Micro-grid interconnection system based on optical storage flexible direct current common direct current bus

Abstract

The invention relates to the technical field of energy storage systems, in particular to a micro-grid interconnection system based on an optical storage flexible direct current common direct current bus, which comprises an energy controller, a flexible direct control protection system, an energy storage system, a charging system and a communication network, the energy controller is used for realizing fusion of the distributed energy light storage and charging system, and the flexible direct control and protection system is used for realizing bidirectional energy flow of an alternating-current power supply and a direct-current power supply; the energy storage system is responsible for managing and monitoring the state of an energy storage battery; the charging system is responsible for monitoring and managing the charging process of the energy storage battery; and the communication network is responsible for monitoring the operation state of each link and realizing real-time communication of the system through a communication protocol. Through integration of the energy controller, the flexible direct control protection system, the energy storage system, the charging system and the communication network, fusion of the distributed energy light storage and charging system can be realized, and resident user load, distributed photovoltaic, energy storage and the like are promoted to participate in regulation and control together.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to a microgrid interconnection system based on a photovoltaic energy storage flexible direct current (DC) bus. Background Art

[0002] With the large-scale development and utilization of renewable energy, renewable energy will become the main source of primary energy in the power grid in the future, which will bring major changes to the structure and operation mode of the power grid. Structurally, due to the mismatch between the geographical distribution of power resources and load resources in the future, and the good temporal and spatial complementarity of renewable energy in a wide area, it is necessary to maintain and develop a large power grid of appropriate size. On the other hand, due to the decentralized nature of renewable energy, distributed generation that utilizes resources on site and microgrids for end users will also appear in large numbers. Therefore, the structure of the future power grid will present a pattern of coexistence of large power grids and microgrids, and it is necessary to implement a standardized and block-based autonomous power supply construction model at the distribution network level.

[0003] Traditional distribution network planning, dispatching, operation and maintenance, and marketing services are divided into different departments such as development, operation and inspection, marketing, and dispatching based on different business types. Different departments are divided into autonomous departments based on different management needs. There are huge differences in the granularity and scope of each autonomy. This is contrary to the goal of achieving multi-professional implementation at the grassroots level, optimizing the overall planning plan's full life cycle cost, strengthening multi-professional collaborative supervision throughout the process, and conducting closed-loop tracking and feedback on project planning, pre-production, planning, construction, and other links with the "autonomous responsibility system."

[0004] The construction of low-voltage flexible direct current interconnection system is an important idea to realize distributed photovoltaic consumption and regional energy optimization. First, through the coordinated control and unified management of DC loads such as power grid, charging piles, and energy storage, an energy interconnection collaborative architecture is formed to improve the carrying capacity, control capacity, and coordination capacity of the distribution network, so as to realize the efficient and reasonable use of photovoltaic power in the substation area; secondly, through flexible interconnection between substations, real-time power mutual assistance is realized, providing a new path for expanding photovoltaic consumption.

[0005] Therefore, it is necessary to propose a microgrid interconnection system based on photovoltaic storage and flexible direct current shared DC bus to realize the autonomous management of terminal and micro-distribution collaborative construction. Summary of the invention

[0006] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and provide a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared DC bus.

[0007] The purpose of the present invention is achieved through the following technical solutions: A microgrid interconnection system based on a photovoltaic storage flexible direct current common direct current bus, including an energy controller, a flexible direct current control and protection system, an energy storage system, a charging system and a communication network;

[0008] The energy controller is used to realize the integration of distributed energy light storage and charging systems, and the flexible direct current control and protection system is used to realize the two-way flow of energy between AC power supply and DC power supply; the energy storage system is responsible for managing and monitoring the status of the energy storage battery; the charging system is responsible for monitoring and managing the charging process of the energy storage battery; the communication network is responsible for monitoring the operating status of each link and realizing real-time communication of the system through communication protocols.

[0009] The present invention is further configured such that the energy controller includes two 300kW AC / DC ports and two 500kW AC / DC ports, which are used to establish connections with four four-quadrant off-grid control converters respectively;

[0010] The energy controller also includes two DC / DC converter interfaces, which are used to establish connections with the energy storage DC-DC converter and the DC charging pile interface respectively.

[0011] The present invention is further configured such that the flexible direct current control and protection system adopts a microgrid controller to realize the control function.

