A charging and discharging system and method for a residential DC microgrid

Abstract

This invention discloses a community DC microgrid charging system and method, relating to the field of electric vehicle charging. It includes: a charging and discharging module for charging and discharging electric vehicles using the community load, the maximum available load of the external grid, and an energy storage battery; an energy storage battery for storing the remaining capacity of the community load and providing additional charging power to electric vehicles during power outages or peak charging periods; a load monitoring module for monitoring the community load, the maximum available load of the external grid, and transmitting the monitored information to an energy management module; and an energy management module for calculating the deficit between renewable energy and charging load based on the community load and the maximum available load of the external grid. When renewable energy is in surplus, the surplus power is transmitted to the community AC grid for charging electric vehicles according to charging priority. When renewable energy is insufficient, the deficit is compensated for by the input power from the main grid to charge electric vehicles. When the input power from the main grid reaches its upper limit, the energy storage battery discharges to charge electric vehicles. This system can significantly improve the utilization rate of the community's electricity capacity.

Description

Technical Field

[0001] This invention relates to community DC microgrid charging technology, and more particularly to a community DC microgrid charging and discharging system and method with V2G and V2V / H functions. Background Technology

[0002] As electric vehicle technology matures and costs continue to decline, more and more consumers are choosing new energy vehicles. According to the China Association of Automobile Manufacturers (CAAM), 6 million new energy vehicles are projected to be sold in 2022, with a market penetration rate exceeding 20%. In today's rapidly growing electric vehicle market, the demand for charging is increasing rapidly, particularly in residential communities where charging issues are becoming increasingly prominent. Electric vehicles can function as both electrical appliances and energy storage devices, participating in peak shaving and valley filling within communities. To improve residents' living standards and further develop electric vehicle technology, establishing new smart grids and smart community-level power grids is crucial.

[0003] Currently, traditional electric vehicle charging technology is mainly constrained by the total power capacity of residential communities. The number of charging stations and other infrastructure cannot match the number of electric vehicles in a community, failing to meet the charging demand. This problem is particularly severe in older communities. In communities where charging stations are already installed, the charging process is not effectively managed, and charging stations are matched only according to the community's maximum power, resulting in a significant waste of effective capacity and an inefficient use of the community's power capacity. In addition, traditional charging infrastructure mainly relies on AC charging, but energy conversion and loss occur during high-power charging, and the construction and maintenance costs of AC charging stations are relatively high.

[0004] In summary, existing electric vehicle charging technologies, when used in communities with existing charging stations, fail to effectively manage the charging process. They simply match charging stations to the community's maximum power output, resulting in unidirectional flow, insufficient charging power, and a significant waste of effective capacity. Consequently, they fail to achieve efficient utilization of the community's electricity capacity. Summary of the Invention

[0005] This invention provides a microgrid charging and discharging system and method for residential communities. The purpose is to solve the technical problem that existing electric vehicle charging technologies for communities with installed charging piles fail to effectively control the charging process. They only match charging piles according to the maximum power of the community, resulting in unidirectional flow, insufficient charging power, a large waste of effective capacity, and failure to achieve effective utilization of the community's power capacity.

