MILP-based hybrid AC / DC micro-grid load management and optimization method

Abstract

The invention discloses a hybrid AC / DC micro-grid load management and optimization method based on MILP, and the method comprises the steps: firstly, enabling a system to determine the current time, adjusting a load reduction strategy according to a time period, and monitoring the state of a power grid to judge whether load reduction is needed or not; and when the power grid is closed and the load exceeds the power generation and energy storage capabilities, the system starts the load reduction mathematical model. And through an MILP algorithm, model evaluation and load priority updating are carried out, an optimal load reduction scheme is calculated, and important loads are guaranteed preferentially. And finally, the system sends an operation signal to the circuit breaker according to an optimization result, load disconnection operation is implemented, and the load of the power grid is kept within a safe range. And if the power grid returns to normal or the energy storage system meets the load requirement, load reduction is not needed. According to the method, the management efficiency and the resource allocation capability of the micro-grid during the load peak period are improved.

Description

Technical Field

[0001] The present invention belongs to the field of power systems and control thereof, and in particular to a hybrid AC / DC microgrid load management and optimization method based on MILP. Background Art

[0002] With the continuous growth of global energy demand and the enhancement of environmental protection awareness, renewable energy power generation technology has developed rapidly. In particular, photovoltaic power generation and wind power generation, due to their clean and renewable characteristics, have gradually become an important part of the future energy structure. However, due to the intermittent and unstable nature of renewable energy, how to maintain the stability of the power system in an isolated operation scenario has become an urgent problem to be solved.

[0003] Hybrid AC / DC microgrids can achieve more efficient power transmission and distribution by combining the advantages of AC and DC systems. However, in the case of a high proportion of renewable energy, it is difficult to maintain the balance between supply and demand in the power grid, and the traditional dispatching strategy cannot be adjusted in real time, resulting in frequency fluctuations and voltage instability, and even the risk of power outages. When the system is in a high proportion of renewable energy operation, the complexity of the power grid increases, and the traditional load management method is not sensitive enough when dealing with system failures, which can easily lead to local overloads or frequency and voltage fluctuations. In addition, the traditional energy balance method cannot fully utilize the potential of energy storage systems in peak shaving and valley filling and coping with sudden load fluctuations. In island mode, if the load and energy balance cannot be managed quickly and accurately, the system may be frequently disconnected from the grid or blackouts, affecting the reliability and safety of the system. Therefore, a new load management and optimization method is urgently needed to improve the stability of the system and the efficiency of resource utilization. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a hybrid AC / DC microgrid load management and optimization method based on MILP. This method can achieve optimal resource allocation and load management for the microgrid, and improve the stability and resource utilization efficiency of the system in an isolated island operation scenario. It is mainly used in microgrid systems with a high proportion of renewable energy, aiming to improve the stability and resource utilization efficiency of the system.

[0005] Technical solution: A hybrid AC / DC microgrid load management and optimization method based on MILP of the present invention comprises the following steps:

[0006] S1. Determine the current time and adjust the load reduction strategy according to different time periods. Based on the grid status and load conditions, determine whether load reduction operations are required. When the grid is shut down and the load exceeds the power generation and energy storage capacity, execute the next step.

[0007] S2. Construct a mathematical model for load reduction, evaluate and update the priority of critical loads, and ensure that important loads are given priority in the event of power shortage; calculate the optimal load reduction plan based on load priority and grid carrying capacity, and determine the loads that need to be disconnected;

[0008] S3. According to the optimal load reduction plan, an operation signal is sent to the selected circuit breaker to implement load disconnection operation to ensure that the grid load remains within a safe range; when the grid returns to normal or the energy storage system can meet the load demand, the load reduction is stopped.

[0009] Further, step S1 is specifically as follows: the system obtains the current time to identify whether the system is in a peak load period or a valley load period, providing a reference for subsequent load management strategies; monitors and determines the operating status of the power grid, specifically including checking whether the power grid is disconnected from the upper power grid, that is, whether it is in a closed state, to ensure that when the power grid is closed, the system can detect it in time and enter the operating state in the island mode; evaluates the current load demand P L and compare it with the system's power generation capacity P Gen And the output power P of the energy storage system bat For comparison; if the load demand exceeds the sum of the power generation capacity and the energy storage output, that is, P L >P Gen +e·P bat , where e is determined according to the working status of the energy storage system, load reduction operation needs to be performed.

[0010] Furthermore, in step S2, the mathematical model of load reduction is solved by a mixed integer linear programming algorithm MILP to achieve optimal load management and power resource allocation, and the calculation process includes the following steps:

[0011] S2.1. Determine the objective function of the load reduction mathematical model;

[0012] S2.2. Determine the constraints of the mathematical model of load reduction and convert the nonlinear problem of the constraints into a linear problem.

