A method and system for coordinated charging and discharging of electric vehicles based on energy storage areas

Abstract

This invention proposes a method and system for coordinated charging and discharging of electric vehicles based on energy storage substations. This method is used to solve the problems of transformer overload and three-phase load imbalance during charging and discharging. The core steps include: Step 1: The centralized controller acquires real-time substation operation data and uploads it to the cloud service controller for analysis; Step 2: Determines whether load imbalance and transformer overload exist; Step 3: When load imbalance and substation transformer overload are detected, a substation scheduling and control model is established to optimize the charging and discharging loads of energy storage batteries, AC charging piles, and DC charging piles; Step 4: Finds the optimal load switching scheme based on the model; Step 5: Evaluates the load balance improvement effect; If the load imbalance exceeds the adjustment range or exceeds the transformer load rate threshold, the DC charging pile can be connected to the 10kV incoming line via the second branch boost inverter where the inverter is located.

Description

Technical Field

[0001] This application belongs to the field of electric vehicle and energy storage technology, and in particular relates to a method and system for coordinated control of electric vehicle charging and discharging based on energy storage substations. Background Technology

[0002] With electric vehicle loads widely connected to distribution transformer areas for charging and discharging, in order to smooth load fluctuations and improve power supply reliability, energy storage units (such as lithium battery energy storage systems) are also gradually connected to distribution transformer areas, forming a new power distribution scenario of "electric vehicle-energy storage" coordinated operation.

[0003] However, in this scenario, the distribution transformer area is facing severe operational challenges: On the one hand, the charging and discharging of electric vehicles has significant spatiotemporal randomness and power concentration. When a large number of electric vehicles are charging at the same time, the instantaneous load of the distribution transformer can exceed the rated capacity threshold, causing a sudden rise in winding temperature, accelerated insulation aging, and even overload tripping accidents. On the other hand, the disorder of the three-phase access of charging piles causes the three-phase load imbalance in the transformer area to generally exceed the imbalance threshold. The resulting negative sequence current increases line losses, reduces the transformer's load-carrying capacity, and interferes with the normal operation of sensitive equipment in the transformer area.

[0004] In existing technologies, single charging pile scheduling or energy storage control strategies are insufficient to address the synergistic optimization requirements of "electric vehicle-energy storage" composite systems. For example, load adjustment solely through phase switching of charging piles cannot fully utilize the flexible adjustment capabilities of energy storage; while independent energy storage charging and discharging control struggles to balance the charging needs of electric vehicle users with grid operation constraints. Therefore, how to construct a synergistic control system that integrates the charging and discharging behavior of electric vehicles with the dynamic adjustment of energy storage units to achieve precise load balancing in distribution areas and effective management of transformer loads has become a critical technical problem urgently needing to be solved in the current field of smart distribution networks. Summary of the Invention

[0005] The main objective of this invention is to propose a method for coordinated control of electric vehicle charging and discharging in a power distribution substation based on energy storage. This method is used to solve the problems of transformer overload and three-phase load imbalance during charging and discharging. By optimizing the power supply structure and control method, the method expands the regulation capability of unbalanced loads in the substation.

[0006] The power distribution structure for implementing the control method includes: a 10kV ring network incoming line, a distribution transformer, AC loads, DC loads, energy storage batteries, inverters, a switch network, a centralized controller, a cloud service controller, and n DC charging piles and m AC charging piles; the 10kV incoming line is stepped down by the distribution transformer and then connected to the AC bus. The AC bus is connected to the AC loads, the rectifier is connected to the DC loads, and the bidirectional AC / DC converter is connected to the energy storage batteries. The AC bus is connected to multiple charging piles through the first switch network. Each DC charging pile is also directly connected to the 10kV incoming line through the inverter and the second switch network, providing two power supply paths: one is to step down the voltage through the transformer and then charge and discharge the charging piles through the first switch network; the other is to step up the voltage through the inverter and then connect to the 10kV incoming line through the second switch network for charging and discharging. The first switch network and the second switch network allow for selection of the incoming phase lines.

[0007] The method includes the following steps:

[0008] Step 1: The centralized controller acquires the operating data of the distribution area in real time and uploads it to the cloud service controller for analysis, including the SOC status of the energy storage unit, the operating status of AC and DC charging piles, and the status of the charging and discharging piles connected to the three phases respectively.

[0009] Step 2: Calculate the unbalance degree and transformer load rate based on the acquired data, and determine whether there is load imbalance or transformer overload;

[0010] Step 3: When it is determined that there is a load imbalance and transformer overload, a dispatch control model for the distribution area is established. The charging and discharging of energy storage batteries, AC charging piles and DC charging piles are optimized and solved. The objective function in the model is to maximize the utilization rate of energy storage batteries and minimize the load transmission through the inverter directly connected to the 10kV line.

[0011] Step 4: Find the optimal load switching scheme based on the model; prioritize load switching through the first switching network to achieve load balance; if the load imbalance exceeds the adjustment range or the transformer load rate threshold, the DC charging pile can be connected to the 10kV incoming line through the second branch where the inverter is located; at the same time, control the energy storage battery to discharge; the charging and discharging power of the energy storage battery is adjusted according to the overload of the transformer and the remaining capacity of the energy storage battery.

[0012] Step 5: Evaluate the load balance improvement effect. Evaluation indicators include: load balance improvement rate, transformer load rate reduction, and energy storage battery utilization rate. If the load balance improvement effect does not meet the standards, repeat steps 1-4.

