Stable and safe correction control method for static voltage of island micro-grid

Abstract

The invention discloses an island micro-grid static voltage stability and safety correction control method. An active power load model and a reactive power load model of electrolytic hydrogen production equipment are established; establishing a nonlinear programming model for evaluating the static voltage stability of the island micro-grid under the condition that electrolytic hydrogen production equipment operates according to a rated power factor, performing convex relaxation on the nonlinear programming model to obtain a second-order cone programming model, and performing optimization solution to obtain a load margin index and each node voltage; and if the load margin index is smaller than the load margin threshold value lambdamin, the reactive power of the hydrogen electrolysis cell is adjusted for voltage control. According to the control method, the load margin index of the island micro-grid can be calculated, the stability degree of the island micro-grid is judged, and the purpose of improving the static voltage stability of the micro-grid is achieved by adopting hydrogen production load control; a reasonable scheduling plan can be made according to the load margin condition in the micro-grid to cope with various emergencies and changes.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid control, and particularly relates to a static voltage stability safety correction control method for an island microgrid. Background Technique

[0002] Since the island area is far from the main power grid, its power supply system is usually an isolated microgrid in operation, and often lacks large-capacity generators. Instead, multiple local distributed power sources (such as wind energy, photovoltaic, diesel generators, and energy storage systems) are used to supply power in a distributed control manner. The power supply in the island has the following characteristics and challenges: (1) The proportion of renewable energy sources such as wind energy and photovoltaic in the island microgrid is relatively high, and their output is greatly affected by weather conditions. The output of renewable energy sources fluctuates randomly, leading to challenges in system power balance and voltage stability. (2) The scale of the island microgrid is small, with low inertia. When disturbed, the voltage is prone to large fluctuations, and even voltage collapse may occur. (3) The island microgrid lacks reactive power support provided by large-scale synchronous generators, and the voltage support ability is insufficient, making it prone to voltage instability problems. Therefore, it is necessary to perform safety correction control on the voltage stability of the island microgrid, that is, a real-time control method that adjusts the operating parameters to restore the system to a safe state when the microgrid faces the risk of voltage instability.

[0003] In recent years, hydrogen production technology has received attention in the island energy system. The hydrogen production load can be integrated with other distributed energy sources to improve the system flexibility. Through an offshore integrated photovoltaic-hydrogen-energy storage system or a decentralized integrated hydrogen production system for wind turbines, hydrogen can be directly produced and stored in an undersea storage tank. Thus, replacing large gas turbines or diesel engines with hydrogen fuel cells can provide clean electric energy for remote islands. Currently, the research mainly focuses on the active power of the hydrogen production load to achieve new energy consumption and optimal dispatching of the system; while little attention has been paid to the research on voltage control of its reactive power characteristics. Summary of the Invention

[0004] The purpose of the present invention is to provide a static voltage stability safety correction control method for an island microgrid, which solves the problems of poor static voltage stability of the integrated energy microgrid in the existing technology and the prone occurrence of power outage accidents due to voltage instability.

[0005] The technical solution adopted by the present invention is as follows: The static voltage stability safety correction control method for an island microgrid, and the specific operation steps are as follows Step 1: Establish an active power load model for the electrolytic hydrogen production equipment; Step 2: Establish a reactive power load model for the electrolytic hydrogen production equipment; Step 3: Establish a non-linear programming model for static voltage stability assessment of the island microgrid under the condition that the electrolytic hydrogen production equipment operates at the rated power factor, and perform convex relaxation on the non-linear programming model to obtain a second-order cone programming model; Step 4: Optimize and solve the second-order cone programming model to obtain the load margin index and the voltage of each node; Step 5: If the load margin index is less than the load margin threshold λ min , then adjust the reactive power of the hydrogen electrolyzer for voltage control.

