Electric vehicle charging and discharging cooperative control method and system based on energy storage area

Abstract

The invention provides an electric vehicle charging and discharging cooperative control method and system based on an energy storage platform area, the method is used for solving the problems of transformer overload and three-phase load imbalance in the charging and discharging process, and the method comprises the core steps: 1, a centralized controller obtains platform area operation data in real time and uploads the platform area operation data to a cloud service controller for analysis; 2, judging whether load imbalance and transformer overload exist or not; 3, when it is judged that the load is unbalanced and the transformer in the transformer area is overloaded, establishing a transformer area dispatching control model, and conducting optimization solution on charge and discharge loads of an energy storage battery and charge and discharge loads of an alternating current charging pile and a direct current charging pile; 4, searching an optimal load switching scheme according to the model; 5, evaluating the load balance improvement effect; if the load unbalance degree exceeds the adjusting range or exceeds the load rate threshold value of the transformer, the direct current charging pile can be connected with the 10kV incoming line through the second branch circuit where the inverter is located in a boost inversion mode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric vehicles and energy storage, and particularly relates to an electric vehicle charging and discharging collaborative control method and system based on an energy storage transformer area. BACKGROUND

[0002] In the case of electric vehicle loads widely accessing a transformer area for charging and discharging, to suppress load fluctuations and improve power supply reliability, energy storage units (such as lithium battery energy storage systems) are also gradually accessed to the distribution transformer area, forming a new distribution scenario of "electric vehicle-energy storage" collaborative operation.

[0003] However, the distribution transformer area in this scenario is facing severe operation challenges: on the one hand, electric vehicle charging and discharging has significant spatiotemporal randomness and power concentration. When a large number of electric vehicles are simultaneously charged, the instantaneous load of the distribution transformer can exceed the rated capacity threshold, causing the winding temperature to rise rapidly, the insulation to age rapidly, and even causing an overload trip accident. On the other hand, the disorderly three-phase access of charging piles makes the transformer area three-phase load unbalance generally exceed the unbalance threshold. The negative sequence current generated thereby increases line loss, reduces transformer load capacity, and causes interference to the normal operation of sensitive equipment in the transformer area.

[0004] In the prior art, a single charging pile scheduling or energy storage control strategy cannot meet the collaborative optimization needs of the "electric vehicle-energy storage" composite system. For example, when load adjustment is performed through charging pile phase switching alone, the flexible adjustment capability of energy storage cannot be fully utilized. Independent energy storage charging and discharging control cannot take into account both the charging needs of electric vehicle users and the power grid operation constraints. Therefore, how to build a collaborative control system that integrates electric vehicle charging and discharging behavior and energy storage unit dynamic adjustment, and achieve accurate balancing of transformer area load and effective management and control of transformer load, has become a key technical problem to be solved in the current smart distribution grid field. SUMMARY

[0005] The main purpose of the present application is to propose an electric vehicle charging and discharging collaborative control method based on energy storage in a distribution transformer area, which solves the problems of transformer overload and three-phase load imbalance in the charging and discharging process, and expands the adjustment capability of transformer area unbalanced load through optimization of power supply structure and control method.

[0006] 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 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 plurality of charging piles through a first switch network, and each direct current charging pile is also connected to the 10kV incoming line through an inverter and a second switch network, having two power supply paths, one being through the transformer for stepping down and through the first switch network for charging and discharging the charging piles, and the other being through the inverter for stepping up and 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 incoming line phase; The method comprises the following steps: Step 1: The centralized controller obtains real-time operation data of the transformer area and uploads the data 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 of the piles connected to the three-phase power supply; Step 2: The unbalance degree and the transformer load rate are calculated according to the obtained data, and it is judged whether there is load imbalance and transformer overload; Step 3: When it is judged that there is load imbalance and transformer overload, a transformer area dispatching control model is established, the charging and discharging of the energy storage battery, the alternating current charging pile and the direct current charging pile are optimized and solved, 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; Step 4: The optimal load switching scheme is found according to the model; the load is switched through the first switch network incoming line preferentially 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 stepping up and inverting; 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: The load balancing improvement effect is evaluated, 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, steps 1-4 are repeated.

[0007] The objective function established in step 3 takes the principle of maximizing the utilization rate of the energy storage battery and minimizing 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, The number sum of 10kV incoming lines connected by the DC charging pile through the second switch network is represented as SDC; For the utilization rate of the energy storage battery, the calculation formula is: 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.

