in turn drives the generator to convert mechanical energy into electrical energy. The mathematical model of a wind turbine can be obtained from the relevant principles of aerodynamics as follows:

[0100] P m =k p C p (β,λ)v 3

[0101]

[0102]

[0103]

[0104]

[0105] Where R is the radius of the wind turbine, P m is the mechanical power generated, β is the blade tip pitch angle, λ is the blade tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind wheel speed, ρ is the air density; k prepresents the proportional constant in the wind turbine calculation formula, which is related to the air density ρ and the radius R of the wind turbine rotor; v represents the wind speed; c1, c2, c3, c4, c5, c6 represent the empirical parameters in the wind energy utilization coefficient formula, c1 = 0.5176, c2 = 116, c3 = 0.4, c4 = 5, c5 = 21, c6 = 0.0068; λ i Represents the intermediate variable related to the blade speed ratio λ, used for the wind energy utilization coefficient C p The precise calculation of .

[0106] The mechanical torque of the wind turbine is T m Satisfies the following formula:

[0107] Therefore, the wind turbine operating principle is as follows Figure 2 As shown:

[0108] Next, the operating mechanism of the energy storage device of the DC-fed wind power generation hydrogen production system is analyzed:

[0109] Wind speed has random and intermittent change characteristics, so the wind power generation system cannot maintain a stable operating state during normal operation, and the intervention of energy storage devices is required to balance the power fluctuations during system operation. The Buck-Boost circuit topology diagram in the energy storage device is as follows: Figure 3 As shown, the working modes of the energy storage device can be divided into two types:

[0110] Working mode 1: Charging mode

[0111] When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit works in the Buck mode, the switch tube S1 is always disconnected, and the switch tube S2 is turned on or off under the control of the drive signal of the control system. The equivalent circuit diagram is as follows: Figure 4 When the switch tube S2 is turned on, Figure 4 As shown in (a), the DC bus provides electrical energy to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the charging time. When the switch tube S2 is turned off, Figure 4 As shown in (b), the inductor current I L The current flows through diode D1 and continues to charge the battery, but I L As the charging time increases, it decreases. In this working mode, the inductor current I L Trends over time are available Figure 5 As shown in the figure, the inductor current is always negative, so the electric energy always flows from the DC bus side to the battery side of the energy storage system, and the DC energy storage system successfully completes the charging action.

[0112] Working mode 2: discharge mode

[0113] When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit works in the Boost mode, the switch tube S2 is always disconnected, and the switch tube S1 is turned on or off under the control of the drive signal of the control system. The equivalent circuit diagram is as follows: Figure 6 When the switch tube S1 is turned on, Figure 6 As shown in (a), the energy storage system battery provides electrical energy to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the discharge time. When the switch tube S1 is turned off, Figure 6 As shown in (b), the inductor current I L The current flows through diode D2 and continues to charge the DC bus, but I L As the discharge time increases, it decreases. In this working mode, the inductor current I L Trends over time are available Figure 7 As shown in the figure, the inductor current is always positive, so the electric energy always flows from the battery side of the energy storage system to the DC bus side, and the DC energy storage system successfully completes the discharge action.

[0114] This wind power generation hydrogen production system can maintain the DC bus voltage stability due to the flexible switching between working mode 1 and working mode 2, so it has the ability to improve the energy utilization efficiency of the system and enhance the reliability, adaptability and flexibility of the hydrogen production system. Figure 8 shown.

[0115] Next, the operating mechanism of the hydrogen production device of the DC-fed wind power generation hydrogen production system is analyzed:

[0116] The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen. Since the UI output characteristics of the electrolyzer are highly nonlinear, the fitting method is used to obtain its output characteristic equation as follows:

[0117]

[0118] Among them, U el Represents the output voltage, I el Represents the working current, n c Represents the number of serial slots, U r represents the reversible voltage, r1 and r2 represent the resistance, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 With k el represents the overvoltage parameter of the electrolytic cell, and A represents the electrode surface area.

[0119] The reversible voltage calculation equation of the electrolytic cell can be expressed as follows:

[0120]

[0121] in, Represents the reversible voltage under standard conditions (temperature is 0℃, pressure is 101.325Kpa), k r Stands for empirical temperature coefficient.

[0122] At the same time, according to the relevant principles of hydrogen production by electrolysis in electrochemical theory, the rate of hydrogen production by electrolysis of water can be expressed by the following equation:

[0123]

[0124]

[0125] Among them, q H2 represents the hydrogen production rate, F represents the Faraday constant (96485C / mol), η F represents the current efficiency. k f1 , k f2 Indicates: Empirical parameter in the current efficiency calculation formula.