[0013] The objective function established in step 3 is based on the principle of maximizing energy storage battery utilization and minimizing load transmission through direct connection of the inverter to the 10kV line. Its expression is:

[0014]

[0015] Where w1 and w2 are weighting coefficients, This represents the total number of DC charging piles connected to the 10kV incoming line via the second switch network. The formula for calculating the utilization rate of energy storage batteries is as follows:

[0016]

[0017] in, The charging and discharging power of the energy storage battery, The maximum charge and discharge power of the energy storage battery is T, and the statistical period is T.

[0018] Step 4 includes finding the optimal load switching scheme, including adjusting the phase line connected to each charging pile, the charging and discharging strategy of the energy storage battery, and whether to enable the inverter to connect to the 10kV incoming line.

[0019] Step 4 includes: according to the optimal load switching scheme, load switching is first performed through the first switching network. According to the phase switching matrix of AC charging piles and DC charging piles, the corresponding charging piles are switched to the optimal phase line to achieve initial load balance. If the load imbalance still exceeds the adjustment range or the transformer load rate exceeds the threshold after the load switching through the first switching network, the second branch adjustment of the DC charging pile is started. The DC charging pile is controlled to be connected to the 10kV ring network incoming line through the second branch where the inverter is located. By adjusting the charging and discharging power and phase selection of the DC charging pile, the adjustment capability of the unbalanced load in the distribution area is further expanded.

[0020] Step 2 includes: setting an overload threshold for the transformer; when the transformer load rate is detected to be close to or exceed the threshold, activating the transformer overload control strategy; for AC charging piles, the centralized controller limits the charging power of some AC charging piles according to the overload level and a set ratio, prioritizing the limitation of charging pile power for non-emergency charging vehicles; for DC charging piles, depending on the actual situation, some DC charging piles are switched to power supply via a second switch network connected to the 10kV incoming line to reduce the transformer load; simultaneously, the energy storage battery is controlled to discharge, providing some energy to the charging piles; the discharge power of the energy storage battery is reasonably adjusted according to the transformer overload level and the remaining capacity of the energy storage battery.

[0021] During off-peak hours, the energy storage battery is charged from the grid while prioritizing the charging needs of electric vehicles; when the charging demand of electric vehicles is low, the energy storage battery is fully charged for use during peak hours.

[0022] During peak grid hours, when electricity prices are high and transformers are prone to overload, energy storage batteries discharge to provide energy for charging electric vehicles, reducing dependence on the grid and lowering the load on transformers.

[0023] When a three-phase load imbalance occurs in the distribution area, the energy storage battery charges and discharges on the corresponding phases according to the three-phase load conditions to help adjust the three-phase load balance.

[0024] The formula for calculating the unbalance ε is:

[0025]

[0026] in, These are the total currents of phases A, B, and C of the transformer in the distribution area;

[0027] The formula for calculating the load rate of a transformer substation is:

[0028]

[0029] in, The total active power of the system includes the active power of AC loads, DC loads, AC charging piles, and DC charging piles through the first switching network; The charging and discharging power of the energy storage battery; This represents the total reactive power of the system. This refers to the rated capacity of the distribution transformer.

[0030] In step 5, the formula for calculating the load balance improvement rate is:

[0031]

[0032] in, The initial imbalance, The imbalance after coordinated control;

[0033] The formula for the reduction in transformer load rate is: ;in, This represents the initial transformer load rate. The transformer load rate is controlled in a coordinated manner.

[0034] A collaborative control system for electric vehicle charging and discharging based on an energy storage substation is also proposed. This system includes: a 10kV ring network incoming line, a distribution transformer, AC loads, DC loads, an energy storage battery, an inverter, a switch network, a centralized controller, a cloud service controller, and n DC charging piles and m AC charging piles. The 10kV incoming line is stepped down by the distribution transformer and then connected to an AC bus. The AC bus is connected to the AC loads, a rectifier is connected to the DC loads, and a bidirectional AC / DC converter is connected to the energy storage battery. The AC bus is connected to multiple charging piles through a first switch network, and each DC charging pile is also directly connected to the 10kV incoming line through an inverter and a second switch network. This collaborative control system is used to implement the steps of the aforementioned collaborative control method for electric vehicle charging and discharging based on an energy storage substation.

[0035] The invention also proposes a program storing a method for coordinated charging and discharging of electric vehicles based on energy storage areas on a computer-readable storage medium, wherein when the program is executed by a processor, it implements the steps of the method for coordinated charging and discharging of electric vehicles based on energy storage areas.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The power supply structure and load adjustment method of the distribution area have been optimized, so that the charging piles have two power supply paths. One is to step down the voltage through the transformer and then charge and discharge the charging piles through the first switching network. The other is to step up the voltage through the inverter and then connect to the 10kV incoming line for charging and discharging through the second switching network. In addition, the first and second switching networks can select the incoming phase lines, which expands the regulation capability and regulation depth of the distribution area, and realizes the coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles under the distribution area.

[0038] 2. By adjusting the charging and discharging power of the charging pile and coordinating the discharge of the energy storage battery, the load on the transformer can be reduced in time when the load is too high, avoiding overload operation of the transformer, improving the service life of the transformer and the reliability of power supply;

[0039] 3. By utilizing the phase selection function of the switching network and the adjustment of the charging pile power, combined with the three-phase coordinated adjustment of the energy storage battery, the three-phase load of the distribution area can be effectively balanced, the imbalance of the three-phase current can be reduced, and the power quality of the distribution system can be improved.

[0040] 4. Achieve coordinated and orderly charging and discharging of electric vehicles. Through the coordinated control of the centralized controller and the cloud service controller, coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles is realized, which improves charging efficiency, meets the charging needs of users, and optimizes the operation of the power distribution system.

