Control strategy for delaying upgrading and reconstruction of distributed energy storage power distribution equipment
By connecting distributed energy storage equipment to the distribution network and scheduling their charging and discharging in real time, the problems of excessive peak-to-valley difference in the distribution network and overload of transformers are solved, load balance and new energy consumption are achieved, and the operating costs and upgrade pressure of the power grid are reduced.
Patent Information
- Application Number
- CN202411635751.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-15
- Publication Date
- 2025-03-11
AI Technical Summary
The peak-to-valley difference in the distribution network load is too large, resulting in an increase in the transformer overload and the distribution network upgrade pressure, and the centralized charging of electric vehicles increases the load peak, making the transformer capacity expansion uneconomically.
Connect distributed energy storage equipment to the outlet or feeder of the distribution network substation, and monitor the load and transformer status in real time, dispatch energy storage equipment to discharge at peak loads and charge at low troughs, optimize the capacity and charging and discharging strategies of energy storage equipment to prevent the transformer from overloading.
Through load balancing and transfer, we can slow down the pressure of upgrading the distribution network, improve transformer utilization, reduce grid operation costs, avoid unnecessary expansion investment, and promote new energy consumption and energy conservation and emission reduction.
Smart Images
Figure CN119602340A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of energy storage technology, and in particular to a distributed energy storage delay distribution equipment upgrade and transformation control strategy. Background Art
[0002] Distributed energy storage is a form of energy storage configuration with small capacity and power, generally no more than 10MWh, power between a few kilowatts and several megawatts, and close to the load end. Distributed energy storage can smooth the output curve of distributed new energy, improve the absorption rate of new energy, and quickly respond to changes in active power and reactive power in the distribution network, adjust frequency and voltage, ease load fluctuations, and improve power supply quality. The application of distributed energy storage helps to promote the construction of active distribution networks and improve the distribution network's ability to connect to and absorb high-proportion distributed new energy. Using energy storage systems to smooth the peaks and fill the valleys of the load curve can effectively optimize the distribution network flow distribution, reduce network losses, and alleviate power congestion. Distributed energy storage systems can charge when electricity prices are low and discharge when electricity prices are high, achieving the effect of smoothing the peaks and filling the valleys. This can not only reduce the user's electricity costs, but also reduce the load pressure of the distribution network and delay the upgrading and transformation of distribution equipment. The power output of the distributed energy storage system can supplement the peak load demand on the user side, thereby avoiding the expansion of the overall system capacity to meet the temporary load power peak demand. This can not only reduce the initial investment of the project, but also improve the utilization rate of equipment. As the number of electric vehicles continues to increase, the load variation in the distribution network is also increasing. Distributed energy storage systems can cooperate with thermal power units to assist in frequency regulation of the distribution network with a high proportion of new energy access, effectively supplementing the defects of slow efficiency and low precision of thermal power units, and alleviating the pressure on frequency regulation of the power system.
[0003] Using energy storage to shift peaks and fill valleys to reduce the peak-valley difference in load can not only alleviate transformer overload, but also reduce the power backflow from the distribution network to the main grid, and improve the distribution network's ability to absorb distributed power sources and new energy sources for electric vehicles. How to design a reasonable energy storage control strategy is the key to solving the problem of excessive peak-valley difference in distribution network load.
[0004] With the development of electric vehicles, the proportion of electric vehicles connected to the distribution network as a charging load is getting higher and higher. Due to the centralized charging behavior of electric vehicles during the peak load of the distribution network, which overlaps with the peak load period of the system, the load peak is further increased, thereby increasing the operating burden of the transformer and causing transformer overload. At the same time, due to the characteristics of centralized charging of electric vehicles, the peak load period of the distribution network is too short, resulting in a short transformer overload time. If the transformer capacity expansion method is adopted, it will not only increase the investment in distribution network equipment, but also reduce the utilization rate of distribution transformer equipment, and the expansion economy is not good.
[0005] Distributed energy storage technology, with its unique characteristics and advantages, plays an important role in delaying the upgrade and transformation of distribution equipment. Through reasonable control strategies and application scenario design, the potential of distributed energy storage can be fully utilized to provide strong support for the safe, stable and economical operation of the power system. Summary of the invention
[0006] The purpose of the present invention is to provide a distributed energy storage control strategy for delaying the upgrade and transformation of distribution equipment. Through the energy storage charging and discharging control strategy, the grid load is balanced and the pressure on the distribution equipment is reduced. The application of energy storage systems can also improve the utilization rate of equipment and avoid expanding the overall system capacity to meet the temporary load power peak demand. Distributed energy storage systems can delay the expansion and upgrade of distribution equipment, thereby reducing the investment and operating costs of the power system.
