Micro-grid group interconnection method based on energy storage support virtual synchronization port

Abstract

The invention relates to the technical field of micro-grid group control, and discloses a micro-grid group interconnection method based on an energy storage support virtual synchronization port, which comprises the following steps: a main micro-grid is accessed to a direct current side through a first multi-port flexible switch, and each slave micro-grid is accessed to the direct current side through a corresponding second multi-port flexible switch; the main micro-grid and the second multi-port flexible switch adopt a virtual synchronous generator control strategy to stabilize the voltage and frequency of the micro-grid group; the slave micro-grid adopts a constant power control strategy to control the power output of the slave micro-grid; the first multi-port flexible switch adopts a direct-current voltage control strategy to stabilize the direct-current side voltage; an energy storage unit is arranged on the DC side of a virtual synchronous port of the micro-grid group, and the stability of the DC side voltage is maintained and the vacant power of the micro-grid is supplemented through a charging and discharging control strategy, so that the micro-grid group achieves dynamic power balance. According to the invention, through the stability of the virtual synchronization port, the power stability of each subnet is ensured; and finally, ensuring mutual power complementation of the micro-grid group through power stability of each sub-grid.

Description

Technical Field

[0001] The present invention relates to the field of microgrid group control technology, and in particular to a microgrid group interconnection method based on energy storage supporting virtual synchronization ports. Background Art

[0002] Due to the randomness of the output of distributed power sources, the adverse effects they bring to the distribution network after being incorporated into the distribution network are becoming more and more significant. To solve this problem, some scholars have proposed the concept of microgrids. Microgrids integrate distributed power sources, loads, and energy storage devices into one. Through the control and energy management of microgrids, the negative effects of distributed power sources due to the randomness of output are reduced, and the utilization rate and power supply reliability of renewable energy are effectively improved. However, the capacity and anti-interference ability of a single microgrid are limited. Therefore, it is proposed to interconnect multiple microgrids that are geographically adjacent to form a microgrid group. Compared with a single microgrid, a microgrid group has a larger capacity. Through the energy control and power mutual assistance of the subgrids within the group, the power supply reliability of the microgrid group is improved, thereby increasing the penetration rate of distributed power sources. However, in traditional microgrid groups, the subgrids in the microgrid group are interconnected through busbars or circuit breakers, and the subgrids have a large mutual influence, which will cause power quality problems to be transmitted within the group, which is not conducive to the stability of the microgrid group and the high anti-interference ability. As a new interconnection solution, multi-terminal soft opening has become a new choice for solving the interconnection of multiple microgrids due to its advantages such as good disturbance isolation, strong regulation ability and fast fault recovery. However, for microgrids operating in isolated islands, the stability of their voltage and frequency is one of the prerequisites for the safe and stable operation of the microgrid. Therefore, the microgrid subnets using constant power control must have voltage and frequency support. However, due to the complexity of its structure, its control difficulty is becoming more and more complicated, so it is very important for the microgrid group to effectively control it. Summary of the invention

[0003] The purpose of the present invention is to provide voltage and frequency support for a microgrid and to provide a microgrid interconnection method based on a virtual synchronization port supported by energy storage.

[0004] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention provides the following technical solutions:

[0005] The microgrid interconnection method based on energy storage supporting virtual synchronization port includes the following steps:

[0006] Step 1: Select a shared energy storage power station or a microgrid subgrid with sufficient remaining energy from the microgrid group as the master microgrid, and the remaining microgrid subgrids as slave microgrids; the master microgrid is connected to the DC side through the first multi-port flexible switch, and each slave microgrid is connected to the DC side through its corresponding second multi-port flexible switch;

[0007] Step 2: The master microgrid and the second multi-port flexible switch adopt a virtual synchronous generator control strategy to stabilize the voltage and frequency of the microgrid group; the slave microgrid adopts a constant power control strategy to control the power output of the slave microgrid; the first multi-port flexible switch adopts a DC voltage control strategy to stabilize the DC side voltage;

[0008] Step 3: Set up an energy storage unit as shared energy storage on the DC side of the virtual synchronization port of the microgrid group, maintain the stability of the DC side voltage and supplement the power shortage from the microgrid through the charge and discharge control strategy, so that the microgrid group can achieve dynamic power balance.

