Microgrid operation control method, control device and microgrid

Abstract

The present application discloses a microgrid operation control method, a control device and a microgrid, and the operation control method includes: determining the operation status of the microgrid grid connection point and the microgrid bus voltage value; formulating management strategies for the operation status of different microgrid grid connection points based on the peak-valley electricity price mechanism, and formulating corresponding control strategies according to different microgrid bus voltages; and controlling the operation of the microgrid using management strategies or control strategies. The microgrid operation control method provided in the present application is based on a composite superconducting energy storage-current-limited microgrid. By combining the peak-valley electricity price to establish a control strategy for the photovoltaic storage system, the power consumption of the large power grid and the dependence of the power-consuming area on the power grid are reduced, the operation cost of the microgrid is reduced, and the power supply quality and the reliability and stability of the power supply are improved.

Description

Technical Field

[0001] The present application relates to the field of microgrid technology, and in particular to a microgrid operation control method and system. Background Art

[0002] The existing photovoltaic storage microgrid system balances the DC bus voltage by adding supercapacitors on the DC side, ensuring the reactive current output of the photovoltaic inverter, so that the photovoltaic storage microgrid grid-connected system meets the requirements of low voltage ride-through. However, the power imbalance during a voltage sag will cause the output current of the photovoltaic inverter to increase, which may exceed the output current limit of the inverter itself, causing the inverter to trigger overcurrent protection and cause the photovoltaic storage microgrid system to be disconnected from the grid. In addition, the existing photovoltaic storage microgrid system is too dependent on the power grid, and the random characteristics of the charging and discharging of the system energy storage device are too large, which cannot reflect the flexibility, safety and economy of the microgrid. At the same time, due to the weak anti-interference ability of the photovoltaic storage microgrid system when operating in an isolated grid, it cannot meet the user's demand for high power supply quality and high energy efficiency. Summary of the invention

[0003] The purpose of this application is to provide a microgrid operation control method and system to reduce the operating cost of the photovoltaic storage microgrid, enhance the low voltage ride-through capability of the photovoltaic storage microgrid system, and improve the power supply stability and quality.

[0004] To achieve the above objectives, the present application provides a microgrid operation control method, comprising:

[0005] Determine the operating status of the microgrid connection point and the microgrid bus voltage value;

[0006] Based on the peak-valley electricity price mechanism, formulate management strategies for the operating status of different microgrid connection points, and formulate corresponding control strategies according to different microgrid bus voltages;

[0007] Use management strategies or control strategies to control microgrid operation.

[0008] Furthermore, the peak-valley electricity price mechanism is used to formulate management strategies for the operation status of different microgrid connection points, including:

[0009] When the grid-connected point is in normal operation, the output power and load power of the photovoltaic system in the microgrid are calculated;

[0010] When the output power is greater than the load power and the photovoltaic system has surplus power supply, the energy storage battery is charged until the energy storage battery is full, and the excess power is transmitted to the large power grid;

[0011] When the output power is less than the load power and the electricity price is at the peak period, the object to supply power to the load is determined according to the charge state of the energy storage battery;

[0012] When the output power is less than the load power and the electricity price is at the valley period, the PV system supplies power to the load, the large power grid provides the load power shortfall, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged;

[0013] When the output power is less than the load power and the electricity price is in non-peak or non-valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the mains power jointly supply power to the load.

[0014] Furthermore, when the output power is less than the load power and the electricity price is at the peak period, determining the object to supply power to the load according to the state of charge of the energy storage battery includes:

[0015] If the state of charge of the energy storage battery is higher than the maximum state of charge, the energy storage battery is used to supply power to the load;

[0016] If the state of charge of the energy storage battery is between the minimum state of charge and the maximum state of charge, and the power it can provide is less than the load shortfall power, the required power is purchased from the mains;

[0017] If the state of charge of the energy storage battery is less than the minimum state of charge, the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

[0018] Furthermore, the management strategy is formulated for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and further includes:

[0019] When there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter, the superconducting current limiter is used to adjust the microgrid to meet the low voltage ride-through requirements and maintain grid connection operation;

[0020] When there is a fault at the grid connection point and the grid current is less than the operating current of the current limiter, the photovoltaic inverter is adjusted to ensure that the microgrid meets the low voltage ride-through requirements and remains connected to the grid.

[0021] Furthermore, the management strategy is formulated for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and further includes:

[0022] When there is a fault at the grid connection point and the microgrid still does not meet the low voltage ride-through requirements after adjustment, a control command is issued to make the microgrid operate off-grid.

[0023] Furthermore, the corresponding control strategy is formulated according to different microgrid bus voltages, including:

[0024] When the microgrid bus voltage is in normal operation, the composite superconducting energy storage device in the microgrid does not operate;

[0025] When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the start-up conditions, the action of the energy storage battery or the composite superconducting energy storage device is determined according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device;

[0026] When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device does not meet the start-up conditions, the voltage regulator is controlled to operate.