[0007] To achieve the above object, the present invention provides the following technical solutions:
[0008] Distributed energy storage devices are connected at the outlet of the distribution network substation or in the feeder. These devices can release electric energy during peak loads and absorb electric energy during low loads, thereby achieving load balance and transfer. In this way, the pressure on the upgrade of the distribution network can be alleviated, the utilization rate of transformers can be improved, and the operating cost of the power grid can be reduced.
[0009] The objective function of the control strategy is set to prevent the transformer from overloading, that is, the apparent power of the transformer should be less than the maximum load capacity of the transformer. By deploying intelligent monitoring equipment, the operating status of the distribution network and transformer is monitored in real time, including parameters such as load power, voltage, and current. Using data analysis technology, the monitoring data is processed and analyzed to obtain the laws and trends of load changes.
[0010] Distributed energy storage devices are dispatched based on real-time monitored load data and transformer operating status. When the load is peak, the energy storage device releases electricity to reduce the burden on the transformer; when the load is low, the energy storage device absorbs electricity for later use.
[0011] By optimizing the capacity, power and charging and discharging strategies of energy storage equipment, we can ensure that energy storage equipment can play its best role under different load conditions. At the same time, we should consider the economy and sustainability of energy storage equipment and select appropriate energy storage technology and equipment types.
[0012] Establish a fault warning mechanism to monitor the fault conditions of energy storage equipment and distribution networks in real time. Once a fault or abnormality is found, immediately initiate emergency response procedures to ensure the safe and stable operation of the power grid.
[0013] Through the charging and discharging operation of energy storage equipment, load balancing and transfer can be achieved. When the load is peak, the energy storage equipment releases electric energy to reduce the burden on the transformer; when the load is low, the energy storage equipment absorbs electric energy for later use. This can effectively alleviate the pressure of upgrading the distribution network.
[0014] By optimizing the configuration and dispatching strategy of energy storage equipment, the utilization rate of transformers can be improved. During peak load, energy storage equipment can replace part of the transformer capacity, thereby extending the service life of the transformer and reducing maintenance costs.
[0015] The operation cost of the power grid can be reduced through the scheduling and optimal configuration of energy storage equipment. Energy storage equipment can absorb low-priced electricity during low-load periods and release high-priced electricity during peak load periods, thereby achieving arbitrage benefits. At the same time, energy storage equipment can also reduce the loss and failure rate of the power grid, further reducing operating costs.
[0016] When the state of charge of the energy storage system is lower than the set lower limit or a charging instruction is received, the energy storage system starts charging. The charging power is limited by equality constraints and inequality constraints to ensure the safety and efficiency of the charging process.
[0017] When the state of charge of the energy storage system is higher than the set upper limit or a discharge instruction is received (and the grid or load requires electrical energy), the energy storage system begins to discharge. The discharge power is also limited by equality constraints and inequality constraints.
[0018] In the power system, the transformer, as a key device for power transmission and distribution, needs to maintain power balance, that is, the power input from the high-voltage side of the transformer should be equal to the power output from the low-voltage side (taking into account the transformer's own losses, the actual output power will be slightly less than the input power).
[0019] When P S+ Greater than P S- When , it means that the transformer provides more electric energy to the distribution network than the electric energy absorbed from the distribution network. At this time, the transformer is in the "sending" state.
[0020] When P S- Greater than P S+ When the transformer absorbs more power from the distribution network than it provides to the distribution network, the transformer is in the "absorption" state, that is, the reverse power state. However, this situation should be avoided as much as possible under normal circumstances, because it may lead to instability of the power system.
[0021] When formulating the control strategy, it is necessary to consider the rated power P of the transformer. T And the actual running P S+ and P S- By monitoring these parameters in real time, it can be determined whether the transformer is in normal operation.
[0022] If P S+ and P S- The sum exceeds the rated power P of the transformer T , it indicates that the transformer may be in an overloaded state and corresponding control measures need to be taken to reduce the load or increase the capacity of the transformer.
[0023] At the same time, factors such as transformer efficiency, losses, and load fluctuations also need to be considered to ensure the stable operation of the power system.
[0024] Based on the above power constraints, corresponding control strategies can be formulated to optimize the operation of the power system. For example, during peak load periods, the output capacity of the transformer can be increased by adjusting the tap position of the transformer or adding parallel transformers.