[0009] In the above scheme, the virtual synchronization port includes at least two multi-port flexible switches, which are arranged on the DC side. The virtual synchronization port is an interconnection interface with virtual synchronization characteristics, which is used to connect the microgrid subnet. The use of the virtual synchronization port is to provide voltage and frequency support for the microgrid subnet connected to it by adopting voltage and frequency control in the multi-port flexible switch. In the microgrid group with a virtual synchronization port, a flexible interconnection method through a multi-port flexible switch is adopted. The multi-port flexible switch is connected to each other back to back through the DC side through multiple bidirectional voltage-type converters. This flexible interconnection method has the advantages of good disturbance isolation and strong anti-interference ability. The microgrid subgrids within the microgrid group are divided into a master microgrid and a slave microgrid. The master microgrid adopts a virtual synchronous generator control strategy to provide itself with voltage and frequency support. However, for the slave microgrid, due to the existence of a multi-port soft switch, the slave microgrid requires additional voltage and frequency support. The slave microgrid generally adopts a constant power control strategy and lacks support for voltage and frequency. Therefore, a virtual synchronous generator control strategy is adopted in the multi-port flexible switch, which provides the slave microgrid with an upper port with virtual synchronization characteristics, namely, a virtual synchronization port, to ensure the voltage and frequency stability of the microgrid group.

[0010] Furthermore, the first multi-port flexible switch and the second multi-port flexible switch are both bidirectional voltage-type converters, which can prevent the power fluctuation and power quality of the microgrid group from being transmitted to each other between the microgrid subgrids within the microgrid group, and smooth the impact of power fluctuations on the microgrid group.

[0011] In the above scheme, multiple microgrid subnets are connected through virtual synchronization ports to improve the group control and group adjustment of multiple voltage-source converters, thereby providing stable voltage and frequency support for the entire microgrid group.

[0012] Furthermore, in step 3, if there is a power deviation in the slave microgrid, power mutual assistance from the master microgrid to the slave microgrid is required, then the output power of the master microgrid and the slave microgrid satisfies:

[0013]

[0014] Among them, the total power transmitted from the master microgrid to all slave microgrids is Pm , the power required by each microgrid load is P L2 ,P L3 ,...,P Ln , each power output from the microgrid is P s2 ,P s3 ,...,P sn ; The mutual power flowing through each multi-port soft switch of the slave microgrid is P v2 ,...,P vn A positive power value indicates that the slave microgrid mutual aid power is in short supply, and other microgrid subgrids provide power to the slave microgrid; a negative power value indicates that the slave microgrid has excess power, and the slave microgrid outputs power to other microgrid subgrids; n is the number of microgrid subgrids.

[0015] In the above scheme, when the slave microgrid is short of power, the master microgrid can be regulated to transmit power to the slave microgrid, thereby realizing power mutual assistance from the master microgrid to the slave microgrid.

[0016] Furthermore, in step 3, after the microgrid reaches dynamic power balance, the DC side voltage remains at the initial value, that is, is zero:

[0017]

[0018] in, is the DC side voltage deviation; is the DC side voltage; is the DC reference voltage.

[0019] Furthermore, in step 3, when the DC side voltage is greater than the initial value, that is, , the energy storage unit is charged, absorbing excess power, and restoring the increased voltage to the initial value; when the DC side voltage is less than the initial value, that is, , the energy storage unit discharges, allowing the dropped voltage to return to its initial value.