[0041] 5. Improve the flexibility and adaptability of the system. The DC charging pile has two power supply paths, which can flexibly select the power supply mode according to the actual situation. The energy storage battery can also adjust the charging and discharging according to the system requirements, making the whole system highly flexible and adaptable, and able to cope with different power consumption scenarios and load changes.

[0042] 6. It has good economic efficiency. By using energy storage batteries to charge during off-peak hours and discharge during peak hours, it can reduce users' charging costs and also reduce the need for grid expansion, thus having good economic efficiency. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of a power supply structure for a transformer substation based on an inverter and a switching network, according to an embodiment of the present invention.

[0045] Figure 2 This is a schematic diagram of a power supply structure for a transformer substation based on an inverter and multiple switch networks, according to an embodiment of the present invention.

[0046] Figure 3 This is a schematic diagram of a power supply structure for a transformer substation, including an AC bus and an AC charging pile, according to an embodiment of the present invention.

[0047] Figure 4 This is a schematic diagram of the steps of the electric vehicle charging and discharging coordinated control method in an embodiment of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this invention, and should not be construed as limiting the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0049] Example 1

[0050] A method for coordinated charging and discharging of electric vehicles in a distribution substation based on energy storage is proposed. This method is used to solve the problems of transformer overload and three-phase load imbalance during charging and discharging, and realizes coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles in the distribution substation.

[0051] As attached Figure 1-3 The power supply structure of the transformer substation shown, and the power distribution structure implementing the control method described, includes: a 10kV incoming line, a distribution transformer, AC loads, DC loads, energy storage batteries, inverters, a switch network, a centralized controller, a cloud service controller, and n DC charging piles and m AC charging piles. The 10kV incoming line is stepped down by the distribution transformer and then connected to the AC bus. The AC bus is connected to the AC loads, the rectifier is connected to the DC loads, and the bidirectional AC / DC converter is connected to the energy storage batteries. The AC bus is connected to multiple charging piles through the first switch network. Each DC charging pile is also directly connected to the 10kV incoming line through the inverter and the second switch network, providing two power supply paths: one is to step down the voltage through the transformer and then charge and discharge the charging pile through the first switch network; the other is to step up the voltage through the inverter and then connect to the 10kV incoming line through the second switch network for charging and discharging. The first and second switch networks allow for selection of the incoming phase, meaning that each charging pile can switch to any one of the three phases (A, B, C).

[0052] like Figure 4 As shown, the method includes the following steps:

[0053] Step 1: The centralized controller acquires the operating data of the distribution area in real time and uploads it to the cloud service controller for analysis, including the SOC status of the energy storage unit, the operating status of AC and DC charging piles, the status of the charging and discharging piles connected to the three phases respectively, and other loads included in the three phases respectively;

[0054] Step 2: Calculate the unbalance degree and transformer load rate based on the acquired data, and determine whether there is load imbalance or transformer overload;

[0055] Step 3: When it is determined that there is a load imbalance and transformer overload, a dispatch control model for the distribution area is established. The charging and discharging of energy storage batteries, AC charging piles and DC charging piles are optimized and solved. The objective function in the model is to maximize the utilization rate of energy storage batteries and minimize the load transmission through the inverter directly connected to the 10kV line.

[0056] Step 4: Find the optimal load switching scheme based on the model; then, according to the scheme, switch the load through the first switching network to achieve load balance. If the load imbalance exceeds the adjustment range or exceeds the transformer load rate threshold, the DC charging pile can be connected to the 10kV incoming line through the second branch where the inverter is located, thereby expanding the adjustment capability of the unbalanced load in the distribution area.

[0057] Step 5: Evaluate the load balance improvement effect. Evaluation indicators include: load balance improvement rate, transformer load rate reduction, and energy storage battery utilization rate. If the load balance improvement effect does not meet the standards, repeat steps 1-4.

[0058] Example 2

[0059] In this embodiment, each DC charging station has two charging and discharging paths:

[0060] Step-down charging / discharging path: The voltage is stepped down by a transformer and then passed through the first switching network to charge and discharge the charging pile. This path utilizes the existing power distribution system structure to provide a stable power supply to the charging pile under normal load conditions.

[0061] Boost inverter charging and discharging path: The voltage is boosted by the inverter and then connected to the 10kV incoming line via the second switching network for charging and discharging. Under special operating conditions, such as severe load imbalance in the distribution area or transformer overload, this path can directly obtain or transmit electrical energy from the high-voltage side, enhancing system flexibility.

[0062] Meanwhile, the switch network phase selection function is available in both the first and second switch networks, allowing each charging pile to switch to any one of the three phases (A, B, and C). This provides the hardware foundation for achieving three-phase load balancing and allows for flexible allocation of charging load to different phases based on real-time load conditions.

[0063] Based on the above power distribution structure, a coordinated control method for charging and discharging electric vehicles is derived:

[0064] Step 1: Data Acquisition and Upload;

[0065] The centralized controller collects real-time operational data from the distribution areas, including the state of charge (SOC) of the energy storage units, the operational status of AC and DC charging piles (such as charging power, charging current, and charging status), the number and power of charging and discharging piles connected to each of the three phases, and other loads connected to each phase (such as residential and commercial electricity). The collected data is then uploaded to the cloud service controller for centralized analysis and processing. The cloud service controller possesses powerful data storage and computing capabilities, enabling comprehensive analysis of data from multiple distribution areas.

[0066] Step 2: Calculation and judgment of imbalance and load rate;

[0067] Calculating unbalance: Based on three-phase current or power data, the three-phase load unbalance of the transformer substation is calculated using standard unbalance calculation formulas. For example, the negative sequence current method can be used to calculate the unbalance, which measures the degree of unbalance by calculating the ratio of negative sequence current to positive sequence current.