[0006] The features of the present invention also lie in that Step 1 is specifically as follows: First, establish an electrolyzer stack model. Through the polarization curve and the electrolyzer stack efficiency characteristics of the electrolyzer stack model, the DC power consumption is obtained as: (1) Wherein, is the DC efficiency, also known as the stack efficiency, represents the ratio of the energy of the output hydrogen to the input energy of the stack; is the hydrogen mass production rate; In the case of ignoring the losses of the power electronic converter, the active power consumption of the hydrogen production equipment by electrolysis is: (2).

[0007] The reactive power output in the reactive power load model of the hydrogen production equipment by electrolysis is controlled at a unity power factor PF under normal operating conditions, that is, the reactive power is 0; in the voltage stability correction control proposed by the present invention, the reactive power of the hydrogen production equipment by electrolysis is adaptively controlled according to its terminal voltage, specifically expressed as: (3) Wherein, is the reactive power output of the hydrogen production equipment; is its terminal voltage; is its rated terminal voltage; is the reactive voltage adaptive control coefficient of the hydrogen production equipment, and this coefficient is set as a variable to be optimized in the optimization model.

[0008] Step 3 is specifically as follows: Step 3.1: Set the objective function of the nonlinear programming model Adopt the load margin λ as the voltage stability index, and the objective function for optimizing the nonlinear programming model is the maximum load margin index λ , that is: (4) Step 3.2: Set the constraint conditions, which include power flow equation constraints, controllable power source capacity inequality constraints, system safe operation inequality constraints, and hydrogen production equipment safety inequality constraints; the specific constraint conditions are as follows: (1) Power flow equation constraints Adopt the power flow equation constraints based on DistFlow. Let be a connected graph representing the power network, where N represents the set of nodes, E represents the set of branches; the node numbers are , for each node , let be the complex voltage at node i , and denote , then the equation constraint is as follows in Equation (5): (5) where the set u ( j ) is the set of the head nodes of the branches with j as the end node in the power grid; the set v ( j ) is the set of the end nodes of the branches with j as the head node in the power grid; P ij , Q ij are the active power and reactive power at the head of branch ij respectively; P j and Q j are the net injection values of the active power and reactive power at node j respectively; P j,G , P j,HE and P j,L are the active power of the power source connected to node j , the active power consumed by the electrolytic hydrogen production equipment, and the active power consumed by other loads except the electrolytic hydrogen production equipment respectively; Q j,G , Q j,HE and Q j,L are the reactive power of the power source connected to node j , the reactive power generated by the electrolytic hydrogen production equipment, and the reactive power consumed by other loads except the electrolytic hydrogen production equipment respectively; r ij , x ijare the resistance and reactance of the branch ij respectively; The active power of the load P j,L and the reactive power Q j,L need to superimpose their growth components, as shown in Equation (6) below: (6) In the formula, P j,L0 and Q j,L0 are the active power and reactive power of the initial load at node j respectively; For the active power and reactive power of the power source P j,G , Q j,G , calculate according to Equation (7) below: (7) P j,CG , Q j,CG are the active power and reactive power of the controllable power source connected to node j respectively, P j,IG , Q j,IG are the total active power and total reactive power of the stochastic power source connected to node j respectively; The controllable power source refers to the set of power sources with controllable output in the island microgrid, usually including diesel generator sets, battery energy storage systems, fuel cells and other power sources; the stochastic power source refers to the power source whose output is affected by natural conditions and is stochastic and uncontrollable. In the island microgrid, it mainly includes wind turbines, photovoltaic systems, wave energy generator sets and other power sources; Each controllable power source adopts a droop control method, and its active and reactive power outputs P j,CG , Q j,CG respectively satisfy the equality constraints of (8) and (9): (8) (9) Among them, m pj , n qj are the droop coefficients of the active power and reactive power of the controllable power source at node j respectively; ω is the system angular frequency; ω0 is the set value of the angular frequency, V 0 is the set value of the voltage; B CG is the set of controllable power supply nodes.