[0008] The step 4 includes: finding an optimal load switching scheme, including adjustment of each charging pile connected to a phase line, charging and discharging strategy of the energy storage battery, and decision whether to enable the inverter to connect the 10kV incoming line.

[0009] The step 4 includes: according to the optimal load switching scheme, first, the load is switched through the first switch network, and according to the phase switching matrix of the AC charging pile and the DC 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 DC charging pile is started, the DC charging pile is connected to the 10kV loop network incoming line through the second branch of the inverter, and the charging and discharging power and phase selection of the DC charging pile are adjusted to further expand the adjustment capacity of the unbalanced load of the substation area.

[0010] The step 2 includes: setting an overload threshold of the transformer, when it is detected that the transformer load rate approaches or exceeds the threshold, starting the transformer overload control strategy; for the AC charging pile, the central controller limits the charging power of part of the AC charging pile according to the overload degree, and preferentially limits the charging pile power of the non-emergency charging vehicle; for the DC charging pile, according to the actual situation, part of the DC charging pile is selected to be switched to the 10kV incoming line for power supply 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 discharge 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.

[0011] During the low valley period of the power grid, the energy storage battery is controlled to charge 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 substation 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.

[0012] The calculation formula of the unbalance degree ε is: Wherein, Ia, Ib and Ic are the total current of the three-phase transformer A, B and C respectively; The calculation formula of the transformer load rate is: Wherein, P is the total active power of the system, including the active power of the AC load, DC load, AC charging pile and DC charging pile through the first switch network; P is the charge and discharge power of the energy storage battery; Q is the total reactive power of the system; K is the rated capacity of the distribution transformer.

[0013] In step 5, the calculation formula of the load balance improvement rate is: Wherein, ε0 is the initial unbalance degree, ε is the unbalance degree after the cooperative control; The formula of the transformer load rate reduction amplitude is: ; wherein, η0 is the initial transformer load rate, η is the transformer load rate after the cooperative control.

[0014] A kind of electric vehicle charging and discharging cooperative control system based on energy storage transformer area is also proposed, the cooperative control system includes: 10kV ring network incoming line, distribution transformer, AC load, DC load, energy storage battery, inverter, switch network, centralized controller, cloud service controller and n DC charging piles and m AC charging piles;10kV incoming line is connected after being stepped down by distribution transformer AC bus, AC bus is connected with AC load, rectifier is connected with DC load, bidirectional AC / DC converter is connected with energy storage battery, AC bus is connected with multiple charging piles by first switch network, each DC charging pile is also connected with 10kV incoming line by inverter and second switch network;The cooperative control system is used to realize the steps of the electric vehicle charging and discharging cooperative control method based on energy storage transformer area.

[0015] The computer readable storage medium has a program of the electric vehicle charging and discharging cooperative control method based on energy storage transformer area stored therein, and when the program is executed by a processor, the steps of the electric vehicle charging and discharging cooperative control method based on energy storage transformer area are realized.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The power supply structure of the transformer area and the load adjustment mode are optimized, so that the charging pile has two power supply paths, one is to charge and discharge the charging pile through the first switch network after voltage reduction by the transformer, and the other is to charge and discharge the charging pile through the second switch network after voltage increase by the inverter; and the first switch network and the second switch network can select the phase line of the incoming line, which expands the adjustment capacity and adjustment depth of the transformer area, and realizes the coordinated and orderly charging and discharging of electric vehicles under the alternating current charging pile and the direct current charging pile in the power distribution transformer area. 2. By adjusting the charging and discharging power of the charging pile and the coordinated discharging of the energy storage battery, the load of the transformer can be reduced in time when the load of the transformer is too high, the overload operation of the transformer can be avoided, and the service life and power supply reliability of the transformer can be improved. 3. By using the phase line selection function of the switch network and adjusting the power of the charging pile, combined with the three-phase coordinated adjustment of the energy storage battery, the three-phase load of the power distribution transformer area can be effectively balanced, the unbalance degree of the three-phase current can be reduced, and the power quality of the power distribution system can be improved. 4. The coordinated and orderly charging and discharging of electric vehicles is realized, the coordinated and orderly charging and discharging of electric vehicles under the alternating current charging pile and the direct current charging pile is realized through the coordinated control of the centralized controller and the cloud service controller, the charging efficiency is improved, the charging demand of users is met, and the operation of the power distribution system is optimized. 5. The flexibility and adaptability of the system are improved, the direct current charging pile has two power supply paths, 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 demand, so that the whole system has high flexibility and adaptability, and can cope with different power consumption scenes and load changes. 6. It has good economy, by using the energy storage battery to charge in the low valley period of the power grid and discharge in the peak period, the charging cost of users can be reduced, the expansion demand of the power grid can be reduced, and good economy can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0018] Figure 1 It is a transformer area power supply structure diagram based on an inverter and a switch network in an embodiment of the present application.

