Direct current fed wind power to hydrogen method and system

Abstract

The application provides a direct-current feeding wind power hydrogen production method and system, step 1: the blades of a wind turbine are rotated under the action of wind, the mechanical energy is output to a generator in the form of torque through the connection of a hub and a main shaft, and the generator is further driven to convert the mechanical energy into electric energy; step 2: the intervention of an energy storage device is used to balance the power fluctuation in the system operation process; step 3: a wind power generation system uses an electrolytic cell to electrolyze water to obtain hydrogen and hydrogen, and a fitting method is used to obtain the output characteristics; step 4: according to a wind turbine mathematical model, the output power characteristics of the wind turbine under different wind speed conditions are obtained; step 5: the optimal tip speed ratio method is used to realize the maximum power MPPT control of wind. The direct-current feeding wind power hydrogen production system provided by the application can save the grid connection link of the wind power generation system, directly connect the hydrogen production system to a direct-current bus, simplify the system structure, reduce the operation cost and energy loss, and improve the energy utilization efficiency.

Description

Technical Field

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

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

[0003] When wind power generation systems are combined with hydrogen production systems, they can achieve peak-shaving and valley-filling of wind energy through hydrogen storage. During periods of excess electricity, the excess electricity can be fully utilized through water electrolysis to produce hydrogen, converting the electricity into stored hydrogen. During periods of power shortage, the stored hydrogen can be used to generate electricity through fuel cells, converting the hydrogen into electricity to maintain power supply. This combined electricity and hydrogen system in wind power generation not only reduces wind energy waste but also provides a flexible energy regulation method, increasing the reliability, stability, flexibility, and resilience of wind power generation systems.

[0004] Currently, there are two main technical routes for hydrogen production from wind power generation. One is the grid-connected offshore hydrogen production technology, which 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, which uses electricity directly to produce hydrogen through electrolysis after the wind turbine generates electricity. In wind power generation systems, off-grid hydrogen production technology reduces dependence on the grid and reduces hydrogen production costs. At the same time, it can achieve local consumption of new energy and improve energy conversion efficiency. At the same time, DC-fed wind power generation systems have excellent stability and controllability compared to traditional wind power generation systems. They are crucial for addressing the volatility and intermittency problems in wind power grid connection. Therefore, DC-fed wind power generation systems have become a hot topic of research in the field of new energy. At present, traditional wind power hydrogen production systems are relatively mature, but the principles and control of DC-fed wind power hydrogen production systems still need to be studied and improved.

[0005] Patent application document CN109004665A proposes a wind power generation system that utilizes excess electrical energy to produce hydrogen, and uses an energy storage device to release electrical energy to the system to stabilize power fluctuations and achieve stable hydrogen production. However, the system cannot achieve maximum power output under fluctuating wind speeds, resulting in low wind energy utilization efficiency and high hydrogen production costs. Simulation verification has not been conducted.

[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, the object of the present invention is to provide a method and system for producing hydrogen through 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 operating mechanism of the wind turbine in a DC-fed wind power generation system: The wind turbine blades rotate under the action of wind and are connected to the main shaft through the hub. They output mechanical energy in the form of torque to the generator, which in turn 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: Use the energy storage device to balance the power fluctuations during system operation;

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

[0013] Step 4: Based on the wind turbine mathematical model, the wind turbine output power characteristics under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the wind turbine output power. 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 wind turbine radius, P m is the generated mechanical power, β is the blade pitch angle, λ is the tip speed ratio, C p is the wind energy utilization coefficient, ω is the wind rotor 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 rotor; v is the wind speed; c1, c2, c3, c4, c5, c6 are empirical parameters in the wind energy utilization coefficient formula; λ i represents an intermediate variable related to the blade speed ratio λ, which is used for the calculation of the wind energy utilization coefficient C p The mechanical torque T m of the wind turbine satisfies:

[0022] Preferably, the bidirectional Buck-Boost circuit structure of the energy storage device is that 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 an output voltage V2 respectively.

[0023] The working mode of the energy storage device is divided into two types:

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

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

[0026] Preferably, the output characteristics thereof are obtained using a fitting method, including:

[0027]

[0028] wherein U el represents the output voltage, I el represents the working current, n c represents the number of series cells, U r represents the reversible voltage, r1 and r2 represent resistances, T el represents the electrolytic cell temperature, k T1 , k T2 , k T3 and k el represent the overvoltage parameters of the electrolytic cell, and A represents the electrode surface area.

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

[0030]

[0031] wherein, represents the reversible voltage size under standard conditions, k r represents the empirical temperature coefficient.