[0006] To achieve the above objectives, the present invention provides a community DC microgrid charging and discharging system, characterized in that it comprises: The charging and discharging module is used to charge and discharge electric vehicles based on the community load, the maximum available load of the community's external network, and the energy storage battery. Energy storage batteries are used to store the remaining capacity of the community load and to provide additional charging power for electric vehicles when the community experiences power outages or during peak charging periods. The load monitoring module is used to monitor the cell load and the maximum available load of the cell's external network, and transmit the monitored information to the energy management module. The energy management module is used to calculate the gap between renewable energy and charging load based on the community load and the maximum available load of the external grid. When renewable energy is in surplus, the surplus power is transmitted to the community's AC grid to charge electric vehicles according to charging priority. When renewable energy is insufficient, the power input from the main grid is used to make up for the community load gap and charge electric vehicles. When the main grid input power reaches its limit, the energy storage battery discharges to charge electric vehicles. When there is a fault in the community grid or the main grid, the important loads of the community are switched to DC microgrid power supply, and the energy storage battery supplies the instantaneous demand power. By calculating the important loads of the community and the renewable energy gap, when the renewable energy demand power is in surplus, the surplus power is used to charge the energy storage battery; when the renewable energy demand power is insufficient, the energy storage battery discharges. The energy management module includes a communication device. When the electric vehicle is connected to its charging / discharging interface, the communication device automatically communicates with the electric vehicle to obtain its battery information. Based on the obtained battery information, the module determines the electric vehicle owner's charging type and bidding intention through a user interface. It then prioritizes the charging type of the electric vehicle based on its charging type and bidding intention, giving priority to vehicles with higher charging levels, and simultaneously publishes real-time electricity prices to the user. The specific content of the priority classification is as follows: The community's critical loads are set as Level 1+ loads, and under any circumstances, the power supply to the community's critical loads must be prioritized; the energy storage batteries are set as Level 4 loads. When electric vehicles are slow-charged, the charging load is Level 2 when the initial SOC of the electric vehicle is 0~30%; and Level 3 when the initial SOC of the electric vehicle is 30~60%. When the initial SOC of an electric vehicle is 60-100%, the charging load is level 4. Meanwhile, vehicle owners can upgrade their charging level through bidding, increasing the charging load by 1 level based on the current charging price (λ). Here, λ is defined as 20% of the current charging price. The fast charging level is defined as level 2. When the charging level of the adjacent DC charging and discharging module is lower than this level, the DC charging and discharging module in parallel is used to give priority to fast charging. When the charging price of fast charging increases by λ, the fast charging level is upgraded to level 1. At this time, the DC charging and discharging modules that are lower than level 1 are connected in parallel to charge the electric vehicle. When multiple electric vehicles with the same charging level are present, a rotating charging mechanism is implemented, and the amount of electricity charged in each rotation is defined as follows: In the formula, For the rated capacity of electric vehicle batteries, This indicates the battery's state of charge.

[0007] Preferably, the energy management module is further configured to, after the DC charging module has established communication between the communication device and the corresponding electric vehicle, transfer the electric vehicle's power to the DC bus when the user is not using the vehicle and is willing to discharge it. The energy management module then allocates the power to the charging / discharging interfaces of electric vehicles that urgently need power or to other electrical loads, realizing V2V, V2H, and V2G functions. The energy management module also provides compensation to users of electric vehicles who are willing to sell their electricity, with the compensation price defined as: In the formula, This is the basic charging electricity price for electric vehicles at that time. For compensation coefficient, The compensation coefficient for supplying power to critical loads during a power outage in the residential area; The basic charging tariff includes the charging tariff for DC microgrids operating in grid-connected mode and the charging tariff for off-grid operation: The off-grid charging price is defined based on the imbalance between electricity load and renewable energy. When renewable energy generation is sufficient, the price is low to encourage electric vehicle charging, and when renewable energy is insufficient, the price is high. The electricity load includes both the community's critical load and the electric vehicle charging load. In the formula, For electrical load, Renewable energy generation capacity configured for DC microgrids Indicates the basic charging electricity price; The grid-connected charging tariff is defined based on the imbalance between the electricity load and the microgrid's input power. The electricity load is the electric vehicle charging load, and the input power includes the power supplied by the renewable energy source and the available input power from the community's AC grid. In the formula, It is the input power of the large power grid. For the community load, This is the charging load.

[0008] Preferably, the charging and discharging module includes an intelligent switching switch. The intelligent switching switch is used to provide charging power to the corresponding electric vehicle charging and discharging interface when a single DC charging and discharging module is working normally; or when the electric vehicle of the DC charging module has a fast charging requirement and the adjacent DC charging module has no charging requirement or a low charging level, the charging price for fast charging is calculated based on the number of charging modules called. After the car owner agrees to the bidding intention based on the calculated fast charging price, the communication device controls the output terminal of the intelligent switching switch to switch to the output interface corresponding to the charging vehicle that needs fast charging to meet the fast charging requirement. The electricity price for fast charging is defined as follows: In the formula, For fast charging price, For this time, slow charging price, =1, 2, ... represents the number of adjacent DC charging modules currently in operation. The compensation coefficient; Alternatively, it can be used to switch adjacent DC charging modules to participate in charging when a single DC module fails.

[0009] Preferably, the charging and discharging module further includes a multi-energy input interface connected to the DC bus. The multi-energy input interface includes hydrogen energy, wind power, and photovoltaic power, which is used to convert the input power into a voltage level that matches the DC bus to increase the power capacity of the community.