[0019] Figure 2 It is a transformer area power supply structure diagram based on an inverter and a plurality of switch networks in an embodiment of the present application.

[0020] Figure 3A schematic diagram of a power supply structure of a distribution area including an AC bus and an AC charging pile in an embodiment of the present application.

[0021] Figure 4 A schematic diagram of a method for coordinated charging and discharging of an electric vehicle in an embodiment of the present application. DETAILED DESCRIPTION

[0022] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described in more detail below with reference to the drawings of the embodiments of the present application. Identical or similar labels represent identical or similar elements or elements with identical or similar functions throughout the drawings. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0023] Embodiment one A method for coordinated charging and discharging of an electric vehicle based on energy storage in a distribution area is proposed. The method is used to solve the problems of transformer overload and three-phase load imbalance during charging and discharging, and to realize coordinated and orderly charging and discharging of electric vehicles under AC charging piles and DC charging piles in a distribution area.

[0024] As shown in the power supply structure of the distribution area, Figures 1-3 the power distribution structure implementing the control method includes a 10kV incoming line, a distribution transformer, an AC load, a DC load, 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 connected to the AC bus after being stepped down by the distribution transformer, the AC bus is connected to the AC load, the rectifier is connected to the DC load, the bidirectional AC / DC converter is connected to the energy storage battery, the AC bus is connected to multiple charging piles through the first switch network, and each DC charging pile is also connected to the 10kV incoming line through the inverter and the second switch network. There are two power supply paths, one is through the transformer to step down and through the first switch network to charge and discharge the charging pile, and the other is through the inverter to step up and through the second switch network to connect the 10kV incoming line to charge and discharge. The first switch network and the second switch network can select the phase line, that is, each charging pile can switch any one of the ABC three-phase.

[0025] As shown in the method, Figure 4 the method includes the following steps: Step 1: The centralized controller obtains real-time operation data of the transformer area and uploads it to the cloud service controller for analysis, including the SOC state of the energy storage unit, the operation of AC and DC piles, and the charging and discharging piles connected to the three-phase power supply. Step 2: Calculate the unbalance degree and transformer load rate based on 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 transformer overload, establish a transformer dispatching control model to optimize the charging and discharging of energy storage batteries, AC charging piles, and DC charging piles. The objective function in the model aims to maximize the utilization rate of energy storage batteries and minimize the load transmission through inverters directly connected to the 10kV line.

[0026] Step 4: Find the optimal load switching scheme based on the model, and then switch the load through the first switch network to achieve load balance. If the load imbalance degree exceeds the adjustment range or the transformer load rate threshold, the DC charging pile can be connected to the 10kV line through the second branch of the inverter, thereby expanding the adjustment capacity of the transformer area.

[0027] Step 5: Evaluate the load balance improvement effect, including load balance improvement rate, transformer load rate reduction, and energy storage battery utilization rate. If the load balance improvement effect is not up to standard, repeat steps 1-4.

[0028] Example Two In this example, each DC charging pile has two charging and discharging paths: Step-down charging and discharging path: Through the transformer, the first switch network is used for charging and discharging of the charging pile. This path utilizes the existing power distribution system structure to provide stable power supply for the charging pile under normal load conditions.

[0029] Step-up inverter charging and discharging path: Through the inverter, the second switch network is connected to the 10kV line for charging and discharging. This path can directly obtain or transmit power from the high-voltage side under special conditions, such as severe load imbalance or transformer overload, thereby enhancing the flexibility of the system.

[0030] At the same time, the switch network has a phase selection function, and the first and second switch networks have a phase selection function. Each charging pile can be switched to any of the three-phase A, B, or C. This provides a hardware foundation for achieving three-phase load balance regulation and allows flexible allocation of charging load to different phase lines based on real-time load conditions.

