Modeling method for electromagnetic transient model of new energy hydrogen production system

Abstract

The invention discloses a modeling method for an electromagnetic transient model of a new energy hydrogen production system. The modeling method comprises the following steps: step 1, planning and designing an overall framework of a model; 2, building a wind electronic system model; step 3, building a photovoltaic subsystem model; 4, building an energy storage subsystem model; 5, building a hydrogen energy subsystem model; according to the method, a foundation is laid for research in different aspects such as further simulation condition setting, system steady-state / transient-state operation characteristic extraction, system parameter and control strategy design, engineering demonstration and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production from renewable energy sources, and in particular to a method for modeling an electromagnetic transient model of a hydrogen production system from renewable energy sources. Background Art

[0002] Compared with grid-connected hydrogen production from new energy sources, off-grid hydrogen production from new energy sources only has a DC conversion link, and the system efficiency is higher; it reduces the investment costs of equipment such as step-up and step-down, grid connection, and the system cost is low; it does not require photovoltaic grid access approval, which can greatly shorten the construction period; there are no requirements for grid access, and the scale and capacity settings are more flexible. Therefore, considering factors such as system efficiency, investment cost, construction period, expansion flexibility, and grid requirements, off-grid hydrogen production from new energy sources will become one of the mainstream development directions of new energy hydrogen production.

[0003] The research and application of new energy off-grid hydrogen production at home and abroad are still in the initial exploration stage. Abroad, many companies and scientific research institutions such as ThyssenKrupp have carried out research on new energy off-grid hydrogen production, but the capacity of the adapted electrolyzer is only MW level, and the system scale is relatively small, which cannot meet the application needs of large-scale new energy hydrogen production; and there is no research on key technologies for new energy off-grid hydrogen production for load regulation needs. Domestically, Tsinghua University and other universities have carried out research on the design of new energy off-grid hydrogen production systems, and the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences and the 718 Institute of China Shipbuilding Industry Corporation are conducting research and manufacturing of PEM pure water hydrogen production equipment. Tsinghua University, Sungrow Power Supply and other units are developing new energy electrolysis hydrogen production power supplies, but the research and equipment development related to new energy off-grid hydrogen production is still in its infancy, and there is no experience in engineering application. . Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a modeling method for the electromagnetic transient model of a new energy hydrogen production system, so as to lay a foundation for further research on different aspects such as simulation condition setting, extraction of system steady-state / transient operation characteristics, design of system parameters and control strategies, and engineering demonstration.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for modeling an electromagnetic transient model of a new energy hydrogen production system, characterized in that it comprises the following steps:

[0006] Step 1: Plan and design the overall architecture of the model;

[0007] Step 2: Build a wind electronic system model;

[0008] Step 3: Build a photovoltaic subsystem model;

[0009] Step 4: Build the energy storage subsystem model;

[0010] Step 5: Build the hydrogen energy subsystem model.

[0011] Furthermore, the step 1 specifically includes: based on the overall project planning and design plan, building a system electromagnetic transient simulation model in the PSCAD / EMTDC environment; the model includes a wind power subsystem model, a photovoltaic subsystem model, an energy storage subsystem model and a hydrogen energy subsystem model.

[0012] Furthermore, the specific process of step 2 is as follows:

[0013] 2.1. Build a wind turbine model:

[0014] The wind turbine in the wind turbine captures the kinetic energy of wind and converts it into mechanical energy for rotor rotation. It is a purely mechanical device for wind power generation. In the simulation modeling of electromagnetic transients, it is simplified to a mathematical model between the current wind speed, rotor speed, and the mechanical power and mechanical torque output by the wind turbine.

[0015] Under normal working conditions, the mechanical power P output by the wind turbine is T As shown in formula (1):

[0016]

[0017] Where: v is the wind speed; R is the impeller radius of the wind blade; ρ is the air density; C p Defined as the wind energy utilization coefficient, it is a function of the wind turbine's pitch angle β and blade tip speed ratio λ. Its functional relationship is shown in formula (2):

[0018]

[0019] The tip speed ratio λ is defined as the ratio of the linear velocity at the tip of the wind blade to the wind speed, that is:

[0020]

[0021] ω T is the angular velocity of the wind blade, considering the speed change of the gearbox, ω T The relationship between the generator rotor angular velocity ω and the generator rotor angular velocity ω is as shown in formula (4):

[0022] ω=kω T (4)

[0023] Wherein, k is the ratio of the speed of the generator rotor to the wind turbine blade rotor;

[0024] Under the conditions of known wind speed v, generator rotor angular velocity ω, and pitch angle β, the current wind turbine output power P can be calculated according to formula (1): T The mechanical torque T that the generator bears at this time is obtained by calculation as shown in formula (5):m :

[0025]

[0026] The wind turbine model calculates the mechanical power and torque output from the wind turbine to the generator in real time based on the input wind speed, generator rotor angular velocity, and pitch angle; the model uses normalized input and output;

[0027] C is specially written in the model p The calculation module uses series expansion to calculate C p Perform numerical calculations with a certain degree of accuracy;

[0028] 2.2. Build the electrical primary model:

[0029] The electrical primary model includes a generator, a wind turbine converter and a circuit breaker. The generator uses a permanent magnet synchronous motor model provided by PSCAD, and its rotor is connected to the input terminal of the wind turbine converter. The wind turbine converter uses a three-level voltage source converter. In addition to the DC capacitor, a DC energy consumption circuit for suppressing DC overvoltage is also configured on the common DC bus.

[0030] 2.3. Build the inner loop control model of a single-machine converter:

[0031] On the machine side of the wind turbine converter, the three-level converter is directly connected to the rotor winding of the permanent magnet direct drive motor. According to the principle of the permanent magnet direct drive motor, the voltage, current and flux of its stator and rotor satisfy the relationship shown in formula (6):

[0032]

[0033] Among them, u sd 、u sq 、u rd 、u rq are the d-axis and q-axis components of the stator and rotor voltages in the rotating rectangular coordinate system respectively; i sd 、i sq 、i rd 、i rq are the d-axis and q-axis components of the stator and rotor currents in the rotating rectangular coordinate system, respectively; ψ sd , sq , rd , rq are the d-axis and q-axis components of the stator and rotor flux in the rotating rectangular coordinate system respectively; R s , R r are stator and rotor winding resistances respectively; L s , L r are the stator and rotor winding self-inductances respectively; L m is the mutual inductance between the stator and rotor windings; p is the number of pole pairs; ω is the stator synchronous angular velocity; ωs is the motor slip angular velocity;

[0034] Assuming that the d-axis of the rotating rectangular coordinate system coincides with the direction of the stator flux, the relationship between the stator current and the rotor current can be deduced from equation (6) as shown in equation (7):

[0035]

[0036] Based on equations (6) and (7), by controlling u rd 、u rq , the stator and rotor current i of the motor can be controlled sd 、i sq 、i rd and i rq , thereby further controlling the active power and reactive power output of the entire wind turbine;

[0037] 2.4. Build a single-machine converter outer loop control model:

[0038] The functional relationship described by equation (2) is plotted as C p Curves that vary with β and λ; there are two cases:

[0039] (1) Under the condition that β remains unchanged, C p As λ increases, it shows a trend of increasing first and then decreasing. Therefore, for a fixed wind speed, there is a maximum value of the mechanical power that the wind turbine can output, and an optimal speed that allows the wind turbine to output the maximum power.