[0027] Furthermore, when the microgrid bus voltage is disturbed and the composite superconducting energy storage device meets the start-up conditions, the action of the energy storage battery or the composite superconducting energy storage device is determined according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device, including:

[0028] When the current of the composite superconducting energy storage device is less than the maximum current limit of the composite superconducting energy storage device, and the bus voltage of the microgrid is greater than the voltage of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to be charged;

[0029] When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load;

[0030] When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode;

[0031] When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

[0032] The present application also provides a microgrid operation control device, comprising:

[0033] The parameter acquisition module is used to determine the operating status of the microgrid grid connection point and the microgrid bus voltage value;

[0034] The strategy determination module is used to formulate management strategies for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and to formulate corresponding control strategies according to different microgrid bus voltages;

[0035] The control module is used to control the operation of the microgrid using a management strategy or a control strategy.

[0036] Furthermore, the strategy determination module includes a normal operation control unit of the grid connection point, which is used to:

[0037] When the grid-connected point is in normal operation, the output power and load power of the photovoltaic system in the microgrid are calculated;

[0038] When the output power is greater than the load power and the photovoltaic system has surplus power supply, the energy storage battery is charged until the energy storage battery is full, and the excess power is transmitted to the large power grid;

[0039] When the output power is less than the load power and the electricity price is at the peak period, the object to supply power to the load is determined according to the charge state of the energy storage battery;

[0040] When the output power is less than the load power and the electricity price is at the valley period, the PV system supplies power to the load, the large power grid provides the load power shortfall, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged;

[0041] When the output power is less than the load power and the electricity price is in non-peak or non-valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the mains power jointly supply power to the load.

[0042] Furthermore, the normal operation control unit of the grid connection point is also used for:

[0043] If the state of charge of the energy storage battery is higher than the maximum state of charge, the energy storage battery is used to supply power to the load;

[0044] If the state of charge of the energy storage battery is between the minimum state of charge and the maximum state of charge, and the power it can provide is less than the load shortfall power, the required power is purchased from the mains;

[0045] If the state of charge of the energy storage battery is less than the minimum state of charge, the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

[0046] Furthermore, the strategy determination module further includes:

[0047] The first control unit for grid connection point fault is used to adjust the microgrid to meet the low voltage ride-through requirement and maintain grid connection operation through the superconducting current limiter when there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter;

[0048] The second control unit for grid connection point fault is used to adjust the photovoltaic inverter so that the microgrid meets the low voltage ride-through requirement and maintains grid-connected operation when the grid connection point fails and the grid current is less than the operating current of the current limiter.

[0049] Furthermore, the strategy determination module further includes a third control unit for a grid connection point failure, configured to:

[0050] When there is a fault at the grid connection point and the microgrid still does not meet the low voltage ride-through requirements after adjustment, a control command is issued to make the microgrid operate off-grid.

[0051] Furthermore, the strategy determination module further includes:

[0052] The bus voltage normal control unit is used to prevent the composite superconducting energy storage device in the microgrid from operating when the bus voltage of the microgrid is in a normal operating state;

[0053] The first control unit for abnormal bus voltage is used to determine the action of the energy storage battery or the composite superconducting energy storage device according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device when the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the starting conditions;

[0054] The bus voltage abnormality second control unit is used to control the voltage regulator to operate when the microgrid bus voltage is disturbed and the composite superconducting energy storage device does not meet the starting conditions.

[0055] Furthermore, the bus voltage abnormality first control unit is further used for:

[0056] When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load;

[0057] When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode;

[0058] When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

[0059] The present application also provides a microgrid, comprising:

[0060] Superconducting current limiter, photovoltaic system, photovoltaic inverter, three-winding transformer, composite superconducting energy storage device, rectifier and microgrid bus;

[0061] Each load is connected to the microgrid bus through the superconducting current limiter;

[0062] The photovoltaic system is connected to the PCC line through the photovoltaic inverter, the three-winding transformer and the superconducting current limiter in sequence;

[0063] The composite superconducting energy storage device is connected to the microgrid bus through the rectifier.

[0064] Compared with the prior art, the beneficial effects of this application are:

[0065] The microgrid operation control method provided in the present application is based on the grid-connected operation of the microgrid with composite superconducting energy storage-current limiting. In combination with the peak-valley electricity price, the control strategy of the photovoltaic storage system is established to reduce the power consumption of the large power grid and the dependence of the power-consuming area on the power grid, make full use of solar photovoltaic resources, and utilize the peak-valley electricity price mechanism to achieve peak-valley arbitrage, reduce the operating cost of the photovoltaic storage microgrid, and reduce the voltage drop amplitude of the grid connection point by limiting the short-circuit current through the superconducting current limiter, thereby enhancing the low-voltage ride-through capability of the photovoltaic storage microgrid system. The composite superconducting energy storage-current limiting device is used to improve the power quality of the microgrid and improve the power supply stability. When the power supply is insufficient or a fault occurs, it can ensure that the regional microgrid is self-contained and operates independently, improve the reliability of power supply in various regions, realize the barrier-free coordinated operation of new energy and the large power grid, improve the intelligence level of the power supply system, enhance the disaster resistance, and provide technical guarantee for improving the service quality of the power-consuming area. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0067] Figure 1 is a schematic diagram of the system structure of a microgrid provided in a certain embodiment of the present application;

[0068] Figure 2 It is a schematic diagram of the principle of low voltage ride-through capability requirements for a photovoltaic grid-connected system provided in a certain embodiment of the present application;

[0069] Figure 3 It is a flowchart of a microgrid operation control method provided by a certain embodiment of the present application;