[0010] Preferably, the energy storage battery is connected to the DC bus via a bidirectional DC / DC converter, the capacity of which is the same as that of the bidirectional PCS. The bidirectional DC / DC converter also includes an extended interface for increasing the capacity of the energy storage battery when other energy sources are connected later. The energy storage battery module is designed to address the uncertainty of renewable energy sources by prioritizing power supply to the community's AC microgrid via the bidirectional PCS during grid connection when renewable energy power is in surplus, with excess power used to charge the energy storage battery. When the energy storage battery's SOC exceeds 0.9, renewable energy is curtailed. Simultaneously, the energy storage battery is charged at high... During peak periods, additional charging power is provided to multiple DC charging modules to provide DC fast charging services for electric vehicles. When the SOC of the energy storage battery is below 0.4, the energy storage battery stops discharging. When off-grid, after renewable energy supplies electric vehicles and important loads in the community, surplus power is used to charge the energy storage battery. If the power is insufficient, the energy storage battery discharges. If the SOC of the energy storage battery is below 0.1, the energy storage battery stops discharging. When responding to excess important loads in the community and the SOC of the energy storage battery is below 0.2, excess power is used to charge the energy storage battery. When the SOC is above 0.4, the electricity price is reduced, and the power of V2V, V2H, and V2G is reduced.

[0011] Preferably, the charging and discharging module further includes a transfer switch, installed at the critical load of the community, for use when the community is powered normally by the community's AC grid, and seamlessly switching to DC microgrid power supply when the community encounters power shortages or external equipment failures prevent normal power supply. At the same time, the DC power is converted into an electrical energy form suitable for the community's AC loads via DC / AC conversion. The electrical energy conversion process is unidirectional from the DC source to the AC load, ensuring that the supply of critical loads in the community is met.

[0012] Preferably, the energy management module is further used to classify the priority of electric vehicles according to their charging type and bidding willingness, randomly select electric vehicles of the same charging level and publish the charging data in turn; the energy management module is connected to a user terminal for communication, and the energy management module is used to receive the charging request from the user terminal App, and send data feedback to the user terminal App on the charging price, charging completion time, and V2V and V2H requests of electric vehicles.

[0013] Preferably, the intelligent switching switch has two input lines, one positive and one negative, and multiple output interfaces, 1+, 1-, ..., m+, m-, ..., n+, n-, at the output end. During normal power supply, each output interface m+ and m- is connected to the corresponding electric vehicle charging / discharging interface m. When there is a fast charging demand at the m electric vehicle charging / discharging interfaces or when the DC charging / discharging module m fails, the adjacent intelligent switching switch switches to m+ and m-. When the electric vehicle has a discharging demand and the adjacent DC charging / discharging module is idle, the adjacent intelligent switching switch switches to the electric vehicle charging / discharging interface corresponding to the electric vehicle that needs to be discharged, so that the electric vehicle outputs power multiple times the capacity of the DC charging / discharging module.

[0014] Preferably, it also includes a method for charging and discharging a DC microgrid in a residential area, comprising the following steps: The load monitoring module monitors the community load and the maximum available load of the external network. The energy management module calculates the deficit between renewable energy and charging load based on the community load and the maximum available load of the external network. When there is a surplus of renewable energy, the surplus power is transmitted to the community's AC grid and electric vehicles are charged according to charging priority. When renewable energy is insufficient, the power input from the main power grid is used to make up for the load shortfall in the community to charge electric vehicles; when the power input from the main power grid reaches its limit, the energy storage battery is discharged to charge electric vehicles. When the community's power grid or the main power grid fails, the community's critical loads are switched to DC microgrid power supply, and the energy storage battery supplies the instantaneous power demand. By calculating the critical loads and the shortage of renewable energy, when there is a surplus of renewable energy demand, the surplus power is used to charge the energy storage battery; when there is a shortage of renewable energy demand, the energy storage battery is discharged.