[0009] Let Perform Taylor expansion and linear approximation near the rated voltage, and substitute it into Equation (9) to obtain: (10); (2) Inequality constraint of controllable power supply capacity The controllable power supply connected to node j also needs to satisfy the capacity limit inequality constraint: (11) Where, and are the upper and lower limit values of the capacity of the controllable power supply respectively; (3) Inequality constraint for safe operation of the system To ensure the normal operation of the system, it is necessary to satisfy the node voltage safety limit constraint and the branch power safety constraint; since the system angular frequency is also one of the variables, the safety constraint of the system angular frequency also needs to be considered during the optimization process: (12) Where, is the current amplitude of branch ij ; and are the upper and lower limit values of the voltage amplitude of node j respectively; and are the upper and lower limit values of the system angular frequency respectively; is the upper limit value of the power amplitude of branch ij ; (4) Inequality constraint for the safety of hydrogen production equipment In the electrolytic hydrogen production equipment model, the active power constraint is considered, as shown in Equation (13): (13) Where, is the active power consumption of the electrolytic hydrogen production equipment, is the minimum technical load, is the maximum value of the active power consumption of the electrolytic hydrogen production equipment; The power of the hydrogen production equipment is limited by the power transmission limit of the inverter, as shown in the following equation: (14) The inequality constraint of Equation (14) is a second-order cone constraint condition; Thus, an optimization model for static voltage stability assessment of an island microgrid is established, with the formula (5) as the objective function and the formulas (6) - (14) as the constraints.

[0010] Step 3.3: Establish a non - linear programming model for static voltage stability assessment of the island microgrid with the objective function in Step 3.1 and the constraints in Step 3.2. Step 3.4: Conduct convex relaxation on the constraints of the non - linear programming model to obtain a second - order cone programming model, specifically as follows: Select the non - linear part in formula (5) and define it as : (15) Where P ij , Q ij are the active power and reactive power at the head of branch ij respectively; is the square of the current amplitude flowing through branch ij ; Transform formula (6) into: (16) Relax formula (15) to get: (17) Convert formula (17) into the standard second - order cone form: (18) Thus, the non - linear programming model for static voltage stability assessment of the island microgrid is relaxed into a second - order cone programming model: (19).

[0011] Step 4: Use typical optimization methods such as the interior - point method or commercial optimization solvers such as Gurobi to optimize and solve the second - order cone programming model to obtain the load margin index and the node voltages.

[0012] The load margin threshold in Step 5 λ min is determined according to the system configuration and the requirements of the load for power supply reliability.

[0013] The beneficial effects of the present invention are: (1) It is applicable to static voltage assessment of island microgrids, can calculate the load margin index of island microgrids, judge the stability degree of island microgrids, and achieve the purpose of improving the static voltage stability of microgrids by controlling the hydrogen - production load. (2)The static voltage stability safety correction control method for island microgrids can formulate a reasonable dispatching plan according to the load margin in the microgrid to cope with various emergencies and changes. For example, in different operating scenarios such as new energy and load power fluctuations and local faults in the system, when the system faces the risk of voltage instability, it can adjust the reactive power of the hydrogen production equipment to ensure that the voltage of the microgrid system is within a safe range, thereby improving the power supply reliability of the system; (3)The static voltage stability safety correction control method for island microgrids proposed by the present invention is of great significance in improving energy utilization efficiency, enhancing system reliability, reducing environmental pollution, and coping with the intermittency and volatility of renewable energy. Description of the Drawings

[0014] Figure 1 is the overall flowchart of the method of the present invention; Figure 2 is the single-line diagram of the microgrid adopted in the embodiment of the method of the present invention. Detailed Embodiments

[0015] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0016] Embodiment 1 The static voltage stability safety correction control method for island microgrids of the present invention is as Figure 1 shown, and the specific operation steps are as follows Step 1: Establish an active power load model for the electrolytic hydrogen production equipment; Step 2: Establish a reactive power load model for the electrolytic hydrogen production equipment; Step 3: Under the condition that the electrolytic hydrogen production equipment operates at the rated power factor, establish a nonlinear programming model for the static voltage stability assessment of the island microgrid, and perform convex relaxation on the nonlinear programming model to obtain a second-order cone programming model; Step 4: Optimize and solve the second-order cone programming model to obtain the load margin index and the voltage of each node; Step 5. If the load margin index is less than the load margin threshold λ min , then adjust the reactive power of the hydrogen electrolyzer for voltage control.

