Large-scale photovoltaic power station AC-DC coupling energy storage design method and verification analysis

Abstract

The invention discloses a large-scale photovoltaic power station AC-DC coupling energy storage design method and verification analysis, and belongs to the fields of new energy, photovoltaic power generation, civil power distribution and electronic power. S1, establishing an AC / DC hybrid energy storage system and a topological structure; s2, constructing a direct current side hybrid energy storage configuration method; s3, constructing an alternating current side hybrid energy storage configuration method; s4, constructing an AC-DC side hybrid energy storage configuration method; s5, performing dual verification of simulation and experiment; an energy storage battery with large power density and long cycle life is configured on the AC side of a photovoltaic power station and is mainly used for primary frequency modulation and other functions, the charging and discharging times of a DC side energy storage device can be effectively reduced, and the service life of the battery is prolonged; an energy storage battery with high energy density is arranged on the direct current side, the capacity ratio of the photovoltaic power station is improved, electric energy loss caused by over-capacity of the photovoltaic power station is reduced, and the power generation benefit of the photovoltaic power station is improved; the direct-current side energy storage device and the photovoltaic string share the centralized inversion and boosting all-in-one machine, so that the utilization rate of alternating-current equipment and cables of the photovoltaic power station is improved, and the investment cost is saved.

Description

Technical Field

[0001] The present invention relates to multiple fields such as new energy, photovoltaic power generation, industrial and civilian power distribution, electronic power, etc., and specifically to a design method and verification analysis of AC / DC coupled energy storage in a large photovoltaic power station. Background Art

[0003] According to data released by the National Energy Administration, by the end of 2021, China's total installed capacity of photovoltaic and wind power will exceed 600,000 MW, accounting for more than 44.6% of the total installed power generation capacity, and the power generation generated by photovoltaic and wind power will exceed 970 million MW.h, accounting for more than 11.7% of China's total electricity consumption. Following the current policy trend, the installed capacity of photovoltaic and wind power and their share of power generation will continue to increase. At the same time, new energy sources such as photovoltaic and wind power have the characteristics of strong volatility in output, weak power support, and strong synchronization performance. If they are connected to the power system in large quantities, it will have a very serious adverse impact on the safe and stable operation of the power system.

[0004] As a flexible and controllable means, energy storage plays a critical role in improving the peak and frequency regulation efficiency of the power system and promoting the consumption of new energy. It is an indispensable facility for building a power system with large-scale new energy, and it is also a key support for achieving the dual carbon goals. According to the "Guiding Opinions on Promoting the Integration of Power Sources, Grids, Loads and Storage and the Development of Multi-Energy Complementarity", each region needs to actively explore the "wind, light and storage integration" model based on its own resource conditions and energy characteristics. It can be clearly seen that under the strong promotion of the dual carbon goals, new energy storage has become an inevitable trend and will surely be widely promoted and applied.

[0005] Most of the research on energy storage configuration for existing photovoltaic projects focuses on the economic comparison and screening of different types of energy storage devices, as well as the primary frequency regulation function of energy storage devices. However, there are two shortcomings. On the one hand, the types of energy storage are relatively single, and the advantages of different types of energy storage devices have not been fully integrated and highlighted. Current energy storage technologies can be roughly divided into five categories, namely mechanical energy storage, electromagnetic energy storage, electrochemical energy storage, thermal energy storage, and chemical energy storage. Various energy storage devices have different advantages. For example, flywheel energy storage in mechanical energy storage is a power-type energy storage device with a large power density and a long cycle life, which is more suitable for primary frequency regulation; while lithium iron phosphate batteries in electrochemical energy storage are energy-type energy storage devices with high energy density, which can achieve deep charging and discharging, and can play a good role in the storage and release of energy. The second reason is that the current energy storage wiring method is relatively simple. It is usually directly connected to the 35kV AC bus switchgear of the photovoltaic project, and then connected to the grid after the main transformer is stepped up. It fails to fully tap the efficiency and role that energy storage can play in improving the capacity ratio of photovoltaic projects and improving power generation efficiency when connected on the DC side.