[0015] Compared with the prior art, the present invention has the following advantages: This invention utilizes a load monitoring module to monitor the cell load and the maximum available load of the external network, and transmits this monitoring information to an energy management module. The energy management module compares the cell load and the maximum available load of the external network to set corresponding charging and discharging policies. This enables the bidirectional transmission of electricity to participate in peak shaving and valley filling of the cell grid in real time. Without increasing the cell grid capacity, it efficiently utilizes the remaining capacity of the cell grid, improves the rechargeable power of charging equipment, and significantly enhances the user charging experience. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 The module relationship diagram provided for this invention; Figure 2 A flowchart for the charging load classification provided by the present invention; Figure 3 A topology diagram of the DC charging module provided by the present invention; Figure 4 Block diagram of grid-connected control strategy for intelligent microgrid system provided by the present invention; Figure 5 Block diagram of off-grid control strategy for smart microgrid system provided by the present invention; Detailed Implementation

[0018] The following will refer to the appendices in the embodiments of the present invention. Figure 1-5 The technical solutions in the embodiments of the present invention will be clearly and completely described. It should be understood that the terminology used in the present invention is only for describing particular implementation methods and is not intended to limit the present invention. Detailed Implementation

[0020] Example A residential community can be equipped with multiple DC microgrids through actual electric vehicles. For example... Figure 1 As shown, the present invention provides a community DC microgrid charging and discharging system, comprising:

[0021] The DC bus is connected to the community power grid through a 100kW grid-connected PCS. At the same time, multiple microgrid charging systems can be configured according to the community capacity to meet the charging load requirements.

[0022] The system features multiple energy input interfaces connected to the DC bus, including interfaces for connecting to output DC equipment and output AC equipment, and is equipped with a 200kW rooftop photovoltaic system for the parking shed. The energy storage battery is connected to the DC bus via a DC / DC converter. Since the main load of the community is 50kW, the bidirectional DC / DC converter is equipped with a capacity of 150kW. The energy storage battery can store electricity during off-peak hours and provide additional charging power during peak hours.

[0023] The energy storage converter (PCS) controls the charging and discharging process of the battery, performing AC / DC conversion. When the PCS detects an abnormal grid-side voltage, it controls the grid-connected switching switch (STS) to disconnect, and simultaneously, the energy storage battery provides voltage support to the microgrid through a bidirectional DC / DC converter, allowing the system to operate in islanded mode. When the energy storage coordinator detects that the grid voltage has returned to normal, the microgrid system synchronizes with the grid voltage and closes the grid-connected switching switch (STS) to connect to the community's AC grid, achieving grid-connected operation.

[0024] The transfer switch, installed at the critical load points of each community, includes a unidirectional DC / AC transfer switch connected to the DC bus and an intelligent transfer switch.

[0025] Ten 10kW DC charging modules are connected at one end to the DC bus and at the other end to the smart switch, and are equipped with corresponding communication equipment. At the same time, the DC charging and discharging modules can realize bidirectional energy flow, thereby realizing V2V and V2H for electric vehicles.

[0026] It includes two sets of intelligent toggle switches, one of which has one positive and one negative input terminal and one output terminal of 1. + 1 - ,2 + 2 - , ..., 5 + 5 - One set has 5 outputs, and the other set has 6 outputs. + 6 - 7 + 7 - , ..., 10 + 10 - It has 5 outputs, guaranteeing a maximum DC fast charging of 50W. Each output port has a corresponding electric vehicle charging / discharging port. Under the control of the energy management module, it can automatically close to transfer power to the adjacent electric vehicle charging / discharging port to charge the electric vehicle.

[0027] The energy management system communicates with DC / DC converters, PCS, smart transfer switches, and smart switches via a self-built CAN local area network, and with user terminal apps via 5G.

[0028] The transfer switch module uses the community's AC grid for power during normal operation. When the community experiences power shortages or external equipment malfunctions, it seamlessly switches the AC power to a DC microgrid, simultaneously converting the DC / AC power to a form suitable for the community's AC loads. This conversion process is unidirectional, from the DC microgrid to the community's critical loads, ensuring that the supply to these loads is adequate.

[0029] The main grid's input power prioritizes meeting residents' daily electricity needs. If the community's load is less than the maximum load available from the external grid, excess energy is supplied to the DC microgrid via a smart PCS. Under the control of the energy management module, and through user interaction via an app and load classification and grading, the system manages the orderly charging / discharging of electric vehicles, the charging / discharging of energy storage batteries, and the power supply to critical loads. If the community's load exceeds the maximum load available from the external grid and there is surplus clean energy, the surplus power is prioritized for supplying power to the community's AC grid via the smart PCS.