[0012] The present invention is further configured as follows: the flexible DC control and protection system includes a flexible DC converter; the flexible DC converter adopts an IGBT-based voltage source three-level converter topology, filtering of switching frequency harmonics is achieved through an AC side filter, filtering of high-frequency harmonic interference is achieved through EMC filters on the AC side and the DC side, load switches and fuses are arranged on the DC side to achieve protection and isolation of DC side faults, and relays and circuit breakers are arranged on the AC side to achieve connection to the AC side power grid and isolation of faults.

[0013] The present invention is further configured such that the energy storage system adopts a lithium battery pack configured in a unitized manner, which is centrally installed in a container, connected to a DC distribution unit of an energy controller via a cable, and operates in a PQ mode. The PQ operation mode is adjusted according to real-time feedback and environmental changes through reinforcement learning to optimize long-term benefits.

[0014] The present invention is further configured as follows: the charging system adopts multiple high-frequency switching power supply modules to operate in parallel with redundant backup; the charging system is provided with an independent monitor for interacting with a human-machine interface, for exchanging information with a master station, and for monitoring system operation; the charging system is provided with a power supply module, and the power supply module adopts resonant double soft switching technology; the power supply module is configured with a standard isolated RS485 interface to communicate with the independent monitor, and the power supply module has a built-in active power factor correction module for suppressing harmonics of the charging equipment, improving the power factor and conversion efficiency.

[0015] The present invention is further configured such that the communication network realizes real-time monitoring and remote operation of the microgrid interconnection system through Ethernet combined with a communication protocol; the communication network analyzes the collected data through a support vector machine, performs fault diagnosis and prediction, identifies potential fault points and abnormal behaviors, issues early warnings, and takes repair measures.

[0016] The present invention is further configured that the charging system comprises the following steps:

[0017] S1. Initialize first, set parameters, and determine the total number of electric vehicles M and the number of cycles N;

[0018] S2, starting from the first electric car, randomly obtain the daily mileage of the mth electric car;

[0019] S3, randomly obtaining the charging start time of the mth electric vehicle;

[0020] S4, calculating the charging time of the mth electric vehicle;

[0021] S5, establishing a charging load model for the mth electric vehicle;

[0022] S6, determining whether the charging load model of all electric vehicles with a total number of M has been completed, otherwise, adding one to m and returning to step S3;

[0023] S7, accumulating the charging load models of m vehicles to obtain the electric vehicle charging load curve calculated in the nth cycle;

[0024] S8, determine whether the set number of cycles has been reached, otherwise add one to n and return to step S2;

[0025] S9. Take the average value of N electric vehicle charging load curves, output the charging load demand of the electric vehicle, and the calculation ends.

[0026] The present invention is further configured as follows:

[0027] In step S2, by formula Randomly obtain the daily mileage of the mth electric vehicle; where d is the mileage of the electric vehicle, μ D , σ D They are the mean and standard deviation of the function lnd, i.e. the logarithmic function of the daily mileage of electric vehicles, and different types of electric vehicles correspond to different values;

[0028] In step S3, the formula Randomly obtain the daily mileage of the mth electric vehicle; where t is the starting time of the electric vehicle charging, μ T , σ Tare the mean and standard deviation of the probability distribution respectively. Different types of electric vehicles correspond to different values.

[0029] The present invention is further configured as follows:

[0030] In step S4, by formula Calculate the charging time of the mth electric car; where W 100 Indicates the power consumption of electric vehicles per 100 kilometers, in kW·h / 100km; P ev is the charging power of the electric vehicle; T CD Indicates charging time; η ev The charging efficiency of the energy storage battery;

[0031] In step S5, by formula Establish the charging load model of the mth electric vehicle.

[0032] Beneficial effects of the invention: The invention can realize the integration of existing distributed energy photovoltaic storage and charging systems by integrating energy controllers, flexible direct current control and protection systems, energy storage systems, charging systems and communication networks, and promote the joint participation of residential user loads, distributed photovoltaics, energy storage, etc. in regulation and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0034] Figure 1 It is a principle block diagram of the present invention; DETAILED DESCRIPTION

[0035] The present invention is further described in conjunction with the following examples.