[0006] Therefore, giving full play to the unique advantages of power-type and energy-type hybrid energy storage on the AC and DC sides can effectively reduce the charging and discharging frequency of the energy storage device on the DC side and extend the service life of the DC side energy storage battery; at the same time, it can also save investment costs in energy storage configuration, improve the capacity ratio of photovoltaic power stations, and reduce the power loss caused by over-allocation of photovoltaic power stations. This is of extremely critical value and significance for achieving the goal of reducing costs and increasing efficiency of photovoltaic power stations in a market-based trading mechanism. Summary of the invention

[0007] The present invention mainly solves the technical problems existing in the above-mentioned prior art and provides a design method and verification analysis of AC / DC coupled energy storage in a large photovoltaic power station.

[0008] The above technical problem of the present invention is mainly solved by the following technical solution: a design method for AC / DC coupled energy storage in a large photovoltaic power station, the design method comprising:

[0009] S1. Establish an AC / DC side coupled energy storage system and topological structure; the centralized photovoltaic power generation system is mainly composed of photovoltaic strings, DC combiner boxes, and centralized inverter and booster equipment;

[0010] S1.1. The DC side energy storage device includes a DC side energy storage battery and a DC side energy storage controller; the DC side energy storage device is connected to the DC side of the centralized inverter and booster by means of a dedicated photovoltaic DC cable;

[0011] S1.2, the AC side energy storage device consists of an AC side energy storage battery and an AC side energy storage controller, which are connected to the booster station energy storage switch cabinet via cables;

[0012] S2. Configuration of hybrid energy storage on the DC side. When the lighting conditions are good and the capacity ratio is high, the input power on the DC side of the photovoltaic power station will exceed the maximum input power allowed by the inverter. The photovoltaic power station will then generate power loss due to the limited power generation on the DC side.

[0013] S3, configuration of AC side hybrid energy storage; the AC side energy storage device is composed of an AC side energy storage battery and an AC side energy storage controller, wherein the AC side energy storage controller is responsible for controlling the energy storage and release of the AC side energy storage battery, and the AC side energy storage device is connected to the energy storage incoming cabinet via an AC cable;

[0014] S4, AC / DC hybrid energy storage configuration; the specific process is as follows:

[0015] S4.1. Ensure that the over-generated energy of the photovoltaic modules will not be lost due to the limited power of the inverter; and only participate in the primary frequency regulation of the system when the primary frequency regulation capacity of the AC side energy storage device cannot meet the demand;

[0016] S4.2. The configuration of the AC side energy storage device shall follow the following principle: its capacity shall be at least half of the primary frequency regulation capacity required by the system, and after being integrated with the DC side energy storage device, it shall be able to meet the minimum standards for energy storage configuration of photovoltaic power stations in various regions;

[0017] S4.3. Rationally optimize the system capacity ratio to further reduce the system's cost per kilowatt-hour. The capacity ratio of a photovoltaic system is the ratio of the photovoltaic module power to the inverter rated power.

[0018] A verification analysis of a design method for AC / DC coupled energy storage in a large photovoltaic power station, the verification analysis:

[0019] S5. In this experimental verification and analysis, a 100MW agricultural photovoltaic power generation project in Shanxi Province was selected as a typical case to further explain the joint design method of AC and DC hybrid energy storage on large photovoltaic power stations;

[0020] S5.1. During the experiment, PVsyst software was used to perform simulation calculations. The result of the calculation showed that the power loss between the photovoltaic module and the centralized inverter-boosting integrated machine was 12.81%. Based on this data, it can be inferred that the minimum power required by the DC side energy storage controller should be 0.241MW. In order to ensure the stable operation of the system and reserve a certain margin, P was finally determined. DCi The value of is 0.25MW;