[0030] The electric vehicle bidirectional DC / DC converter has an expansion interface to facilitate the connection of other energy sources in the future. In order to better absorb energy, the capacity of the energy storage battery can be increased. The main function of the energy storage battery is to balance the active power imbalance of the system at multiple time scales caused by the randomness, volatility and uncertainty of the output of new energy sources such as wind power and photovoltaics. At the same time, it can also realize peak shaving and valley filling of the community power grid. When there are many V2V and V2H responses in the DC charging microgrid and the SOC of the energy storage battery is below 20%, it can store the excess response power.

[0031] The multi-energy input interface, including the corresponding power conversion equipment, can convert the input power into a voltage level that matches the DC bus. Its function is to facilitate the connection of clean energy sources such as photovoltaic, wind power, and hydrogen energy, as well as power resources such as diesel generators, to realize the power capacity expansion of the community.

[0032] The intelligent switching switch is a single-input, 5-output switch. Under normal operation, DC charging module 1 provides charging power to the corresponding charging gun 1. When an adjacent DC charging module is unloaded and the electric vehicle using that module needs fast charging, the energy management module calculates the fast charging price based on the number of idle adjacent DC charging modules. After the vehicle owner agrees to the charging price, the intelligent switch switches its output to charging gun 1 to charge the vehicle requiring fast charging, thus achieving fast and slow charging compatibility and improving the user's charging experience. Furthermore, if a single DC module fails, it can switch to an adjacent DC charging module to participate in charging, improving power supply reliability.

[0033] like Figure 2As shown, the charging level is divided as follows: The energy management module is equipped with corresponding communication equipment, which is used to automatically communicate with the electric vehicle when the electric vehicle is connected to the electric vehicle charging and discharging interface to obtain the electric vehicle's battery information; based on the obtained electric vehicle's battery information, the charging type and bidding intention of the electric vehicle are determined through the user APP interface. The critical loads in the community are designated as Level 1+ loads, and their power supply must be prioritized under all circumstances. Energy storage batteries are designated as Level 4 loads. When electric vehicles are slow-charged, the charging load is Level 2 when the initial SOC is 0-30%; Level 3 when the initial SOC is 30-60%; and Level 4 when the initial SOC is 60-100%.

[0034] Meanwhile, car owners can upgrade their charging level through bidding, which will increase the charging price by λ (λ is 10% of the base charging price at this time), and the charging load will be upgraded by 1 level. Fast charging is defined as Level 2. At this point, the charging price is increased by λ, and the charging level is upgraded to Level 1.

[0035] The basic charging price is a real-time electricity price, defined by the electricity deficit at a certain moment. The basic charging price is divided into DC microgrid grid-connected charging price and off-grid charging price, where: Off-grid charging tariffs are defined by the imbalance between electricity load and renewable energy. When renewable energy generation is abundant, low tariffs encourage electric vehicle charging; conversely, when renewable energy is insufficient, high tariffs are implemented. Electricity load includes both critical loads within the community and electric vehicle charging loads.

[0036] In the formula, For electrical load, Renewable energy generation capacity configured for DC microgrids, Indicates the basic charging electricity price; The grid-connected charging tariff is defined by the imbalance between the electricity load and the microgrid input power. The electricity load is the electric vehicle charging load, and the input power includes the input power of the equipped renewable energy and the community's AC grid.

[0037] In the formula, It is the input power of the large power grid. For the community load, This is the charging load.

[0038] The charging electricity price for fast charging can be defined as: In the formula, For fast charging price, =1, 2, ... represents the number of adjacent DC charging modules that are below the fast charging level. The compensation coefficient is set at 0.8 yuan / kWh.

[0039] When multiple electric vehicles with the same charging level are present, they will take turns charging. The amount of electricity charged during each turn is defined as follows: like Figure 3 As shown, the smart switch has two input terminals, one positive and one negative, and has an output terminal with 1. + 1 - ,2 + 2 - , ..., 5 + 5 - Multiple output interfaces. Each output interface has m... + m - Each is connected to the corresponding charging gun m. Each DC charging module is adjacent to three surrounding DC charging modules, meaning that each electric vehicle can have up to five DC charging modules connected in parallel for fast charging.

[0040] The DC charging / discharging module, after receiving a V2V or V2G signal from the energy management module, communicates with the corresponding electric vehicle and transmits the vehicle's electricity to the DC bus. The energy management module then allocates this electricity to loads in urgent need of power, such as critical loads in residential areas. Simultaneously, it compensates electric vehicle owners who are willing to sell their electricity. This compensation can be defined as:

[0041] In the formula, This refers to the slow charging price for electric vehicles at this time. For compensation coefficient, This is the compensation coefficient for supplying power to critical loads during a power outage in the residential area.