[0040] (2) As β increases, the maximum mechanical power that the wind turbine can output shows a decreasing trend, that is, the pitch angle can be used to control the wind turbine's capture of wind energy;

[0041] Based on the above two conclusions, for a wind turbine generator set, its overall outer loop control architecture is as follows: ① The wind turbine is set with a maximum power tracking function, and the upper limit of the maximum active power that the wind turbine can generate is calculated in real time according to the wind speed and pitch angle; ② The station coordinated control or the grid dispatcher gives the active power instruction of the wind turbine within the maximum active power range that can be generated; ③ The wind turbine converter adjusts the rotor excitation according to the received active power instruction, so that the overall output of the wind turbine meets the active power required by the instruction; ④ The wind turbine controls the pitch angle according to the principle of stabilizing the rotor speed, dynamically maintaining the balance between the mechanical torque and the electromagnetic torque of the generator, so that the wind energy captured by the wind turbine matches the electric energy power sent by the generator according to the requirements of the grid;

[0042] 2.5. Build the converter modulation model:

[0043] The machine-side converters in wind power converters all adopt conventional three-level topology voltage source converters, and the modulation of the switching device trigger signal also adopts the three-level ANPC PWM method.

[0044] Furthermore, the specific process of step 3 is as follows:

[0045] 3.1. Build a photovoltaic string converter model:

[0046] The photovoltaic string converter consists of a maximum power tracking control circuit and a DC / DC converter. In this model, the DC / DC converter uses a Boost chopper circuit.

[0047] The circuit consists of a main inductor L, a main capacitor C, a diode D, and a fully controlled switch device T. f , C f It is a filter circuit. During normal operation, when T is turned on, the low-voltage side power supply forms a large current on L. When T is turned off, the current on L charges C through the continuous flow of D. By controlling the trigger pulse duty cycle of T in a switching cycle, the charging voltage of the main capacitor C can be adjusted, thereby realizing boost chopping.

[0048] The current direction supported by this circuit is unidirectional flow from the low-voltage side to the high-voltage side. Within a reasonable design range, as the trigger pulse duty cycle increases, the average current sent by the low-voltage side power supply in one switching cycle shows an upward trend, and the voltage of the main capacitor C also shows an upward trend under the condition that the external circuit conditions remain unchanged;

[0049] The trigger signal of the switch device in the boost chopper circuit is generated by modulating the carrier of a given frequency with the duty cycle signal;

[0050] 3.2. Build a photovoltaic cell array model:

[0051] The photovoltaic cell array connected to each string inverter is modeled using the photovoltaic cell module provided by PSCAD.

[0052] 5. The electromagnetic transient modeling method for a new energy hydrogen production system according to claim 1 is characterized in that: the specific process of step 4 is as follows:

[0053] 4.1. Build the energy storage converter model:

[0054] The energy storage battery relies on the energy storage converter to control the power of the energy storage battery; the high-voltage side of the energy storage converter stabilizes the DC bus voltage, and the voltage on the energy storage side is determined by the energy storage battery. The energy storage converter works in a constant voltage mode, and controls the high-voltage side voltage of the energy storage converter to track the changes of a given reference value;

[0055] 4.2. Build energy storage battery stack model:

[0056] The energy storage battery stack managed by the energy storage inverter is composed of multiple energy storage battery clusters connected in parallel. Each energy storage battery cluster is modeled using the battery module provided by PSCAD.

[0057] Furthermore, the specific process of step 5 is as follows:

[0058] 5.1. Build an alkaline electrolyzer model:

[0059] According to the different time scales of the research, the model of the electrolyzer can be divided into two typical forms, namely the electrochemical empirical model considering the electrical characteristics of the electrolyzer, and the thermal dynamic model considering the temperature changes over a longer time scale; Establishing the empirical model of the alkaline electrolyzer:

[0060] The empirical formula for alkaline electrolyzer is as follows:

[0061]

[0062] Where U EL is the cell terminal voltage (V); I EL is the current at the electrolytic cell end (A); U rev is the reversible open circuit voltage (V); A is the cross-sectional area of ​​the electrolytic cell (cm 2 ); r, s, t are empirical parameters that can be measured experimentally; the empirical model does not consider the changes in the characteristics of the electrolytic cell at different temperatures, and the error is large when the temperature of the electrolytic cell changes greatly; therefore, an improved empirical model is used as shown in formula (9); the following two assumptions are made in this model: 1) the hydrogen and oxygen produced in the electrolytic cell are both ideal gases; 2) water is an incompressible liquid;

[0063]

[0064] Where T is the cell temperature (K); r1 and r2 are related parameters of the cell's internal resistance, r2 reflects the change of the cell's internal resistance with temperature; s, t1, t2, t3 are related parameters of the overvoltage caused by polarization of electrodes and electrolytes in the cell, t2 and t3 reflect the change of the overvoltage in the cell with temperature; r1, r2, t1, t2, t3 are all empirical parameters, measured by experiments; the reversible open circuit voltage U in the formula is rev It reflects the minimum potential between the electrodes of each electrolytic monomer in the electrolytic cell when electrolyzing water:

[0065]

[0066] Wherein, ΔG is the change in Gibbs free energy (J / mol); ΔH is the change in enthalpy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); T is the operating temperature of the electrolyzer (K);

[0067] In practical applications, the electrolyzer consists of multiple monomers connected in series to achieve the required hydrogen production; the number of monomers in series is n EL When , the terminal voltage of the electrolytic cell stack is:

[0068]

[0069] 5.2. Build a hydrogen storage tank model:

[0070] The capacity of the hydrogen energy storage system is determined by the amount of gas stored in the hydrogen storage tank. Assuming that the hydrogen in the hydrogen storage tank is an ideal gas, the ideal gas equation can be obtained:

[0071] p tank V tank =n H2 RT tank (12)

[0072] In the formula, p tank is the pressure of the gas in the hydrogen storage tank (kPa); V tank is the volume of the hydrogen storage tank (m 3 );T tank is the temperature of the gas in the hydrogen storage tank; n H2 is the amount of hydrogen in the hydrogen storage tank (mol); R is the ideal gas constant, which is 8.3143 J / K·mol; it can be seen that the amount of hydrogen in the hydrogen storage tank is proportional to the pressure. When the upper and lower limits of the pressure of the available hydrogen in the hydrogen tank are p tank_max With p tank_min When , the amount of substance available for hydrogen is:

[0073]

[0074] Using SOC to represent the amount of remaining available hydrogen, we have:

[0075]

[0076] It can be seen from the above formula that, assuming that the hydrogen in the hydrogen storage tank is an ideal gas and the temperature of the hydrogen storage tank is constant, the SOC value of the hydrogen energy storage system is only related to the pressure of the hydrogen storage tank;

[0077] The pressure inside the hydrogen storage tank is:

[0078]

[0079] Where:

[0080] n——number of moles;

[0081] R——universal gas constant (8.314 J / K / mol);

[0082] V——volume of hydrogen storage tank;

[0083] T cr , P cr ——are the critical temperature and pressure respectively;

[0084] 5.3. Build a fuel cell model;

[0085] Establish a simulation model of a proton exchange membrane fuel cell. There are many models for PEMFC, with different focuses and scopes of application. According to the different time scales of the research problems, the models are divided into three forms: (1) an equivalent circuit model that considers the short-term dynamics of the double-layer effect; (2) a medium-term dynamic model that considers the change in gas pressure; (3) a thermal dynamic model that considers the thermodynamic process of temperature change over a long period of time. This step considers the electrical characteristics of the fuel cell, so an equivalent circuit model is established.