[0021] S5.2. Under normal circumstances, during the period from 10:30 to 14:20, the lighting conditions are ideal, and the input power on the DC side of the centralized inverter-boosting machine often exceeds the maximum input power allowed on the AC side. If the DC side is not equipped with an energy storage device, this excess energy will be wasted. The following are the specific configuration details of the energy storage on the DC side of the photovoltaic array:

[0022] Formula (7):

[0023]

[0024] Taking into account the requirements of the local power grid for energy storage and primary frequency regulation, the requirements for energy storage devices on the AC side of the photovoltaic power station can be determined as follows:

[0025] Formula (8):

[0026]

[0027] Based on the above requirements, after comprehensive and integrated consideration and analysis, the specific configuration details of the AC and DC side energy storage device of the photovoltaic power station are as follows:

[0028] Formula (9):

[0029]

[0030] In the selection of energy storage equipment on the DC side, lithium iron phosphate batteries with higher energy density were used. A comparative analysis was conducted on the power generation of the photovoltaic power station before and after the configuration of the energy storage device. Taking this 100MW agricultural-photovoltaic complementary photovoltaic power generation project as an example, it was demonstrated that under the conditions of different capacity ratios, the configuration of AC and DC side energy storage devices can increase the power generation of the photovoltaic power station.

[0031] S5.3. A photovoltaic power station model was successfully constructed with the help of MATLAB. At the same time, based on the simulation results, a detailed comparison was made on the number of times the photovoltaic power station energy storage battery participated in a frequency modulation under the AC side energy storage configuration strategy and the AC / DC side hybrid energy storage configuration strategy.

[0032] Preferably, in said S1.1, on the DC side, a storage battery with a high energy density is selected to undertake the work of storing and releasing energy, while also having a primary frequency regulation auxiliary function.

[0033] Preferably, in said S1.2, the AC side uses a storage battery with high power density and long cycle life, with a primary frequency regulation function as the main function and energy storage and release as the auxiliary function.

[0034] Preferably, in S2, an energy storage device is provided on the DC side of the photovoltaic power station. This can, on the one hand, give full play to the efficiency of the centralized inverter-boosting integrated machine in the photovoltaic array, and on the other hand, store energy when the DC side is fully generated to prevent power loss, and release energy when the DC side is weakly generated to ensure the stability of photovoltaic power generation. The specific process is as follows:

[0035] S2.1, Assume that the power of the centralized inverter-boosting integrated machine on the AC side of the i-th photovoltaic power generation unit is P 0i , the power generated by the PV module on the DC side is P ri , the design volume ratio is set to r i , the power loss from the photovoltaic module to the centralized inverter booster is recorded as η i , this loss covers the loss of the centralized inverter booster itself; in order to prevent the DC side from losing power due to over-distribution, the power P of the energy storage battery on the DC side of each centralized inverter booster is DCi The configuration should meet the following requirements:

[0036] Formula (1):

[0037]

[0038] In view of the fact that the inverter and box-type transformer have an overload capacity of 1.1 times in the long-term operation, the power of the DC-side energy storage controller should not be less than the difference between the maximum power of the DC-side of the centralized inverter-boost integrated machine and the maximum allowable power of the AC-side, which helps to maintain the stable operation of the entire system and the effective regulation of electric energy;

[0039] S2.2, select the day with the best power generation efficiency of the photovoltaic power station in a year, and calculate the DC side power generation power P of the photovoltaic module in the i-th photovoltaic power generation unit centralized inverter booster ri Exceeds the maximum allowable output power on the AC side by 1.1 P0i The excess power generated during this period is calculated; then, the DC side energy storage battery capacity E of the array DCi The following conditions should be met:

[0040] Formula (2):

[0041]

[0042] S2.3. Select the DC side energy storage controller and DC side energy storage battery according to the energy storage configuration power and capacity requirements of each photovoltaic power generation unit on the DC side; the total power P of the DC side energy storage device DC With total capacity E DC The expression is as follows:

[0043] Formula (3):

[0044]

[0045] In order to prevent the loss of the electric energy generated by the photovoltaic modules due to the limitation of the inverter or box transformer, the capacity ratio of the photovoltaic power station is usually set at 1.1 / (1-η), so as to ensure that the electric energy generated by the photovoltaic modules can be smoothly transmitted through the inverter. If the capacity ratio is further increased, although the cost of electricity of the photovoltaic power station can be reduced to a certain extent, the electric energy generated by the photovoltaic modules will be limited by the inverter, resulting in electric energy loss. According to formula (1), it can be deduced that there is a relationship between the capacity ratio of the photovoltaic power generation unit and the DC side energy storage as shown in formula (4):

[0046] Formula (4):

[0047]

[0048] Preferably, the AC side energy storage device in S3 should be configured in accordance with the following principle: its capacity should be at least half of the primary frequency regulation capacity required by the system, and after working in coordination with the DC side energy storage device, it should be able to meet the minimum standards set by various regions for photovoltaic power station energy storage configuration; the specific implementation steps are as follows:

[0049] S3.1. Meet the minimum energy storage configuration requirements of photovoltaic power stations. Generally, each region has put forward specific requirements for the energy storage configuration of photovoltaic power stations. Taking Jiangxi Province as an example, it stipulates that new energy must be equipped with energy storage devices that are not less than 10% of the installed capacity and have a duration of 1 hour. Based on the total installed capacity data of photovoltaic power stations, the minimum configuration power P of energy storage can be calculated. C And capacity E C ; From this, we can know that the AC side energy storage power of the photovoltaic power station P AC and capacity E AC The following conditions should be met:

[0050] Formula (5):

[0051]

[0052] S3.2, meet the system's primary frequency regulation requirements; if the maximum power of the photovoltaic power station required by the system is P f , the maximum capacity is E f , then the AC side energy storage power P of the photovoltaic power station can be derived AC and capacity E AC The following conditions must be met:

[0053] Formula (6):

[0054]

[0055] According to formula (6), the AC side energy storage controller and the AC side energy storage battery can be screened; generally speaking, in daily operation, the energy storage battery can participate in the primary frequency modulation action thousands of times, while the deep frequency modulation is only about a hundred times; because the AC side energy storage device preferentially participates in the primary frequency modulation, it can greatly reduce the charging and discharging frequency of the DC side energy storage battery, thereby effectively extending the service life of the DC side energy storage device.

[0056] The present invention has the beneficial effects:

[0057] In the present invention: S1, establish an AC / DC hybrid energy storage system and topological structure; S2, construct a DC side hybrid energy storage configuration method; S3, construct an AC side hybrid energy storage configuration method; S4, construct an AC / DC side hybrid energy storage configuration method; S5, the method of the present invention is double-verified by simulation and experiment; configure energy storage batteries with high power density and long cycle life on the AC side of the photovoltaic power station, which are mainly used for primary frequency modulation and other functions, and can effectively reduce the number of charge and discharge times of the DC side energy storage device and increase battery life; configure energy storage batteries with high energy density on the DC side, improve the capacity ratio of the photovoltaic power station, reduce the power loss caused by the over-allocation of the photovoltaic power station, and improve the power generation efficiency of the photovoltaic power station. In addition, the DC side energy storage device and the photovoltaic string share the centralized inverter and booster, which can improve the utilization rate of the photovoltaic power station AC equipment and cables, and save the investment cost of the photovoltaic project energy storage configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The AC / DC hybrid energy storage system and topological structure diagram of the present invention;

[0059] Figure 2 It is a topological structure diagram of the energy storage controller in the present invention;

[0060] Figure 3 This is a monthly power generation diagram of the photovoltaic power station before and after the AC / DC hybrid energy storage configuration in the present invention;