[0070] Figure 4 It is a flowchart of the steps of a microgrid operation control method provided by a certain embodiment of the present application;

[0071] Figure 5 It is a flowchart of the steps of a microgrid operation control method provided by another embodiment of the present application;

[0072] Figure 6 It is a structural schematic diagram of a microgrid operation control device provided in a certain embodiment of the present application;

[0073] Figure 7 yes Figure 6 Schematic diagram of submodules of strategy determination module 02. DETAILED DESCRIPTION

[0074] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0075] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0076] It should be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0077] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0078] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0079] It should be noted that after the concept of microgrid was proposed, it has received widespread attention and demonstration applications around the world, but the definition and research focus of microgrids are different. For example, my country believes that distributed photovoltaic storage microgrids are one of the effective ways to ensure the sustainable development of world energy. Therefore, the development of distributed energy must also be a top priority, and the development of distributed power sources is one of the directions of energy transformation. The development of distributed power sources based on photovoltaics should be based on the principle of "adapting measures to local conditions and scientific utilization", mainly to install power sources near the user side and consume them nearby, thereby improving power efficiency and reducing transmission losses and costs.

[0080] The integrated photovoltaic and energy storage system is generally composed of photovoltaic modules and energy storage modules, and is powered by the power grid. This system is used as the main power supply source, and the power grid is used as a backup power source. However, with the continuous improvement of the penetration of photovoltaic systems, the safe and stable operation of the power system requires that the microgrid system should have low voltage ride through (LVRT) capabilities, that is, during grid failures, the photovoltaic system should maintain uninterrupted grid-connected operation for a certain period of time. In addition, in the microgrid system, the presence of energy storage batteries can also complete auxiliary functions such as smoothing photovoltaic power generation fluctuations, peak load regulation and frequency regulation, and improve the reliability and stability of photovoltaic energy access. At the same time, in order to achieve harmonious power supply between the power grid and photovoltaic energy storage equipment and avoid energy waste, corresponding power supply control strategies must be formulated to achieve the following goals:

[0081] 1) When a grid fault or voltage disturbance causes a short-term drop in the grid connection point voltage, the microgrid system can remain connected to the grid and can even deliver a certain amount of reactive power to the grid to support the grid connection point voltage until the grid voltage returns to normal, thereby "traveling through" this period of low voltage and meeting the requirements of low voltage ride-through.

[0082] 2) When the photovoltaic power generation is greater than the power load, the photovoltaic power generation supplies power to the load, and the excess power is stored in the energy storage battery. Even when the energy storage battery is fully charged, the excess power can be transmitted to the power grid.

[0083] 3) When photovoltaic power generation is less than the power load, the load is powered by energy storage batteries and photovoltaics together.

[0084] 4) When the photovoltaic power generation is equal to the power load, the photovoltaic power generation supplies power to the load, and the energy storage battery does not charge or discharge, maintaining the energy unchanged.

[0085] 5) When photovoltaic power generation is less than the power load, if the energy storage battery is insufficient, switch to grid power supply.

[0086] However, when the photovoltaic power generation system is operating in an isolated grid mode due to planned or unplanned islanding, when a branch of the local load fails, the bus voltage is difficult to maintain stability due to the low anti-interference ability of the microgrid, resulting in voltage fluctuations, which have the following impacts on the electrical equipment: 1) Accelerate the aging of the insulation layer of the electrical equipment and shorten the service life of the electrical equipment; 2) Increase the loss of electrical equipment and reduce the efficiency of the power grid; 3) Electrical equipment cannot work normally, seriously affecting the quality of products and services; 4) It may lead to misoperation of electrical equipment and cause production accidents; 5) Severe overvoltage failures will endanger personal safety and the safety of electrical equipment. The main reason for the above problems is that the existing photovoltaic storage microgrid balances the DC bus voltage by adding supercapacitors on the DC side, ensuring the reactive current output of the photovoltaic inverter, so that the photovoltaic storage microgrid grid-connected system meets the requirements of low voltage ride-through. However, the power imbalance during a voltage sag will cause the output current of the photovoltaic inverter to increase, which may exceed the output current limit of the inverter itself, causing the inverter to trigger overcurrent protection and cause the photovoltaic storage microgrid system to be disconnected from the grid. At the same time, the existing photovoltaic storage microgrid system is too dependent on the power grid, and the random charging and discharging characteristics of the system energy storage device are too large, resulting in weak anti-interference ability of the microgrid when operating in an isolated network, and cannot meet users' needs for high-quality power supply.

[0087] Based on the above problems, a certain embodiment of the present application first provides a system structure of a microgrid, such as Figure 1 As shown. The microgrid includes:

[0088] Superconducting current limiter, photovoltaic system, photovoltaic inverter, three-winding transformer, composite superconducting energy storage device, rectifier and microgrid bus;

[0089] Each load is connected to the microgrid bus through the superconducting current limiter;

[0090] The photovoltaic system is connected to the PCC line through the photovoltaic inverter, the three-winding transformer and the superconducting current limiter in sequence;

[0091] The composite superconducting energy storage device is connected to the microgrid bus through the rectifier.