[0086] U FC is the output voltage of the fuel cell (V); I FC is the output current of the fuel cell; E nernst is the reversible open circuit voltage, also known as the "Nernst voltage"; R ohm is the ohmic overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop caused by ions passing through the electrolyte and electrons passing through the electrodes and connecting parts; R act is the activation overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop generated by the activation of the anode and cathode of the fuel cell; R con is the concentration overvoltage equivalent resistance (mΩ), which is used to indicate the pressure drop caused by the change in the concentration of the reaction gas; C d To reflect the equivalent capacitance (F) of the double layer effect of the fuel cell, it is used to simulate the delay characteristics of activation and concentration overvoltage caused by the double layer effect. The time constant τ = C d (R act +R con ); respectively record R ohm , R act , R con The voltage drop on the ohm , U act , U con , called ohmic overvoltage, activation overvoltage, concentration overvoltage; when C d After the upper voltage enters the steady state, U FC Expressed as follows:

[0087] U FC =Enernst -U ohm -U act -U con (16)

[0088] This formula can more directly express the electrochemical characteristics of the fuel cell, and the calculation methods of each part are as follows:

[0089] Reversible open circuit voltage E nernst The electromotive force for a fuel cell at an open circuit, at a given temperature and gas pressure, is given by:

[0090]

[0091] Where ΔG is the change in Gibbs free energy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); R is the gas constant (8.314J / (K·mol)); T is the operating temperature of the fuel cell (K); T ref represents the reference temperature (K); p H2 and p O2 are the partial pressures of hydrogen and oxygen respectively (kPa); Substitute ΔG and ΔS under standard conditions into the above formula, and set T ref The room temperature is 25℃, we can get:

[0092]

[0093] Ohmic overvoltage U of PEMFC ohm It is linearly related to the current density, and the ohmic overvoltage equivalent resistance R ohm Equal to the sum of the exchange membrane resistance and the connection resistance:

[0094] R ohm =R M +R C (19)

[0095] In the formula, R c Represents the connection resistance, which is a constant and can be obtained from the parameters provided by the fuel cell manufacturer;

[0096] Exchange membrane resistance R M It is expressed as:

[0097]

[0098] In the formula, ρ M is the resistivity of the electrolyte membrane (Ω·cm); l is the thickness of the electrolyte membrane (cm); A is the active area of ​​the fuel cell (cm 2 ); The resistivity of the Nafion exchange membrane used in PEMFC is calculated by the following formula:

[0099]

[0100] Wherein, at temperatures of 0 and 30°C, the resistivity is 181.6 / (λ-0.634), the exponential part in the denominator is the temperature correction coefficient; λ is an adjustment coefficient, which is affected by the preparation process of the exchange membrane and is related to the humidity of the anode gas. At an ideal relative humidity of 100%, λ=14, and under supersaturated conditions, λ=22 or 23;

[0101] Activation overvoltage U of PEMFC act Calculated by the following formula:

[0102]

[0103] In the formula, I n is the internal short-circuit current (A); C O2 is the oxygen concentration on the cathode catalyst surface (mol / cm 3 ), and calculated using Henry's law:

[0104]

[0105] Henry's law states that at a certain temperature, the saturation concentration of a gas in a liquid is proportional to the equilibrium partial pressure of the gas on the liquid surface, and the coefficient is related to factors such as the characteristics of the solute and solvent and temperature; ξ1~ξ4 are activation overvoltage coefficients, which are calculated using the following formula:

[0106]

[0107] Where A is the active area of ​​the fuel cell (cm 2 );C H2 is the hydrogen concentration on the anode catalyst surface (mol / cm 3 ), using Henry's law, we can get:

[0108]

[0109] The activation overvoltage equivalent resistance in the equivalent circuit model is:

[0110]

[0111] Concentration overvoltage U of PEMFC con It is caused by the change in the concentration of reactants on the electrode surface and can be calculated by the following formula:

[0112]

[0113] Where B is the concentration overvoltage coefficient (V); J is the actual current density of the battery (A / cm 2);Maximum current density J max (A / cm 2 ), at the maximum current density, hydrogen is delivered to the fuel cell at the maximum flow rate; because the flow rate of hydrogen is limited, the current density J cannot exceed the maximum current density J during operation. max ; Concentration overvoltage has a greater impact at high current density and a smaller impact under normal operating conditions; the concentration overvoltage equivalent resistance can be calculated by the following formula:

[0114]

[0115] In practice, a fuel cell stack is composed of multiple fuel cell monomers connected in series. In this case, the model of the fuel cell stack can expand the above equivalent circuit model. Assuming that the parameters of each fuel cell monomer are the same, the parameters in the equivalent circuit structure of the fuel cell stack can be deduced based on the basic circuit formula. When the number of monomers in series is n FC When , the parameters are:

[0116]

[0117] The above is the mathematical model of the fuel cell. According to the mathematical model of the fuel cell, a simulation model of the fuel cell is established in PSCAD; the fuel cell simulation model consists of a main circuit module and a parameter calculation module. The main circuit simulates the electrical characteristics of the fuel cell, and the parameter calculation module calculates the various parameters in the main circuit of the fuel cell.

[0118] Beneficial effects of the present invention: Based on the PSCAD simulation environment, the present invention establishes an electromagnetic transient simulation model and constructs an overall simulation model of the off-grid system according to the operating principles and control strategies of the wind power subsystem, photovoltaic subsystem, energy storage subsystem and hydrogen energy subsystem; based on the established electromagnetic transient simulation model, it lays the foundation for further research in different aspects such as simulation condition setting, extraction of system steady-state / transient operation characteristics, design of system parameters and control strategies, and engineering demonstration. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] Figure 1 This is a schematic diagram of the electromagnetic transient model of the wind-solar-hydrogen storage off-grid system;

[0120] Figure 2 This is a schematic diagram of a wind turbine model;

[0121] Figure 3 This is a schematic diagram of a wind turbine model;

[0122] Figure 4 This is a schematic diagram of the internal structure of the wind turbine model;

[0123] Figure 5 This is a schematic diagram of the primary electrical model of the fan;

[0124] Figure 6 It is a schematic diagram of the inner loop control model of the converter machine side;

[0125] Figure 7 It is a schematic diagram of wind energy utilization coefficient curve of wind turbine;

[0126] Figure 8 It is a schematic diagram of the converter machine side outer loop control model;

[0127] Fig. 9 It is a schematic diagram of the pitch angle control model;

[0128] Fig.10 It is a schematic diagram of the modulation model of the trigger signal of the switch device;

[0129] Fig.11 It is a schematic diagram of the overall model of the photovoltaic unit;

[0130] Fig.12 It is a schematic diagram of the primary circuit model of the photovoltaic unit boost chopper circuit;

[0131] Fig.13 This is a schematic diagram of the control link model of the photovoltaic unit boost chopper circuit;

[0132] Fig.14 It is a schematic diagram of the modulation link model of the photovoltaic unit boost chopper circuit;

[0133] Fig.15 This is a schematic diagram of a photovoltaic cell array model;

[0134] Fig.16 It is a schematic diagram of the overall model of the energy storage system;

[0135] Fig.17 It is a schematic diagram of the main circuit model of the energy storage converter;

[0136] Fig.18 It is a schematic diagram of the energy storage converter control model;

[0137] Fig.19 It is a schematic diagram of the energy storage battery stack model;

[0138] Fig. 20 It is a schematic diagram of the electromagnetic transient simulation model of the alkaline electrolyzer;

[0139] Fig.21 This is a schematic diagram of the hydrogen storage tank simulation model;

[0140] Fig. 22 It is a schematic diagram of the equivalent circuit model of a fuel cell;

[0141] Fig.23 Schematic diagram of the fuel cell simulation model. DETAILED DESCRIPTION

[0142] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0143] Embodiment 1: A method for modeling an electromagnetic transient model of a new energy hydrogen production system, comprising the following steps:

[0144] 1. Planning and designing the overall architecture of the model

[0145] Based on the overall project planning and design, this patent builds a system electromagnetic transient simulation model in the PSCAD / EMTDC environment. The model includes key subsystems of the system such as wind power subsystem, photovoltaic subsystem, hydrogen energy subsystem, etc. Based on the simulation model, the steady-state, dynamic and transient simulation research of the system can be carried out.