[0025] During the low load period, the transformer loss and energy consumption can be reduced by lowering the transformer output voltage or reducing the number of parallel transformers.
[0026] In addition, advanced technologies such as energy storage systems and renewable energy can be combined to achieve intelligent management and optimized operation of the power system.
[0027] Peak shaving and valley filling: Through the charging and discharging of the energy storage system, the peak shaving and valley filling of the distribution network load is achieved. During the peak load period, the energy storage is discharged to reduce the burden on the transformer; during the low load period, the energy storage is charged to store electrical energy.
[0028] Power balance: Ensure that the energy storage system maintains power balance during the charging and discharging process, that is, the charging power is equal to the discharging power, so as to maintain the stable operation of the energy storage system.
[0029] State of charge management: By reasonably setting the upper and lower limits of the energy storage system's state of charge, and adjusting the value of the valley fill line through iterative calculation, it is ensured that the energy storage system's charge and discharge amounts are equal on a typical day, so that the energy storage's state of charge operates within a reasonable range.
[0030] The working mechanism of the distributed energy storage delay distribution equipment upgrade and transformation control strategy is a complex and delicate process involving multi-faceted coordinated operations, which aims to optimize the operating status of the distribution network and achieve multiple benefits through the rational use of distributed energy storage equipment.
[0031] First, at the level of the distribution network architecture, choose to connect distributed energy storage devices at the outlet of the distribution network substation or in the feeder. This layout allows energy storage devices to be deeply integrated into the power transmission link of the distribution network, becoming a key link in regulating the balance of power supply and demand.
[0032] In daily operation, energy storage equipment plays a unique role in regulating electricity according to the real-time changes in load. During peak load periods, such as during the daytime on weekdays, the demand for electricity for industrial production and residents' daily life increases sharply, and the load pressure on the power grid increases sharply. Distributed energy storage equipment will start the discharge mode and release the pre-stored electric energy to the power grid, thereby effectively reducing the burden on distribution equipment such as transformers and avoiding problems such as overload due to excessive load in a short period of time.
[0033] During low-load periods, such as at night when most residential and commercial electricity demand is reduced, there is excess electricity in the power grid. At this time, the energy storage device switches to charging mode to absorb and store the low-priced electricity during these low-load periods, preparing for the subsequent peak power consumption period. Through this charging and discharging cycle operation at different time periods, the "peak shaving and valley filling" of the distribution network load is achieved, making the power grid load curve smoother, greatly alleviating the upgrade pressure faced by the distribution network due to excessive load fluctuations.
[0034] At the same time, in order to ensure the efficient and stable operation of the entire system, a series of monitoring, analysis and control measures are closely coordinated. By deploying intelligent monitoring equipment, various operating status parameters of the distribution network and transformers can be monitored in real time and accurately, covering key indicators such as load power, voltage, and current. With the help of advanced data analysis technology, these massive monitoring data are deeply processed and carefully analyzed to accurately grasp the laws and trends of load changes.
[0035] Based on these real-time monitoring data and analysis results, the distributed energy storage equipment is finely dispatched. Not only should the charging and discharging timing of the energy storage equipment be determined according to the specific conditions of the load peak and valley, but the capacity, power and charging and discharging strategies of the energy storage equipment should also be further optimized. For example, according to the electricity consumption characteristics of different seasons and regions, the discharge power of the energy storage equipment is reasonably adjusted to ensure that it can provide sufficient power support during peak hours, and at the same time, it can make full use of the power resources during valley hours when charging, without causing negative impact on the power grid. When selecting energy storage equipment, its economy and sustainability are also fully considered, and the most suitable solution for the current distribution network operating environment is selected from a variety of energy storage technologies and equipment types to achieve long-term stable and economical and efficient operation.
[0036] In addition, to ensure the safe and stable operation of the power grid, a complete fault warning mechanism has been established. This mechanism can monitor the possible faults of energy storage equipment and distribution network in real time. Once any abnormal condition is detected, whether it is a fault of the energy storage equipment itself, such as battery overheating, abnormal charging and discharging, etc., or a fault of the distribution network line, such as short circuit, leakage, etc., the emergency handling procedure will be immediately initiated. By taking corresponding measures in a timely manner, such as cutting off the faulty line and adjusting the operation mode of the energy storage equipment, it is ensured that the power grid can continuously and stably provide power services to users.