[0017] Embodiment 2 Step 1: Establish an active power load model for the electrolytic hydrogen production equipment; specifically as follows: First, establish an electrolytic cell stack model. Through the polarization curve and the electrolytic stack efficiency characteristics of the electrolytic cell stack model, the DC power consumption is obtained as: (1) Among them, is the DC efficiency, also known as the stack efficiency, It represents the ratio of the energy of the output hydrogen to the input energy of the stack; is the hydrogen mass production rate; Ignoring the losses of the power electronic converter, the active power consumption of the electrolytic hydrogen production equipment is: (2).

[0018] Step 2: Establish a reactive power load model for the electrolytic hydrogen production equipment; The reactive power output in the reactive power load model of the electrolytic hydrogen production equipment in Step 2 Under normal operating conditions, it is controlled according to the unity power factor PF That is, the reactive power is 0; in the voltage stability correction control proposed in the present invention, the reactive power of the electrolytic hydrogen production equipment is adaptively controlled according to its terminal voltage, specifically expressed as: (3) Wherein, is the reactive power output of the hydrogen production equipment; is its terminal voltage; is its rated terminal voltage; is the reactive voltage adaptive control coefficient of the hydrogen production equipment, and this coefficient is set as an optimization variable to be determined in the optimization model.

[0019] Step 3: Establish a nonlinear programming model for the static voltage stability assessment of the island microgrid under the condition that the electrolytic hydrogen production equipment operates at the rated power factor, and perform convex relaxation on the nonlinear programming model to obtain a second-order cone programming model; Step 4: Optimally solve the second-order cone programming model to obtain the load margin index and the node voltages; Step 5. If the load margin index is less than the load margin threshold λ min , then adjust the reactive power of the hydrogen electrolyzer for voltage control.

[0020] Example 3 Based on Example 2, Step 3 is specifically as follows: Step 3.1: Set the objective function of the nonlinear programming model Adopt the load margin λ as the voltage stability index, and the objective function for optimizing the nonlinear programming model is the load margin index λ to be the maximum, that is: (4) Step 3.2: Set the constraint conditions, and the constraint conditions include power flow equation constraints, controllable power source capacity inequality constraints, system safe operation inequality constraints, and hydrogen production equipment safety inequality constraints; the constraint conditions are specifically as follows: (1)Power flow equation constraints The power flow equation constraints based on DistFlow are adopted. Let be a connected graph representing the power network, where N represents the set of nodes, E represents the set of branches; the node numbers are , for each node , let be the complex voltage at node i . Denote , Then the equation constraint is as follows in Equation (5): (5) where the set u ( j ) is the set of the head nodes of the branches with j as the end node in the power grid; the set v ( j ) is the set of the end nodes of the branches with j as the head node in the power grid; P ij 、 Q ij are the active power and reactive power at the head of branch ij respectively; P j and Q j are the net injection values of active power and reactive power at node j respectively; P j,G 、 P j,HE and P j,L are the active power of the power source connected to node j , the active power consumed by the electrolytic hydrogen production equipment, and the active power consumed by other loads except the electrolytic hydrogen production equipment respectively; Q j,G 、 Q j,HE and Q j,L are the reactive power of the power source connected to node j , the reactive power generated by the electrolytic hydrogen production equipment, and the reactive power consumed by other loads except the electrolytic hydrogen production equipment respectively; r ij 、 x ij are the resistance and reactance of branch ij respectively; The active power of the load P j,L and the reactive powerQ j,L The growth component needs to be superimposed, as shown in the following formula (6): (6) In the formula, P j,L0 and Q j,L0 are respectively the active power and reactive power of the initial load of node j ; For the active power and reactive power of the power supply P j,G , Q j,G , they are calculated by the following formula (7): (7) P j,CG , Q j,CG are respectively the active power and reactive power of the controllable power supply connected to node j ; P j,IG , Q j,IG are respectively the total active power and total reactive power of the stochastic power supply connected to node j ; The controllable power supply refers to the set of power supplies with controllable output in the island microgrid, usually including power supplies such as diesel generator sets, battery energy storage systems, and fuel cells; the stochastic power supply refers to the power supply whose output is affected by natural conditions and is stochastic and uncontrollable. In the island microgrid, it mainly includes power supplies such as wind turbines, photovoltaic systems, and wave energy generator sets; Each controllable power supply adopts a droop control method, and its active and reactive power outputs P j,CG , Q j,CG respectively satisfy the equality constraints of (8) and (9): (8) (9) Among them, m pj , n qj are respectively the droop coefficients of the active power and reactive power of the controllable power supply of node j ; ω is the system angular frequency; ω 0 is the set value of the angular frequency, V 0 is the set value of the voltage; B CG is the set of controllable power supply nodes.