[0146] 2. Build a wind power system model

[0147] The overall model of the wind turbine is as follows: Figure 2 The model simulates the wind power subsystem configured in the system, which consists of a wind turbine model, a permanent magnet synchronous generator, and a wind power converter.

[0148] 2.1 Building a wind turbine model

[0149] The wind turbine in the wind turbine captures the kinetic energy of wind and converts it into mechanical energy for rotor rotation. It is a purely mechanical device for wind power generation. Therefore, in the simulation modeling of electromagnetic transients, it is simplified to a mathematical model between the current wind speed, rotor speed, and the mechanical power and mechanical torque output by the wind turbine.

[0150] Under normal working conditions, the mechanical power P output by the wind turbine is T As shown in formula (1).

[0151]

[0152] Where: v is the wind speed; R is the impeller radius of the wind blade; ρ is the air density; C p It is defined as the wind energy utilization coefficient, which is a function of the wind turbine's pitch angle β and blade tip speed ratio λ. The functional relationship is shown in formula (2).

[0153]

[0154] The tip speed ratio λ is defined as the ratio of the linear velocity at the tip of the wind blade to the wind speed, that is,

[0155]

[0156] ω T is the angular velocity of the wind blade, considering the speed change of the gearbox, ω T The relationship between it and the generator rotor angular velocity ω follows the relationship shown in equation (4).

[0157] ω=kω T (4)

[0158] Wherein, k is the ratio of the speed of the generator rotor to the speed of the wind turbine blade rotor.

[0159] Obviously, under the conditions of known wind speed v, generator rotor angular velocity ω, and pitch angle β, the current wind turbine output power P can be calculated according to formula (1): T The mechanical torque T that the generator bears at this time is obtained by simple calculation as shown in formula (5): m .

[0160]

[0161] According to the above principles, a simulation model of the wind turbine is established. Figure 3 shown.

[0162] The wind turbine model calculates the mechanical power and torque output from the wind turbine to the generator in real time based on the input wind speed, generator rotor angular velocity, and pitch angle. The model uses normalized input and output, and its internal structure is as follows: Figure 4 shown.

[0163] Among them, since formula (2) is relatively complex, C is specially written in the model. p The calculation module uses series expansion to calculate C p Perform numerical calculations with a certain precision.

[0164] 2.2 Build the electrical primary model

[0165] The electrical primary model of a single wind turbine is as follows: Figure 5 shown.

[0166] The model consists of a generator, a wind turbine converter, and a circuit breaker. The generator uses the permanent magnet synchronous motor model provided by PSCAD, and its rotor is connected to the input terminal of the wind turbine converter. The wind turbine converter uses a three-level voltage source converter. In addition to the DC capacitor, the common DC bus is also equipped with a DC energy consumption circuit for suppressing DC overvoltage.

[0167] 2.3 Building a single-machine converter inner loop control model

[0168] On the wind turbine inverter side, the three-level converter is directly connected to the permanent magnet direct drive motor rotor winding. According to the principle of permanent magnet direct drive motor, the voltage, current and flux of its stator and rotor satisfy the relationship shown in equation (6).

[0169]

[0170] Among them, u sd、u sq 、u rd 、u rq are the d-axis and q-axis components of the stator and rotor voltages in the rotating rectangular coordinate system respectively; i sd 、i sq 、i rd 、i rq are the d-axis and q-axis components of the stator and rotor currents in the rotating rectangular coordinate system, respectively; ψ sd , sq , rd , rq are the d-axis and q-axis components of the stator and rotor flux in the rotating rectangular coordinate system respectively; R s , R r are stator and rotor winding resistances respectively; L s , L r are the stator and rotor winding self-inductances respectively; L m is the mutual inductance between the stator and rotor windings; p is the number of pole pairs; ω is the stator synchronous angular velocity; ω s is the motor slip angular velocity.

[0171] Assuming that the d-axis of the rotating rectangular coordinate system coincides with the direction of the stator flux, the relationship between the stator current and the rotor current can be deduced from equation (6) as shown in equation (7).

[0172]

[0173] Based on equations (6) and (7), by controlling u rd 、u rq , the stator and rotor current i of the motor can be controlled sd 、i sq 、i rd and i rq , thereby further controlling the active power and reactive power output of the entire wind turbine. The inner loop control model of the machine-side converter of the wind turbine converter is as follows: Figure 6 shown.

[0174] 2.4 Building a single-machine converter outer loop control model

[0175] The functional relationship described by equation (2) is plotted as C p The curves that vary with β and λ are as follows Figure 7 shown.

[0176] according to Figure 7 It can be seen that:

[0177] (1) Under the condition that β remains unchanged, C p As λ increases, it shows a trend of first increasing and then decreasing. Therefore, for a fixed wind speed, there is a maximum value of the mechanical power that the wind turbine can output, and an optimal speed that allows the wind turbine to output the maximum power.

[0178] (2) As β increases, the maximum mechanical power that the wind turbine can output shows a decreasing trend, that is, the pitch angle can be used to control the wind turbine's capture of wind energy.

[0179] Based on the above two conclusions, for a wind turbine generator set, its overall outer loop control architecture is as follows: ① The wind turbine is set with the maximum power point tracking (MPPT) function to calculate the upper limit of the maximum active power that the wind turbine can generate in real time according to the wind speed and pitch angle; ② The station coordinated control or the grid dispatcher gives the active power instruction of the wind turbine within the maximum active power range that can be generated; ③ The wind turbine converter adjusts the rotor excitation according to the received active power instruction so that the overall output of the wind turbine meets the active power required by the instruction; ④ The wind turbine controls the pitch angle according to the principle of stabilizing the rotor speed, dynamically maintaining the balance between the mechanical torque and the electromagnetic torque of the generator, so that the wind energy captured by the wind turbine matches the electric energy power delivered by the generator according to the requirements of the grid.

[0180] Based on the above architecture, the outer loop control model of the machine-side converter is as follows: Figure 8 As shown in the figure; the blade angle control model of the wind turbine in the unit is as follows Fig. 9 shown.

[0181] Among them, the MPPT module of wind turbines is specially written in the model. According to the wind energy utilization coefficient curve, this module calculates the maximum active power that the wind turbine can generate under different wind speed conditions in advance, and uses the table lookup method to dynamically output the maximum power (per unit value) of the unit corresponding to the current wind speed, which is used as the upper limit of the active power command issued to the wind turbine by the station coordination control or dispatcher.

[0182] 2.5 Build the converter modulation model

[0183] The machine-side converters in wind power converters all use conventional three-level topology voltage source converters, and the modulation of the switch device trigger signal also uses the most conventional three-level ANPC PWM method. The modulation model is as follows: Fig.10 shown.

[0184] 3. Build a photovoltaic subsystem model

[0185] The overall model of the photovoltaic unit is as follows Fig.11 This model simulates a photovoltaic subsystem in the system, which consists of a photovoltaic cell array model and a Boost circuit model.

[0186] 3.1 Building a photovoltaic string converter model

[0187] The photovoltaic string converter consists of a maximum power point tracking (MPPT) control circuit and a DC / DC converter. In this model, the DC / DC converter uses a Boost chopper circuit.

[0188] The primary circuit model of the boost chopper circuit is as follows: Fig.12 shown.

[0189] The circuit is mainly composed of main inductor L, main capacitor C, diode D, and fully controlled switch device T. f , C f It is a filter circuit. In normal operation, when T is turned on, the low-voltage side power supply forms a large current on L; when T is turned off, the current on L charges C through the continuous flow of D. By controlling the trigger pulse duty cycle of T in a switching cycle, the charging voltage of the main capacitor C can be adjusted, thereby realizing boost chopping.