[0068] Calculate the transformer load rate: Compare the total load of the distribution area (including electric vehicle charging load and other loads) with the rated capacity of the transformer to obtain the transformer load rate. Load rate = Total load of distribution area / Rated capacity of transformer × 100%. Identify abnormal situations: Compare the calculated unbalance and load rate with preset thresholds. If the unbalance exceeds the specified range (e.g., the national standard stipulates a three-phase voltage unbalance limit of 2%, which should not exceed 4% for short periods), a load imbalance problem is identified; if the load rate exceeds the transformer's rated load rate threshold (generally 80%-90%), a transformer overload problem is identified.

[0069] Step 3: Establish a dispatch and control model for the distribution area;

[0070] Construct the objective function: (1) Maximize the utilization rate of the energy storage battery, aiming to maximize the number of charge-discharge cycles and the depth of charge-discharge of the energy storage battery, give full play to the regulating role of the energy storage battery, extend its service life and improve economic benefits. The energy storage battery can be operated efficiently under different working conditions by optimizing the charge-discharge power and SOC of the energy storage battery. (2) Minimize the transmission of load through direct connection of the inverter to the 10kV line: Minimize the situation of load transmission through direct connection of the inverter to the 10kV incoming line, because there is energy loss in the inverter conversion process. This path is only used when the load in the distribution area is severely unbalanced or the transformer is overloaded and cannot be effectively regulated by other means.

[0071] Setting constraints: (1) Energy storage battery constraints, including the charging and discharging power limits of energy storage batteries, SOC upper and lower limits, etc. For example, the charging power of energy storage batteries cannot exceed their rated charging power, and the discharging power cannot exceed their rated discharging power; SOC needs to be kept within a certain range, such as 20%-80%, to ensure battery life and system stability. (2) Charging pile constraints: The charging and discharging power of AC charging piles and DC charging piles should be within their rated power range and meet the user's charging needs and time requirements. At the same time, the start-stop frequency limit of charging piles should be considered to avoid damage to equipment caused by frequent start-stop. (3) Power grid constraints: The three-phase voltage imbalance of the distribution area needs to be controlled within the specified range to ensure power quality; the current of each phase of the transformer cannot exceed its rated current to prevent the transformer from overheating and being damaged.

[0072] Step 4: Load switching and adjustment;

[0073] Finding the optimal load switching scheme: Utilizing optimization algorithms (such as genetic algorithms and particle swarm optimization) to solve the distribution area dispatch control model, the goal is to find the load switching scheme that optimizes the objective function. This scheme should include decisions such as adjusting the phase lines connected to each charging pile, the charging and discharging strategies of the energy storage batteries, and whether to enable the inverter to connect to the 10kV incoming line.

[0074] Load switching implementation: Based on the determined optimal load switching scheme, the access phase lines of the charging piles are switched through the first switching network to achieve a redistribution of the three-phase load and thus achieve load balance. For example, some loads are switched from overloaded phases to lightly loaded phases, making the three-phase loads more balanced.

[0075] Expanding regulation capacity: If the load imbalance still exceeds the regulation range or the transformer load rate continues to exceed the threshold after load switching, the DC charging pile is connected to the 10kV incoming line through the second branch where the inverter is located, and directly obtains or transmits power from the high-voltage side, thereby further expanding the regulation capacity of the unbalanced load in the distribution area and ensuring the stable operation of the distribution area.

[0076] Example 3

[0077] The power distribution structure involved in this technical solution mainly includes a 10kV incoming line, a distribution transformer, AC loads, DC loads, energy storage batteries, inverters, a switch network, a centralized controller, a cloud service controller, and n DC charging piles and m AC charging piles. The specific connection relationships are as follows:

[0078] The 10kV incoming line is stepped down by a distribution transformer and then connected to the AC bus. The AC bus is connected to AC loads, a rectifier connects to DC loads, and a bidirectional AC / DC converter connects to energy storage batteries. The AC bus connects to multiple charging piles via a first switching network. Each DC charging pile is also directly connected to the 10kV incoming line via an inverter and a second switching network. There are two power supply paths: one is to step down the voltage through the transformer and then charge / discharge the charging piles via the first switching network; the other is to step up the voltage through the inverter and then connect to the 10kV incoming line via the second switching network for charging / discharging. Furthermore, the first and second switching networks allow for phase selection, meaning each charging station can switch between any one of the three phases (A, B, and C).

[0079] This technical solution constructs a collaborative control framework centered on a centralized controller and a cloud service controller. The centralized controller monitors the load of the distribution transformer, the three-phase load balance, and the status of the energy storage battery in real time, while simultaneously managing the phase selection of the first and second switching networks. For AC charging piles, they are connected to the AC bus via the first switching network, and the centralized controller adjusts their charging and discharging power according to the transformer load. For DC charging piles, power can be flexibly supplied via the first switching network after voltage reduction by the transformer, or directly connected to the 10kV incoming line via the second switching network after voltage boosting by the inverter. Meanwhile, the energy storage battery participates in load regulation through a bidirectional AC / DC converter to address transformer overload and three-phase load imbalance issues. The cloud service controller collects data uploaded by the centralized controller, performs big data analysis and optimization calculations, generates long-term charging and discharging optimization strategies, and distributes them to the centralized controller for execution, achieving optimized management of the charging and discharging process throughout the entire distribution area.

[0080] Develop specific control strategies:

[0081] (1) Data acquisition and processing

[0082] The centralized controller collects real-time operating data from various devices within the distribution substation area, including transformer input and output voltage, current, and load rate; amplitude and phase of three-phase voltage and current; charging and discharging power and status of each charging pile; and terminal voltage, charging and discharging current, and remaining capacity of energy storage batteries. The collected data undergoes preprocessing such as filtering and noise reduction before being transmitted to the cloud service controller for storage and further analysis, providing accurate data support for subsequent control strategies.