[0036] Depend on Figure 1 It can be seen that the microgrid interconnection system based on a photovoltaic storage and flexible direct current shared DC bus described in this embodiment includes an energy controller, a flexible direct current control and protection system, an energy storage system, a charging system, and a communication network. The energy controller is used to realize the integration of distributed energy photovoltaic storage and charging systems (i.e., an integrated system of photovoltaic power generation, energy storage and charging facilities), the flexible direct current control and protection system is used to realize the two-way flow of energy between the AC system and the DC system, the energy storage system is responsible for managing and monitoring the battery status to ensure the safety and life of the battery, the charging system is responsible for monitoring and managing the charging process to ensure safe charging of the battery and the optimal battery life, and the communication network is responsible for monitoring the operating status and performance of each link, and realizing real-time communication of the system through communication protocols.

[0037] The energy controller includes two 300kW AC / DC ports and two 500kW AC / DC ports, which are used to establish connections with four four-quadrant off-grid control converters respectively, and two DC / DC converter interfaces are reserved on the DC bus for establishing connections with the energy storage DC-DC converter and the DC charging pile interface respectively. The energy controller is also equipped with a set of autonomous management terminals to communicate with each converter module and the four-quadrant off-grid control converter fusion terminal to realize the issuance of control instructions and the upload of measurement and status information.

[0038] The flexible direct current control and protection system adopts a microgrid controller to realize the control function, and adopts modular flexible direct current converter to configure different numbers of standard power modules according to the power requirements of different substations. In addition, each converter in the system is equipped with a fault protection function to monitor its own working status as well as the status of the energy storage battery and the AC power grid in real time.

[0039] The power coordination of the microgrid is carried out with voltage as the reference benchmark. The control process of its control strategy is as follows: the inverter collects the DC voltage of the busbars at both ends, calculates the effective value, and uses the following formula to calculate the amplitude reference value of the voltage compensation. After the PI link is adjusted, the correction term of the control link is generated and added to the control link. The adjustment of the tie line flow depends on the voltage difference between the two DC buses. After the voltage deviation is corrected, the reasonable distribution of the power of the interconnected microgrids in the two regions can be realized, and the reliable and stable operation of the microgrid can be realized. pcc2 +U tie =U corr Where U pcc2 is the voltage of the DC bus of one of the interconnected microgrids, U tie is the interconnection line voltage value, which is calculated by the voltage difference between the two interconnected DC buses. corrIt is the reference voltage after voltage compensation. The fault protection functions configured for each AC converter in the system include the following: AC over / undervoltage protection: During the grid-connected operation of the converter, the grid voltage at the grid interface is allowed to deviate by ±10% of the rated value. When the grid voltage exceeds the specified range, the converter stops working and displays the corresponding alarm information on the LCD screen of the control device. AC over / underfrequency protection: During the grid-connected operation of the converter, when the grid frequency exceeds the specified range, the converter stops working and displays the corresponding alarm information on the LCD screen of the control device. AC overcurrent protection: During the grid-connected operation of the converter, when a short circuit occurs in the grid, the converter can limit the AC output current to within 120% of the rated value, and disconnect the energy storage device from the grid within the set time; when the converter is seriously overcurrent, the converter triggers the quick-break protection and immediately issues the corresponding alarm information. Negative sequence current protection: During the grid-connected operation of the converter, when the grid load current exceeds the allowable range, the inverter stops supplying power to the grid and issues the corresponding alarm information. Load voltage protection: During the grid-connected operation of the converter, when the load voltage of the grid exceeds the allowable range, the inverter stops working and issues a corresponding alarm message. Island monitoring protection: The flexible DC converter device is equipped with active and passive dual island detection methods. When an island fault occurs in the grid, the converter can quickly detect the grid island fault, disconnect the energy storage device from the grid, and issue a corresponding alarm message. DC overvoltage protection: The flexible DC converter comprehensively determines the limit value of DC overvoltage protection based on the characteristics of the battery and the withstand voltage level of the components inside the PCS. When the converter detects that the input voltage is higher than this limit value, the converter will disconnect the energy storage device from the grid and issue a corresponding alarm message. DC undervoltage protection: When the flexible DC converter detects that the DC voltage is lower than the set undervoltage setting, the inverter will shut down for protection and issue a corresponding alarm message. DC side reverse polarity protection: The flexible DC converter detects the DC input line voltage of the inverter in real time. When the inverter detects that the input line is reversely connected, it will automatically disconnect the AC and DC side connections. After the polarity connection is normal, the inverter can resume normal operation. DC overcurrent protection: The flexible DC converter can monitor the DC side current in real time. When the current value exceeds the limit value, the converter will disconnect the energy storage device from the grid and issue a corresponding alarm message. Its constant setting needs to be coordinated with the battery charge and discharge limit current. Insulation monitoring: The flexible DC converter monitors the insulation condition of the DC side to the ground in real time. When insulation abnormalities occur, the inverter issues a corresponding alarm message. Drive protection: During the operation of the flexible DC converter, the status of the IGBT module is monitored in real time. When a drive failure occurs in the IGBT, the inverter immediately shuts down and issues a corresponding alarm message. PT abnormal protection: During the operation of the flexible DC converter, the AC voltage deviation of the front and rear ends of the AC side grid-connected contactor is monitored in real time. When the voltage is abnormal, the inverter shuts down and issues a corresponding alarm message.Auxiliary power supply protection: The status of the auxiliary power supply is continuously monitored during the operation of the flexible DC converter. When the power supply fails, the PCS will shut down for protection and issue a corresponding alarm message. Inverter overtemperature protection: The inverter temperature is monitored in real time during the operation of the flexible DC converter. When the temperature is too high, the inverter will start the fan to dissipate heat and operate at limited power. When the temperature is still higher than the high temperature limit, the inverter will stop running to protect the stable operation of the equipment. Communication fault protection: During the operation of the flexible DC converter, the communication status with the BMS and the host computer is monitored in real time. When the communication is interrupted, the PCS will shut down for protection and issue a corresponding alarm message. External interlock protection: The flexible DC converter can be connected to an external interlock protection signal. When external interlock protection is required, the PCS will shut down for protection accordingly and issue an alarm message.