[0037] During the operation of the entire system, we also focus on achieving multiple key operating goals to ensure overall benefits. In terms of power balance, we ensure that the energy storage system maintains equal charging power and discharging power during the charging and discharging process. This can maintain the stable operation of the energy storage system itself and avoid a series of problems caused by power imbalance, such as reduced power quality and equipment damage. In terms of state of charge management, by reasonably setting the upper and lower limits of the state of charge of the energy storage system and accurately adjusting the value of the valley fill line with the help of iterative calculations and other means, the energy storage system can achieve an equal state of charge and discharge on a typical day, thereby ensuring that the state of charge of the energy storage always operates within a reasonable range, which can not only fully utilize the energy storage capacity of the energy storage equipment, but also effectively extend its service life.
[0038] Through the coordinated operation of the above links, the distributed energy storage delay distribution equipment upgrade control strategy has achieved significant advantages in many aspects. On the one hand, load transfer and balance are realized, which effectively slows down or even avoids the upgrade demand of the distribution network, improves the utilization rate of existing equipment, and at the same time improves the utilization rate of transformer expansion capacity, avoiding unnecessary expansion investment. On the other hand, the stability and reliability of the power grid are enhanced, and the stable operation of the power grid is guaranteed by preventing transformer overload. In addition, when an emergency occurs, the distributed energy storage equipment can be used as an emergency backup power supply to provide power support for critical loads. In addition, it also promotes the consumption of new energy and energy conservation and emission reduction. By combining with distributed new energy and optimizing the charging and discharging strategy of energy storage equipment, the efficient utilization and consumption of new energy are realized, while the energy consumption and emissions of the power grid are reduced. Finally, it brings significant economic benefits, which not only reduces the investment cost of power grid enterprises, but also increases the benefits of users who access distributed energy storage equipment.
[0039] In summary, the working mechanism of this control strategy achieves all-round optimization of the distribution network through the close integration of distributed energy storage equipment and distribution network and a series of supporting monitoring, regulation and guarantee measures, and plays an important role in the sustainable development of the power system.
[0040] The advantages of the control strategy of distributed energy storage to delay the upgrade and transformation of distribution equipment are mainly reflected in the following aspects:
[0041] 1. Improve equipment utilization and delay upgrades
[0042] Load transfer and balancing: This strategy can achieve effective load transfer by connecting distributed energy storage devices at the outlet of the distribution network substation or in the feeder. During peak hours, energy storage devices can release electricity to reduce the burden on transformers; during off-peak hours, energy storage devices can absorb electricity to prepare for peak hours. This load transfer mechanism helps to slow down or even avoid the need to upgrade the distribution network and improve the utilization rate of existing equipment.
[0043] Transformer expansion capacity utilization rate improvement: By defining the transformer expansion capacity utilization rate η T This strategy can quantify the actual utilization effect of the transformer after capacity expansion. By optimizing the charging and discharging strategy of the energy storage device, it can ensure that the actual utilization rate of the transformer after capacity expansion is improved, thereby avoiding unnecessary expansion investment.
[0044] 2. Enhance grid stability and reliability
[0045] Prevent transformer overload: This strategy sets an objective function to ensure that the transformer operating apparent power is less than its maximum load capacity. This helps prevent the transformer from being damaged due to overload and ensures stable operation of the power grid.
[0046] Improve the grid's ability to respond to emergencies: Distributed energy storage equipment can serve as an emergency backup power source for the grid, providing power support for critical loads when emergencies occur, thereby enhancing the reliability of the grid.
[0047] 3. Promote the consumption of new energy and energy conservation and emission reduction
[0048] Promote the access and consumption of distributed renewable energy: Distributed energy storage equipment can be combined with distributed renewable energy to achieve efficient utilization and consumption of renewable energy by optimizing the charging and discharging strategies of energy storage equipment.
[0049] Energy saving and emission reduction: By reducing the need for distribution network upgrades and improving equipment utilization, this strategy helps reduce the energy consumption and emissions of the power grid, in line with the green and low-carbon development concept.
[0050] 4. Significant economic benefits
[0051] Reduce investment costs: By delaying the need to upgrade the distribution network, this strategy can reduce the investment costs of power grid companies and improve economic benefits.
[0052] Improve user benefits: For users who access distributed energy storage devices, by optimizing the charging and discharging strategies of energy storage devices, they can reduce their own electricity costs and improve economic benefits.