[0021] Perform Taylor expansion and linear approximation near the rated voltage, and substitute into Equation (9) to obtain: In the vicinity of the rated voltage, perform Taylor expansion and linear approximation, and substitute into Equation (9) to get: (10); (2) Inequality constraint of controllable power source capacity The access node j For the controllable power source, the capacity limit inequality constraint also needs to be satisfied: (11) Wherein, and are the upper and lower limit values of the capacity of the controllable power source respectively; (3) Inequality constraint for safe operation of the system To ensure the normal operation of the system, the node voltage safety limit constraint and the branch power safety constraint need to be satisfied; since the system angular frequency is also one of the variables, the safety constraint of the system angular frequency also needs to be considered during the optimization process: (12) Wherein, is the current amplitude of branch ij ; and are the upper and lower limit values of the node j voltage amplitude respectively; and are the upper and lower limit values of the system angular frequency respectively; is the upper limit value of the branch ij power amplitude; (4) Inequality constraint for safety of hydrogen production equipment In the electrolytic hydrogen production equipment model, the active power constraint is considered, as shown in Equation (13): (13) Wherein, is the active power consumption of the electrolytic hydrogen production equipment, is the minimum technical load, is the maximum value of the active power consumption of the electrolytic hydrogen production equipment; The power of the hydrogen production equipment is subject to the power transmission limit of the inverter, as shown in the following equation: (14) The inequality constraint of Equation (14) is a second-order cone constraint condition; Thus, an optimization model for static voltage stability assessment of an island microgrid is established with Equation (5) as the objective function and Equations (6) - (14) as the constraint conditions.

[0022] Step 3.3: Establish a nonlinear programming model for the static voltage stability assessment of the island microgrid with the objective function in Step 3.1 and the constraint conditions in Step 3.2; Example 4 On the basis of Example 3, Step 3.4 is specifically as follows: Perform convex relaxation on the constraint conditions of the nonlinear programming model to obtain a second-order cone programming model, specifically as follows: Select the nonlinear part in formula (5) and define it as : (15) Where, P ij , Q ij are the active power and reactive power at the head end of branch ij respectively; is the square of the current amplitude flowing through branch ij ; Transform formula (6) into: (16) Relax formula (15) to obtain: (17) Convert formula (17) into the standard second-order cone form: (18) Thus, the nonlinear programming model for the static voltage stability assessment of the island microgrid is relaxed into a second-order cone programming model: (19).

[0023] Example 5 On the basis of Example 4, in Step 4, a typical optimization method such as the interior point method or a commercial optimization solver such as Gurobi is used to optimize and solve the second-order cone programming model to obtain the load margin index and the voltage of each node. The load margin threshold in Step 5 λ min is determined according to the system configuration and the requirements of the load for power supply reliability.

[0024] Example 6 The static voltage stability and security correction control method for the island microgrid of the present invention is configured with micro-sources and operates in island mode by the IEEE 33-node system as Figure 2 shown.