[0031] Based on the above power distribution structure, the cooperative control method for electric vehicle charging and discharging is obtained: Step 1: Data acquisition and uploading; Real-time acquisition of substation operation data by centralized controller, including state of charge (SOC) of energy storage units, operation status of AC and DC piles (such as charging power, charging current, charging status, etc.), number and power of charge and discharge piles connected to three-phase respectively, and other loads (such as residential electricity, commercial electricity, etc.) carried by three-phase respectively; upload the collected substation operation data to the cloud service controller for centralized analysis and processing. The cloud service controller has strong data storage and computing capabilities and can comprehensively analyze multiple substation data.

[0032] Step 2: imbalance degree and load rate calculation and judgment; Calculate the imbalance degree: according to the three-phase current or power data, use the standard imbalance degree calculation formula to calculate the three-phase load imbalance degree of the substation. For example, use the negative sequence current method to calculate the imbalance degree, that is, measure the imbalance degree by calculating the ratio of negative sequence current to positive sequence current.

[0033] Calculate the transformer load rate of the substation: compare the total load of the substation (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 substation / rated capacity of transformer x 100%. Judge abnormal conditions: compare the calculated imbalance degree and load rate with the preset threshold. If the imbalance degree exceeds the specified range (such as the national standard three-phase voltage imbalance degree limit value is 2%, and the short time shall not exceed 4%), it is determined that there is a load imbalance problem; if the load rate exceeds the transformer rated load rate threshold (such as generally 80%-90%), it is determined that there is a transformer overload problem.

[0034] Step 3: establish a substation dispatching control model; Construct the objective function: (1) the highest utilization rate of energy storage battery, aiming to maximize the charge and discharge cycle times and depth of energy storage battery, fully play the role of energy storage battery, prolong its service life and improve economic benefit. The charge and discharge power and SOC of the energy storage battery can be optimized and controlled to make the energy storage battery run efficiently under different working conditions. (2) the lowest load transmission through the inverter directly connected to the 10kV line: try to reduce the load transmission through the inverter directly connected to the 10kV line, because there is energy loss in the inverter conversion process. Only when the substation load is seriously unbalanced or the transformer is overloaded and cannot be effectively adjusted by other means, this path is enabled.

[0035] Set constraints: (1) Energy storage battery constraints, including energy storage battery charge and discharge power limits, SOC upper and lower limit constraints, etc. For example, the charging power of the energy storage battery cannot exceed its rated charging power, and the discharging power cannot exceed the rated discharging power; the 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 charge and discharge power of AC charging piles and DC charging piles should be within their rated power range, and meet the charging needs and time requirements of users. At the same time, the start-stop frequency limit of the charging pile should be considered to avoid damage to the equipment caused by frequent start-stop. (3) Grid constraints: the unbalance degree of the three-phase voltage of the transformer should be controlled within the specified range to ensure power quality; the current of each phase of the transformer should not exceed its rated current to prevent overheating and damage to the transformer.

[0036] Step 4: Load switching and adjustment; Finding the optimal load switching scheme: use optimization algorithms (such as genetic algorithms, particle swarm optimization algorithms, etc.) to solve the transformer dispatching control model and find the load switching scheme that can optimize the objective function. This scheme should include the adjustment of the charging pile connection phase line, the charging and discharging strategy of the energy storage battery, and the decision of whether to enable the inverter to connect the 10kV incoming line.

[0037] Load switching implementation: according to the determined optimal load switching scheme, the first switch network is used to switch the charging pile connection phase line to achieve the redistribution of three-phase load and achieve the purpose of load balancing. For example, part of the load is switched from the overloaded phase to the light load phase to make the three-phase load tend to be balanced.

[0038] Expand the adjustment capacity: if the load imbalance degree still exceeds the adjustment range or the transformer load rate continues to exceed the threshold after load switching, the DC charging pile connects the 10kV incoming line through the second branch of the inverter to obtain or transmit power directly from the high-voltage side, thereby further expanding the adjustment capacity of the transformer unbalanced load and ensuring the stable operation of the transformer.

[0039] Example three The power distribution structure involved in the 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 relationship is as follows: 10kV incoming line is connected to an AC bus after being stepped down by a distribution transformer, the AC bus is connected to an AC load, the rectifier is connected to a DC load, the bidirectional AC-DC converter is connected to an 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. There are two power supply paths, one is to charge and discharge the charging pile through the first switch network after being stepped down by the transformer, and the other is to charge and discharge the charging pile through the second switch network after being stepped up by the inverter. Moreover, the first switch network and the second switch network can select the phase line, that is, each charging station can switch any one of the ABC three-phase.