[0061] Figure 4 A diagram showing the improvement ratio of the power generation of a photovoltaic power station by the AC / DC hybrid energy storage configuration under different capacity ratios in the present invention;

[0062] Figure 5 It is a MATLAB simulation diagram of the AC / DC hybrid energy storage system of the photovoltaic power station in the present invention;

[0063] Figure 6 This is a comparison chart of the number of times the photovoltaic power station energy storage battery participates in a frequency modulation under the AC side energy storage configuration strategy and the AC / DC side hybrid energy storage configuration strategy in the present invention. DETAILED DESCRIPTION

[0064] The invention will be further described below with reference to the accompanying drawings and in combination with specific implementations, so that those skilled in the art can implement the invention with reference to the description. The protection scope of the invention is not limited to the specific implementations.

[0065] Generally speaking, conventional photovoltaic power generation systems can be mainly divided into two types: centralized solutions and string solutions. The centralized solution has the characteristics of relatively fewer inverters, which makes it more reliable and more convenient to manage. Its cost is lower than that of the string solution, so it has been widely used in photovoltaic power generation systems. The present invention selects a centralized photovoltaic power station as an example to illustrate a design method for AC / DC coupled energy storage in a large photovoltaic power station.

[0066] The present invention relates to a large-scale photovoltaic power station AC / DC coupled energy storage design method, the method comprising the following steps:

[0067] S1. Establish an AC / DC side coupled energy storage system and topological structure; the centralized photovoltaic power generation system is mainly composed of photovoltaic strings, DC combiner boxes, centralized inverter booster and other equipment (see Figure 1 );

[0068] S1.1. The DC side energy storage device includes the DC side energy storage battery and the DC side energy storage controller. It is connected to the DC side of the centralized inverter and booster with the help of a dedicated DC cable for photovoltaics. On the DC side, energy storage batteries with high energy density are selected, which are mainly responsible for energy storage and release, and also have auxiliary functions such as primary frequency regulation.

[0069] S1.2, the AC side energy storage device consists of an AC side energy storage battery and an AC side energy storage controller, which are connected to the booster station energy storage switch cabinet through cables. The AC side mainly uses energy storage batteries with high power density and long cycle life, with primary frequency regulation and other functions as the main function, supplemented by energy storage and release;

[0070] S2. Configuration of hybrid energy storage on the DC side. When the lighting conditions are good and the capacity ratio is high, the input power on the DC side of the photovoltaic power station will exceed the maximum input power allowed by the inverter. As a result, the photovoltaic power station will suffer power loss due to the limited power generation on the DC side. Therefore, an energy storage device is installed on the DC side of the photovoltaic power station. This can fully utilize the efficiency of the centralized inverter booster in the photovoltaic array, and can store energy when the DC side is fully powered to prevent power loss, and release energy when the DC side is weak to ensure the stability of photovoltaic power generation. The specific process is as follows:

[0071] S2.1, Assume that the power of the centralized inverter-boosting integrated machine on the AC side of the i-th photovoltaic power generation unit is P 0i , the power generated by the PV module on the DC side is P ri, the design volume ratio is set to r i , the power loss from the photovoltaic module to the centralized inverter booster is recorded as η i (This loss includes the loss of the centralized inverter booster itself); To prevent the DC side from losing power due to over-distribution, the power P of the energy storage battery on the DC side of each centralized inverter booster is DCi The configuration should meet the following requirements:

[0072]

[0073] In view of the fact that the inverter and box-type transformer have an overload capacity of 1.1 times in the long-term operation, the power of the DC-side energy storage controller should not be less than the difference between the maximum power of the DC side of the centralized inverter-boost integrated machine and the maximum allowable power of the AC side. Such a design helps to maintain the stable operation of the entire system and the effective regulation of electric energy;