[0025] Four droop-controlled micro-sources (fuel cells, gas turbines, battery energy storage, etc.) are connected to the system to form a microgrid, which is disconnected from the main grid and operates as an island, and a load of 0.06 + j0.03 is connected to Node 1. The connection locations and parameters of each micro-source (all in per-unit values, rated capacity S B = 1 MVA) are shown in Table 1. Photovoltaic systems of 0.8 MW are connected to Nodes 3 and 10 respectively. A proton exchange membrane hydrogen electrolyzer with a rated capacity of 1 MVA is connected to Node 10 of the microgrid, and the active power is 0.4 MW.

[0026] Table 1. Connection locations and parameters of controllable micro-sources

[0027] Step 1: Establish an optimization model for the static voltage stability assessment of the islanded microgrid with Equation (5) as the objective function and Equations (6) - (14) as the constraints. Considering that this model is a non-linear programming model and it is not easy to obtain the optimal solution. Therefore, by relaxing the constraints, a second-order cone programming model is established.

[0028] Step 2: Assume that the hydrogen electrolyzer operates at unity power factor, and use a typical optimization solution method to optimize and solve the model, and calculate the load margin of the system. When the photovoltaic output is zero, the load margin obtained by solving is λ = 1.8052e-04, indicating that the system is in a critical state of voltage instability; at this time, considering the random volatility of the load, if the load increases by more than 0.018052%, the system voltage will collapse. For example, assume the load increases by 1%, then the power flow calculation has no solution. When the photovoltaic outputs are both 0.5 MW, the load margin index is λ = 0.1279. At this time, if the load increases by more than 12.79%, the system voltage will collapse and the power flow calculation has no solution.

[0029] According to the load fluctuation situation in the actual system, the load margin threshold can be taken as λ min = 0.15.

[0030] It can be seen that when the hydrogen electrolyzer operates at unity power factor, the voltage stability margin of the system λ < λ min , the voltage level is low, and the fluctuations of photovoltaic output or load can easily lead to system voltage instability. Therefore, voltage stability correction control is carried out by adjusting the reactive power output of the hydrogen production equipment.

[0031] Step 3: Adopt the proposed static voltage stability and security correction control strategy to regulate the reactive power output of the grid-connected inverter of the hydrogen electrolyzer to improve the voltage stability of the microgrid. Determine the reactive power output of the electrolyzer according to Equation (3), establish a second-order cone programming model, and calculate the load margin of the system.

[0032] Step 4: Use typical optimization methods such as the interior point method or commercial optimization solvers such as Gurobi for optimization. When the PV output is zero, the load margin index obtained by solving is λ = 0.1561. It can be seen that by using the hydrogen electrolyzer to participate in voltage control, the system can maintain static voltage stability when the load increases by 15.61%. The stability margin of the system, that is, the degree of static voltage stability, has been improved. When the load has a 15% increase fluctuation, the system can still maintain static voltage stability. At this time, the nodal voltages obtained by solving the power flow are shown in Table 2.

[0033] When the PV outputs are all 0.5 MW, the load margin index obtained by solving is λ = 0.3661. It can be seen that by using the hydrogen electrolyzer to participate in voltage control, the system can maintain static voltage stability when the load increases by 36.61%. The stability margin of the system, that is, the degree of static voltage stability, has been improved. Compared with the case where the hydrogen production load does not participate in voltage control, the load margin index has increased by 186.71%. At this time, the reactive power output of the electrolytic hydrogen production equipment is 0.5889. When the load has a 15% increase fluctuation, the system can still maintain static voltage stability. At this time, the nodal voltages are shown in Table 3.

[0034] Table 2. Nodal voltages when the hydrogen electrolyzer participates in voltage control (PV output is 0 MW)

[0035] Table 3. Nodal voltages when the hydrogen electrolyzer participates in voltage control (PV output is 0.5 MW)

[0036] Step 4: By comparing the two methods, the conclusion can be drawn that when the island microgrid faces the risk of voltage instability, voltage security correction control through the hydrogen electrolyzer can effectively improve the voltage stability degree of the island microgrid, and the voltage levels and qualities of all nodes in the system have been improved as a whole.