[0092] It is necessary to explain that according to GB / T 19964-2012 "Technical Regulations for Photovoltaic Power Station Access to Power System", there are requirements for low voltage ride-through of photovoltaic grid-connected systems. Figure 2As shown, when the grid-connected point voltage is above curve 1, the photovoltaic grid-connected system should be able to maintain grid-connected operation, and when the grid-connected point voltage is below curve 1, the photovoltaic grid-connected system is allowed to be disconnected from the grid. The grid-connected point voltage is allowed to drop to 0V within 0-150ms, and within 2000ms after the fault occurs, the grid-connected point voltage must be restored to more than 90% before the voltage drop. Ignoring the loss of the photovoltaic grid-connected inverter itself, the vector control principles based on grid voltage orientation are:

[0093]

[0094] Where U dc is the DC bus voltage, I dc is the photovoltaic cell output current, u sd is the d-axis component of the grid voltage, i d The inverter output current.

[0095] From the above formula (1), it can be seen that when the grid voltage remains unchanged and the loss of the grid-connected inverter itself is not considered, its DC side voltage U dc With the output current I dc Directly proportional. Since solar energy has the defects of intermittency, volatility and instability, in order to obtain high-quality, efficient, stable, safe and reliable electricity supply, it is necessary to configure an electric energy storage device with high sensitivity, fast response and strong compensation ability. Therefore, in this embodiment, a superconducting energy storage system (Superconducting Magnetic Energy Storage, SMES) with fast response speed and high power density will replace the traditional battery energy storage system (Battery Energy Storage, BES) with slow response speed. In this embodiment, it is specifically a composite superconducting energy storage device. In the early stage of a load voltage failure, a superconducting energy storage system is selected for compensation; but the capacity of superconducting magnetic energy storage is limited, so when the superconducting energy storage system cannot meet the energy requirements of the load system, the battery energy storage system is used for compensation.

[0096] like Figure 1 As shown in the figure, when the superconducting current limiter is not installed at the grid connection point of the photovoltaic grid-connected system, when a grid fault occurs and causes a voltage drop, u sd Reduce, under the condition of power balance i d will increase, and u sd The greater the fall, the d The inverter itself has a certain current limiting function, which is usually set to 1.1I N , when i d >1.1I N When the inverter output power will be reduced, the remaining power will be in the inverter DC side capacitor C dcThe voltage on the DC side of the inverter will accumulate, resulting in an increase in the bus voltage on the DC side of the inverter. When it rises to a certain value, the DC side overvoltage protection will be triggered, causing the photovoltaic grid-connected system to disconnect from the grid. At the same time, the power imbalance during the voltage sag will cause the output current of the photovoltaic inverter to increase, which may exceed the output current limit of the inverter itself, causing the inverter to disconnect from the grid due to triggering the overcurrent protection. The large-scale disconnection of the photovoltaic grid-connected system will inevitably cause a large loss of system power, which may aggravate the grid oscillation and increase the difficulty of system voltage recovery. At the same time, it will also cause the disconnection of adjacent photovoltaic grid-connected systems, causing large-scale power outages.

[0097] In this embodiment, when a superconducting current limiter is installed at the grid connection point of the photovoltaic grid-connected system, when a short circuit occurs in the grid, due to the grid voltage u sd Reduce, i d Increases to a value greater than the operating current I of the current limiter ds , it is suppressed because of the “high impedance” response of the current limiter, thus ensuring i d Keep at 1.1I N Within the range, the inverter output power remains stable and the photovoltaic power generation system meets the requirements of low voltage ride-through. If after 2000ms, the fault is not removed and the bus voltage at the grid connection point is lower than 0.9PU, the management center shall issue instructions to control the photovoltaic storage microgrid system to operate off the grid.

[0098] Furthermore, in order to help understanding, this embodiment also explains the working principle of the battery energy storage system. The battery energy storage system (BES) is an energy storage device that stores energy in the form of electrical energy and can realize the mutual conversion of chemical energy and electrical energy. According to the characteristics of the energy storage battery, the charging and discharging power and the remaining power of the battery have the following relationship:

[0099] When charging:

[0100] E(t)=E(t-1)+ΔT·P 充 (t)η 充 (2)

[0101] In discharge state:

[0102]

[0103] The battery state of charge is:

[0104]

[0105] To prevent overcharge and over discharge of energy storage batteries, the charge state must meet the following conditions:

[0106] SOC min≤ SOC≤SOC max (5)

[0107] Where, E(t) is the total energy of the energy storage battery at time t; P 充 (t), P 放 (t) are the charging and discharging power of the battery at time t, respectively. The charging power of the energy storage battery is specified to be positive, and the discharging power is specified to be negative. η 充 , η 放 are the charge and discharge efficiency of the energy storage battery; ΔT is the charge and discharge time period of the battery; SOCmin and SOCmax are the upper and lower limits of the SOC during the charge and discharge process of the battery; Q c Battery capacity, I bat is the charging current.

[0108] According to the peak-valley electricity price mechanism, energy storage batteries can be used as a power source to provide power in the photovoltaic storage microgrid system, and can also be used as a load to absorb power, playing the role of peak shaving and valley filling. Assuming that the exchange power between the grid and the photovoltaic storage microgrid system is P, if the load and the photovoltaic storage system use the power of the grid, then P>0, that is, the grid sells electricity to the photovoltaic storage microgrid system; if the photovoltaic storage microgrid system provides electricity to the grid, then P<0, that is, the photovoltaic storage microgrid sells electricity to the grid.