[0040] The technical solution constructs a collaborative control framework with a centralized controller and a cloud service controller as the core. The centralized controller monitors the load of the distribution transformer, the three-phase load balance status and the state of the energy storage battery in real time, and manages the phase line selection of the first switch network and the second switch network. For AC charging piles, the centralized controller adjusts their charging and discharging power according to the transformer load; for DC charging piles, they can be flexibly selected to be powered through the first switch network after being stepped down by the transformer, or to be directly connected to the 10kV incoming line through the second switch network after being stepped up by the inverter. At the same time, the energy storage battery participates in load regulation through the bidirectional AC-DC converter to solve the problems of transformer overload and three-phase load imbalance. The cloud service controller collects the data uploaded by the centralized controller, performs big data analysis and optimization calculation, generates long-term charging and discharging optimization strategy, and issues it to the centralized controller for execution, realizing the optimization management of the entire distribution area charging and discharging process.

[0041] Build specific control strategy: (1) Data acquisition and processing The centralized controller collects the operation data of each device in the distribution area in real time, including the input and output voltage, current and load rate of the transformer, the amplitude and phase of three-phase voltage and current, the charging and discharging power and state of each charging pile, the terminal voltage, charging and discharging current and remaining capacity of the energy storage battery, etc. The collected data is preprocessed by filtering, denoising, etc., and then the processed data is transmitted to the cloud service controller for storage and further analysis, providing accurate data support for subsequent control strategy.

[0042] (2) Transformer overload control Set the overload threshold of the transformer, when the transformer load rate is close to or exceeds the threshold, start the transformer overload control strategy. The specific measures are as follows: For AC charging piles, the centralized controller limits the charging power of part of the AC charging piles according to the overload degree, and preferentially limits the power of the charging pile of non-emergency charging vehicles.

[0043] For DC charging piles, according to actual conditions, some DC charging piles can be switched to be powered by the 10kV incoming line through the second switch network to reduce the load of the transformer.

[0044] At the same time, the energy storage battery is controlled to discharge to provide part of the energy for the charging pile and share the load of the transformer. The discharge 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.

[0045] (3) Three-phase load balance control The standard for three-phase load balance is determined, usually aiming at the unbalance degree of three-phase current not exceeding the specified value. When the unbalance degree of three-phase load is detected to exceed the standard, the following measures are taken to achieve balance: The phase lines of each charging pile are reselected through the first switch network and the second switch network, and the charging piles are distributed to different phase lines to adjust the load distribution of each phase.

[0046] For AC charging piles and DC charging piles (when powered through the first switch network), the centralized controller adjusts their charge and discharge power to balance the power of each phase as much as possible. For example, for the phase with heavier load, reduce the charging power or increase the discharging power of part of the charging piles on the phase; for the phase with lighter load, appropriately increase the charging power of the charging piles on the phase.

[0047] The energy storage battery also participates in the three-phase load balance adjustment, and according to the load condition of each phase, the energy storage battery is controlled to charge and discharge on the corresponding phase to balance the three-phase load.

[0048] (4) Energy storage battery cooperative control The charge and discharge strategy of the energy storage battery is defined to cooperate with the charge and discharge of the charging pile. Specifically as follows: During the low valley period of the power grid, when the electricity price is low, the energy storage battery is controlled to charge from the power grid, and at the same time, the charging demand of electric vehicles is preferentially met. When the charging demand of electric vehicles is small, the energy storage battery is fully charged for use during the peak period. During the peak period of the power grid, when the electricity price is high and the transformer is prone to overload, the energy storage battery discharges to provide energy for the charging of electric vehicles, reduces the dependence on the power grid, and reduces the load of the transformer.

[0049] When the three-phase load of the distribution area is unbalanced, 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.

[0050] The charge and discharge process of the energy storage battery also needs to consider factors such as its remaining capacity and service life, and reasonable charge and discharge depth and cycle number are formulated to prolong the service life of the energy storage battery.

[0051] The specific implementation steps include: (1) system initialization, initializing and setting the centralized controller, cloud service controller, each switch network, charging pile, energy storage battery and other devices, including parameter configuration, communication connection establishment, etc. Set the transformer overload threshold, three-phase load imbalance standard and other control parameters.