[0053] In summary, the distributed energy storage delayed distribution equipment upgrade and transformation control strategy has shown significant advantages in improving equipment utilization, enhancing grid stability and reliability, promoting new energy consumption and energy conservation and emission reduction, and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS
[0054] Figure 1 It is an IEEE33-node calculation system;
[0055] Figure 2 The DG output and load of S1 and the electric vehicle load curve on a typical day;
[0056] Figure 3 Comparison of distribution network load before and after the access of distributed power sources and electric vehicles;
[0057] Figure 4 Comparison of distribution network load before and after energy storage access The energy storage control strategy is determined using the method in this section;
[0058] Figure 5 Energy storage charging and discharging power for each node;
[0059] Figure 6 This is the flow chart of energy storage control strategy. DETAILED DESCRIPTION
[0060] The technical solutions in the embodiments of the present invention will be fully described below in conjunction with the accompanying drawings in the embodiments of the present invention.
[0061] like Figure 1-6 As shown in FIG. 1 , the control strategy for delaying the upgrade and transformation of distribution equipment by distributed energy storage includes the following steps:
[0062] Connecting distributed energy storage devices at the substation exit or in the feeder to achieve load transfer can slow down or even avoid distribution network upgrades and improve the utilization rate of existing equipment.
[0063] Definition η T To expand the capacity utilization of transformers
[0064]
[0065] E ex =(P T1 -P T2 )×T
[0066]
[0067] Among them, E ol is the transformer overload power, E ex The additional power brought by the transformer expansion, P T1 is the power after transformer expansion, P T2is the power of the transformer before expansion, T is the period, P s (t i ) is the load power; the transformer expansion capacity utilization rate is the ratio of the additional power required by the load to the power transmitted after the transformer expansion, which represents the actual utilization rate of the transformer after expansion;
[0068] P T1 is the rated power of the transformer after expansion, P T2 is the power of the transformer before expansion. The original load peak is 3715kW. The peak of power demand is solved by expanding the transformer capacity. The capacity utilization rate of the expanded transformer is about 13%, and the cost of upgrading the power grid is huge. Solving the peak of power demand by expanding the transformer will cause serious waste of resources. Through the regulation of energy storage, energy storage is used to bear the load curve after the peak power demand. Energy storage regulation alleviates the requirements for upgrading and expanding the power grid transformer. After the energy storage is connected, the transformer capacity utilization rate is 37.2%, and the transformer capacity utilization rate is increased by 24.2%. Therefore, energy storage can greatly improve the transformer capacity utilization rate, which not only effectively delays the upgrading and transformation of distribution transformers, but also can replace the construction of grids. Especially for distribution networks in remote areas, distributed energy storage is more economical to delay the upgrading and transformation of distribution equipment.
[0069] To prevent the transformer from overloading, the transformer operating apparent power should be less than the transformer maximum load. The objective function is set as:
[0070]
[0071] Among them, P S+ (t), P S- (t) are two non-negative variables, P S+ (t) represents the active power flowing from the high-voltage side of the main transformer to the distribution network at time t, P S -(t) is the active power sent back from the high-voltage side of the main transformer to the upper grid at time t, and P S+ (t), P S- (t) satisfies P S+ (t)P S- (t) = 0, α is the maximum load rate of the transformer, S T Rated apparent power of the main transformer.
[0072] Set the charging and discharging power and power constraints of the energy storage system
[0073] The constraints include equality constraints during the energy storage charging and discharging process and inequality constraints on the energy storage charge state:
[0074] The equality constraints are as follows:
[0075] Charging process:
[0076]
[0077] Discharge process:
[0078]
[0079] Among them, SOC(t) is the state of charge of the energy storage at time t, and SOC(t+Δt) is the state of charge of the energy storage at the next time; P dc (t) is the energy storage discharge power, in kW; P c (t) is the energy storage charging power, in kW; charging is negative and discharging is positive; Δt is the time interval;
[0080] Its inequality constraints are:
[0081] SOC min <SOC(t)<SOC max
[0082] Among them, SOC(t) is the state of charge of the energy storage at time t, SOC min , SOC max They are the upper and lower limits of the energy storage charge state; during the operation of the energy storage, the charge state should not exceed the set upper and lower limits, otherwise overcharging and over-discharging will occur.
[0083] Transformer operation constraints:
[0084] max{P S+ ,P S-}≤P T
[0085] Among them, P T is the transformer rated power, P S+ Represents the active power flowing from the high voltage side of the main transformer to the distribution network, P S- It represents the active power sent back from the high-voltage side of the main transformer to the upper grid, and P S+ , P S- Satisfy P S+ P S- =0.
[0086] Energy storage charging and discharging control strategy design
[0087] The basic idea of the developed control strategy is to use energy storage to store electric energy during the period of power backfeed from the distribution network to the main grid, and release electric energy during transformer overload, so as to delay the expansion of transformer capacity. Considering the initial state of charge of energy storage in a typical day, the discharge amount of energy storage in a typical day is made the same as the discharge amount of reducing the transformer load rate, so that the energy storage charge state can operate in a reasonable range.