[0013] Furthermore, step S2.1 is specifically as follows: the objective function of the load reduction mathematical model is:

[0014]

[0015] Where NC and C are the total number of non-critical loads and critical loads respectively; A and B are priority coefficients; m i 、m j Indicates the circuit breaker status; L i , L jare the power requirements of critical load and non-critical load respectively; x and a are virtual variables and their coefficients respectively. The virtual variable x is a binary variable with a value of 0 or 1, indicating whether the load point is disconnected, and the coefficient a determines the importance weight of the disconnected load point in the optimization. The priority of load disconnection is controlled by adjusting a.

[0016] Furthermore, step S2.2 is specifically as follows: the constraints of the load reduction mathematical model are:

[0017] Formula (2) is the power balance constraint;

[0018]

[0019] P total =P m +g·P Grid +e·P Bat (3)

[0020]

[0021] DOD≤SOC≤FC (6)

[0022]

[0023] In the above formula, formula (2) is the power balance constraint; formula (3) is the power source on the power supply side; formula (4) is the battery charging and discharging state; formula (5) is the power interaction state between the microgrid and the large power grid; formula (6) is the energy storage battery constraint; formula (7) is the circuit breaker state; where P total is the total system output power; P m Renewable energy generation power; P Grid Grid input power; P Bat Battery storage power; SOC, DOD, and FC are the battery's state of charge, depth of discharge, and fully charged state, respectively. e represents the charge and discharge state of the energy storage system. g represents the regulation state of the grid power, specifically indicating whether the grid needs to intervene to supply power or absorb excess power.

[0024] Convert the nonlinear problem of formula (2) into a linear problem:

[0025]

[0026] Furthermore, step S3 is specifically as follows: according to the optimization result of the aforementioned load shedding mathematical model, determine the load to be disconnected and generate a corresponding operation signal; send the operation signal to the corresponding circuit breaker control device, specifically including controlling the execution sequence and time of load disconnection; after the load disconnection operation is completed, monitor the grid status and the operation of the energy storage system in real time; if the grid status returns to normal or the output power of the energy storage system is sufficient to meet the current load demand, terminate the load shedding operation and restore normal power supply; record the operation data and grid status during the entire load shedding process for subsequent analysis and optimization.

[0027] The present invention also discloses a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method of the present invention.

[0028] The present invention also discloses a computer-readable storage medium on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the present invention are implemented.

[0029] The present invention also discloses a computer program product, comprising a computer program / instruction, which implements the steps of the method of the present invention when executed by a processor.

[0030] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0031] 1. Enhanced system stability and reliability: The proposed load and energy management strategy significantly improves the overall stability of the hybrid AC / DC microgrid by effectively managing load priorities and energy storage systems, thereby reducing the risk of power outages.

[0032] 2. Reduced reliance on the power grid: By optimizing the load management strategy, the system can be more effectively self-sufficient during peak load periods or in island mode, thereby reducing reliance on the external power grid and improving energy autonomy.

[0033] 3. Prioritize critical loads: The mathematical modeling technology in the present invention can flexibly handle load priorities, ensuring that critical loads are given priority power supply when resources are limited, thereby improving users' sense of security and satisfaction.

[0034] 4. Elasticity in handling large-scale loads: This strategy shows good elasticity when the number of loads increases, and can effectively manage more loads without affecting the overall performance of the system. Compared with the exhaustive search method, it has better applicability and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a low-voltage distribution network of IEEE33 nodes used in the simulation experiment of the present invention;

[0036] Figure 2 This is the energy storage charging algorithm process provided by the present invention;

[0037] Figure 3 This is the energy storage discharge algorithm process provided by the present invention;

[0038] Figure 4 This is the load reduction strategy process provided by the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0040] A hybrid AC / DC microgrid load management and optimization method based on MILP includes the following steps:

[0041] S1, determine the current time so that the load reduction strategy can be adjusted according to different time periods. Then, determine the grid status and load conditions to determine whether load reduction operations are required. When the grid is shut down and the load exceeds the power generation and energy storage capacity, perform the next step.

[0042] S2, start the mathematical model of load reduction, evaluate and update the priority of critical loads, and ensure that important loads are given priority in the event of power shortage. According to the load priority and grid carrying capacity, calculate the optimal load reduction plan and determine the loads that need to be disconnected.

[0043] S3, based on the optimization results, sends an operation signal to the selected circuit breaker to implement load disconnection operation to ensure that the grid load remains within a safe range. If the grid returns to normal or the energy storage system can meet the load demand, there is no need to perform load reduction.