[0190] Obviously, the current direction supported by this circuit is unidirectional flow from the low-voltage side to the high-voltage side. Within a reasonable design range, as the trigger pulse duty cycle increases, the average current sent by the low-voltage side power supply in a switching cycle shows an upward trend, and the voltage of the main capacitor C also shows an upward trend under the condition that the external circuit conditions remain unchanged. The control link model of the boost chopper circuit is established as follows Fig.13 shown.

[0191] The trigger signal of the switch device in the boost chopper circuit is generated by modulating the carrier of a given frequency with the duty cycle signal. The model of the modulation link is as follows: Fig.14 shown.

[0192] 3.2 Building a photovoltaic cell array model

[0193] The photovoltaic cell array connected to each string inverter is modeled using the photovoltaic cell module provided by PSCAD. According to the collected data, the total photovoltaic installed capacity is 550Wp×236. Fig.15 A model of a photovoltaic array is given.

[0194] 4. Build the energy storage subsystem model

[0195] Fig.16 It is the overall model of the energy storage subsystem. The model consists of an energy storage converter (DAB) and an energy storage battery stack.

[0196] 4.1 Building the Energy Storage Converter Model

[0197] The detailed main circuit model of the energy storage converter is as follows: Fig.17 shown.

[0198] The energy storage battery relies on the energy storage converter to control the power (or charge) of the energy storage battery. The high-voltage side of the energy storage converter stabilizes the DC bus voltage, and the voltage on the energy storage side is determined by the energy storage battery. Therefore, the energy storage converter works in a constant voltage mode, controlling the high-voltage side voltage of the energy storage converter to track the given reference value changes. Fig.18The controller model of DC converter is given.

[0199] 4.2 Building an energy storage battery stack model

[0200] The energy storage battery stack managed by the energy storage converter consists of multiple energy storage battery clusters connected in parallel. Each energy storage battery cluster is modeled using the battery module provided by PSCAD. Fig.19 A model of a battery stack managed by an energy storage inverter.

[0201] 5. Build a hydrogen energy subsystem model

[0202] 5.1 Building an alkaline electrolyzer model

[0203] According to the different time scales of the study, the models of the electrolyzer can be divided into two typical forms, namely the electrochemical empirical model that considers the electrical characteristics of the electrolyzer, and the thermal dynamic model that considers the temperature changes over a longer time scale. This study mainly studies the electrical characteristics, so an empirical model of the alkaline electrolyzer is established.

[0204] The empirical formula for alkaline electrolyzer is as follows:

[0205]

[0206] Where U EL is the cell terminal voltage (V); I EL is the current at the electrolytic cell end (A); U rev is the reversible open circuit voltage (V); A is the cross-sectional area of ​​the electrolytic cell (cm 2 ); r, s, and t are empirical parameters that can be measured experimentally. This empirical model does not take into account the changes in the characteristics of the electrolyzer at different temperatures. When the temperature of the electrolyzer changes greatly, the error is large. For this reason, an improved empirical model is used as shown in formula (9). The following two assumptions are made in this model: 1) The hydrogen and oxygen produced in the electrolyzer are both ideal gases; 2) Water is an incompressible liquid.

[0207]

[0208] In the formula, T is the cell temperature (K); r1 and r2 are the parameters related to the internal resistance of the cell, and r2 reflects the change of the internal resistance of the cell with temperature; s, t1, t2, and t3 are the parameters related to the overvoltage caused by polarization of electrodes and electrolytes in the cell, among which t2 and t3 reflect the change of the overvoltage in the cell with temperature; r1, r2, t1, t2, and t3 are all empirical parameters that can be measured experimentally. The reversible open circuit voltage U in the formula rev It reflects the minimum potential between the electrodes of each electrolytic cell when electrolyzing water.

[0209]

[0210] In the formula, ΔG is the change in Gibbs free energy (J / mol); ΔH is the change in enthalpy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); and T is the operating temperature of the electrolyzer (K). Substituting ΔH and ΔS under standard conditions into the above formula, we can get U rev =1.229V, which increases with decreasing temperature or increasing water vapor pressure in the electrolytic cell, and decreases otherwise.

[0211] In practical applications, the electrolyzer is generally composed of multiple monomers connected in series to achieve the required hydrogen production. The number of monomers in series is n EL When the terminal voltage of the electrolytic cell stack is

[0212]

[0213] According to the above alkaline electrolytic cell principle, the electrolytic cell simulation model is established in PSCAD as follows Fig. 20 The simulation model is mainly composed of an electrical part and a hydrogen part, which respectively simulate the electrical operating characteristics and hydrogen operating characteristics in the electrolyzer.

[0214] 5.2 Build a hydrogen storage tank model

[0215] The capacity of a hydrogen energy storage system is determined by the amount of gas stored in the hydrogen storage tank. In practice, the high-pressure hydrogen storage tank used can be a large gas tank, or multiple gas tanks connected in series. The latter only needs to add new gas tanks when expanding the capacity, and the expansion cost is much lower than that of battery-type energy storage. Assuming that the hydrogen in the hydrogen storage tank is an ideal gas, the ideal gas equation can be obtained

[0216]

[0217] In the formula, p tank is the pressure of the gas in the hydrogen storage tank (kPa); V tank is the volume of the hydrogen storage tank (m 3 );T tank is the temperature of the gas in the hydrogen storage tank; n H2 is the amount of hydrogen in the hydrogen storage tank (mol); R is the ideal gas constant, which is 8.3143 J / K·mol. It can be seen that the amount of hydrogen in the hydrogen storage tank is proportional to the pressure. When the upper and lower limits of the available hydrogen pressure in the hydrogen tank are p tank_max With p tank_min When the amount of hydrogen available is

[0218]

[0219] Using SOC to represent the amount of remaining available hydrogen, we have

[0220]

[0221] It can be seen from the above formula that when it is assumed that the hydrogen in the hydrogen storage tank is an ideal gas and the temperature of the hydrogen storage tank is constant, the SOC value of the hydrogen energy storage system is only related to the pressure of the hydrogen storage tank.

[0222] The pressure inside the hydrogen storage tank is

[0223]

[0224] In the formula

[0225] n——number of moles;

[0226] R——universal gas constant (8.314 J / K / mol);

[0227] V——volume of hydrogen storage tank;

[0228] T cr , P cr ——are the critical temperature and pressure respectively.

[0229] According to the above hydrogen storage tank principle, a hydrogen storage tank simulation model is established in PSCAD as follows Fig.21 shown.

[0230] 5.3 Building a fuel cell model

[0231] This step establishes a proton exchange membrane fuel cell (PEMFC) simulation model. There are many models for PEMFC, and their focus and scope of application are different. According to the different time scales of the research problems, the models can be divided into three forms: (1) an equivalent circuit model that considers the short-term dynamics of the double layer effect; (2) a medium-term dynamic model that considers the change in gas pressure; (3) a thermal dynamic model that considers the thermodynamic process of temperature change over a long period of time. The present invention mainly considers the electrical characteristics of the fuel cell, so an equivalent circuit model is established.

[0232] The equivalent circuit model of a fuel cell is as follows: Fig. 22 As shown, this model is the most widely used equivalent circuit model. It can be used not only for low-temperature fuel cells such as proton exchange membranes, but also for high-temperature fuel cells such as solid oxide fuel cells. The difference lies in the parameter calculation.