[0088] The steps to develop a control strategy are as follows:
[0089] S31: Data processing layer, input typical daily distribution network load, distributed power, electric vehicle data, distribution transformer rated power P T 、Energy storage rated capacity E ESS , charge and discharge efficiency c, d, state of charge SOC at the initial moment of energy storage 0 , upper and lower limits of state of charge SOC max , SOC min ; Simulate the operation of distributed power sources and electric vehicles connected to the distribution network, perform power flow calculation, and obtain the main grid power supply load power P after calculation S (t), determine its minimum value P within a typical day Smin =min{P S (t)};
[0090] S32: Energy storage discharge calculation layer, in order to prevent transformer overload, according to the determined distribution network transformer rated power P T , using this power as the distribution network load P S The peak shaving line is then used to calculate the energy storage discharge power and the amount of electricity that needs to be released by the energy storage in a typical day based on the difference between this and the main grid power supply load; that is, when the distribution network load power P S (t) is greater than the transformer rated power P T When , the energy storage is discharged, and the energy storage discharge power is Pdc(t) = (PL(t)-PT) / d, otherwise the discharge power is 0, the discharge amount is calculated (Edc = ΣPdc(t)Δt), and the energy storage discharge power is recorded as Pdc(t);
[0091] S33: Energy storage charging iterative calculation layer: Set the initial value of the valley line to the load valley value Pgh = PSmin, start charging from the main grid power supply load valley, and calculate the energy storage charging power Pc(t) and the typical daily energy storage charging amount E according to the load valley value and the load difference. C ;
[0092] S34: Energy storage output power layer: Determine whether the energy storage charge and discharge amounts are close to the same. If so, the iteration ends. Otherwise, move the valley filling line up according to Pgh=Pgh+dpc, where dpc is a very small iteration step. Return the updated valley filling line value to the energy storage charging iteration calculation layer until the iteration condition that the calculated energy storage daily charge and discharge amounts are the same is met, and output the typical daily charge and discharge power of the energy storage.
[0093] Energy storage charging and discharging power P ESS :
[0094]
[0095] Example parameters, see Figure 1, the IEEE33 node example system is selected, which is a typical radial distribution network. The system voltage level, that is, the base voltage is 10kV, the system base capacity is SB=10MVA, and the total system load is 3715+j2400kVA. The rated capacity of the distribution transformer is 3500kVA, and the rated power PT=2976kW.
[0096] The total power of electric vehicle charging load is 2MW. The electric vehicle charging load is evenly distributed at the 14, 15, 16, 17, 18, 30, 31, and 32 nodes with smaller loads at the end of the line. The rated charging power is 200kW. Distributed power sources are distributed at nodes with larger loads. The total photovoltaic capacity connected is 2MW. Nodes 24 and 25 are connected to photovoltaic power of 800kW each, and nodes 30 and 32 are connected to photovoltaic power of 200kW each. The total wind power capacity connected is 0.8MW, and wind power of 200kW is connected to nodes 4, 7, 8, and 14. In order to verify the effectiveness of the energy storage control strategy, the energy storage capacity is formulated based on the scenario with the greatest demand for energy storage discharge. Energy storage is configured at the photovoltaic access node at the same time. 8 nodes are configured with 0.17MW / 0.48MWh, 24 nodes are configured with 1MW / 2.83MWh, and 25 nodes are configured with 0.33MW / 0.94MWh. See Figure 1 .
[0097] Energy storage selection: Figure 2 It can be seen that the discharge duration of lithium iron phosphate batteries is from seconds to hours, and the charging and discharging efficiency is high. Therefore, the energy storage unit of this example adopts lithium iron phosphate batteries, whose upper and lower limits of state of charge SOC are 0.1-0.9, and the charging and discharging efficiency is 95%.
[0098] In order to test the effectiveness of the control strategies involved, Figure 2 Taking the scenario as an example, this typical scenario belongs to the spring and winter seasons. The wind is strong in this season, so the wind power output level is high and the wind power output curve is relatively stable. At the same time, this typical day is sunny, so the photovoltaic output is large.
[0099] Depend on Figure 2 It can be seen that during 0:00-8:00, the load level is not high. At this time, the electric vehicle charging load is large, the photovoltaic output is low, and the distribution network load level is not high. During 11:00-18:00, the distributed power output is large, and power reverse occurs. During 19:00-25:00, the photovoltaic power is out of operation, and the charging load overlaps with the peak load. At this time, the distribution network load is at its peak and the transformer is overloaded.