[0044] Specifically, the step S1 includes the following sub-steps:

[0045] Step S1-1: Get the current time and make preliminary adjustments to the load reduction strategy based on the load characteristics of different time periods. By getting the current time, it is possible to identify whether the system is in a peak load period or a valley load period, thereby providing a reference for subsequent load management strategies.

[0046] Step S1-2: monitor and determine the operating status of the power grid, specifically including checking whether the power grid is disconnected from the upper power grid, that is, whether it is in a closed state. This step ensures that when the power grid is closed, the system can detect it in time and enter the operating state in the island mode.

[0047] Step S1-3: Evaluate the current load demand (P L ) and compare it with the system's power generation capacity (P Gen ) and the output power of the energy storage system (Pbat If the load demand exceeds the sum of the generation capacity and the storage output (i.e. P L >P Gen +e·P bat , where e is determined according to the working status of the energy storage system), load shedding operation needs to be performed. This step determines whether there is a risk of negative power imbalance by comprehensively considering load demand and power supply. When it is detected that the power grid is shut down and the load demand exceeds the power supply capacity, the system will enter load shedding mode, providing data support and judgment basis for subsequent steps to ensure the rationality and effectiveness of the load shedding strategy.

[0048] Specifically, the load reduction mathematical model in step S2 is solved by a MILP (mixed integer linear programming) algorithm to achieve optimal load management and power resource allocation, specifically including:

[0049] Step S2-1, the objective function of the load reduction mathematical model is:

[0050]

[0051] Where NC and C are the total number of non-critical loads and critical loads respectively; A and B are priority coefficients; m i 、m j Indicates the circuit breaker status; L i , L j are the power requirements of critical load and non-critical load respectively; x and a are virtual variables and their coefficients respectively. The virtual variable x is a binary variable with a value of 0 or 1, indicating whether the load point is disconnected, and the coefficient a determines the importance weight of the disconnected load point in the optimization. By adjusting a, the priority control of load disconnection can be achieved.

[0052] Step S2-2, the constraints of the load reduction mathematical model are:

[0053] Formula (2) is the power balance constraint;

[0054]

[0055] P total =P m +g·P Grid +e·P Bat (3)

[0056]

[0057] DOD≤SOC≤FC (6)

[0058]

[0059] In the above formula, formula (2) is the power balance constraint; formula (3) is the power source on the power supply side; formula (4) is the battery charging and discharging status; formula (5) is the power interaction status between the microgrid and the large power grid; formula (6) is the energy storage battery constraint; formula (7) is the circuit breaker status. total is the total system output power; P m Renewable energy generation power; P Grid Grid input power; P Bat Battery storage power; SOC, DOD, and FC are the battery's state of charge, depth of discharge, and fully charged state, respectively; e represents the charge and discharge state of the energy storage system, and g represents the regulation state of the grid power, specifically indicating whether the grid needs to intervene to supply power or absorb excess power.

[0060] In step S2-2, the nonlinear problem of formula (2) is converted into a linear problem:

[0061]

[0062] Specifically, step S3 is as follows: according to the optimization result of the aforementioned load shedding mathematical model, determine the load to be disconnected and generate the corresponding operation signal; send the operation signal to the corresponding circuit breaker control device, specifically including precise control of the execution sequence and time of load disconnection to avoid affecting the critical load; after the load disconnection operation is completed, monitor the grid status and the operation of the energy storage system in real time. If the grid status returns to normal or the output power of the energy storage system is sufficient to meet the current load demand, immediately terminate the load shedding operation and restore normal power supply; record the operation data and grid status during the entire load shedding process for subsequent analysis and optimization.

[0063] Example:

[0064] use Figure 1 The IEEE33-node low-voltage distribution network shown in the figure verifies the effectiveness of the proposed MILP-based load management and optimization method. This method aims to improve the management efficiency and resource allocation capabilities of the microgrid during peak load periods. Take a typical summer day wind and solar load data, which has three power imbalance periods in the evening, as shown in Table 1. If not resolved, it will lead to voltage instability and trigger a system power outage due to the undervoltage protection system. In order to verify the feasibility of the method proposed in this paper, the load reduction strategy proposed in this paper and the traditional exhaustive search method are used to disconnect the load. Table 1 shows its load optimization results.

[0065] The analysis shows that the proposed scheme produces similar results compared to the exact exhaustive search method and does not disconnect any critical load. The exhaustive search method does not consider load priority, so a critical load is disconnected in all three time periods. The proposed method can stabilize the system without disconnecting any critical load, verifying the feasibility of the proposed mathematical model and its ability to consider load priority.