[0040] The flexible DC converter of the flexible DC control and protection system adopts an IGBT-based voltage source three-level converter topology. The switching frequency harmonics are filtered through the AC side filter, and the high-frequency harmonic interference is filtered through the AC and DC side EMC filters. Load switches and fuses are set on the DC side to protect and isolate DC side faults. Relays and circuit breakers are set on the AC side to connect to the AC side grid and isolate faults.

[0041] The energy storage system uses a unitized lithium battery pack, which is centrally installed in a container and connected to the DC distribution unit of the energy controller via a cable. The 100kW / 200kWh lithium battery pack includes two battery clusters, each with 103.68kWh. The battery capacity is 460.8V / 225Ah (3P*12S*12S*2P), totaling 207.36kWh. A single lithium battery uses a standard 75Ah lithium iron phosphate (LFP) square aluminum shell battery cell as the basic unit battery cell, with a single rated capacity of 100kW / 200kWh. The rated capacity is 75Ah, the rated voltage is 3.2V, and the rated energy is 240Wh. Each battery module consists of 36 single cells in 3 parallel and 12 series. It is equipped with a collection harness, bus, NTC, and isolation plate. It is combined through ultrasonic welding, laser welding, glue bonding and other processes. Its rated voltage is 38.4V, the rated capacity is 225Ah, and the rated energy is 8.64kWh. It operates in PQ mode and adjusts its PQ operation mode according to real-time feedback and environmental changes through reinforcement learning to optimize long-term benefits.

[0042] The charging system uses multiple high-frequency switching power modules in parallel for redundant backup operation. It is equipped with an independent monitor to exchange information with the human-machine interface and the main station to monitor the operation of the system. The power module uses resonant dual soft switching technology and is equipped with a standard isolated RS485 interface to communicate with the monitor. It also has a built-in active power factor correction module to suppress harmonics in the charging equipment and improve the power factor and conversion efficiency.

[0043] The communication network uses Ethernet combined with communication protocols to achieve real-time monitoring and remote operation of the microgrid, ensuring the safe and stable operation of the system. It uses support vector machines to analyze the collected data, perform fault diagnosis and prediction, identify potential fault points and abnormal behaviors, provide early warnings, and take repair measures.

[0044] The existing transformer 380V side is single busbar connection, using low-voltage flexible direct current ring solution, and building a four-port energy controller container, including: 1 DC 750V DC bus; 4 AC / DC converters, input voltage is 0.4kV, 2 of which have a port power of 300kW and the other 2 have a port power of 500kW; 1 DC / DC converter, connected to a 100kW / 200kWh energy storage system; 1 DC output port, output voltage is 750V, connected to a 160kW group-controlled DC charger, equipped with 2 charging terminals, a total of 4 parking spaces. This solution has a total of four 0.4kV power supplies, drawn from the low-voltage side of four transformers in the community, and the cable uses ZC-YJY22-0.6 / 1kV-4×95+1×50mm2, and is laid in pipes.