[0233] Fig. 22 Middle,U FC is the output voltage of the fuel cell (V); I FC is the output current of the fuel cell; E nernst is the reversible open circuit voltage, also known as the "Nernst voltage"; R ohmis the ohmic overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop caused by ions passing through the electrolyte and electrons passing through the electrodes and connecting parts; R act is the activation overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop generated by the activation of the anode and cathode of the fuel cell; R con is the concentration overvoltage equivalent resistance (mΩ), which is used to indicate the pressure drop caused by the change in the concentration of the reaction gas; C d To reflect the equivalent capacitance (F) of the double layer effect of the fuel cell, it is mainly used to simulate the delay characteristics of activation and concentration overvoltage caused by the double layer effect. The time constant τ = C d (R act +R con ), usually within 1s. ohm , R act , R con The voltage drop on the ohm , U act , U con , called ohmic overvoltage, activation overvoltage, and concentration overvoltage. d After the upper voltage enters the steady state, U FC It can be expressed as follows:

[0234] U FC =E nernst -U ohm -U act -U con (16)

[0235] This formula can more directly express the electrochemical characteristics of the fuel cell, and the calculation methods of each part are as follows:

[0236] Reversible open circuit voltage E nernst When the fuel cell is open circuited, the electromotive force at a given temperature and gas pressure can be given by:

[0237]

[0238] Where ΔG is the change in Gibbs free energy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); R is the gas constant (8.314J / (K·mol)); T is the operating temperature of the fuel cell (K); T ref represents the reference temperature (K); p H2 and p O2 are the partial pressures of hydrogen and oxygen respectively (kPa). Substitute ΔG and ΔS under standard conditions into the above formula, and set T ref At room temperature 25°C, we can get

[0239]

[0240] Ohmic overvoltage U of PEMFC ohm It is linearly related to the current density, and the ohmic overvoltage equivalent resistance R ohm Equal to the sum of the exchange membrane resistance and the connection resistance:

[0241] R ohm =R M +R C (19)

[0242] In the formula, R c Represents the connection resistance, which is usually a constant and can generally be obtained from the parameters provided by the fuel cell manufacturer. M Expressed as

[0243]

[0244] In the formula, ρ M is the resistivity of the electrolyte membrane (Ω·cm); l is the thickness of the electrolyte membrane (cm); A is the active area of ​​the fuel cell (cm 2 The resistivity of the Nafion exchange membrane, which is widely used in PEMFC, can be calculated by the following formula:

[0245]

[0246] Wherein, at temperatures of 0 and 30°C, the resistivity is 181.6 / (λ-0.634), the exponential part in the denominator is the temperature correction coefficient; λ is an adjustment coefficient, which is affected by the preparation process of the exchange membrane and is related to the humidity of the anode gas. At an ideal relative humidity of 100%, λ=14, and under supersaturated conditions, λ=22 or 23.

[0247] Activation overvoltage U of PEMFC act It can be calculated by the following formula

[0248]

[0249] In the formula, I n is the internal short-circuit current (A); C O2 is the oxygen concentration on the cathode catalyst surface (mol / cm 3 ), which can be calculated using Henry’s law

[0250]

[0251] Henry's law states that at a certain temperature, the saturation concentration of a gas in a liquid is proportional to the equilibrium partial pressure of the gas on the liquid surface, and the coefficient is related to factors such as the properties of the solute and solvent and temperature. ξ1~ξ4 are activation overvoltage coefficients, which can generally be calculated using the following formula:

[0252]

[0253] Where A is the active area of ​​the fuel cell (cm 2 );C H2 is the hydrogen concentration on the anode catalyst surface (mol / cm 3 ), using Henry's law, we can get

[0254]

[0255] The activation overvoltage equivalent resistance in the equivalent circuit model is:

[0256]

[0257] Concentration overvoltage U of PEMFC con It is caused by the change in the concentration of reactants on the electrode surface and can be calculated by the following formula

[0258]

[0259] Where B is the concentration overvoltage coefficient (V); J is the actual current density of the battery (A / cm 2 );Maximum current density J max (A / cm 2 ), at the maximum current density, hydrogen is delivered to the fuel cell at the maximum flow rate. Because the flow rate of hydrogen is limited, the current density J cannot exceed the maximum current density J during operation. max Concentration overvoltage has a greater impact at high current density and a smaller impact under normal operating conditions. The concentration overvoltage equivalent resistance can be calculated by the following formula:

[0260]

[0261] In practice, a fuel cell generally consists of multiple fuel cell monomers connected in series to form a fuel cell stack. In this case, the model of the fuel cell stack can expand the above equivalent circuit model. Assuming that the parameters of each fuel cell monomer are the same, the equivalent circuit structure of the fuel cell stack is the same as Fig. 22 The same, each parameter can be derived according to the basic circuit formula. When the number of monomers in series is n FC When , the parameters are

[0262]

[0263] The above is the mathematical model of the fuel cell. Based on the mathematical model of the fuel cell, the simulation model of the fuel cell is established in PSCAD as follows: Fig.23 The fuel cell simulation model is mainly composed of a main circuit module and a parameter calculation module. The main circuit mainly simulates the electrical characteristics of the fuel cell, and the parameter calculation module calculates the various parameters in the main circuit of the fuel cell.

[0264] Example 2: Simulation data statistics and analysis

[0265] The transient simulation data statistics are shown in Table 1. Analysis shows that after a short-circuit fault occurs at a key position of the system, overvoltage and overcurrent phenomena occur at various key positions of the system. Among them, the more serious fault conditions are Fbus20, FWinAC11, FPV11, and FPV20. When this fault condition occurs, a short-circuit current of 10kA or even more than 20kA is generated. When designing the system, special attention should be paid to the system overcurrent tolerance problem when such conditions occur. At the same time, special attention should be paid to the protection problem of such conditions when performing secondary design.

[0266] Table 1 Transient simulation data statistics and analysis table

[0267]

[0268]

[0269] Based on the established simulation model, the present invention carries out steady-state and transient simulations. The simulation results prove the accuracy of the established model on the one hand, and reveal the relevant operating characteristics of the wind-solar-hydrogen storage and off-grid system on the other hand, which can provide a certain reference for the subsequent control strategy design and parameter design.

[0270] Based on the steady-state simulation results obtained, the applicability of the electrochemical energy storage capacity and energy storage converter power proposed in the present invention is verified; at the same time, based on the transient simulation results, the transient operating characteristics of the wind-solar-hydrogen storage off-grid system under typical fault conditions are preliminarily extracted.

[0271] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for modeling an electromagnetic transient model of a new energy hydrogen production system, characterized by: It includes the following steps: Step 1: Plan and design the overall architecture of the model; Step 2: Build a wind electronic system model; Step 3: Build a photovoltaic subsystem model; Step 4: Build the energy storage subsystem model; Step 5: Build the hydrogen energy subsystem model.

2. The electromagnetic transient modeling method of a new energy hydrogen production system according to claim 1 is characterized by: The step 1 specifically includes: building a system electromagnetic transient simulation model in the PSCAD / EMTDC environment based on the overall project planning and design plan; the model includes a wind power subsystem model, a photovoltaic subsystem model, an energy storage subsystem model and a hydrogen energy subsystem model.

3. The electromagnetic transient modeling method of a new energy hydrogen production system according to claim 1 is characterized by: The specific process of step 2 is as follows: 2.