[0066] Table 1 Load management results of the load reduction algorithm and the exhaustive search method in the simulation experiment of the present invention

[0067]

Claims

1. A hybrid AC / DC microgrid load management and optimization method based on MILP, characterized in that: The steps include: S1. Determine the current time and adjust the load reduction strategy according to different time periods. Based on the grid status and load conditions, determine whether load reduction operations are required. When the grid is shut down and the load exceeds the power generation and energy storage capacity, execute the next step. S2. Construct a mathematical model for load reduction, evaluate and update the priority of critical loads, and ensure that important loads are given priority in the event of power shortage; calculate the optimal load reduction plan based on load priority and grid carrying capacity, and determine the loads that need to be disconnected; S3. According to the optimal load reduction plan, an operation signal is sent to the selected circuit breaker to implement load disconnection operation to ensure that the grid load remains within a safe range; when the grid returns to normal or the energy storage system can meet the load demand, the load reduction is stopped.

2. The method for load management and optimization of a hybrid AC / DC microgrid based on MILP according to claim 1, characterized in that: Step S1 is as follows: the system obtains the current time to identify whether the system is in a peak load period or a valley load period, providing a reference for subsequent load management strategies; monitors and determines the operating status of the power grid, including checking whether the power grid is disconnected from the upper power grid, that is, whether it is in a closed state, to ensure that when the power grid is closed, the system can detect it in time and enter the operating state in the island mode; evaluates the current load demand P L and compare it with the system's power generation capacity P Gen And the output power P of the energy storage system bat For comparison; if the load demand exceeds the sum of the power generation capacity and the energy storage output, that is, P L >P Gen +e·P bat , where e is determined according to the working status of the energy storage system, load reduction operation needs to be performed.

3. The method for load management and optimization of a hybrid AC / DC microgrid based on MILP according to claim 1, characterized in that: In step S2, the mathematical model of load reduction is solved by a mixed integer linear programming algorithm MILP to achieve optimal load management and power resource allocation. The calculation process includes the following steps: S2.

1. Determine the objective function of the load reduction mathematical model; S2.

2. Determine the constraints of the mathematical model of load reduction and convert the nonlinear problem of the constraints into a linear problem.

4. The method for load management and optimization of a hybrid AC / DC microgrid based on MILP according to claim 3, characterized in that: Step S2.1 is as follows: The objective function of the load reduction mathematical model is: Where NC and C are the total number of non-critical loads and critical loads respectively; A and B are priority coefficients; m i 、m j Indicates the circuit breaker status; L i , L j are the power requirements of critical load and non-critical load respectively; x and a are virtual variables and their coefficients respectively. The virtual variable x is a binary variable with a value of 0 or 1, indicating whether the load point is disconnected, and the coefficient a determines the importance weight of the disconnected load point in the optimization. The priority of load disconnection is controlled by adjusting a.

5. The method for load management and optimization of a hybrid AC / DC microgrid based on MILP according to claim 3, characterized in that: Step S2.2 is specifically as follows: The constraints of the load reduction mathematical model are: Formula (2) is the power balance constraint; P total =P m +g·P Grid +e·P Bat (3) DOD≤SOC≤FC (6) In the above formula, formula (2) is the power balance constraint; formula (3) is the power source on the power supply side; formula (4) is the battery charging and discharging state; formula (5) is the power interaction state between the microgrid and the large power grid; formula (6) is the energy storage battery constraint; formula (7) is the circuit breaker state; where P total is the total system output power; P m Renewable energy generation power; P Grid Grid input power; P Bat Battery storage power; SOC, DOD, and FC are the battery's state of charge, depth of discharge, and fully charged state, respectively; e represents the charge and discharge state of the energy storage system; and g represents the regulation state of the grid power; Convert the nonlinear problem of formula (2) into a linear problem:

6. The method for load management and optimization of a hybrid AC / DC microgrid based on MILP according to claim 1, characterized in that: Step S3 specifically includes: determining the load to be disconnected according to the optimization result of the aforementioned load shedding mathematical model, and generating a corresponding operation signal; sending the operation signal to the corresponding circuit breaker control device, specifically including controlling the execution sequence and time of load disconnection; after the load disconnection operation is completed, monitoring the grid state and the operation of the energy storage system in real time; if the grid state returns to normal or the output power of the energy storage system is sufficient to meet the current load demand, terminating the load shedding operation and restoring normal power supply; The operation data and grid status during the entire load reduction process are recorded for subsequent analysis and optimization.

7. A computer device comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method of claim 1.

8. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to claim 1 are implemented.

9. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to claim 1 are implemented.

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