[0020] Furthermore, in step 3, the difference between the output power of the main microgrid and the total power deficit of the slave microgrid at time t of the microgrid group is It is expressed as:

[0021]

[0022] in, is the active power output of the main microgrid at time t; is the active power given by the i-th slave microgrid at time t; is the load power of the Lth slave microgrid at time t; n` is the number of slave microgrids;

[0023] The size of determines the charging and discharging state of the energy storage unit. When the power output of the main microgrid is greater than the power shortage of the slave microgrid, the excess power is absorbed by the DC side energy storage unit to maintain the charge state of the energy storage unit at a reasonable level; when When the power output of the main microgrid is less than the shortfall of the slave microgrid, the energy storage unit temporarily discharges to provide the shortfall power; When it approaches zero, the charge state value of the energy storage unit remains stable. At this time, the output power of the main microgrid approaches the power deficit of the slave microgrid, and the energy storage unit no longer absorbs and provides power.

[0024] In the above scheme, for the microgrid group with flexible DC interconnection, if the supply and demand in the microgrid group is unbalanced, the DC side voltage will drop or rise. Ensuring the stability of the DC side voltage is to ensure the power balance of the entire microgrid group. For the energy storage unit, the drop of the DC side voltage can be compensated by discharging, and the excess power on the DC side can be absorbed by charging to reduce the rise of the DC side voltage. However, if the energy storage unit is not charged and discharged, it will cause overcharging and over-discharging of the energy storage unit, which will not only affect the service life of the energy storage unit, but also aggravate the drop or rise of the DC side voltage, thereby affecting the power balance of the microgrid group. As a large-capacity unit, the energy storage unit can realize the bidirectional flow of power. Therefore, the energy storage unit is incorporated at both ends of the DC side capacitor of the virtual synchronous port of the microgrid group, and the energy of the energy storage unit is used to make up for the problem of insufficient capacitor capacity, so as to realize the smooth mutual dispatch of the power of the microgrid subnet, and maintain the stability of the DC side voltage of the interconnected converter to avoid excessive drop from the microgrid voltage distortion and power fluctuation.

[0025] Compared with the prior art, the present invention has the following beneficial effects: first, an energy storage unit is incorporated into the DC side of the virtual synchronization port, and the energy storage unit on the DC side supplements the problem of insufficient energy of the DC side capacitor, so that the energy storage unit can temporarily provide power when the microgrid power is insufficient; second, the DC side capacitor supports the stability of the DC side voltage, so that the power on the DC side is balanced; third, the stability of the virtual synchronization port is maintained by the stability of the DC side voltage; fourth, the power stability of each subnet is guaranteed by the stability of the virtual synchronization port; finally, the power mutual assistance of the microgrid group is guaranteed by the power stability of each subnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A schematic diagram of adding a multi-port flexible switch to a microgrid group of the present invention;

[0028] Figure 2 A schematic diagram of the control strategy of a master microgrid, a slave microgrid, a first multi-port flexible switch, and a second multi-port flexible switch in a microgrid group of the present invention;

[0029] Figure 3 A schematic diagram of a charge and discharge control strategy for an energy storage unit according to an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of adding an energy storage unit to the DC side of a microgrid group according to the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0032] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance, or implying any such actual relationship or order between these entities or operations. In addition, the terms "connected", "connected", etc. can be directly connected between elements, or indirectly connected via other elements.

[0033] Embodiment 1:

[0034] The present invention is achieved through the following technical solutions: Figure 1 As shown, the microgrid interconnection method based on energy storage supporting virtual synchronization port includes the following steps:

[0035] Step 1: Select a shared energy storage power station or a microgrid subgrid with sufficient remaining energy from the microgrid group as the master microgrid, and the remaining microgrid subgrids as slave microgrids; the master microgrid is connected to the DC side through the first multi-port flexible switch, and each slave microgrid is connected to the DC side through its corresponding second multi-port flexible switch.