[0074] S2.2, select the day with the best power generation efficiency of the photovoltaic power station in a year, and calculate the DC side power generation power P of the photovoltaic module in the i-th photovoltaic power generation unit centralized inverter booster ri Exceeds the maximum allowable output power on the AC side by 1.1 P0i The excess power generated during this period is calculated; then, the DC side energy storage battery capacity E of the array DCi The following conditions should be met:

[0075]

[0076] S2.3. Select the DC side energy storage controller and DC side energy storage battery according to the energy storage configuration power and capacity requirements of each photovoltaic power generation unit on the DC side; the total power P of the DC side energy storage device DC With total capacity E DC The expression is as follows:

[0077]

[0078] In the relevant formula, n represents the number of photovoltaic power generation units in the photovoltaic power station. In order to prevent the power generated by the photovoltaic modules from being lost due to the limitation of the inverter or box transformer, the capacity ratio of the photovoltaic power station is usually set at around 1.1 / (1-η), so as to ensure that the power generated by the photovoltaic modules can eventually be smoothly transmitted through the inverter. If the capacity ratio is further increased, although the cost per kilowatt-hour of the photovoltaic power station can be reduced to a certain extent, the power generated by the photovoltaic modules will be limited by the inverter, resulting in power loss. According to formula (1), it can be deduced that there is a relationship between the capacity ratio of the photovoltaic power generation unit and the DC side energy storage as shown in formula (4):

[0079]

[0080] Based on this, after the DC side of the photovoltaic power station is equipped with energy storage devices, the capacity ratio of the photovoltaic power generation unit can be appropriately increased; the principle is that the extra electric energy generated by the components can be first stored in the energy storage battery, and then released when the output power of the photovoltaic components is lower than the power limit of the inverter and the box transformer; for example, if a 10% capacity energy storage battery is configured on the DC side, the capacity ratio of the photovoltaic power generation unit can be increased by about 10%. The following Table 1 shows the configuration requirements for new energy storage in some regions:

[0081] Table 1 New energy storage configuration requirements in some provinces and regions

[0082]

[0083]

[0084] S3. Configuration of hybrid energy storage on the AC side; the AC side energy storage device consists of an AC side energy storage battery and an AC side energy storage controller, where the AC side energy storage controller is responsible for controlling the energy storage and release of the AC side energy storage battery, and the AC side energy storage device is connected to the energy storage incoming cabinet with the help of an AC cable; when configuring the AC side energy storage device, the following principle must be followed: its capacity must be at least half of the primary frequency regulation capacity required by the system, and after working in coordination with the DC side energy storage device, it can meet the minimum standards set by various regions for the energy storage configuration of photovoltaic power stations; the specific implementation steps are as follows:

[0085] S3.1. Meet the minimum energy storage configuration requirements of photovoltaic power stations. Generally, each region has put forward specific requirements for the energy storage configuration of photovoltaic power stations. Taking Jiangxi Province as an example, it stipulates that new energy must be equipped with energy storage devices that are not less than 10% of the installed capacity and have a duration of 1 hour; Shandong Province requires that new energy be equipped with energy storage devices that are not less than 10% of the installed capacity and have a duration of 2 hours, etc. Based on the total installed capacity data of photovoltaic power stations, the minimum configuration power P of energy storage can be calculated. C And capacity E C ; From this, we can know that the AC side energy storage power of the photovoltaic power station P AC and capacity E AC The following conditions should be met:

[0086]

[0087] S3.2. Satisfy the primary frequency regulation requirements of the system. In some areas such as Shandong, Fujian and Northeast China, there are requirements for energy storage to participate in the primary frequency regulation of the system. If the maximum power of the primary frequency regulation of the photovoltaic power station required by the system is P f , the maximum capacity is E f , then the AC side energy storage power P of the photovoltaic power station can be derived ACand capacity E AC The following conditions must be met:

[0088]