[0109] The power balance relationship between the photovoltaic storage microgrid system and the large power grid system is as follows:

[0110] When P>0,

[0111] P load (t) = P pv (t)+P bat (t)+P(t) (6)

[0112] When P < 0,

[0113] P load (t) = P pv (t)+P bat (t)-P(t) (7)

[0114] Where P load (t) is the load power at time t, P pv (t) is the photovoltaic output power, where when the energy storage battery is discharged, P bat >0 When the battery is charging, P bat <0; when P bat =0, the battery is neither charged nor discharged.

[0115] The charging and discharging of the energy storage battery is realized through the control of the energy storage converter according to the power command issued by the energy management center, and the battery is charged or discharged. Therefore, it is necessary to formulate a management strategy for the photovoltaic storage microgrid system in combination with the photovoltaic system output, load characteristics, battery charge state and peak-valley electricity price mechanism.

[0116] This embodiment connects a superconducting current limiter in the microgrid to limit the short-circuit current and reduce the voltage drop amplitude at the grid connection point, thereby enhancing the low voltage ride-through capability of the photovoltaic storage microgrid system.

[0117] Specifically, see Figure 3 , a certain embodiment of the present application provides a microgrid operation control method. Figure 3 As shown, the microgrid operation control method includes steps S10 to S30. The specific steps are as follows:

[0118] S10, determining the operating status of the microgrid grid connection point and the microgrid bus voltage value;

[0119] S20. Based on the peak-valley electricity price mechanism, formulate management strategies for the operating status of different microgrid connection points, and formulate corresponding control strategies according to different microgrid bus voltages;

[0120] S30. Control the operation of the microgrid using a management strategy or a control strategy.

[0121] In this embodiment, the operating status of the microgrid grid connection point and the microgrid bus voltage value are first determined, and then the corresponding management strategy and control strategy are formulated in combination with the peak-valley electricity price mechanism, and finally the microgrid operation is controlled.

[0122] See also Figure 4 ,Specifically, a management strategy is formulated for the operation status of different ,microgrid grid connection points, including the following steps:

[0123] 1) When the grid-connected point is in normal operation, calculate the output power and load power of the photovoltaic system in the microgrid;

[0124] 1.1) When the output power P pv Greater than the load power P load , and when there is surplus power supplied by the photovoltaic system, the energy storage battery is charged until the energy storage battery is fully charged, that is, the SOC max After that, the excess electricity is transmitted to the large power grid;

[0125] 1.2) When the output power P pv Less than load power P load , and when the electricity price is at the peak period, the object of load power supply is determined according to the charge state of the energy storage battery;

[0126] 1.3) When the output power Ppv Less than load power P load When the electricity price is at the valley period, the photovoltaic system supplies power to the load, the large power grid provides the load power shortage, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged;

[0127] 1.4) When the output power P pv Less than load power P load When the electricity price is not at the peak or valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the city power supply jointly supply power to the load.

[0128] Furthermore, step 1.2) specifically includes:

[0129] 1.2.1) If the state of charge (SOC) of the energy storage battery is higher than the maximum state of charge (SOC) max , the energy storage battery is used to supply power to the load;

[0130] 1.2.2) If the state of charge (SOC) of the energy storage battery is between the minimum state of charge and the maximum state of charge, it belongs to [SOC min , SOC max ] range, and the power available is less than the load shortfall power, the required power is purchased from the mains;

[0131] 1.2.3) If the state of charge of the energy storage battery is less than the minimum state of charge SOC min , the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

[0132] In a certain embodiment, based on the peak-valley electricity price mechanism, a management strategy is formulated for the operation status of different microgrid connection points, further comprising:

[0133] 2) When there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter, that is, I d >I ds When the superconducting current limiter is used to adjust, the microgrid meets the low voltage ride-through requirements and maintains grid-connected operation;

[0134] 3) When there is a fault at the grid connection point and the grid current is less than the operating current of the current limiter, that is, I d <I ds When the power is off, the photovoltaic inverter is adjusted to ensure that the microgrid meets the low voltage ride-through requirements and remains connected to the grid.

[0135] It should be noted that after the fault is removed, the microgrid system is still in the grid-connected operation state. At this time, the microgrid system should follow the management and control strategy of the normal operation state.

[0136] Furthermore, based on the peak-valley electricity price mechanism, management strategies are formulated for the operating status of different microgrid connection points, including:

[0137] 4) When there is a fault at the grid connection point and the microgrid still does not meet the low voltage ride-through requirements after adjustment, a control command is issued to make the microgrid operate off-grid. At this time, the microgrid system follows the isolated grid operation management and control strategy.

[0138] See also Figure 5 In one embodiment, the control strategy is formulated according to different microgrid bus voltages, including:

[0139] 5) When the microgrid bus voltage is in normal operation, the composite superconducting energy storage device in the microgrid does not operate;

[0140] 6) When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the start-up conditions, the action of the energy storage battery or the composite superconducting energy storage device is determined according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device;

[0141] 7) When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device does not meet the starting conditions, the voltage regulator is controlled to operate.