[0045] The main wiring scheme is as follows:

[0046] This solution builds a set of four-port energy controllers (as described above) and installs them in one container. The planned construction scale of the energy storage system in this solution is 100kW / 200kWh, and the lithium battery pack is configured in units and installed in one container. The energy storage system is connected to the DC distribution unit via cables.

[0047] The system can also be equipped with a flexible energy storage cabin, which is composed of an AC unit composed of multiple AC / DCs, a local monitoring and related energy management system, and a power generation unit. The flexible energy storage cabin is equipped with an isolation transformer to provide three-phase four-wire power supply when the system is off-grid, ensuring the normal operation of the power supply line. Its energy storage converter module AC / DC adopts a three-level design to improve the switching frequency, conversion efficiency and system stability.

[0048] The microgrid interconnection system based on the photovoltaic storage flexible direct current and direct current bus described in this embodiment includes the following steps in the charging system:

[0049] S1. Initialize first, set parameters, and determine the total number of electric vehicles M and the number of cycles N;

[0050] S2, starting from the first electric car, randomly obtain the daily mileage of the mth electric car;

[0051] S3, randomly obtaining the charging start time of the mth electric vehicle;

[0052] S4, calculating the charging time of the mth electric vehicle;

[0053] S5, establishing a charging load model for the mth electric vehicle;

[0054] S6, determining whether the charging load model of all electric vehicles with a total number of M has been completed, otherwise, adding one to m and returning to step S3;

[0055] S7, accumulating the charging load models of m vehicles to obtain the electric vehicle charging load curve calculated in the nth cycle;

[0056] S8, determine whether the set number of cycles has been reached, otherwise add one to n and return to step S2;

[0057] S9. Take the average value of N electric vehicle charging load curves, output the charging load demand of the electric vehicle, and the calculation ends.

[0058] In the microgrid interconnection system based on the photovoltaic storage flexible direct current shared direct current bus described in this embodiment, in step S2, the formula Randomly obtain the daily mileage of the mth electric vehicle; where d is the mileage of the electric vehicle, μ D , σ D They are the mean and standard deviation of the function lnd, i.e. the logarithmic function of the daily mileage of electric vehicles, and different types of electric vehicles correspond to different values;

[0059] In step S3, the formula Randomly obtain the daily mileage of the mth electric vehicle; where t is the starting time of the electric vehicle charging, μ T , σ T are the mean and standard deviation of the probability distribution respectively. Different types of electric vehicles correspond to different values.

[0060] The present invention is further configured as follows:

[0061] In step S4, by formula Calculate the charging time of the mth electric car; where W 100 Indicates the power consumption of electric vehicles per 100 kilometers, in kW·h / 100km; P ev is the charging power of the electric vehicle; T CD Indicates charging time; η ev The charging efficiency of the energy storage battery;

[0062] In step S5, by formula The charging load model of the mth electric vehicle is established. The above settings can balance the charging load of the charging system, thereby improving the charging efficiency.

[0063] From the above, it can be seen that the present invention brings together AC and DC elements such as AC and DC energy storage and charging piles, gives full play to the role of the intelligent fusion terminal in the substation area, and relies on high-efficiency conversion technology to achieve real-time closed-loop operation between substations; realizes the integration of distributed energy photovoltaic storage and charging systems, and promotes the joint participation of residential user loads, distributed photovoltaics, energy storage, etc. in regulation; explores high-penetration distributed photovoltaics based on autonomous technology. Friendly, efficient grid-connected access and consumption provides a new template for the construction of distribution energy interconnection.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus, characterized in that: Including energy controller, flexible direct current control and protection system, energy storage system, charging system and communication network; The energy controller is used to realize the integration of distributed energy light storage and charging system, and the flexible direct current control and protection system is used to realize the bidirectional flow of energy between AC power supply and DC power supply; the energy storage system is responsible for managing and monitoring the status of energy storage batteries; the charging system is responsible for monitoring and managing the charging process of energy storage batteries; The communication network is responsible for monitoring the operating status of each link and realizing real-time communication of the system through the communication protocol.