[0036] The virtual synchronization port is an interconnection interface with virtual synchronization characteristics, which is used to connect microgrid subnets and provide stable voltage and frequency support for microgrid subnets. In the microgrid group with virtual synchronization ports, a flexible interconnection method through multi-port flexible switches is adopted. Each multi-port soft switch is connected to each other back-to-back through the DC side by a bidirectional voltage-type converter. The DC side contains a DC side capacitor C1, which is responsible for stabilizing the DC side voltage. The multi-port flexible switch can realize the bidirectional flow of power between microgrid subnets.

[0037] The microgrid group as a whole adopts master-slave control, and the microgrid subgrids in the microgrid group are divided into one master microgrid and multiple slave microgrids. The master microgrid is undertaken by a shared energy storage power station or a microgrid subgrid with sufficient remaining energy, and serves as a peak-shaving unit in the microgrid group to play a role in peak shaving and valley filling; the remaining microgrid subgrids serve as slave microgrids. By connecting the master microgrid and the slave microgrid to the DC side through a multi-port flexible switch, power mutual assistance between the master microgrid and the slave microgrid can be achieved, and the power fluctuations and power quality problems of the microgrid group can be limited to the local area, avoiding mutual transmission between the microgrid subgrids in the microgrid group, and can smooth the impact of microgrid fluctuations on the system and improve the operation stability of the microgrid group. Figure 1 As shown, the DC side is provided with capacitor C1, the bidirectional voltage source converter in the virtual synchronous port is a multi-port flexible switch, the main microgrid is connected to the DC side by connecting to the first multi-port soft switch, and each slave microgrid is connected to the DC side by a correspondingly connected second multi-port flexible switch.

[0038] In step 2, the main microgrid and the second multi-port flexible switch adopt a virtual synchronous generator control strategy to stabilize the voltage and frequency of the microgrid group; the slave microgrid adopts a constant power control strategy to control the power output of the slave microgrid; the first multi-port flexible switch adopts a DC voltage control strategy to stabilize the DC side voltage.

[0039] Since the microgrid group operates in an isolated island without the voltage and frequency support of the large power grid, the stability of voltage and frequency is crucial for the stable operation of the entire microgrid group. On this basis, a virtual synchronous port control strategy is adopted for the microgrid group. In this strategy, the main microgrid adopts a virtual synchronous generator control strategy to stabilize the voltage and frequency of the main microgrid, and because the virtual synchronous generator control strategy simulates the inertia and damping characteristics of the synchronous generator, it has a strong anti-interference ability. Due to the existence of multi-port flexible switches, the slave microgrid requires additional voltage and frequency support. Therefore, the bidirectional voltage-type converter of the multi-port flexible switch on the slave microgrid side adopts a virtual synchronous generator control strategy to provide the slave microgrid with an interface with synchronous generator characteristics, namely, a virtual synchronous port, to maintain the voltage and frequency stability of the slave microgrid. The above-mentioned virtual synchronous generator control strategy provides stable voltage and frequency support for the entire microgrid group. The bidirectional voltage-type transformer on the main microgrid side adopts a fixed DC voltage control strategy to stabilize the DC side voltage, and the slave microgrid adopts a constant power control strategy to control the power output of the slave microgrid, thereby controlling the power output of the virtual synchronous port. By adopting the virtual synchronous control strategy in the multi-port flexible switch, the group control and group adjustment of multiple bidirectional voltage source converters are improved, and the upper port with virtual synchronization characteristics is provided for the microgrid to ensure the rapid power mutual assistance of the microgrid group. The control strategy is as follows Figure 2 shown.

[0040] Step 3: Set up an energy storage unit as shared energy storage on the DC side of the virtual synchronization port of the microgrid group, maintain the stability of the DC side voltage and supplement the power shortage from the microgrid through the charge and discharge control strategy, so that the microgrid group can achieve dynamic power balance.