[0142] Further, step 6) specifically includes:

[0143] 6.1) When the current of the composite superconducting energy storage device is less than the maximum current limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the voltage of the composite superconducting energy storage device, control the composite superconducting energy storage device to charge;

[0144] 6.2) When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load;

[0145] 6.3) When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode;

[0146] 6.4) When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

[0147] It should be noted that, in this embodiment, when the microgrid bus voltage U is in a normal operating state, that is, U min <U<U max, the composite superconducting energy storage system does not work. When the photovoltaic storage microgrid is isolated, due to the weak anti-interference ability of the microgrid, the switching of large loads will cause fluctuations in the microgrid bus voltage. If U>U max The control system must first determine whether the current of the superconducting energy storage coil meets this condition (I SMES max ) and the bus voltage U is greater than the charging voltage U of the superconducting energy storage system SMES , the system will instantly start the charging mode of the superconducting energy storage system, and the bus voltage U will be maintained within the normal range to ensure the voltage stability of the remaining loads; when the superconducting energy storage system voltage U SMES Greater than the limit U max , and the bus voltage U is greater than the battery charging start voltage U BES When U<U max The control system must first determine whether the current of the superconducting magnetic energy storage coil meets this condition (I SMES >I min ), the system will instantly start the discharge mode of the superconducting energy storage system, and the bus voltage U will be maintained within the normal range to ensure the voltage stability of the remaining loads; when the superconducting energy storage system voltage U SMES Less than the limit value U min , and the battery discharge voltage U BES Greater than the discharge voltage U min When the bus voltage is disturbed, the battery will compensate for the bus voltage shortfall. If the microgrid bus voltage is disturbed and the composite superconducting energy storage system does not meet the startup conditions, other measures will be used to solve the problem (voltage regulator, etc.).

[0148] As a device used in series in the line, an important operating parameter of the superconducting current limiter is the equipment impedance when the line is transmitting normally, sometimes called steady-state impedance. The smaller its value, the smaller the negative impact of the current limiter on the transmission line (such as equipment voltage drop and transmission loss). When the circuit is transmitting normally, the current limiter is in a superconducting state, the impedance is zero, there is no transmission loss, and it does not affect the transmission efficiency.

[0149] like Figure 1 As shown in the figure, there are n branches in parallel operation at the busbar of the composite superconducting energy storage-current limiting microgrid. When a short circuit occurs in the branch without a current limiter (assuming it is local load 1), the load current i f Will increase sharply, the load voltage V f If the current of the power supply bus is i f Increases to a value greater than the operating current I of the current limiter ds ​When the current limiter is in high impedance response, it is suppressed, and the load current and voltage of the non-fault parallel branch remain basically unchanged. At the same time, the response of the superconducting energy storage device further maintains the stability of the bus voltage, ensuring the stable operation of the non-fault branch. It is worth noting that after a short-circuit fault occurs in local load 1, the increase in the short-circuit fault current triggers the superconducting current limiting action, so that the superconducting current limiter presents high impedance to limit the short-circuit current, and the relay protection device in the protection system will not be damaged by the short-circuit current. At the same time, the voltage of the superconducting current limiter when it loses time (the steady-state operating voltage is 0V) can be used to coordinate with the relay protection, so as to ensure that the protection is not rejected or malfunctioned when it is triggered, and the fault line can be cut off in time and correctly.

[0150] The microgrid operation control method provided in this embodiment determines the configuration capacity of the photovoltaic system and the energy storage system according to the load characteristics of the photovoltaic and energy storage microgrid system and the peak-valley electricity price information, and proposes a photovoltaic and energy storage power coordination control strategy based on the peak-valley electricity price difference, in order to obtain the maximum economic benefit, reduce the operation cost of the photovoltaic and energy storage microgrid, improve the power quality of the microgrid, and enhance the power supply stability. When the power supply is insufficient or a fault occurs, it can ensure that the regional microgrid is self-contained and operates independently, thereby improving the reliability of power supply in various regions, realizing the barrier-free coordinated operation of new energy and large power grids, improving the intelligence level of the power supply system, and enhancing the disaster resistance. It provides technical guarantee for improving the service quality in power-consuming areas.

[0151] See also Figure 6 In one embodiment of the present application, a microgrid operation control device is also provided, comprising:

[0152] Parameter acquisition module 01, used to determine the operating status of the microgrid grid connection point and the microgrid bus voltage value;

[0153] Strategy determination module 02, used to formulate management strategies for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and formulate corresponding control strategies according to different microgrid bus voltages;

[0154] The control module 03 is used to control the operation of the microgrid using a management strategy or a control strategy.

[0155] See also Figure 7 In one embodiment, the strategy determination module 02 includes:

[0156] The grid-connected point normal operation control unit 021 is used to calculate the output power and load power of the photovoltaic system in the microgrid when the grid-connected point is in a normal operation state;

[0157] When the output power is greater than the load power and the photovoltaic system has surplus power supply, the energy storage battery is charged until the energy storage battery is full, and the excess power is transmitted to the large power grid;

[0158] When the output power is less than the load power and the electricity price is at the peak period, the object to supply power to the load is determined according to the charge state of the energy storage battery;

[0159] When the output power is less than the load power and the electricity price is at the valley period, the PV system supplies power to the load, the large power grid provides the load power shortfall, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged;

[0160] When the output power is less than the load power and the electricity price is in non-peak or non-valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the mains power jointly supply power to the load.