2. According to claim 1, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized by: The energy controller includes two 300kW AC / DC ports and two 500kW AC / DC ports, which are used to establish connections with four four-quadrant off-grid control converters respectively; The energy controller also includes two DC / DC converter interfaces, which are used to establish connections with the energy storage DC-DC converter and the DC charging pile interface respectively.

3. According to claim 1, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized by: The flexible direct current control and protection system adopts a microgrid controller to realize the control function.

4. According to claim 3, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized in that: The flexible direct current control and protection system includes a flexible direct current converter; the flexible direct current converter adopts an IGBT-based voltage source three-level converter topology, filtering of switching frequency harmonics is achieved through an AC side filter, filtering of high-frequency harmonic interference is achieved through EMC filters on the AC and DC sides, a load switch and a fuse are arranged on the DC side to achieve protection and isolation of DC side faults, and a relay and a circuit breaker are arranged on the AC side to achieve connection to the AC side power grid and isolation of faults.

5. According to claim 1, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized in that: The energy storage system uses a unitized lithium battery pack, which is centrally installed in a container and connected to the DC distribution unit of the energy controller via a cable. It operates in PQ mode and adjusts its PQ operation mode according to real-time feedback and environmental changes through reinforcement learning to optimize long-term benefits.

6. According to claim 5, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized in that: The charging system uses multiple high-frequency switching power supply modules in parallel for redundant backup operation; the charging system is provided with an independent monitor for interacting with the human-machine interface, for exchanging information with the main station, and for monitoring the operation of the system; the charging system is provided with a power supply module, which uses resonant double soft switching technology; the power supply module is equipped with a standard isolated RS485 interface to communicate with the independent monitor, and the power supply module has a built-in active power factor correction module for suppressing harmonics of the charging equipment and improving the power factor and conversion efficiency.

7. According to claim 5, a microgrid interconnection system based on a photovoltaic and energy storage flexible direct current shared direct current bus is characterized in that: The communication network realizes real-time monitoring and remote operation of the microgrid interconnection system through Ethernet combined with communication protocols; the communication network analyzes the collected data through support vector machines, performs fault diagnosis and prediction, identifies potential fault points and abnormal behaviors, and issues early warnings and takes repair measures.

8. The microgrid interconnection system based on photovoltaic and energy storage flexible direct current shared direct current bus according to claim 1 is characterized by: The charging system comprises the following steps: S1. Initialize first, set parameters, and determine the total number of electric vehicles M and the number of cycles N; S2, starting from the first electric car, randomly obtain the daily mileage of the mth electric car; S3, randomly obtaining the charging start time of the mth electric vehicle; S4, calculating the charging time of the mth electric vehicle; S5, establishing a charging load model for the mth electric vehicle; S6, determining whether the charging load model of all electric vehicles with a total number of M has been completed, otherwise, adding one to m and returning to step S3; S7, accumulating the charging load models of m vehicles to obtain the charging load curve of the electric vehicle calculated in the nth cycle; S8, determine whether the set number of cycles has been reached, otherwise add one to n and return to step S2; S9. Take the average value of N electric vehicle charging load curves, output the charging load demand of the electric vehicle, and the calculation ends.

9. A microgrid interconnection system based on a photovoltaic-storage-flexible-DC-shared-DC bus according to claim 8, characterized in that: In step S2, by formula Randomly obtain the daily mileage of the mth electric vehicle; where d is the mileage of the electric vehicle, μ D , σ D They are the mean and standard deviation of the function lnd, i.e. the logarithmic function of the daily mileage of electric vehicles, and different types of electric vehicles correspond to different values; In step S3, the formula Randomly obtain the daily mileage of the mth electric vehicle; where t is the starting time of the electric vehicle charging, μ T , σ T are the mean and standard deviation of the probability distribution respectively. Different types of electric vehicles correspond to different values.

10. The microgrid interconnection system based on photovoltaic and energy storage flexible direct current shared direct current bus according to claim 8 is characterized by: In step S4, by formula Calculate the charging time of the mth electric car; where W 100 Indicates the power consumption of electric vehicles per 100 kilometers, in kW·h / 100km; P ev is the charging power of the electric vehicle; T CD Indicates charging time; η ev The charging efficiency of the energy storage battery; In step S5, by formula Establish the charging load model of the mth electric vehicle.

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