1. Build a wind turbine model: The wind turbine in the wind turbine captures the kinetic energy of wind and converts it into mechanical energy for rotor rotation. It is a purely mechanical device for wind power generation. In the simulation modeling of electromagnetic transients, it is simplified to a mathematical model between the current wind speed, rotor speed, and the mechanical power and mechanical torque output by the wind turbine. Under normal working conditions, the mechanical power P output by the wind turbine is T As shown in formula (1): Where: v is the wind speed; R is the impeller radius of the wind blade; ρ is the air density; C p Defined as the wind energy utilization coefficient, it is a function of the wind turbine's pitch angle β and blade tip speed ratio λ. Its functional relationship is shown in formula (2): The tip speed ratio λ is defined as the ratio of the linear velocity at the tip of the wind blade to the wind speed, that is: ω T is the angular velocity of the wind blade, considering the speed change of the gearbox, ω T The relationship between the generator rotor angular velocity ω and the generator rotor angular velocity ω is as shown in formula (4): ω=kω T (4) Wherein, k is the ratio of the speed of the generator rotor to the wind turbine blade rotor; Under the conditions of known wind speed v, generator rotor angular velocity ω, and pitch angle β, the current wind turbine output power P can be calculated according to formula (1): T The mechanical torque T that the generator bears at this time is obtained by calculation as shown in formula (5): m : The wind turbine model calculates the mechanical power and torque output from the wind turbine to the generator in real time based on the input wind speed, generator rotor angular velocity, and pitch angle; the model uses normalized input and output; C is specially written in the model p The calculation module uses series expansion to calculate C p Perform numerical calculations with a certain degree of accuracy; 2.

2. Build the electrical primary model: The electrical primary model includes a generator, a wind turbine converter and a circuit breaker. The generator uses a permanent magnet synchronous motor model provided by PSCAD, and its rotor is connected to the input terminal of the wind turbine converter. The wind turbine converter uses a three-level voltage source converter. In addition to the DC capacitor, a DC energy consumption circuit for suppressing DC overvoltage is also configured on the common DC bus. 2.

3. Build the inner loop control model of a single-machine converter: On the machine side of the wind turbine converter, the three-level converter is directly connected to the rotor winding of the permanent magnet direct drive motor. According to the principle of the permanent magnet direct drive motor, the voltage, current and flux of its stator and rotor satisfy the relationship shown in formula (6): Among them, u sd 、u sq 、u rd 、u rq are the d-axis and q-axis components of the stator and rotor voltages in the rotating rectangular coordinate system respectively; i sd 、i sq 、i rd 、i rq are the d-axis and q-axis components of the stator and rotor currents in the rotating rectangular coordinate system, respectively; ψ sd , sq , rd , rq are the d-axis and q-axis components of the stator and rotor flux in the rotating rectangular coordinate system respectively; R s , R r are stator and rotor winding resistances respectively; L s , L r are the stator and rotor winding self-inductances respectively; L m is the mutual inductance between the stator and rotor windings; p is the number of pole pairs; ω is the stator synchronous angular velocity; ω s is the motor slip angular velocity; Assuming that the d-axis of the rotating rectangular coordinate system coincides with the direction of the stator flux, the relationship between the stator current and the rotor current can be deduced from equation (6) as shown in equation (7): Based on equations (6) and (7), by controlling u rd 、u rq , the stator and rotor current i of the motor can be controlled sd 、i sq 、i rd and i rq , thereby further controlling the active power and reactive power output of the entire wind turbine; 2.

4. Build a single-machine converter outer loop control model: Plot the functional relationship described by equation (2) as C p Curves that vary with β and λ; there are two cases: (1) Under the condition that β remains unchanged, C p As λ increases, it shows a trend of increasing first and then decreasing. Therefore, for a fixed wind speed, there is a maximum value of the mechanical power that the wind turbine can output, and an optimal speed that allows the wind turbine to output the maximum power. (2) As β increases, the maximum mechanical power that the wind turbine can output shows a decreasing trend, that is, the pitch angle can be used to control the wind turbine's capture of wind energy; Based on the above two conclusions, for a wind turbine generator set, its overall outer loop control architecture is as follows: ① The wind turbine is set with a maximum power tracking function, and the upper limit of the maximum active power that the wind turbine can generate is calculated in real time according to the wind speed and pitch angle; ② The station coordinated control or the grid dispatcher gives the active power instruction of the wind turbine within the maximum active power range that can be generated; ③ The wind turbine converter adjusts the rotor excitation according to the received active power instruction, so that the overall output of the wind turbine meets the active power required by the instruction; ④ The wind turbine controls the pitch angle according to the principle of stabilizing the rotor speed, dynamically maintaining the balance between the mechanical torque and the electromagnetic torque of the generator, so that the wind energy captured by the wind turbine matches the electric energy power sent by the generator according to the requirements of the grid; 2.

5. Build the converter modulation model: The machine-side converters in wind power converters all adopt conventional three-level topology voltage source converters, and the modulation of the switching device trigger signal also adopts the three-level ANPC PWM method.

4. The electromagnetic transient modeling method for a new energy hydrogen production system according to claim 1 is characterized in that: The specific process of step 3 is as follows: 3.

1. Build a photovoltaic string converter model: The photovoltaic string converter consists of a maximum power tracking control circuit and a DC / DC converter. In this model, the DC / DC converter uses a Boost chopper circuit. The circuit consists of a main inductor L, a main capacitor C, a diode D, and a fully controlled switch device T. f , C f It is a filter circuit. During normal operation, when T is turned on, the low-voltage side power supply forms a large current on L. During the off period of T, the current on L charges C through the freewheeling of D. By controlling the trigger pulse duty ratio of T in a switching cycle, the charging voltage of the main capacitor C can be adjusted, thereby realizing boost chopping. The current direction supported by this circuit is unidirectional flow from the low-voltage side to the high-voltage side. Within a reasonable design range, as the trigger pulse duty cycle increases, the average current sent by the low-voltage side power supply in one switching cycle shows an upward trend, and the voltage of the main capacitor C also shows an upward trend under the condition that the external circuit conditions remain unchanged; The trigger signal of the switch device in the boost chopper circuit is generated by modulating the carrier of a given frequency with the duty cycle signal; 3.

2. Build a photovoltaic cell array model: The photovoltaic cell array connected to each string inverter is modeled using the photovoltaic cell module provided by PSCAD.

5. The electromagnetic transient modeling method for a new energy hydrogen production system according to claim 1 is characterized by: The specific process of step 4 is as follows: 4.

1. Build the energy storage converter model: The energy storage battery relies on the energy storage converter to control the power of the energy storage battery; the high-voltage side of the energy storage converter stabilizes the DC bus voltage, and the voltage on the energy storage side is determined by the energy storage battery. The energy storage converter works in a constant voltage mode, and controls the high-voltage side voltage of the energy storage converter to track the changes of a given reference value; 4.

2. Build energy storage battery stack model: The energy storage battery stack managed by the energy storage converter consists of multiple energy storage battery clusters connected in parallel. Each energy storage battery cluster is modeled using the battery module provided by PSCAD.

6. The electromagnetic transient modeling method for a new energy hydrogen production system according to claim 1 is characterized by: The specific process of step 5 is as follows: 5.

1. Build an alkaline electrolyzer model: According to the different time scales of the research, the model of the electrolyzer can be divided into two typical forms, namely the electrochemical empirical model considering the electrical characteristics of the electrolyzer, and the thermal dynamic model considering the temperature changes over a longer time scale; Establishing the empirical model of the alkaline electrolyzer: The empirical formula for alkaline electrolyzer is as follows: Where U EL is the cell terminal voltage (V); I EL is the current at the electrolytic cell end (A); U rev is the reversible open circuit voltage (V); A is the cross-sectional area of ​​the electrolytic cell (cm 2 ); r, s, t are empirical parameters that can be measured experimentally; the empirical model does not take into account the changes in the characteristics of the electrolytic cell at different temperatures, and the error is large when the temperature of the electrolytic cell changes greatly; To this end, an improved empirical model is used as shown in formula (9); the following two assumptions are made in this model: 1) the hydrogen and oxygen produced in the electrolyzer are ideal gases; 2) water is an incompressible liquid; Where T is the cell temperature (K); r1 and r2 are related parameters of the cell's internal resistance, r2 reflects the change of the cell's internal resistance with temperature; s, t1, t2, t3 are related parameters of the overvoltage caused by polarization of electrodes and electrolytes in the cell, t2 and t3 reflect the change of the overvoltage in the cell with temperature; r1, r2, t1, t2, t3 are all empirical parameters, measured by experiments; the reversible open circuit voltage U in the formula is rev It reflects the minimum potential between the electrodes of each electrolytic monomer in the electrolytic cell when electrolyzing water: Wherein, ΔG is the change in Gibbs free energy (J / mol); ΔH is the change in enthalpy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); T is the operating temperature of the electrolyzer (K); In practical applications, the electrolyzer consists of multiple monomers connected in series to achieve the required hydrogen production; the number of monomers in series is n EL When , the terminal voltage of the electrolytic cell stack is: 5.