[0161] In one embodiment, the normal operation control unit 021 of the grid connection point is further used for:

[0162] If the state of charge of the energy storage battery is higher than the maximum state of charge, the energy storage battery is used to supply power to the load;

[0163] If the state of charge of the energy storage battery is between the minimum state of charge and the maximum state of charge, and the power it can provide is less than the load shortfall power, the required power is purchased from the mains;

[0164] If the state of charge of the energy storage battery is less than the minimum state of charge, the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

[0165] In one embodiment, the strategy determination module 02 further includes a first grid connection point failure control unit 022 and a second grid connection point failure control unit 023. Figure 7 As shown, specifically:

[0166] The first control unit 022 for a grid connection point fault is used to adjust the microgrid to meet the low voltage ride-through requirement and maintain grid connection operation through the superconducting current limiter when there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter;

[0167] The second control unit 023 for grid connection point fault is used to adjust the photovoltaic inverter so that the microgrid meets the low voltage ride-through requirement and maintains grid connection operation when the grid connection point fails and the grid current is less than the action current of the current limiter.

[0168] In one embodiment, the strategy determination module 02 further includes a third control unit 024 for a grid connection point failure, such as Figure 7 As shown, specifically:

[0169] The third control unit 024 for grid connection point failure is used to issue a control instruction to make the microgrid run off-grid when there is a fault in the grid connection point and the microgrid still does not meet the low voltage ride-through requirement after adjustment.

[0170] In one embodiment, the strategy determination module 02 further includes a bus voltage normal control unit 025, a bus voltage abnormal first control unit 026 and a bus voltage abnormal second control unit 027. Figure 7 As shown, specifically:

[0171] The bus voltage normal control unit 025 is used to prevent the composite superconducting energy storage device in the microgrid from operating when the bus voltage of the microgrid is in a normal operating state;

[0172] The bus voltage abnormality first control unit 026 is used to determine the action of the energy storage battery or the composite superconducting energy storage device according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device when the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the start-up conditions;

[0173] The bus voltage abnormality second control unit 027 is used to control the voltage regulator to operate when the microgrid bus voltage is disturbed and the composite superconducting energy storage device does not meet the startup conditions.

[0174] In one embodiment, the bus voltage abnormality first control unit 026 is further configured to:

[0175] When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load;

[0176] When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode;

[0177] When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

[0178] It can be understood that the device provided in this embodiment is used to execute the microgrid operation control method as described in the above embodiment, and achieve the same technical effect as achieved by the above method, which will not be further described here.

[0179] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods when implementing them in actual applications. For example, multiple units or page components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0180] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0181] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0182] The above-mentioned integrated unit implemented in the form of a software functional unit can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to perform some steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A microgrid operation control method, characterized in that: include: Determine the operating status of the microgrid connection point and the microgrid bus voltage value; Based on the peak-valley electricity price mechanism, formulate management strategies for the operating status of different microgrid connection points, and formulate corresponding control strategies according to different microgrid bus voltages; Controlling microgrid operation using management strategies or control strategies; The corresponding control strategy is formulated according to different microgrid bus voltages, including: When the microgrid bus voltage is in normal operation, the composite superconducting energy storage device in the microgrid does not operate; When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the start-up conditions, the action of the energy storage battery or the composite superconducting energy storage device is determined according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device; When the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device does not meet the start-up conditions, the voltage regulator is controlled to operate.

2. The microgrid operation control method according to claim 1, characterized in that: Based on the peak-valley electricity price mechanism, management strategies are formulated for the operation status of different microgrid connection points, including: When the grid-connected point is in normal operation, the output power and load power of the photovoltaic system in the microgrid are calculated; When the output power is greater than the load power and the photovoltaic system has surplus power supply, the energy storage battery is charged until the energy storage battery is full, and the excess power is transmitted to the large power grid; When the output power is less than the load power and the electricity price is at the peak period, the object to supply power to the load is determined according to the charge state of the energy storage battery; When the output power is less than the load power and the electricity price is at the valley period, the PV system supplies power to the load, the large power grid provides the load power shortfall, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged; When the output power is less than the load power and the electricity price is in non-peak or non-valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the mains power jointly supply power to the load.

3. The microgrid operation control method according to claim 2, characterized in that: When the output power is less than the load power and the electricity price is at the peak period, the object to be supplied with power to the load is determined according to the state of charge of the energy storage battery, including: If the state of charge of the energy storage battery is higher than the maximum state of charge, the energy storage battery is used to supply power to the load; If the state of charge of the energy storage battery is between the minimum state of charge and the maximum state of charge, and the power it can provide is less than the load shortfall power, the required power is purchased from the mains; If the state of charge of the energy storage battery is less than the minimum state of charge, the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

4. The microgrid operation control method according to claim 2, characterized in that: The management strategy is formulated for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and further includes: When there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter, the superconducting current limiter is used to adjust the microgrid to meet the low voltage ride-through requirements and maintain grid connection operation; When there is a fault at the grid connection point and the grid current is less than the operating current of the current limiter, the photovoltaic inverter is adjusted to ensure that the microgrid meets the low voltage ride-through requirements and remains connected to the grid.

5. The microgrid operation control method according to claim 2, characterized in that: The management strategy is formulated for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and further includes: When there is a fault at the grid connection point and the microgrid still does not meet the low voltage ride-through requirements after adjustment, a control command is issued to make the microgrid operate off-grid.