[0037] The present invention proposes a static voltage stability and security correction control method for an island microgrid considering the reactive voltage regulation ability of the hydrogen production load. When the load margin of the island microgrid is low, correction control is carried out by exploiting the regulation ability of the hydrogen production load to improve the static voltage stability of the island microgrid.

[0038] It should be noted that the present invention is not limited to the above specific embodiments. For those of ordinary skill in the art, based on the concept of the present invention, several improvements or substitutions can be made, which should all be regarded as falling within the scope covered by the present invention.

Claims

1. A static voltage stability safety correction control method for an island microgrid, characterized in that The specific operation steps are as follows: Step 1: Establish an active power load model for the electrolytic hydrogen production equipment; Step 2: Establish a reactive power load model for the electrolytic hydrogen production equipment; Step 3: Establish a nonlinear programming model for the static voltage stability assessment of the island microgrid, and perform convex relaxation on the nonlinear programming model to obtain a second-order cone programming model; Step 4: Optimally solve the second-order cone programming model to obtain the load margin index and the voltage of each node; Step 5: If the load margin index is less than the load margin threshold λ min , then adjust the reactive power of the hydrogen electrolyzer for voltage control.

2. The static voltage stability and safety correction control method for the island microgrid according to claim 1, characterized in that Specifically, Step 1 is as follows: First, establish an electrolyzer stack model. Through the polarization curve and the electrolyzer stack efficiency characteristics of the electrolyzer stack model, the DC power consumption is obtained as: （1） Among them, is the DC efficiency, also known as the stack efficiency, which represents the ratio of the energy of the output hydrogen to the energy input to the stack; is the hydrogen mass production rate; Ignoring the losses of the power electronic converter, the active power consumption of the electrolytic hydrogen production equipment is: （2） 。 3. The static voltage stability and security correction control method for the island microgrid according to claim 2, wherein, In Step 2, the reactive power of the electrolytic hydrogen production equipment is adaptively controlled according to the terminal voltage, and the reactive power output in the reactive power load model is expressed as: （3） Wherein, is the reactive power output of the hydrogen production equipment; is the terminal voltage; is the rated value of the terminal voltage; is the reactive voltage adaptive control coefficient of the hydrogen production equipment.

4. The static voltage stability and security correction control method for the island microgrid according to claim 3, characterized in that, Specifically, Step 3 is as follows: Step 3.1: Set the objective function of the nonlinear programming model Using load margin λ as the voltage stability index, the objective function of the optimized nonlinear programming model is the load margin index λ is maximized, that is: （4） Step 3.2: Set the constraint conditions, which include power flow equality constraints, controllable power source capacity inequality constraints, system safe operation inequality constraints, and hydrogen production equipment safety inequality constraints; Step 3.3: Establish a nonlinear programming model for the static voltage stability assessment of the island microgrid with the objective function in Step 3.1 and the constraint conditions in Step 3.2; Step 3.4: Perform convex relaxation on the constraint conditions of the nonlinear programming model to obtain a second-order cone programming model.