[0032] At the same time, according to the related principles of electrolytic hydrogen production in electrochemistry theory, the rate of hydrogen production by electrolysis of water is:

[0033]

[0034]

[0035] wherein q H2 represents the hydrogen production rate, F represents the Faraday constant, η F represents the current efficiency, k f1 , k f2 represent the empirical parameters in the current efficiency calculation formula.

[0036] Preferably, when the wind power system is in normal operation, the actual tip speed ratio is calculated by measuring the real-time wind speed and the fan speed, 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] When the ideal speed signal is obtained through the optimal tip speed ratio control method, the speed signal is responded by using the double closed-loop control mode of speed outer ring-current inner ring for the machine side rectifier of the permanent magnet synchronous generator;

[0038] The double closed-loop control mode of speed outer ring-current inner ring comprises: the ideal wind turbine speed calculated by the optimal tip speed ratio method is taken as the input quantity of the speed outer ring, compared with the motor speed of the permanent magnet synchronous generator in actual operation, then the reference size of the d-axis current and the q-axis current is obtained through the action of zero d-axis current control and PI regulator, and the q-axis current iq is adjusted to change the electromagnetic torque of the permanent magnet synchronous generator, so that the motor speed approaches the ideal wind turbine speed, and the speed regulation control is realized; then the motor d-axis voltage and q-axis voltage are decoupled through voltage feedforward control, the voltage signal is processed through coordinate transformation, and finally the appropriate PWM driving signal is output through the SVPWM space vector modulation method, the on-off state of the switching tube of the three-phase bridge rectifier circuit is controlled, and the direct current feeding function of the wind power system is realized.

[0039] According to the direct current feeding wind power hydrogen production system provided by the application, the direct current feeding wind power hydrogen production system comprises:

[0040] Module M1: analyze the operation mechanism of the wind turbine of the direct current feeding wind power system: the blades of the wind turbine rotate under the action of wind force, are connected with the main shaft through the hub, output mechanical energy to the generator in the form of torque, and drive the generator to convert mechanical energy into electrical energy;

[0041] Module M2: analyze the operation mechanism of the energy storage device of the direct current feeding wind power hydrogen production system: the power fluctuation in the system operation process is balanced through the intervention of the energy storage device;

[0042] Module M3: analyze the operation mechanism of the hydrogen production device of the direct current feeding wind power hydrogen production system: the electrolytic cell is used to electrolyze water to obtain hydrogen, and a fitting method is used to obtain the output characteristics of the electrolytic cell;

[0043] 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, and within a preset wind speed range, the greater the wind speed, the greater the output power of the wind turbine; under the same wind speed condition, the wind turbine outputs the maximum power at a certain fan speed.

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

[0045] Preferably, the mathematical model of the wind turbine is as follows according to aerodynamic principles:

[0046] P m =k p C p (β, λ)v 3

[0047]

[0048]

[0049]

[0050]

[0051] Wherein, R is the radius of the wind turbine, P m is the generated mechanical power, β is the tip pitch angle, λ is the 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 a 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 empirical parameters in the wind energy utilization coefficient formula; λ i represents the intermediate variable related to the blade speed ratio λ, which is used for the calculation of the wind energy utilization coefficient C p The mechanical torque T m of the wind turbine satisfies:

[0052] Preferably, the bidirectional Buck-Boost circuit structure of the energy storage device is: the input voltage source V1 is connected in parallel with the capacitor C1, one end of the capacitor C1 is connected to the inductor L, the other end of the capacitor C1 is connected to the output capacitor C2, the other end of the inductor L is connected to the switch tube S1 and S2 respectively, the switch tube S1 and S2 are connected in reverse parallel with the diode D1 and D2 respectively, the common node of the switch tube 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.

[0053] The working mode of the energy storage device is divided into two kinds:

[0054] Charging mode: When the DC energy storage system is in the charging state, the bidirectional Buck-Boost circuit operates 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 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 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 operates 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 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 includes:

[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 equation for calculating the reversible voltage 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 electrolytic hydrogen production 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 based on 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 permanent magnet synchronous generator side rectifier uses a dual closed-loop control method of speed outer loop and current inner loop to respond to the speed signal;

[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 wind turbine speed output by the optimal tip speed ratio method as the input of the outer loop, compares it with the motor speed of the permanent magnet synchronous generator during actual operation, then obtains the reference sizes of the d-axis current and the q-axis current through the action of zero d-axis current control and the PI regulator, and adjusts the q-axis current iq to change the electromagnetic torque of the permanent magnet synchronous generator so that its motor speed approaches the ideal speed of the wind turbine, thereby realizing speed regulation control; then, voltage feedforward control is used to realize decoupling of the motor d-axis voltage and q-axis voltage, and the voltage signal is coordinate-transformed. Finally, an 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.