[0083] (2) Transformer overload control

[0084] Set an overload threshold for the transformer. When the transformer load rate is detected to be close to or exceed this threshold, activate the transformer overload control strategy. Specific measures are as follows:

[0085] For AC charging piles, the centralized controller limits the charging power of some AC charging piles according to the overload level and a set ratio, giving priority to limiting the charging power of charging piles for non-emergency charging vehicles.

[0086] For DC charging piles, depending on the actual situation, some DC charging piles can be switched to be powered by the 10kV incoming line connected through the second switch network to reduce the load on the transformer.

[0087] Simultaneously, the energy storage battery is controlled to discharge, providing some energy to the charging pile and relieving the load on the transformer. The discharge power of the energy storage battery is adjusted reasonably according to the overload level of the transformer and the remaining capacity of the energy storage battery.

[0088] (3) Three-phase load balance control

[0089] The standard for determining three-phase load balance is usually based on the goal that the imbalance of the three-phase current does not exceed a specified value. When the imbalance of the three-phase load is detected to exceed the standard, the following measures are taken to achieve balance:

[0090] The phase lines of each charging pile are reselected by the first and second switching networks, and the charging piles are assigned to different phase lines to adjust the load distribution of each phase.

[0091] For both AC and DC charging piles (when powered through the first switching network), the centralized controller adjusts their charging and discharging power to balance the power of each phase as much as possible. For example, for a phase with a heavier load, the charging power of some charging piles on that phase is reduced or the discharging power is increased; for a phase with a lighter load, the charging power of the charging piles on that phase is appropriately increased.

[0092] The energy storage battery also participates in the three-phase load balancing regulation. According to the load conditions of each phase, the energy storage battery is controlled to charge and discharge on the corresponding phase in order to balance the three-phase load.

[0093] (4) Cooperative control of energy storage batteries

[0094] Define the charging and discharging strategy of the energy storage battery to coordinate with the charging and discharging of the charging pile. Specifically:

[0095] During off-peak hours when electricity prices are low, the energy storage battery is charged from the grid, prioritizing the charging needs of electric vehicles. When electric vehicle charging demand is low, the energy storage battery is fully charged for use during peak hours.

[0096] During peak grid hours, when electricity prices are high and transformers are prone to overload, energy storage batteries discharge to provide energy for charging electric vehicles, reducing dependence on the grid and lowering the load on transformers.

[0097] When a three-phase load imbalance occurs in the distribution area, the energy storage battery charges and discharges on the corresponding phases according to the three-phase load conditions to help adjust the three-phase load balance.

[0098] The charging and discharging process of energy storage batteries also needs to take into account factors such as their remaining capacity and lifespan, and formulate reasonable charging and discharging depths and cycle counts in order to extend the service life of energy storage batteries.

[0099] The specific implementation steps include: (1) System initialization, initializing the centralized controller, cloud service controller, various switch networks, charging piles, energy storage batteries and other equipment, including parameter configuration, communication connection establishment, etc. Set control parameters such as transformer overload threshold and three-phase load imbalance standard.

[0100] (2) Real-time data acquisition: The centralized controller collects the operating data of each device in the distribution area in real time according to the set sampling frequency, as described above.

[0101] (3) Data analysis and judgment: The centralized controller performs preliminary analysis on the collected data to determine whether the transformer is overloaded and whether the three-phase load is unbalanced. At the same time, the data is transmitted to the cloud service controller, which performs more in-depth data analysis and optimization calculations to generate long-term charging and discharging optimization strategies.

[0102] (4) Execute control strategies. Based on the results of data analysis and judgment, the centralized controller executes the corresponding control strategies. For example, when the transformer is overloaded, the overload control strategy is executed; when the three-phase load is unbalanced, the three-phase load balancing control strategy is executed; at the same time, according to the energy storage battery collaborative control strategy, the charging and discharging of the energy storage battery and its collaborative operation with the charging pile are controlled.

[0103] (5) Effect evaluation and strategy optimization: Evaluate the effectiveness of the control strategy, and check whether the transformer load has been reduced to a safe range and whether the three-phase load imbalance has been reduced to within the standard. Based on the evaluation results, the cloud service controller optimizes the control strategy to continuously improve the system's operating efficiency and stability.

[0104] The technical solution of this embodiment can effectively solve the transformer overload problem. By adjusting the charging and discharging power of the charging pile and coordinating the discharge of the energy storage battery, the load on the transformer can be reduced in time when the load is too high, avoiding overload operation of the transformer, and improving the service life of the transformer and the reliability of power supply.

[0105] It can also significantly improve three-phase load imbalance. By utilizing the phase selection function of the switching network and the adjustment of the charging pile power, combined with the three-phase coordinated adjustment of the energy storage battery, it can effectively balance the three-phase load of the distribution area, reduce the imbalance of the three-phase current, and improve the power quality of the distribution system.

[0106] It can also achieve coordinated and orderly charging and discharging of electric vehicles. Through the coordinated control of the centralized controller and the cloud service controller, it realizes coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles, which improves charging efficiency, meets users' charging needs, and optimizes the operation of the power distribution system.

[0107] It can also improve the flexibility and adaptability of the system. The DC charging pile has two power supply paths, and the power supply mode can be flexibly selected according to the actual situation. The energy storage battery can also be charged and discharged according to the system requirements, making the whole system highly flexible and adaptable, and able to cope with different power consumption scenarios and load changes.

[0108] At the same time, it has good economic efficiency. By using energy storage batteries to charge during off-peak hours and discharge during peak hours, it can reduce users' charging costs and also reduce the need for grid expansion, thus having good economic efficiency.