[0042] like Figure 4 As shown, this application also proposes a charging and discharging method for a residential DC microgrid, which includes the following steps during grid connection: The load monitoring module monitors the available power input to the community, the remaining capacity of the energy storage battery, the actual power load, and the input power of the distributed generation equipment. The energy management module calculates the available power of the DC slow charging microgrid. If there is a surplus in photovoltaic power generation after meeting the charging power of electric vehicles, the surplus power is output through the PCS to a maximum of 100kW of the rated power of the grid-connected converter, while attracting users to charge through real-time electricity prices; if the photovoltaic power generation is still surplus, the excess power is used to charge the energy storage battery. If the SOC of the energy storage battery is greater than 0.9, photovoltaic power is curtailed; the input power of the community from the main grid is the community load minus the input power of the DC microgrid.

[0043] If the photovoltaic power generation capacity is insufficient to meet the electric vehicle charging capacity, the grid input power is the sum of the community load and the electric vehicle charging capacity. If the input power is at the transformer's upper limit, the energy storage battery discharges, and the energy management module disconnects lower-level loads according to the charging load level. If this still does not meet the charging demand, electric vehicles of the same priority are randomly selected for round-trip charging. When the energy storage battery's SOC is below 0.4%, the energy storage battery stops discharging and V2G and V2V electric vehicle charging are initiated.

[0044] In the event of a grid failure in the residential area or the main grid, critical loads in the residential area will be seamlessly switched to DC microgrid power supply. Under the control of the energy management module, the connection between the microgrid and the grid will be disconnected by an off-grid transfer switch. The energy storage battery will convert the DC power from the energy storage system into the voltage required by the DC microgrid through a DC / DC converter to supply the microgrid load for short periods.

[0045] like Figure 5 As shown, the off-grid DC microgrid operation control strategy is as follows: The system calculates the power deficit between renewable energy, charging load, and critical load in the community. If there is a power surplus, it issues electricity prices to attract users to charge, and excess power is used to charge the energy storage battery. Charging stops when the energy storage battery's SOC is greater than 0.9, and renewable energy is curtailed. If there is a power shortage, the energy storage battery discharges while issuing higher electricity prices to reduce charging load. Based on available power, it disconnects charging power for lower-level electric vehicles and implements a rotation charging mechanism for vehicles of the same level. When the energy storage battery's SOC is below 0.4, the energy management module issues V2V, V2G, and V2H requests to the user terminal app, and simultaneously disconnects all electric vehicle loads. When the response power exceeds the critical load in the community and the energy storage battery's SOC is below 0.4, excess power is used to charge the energy storage battery. When the SOC is above 0.6, the electricity price is reduced, decreasing the response power for V2V, V2H, and V2G.

[0046] The community DC microgrid charging system proposed in this application can also eliminate the need for onboard computer (OBC), thereby reducing the overall vehicle cost.

[0047] By utilizing the bidirectional power transmission characteristics of the charging network and the community power grid, the peak shaving and valley filling of the community power grid can be carried out in real time, and the remaining capacity of the community power grid can be used efficiently without increasing the capacity of the community power grid.

[0048] By interacting with the user terminal through the energy management module, the initiative of users to participate in peak shaving and valley filling is enhanced. At the same time, the utilization of electric vehicle loads is realized through V2V and V2H technologies as an additional power supply to ensure the normal power supply of important loads in the community.