[0100] like Figure 3As shown in the figure, after the access of new energy, the peak-to-valley difference of the system load increases. During the period from 20:00 to 22:00 in the evening, since the output of photovoltaic power is basically 0 at night, and the output of wind power is less than that of electric vehicles, electric vehicles are charged in a centralized manner at this time, the load of the distribution network is at its peak, and the transformer is in an overloaded state, as shown in the red shaded part in the figure. At this time, the load of the distribution network is in the overload zone. During the period from 7:55 to 8:00 and 15:00 to 16:40, due to the large output of photovoltaic power, the superimposed load of electric vehicles and loads is small, and the output of distributed power sources fully meets the load demand, resulting in power reverse transmission. At this time, the load of the distribution network is in the reverse transmission zone. Using energy storage to shift the electric energy in the reverse transmission zone to the overload zone can not only effectively solve the transformer overload problem, but also reduce the power reverse transmission from the distribution network to the main grid.
[0101] Figure 4 Comparison of distribution network load before and after energy storage access The energy storage control strategy is determined using the method in this section, such as Figure 4 As shown in the figure, after the energy storage is connected, the peak-to-valley difference of the distribution network load is reduced. During the power reverse transmission period, the electric energy is stored, so that the distribution network load is greater than 0, reducing the power reverse transmission to the main grid, which is beneficial to the distribution network's consumption of distributed power sources. During the transformer overload period, the electric energy is released, which reduces the transformer load rate, which is beneficial to the increase in the proportion of electric vehicles connected to the distribution network. Therefore, the access of energy storage flattens the load curve, effectively reduces the peak-to-valley difference of the load, and effectively solves the transformer overload and power reverse transmission problems brought to the distribution network by the high penetration rate of new energy access. Figure 5 Store energy for each node and charge and discharge power.
Claims
1. A distributed energy storage delay distribution equipment upgrade control strategy, characterized in that: The following steps are involved: S1: Connect distributed energy storage equipment at the outlet of the distribution network substation or in the feeder; realize load transfer, slow down or even avoid the upgrade of the distribution network, and improve the utilization rate of existing equipment; Definition η T is the transformer expansion capacity utilization rate, and its formula is: E ex =(P T1 -P T2 )×T Among them, E ol is the transformer overload power, E ex The additional power brought by the transformer expansion, P T1 is the power after transformer expansion, P T2 is the power of the transformer before expansion, T is the period, P s (t i is the load power; the transformer expansion capacity utilization rate is the ratio of the additional power required by the load to the power transmitted after the transformer expansion, which represents the actual utilization rate of the transformer after expansion; S2: Control strategy formulation; To prevent the transformer from overloading, the transformer operating apparent power should be less than the transformer maximum load. The objective function is set as: Among them, P S+ (t), P S- (t) are two non-negative variables, P S+ (t) represents the active power flowing from the high-voltage side of the main transformer to the distribution network at time t, P S- (t) is the active power sent back from the high-voltage side of the main transformer to the upper grid at time t, and P S+ (t), P S- (t) satisfies P S+ (t)P S- (t) = 0, α is the maximum load rate of the transformer, S T Rated apparent power of the main transformer.
2. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 1 is characterized in that: The control strategy is formulated, and the energy storage system charging and discharging power constraints are set as: The constraints include equality constraints during the energy storage charging and discharging process and inequality constraints on the energy storage charge state: The equality constraints are as follows: Charging process: Discharge process: Among them, SOC(t) is the state of charge of the energy storage at time t, and SOC(t+Δt) is the state of charge of the energy storage at the next time; P dc (t) is the energy storage discharge power, in kW; P c (t) is the energy storage charging power, in kW; charging is negative and discharging is positive; Δt is the time interval; Its inequality constraints are: SOC min <SOC(t)<SOC max Among them, SOC(t) is the state of charge of the energy storage at time t, SOC min , SOC max They are the upper and lower limits of the energy storage charge state; during the operation of the energy storage, the charge state should not exceed the set upper and lower limits, otherwise overcharging and over-discharging will occur.
3. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 1 is characterized in that: The control strategy is formulated and the power constraint condition is set as: Transformer operation constraints: max{P S+ ,P S- }≤P T Among them, P T is the transformer rated power, P S+ Represents the active power flowing from the high voltage side of the main transformer to the distribution network, P S- It represents the active power sent back from the high-voltage side of the main transformer to the upper grid, and P S+ , P S- Satisfy P S+ P S- =0.