[0041] If there are n microgrid subgrids in the microgrid group, the first microgrid subgrid is the master microgrid 1, and the remaining microgrid subgrids are slave microgrids 2 to n. Now assume that there is a power deviation in the slave microgrids in the microgrid group, and it is necessary to achieve power mutual assistance from the master microgrid to the slave microgrid, and the total power transmitted from the master microgrid to all the slave microgrids is P m , the power required by each microgrid load is P L2 ,P L3 ,...,P Ln , each power output from the microgrid is P s2 ,P s3 ,...,P sn Therefore, the mutual power flowing through each multi-port soft switch of the slave microgrid is P v2 ,...,P vn , where a positive power value indicates that the slave microgrid mutual aid power is in short supply, and other microgrid subgrids provide power to the slave microgrid; a negative power value indicates that the slave microgrid has excess power, and the slave microgrid outputs power to other microgrid subgrids, satisfying the following relationship:

[0042]

[0043] In addition, if there are both slave microgrids with power shortage and slave microgrids with excess power, the slave microgrid with excess power can provide excess power to the slave microgrid with power shortage, thereby achieving power mutual assistance between the slave microgrids.

[0044] When the microgrid group is initially running, there is a power shortage in the slave microgrid, so the master microgrid will transfer the shortage power to the slave microgrid. However, the master microgrid reacts slowly and cannot quickly provide the shortage power, resulting in a voltage drop on the DC side. However, since the DC side voltage drop is small and the DC side voltage can be restored to the initial value when the master microgrid reaches the reaction time, it will not affect the stable operation of the microgrid group.

[0045] However, in the above-mentioned flexible interconnected microgrid group with high-power load to transmit power from the main microgrid to the slave microgrid, if the DC side voltage drops excessively, it is difficult to recover to the initial value. After analysis, it is because of the insufficient energy of the virtual synchronous port DC side capacitor C1. Due to the insufficient energy of the virtual synchronous port DC side capacitor C1, when the slave microgrid power is insufficient and the main microgrid fails to provide the insufficient power in time, the DC side capacitor C1 also fails to quickly provide the insufficient power. Therefore, it leads to the problem of excessive drop of the virtual synchronous port DC side voltage and transient power imbalance of the microgrid group.

[0046] Based on the above problems, this solution proposes that the energy storage unit be incorporated into the virtual synchronous port DC side as a shared energy storage method. The capacity of the energy storage unit is used to make up for the problem of insufficient capacity of the DC side capacitor C1. Compared with the uncontrollable charging and discharging and limited capacity of capacitor C1, the energy storage unit has advantages that the capacitor does not have, such as large energy and controllable charging and discharging. As a large energy unit, the energy storage unit can maintain the power balance on the direct bus through the charging and discharging control strategy, maintain the stability of the DC side voltage, and avoid voltage distortion and power fluctuations caused by excessive transient voltage drop on the DC side. When the DC bus voltage is stable, the main microgrid in the microgrid group can provide power to the slave microgrid with power shortage through the virtual synchronous port; the slave microgrid in the power process can also provide power to the slave microgrid with power shortage through the virtual synchronous port. In short, all microgrid subgrids in the microgrid group need to use the virtual synchronous port to perform multi-port DC transmission in the form of AC-DC-AC for power scheduling.

[0047] Furthermore, integrating the charging and discharging control strategy of the energy storage unit into the microgrid system can prevent the overcharging and discharging of the energy storage unit from affecting the life of the energy storage unit, while also avoiding affecting the power balance of the microgrid.

[0048] After the energy storage unit is incorporated into the virtual synchronous port, if there is a power shortage in the microgrid, the energy storage unit may be in a discharging state all the time, which is not conducive to the stability of the virtual synchronous port supported by the energy storage unit, and may even cause the DC side voltage to rise, affecting the power balance of the microgrid group. In order to ensure the stable power mutual assistance of the microgrid group, the charging and discharging of the energy storage unit must be controlled to keep the charge state value of the energy storage unit at a reasonable level, that is, the DC side voltage of the virtual synchronous port can be kept stable through charging and discharging, which can extend the life of the energy storage and ensure the power balance of the microgrid group.