6. The microgrid operation control method according to claim 1, characterized in that: When the microgrid bus voltage is disturbed and the composite superconducting energy storage device meets the start-up conditions, the action of the energy storage battery or the composite superconducting energy storage device is determined according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device, including: When the current of the composite superconducting energy storage device is less than the maximum current limit of the composite superconducting energy storage device, and the bus voltage of the microgrid is greater than the voltage of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to be charged; When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load; When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode; When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

7. A microgrid operation control device, characterized in that: include: The parameter acquisition module is used to determine the operating status of the microgrid grid connection point and the microgrid bus voltage value; The strategy determination module is used to formulate management strategies for the operation status of different microgrid connection points based on the peak-valley electricity price mechanism, and to formulate corresponding control strategies according to different microgrid bus voltages; A control module, used for controlling the operation of the microgrid using a management strategy or a control strategy; The strategy determination module further includes: The bus voltage normal control unit is used to prevent the composite superconducting energy storage device in the microgrid from operating when the bus voltage of the microgrid is in a normal operating state; The first control unit for abnormal bus voltage is used to determine the action of the energy storage battery or the composite superconducting energy storage device according to the voltage and current of the energy storage battery and the voltage and current of the composite superconducting energy storage device when the bus voltage of the microgrid is disturbed and the composite superconducting energy storage device meets the starting conditions; The bus voltage abnormality second control unit is used to control the voltage regulator to operate when the microgrid bus voltage is disturbed and the composite superconducting energy storage device does not meet the starting conditions.

8. The microgrid operation control device according to claim 7, characterized in that: The strategy determination module includes a normal operation control unit of the grid connection point, which is used to: When the grid-connected point is in normal operation, the output power and load power of the photovoltaic system in the microgrid are calculated; When the output power is greater than the load power and the photovoltaic system has surplus power supply, the energy storage battery is charged until the energy storage battery is full, and the excess power is transmitted to the large power grid; When the output power is less than the load power and the electricity price is at the peak period, the object to supply power to the load is determined according to the charge state of the energy storage battery; When the output power is less than the load power and the electricity price is at the valley period, the PV system supplies power to the load, the large power grid provides the load power shortfall, and the large power grid is used to charge the energy storage battery until the energy storage battery is fully charged; When the output power is less than the load power and the electricity price is in non-peak or non-valley period, the energy storage battery does not charge or discharge, and the photovoltaic system and the mains power jointly supply power to the load.

9. The microgrid operation control device according to claim 8, characterized in that: The normal operation control unit of the grid connection point is also used for: If the state of charge of the energy storage battery is higher than the maximum state of charge, the energy storage battery is used to supply power to the load; If the state of charge of the energy storage battery is between the minimum state of charge and the maximum state of charge, and the power it can provide is less than the load shortfall power, the required power is purchased from the mains; If the state of charge of the energy storage battery is less than the minimum state of charge, the energy storage battery stops discharging, and the photovoltaic system and the large power grid jointly supply power to the load.

10. The microgrid operation control device according to claim 8, characterized in that: The strategy determination module further includes: The first control unit for grid connection point fault is used to adjust the microgrid to meet the low voltage ride-through requirement and maintain grid connection operation through the superconducting current limiter when there is a fault at the grid connection point and the grid current is greater than the operating current of the current limiter; The second control unit for grid connection point fault is used to adjust the photovoltaic inverter so that the microgrid meets the low voltage ride-through requirement and maintains grid-connected operation when the grid connection point fails and the grid current is less than the operating current of the current limiter.

11. The microgrid operation control device according to claim 8, characterized in that: The strategy determination module further includes a third control unit for a grid connection point failure, which is used to: When there is a fault at the grid connection point and the microgrid still does not meet the low voltage ride-through requirements after adjustment, a control command is issued to make the microgrid operate off-grid.

12. The microgrid operation control device according to claim 7, characterized in that: The bus voltage abnormality first control unit is further used for: When the voltage of the composite superconducting energy storage device is greater than the maximum voltage limit of the composite superconducting energy storage device, and the microgrid bus voltage is greater than the charging start voltage of the energy storage battery, the composite superconducting energy storage device is controlled to absorb excess electric energy of the load; When the microgrid bus voltage is less than the maximum voltage limit of the composite superconducting energy storage device, and the current of the composite superconducting energy storage device is greater than the minimum current limit of the composite superconducting energy storage device, the composite superconducting energy storage device is controlled to enter the discharge mode; When the voltage of the composite superconducting energy storage device is less than the minimum voltage limit of the composite superconducting energy storage device, and the charging start voltage of the energy storage battery is greater than the minimum voltage limit of the composite superconducting energy storage device, the energy storage battery is compensated.

13. A microgrid, characterized in that: The microgrid is used to implement the microgrid operation control method according to any one of claims 1 to 6, and the microgrid includes: Superconducting current limiter, photovoltaic system, photovoltaic inverter, three-winding transformer, composite superconducting energy storage device, rectifier and microgrid bus; Each load is connected to the microgrid bus through the superconducting current limiter; The photovoltaic system is connected to the PCC line through the photovoltaic inverter, the three-winding transformer and the superconducting current limiter in sequence; The composite superconducting energy storage device is connected to the microgrid bus through the rectifier.

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