[0126] At this point, the UI output characteristics and hydrogen production rate of the electrolyzer in the wind power generation system during normal operation can be obtained. The operating principle diagram of the hydrogen production device is as follows: Fig. 9 As shown, the device can be connected to the DC bus and output the hydrogen production power, hydrogen production rate and hydrogen production volume of the electrolyzer.

[0127] C. Characteristic Analysis of DC-fed Wind Power Generation Hydrogen Production System

[0128] According to the mathematical model of the wind turbine, the output power characteristics of the wind turbine under different wind speed conditions can be obtained. Within a certain wind speed range, the output power of the wind turbine changes with the wind speed. The greater the wind speed, the greater the output power of the wind turbine. Under the same wind speed conditions, the output power of the wind turbine changes with the change of the wind rotor speed. However, under this wind speed condition, the wind turbine can only output the maximum power at a specific wind turbine speed. Exceeding or less than this wind turbine speed will cause the wind turbine output power to decrease.

[0129] Analyzed by the following formula:

[0130] P m =k p C p (β,λ)v 3

[0131]

[0132]

[0133] In order to maintain the wind turbine at the optimal power output state, it is necessary to control the wind energy utilization coefficient C p Keep it at maximum value.

[0134] Analyzed by the following formula:

[0135]

[0136]

[0137]

[0138] In order to make the wind energy utilization coefficient C D To maintain the maximum value, it is necessary to control the rotation speed ω of the wind turbine and the generator to ensure that the tip speed ratio λ of the wind turbine is close to the maximum value, so that the wind turbine can always maintain the optimal power output state when the wind speed changes, and maximize the utilization of wind energy.

[0139] According to the above analysis, in order to maximize wind energy capture, achieve wind maximum power point tracking, and improve the energy utilization efficiency of the hydrogen production device in the DC-fed wind power generation hydrogen production system, the key is to accurately control the wind rotor speed ω and blade tip speed ratio λ to maintain the wind energy utilization coefficient C. D near its maximum value.

[0140] D. Control strategy of DC-fed wind power generation hydrogen production system

[0141] This system uses the optimal tip speed ratio method to achieve wind MPPT control, and its control strategy is shown in the figure. Taking the above working condition as an example, the control strategy is as follows Fig.10 shown.

[0142] When the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the real-time wind speed and wind turbine speed of the system, and compared with the theoretical optimal tip speed ratio. If the actual tip speed ratio matches or is very close to the optimal tip speed ratio, it means that the system is operating at the optimal power point, achieving efficient and stable operation of the wind turbine; conversely, if there is a difference between the actual tip speed ratio and the theoretical optimal tip speed ratio, the controller will automatically adjust according to the difference, and control the wind turbine speed of the wind power system based on the analysis results to reduce the deviation between the actual tip speed ratio and the optimal tip speed ratio, so as to ensure that the system maintains the best operating state as much as possible and achieve maximum wind energy capture and power output.

[0143] When the optimal tip speed ratio control method obtains the ideal speed signal, the permanent magnet synchronous generator side rectifier responds to the speed signal using a dual closed-loop control method of speed outer loop-current inner loop. The control principle diagram of the system is shown in the figure. Fig.11 shown.

[0144] The speed outer loop of the dual closed-loop control system uses the optimal tip speed ratio method to calculate the ideal speed of the wind turbine as the input of the outer loop, and compares it with the motor speed of the permanent magnet synchronous generator during actual operation. Then, the reference size of the d-axis current and the q-axis current is obtained by the zero d-axis current control and the PI regulator, and the q-axis current iq is adjusted to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed is close to the ideal speed of the wind turbine, thereby realizing speed regulation control. Next, the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, and the voltage signal is processed by coordinate transformation. Finally, the appropriate PWM drive signal is output through the SVPWM space vector modulation method to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thus completing the DC feed-out function of the wind power generation system.

[0145] Example 2

[0146] In order to verify the feasibility and effectiveness of the new DC-fed wind power generation hydrogen production system operation scheme proposed in this patent, a DC-fed wind power generation hydrogen production system was built in the MATLAB / Simulink platform. Fig.12 As shown. Among them, the wind speed model simulates the wind speed signal V wind Input to the wind turbine model and wind MPPT control system. The wind turbine model uses torque T m The mechanical energy is transmitted to the permanent magnet synchronous generator, and the wind MPPT control system uses the ideal blade tip speed ratio λ opt As a reference value, output the ideal speed signal ω * To the permanent magnet synchronous generator side rectification control system, finally control the permanent magnet synchronous generator speed to adjust to the ideal speed to achieve maximum wind energy capture. After that, the DC bus is obtained through rectification, and the hydrogen production equipment is connected to the DC bus for operation. At the same time, the energy storage device is connected to the DC bus to maintain the bus voltage stable when the system power fluctuates, so that the hydrogen production device can work stably.