[0109] Example 4

[0110] The power distribution structure involved in this technical solution mainly includes a 10kV incoming line, a distribution transformer, AC loads, DC loads, energy storage batteries, inverters, a switch network, a centralized controller, a cloud service controller, and n DC charging piles and m AC charging piles. The specific connection relationships are as follows:

[0111] The 10kV incoming line is stepped down by a distribution transformer and then connected to the AC bus. The AC bus is connected to AC loads, a rectifier connects to DC loads, and a bidirectional AC / DC converter connects to energy storage batteries. The AC bus connects to multiple charging piles via a first switching network. Each DC charging pile is also directly connected to the 10kV incoming line via an inverter and a second switching network. There are two power supply paths: one is to step down the voltage through the transformer and then charge / discharge the charging piles via the first switching network; the other is to step up the voltage through the inverter and then connect to the 10kV incoming line via the second switching network for charging / discharging. Furthermore, the first and second switching networks allow for phase selection, meaning each charging station can switch between any one of the three phases (A, B, and C).

[0112] The steps of the electric vehicle charging and discharging coordinated control method based on the above power distribution structure include:

[0113] Step 1: Data Collection and Upload

[0114] The centralized controller, as the core device for data acquisition, obtains real-time operating data from various devices within the distribution area. This data forms the basis for subsequent analysis and control. Specific data collected includes: Energy storage unit status: Real-time monitoring of the remaining capacity (SOC) of the energy storage batteries, a key parameter for assessing battery availability. Charging pile operation status: Obtaining the operating status of AC and DC charging piles, such as whether they are charging / discharging and the charging / discharging power. Charging pile connection status: Recording the number and distribution of charging / discharging piles connected to each of the three phases, clarifying the load source for each phase. Other load information: Understanding the other loads included in each of the three phases, such as the size and distribution of conventional loads like residential and commercial electricity consumption.

[0115] The centralized controller performs preliminary processing on the collected real-time operational data before uploading it to the cloud service controller. The cloud service controller possesses powerful data storage and analysis capabilities, enabling in-depth analysis of the uploaded data and providing strong support for subsequent decision-making.

[0116] Step 2: Calculation and judgment of imbalance and load rate:

[0117] (1) Calculation of unbalance

[0118] Three-phase load unbalance is an important indicator for measuring the balance of three-phase loads in a power distribution system. This scheme uses a current-based unbalance calculation method, and the specific steps are as follows:

[0119] First, calculate the total current for each phase. For each phase (A, B, C) in a three-phase system, the total current includes the current of the AC charging pile on that phase, the current of the DC charging pile connected to that phase through the first switching network, the current of other conventional loads, and the charging and discharging current of the energy storage battery in that phase.

[0120] Then, the unbalance is calculated based on the total current of each phase. The formula for calculating the unbalance ε is:

[0121]

[0122] in, These are the total currents of phases A, B, and C, respectively.

[0123] (2) Calculation of transformer load rate

[0124] Transformer load factor is a key parameter for evaluating the operating status of a transformer, and its calculation formula is as follows:

[0125]

[0126] in, The total active power of the system includes the active power of AC loads, DC loads, AC charging piles, and DC charging piles through the first switching network; The charging and discharging power of the energy storage battery (positive value for discharging, negative value for charging). This represents the total reactive power of the system. This refers to the rated capacity of the distribution transformer.

[0127] (3) Determine whether there is load imbalance and transformer overload, and set an imbalance threshold. ) and transformer load rate threshold ( When the calculated unbalance ε ≥ When the transformer load factor λ ≥ 1, it is determined that there is a load imbalance problem; At that time, it was determined that there was a transformer overload problem.

[0128] Step 3: Establish a scheduling control model and optimize the solution.

[0129] When load imbalance and transformer overload are detected, a dispatch control model for the distribution area is established to optimize the charging and discharging of energy storage batteries, AC charging piles, and DC charging piles.

[0130] (1) Construct the objective function

[0131] The objective function of this model aims to maximize the utilization rate of energy storage batteries and minimize the load transmission rate via direct connection to the 10kV line through the inverter. The specific expression is as follows:

[0132]

[0133] Among them, w1 and w2 are weighting coefficients used to balance the importance of the two objectives;

[0134] The formula for calculating the utilization rate of energy storage batteries is as follows:

[0135]

[0136] in, The charging and discharging power of the energy storage battery, The maximum charge and discharge power of the energy storage battery is T, and the statistical period is T. This indicates the degree to which energy storage batteries are not utilized; minimizing this value means pursuing the highest utilization rate of energy storage batteries. This represents the total number of DC charging piles connected to the 10kV incoming line through the second switch network. Minimizing this value achieves the goal of minimizing the load transmission through the inverter directly connected to the 10kV line.

[0137] (2) Constructing decision variables

[0138] The model's decision variables include: the charging and discharging power of the energy storage battery. Phase switching matrix of AC charging pile This is used to represent the optimized connection status of AC charging piles in the three phases; the phase switching matrix of DC charging piles. (For DC charging stations powered via the first switching network only); Path selection vector for DC charging stations This is used to indicate whether the DC charging pile selects the first or second path.

[0139] (3) Set constraints

[0140] To ensure the feasibility and safety of the model, the following constraints are set:

[0141] Energy storage battery constraints:

[0142]

[0143] in, and These are the minimum and maximum charge and discharge power of the energy storage battery, respectively. and These represent the minimum and maximum allowable remaining capacity of the energy storage battery, respectively.

[0144] Charging station power constraints:

[0145]

[0146] in, and These are the charging / discharging power and maximum charging / discharging power of the i-th AC charging pile, respectively. and These are the charging / discharging power and maximum charging / discharging power of the j-th DC charging pile, respectively.