[0049] After the energy storage unit is incorporated into the DC side of the virtual synchronous port, a voltage-current dual-loop control strategy is adopted for the energy storage unit, in which the voltage outer loop stabilizes its output voltage, and the current inner loop improves the dynamic response speed of the system. The voltage-current dual-loop control strategy can achieve the purpose of controlling the DC bus voltage and the bidirectional flow of energy. In addition, by setting the reference voltage as the initial value of the DC side voltage, the DC side voltage is controlled by the energy storage. When the entire microgrid group reaches dynamic power balance, the DC side voltage basically remains at the initial value, that is, is zero.

[0050]

[0051] in, is the DC side voltage deviation; is the DC side voltage; is the DC reference voltage.

[0052] From the perspective of DC side voltage, when the DC side voltage is greater than the initial value during the process of the energy storage unit controlling the DC side voltage, that is, , the energy storage unit is charged, absorbing the excess power, and restoring the increased voltage to the initial value; similarly, when the DC side voltage is less than the initial value, that is, , the energy storage unit discharges to restore the dropped voltage to the initial value. Through the charge and discharge control strategy of the energy storage unit, it can be ensured that the DC side voltage is basically maintained at the initial value.

[0053] From the perspective of the charging and discharging power of the energy storage unit, the charging and discharging power of the energy storage unit is related to the difference between the output active power of the main microgrid and the total power deficit of the slave microgrid. It can be expressed as:

[0054]

[0055] in, is the active power output of the main microgrid at time t; is the active power given by the i-th slave microgrid at time t; is the load power of the Lth slave microgrid at time t; n` is the number of slave microgrids.

[0056] The size of determines the charging and discharging state of the energy storage unit. When the energy storage unit decides whether to charge according to its state of charge value, the power output of the main microgrid is greater than the power shortage of the slave microgrid, and the excess power is absorbed by the DC side energy storage unit to maintain the state of charge of the energy storage unit at a reasonable level; when When the energy storage unit decides whether to discharge according to its state of charge, the power output of the main microgrid is less than the shortfall function of the slave microgrid, and the energy storage unit temporarily discharges to provide the shortfall power; when When it approaches zero, the charge state value of the energy storage unit remains basically stable. At this time, the output power of the main microgrid approaches the power deficit of the slave microgrid, and the energy storage unit basically no longer absorbs and provides power.

[0057] and and The size of is consistent. Since there is a power shortage in the microgrid, When the DC side capacitor C1 is discharged temporarily to provide the missing power, the DC side voltage will drop. The opposite is also true. By controlling the charging and discharging strategy of the energy storage unit, the life of the energy storage unit can be extended, the stable operation of the flexible interconnected microgrid group can be guaranteed, and power mutual assistance can be achieved. For specific energy storage unit control strategies, please refer to Figure 3 .

[0058] In summary, when a microgrid group controlled by a virtual synchronous port is used for high-power dispatching, voltage distortion and power fluctuation problems occur. After analysis, it is found that this is caused by insufficient energy of the capacitor on the DC side of the virtual synchronous port. Due to insufficient energy of the capacitor on the DC side of the virtual synchronous port, when the slave microgrid is short of power and the master microgrid fails to provide the shortfall in time, the capacitor on the DC side also fails to quickly provide the shortfall. This leads to excessive voltage drop on the DC side of the virtual synchronous port and transient power imbalance in the microgrid group. In response to the above problems, an energy storage unit is set on the DC side of the virtual synchronous port of the microgrid group as a shared energy storage to maintain the stability of the DC side voltage, which can avoid voltage distortion and power fluctuation caused by excessive transient voltage drop on the DC side, and realize smooth power mutual assistance of the microgrid group.