[0147] Set the wind speed model to a step model to simulate the situation where the wind speed jumps from 8m / s to 6m / s in 3s. At this time, the power fluctuation of the wind turbine under wind MPPT control is as follows: Fig.13 As shown in the figure, the ideal maximum output power of the wind turbine changes in direct proportion to the wind speed fluctuation, and under the control effect of wind maximum power point tracking, the actual output power of the wind turbine and the actual output power of the permanent magnet synchronous generator are very close to the ideal maximum output power of the wind turbine, and the response speed is very fast.

[0148] Under the same wind speed change, the action of the energy storage device is as follows: Fig.14As shown in the figure, before the wind speed decreases, the energy storage battery is in a charging state, the remaining battery power increases, energy flows from the DC bus end to the battery end, and the battery operating current is negative; after the wind speed decreases, the energy storage battery is in a discharging state, the remaining battery power decreases, energy flows from the battery end to the DC bus end, and the battery operating current is negative. At this time, the voltage change of the DC bus is as follows Fig.15 As shown in the figure, after the system starts running, the DC bus voltage gradually stabilizes to the set reference voltage value of 1800V; after the wind speed jumps from 8m / s to 6m / s, the DC bus voltage fluctuates, but quickly stabilizes to 1800V after the energy storage device takes effect.

[0149] Under the same wind speed change, with the intervention of wind MPPT control and energy storage device, the operation results of the hydrogen production device are as follows: Fig.16 Affected by wind speed fluctuations, when the hydrogen production module and the DC load are connected to the DC bus, the hydrogen production power and rate will also fluctuate. However, with the help of the energy storage device, the DC bus voltage can be maintained at the reference voltage value, so the hydrogen production device will quickly return to stability, and the hydrogen production rate can still be maintained at 1.72×10 -4 mol / s, and the hydrogen production power can be maintained at around 100W.

[0150] The simulation results show that wind speed fluctuations can cause power fluctuations in the system and affect the normal operation of the hydrogen production device, but the energy storage device and the wind MPPT control system can function normally, improving the efficiency of wind energy utilization, maintaining bus voltage stability, and ensuring that the hydrogen production device operates in a stable state.

[0151] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing the method and structures within the hardware component.

[0152] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for producing hydrogen by direct current-fed wind power generation, characterized in that: include: Step 1: Analyze the wind turbine operation mechanism of the DC-fed wind power generation system: The blades of the wind turbine rotate under the action of wind, connected to the main shaft through the hub, and output mechanical energy in the form of torque to the generator, which then drives the generator to convert mechanical energy into electrical energy; Step 2: Analyze the operating mechanism of the energy storage device in the DC-fed wind power generation hydrogen production system: balance the power fluctuations during system operation through the intervention of the energy storage device; Step 3: Analyze the operating mechanism of the hydrogen production device of the DC-fed wind power generation hydrogen production system: The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen, and uses the fitting method to obtain its output characteristics; Step 4: According to the mathematical model of the wind turbine, the output power characteristics of the wind turbine under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the output power of the wind turbine; Under the same wind speed conditions, the wind turbine outputs maximum power at a certain wind turbine speed; Step 5: Use the optimal tip speed ratio method to achieve wind maximum power MPPT control.

2. The method for producing hydrogen by direct current-fed wind power generation according to claim 1, characterized in that: According to the relevant principles of aerodynamics, the mathematical model of the wind turbine is as follows: P m =k p C p (b,l)v 3 Where R is the radius of the wind turbine, P m is the mechanical power generated, β is the blade tip pitch angle, λ is the blade tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind wheel speed, ρ is the air density; k p is the proportional constant in the wind turbine calculation formula, which is related to the air density ρ and the radius R of the wind turbine rotor; v is the wind speed; c1, c2, c3, c4, c5, c6 are the empirical parameters in the wind energy utilization coefficient formula; λ i Represents the intermediate variable related to the blade speed ratio λ, used for the wind energy utilization coefficient C p Calculation of mechanical torque T of wind turbine m satisfy:

3. The method for producing hydrogen by direct current-fed wind power generation according to claim 2, characterized in that: The bidirectional Buck-Boost circuit structure of the energy storage device is as follows: an input voltage source V1 is connected in parallel with a capacitor C1, one end of the capacitor C1 is connected to an inductor L, the other end of the capacitor C1 is connected to an output capacitor C2, the other end of the inductor L is connected to switch tubes S1 and S2 respectively, the switch tubes S1 and S2 are connected in reverse parallel with diodes D1 and D2 respectively, the common node of the switch tubes S1 and S2 is connected to the output capacitor C2, and the two ends of the output capacitor C2 are the positive and negative electrodes of the output voltage V2 respectively; There are two working modes of energy storage devices: Charging mode: When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit works in Buck mode, the switch tube S1 is always off, and the switch tube S2 is turned on or off under the control of the drive signal of the control system; when the switch tube S2 is turned on, the DC bus provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the charging time. When the switch tube S2 is turned off, the inductor current I L The current flows through diode D1 and continues to charge the battery, but I L It decreases with the increase of charging time; Discharge mode: When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit works in the Boost mode, the switch tube S2 is always off, and the switch tube S1 is turned on or off under the control of the drive signal of the control system; when the switch tube S1 is turned on, the energy storage system battery provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the discharge time. When the switch tube S1 is turned off, the inductor current I L The current flows through diode D2 and continues to charge the DC bus, but I L It decreases with the increase of discharge time.

4. The method for producing hydrogen by direct current-fed wind power generation according to claim 3, characterized in that: The output characteristics obtained using the fitting method include: Among them, U el Represents the output voltage, I el Represents the working current, n c Represents the number of serial slots, U r represents the reversible voltage, r1 and r2 represent the resistance, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 With k el represents the overvoltage parameter of the electrolytic cell, and A represents the electrode surface area; The reversible voltage calculation equation of the electrolytic cell is: in, Represents the reversible voltage under standard conditions, k r represents the empirical temperature coefficient; At the same time, according to the relevant principles of hydrogen production by electrolysis in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as: Among them, q H2 represents the hydrogen production rate, F represents the Faraday constant, η F represents the current efficiency, k f1 , k f2 Represents the empirical parameter in the current efficiency calculation formula.

5. The method for producing hydrogen by direct current-fed wind power generation according to claim 1, characterized in that: When the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the real-time wind speed and the fan speed of the system, and compared with the theoretical optimal tip speed ratio. If the actual tip speed ratio matches the optimal tip speed ratio or the difference is within the preset range, the system is operating at the optimal power point; otherwise, the controller automatically adjusts according to the difference, and controls the fan speed of the wind power system according to the analysis results to reduce the deviation between the actual tip speed ratio and the optimal tip speed ratio; After the ideal speed signal is obtained through the optimal tip speed ratio control method, the speed signal is responded to by using the double closed-loop control method of speed outer loop and current inner loop on the rectifier side of the permanent magnet synchronous generator; The dual closed-loop control method of the speed outer loop and the current inner loop includes: the speed outer loop calculates the ideal speed of the wind turbine output by the optimal blade tip speed ratio method as the input of the outer loop, and compares it with the motor speed of the permanent magnet synchronous generator during actual operation, and then obtains the reference size of the d-axis current and the q-axis current by the action of the zero d-axis current control and the PI regulator, and adjusts the q-axis current i q Adjustments are made to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed is close to the ideal speed of the wind turbine, thereby realizing speed regulation control; then, the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, and the voltage signal coordinates are transformed. Finally, the appropriate PWM drive signal is output through the SVPWM space vector modulation method to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed-out function of the wind power generation system.

6. A DC-fed wind power generation hydrogen production system, characterized in that: include: Module M1: Analysis of the wind turbine operating mechanism of the DC-fed wind power generation system: The blades of the wind turbine rotate under the action of wind, connected to the main shaft through the hub, and output mechanical energy to the generator in the form of torque, which in turn drives the generator to convert mechanical energy into electrical energy; Module M2: Analysis of the operating mechanism of the energy storage device in the DC-fed wind power generation hydrogen production system: balancing the power fluctuations during system operation through the intervention of the energy storage device; Module M3: Analysis of the operating mechanism of the hydrogen production device of the DC-fed wind power generation hydrogen production system: The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen, and the fitting method is used to obtain its output characteristics; Module M4: According to the mathematical model of the wind turbine, the output power characteristics of the wind turbine under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the output power of the wind turbine; Under the same wind speed conditions, the wind turbine outputs maximum power at a certain wind turbine speed; Module M5: Use the optimal tip speed ratio method to achieve wind maximum power MPPT control.