[0147] Transformer load factor constraint: λ ≤

[0148] Imbalance constraint: ε ≤

[0149] DC pile path switching constraints: ;

[0150] (4) Optimize the solution method

[0151] The model is solved using optimization algorithms such as mixed integer programming to find the optimal combination of decision variables that minimizes the objective function while satisfying all constraints.

[0152] Step 4: Load switching and regulation execution

[0153] (1) Execution of the optimal load switching scheme: Based on the optimal scheme obtained from the optimization model, the load is first switched through the first switching network. Specifically, according to the phase switching matrices of AC charging piles and DC charging piles (powered through the first switching network)... and The corresponding charging piles are switched to the optimal phase line to achieve initial load balancing.

[0154] (2) The starting conditions and execution of the second branch regulation: if the load imbalance still exceeds the regulation range (ε≥) after the load switching of the first switch network. Or the transformer load rate exceeds the threshold (λ≥ If the DC charging pile is activated, the second branch regulation of the DC charging pile will be started. That is, the DC charging pile is controlled to be connected to the 10kV incoming line through the second branch of the inverter. By adjusting the charging and discharging power and phase selection of these DC charging piles, the regulation capability of the unbalanced load in the distribution area is further expanded, so as to reduce the unbalance and transformer load rate.

[0155] This technical solution can efficiently solve the transformer overload problem. By regulating the charging and discharging of the energy storage battery and flexibly switching the power supply path of the DC charging pile, the load on the transformer can be reduced in time when the load is too high, avoiding overload operation of the transformer and effectively improving the service life of the transformer and the reliability of power supply.

[0156] It can also significantly improve three-phase load imbalance. Combined with the load switching of the first switching network and the coordinated regulation of the energy storage battery, it can accurately adjust the three-phase load distribution, significantly reduce the three-phase load imbalance, and improve the power quality of the power distribution system.

[0157] Improving the utilization rate of energy storage batteries is one of the objectives in the objective function, which is to maximize the utilization rate of energy storage batteries. By optimizing the control strategy, the regulation capability of energy storage batteries can be fully utilized to improve their efficiency and reduce the investment cost of energy storage systems.

[0158] Reduce reliance on the 10kV incoming line, aiming to minimize the load transmission through direct connection to the 10kV line via inverter, minimize the situation where DC charging piles are connected to the 10kV incoming line via a second branch, reduce the impact on the high-voltage power grid, and improve the independence and stability of the distribution substation.

[0159] To achieve coordinated and orderly charging and discharging, the centralized controller and cloud service controller work together to realize coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles, which not only meets the charging needs of users, but also optimizes the operation of the power distribution system.

[0160] Example 5

[0161] In this embodiment, the evaluation of the load balance improvement effect is also included. The improvement effect of the scheme on the three-phase load imbalance is evaluated by calculating indicators such as the load balance improvement rate, the reduction of transformer load rate, and the utilization rate of energy storage battery.

[0162] (1) The formula for calculating the load balance improvement rate is:

[0163]

[0164] in, The initial imbalance, The imbalance after coordinated control.

[0165] (2) Calculate the reduction in transformer load rate using the following formula: ;

[0166] in, This represents the initial transformer load rate. The transformer load rate is controlled in a coordinated manner.

[0167] (3) Evaluate the utilization rate of energy storage batteries, using the following formula:

[0168]

[0169] (4) Statistically analyze the usage frequency of DC charging piles connected to the 10kV incoming line via the second branch, and evaluate the effectiveness of the scheme in reducing dependence on the 10kV incoming line.

[0170] The above evaluation indicators can be used to comprehensively measure the implementation effect of this technical solution, providing a basis for further optimization and promotion of the solution.

[0171] The above-described specific examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention. It is readily understood that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the scope of the patent. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this patent.

Claims

1. A method for coordinated control of electric vehicle charging and discharging based on energy storage substation, characterized in that: The power distribution structure for implementing the control method comprises: a 10kV ring network incoming line, a distribution transformer, an alternating current load, a direct current load, an energy storage battery, an inverter, a switch network, a centralized controller, a cloud service controller, and n direct current charging piles and m alternating current charging piles; the 10kV incoming line is connected to the alternating current bus after being stepped down by the distribution transformer, the alternating current bus is connected to the alternating current load, the rectifier is connected to the direct current load, the bidirectional AC / DC converter is connected to the energy storage battery, the alternating current bus is connected to multiple charging piles through the first switch network, and each direct current charging pile is also connected to the 10kV incoming line through the inverter and the second switch network, having two power supply paths, one being through the transformer for step-down and then through the first switch network for charging and discharging of the charging pile, and the other being through the inverter for step-up and then through the second switch network for connecting the 10kV incoming line for charging and discharging, and the first switch network and the second switch network can select the phase line; The method comprises the following steps: Step 1: The centralized controller obtains the substation operation data in real time and uploads them to the cloud service controller for analysis, including the SOC state of the energy storage unit, the operation of the alternating current pile and the direct current pile, and the charging and discharging pile connected to the three phases respectively; Step 2: Calculate the unbalance degree and the substation transformer load rate according to the obtained data, and determine whether there is load imbalance and transformer overload; Step 3: When it is determined that there is load imbalance and substation transformer overload, a substation dispatching control model is established to optimize and solve the charging and discharging of the energy storage battery, the alternating current charging pile and the direct current charging pile, and the objective function in the model is to maximize the utilization rate of the energy storage battery and minimize the load directly connected to the 10kv line through the inverter; the objective function established in the step 3 is to maximize the utilization rate of the energy storage battery and minimize the load directly connected to the 10kV line through the inverter as the principle, and the expression is: Wherein, w1 and w2 are weight coefficients, Indicates the number of 10kV incoming lines connected by the DC charging pile through the second switch network. The utilization rate of the energy storage battery is calculated by the following formula: wherein, is the charging and discharging power of the energy storage battery, is the maximum charging and discharging power of the energy storage battery, and T is a statistical period. Step 4: Find the optimal load switching scheme according to the model; preferentially switch the load through the first switch network incoming line to realize load balancing; if the load unbalance degree has exceeded the adjustment range or the transformer load rate threshold, the direct current charging pile can be connected to the 10kV incoming line through the second branch of the inverter for step-up inversion; at the same time, the energy storage battery is controlled to discharge; the charging and discharging power of the energy storage battery is adjusted according to the overload degree of the transformer and the remaining capacity of the energy storage battery; Step 5: Evaluate the load balancing improvement effect, and the evaluation indexes include: load balancing improvement rate, transformer load rate reduction amplitude, and energy storage battery utilization rate; if the load balancing improvement effect is not up to standard, repeat steps 1-4.