[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 eliminate the grid connection link of the wind power generation system and directly connect the hydrogen production system to the DC bus, thereby simplifying the system structure, reducing operating costs and energy loss, and improving energy utilization efficiency;

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

[0072] (3) The DC-fed wind power generation and 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 ensures stable operation of the hydrogen production system. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments 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 in 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 bidirectional Buck-Boost equivalent circuit diagram of the DC-fed wind power generation hydrogen production system energy storage device operating mode 1: charging mode; Figure 4 (a) in the figure indicates that S2 is conducting. Figure 4 (b) in the figure shows S2 is turned off;

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

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

[0080] Figure 7 This is the second operating mode of the energy storage device of the DC-fed wind power generation hydrogen production system: the bidirectional Buck-Boost inductor current variation diagram in 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] Figure 9 This is the operating principle diagram of the hydrogen production device of the DC-fed wind power generation hydrogen production system;

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

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

[0085] Figure 12 This is the simulation model block diagram of the DC-fed wind power generation system;

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

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

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

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

[0090] The present invention will be described in detail below with reference to specific embodiments. The following examples 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 skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0091] Example 1

[0092] The present invention proposes a novel DC-fed wind power generation and hydrogen production system. This wind power generation and hydrogen production system eliminates 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 wind energy utilization. It is applicable in 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 energy storage device is connected to the DC bus.

[0095] The structure can be specifically described as follows: a DC-fed wind power generation system primarily consists of a wind turbine, a permanent magnet synchronous generator (PMSG), a rectifier, a DC energy storage device, a wind power hydrogen production system, and a wind MPPT control system. The wind turbine and PMSG constitute the core of the system. The wind turbine senses changes in wind speed and generates mechanical energy, which drives the PMSG to generate electricity. Under the control of the wind MPPT control strategy, the turbine responds to wind speed fluctuations and adjusts the system's power output. After processing by the rectifier, the electrical energy is fed into the hydrogen production system on the DC bus for hydrogen production. Simultaneously, the DC bus is connected to the energy storage device, which, under the control of the energy storage control system, performs charging and discharging operations to maintain a stable DC bus voltage, ensuring stable operation of the hydrogen production system.

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

[0097] B. Operational Mechanism of DC-fed Wind Power Hydrogen Production System

[0098] First, the operating 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 influence of wind, connected to the main shaft through the hub, and output mechanical energy in the form of torque to the generator, which in turn drives the generator to convert mechanical energy into electrical energy. The mathematical model of a wind turbine, derived from the relevant principles of aerodynamics, is 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, and 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, and c6 represent the empirical parameters in the wind energy utilization coefficient formula, c1 = 0.5176, c2 = 116, c3 = 0.4, c4 = 5, c5 = 21, and 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 T of the wind turbine m Satisfies the following formula:

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

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

[0109] Wind speed has random and intermittent changing 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 operates 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. Its equivalent circuit diagram is as follows: Figure 4 When the switch tube S2 is turned on, as shown in 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 It decreases with the increase of charging time. 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 operation.

[0112] Working mode 2: discharge mode

[0113] When the DC energy storage system is in the discharge state, the bidirectional Buck-Boost circuit operates 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. The equivalent circuit diagram is as follows: Figure 6 When the switch tube S1 is turned on, as shown in Figure 6 As shown in (a), 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, 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 It decreases with the increase of discharge time. 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 stability of the DC bus voltage due to the flexible switching between working mode 1 and working mode 2, thus improving the energy utilization efficiency of the system and enhancing the reliability, adaptability and flexibility of the hydrogen production system. Figure 8 shown.

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

[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 electrolytic hydrogen production 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 under the wind power generation system during normal operation can be obtained. The operating principle diagram of the hydrogen production device is as follows: Figure 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 Hydrogen Generation 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 keep the wind turbine in 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 speed change of the wind turbine and generator ω 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 lies in accurately controlling 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 Figure 10 shown.

[0142] When the wind power generation system is operating normally, the actual tip speed ratio is calculated by measuring the system's real-time wind speed and wind turbine speed, 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 optimal 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 and current inner loop. The control principle diagram of the system is shown in the figure below. Figure 11 shown.