5. The static voltage stability and safety correction control method for the island microgrid according to claim 4, characterized in that, The power flow equality constraints in Step 3.2 are as follows: Using the power flow equation constraints based on DistFlow, assume that is a connected graph representing the power network, where N represents the set of nodes, E represents the set of branches; the node numbers are , for each node , assume that is the complex voltage at node i , and denote , Then the power flow equality constraints are as shown in Equation (5) below: （5） Among them, the set u ( j ) is the set of the head node of the branch with j as the end node in the power grid; the set v ( j ) is the set of the end node of the branch with j as the head node in the power grid; P ij and Q ij are the active power and reactive power of the head of the branch ij respectively; P j and Q j are the net injection values of the active power and reactive power of the node j respectively; P j,G , P j,HE and P j,L are the active power of the power source connected to the node j , the active power consumed by the electrolytic hydrogen production equipment, and the active power consumed by other loads except the electrolytic hydrogen production equipment respectively; Q j,G , Q j,HE and Q j,L are the reactive power of the power source connected to the node j , the reactive power generated by the electrolytic hydrogen production equipment, and the reactive power consumed by other loads except the electrolytic hydrogen production equipment respectively; r ij , x ij are the resistance and reactance of the branch ij respectively; The active power of the load P j,L and reactive power Q j,L It is necessary to superimpose its growth component, as shown in the following formula (6): （6） In the formula, P j,L0 and Q j,L0 are the active power and reactive power of the initial load of node j respectively; For the active power and reactive power of the power supply P j,G 、 Q j,G , they are calculated by the following formula (7): （7） P j,CG and Q j,CG are respectively the active power and reactive power of the controllable power sources connected to node j . P j,IG and Q j,IG are respectively the total active power and total reactive power of the stochastic power sources connected to node j . The controllable power sources refer to the set of power sources with controllable output in the island microgrid, including diesel generator sets, battery energy storage systems, and fuel cells. The stochastic power sources refer to the power sources with stochastic and uncontrollable output affected by natural conditions, and mainly include wind turbine generators, photovoltaic systems, and wave energy generator sets in the island microgrid; Each controllable power source adopts a droop control method, and its active and reactive power outputs P j,CG and Q j,CG respectively satisfy the equality constraints in (8) and (9): （8） （9） Among them, m pj and n qj are the droop coefficients of the active power and reactive power of the controllable power source of node j respectively; ω is the system angular frequency; ω 0 is the set value of the angular frequency, V 0 is the set value of the voltage; B CG is the set of controllable power source nodes; Substitute Perform Taylor expansion and linear approximation near the rated voltage, and substitute it into Equation (9) to obtain: （10）； The controllable power source capacity inequality constraints are as follows: Access node j The controllable power supply should also satisfy the capacity limit inequality constraint: （11） Among them, and are respectively the upper and lower limit values of the capacity of the controllable power supply; The system safe operation inequality constraints are as follows: To ensure the normal operation of the system, it is necessary to satisfy the node voltage safety limit constraint and the branch power safety constraint; since the system angular frequency is also one of the variables, the safety constraint of the system angular frequency also needs to be considered during the optimization process: （12） Among them, is the current amplitude of branch ij ; and are the upper and lower limits of the voltage amplitude of node j respectively; and are the upper and lower limits of the system angular frequency respectively; is the upper limit value of the power amplitude of branch ij ; The hydrogen production equipment safety inequality constraints are as follows: Consider the active power constraint in the electrolytic hydrogen production equipment model, as shown in Equation (13): （13） Among them, is the active power consumption of the electrolytic hydrogen production equipment, is the minimum technical load, is the maximum value of the active power consumption of the electrolytic hydrogen production equipment; The power of the hydrogen production equipment is limited by the power transmission limit of the inverter, as shown in the following formula: constrained as shown in the following equation: （14） The inequality constraint in Equation (14) is a second-order cone constraint condition; Thus, an optimization model for the static voltage stability assessment of the island microgrid can be established with Equation (5) as the objective function and Equations (6) to (14) as the constraint conditions.

6. The static voltage stability and security correction control method for the island microgrid according to claim 5, characterized in that, The method in Step 3.4 of transforming the nonlinear programming model into a second-order cone programming model by convex relaxation is specifically as follows: Select the non-linear part in formula (5) and define it as :[[]]END]] （15） Among them, P ij and Q ij are the active power and reactive power at the head end of branch ij respectively; is the square of the current amplitude flowing through branch ij ; Transform Equation (6) into: （16） Relax Equation (15) to obtain: （17） Convert Equation (17) into the standard second-order cone form: （18） Thus, the nonlinear programming model for the static voltage stability assessment of the island microgrid is relaxed into a second-order cone programming model: （19）。 7. The static voltage stability safety correction control method for the island microgrid according to claim 6, wherein In Step 4, use the interior point method or the optimization solver Gurobi to optimally solve the second-order cone programming model to obtain the load margin index and the voltage of each node.

8. The static voltage stability and security correction control method for the island microgrid according to claim 7, characterized in that The load margin threshold described in step 5 λ min It is determined according to the system configuration and the requirements of the load for power supply reliability.

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