[0052] (2) Real-time data acquisition, the centralized controller acquires the running data of each device in the distribution area in real time according to the set sampling frequency, such as the data acquisition content described above.

[0053] (3) Data analysis and judgment, the centralized controller preliminarily analyzes the collected data to judge whether the transformer is overloaded and whether the three-phase load is balanced. At the same time, the data is transmitted to the cloud service controller, which performs more in-depth data analysis and optimization calculation to generate long-term charging and discharging optimization strategy.

[0054] (4) Execute control strategy, according to the result of data analysis and judgment, the centralized controller executes the corresponding control strategy. 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 cooperative control strategy, the charging and discharging of the energy storage battery and the cooperative work with the charging pile are controlled.

[0055] (5) Effect evaluation and strategy optimization, evaluate the execution effect of the control strategy, check whether the transformer load is reduced to the safe range and whether the three-phase load imbalance is reduced to the standard. According to the evaluation result, the cloud service controller optimizes the control strategy to continuously improve the operation efficiency and stability of the system.

[0056] Through the technical scheme of the embodiment, the transformer overload problem can be effectively solved. By adjusting the charging and discharging power of the charging pile and the cooperative discharge of the energy storage battery, the load of the transformer can be reduced when the load of the transformer is too high, avoiding the overload operation of the transformer and improving the service life and power supply reliability of the transformer.

[0057] It can also significantly improve the three-phase load imbalance. By using the phase line selection function of the switch network and adjusting the power of the charging pile, combined with the three-phase cooperative adjustment of the energy storage battery, the three-phase load of the distribution area can be effectively balanced, the three-phase current imbalance can be reduced, and the power quality of the power distribution system can be improved.

[0058] It can also realize the cooperative and orderly charging and discharging of electric vehicles. Through the cooperative control of the centralized controller and the cloud service controller, the cooperative and orderly charging and discharging of electric vehicles under alternating current charging piles and direct current charging piles are realized, the charging efficiency is improved, the charging demand of users is met, and the operation of the power distribution system is optimized.

[0059] The system flexibility and adaptability can also be improved. 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 demand, so that the entire system has high flexibility and adaptability, and can cope with different power consumption scenarios and load changes.

[0060] At the same time, it has good economic efficiency. By using the energy storage battery to charge during the low valley period of the power grid and discharge during the peak period, the charging cost of the user can be reduced, and the expansion demand of the power grid can also be reduced, which has good economic efficiency.

[0061] Embodiment four The power distribution structure involved in the technical solution mainly includes a 10kV incoming line, a power 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 DC charging piles and m AC charging piles. The specific connection relationship is as follows: The 10kV incoming line is connected to the AC bus after being stepped down by the power distribution transformer. The AC bus is connected to the AC load. The rectifier is connected to the DC load. The bidirectional AC / DC converter is connected to the energy storage battery. The AC bus is connected to multiple charging piles through the first switch network. Each DC charging pile is also connected to the 10kV incoming line through the inverter and the second switch network. There are two power supply paths. One is to charge and discharge the charging pile through the first switch network after being stepped down by the transformer. The other is to charge and discharge the charging pile through the second switch network after being stepped up by the inverter. In addition, the first switch network and the second switch network can select the phase line, that is, each charging station can switch any phase in the ABC three-phase.

[0062] The electric vehicle charging and discharging collaborative control method based on the above power distribution structure includes the following steps: Step 1: Data acquisition and uploading The centralized controller is the core device of data acquisition, which can obtain the running data of each device in the transformer area in real time. These data are the basis for subsequent analysis and control. The specific acquisition content includes: energy storage unit state: real-time monitoring of the remaining capacity (SOC) state of the energy storage battery, which is a key parameter for evaluating the available capacity of the energy storage battery. Charging pile operation: obtain the operation state of the AC charging pile and the DC charging pile, such as whether it is charging or discharging, the size of the charging and discharging power, and other information. Charging pile access: record the number and specific distribution of charging piles connected in each phase of the three-phase, and determine the load source of each phase. Other load information: master the size and distribution of other loads in each phase of the three-phase, such as residential electricity, commercial electricity and other conventional loads.

[0063] The centralized controller will collect these real-time operation data for preliminary processing and upload to the cloud service controller. The cloud service controller has strong data storage and analysis capabilities, and can provide strong support for subsequent decision-making through in-depth analysis of uploaded data.