[0144] The speed outer loop of this dual closed-loop control system calculates the ideal wind turbine speed using the optimal tip speed ratio method. This input is then compared with the actual operating speed of the permanent magnet synchronous generator (PMSG). Zero d-axis current control and a PI regulator then determine the reference values ​​for the d- and q-axis currents. The q-axis current iq is then adjusted to alter the PMSG's electromagnetic torque, bringing its speed close to the ideal wind turbine speed, achieving speed regulation. Next, voltage feedforward control is used to decouple the d- and q-axis voltages of the motor, transforming the voltage signal. Finally, SVPWM space vector modulation is used to output an appropriate PWM drive signal to control the on / off states of the three-phase bridge rectifier circuit, completing the DC feedback function of the wind turbine 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. Figure 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 * The system then sends the power to the permanent magnet synchronous generator (PMSG) on the generator side, adjusting the generator's speed to the ideal value to maximize wind energy capture. Afterwards, the DC bus is generated through rectification, and the hydrogen production equipment is connected to this DC bus for operation. Energy storage equipment is also connected to this DC bus to maintain bus voltage stability during system power fluctuations, ensuring stable operation of the hydrogen production unit.

[0147] Set the wind speed model to a step model to simulate the wind speed jumping 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: Figure 13 As shown in the figure, the ideal maximum output power of the wind turbine varies in direct proportion to wind speed fluctuations. 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: Figure 14As shown in Figure 1, 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: Figure 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: Figure 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] Simulation results show that wind speed fluctuations can cause power fluctuations in the system and affect the normal operation of the hydrogen production device. However, the energy storage device and the wind power 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 will appreciate that, in addition to implementing the system, device, and various modules provided by the present invention in 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, embedded microcontrollers, and the like by logically programming the method steps. Therefore, the system, device, and various modules provided by the present invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; the modules for implementing various functions can also be considered both software programs for implementing the method and structures within the hardware component.

[0152] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for producing hydrogen by direct current-fed wind power generation, characterized in that: include: Step 1: Analyze the operating mechanism of the wind turbine in a DC-fed wind power generation system: The wind turbine blades rotate under the action of wind and are connected to the main shaft through the hub. They output mechanical energy in the form of torque to the generator, which in turn 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: Use the energy storage device to balance the power fluctuations during system operation; Step 3: Analyze the operating mechanism of the hydrogen production device of the DC-fed wind power generation system: The wind power generation system uses an electrolyzer to electrolyze water to obtain hydrogen and hydrogen, and use the fitting method to obtain its output characteristics; Step 4: Based on the wind turbine mathematical model, the wind turbine output power characteristics under different wind speed conditions are obtained. Within the preset wind speed range, the greater the wind speed, the greater the wind turbine output power; 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; The bidirectional Buck-Boost circuit structure of the energy storage device is: input voltage source With capacitor Parallel, capacitors One end of the inductor is connected to , capacitor The other end of the output capacitor is connected ,inductance The other end is connected to the switch tube and , switch tube and Respectively with diode and Reverse parallel, switch tube and The common node is connected to the output capacitor , output capacitor The two ends are the output voltage The positive and negative poles; 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, and the switch tube Always disconnect, switch The switch is turned on or off under the control of the drive signal of the control system; When conducting, the DC bus provides power to the inductor Charging, inductor current Flows from the DC bus side to the battery side and increases with the charging time; when the switch tube When turned off, the inductor current Flow through the diode Continue to charge the battery, but 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, and the switch tube Always disconnect, switch The switch is turned on or off under the control of the drive signal of the control system; When the conduction is on, the energy storage system battery provides power to the inductor Charging, inductor current Flows from the DC bus side to the battery side and increases with the discharge time; when the switch tube When turned off, the inductor current Flow through the diode Continue to charge the DC bus, but It decreases with the increase of discharge time; The output characteristics obtained using fitting methods include: in, represents the output voltage, Represents the working current, Represents the number of serial slots, represents the reversible voltage, and represents resistance, represents the electrolytic cell temperature, 、 、 and represents the overvoltage parameter of the electrolyzer, represents the electrode surface area; The equation for calculating the reversible voltage of the electrolytic cell is: in, Represents the reversible voltage under standard conditions, represents the empirical temperature coefficient; At the same time, according to the relevant principles of electrolytic hydrogen production in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as: in, represents the hydrogen production rate, represents the Faraday constant, represents the current efficiency, 、 Represents the empirical parameter in the current efficiency calculation formula.

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: in, is the radius of the wind turbine, is the mechanical power generated, is the blade tip pitch angle, is the tip speed ratio, is the wind energy utilization coefficient, is the wind wheel speed, is the air density; is the proportional constant in the wind turbine calculation formula, and is related to the air density and the radius of the wind turbine rotor related; is the wind speed; 、 、 、 、 、 is the empirical parameter in the formula of wind energy utilization coefficient; Indicates blade speed ratio Related intermediate variables for wind energy utilization coefficient Calculation of mechanical torque of wind turbine satisfy: .