[0049] The above-described embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any simple changes or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A community DC microgrid charging and discharging system, characterized in that, include: The charging and discharging module is used to charge and discharge electric vehicles based on the community load, the maximum available load of the community's external network, and the energy storage battery. Energy storage batteries are used to store the remaining capacity of the community load and to provide additional charging power for electric vehicles when the community experiences power outages or during peak charging periods. The load monitoring module is used to monitor the cell load and the maximum available load of the cell's external network, and transmit the monitored information to the energy management module. The energy management module is used to calculate the gap between renewable energy and charging load based on the community load and the maximum available load of the external grid. When renewable energy is in surplus, the surplus power is transmitted to the community's AC grid to charge electric vehicles according to charging priority. When renewable energy is insufficient, the power input from the main grid is used to make up for the community load gap and charge electric vehicles. When the main grid input power reaches its limit, the energy storage battery is discharged to charge electric vehicles. When there is a fault in the community grid or the main grid, the important loads of the community are switched to DC microgrid power supply, and the energy storage battery supplies the instantaneous demand power. By calculating the important loads of the community and the renewable energy gap, when the renewable energy demand power is in surplus, the surplus power is used to charge the energy storage battery; when the renewable energy demand power is insufficient, the energy storage battery is discharged. The energy management module includes a communication device. When the electric vehicle is connected to its charging / discharging interface, the communication device automatically communicates with the electric vehicle to obtain its battery information. Based on the obtained battery information, the module determines the electric vehicle owner's charging type and bidding intention through a user interface. It then prioritizes the charging type of the electric vehicle based on its charging type and bidding intention, giving priority to vehicles with higher charging levels, and simultaneously publishes real-time electricity prices to the user. The specific content of the priority classification is as follows: The community's critical loads are set as Level 1+ loads, and under any circumstances, the power supply to the community's critical loads must be prioritized; the energy storage batteries are set as Level 4 loads. When electric vehicles are slow-charged, the charging load is Level 2 when the initial SOC of the electric vehicle is 0~30%; and Level 3 when the initial SOC of the electric vehicle is 30~60%. When the initial SOC of an electric vehicle is 60-100%, the charging load is level 4. Meanwhile, vehicle owners can upgrade their charging level through bidding, increasing the charging load by 1 level based on the current charging price (λ). Here, λ is defined as 20% of the current charging price. The fast charging level is defined as level 2. When the charging level of the adjacent DC charging and discharging module is lower than this level, the DC charging and discharging module in parallel is used to give priority to fast charging. When the charging price of fast charging increases by λ, the fast charging level is upgraded to level 1. At this time, the DC charging and discharging modules that are lower than level 1 are connected in parallel to charge the electric vehicle. When multiple electric vehicles with the same charging level are present, a rotating charging mechanism is implemented, and the amount of electricity charged in each rotation is defined as follows: In the formula, For the rated capacity of electric vehicle batteries, This indicates the battery's state of charge.

2. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The energy management module is also used to transfer the electric vehicle's power to the DC bus when the DC charging module communicates with the corresponding electric vehicle after the communication device has established communication, and the user is not using the vehicle and is willing to discharge power. The energy management module then allocates the power to the charging / discharging interfaces of electric vehicles that urgently need power or to other electrical loads, realizing V2V, V2H, and V2G functions. The energy management module also provides compensation to users of electric vehicles who are willing to sell their electricity, with the compensation price defined as follows: In the formula, This is the basic charging electricity price for electric vehicles at that time. For compensation coefficient, The compensation coefficient for supplying power to critical loads during a power outage in the residential area; The basic charging tariff includes the charging tariff for DC microgrids operating in grid-connected mode and the charging tariff for off-grid operation: The off-grid charging price is defined based on the imbalance between electricity load and renewable energy. When renewable energy generation is sufficient, the price is low to encourage electric vehicle charging, while the price is high when renewable energy is insufficient. The electricity load includes both critical loads in the community and electric vehicle charging loads. In the formula, For electrical load, Renewable energy generation capacity configured for DC microgrids Indicates the basic charging electricity price; The grid-connected charging electricity price is defined based on the imbalance between the electricity load and the microgrid's input power. The electricity load is the electric vehicle charging load, and the input power includes the power supplied by the renewable energy source and the available input power from the community's AC grid. In the formula, It is the input power of the large power grid. For the load of the community, This is the charging load.

3. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The charging and discharging module includes an intelligent switching switch. The intelligent switching switch is used to provide charging power to the corresponding electric vehicle charging and discharging interface when a single DC charging and discharging module is working normally; or when the electric vehicle of the DC charging module has a fast charging requirement and the adjacent DC charging module has no charging requirement or a low charging level, the charging price for fast charging is calculated based on the number of charging modules called. After the car owner agrees to the bidding intention based on the calculated fast charging price, the communication device controls the output terminal of the intelligent switching switch to switch to the output interface corresponding to the charging vehicle that needs fast charging to meet the fast charging requirement. The electricity price for fast charging is defined as follows: In the formula, For fast charging price, For this time, slow charging price, =1, 2, ... represents the number of adjacent DC charging modules currently in operation. The compensation coefficient; Alternatively, it can be used to switch adjacent DC charging modules to participate in charging when a single DC charging module fails.

4. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The charging and discharging module also includes a multi-energy input interface connected to the DC bus. The multi-energy input interface includes hydrogen energy, wind power, and photovoltaic power, which is used to convert the input power into a voltage level that matches the DC bus to increase the power capacity of the community.

5. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The energy storage battery is connected to the DC bus via a bidirectional DC / DC converter, the capacity of which is the same as that of the bidirectional PCS. The bidirectional DC / DC converter also includes an extended interface for increasing the capacity of the energy storage battery when other energy sources are connected later. To address the uncertainty of renewable energy sources, during grid connection, when there is a power surplus from renewable energy, power is preferentially supplied to the community's AC microgrid via the bidirectional PCS, with excess power used to charge the energy storage battery. When the energy storage battery's SOC exceeds 0.9%, renewable energy is curtailed. Simultaneously, the energy storage battery provides power during peak charging periods. The system provides additional charging power to multiple DC charging modules to provide DC fast charging services for electric vehicles. When the SOC of the energy storage battery is below 0.4, the energy storage battery stops discharging. When off-grid, after renewable energy supplies electric vehicles and important loads in the community, the surplus power is used to charge the energy storage battery. If the power is insufficient, the energy storage battery discharges. If the SOC of the energy storage battery is below 0.1, the energy storage battery stops discharging. When responding to excess important loads in the community and the SOC of the energy storage battery is below 0.2, the surplus power is used to charge the energy storage battery. When the SOC is above 0.4, the electricity price is reduced, and the power of V2V, V2H, and V2G is reduced.

6. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The charging and discharging module also includes a transfer switch, which is installed at the critical loads of the community. When the community is powered normally, it uses the community's AC grid for power supply. When the community encounters a power shortage or external equipment failure and cannot supply power normally, it seamlessly switches to DC microgrid power supply. At the same time, it converts the DC power into an electrical energy form suitable for the community's AC loads via DC / AC conversion. The power conversion process is unidirectional, from the DC source to the AC load, ensuring that the supply of critical loads in the community is met.

7. The community DC microgrid charging and discharging system as described in claim 1, characterized in that, The energy management module is also used to prioritize electric vehicles according to their charging type and bidding willingness, randomly select electric vehicles of the same charging level and publish the charging data in turn; the energy management module is communicatively connected to a user terminal App, and the energy management module is used to receive charging requests from the user terminal App and send data feedback to the user terminal App, including charging price, charging completion time, and V2V and V2H requests from electric vehicles.

8. The community DC microgrid charging and discharging system as described in claim 3, characterized in that, The intelligent switching switch has two input terminals, one positive and one negative, and multiple output interfaces, 1+, 1-, ..., m+, m-, ..., n+, n-. Under normal power supply, each of the output interfaces m+ and m- is connected to the corresponding electric vehicle charging / discharging interface m. When there is a fast charging demand at the m electric vehicle charging / discharging interfaces or when the DC charging / discharging module m fails, the adjacent intelligent switching switch switches to m+ and m-. When the electric vehicle has a discharging demand and the adjacent DC charging / discharging module is idle, the adjacent intelligent switching switch switches to the electric vehicle charging / discharging interface corresponding to the electric vehicle that needs to be discharged, so that the electric vehicle outputs power multiple times the capacity of the DC charging / discharging module.

9. A method for charging and discharging a residential DC microgrid, applied to the residential DC microgrid charging and discharging system as described in any one of claims 1-8, characterized in that, Includes the following steps: The load monitoring module monitors the community load and the maximum available load of the external network. The energy management module calculates the deficit between renewable energy and charging load based on the community load and the maximum available load of the external network. When there is a surplus of renewable energy, the surplus power is transmitted to the community's AC grid and electric vehicles are charged according to charging priority. When renewable energy is insufficient, the power input from the main power grid is used to make up for the load shortfall in the community to charge electric vehicles; when the power input from the main power grid reaches its limit, the energy storage battery is discharged to charge electric vehicles. When the community's power grid or the main power grid fails, the community's critical loads are switched to DC microgrid power supply, and the energy storage battery supplies the instantaneous power demand. By calculating the critical loads and the shortage of renewable energy, when there is a surplus of renewable energy demand, the surplus power is used to charge the energy storage battery; when there is a shortage of renewable energy demand, the energy storage battery is discharged.

Images