[0064] Step 2: Unbalance degree and load rate calculation and judgment: (1) Unbalance degree calculation Three-phase load unbalance degree is an important indicator to measure the balance of three-phase load in distribution system. This scheme adopts current-based unbalance degree calculation method, the specific steps are as follows: First, calculate the total current of each phase. For each phase (A, B, C phase) in the three-phase system, the total current includes the current of the AC charging pile on the phase, the current of the DC charging pile through the first switch network into the phase, the current of other conventional loads, and the charge and discharge current of the energy storage battery in the phase.

[0065] Then, calculate the unbalance degree according to the total current of each phase. The calculation formula of unbalance degree ε is: Where, Ia, Ib, Ic are the total currents of A, B, C three-phase respectively.

[0066] (2) Transformer load rate calculation Transformer load rate is a key parameter to evaluate the operation state of transformer, the calculation formula is: Where, Ptotal is the total active power of the system, including AC load, DC load, AC charging pile and DC charging pile through the first switch network active power; Pbat is the charge and discharge power of the energy storage battery (positive value for discharge, negative value for charge); Qtotal is the total reactive power of the system; S is the rated capacity of the distribution transformer.

[0067] (3) Determine whether there is load imbalance and transformer overload Set unbalance degree threshold ( ) and transformer load rate threshold ( ). When the calculated unbalance degree ε≥ , it is judged that there is a load imbalance problem; when the transformer load rate λ≥ , it is judged that there is a transformer overload problem.

[0068] Step 3: Establish a dispatching control model and optimize the solution When it is judged that load imbalance and transformer overload occur, a substation dispatching control model is established to optimize and solve the charging and discharging load of energy storage batteries, AC charging piles and DC charging piles.

[0069] (1) Construction of objective function The objective function of the model is to maximize the utilization rate of energy storage batteries and minimize the load transmission through inverters directly connected to 10kV lines. The specific expression is: where w1 and w2 are weight coefficients for balancing the importance of the two objectives. The utilization rate of energy storage batteries is calculated as follows: where is the charging and discharging power of energy storage batteries, is the maximum charging and discharging power of energy storage batteries, and T is the statistical period. represents the degree of non-utilization of energy storage batteries, and minimizing this value means maximizing the utilization rate of energy storage batteries. represents the total number of DC charging piles connected to 10kV lines through the second switch network, and minimizing this value means achieving the goal of minimizing the load transmission through inverters directly connected to 10kV lines.

[0070] (2) Construction of decision variables The decision variables of the model include: the charging and discharging power of energy storage batteries ; the phase switching matrix of AC charging piles , which indicates the connection of AC charging piles in three phases after optimization; the phase switching matrix of DC charging piles (only for DC charging piles supplied by the first switch network); and the path selection vector of DC charging piles

[0071] (3) Setting constraints To ensure the feasibility and safety of the model, the following constraints are set: Energy storage battery constraints: where and are the minimum and maximum charging and discharging power of energy storage batteries, and are the minimum and maximum residual capacity allowed for energy storage batteries.

[0072] Charging pile power constraints: wherein, and are the charge-discharge power and the maximum charge-discharge power of the i-th alternating current charging pile, respectively, and are the charge-discharge power and the maximum charge-discharge power of the j-th direct current charging pile, respectively.

[0073] Transformer load rate constraint: λ ≤ Unbalance degree constraint: ε ≤ Direct current pile path switching constraint: (4) Optimization solving method The model is solved by using an optimization algorithm such as mixed integer programming to find the optimal combination of decision variables, so that the objective function is minimized while satisfying all the constraints. Step 4: Load switching and adjustment execution (1) Optimal load switching scheme execution: According to the optimal scheme obtained by solving the optimization model, first, the load is switched through the first switch network. Specifically, according to the phase selection matrix of the alternating current charging pile and the direct current charging pile (powered through the first switch network) and , the corresponding charging pile is switched to the optimal phase line to achieve the preliminary balance of the load. (2) Second branch adjustment starting condition and execution: If after the load switching through the first switch network, the load unbalance degree still exceeds the adjustment range (ε ≥ ) or the transformer load rate exceeds the threshold value (λ ≥ ), the second branch adjustment of the direct current charging pile is started. That is, the direct current charging pile is connected to the 10kV incoming line through the second branch booster inverter, and by adjusting the charge-discharge power and phase selection of these direct current charging piles, the adjustment capability of the unbalanced load of the transformer area is further expanded to reduce the unbalance degree and the transformer load rate.