3. The method for producing hydrogen by DC-fed wind power generation according to claim 1, characterized in that: During normal operation of a wind power generation system, the actual tip speed ratio is calculated by measuring the system's real-time wind speed and wind turbine speed, 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 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. After the ideal speed signal is obtained through the optimal tip speed ratio control method, the permanent magnet synchronous generator side rectifier uses a dual closed-loop control method of speed outer loop and current inner loop to respond to the speed signal; 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, 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. 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, voltage feedforward control is used to decouple the motor d-axis voltage and q-axis voltage, and the voltage signal is coordinate-transformed. Finally, the SVPWM space vector modulation method is used to output a suitable PWM drive signal to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed function of the wind power generation system.

4. A DC-fed wind power generation hydrogen production system, characterized in that: include: Module M1: Analyze the operating mechanism of a wind turbine in a DC-fed wind power generation system: The blades of a 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 in turn drives the generator to convert mechanical energy into electrical energy; Module M2: 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; Module M3: Analyze the operating mechanism of the hydrogen production device of the DC-fed wind power generation 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; Module M4: Based on the mathematical model of the wind turbine, the wind turbine output power characteristics 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; The bidirectional Buck-Boost circuit structure of the energy storage device is: input voltage source With capacitor Parallel, capacitors One end of the inductor is connected to , capacitor The other end of the output capacitor is connected ,inductance The other end is connected to the switch tube and , switch tube and Respectively with diode and Reverse parallel, switch tube and The common node is connected to the output capacitor , output capacitor The two ends are the output voltage The positive and negative poles; 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, and the switch tube Always disconnect, switch The switch is turned on or off under the control of the drive signal of the control system; When conducting, the DC bus provides power to the inductor Charging, inductor current Flows from the DC bus side to the battery side and increases with the charging time; when the switch tube When turned off, the inductor current Flow through the diode Continue to charge the battery, but 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, and the switch tube Always disconnect, switch The switch is turned on or off under the control of the drive signal of the control system; When the conduction is on, the energy storage system battery provides power to the inductor Charging, inductor current Flows from the DC bus side to the battery side and increases with the discharge time; when the switch tube When turned off, the inductor current Flow through the diode Continue to charge the DC bus, but It decreases with the increase of discharge time; The output characteristics obtained using fitting methods include: in, represents the output voltage, Represents the working current, Represents the number of serial slots, represents the reversible voltage, and represents resistance, represents the electrolytic cell temperature, 、 、 and represents the overvoltage parameter of the electrolyzer, represents the electrode surface area; The equation for calculating the reversible voltage of the electrolytic cell is: in, Represents the reversible voltage under standard conditions, represents the empirical temperature coefficient; At the same time, according to the relevant principles of electrolytic hydrogen production in electrochemical theory, the rate of hydrogen production by electrolysis of water is expressed as: in, represents the hydrogen production rate, represents the Faraday constant, represents the current efficiency, 、 Represents the empirical parameter in the current efficiency calculation formula.

5. The DC-fed wind power generation hydrogen production system according to claim 4, characterized in that: According to the relevant principles of aerodynamics, the mathematical model of the wind turbine is as follows: in, is the radius of the wind turbine, is the mechanical power generated, is the blade tip pitch angle, is the tip speed ratio, is the wind energy utilization coefficient, is the wind wheel speed, is the air density; is the proportional constant in the wind turbine calculation formula, and is related to the air density and the radius of the wind turbine rotor related; is the wind speed; 、 、 、 、 、 is the empirical parameter in the formula of wind energy utilization coefficient; Indicates blade speed ratio Related intermediate variables for wind energy utilization coefficient Calculation of mechanical torque of wind turbine satisfy: .

6. The DC-fed wind power generation hydrogen production system according to claim 4, characterized in that: During normal operation of a wind power generation system, the actual tip speed ratio is calculated by measuring the system's real-time wind speed and wind turbine speed, 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 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. After the ideal speed signal is obtained through the optimal tip speed ratio control method, the permanent magnet synchronous generator side rectifier uses a dual closed-loop control method of speed outer loop and current inner loop to respond to the speed signal; 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, 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. 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, voltage feedforward control is used to decouple the motor d-axis voltage and q-axis voltage, and the voltage signal is coordinate-transformed. Finally, the SVPWM space vector modulation method is used to output a suitable PWM drive signal to control the on-off state of the switch tube of the three-phase bridge rectifier circuit, thereby realizing the DC feed function of the wind power generation system.

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