7. The DC-fed wind power generation hydrogen production system according to claim 6, characterized in that: According to the relevant principles of aerodynamics, the mathematical model of the wind turbine is as follows: P m =k p C p (b,l)v 3 Where R is the radius of the wind turbine, P m is the mechanical power generated, β is the blade tip pitch angle, λ is the blade tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind wheel speed, ρ is the air density; k p is the proportional constant in the wind turbine calculation formula, which is related to the air density ρ and the radius R of the wind turbine rotor; v is the wind speed; c1, c2, c3, c4, c5, c6 are the empirical parameters in the wind energy utilization coefficient formula; λ i Represents the intermediate variable related to the blade speed ratio λ, used for the wind energy utilization coefficient C p Calculation of mechanical torque T of wind turbine m satisfy:

8. The DC-fed wind power generation hydrogen production system according to claim 7, characterized in that: The bidirectional Buck-Boost circuit structure of the energy storage device is as follows: an input voltage source V1 is connected in parallel with a capacitor C1, one end of the capacitor C1 is connected to an inductor L, the other end of the capacitor C1 is connected to an output capacitor C2, the other end of the inductor L is connected to switch tubes S1 and S2 respectively, the switch tubes S1 and S2 are connected in reverse parallel with diodes D1 and D2 respectively, the common node of the switch tubes S1 and S2 is connected to the output capacitor C2, and the two ends of the output capacitor C2 are the positive and negative electrodes of the output voltage V2 respectively; There are two working modes of energy storage devices: Charging mode: When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit works in Buck mode, the switch tube S1 is always off, and the switch tube S2 is turned on or off under the control of the drive signal of the control system; when the switch tube S2 is turned on, the DC bus provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the charging time. When the switch tube S2 is turned off, the inductor current I L The current flows through diode D1 and continues to charge the battery, but I L It decreases with the increase of charging time; Discharge mode: When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit works in the Boost mode, the switch tube S2 is always off, and the switch tube S1 is turned on or off under the control of the drive signal of the control system; when the switch tube S1 is turned on, the energy storage system battery provides power to charge the inductor L, and the inductor current I L It flows from the DC bus side to the battery side and increases with the discharge time. When the switch tube S1 is turned off, the inductor current I L The current flows through diode D2 and continues to charge the DC bus, but I L It decreases with the increase of discharge time.

9. The DC-fed wind power generation hydrogen production system according to claim 8, characterized in that: The output characteristics obtained using the fitting method include: Among them, U el Represents the output voltage, I el Represents the working current, n c Represents the number of serial slots, U r represents the reversible voltage, r1 and r2 represent the resistance, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 With k el represents the overvoltage parameter of the electrolytic cell, and A represents the electrode surface area; The reversible voltage calculation equation of the electrolytic cell is: in, Represents the reversible voltage under standard conditions, k r represents the empirical temperature coefficient; At the same time, according to the relevant principles of hydrogen production by electrolysis in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as: Among them, q H2 represents the hydrogen production rate, F represents the Faraday constant, η F represents the current efficiency, k j1 , k f2 Represents the empirical parameter in the current efficiency calculation formula.

10. The DC-fed wind power generation hydrogen production system according to claim 6, characterized in that: When the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the real-time wind speed and the fan speed of the system, and compared with the theoretical optimal tip speed ratio. If the actual tip speed ratio matches the optimal tip speed ratio or the difference is within the preset range, the system is operating at the optimal power point; otherwise, the controller automatically adjusts according to the difference, and controls the fan speed of the wind power system according to the analysis results to reduce the deviation between the actual tip speed ratio and the optimal tip speed ratio; After the ideal speed signal is obtained through the optimal tip speed ratio control method, the speed signal is responded to by using the double closed-loop control method of speed outer loop and current inner loop on the rectifier side of the permanent magnet synchronous generator; The dual closed-loop control method of the speed outer loop and the current inner loop includes: the speed outer loop calculates the ideal speed of the wind turbine output by the optimal blade tip speed ratio method as the input of the outer loop, and compares it with the motor speed of the permanent magnet synchronous generator during actual operation, and then obtains the reference size of the d-axis current and the q-axis current by the action of the zero d-axis current control and the PI regulator, and adjusts the q-axis current i q Adjustments are made to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed is close to the ideal speed of the wind turbine, thereby realizing speed regulation control; then, the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, and the voltage signal coordinates are transformed. Finally, the appropriate PWM drive signal is output through the SVPWM space vector modulation method to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed-out function of the wind power generation system.

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