[0059] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A microgrid interconnection method based on energy storage supporting virtual synchronization ports, characterized in that: The following steps are involved: Step 1: Select a shared energy storage power station or a microgrid subgrid with sufficient remaining energy from the microgrid group as the master microgrid, and the remaining microgrid subgrids as slave microgrids; the master microgrid is connected to the DC side through the first multi-port flexible switch, and each slave microgrid is connected to the DC side through its corresponding second multi-port flexible switch; Step 2: The master microgrid and the second multi-port soft switch adopt a virtual synchronous generator control strategy to stabilize the voltage and frequency of the microgrid group; the slave microgrid adopts a constant power control strategy to control the power output of the slave microgrid; the first multi-port flexible switch adopts a DC voltage control strategy to stabilize the DC side voltage; Step 3: Set up an energy storage unit as shared energy storage on the DC side of the virtual synchronization port of the microgrid group, maintain the stability of the DC side voltage and supplement the power shortage from the microgrid through the charge and discharge control strategy, so that the microgrid group can achieve dynamic power balance.

2. According to claim 1, the microgrid interconnection method based on energy storage supporting virtual synchronization port is characterized in that: The first multi-port flexible switch and the second multi-port flexible switch are both bidirectional voltage-type converters, which can prevent the power fluctuation and power quality of the microgrid group from being transmitted to each other between the microgrid subgrids in the microgrid group, and smooth the impact of power fluctuations on the microgrid group.

3. The microgrid interconnection method based on energy storage supporting virtual synchronization port according to claim 1 is characterized in that: In step 3, if there is a power deviation in the slave microgrid, power mutual assistance from the master microgrid to the slave microgrid is required, then the output power of the master microgrid and the slave microgrid satisfies: Among them, the total power transmitted from the master microgrid to all slave microgrids is P m , the power required by each microgrid load is P L2 ,P L3 ,...,P Ln , each power output from the microgrid is P s2 ,P s3 ,...,P sn ; The mutual power flowing through each multi-port soft switch of the slave microgrid is P v2 ,...,P vn A positive power value indicates that the slave microgrid mutual aid power is in short supply, and other microgrid subgrids provide power to the slave microgrid; a negative power value indicates that the slave microgrid has excess power, and the slave microgrid outputs power to other microgrid subgrids; n is the number of microgrid subgrids.

4. The microgrid interconnection method based on energy storage supporting virtual synchronization port according to claim 1 is characterized in that: In step 3, after the microgrid reaches dynamic power balance, the DC side voltage remains at the initial value, that is, is zero: in, is the DC side voltage deviation; is the DC side voltage; is the DC reference voltage.

5. The microgrid interconnection method based on energy storage supporting virtual synchronization port according to claim 4 is characterized in that: In step 3, when the DC side voltage is greater than the initial value, that is, , the energy storage unit is charged, absorbing excess power, and restoring the increased voltage to the initial value; when the DC side voltage is less than the initial value, that is, , the energy storage unit discharges, allowing the dropped voltage to return to its initial value.

6. The microgrid interconnection method based on energy storage supporting virtual synchronization port according to claim 4 is characterized in that: In step 3, the difference between the output power of the main microgrid and the total power deficit of the slave microgrid at time t of the microgrid group is It is expressed as: in, is the active power output of the main microgrid at time t; is the active power given by the i-th slave microgrid at time t; is the load power of the Lth slave microgrid at time t; n` is the number of slave microgrids; The size of determines the charging and discharging state of the energy storage unit. When the power output of the main microgrid is greater than the power shortage of the slave microgrid, the excess power is absorbed by the DC side energy storage unit to maintain the charge state of the energy storage unit at a reasonable level; when When the power output of the main microgrid is less than the shortfall of the slave microgrid, the energy storage unit temporarily discharges to provide the shortfall power; When it approaches zero, the charge state value of the energy storage unit remains stable. At this time, the output power of the main microgrid approaches the power deficit of the slave microgrid, and the energy storage unit no longer absorbs and provides power.

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