2. Build a hydrogen storage tank model: The capacity of the hydrogen energy storage system is determined by the amount of gas stored in the hydrogen storage tank. Assuming that the hydrogen in the hydrogen storage tank is an ideal gas, the ideal gas equation can be obtained: In the formula, p tank is the pressure of the gas in the hydrogen storage tank (kPa); V tank is the volume of the hydrogen storage tank (m 3 );T tank is the temperature of the gas in the hydrogen storage tank; n H2 is the amount of hydrogen in the hydrogen storage tank (mol); R is the ideal gas constant, which is 8.3143 J / K·mol; it can be seen that the amount of hydrogen in the hydrogen storage tank is proportional to the pressure. When the upper and lower limits of the pressure of the available hydrogen in the hydrogen tank are p tank_max With p tank_min When , the amount of substance available for hydrogen is: Using SOC to represent the amount of remaining available hydrogen, we have: It can be seen from the above formula that, assuming that the hydrogen in the hydrogen storage tank is an ideal gas and the temperature of the hydrogen storage tank is constant, the SOC value of the hydrogen energy storage system is only related to the pressure of the hydrogen storage tank; The pressure inside the hydrogen storage tank is: Where: n——number of moles; R——universal gas constant (8.314 J / K / mol); V——volume of hydrogen storage tank; T cr , P cr ——are the critical temperature and pressure respectively; 5.

3. Build a fuel cell model; Establish a simulation model of a proton exchange membrane fuel cell. There are many models for PEMFC, with different focuses and scopes of application. According to the different time scales of the research problems, the models are divided into three forms: (1) an equivalent circuit model that considers the short-term dynamics of the double-layer effect; (2) a medium-term dynamic model that considers the change in gas pressure; (3) a thermal dynamic model that considers the thermodynamic process of temperature change over a long period of time. This step considers the electrical characteristics of the fuel cell, so an equivalent circuit model is established. U FC is the output voltage of the fuel cell (V); I FC is the output current of the fuel cell; E nernst is the reversible open circuit voltage, also known as the "Nernst voltage"; R ohm is the ohmic overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop caused by ions passing through the electrolyte and electrons passing through the electrodes and connecting parts; R act is the activation overvoltage equivalent resistance (mΩ), which is used to represent the voltage drop generated by the activation of the anode and cathode of the fuel cell; R con is the concentration overvoltage equivalent resistance (mΩ), which is used to indicate the pressure drop caused by the change in the concentration of the reaction gas; C d To reflect the equivalent capacitance (F) of the double layer effect of the fuel cell, it is used to simulate the delay characteristics of activation and concentration overvoltage caused by the double layer effect. The time constant τ = C d (R act +R con ); respectively record R ohm , R act , R con The voltage drop on the ohm , U act , U con , called ohmic overvoltage, activation overvoltage, concentration overvoltage; when C d After the upper voltage enters the steady state, U FC Expressed as follows: IN FC =E nernst -IN ohm -IN act -IN con (16) This formula can more directly express the electrochemical characteristics of the fuel cell, and the calculation methods of each part are as follows: Reversible open circuit voltage E nernst The electromotive force for a fuel cell at an open circuit, at a given temperature and gas pressure, is given by: Where ΔG is the change in Gibbs free energy (J / mol); ΔS is the change in entropy (J / (K·mol)); F is the Faraday constant (96485C / mol); R is the gas constant (8.314J / (K·mol)); T is the operating temperature of the fuel cell (K); T ref represents the reference temperature (K); p H2 and p O2 are the partial pressures of hydrogen and oxygen respectively (kPa); Substitute ΔG and ΔS under standard conditions into the above formula, and set T ref The room temperature is 25℃, we can get: Ohmic overvoltage U of PEMFC ohm It is linearly related to the current density, and the ohmic overvoltage equivalent resistance R ohm Equal to the sum of the exchange membrane resistance and the connection resistance: R ohm =R M +R C (19) In the formula, R c Represents the connection resistance, which is a constant and can be obtained from the parameters provided by the fuel cell manufacturer; Exchange membrane resistance R M It is expressed as: In the formula, ρ M is the resistivity of the electrolyte membrane (Ω·cm); l is the thickness of the electrolyte membrane (cm); A is the active area of ​​the fuel cell (cm 2 ); The resistivity of the Nafion exchange membrane used in PEMFC is calculated by the following formula: Wherein, at temperatures of 0 and 30°C, the resistivity is 181.6 / (λ-0.634), the exponential part in the denominator is the temperature correction coefficient; λ is an adjustment coefficient, which is affected by the preparation process of the exchange membrane and is related to the humidity of the anode gas. At an ideal relative humidity of 100%, λ=14, and under supersaturated conditions, λ=22 or 23; Activation overvoltage U of PEMFC act Calculated by the following formula: In the formula, I n is the internal short-circuit current (A); C O2 is the oxygen concentration on the cathode catalyst surface (mol / cm 3 ), and calculated using Henry's law: Henry's law states that at a certain temperature, the saturation concentration of a gas in a liquid is proportional to the equilibrium partial pressure of the gas on the liquid surface, and the coefficient is related to factors such as the characteristics of the solute and solvent and temperature; ξ1~ξ4 are activation overvoltage coefficients, which are calculated using the following formula: Where A is the active area of ​​the fuel cell (cm 2 );C H2 is the hydrogen concentration on the anode catalyst surface (mol / cm 3 ), using Henry's law, we can get: The activation overvoltage equivalent resistance in the equivalent circuit model is: Concentration overvoltage U of PEMFC con It is caused by the change in the concentration of reactants on the electrode surface and can be calculated by the following formula: Where B is the concentration overvoltage coefficient (V); J is the actual current density of the battery (A / cm 2 );Maximum current density J max (A / cm 2 ), at the maximum current density, hydrogen is delivered to the fuel cell at the maximum flow rate; because the flow rate of hydrogen is limited, the current density J cannot exceed the maximum current density J during operation. max ; Concentration overvoltage has a greater impact at high current density and a smaller impact under normal operating conditions; the concentration overvoltage equivalent resistance can be calculated by the following formula: In practice, a fuel cell stack is composed of multiple fuel cell monomers connected in series. In this case, the model of the fuel cell stack can expand the above equivalent circuit model. Assuming that the parameters of each fuel cell monomer are the same, the parameters in the equivalent circuit structure of the fuel cell stack can be deduced based on the basic circuit formula. When the number of monomers in series is n FC When , the parameters are: The above is the mathematical model of the fuel cell. According to the mathematical model of the fuel cell, a simulation model of the fuel cell is established in PSCAD; the fuel cell simulation model consists of a main circuit module and a parameter calculation module. The main circuit simulates the electrical characteristics of the fuel cell, and the parameter calculation module calculates the various parameters in the main circuit of the fuel cell.

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