4. The distributed energy storage delay distribution equipment upgrade control strategy according to any one of claims 1 to 3, characterized in that: Including energy storage charging and discharging control strategy: Energy storage is used to store electric energy during the period of power reverse transmission from the distribution network to the main grid, and electric energy is released during transformer overload to delay transformer expansion. The initial charge state of energy storage in a typical day is considered, so that the discharge amount of energy storage in a typical day is the same as the discharge amount of reducing the transformer load rate, so that the energy storage charge state can operate in a reasonable range; The control strategy steps are as follows: S31: Data processing layer, input typical daily distribution network load, distributed power, electric vehicle data, distribution transformer rated power P T 、Energy storage rated capacity E ESS , charge and discharge efficiency c, d, state of charge SOC0 at the initial moment of energy storage, upper and lower limits of state of charge SOC max , SOC min ; Simulate the operation of distributed power sources and electric vehicles connected to the distribution network, perform power flow calculation, and obtain the main grid power supply load power P after calculation S (t), determine its minimum value P within a typical day Smin =min{P S (t)}; S32: Energy storage discharge calculation layer, in order to prevent transformer overload, according to the determined distribution network transformer rated power P T , using this power as the distribution network load P S The peak shaving line is then used to calculate the energy storage discharge power and the amount of electricity that needs to be released by the energy storage in a typical day based on the difference between this and the main grid power supply load; that is, when the distribution network load power P S (t) is greater than the transformer rated power P T When , the energy storage is discharged, and the energy storage discharge power is Pdc(t) = (PL(t)-PT) / d, otherwise the discharge power is 0, the discharge amount is calculated (Edc = ΣPdc(t)Δt), and the energy storage discharge power is recorded as Pdc(t); S33: Energy storage charging iterative calculation layer: Set the initial value of the valley line to the load valley value Pgh = PSmin, start charging from the main grid power supply load valley, and calculate the energy storage charging power Pc(t) and the typical daily energy storage charging amount E according to the load valley value and the load difference. C ; S34: Energy storage output power layer: Determine whether the energy storage charge and discharge amounts are close to the same. If so, the iteration ends. Otherwise, move the valley filling line up according to Pgh=Pgh+dpc, where dpc is a very small iteration step. Return the updated valley filling line value to the energy storage charging iteration calculation layer until the iteration condition that the calculated energy storage daily charge and discharge amounts are the same is met, and output the typical daily charge and discharge power of the energy storage.
5. The distributed energy storage delay distribution equipment upgrade control strategy according to any one of claims 1 to 3, characterized in that: Energy storage charging and discharging power P ESS :
6. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 1 is characterized in that: The IEEE 33-node example system is selected. The system voltage level is 10 kV, the system base capacity is SB = 10 MVA, the system total load is 3715 + i2400 kVA, the distribution transformer rated capacity is 3500 kVA, and the rated power P T =2976kW.
7. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 6 is characterized in that: The total photovoltaic capacity connected to the IEEE33-node example system is 2MW, 800kW photovoltaic capacity is connected to nodes 24 and 25, 200kW photovoltaic capacity is connected to nodes 30 and 32, and the total wind power capacity connected is 0.8MW. 200kW wind power is connected to nodes 4, 7, 8, and 14. In order to verify the effectiveness of the energy storage control strategy, the energy storage capacity is formulated based on the scenario with the greatest demand for energy storage discharge. Energy storage is configured at the photovoltaic access node at the same time. 8 nodes are configured with 0.17MW / 0.48MWh, 24 nodes are configured with 1MW / 2.83MWh, and 25 nodes are configured with 0.33MW / 0.94MWh.
8. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 6 is characterized in that: The energy storage unit of the IEEE33-node example system uses lithium iron phosphate batteries, with the upper and lower limits of the state of charge SOC being 0.1-0.9 and the charge and discharge efficiency being 95%.
9. The distributed energy storage delay distribution equipment upgrade control strategy according to claim 1 is characterized in that: When the output of distributed power sources fully meets the load demand and power reverse is generated, the load of the distribution network is in the reverse zone. By using energy storage to transfer the electric energy in the reverse zone to the overload zone, the transformer overload problem can be effectively solved and the power reverse from the distribution network to the main grid can be reduced.
10. A distributed energy storage delay distribution equipment upgrade control strategy according to claim 1, characterized in that: The strategy is put into test to test the effectiveness of the control strategy, specifically by selecting a typical scenario and a typical day, and testing its effect with the distributed power output and load and electric vehicle load curve of the typical scenario and the typical day.