2. The method for coordinated control of electric vehicle charging and discharging according to claim 1, characterized in that: The step 4 comprises: finding the optimal load switching scheme, including adjustment of the phase line connected to each charging pile, charging and discharging strategy of the energy storage battery, and decision whether to enable the inverter to connect to the 10kV incoming line.

3. The method for coordinated control of electric vehicle charging and discharging according to claim 2, characterized in that: The step 4 comprises: according to the optimal load switching scheme, first, load switching is carried out through the first switch network, and according to the phase switching matrix of the alternating current charging pile and the direct current charging pile, the corresponding charging pile is switched to the optimal phase line to realize the preliminary balance of the load; if the load imbalance degree still exceeds the adjustment range or the transformer load rate exceeds the threshold value after the load switching through the first switch network, the second branch adjustment of the direct current charging pile is started, the direct current charging pile is connected to the 10kV ring network incoming line through the second branch of the inverter, and the adjustment capacity of the unbalanced load of the transformer area is further expanded by adjusting the charging and discharging power of the direct current charging pile and the phase selection.

4. The electric vehicle charging and discharging cooperative control method according to claim 1, characterized in that: The step 2 comprises: setting an overload threshold value of the transformer, and starting the transformer overload control strategy when it is detected that the transformer load rate approaches or exceeds the threshold value; for the alternating current charging pile, the centralized controller limits the charging power of part of the alternating current charging piles according to the overload degree, and preferentially limits the charging pile power of the non-emergency charging vehicle; for the direct current charging pile, according to the actual situation, part of the direct current charging piles are switched to be supplied by the 10kV incoming line through the second switch network to reduce the load of the transformer; at the same time, the energy storage battery is controlled to discharge to provide part of the energy for the charging pile; the discharging power of the energy storage battery is reasonably adjusted according to the overload degree of the transformer and the remaining capacity of the energy storage battery.

5. The method of claim 1, wherein: The step 4 comprises: During the low valley period of the power grid, the energy storage battery is controlled to be charged from the power grid, and at the same time, the charging demand of the electric vehicle is preferentially met; when the charging demand of the electric vehicle is small, the energy storage battery is fully charged for use during the peak period; During the peak period of the power grid, the price is high and the transformer is prone to overload, the energy storage battery discharges to provide energy for the electric vehicle charging, reduces the dependence on the power grid, and reduces the load of the transformer; When the three-phase load imbalance occurs in the distribution area, the energy storage battery charges and discharges on the corresponding phase according to the three-phase load condition to assist in adjusting the three-phase load balance.

6. The electric vehicle charging and discharging cooperative control method according to claim 1, characterized in that: The calculation formula of the imbalance degree ε is: wherein, Ia, Ib, Ic are the total current of the three-phase transformer A, B, C, respectively; The calculation formula of the transformer load rate of the transformer area is: wherein, Ptotal is the total active power of the system, including the active power of the AC load, the DC load, the AC charging pile and the DC charging pile through the first switch network; Pcharge-discharge is the charge-discharge power of the energy storage battery; Qtotal is the total reactive power of the system; Srated is the rated capacity of the distribution transformer.

7. The electric vehicle charging and discharging cooperative control method according to claim 1, characterized in that: In the step 5, the calculation formula of the load balance improvement rate is: wherein, is the initial unbalance degree, is the unbalance degree after cooperative control; The formula for the reduction in transformer load factor is: ; where, is the initial transformer load factor, is the transformer load factor after coordinated control.

8. A power storage substation-based electric vehicle charging and discharging collaborative control system, characterized in that, The synergic control system comprises a 10kV looped network incoming line, a distribution transformer, an alternating current load, a direct current load, an energy storage battery, an inverter, a switch network, a centralized controller, a cloud service controller, n direct current charging piles and m alternating current charging piles; the 10kV incoming line is connected to an alternating current bus after being stepped down by the distribution transformer, the alternating current bus is connected to the alternating current load, a rectifier is connected to the direct current load, a bidirectional alternating current-direct current converter is connected to the energy storage battery, the alternating current bus is connected to the multiple charging piles through a first switch network, and each direct current charging pile is directly connected to the 10kV incoming line through an inverter and a second switch network; the synergic control system is used to realize the steps of the electric vehicle charging and discharging synergic control method based on an energy storage transformer area according to any one of claims 1-7.

9. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a program of the electric vehicle charging and discharging synergic control method based on an energy storage transformer area, wherein when the program is executed by a processor, the steps of the electric vehicle charging and discharging synergic control method based on an energy storage transformer area according to any one of claims 1-7 are realized.

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