[0074] By using the technical solution, the transformer overload problem can be efficiently solved. Through the charge-discharge adjustment of the energy storage battery and the flexible switching of the direct current charging pile power supply path, the load of the transformer can be reduced in time when the transformer load is too high, avoiding the overload operation of the transformer, effectively improving the service life and power supply reliability of the transformer.

[0075] It can also significantly improve the three-phase load unbalance. Combined with the load switching of the first switch network and the cooperative adjustment of the energy storage battery, the three-phase load distribution can be accurately adjusted, the three-phase load unbalance degree can be significantly reduced, and the power quality of the power distribution system can be improved.

[0076] ​Improve the utilization rate of energy storage batteries. The highest utilization rate of energy storage batteries is one of the target functions. Through optimization control strategy, the adjustment capacity of energy storage batteries is fully utilized, the use efficiency is improved, and the investment cost of energy storage system is reduced. Reduce the dependence on 10kV incoming line. The target is to reduce the dependence on 10kV incoming line as much as possible. The second branch is connected to the 10kV incoming line to reduce the influence on the high-voltage power grid and improve the independence and stability of the distribution area.

[0077] Achieve coordinated and orderly charging and discharging. Through the coordinated work of the centralized controller and the cloud service controller, the coordinated and orderly charging and discharging of electric vehicles under alternating current charging piles and direct current charging piles are realized, which not only meets the charging demand of users, but also optimizes the operation of the power distribution system.

[0078] Example five In this embodiment, the evaluation of the improvement effect of load balancing is also included. The improvement effect of the scheme on three-phase load imbalance is evaluated by calculating the load balancing improvement rate, transformer load rate reduction, and energy storage battery utilization rate.

[0079] (1) The calculation formula of load balancing improvement rate is: Wherein, is the initial imbalance degree, is the imbalance degree after coordinated control.

[0080] (2) Calculate the transformer load rate reduction, the formula is: ; Wherein, is the initial transformer load rate, is the transformer load rate after coordinated control. (3) Evaluate the utilization rate of energy storage batteries, the formula is: (4) Calculate the use frequency of direct current charging piles connected to 10kV incoming line through the second branch, and evaluate the effect of the scheme on reducing the dependence on 10kV incoming line. Through the above evaluation indexes, the implementation effect of the technical scheme can be comprehensively measured, which provides basis for further optimization and popularization and application of the scheme.

[0081] The above application of specific examples to the present invention is described, only for help to understand the present invention, and not to limit the present invention. For the skilled in the art to which the present invention belongs, according to the idea of the present invention, a number of simple deduction, deformation or replacement can be made. The skilled in the art can easily understand that the above is only the preferred embodiment of the present invention patent, and does not limit the present invention patent, any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present invention patent, should be included in the protection scope of the present invention patent.

Claims

1. A method for coordinated charging and discharging control of electric vehicles based on energy storage areas, characterized in that: 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. The method includes the following steps: 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. 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; 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. 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. 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.

2. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: 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: 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: 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.

3. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: 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.

4. The electric vehicle charging and discharging coordinated control method according to claim 3, characterized in that: 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.

5. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: 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.

6. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: Step 4 includes: 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. 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. 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.

7. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: The formula for calculating the unbalance ε is: in, These are the total currents of phases A, B, and C of the transformer in the distribution area; The formula for calculating the load rate of a transformer substation is: 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.

8. The electric vehicle charging and discharging coordinated control method according to claim 1, characterized in that: In step 5, the formula for calculating the load balance improvement rate is: in, The initial imbalance, The imbalance after coordinated control; 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.

9. A coordinated charging and discharging control system for electric vehicles based on energy storage substations, characterized in that, The collaborative control system 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 connected to an AC bus after being stepped down by the distribution transformer, the AC bus is connected to AC loads, a rectifier is connected to DC loads, 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; the collaborative control system is used to implement the steps of the electric vehicle charging and discharging collaborative control method based on an energy storage area as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a program for a method of coordinated charging and discharging of electric vehicles based on energy storage areas, wherein when the program is executed by a processor, it implements the steps of the method of coordinated charging and discharging of electric vehicles based on energy storage areas as described in any one of claims 1-8.

Images