[0089] According to formula (6), the AC side energy storage controller and the AC side energy storage battery can be screened; generally speaking, the energy storage battery can participate in the primary frequency modulation action thousands of times in daily operation, while the deep frequency modulation is only about a hundred times; the AC side energy storage device can greatly reduce the charging and discharging frequency of the DC side energy storage battery due to its priority participation in the primary frequency modulation, thereby effectively extending the service life of the DC side energy storage device; the topological structure of the energy storage controller is shown in Figure 2 , which is usually adopted Figure 2 The voltage source inverter shown in the figure; in the figure, U* dc Represents the inverter DC voltage command value, U dc Indicates the inverter DC bus voltage, u abc is the terminal voltage, i* cd is the command value of the current controller, e* abc is the inverter output internal potential command value, e abc is the internal potential of the inverter output; when the primary frequency regulation demand command value P of the photovoltaic power station fref When applied to the input of the DC voltage controller of the energy storage controller, the inverter will use the DC voltage controller to adjust the command value i* input to the current controller cd Then the current controller outputs the internal potential command value e* to the inverter. abc After space vector pulse width modulation (SVPWM), the inverter outputs an internal potential e abc Changes occur, which ultimately changes the active power input to the system by the inverter, providing strong support for primary frequency regulation of the system; Common energy storage devices and their advantages and disadvantages are listed in Table 2;

[0090] Table 2 Advantages and disadvantages of different types of energy storage devices

[0091]

[0092] On the DC side, electrochemical energy storage devices such as lithium iron phosphate can be selected, which can fully demonstrate its advantages of high energy density and outstanding comprehensive cost performance; on the AC side, supercapacitor devices can be used to fully demonstrate their high power density and long cycle life. Since most of the primary frequency regulation tasks in the system are undertaken by the AC side energy storage device, the charging and discharging frequency of the DC side energy storage device can be greatly reduced, thereby effectively extending the service life of the DC side energy storage device.

[0093] S4, AC / DC hybrid energy storage configuration; the specific process is as follows:

[0094] S4.1. Ensure that the over-generated energy of the photovoltaic modules will not be lost due to the limited power of the inverter; and only participate in the primary frequency regulation of the system when the primary frequency regulation capacity of the AC side energy storage device cannot meet the demand;

[0095] S4.2. The configuration of the AC side energy storage device shall follow the following principle: its capacity shall be at least half of the primary frequency regulation capacity required by the system, and after being integrated with the DC side energy storage device, it shall be able to meet the minimum standards for energy storage configuration of photovoltaic power stations in various regions;

[0096] S4.3. Rationally optimize the system capacity ratio to further reduce the system's cost of electricity. The capacity ratio of a photovoltaic system is the ratio of the photovoltaic module power to the inverter rated power. According to the "Design Specifications for Photovoltaic Power Stations", the capacity ratio in Class I solar energy resource areas should not exceed 1.2, Class II areas should not exceed 1.4, and Class III areas should not exceed 1.8;

[0097] S5. Experimental verification and analysis. In this experimental verification and analysis, a 100MW agricultural photovoltaic complementary photovoltaic power generation project in Shanxi Province was selected as a typical case to explain in depth the joint design method of hybrid energy storage on the AC and DC sides of large photovoltaic power stations. According to the specific requirements of the local power grid, this photovoltaic power station needs to be equipped with an energy storage device with a capacity ratio of 15% and a duration of 2 hours, and the energy storage system must participate in the primary frequency regulation of the system. The capacity of the primary frequency regulation must not be less than 10% of the installed capacity of the photovoltaic AC side, and the frequency regulation duration must not be less than 60 seconds. The project adopts a centralized inverter-boost integrated solution, with a total of 32 box inverters with a power of 3.125MW. From the overall perspective of the project, its AC side capacity is 100MW, and the capacity ratio is calculated to be about 1.35. Through in-depth analysis of the project, it can more intuitively demonstrate the application of the AC and DC side hybrid energy storage joint design method in actual large-scale photovoltaic power stations and its effectiveness in responding to power grid requirements.

[0098] S5.1. During the experiment, PVsyst software was used to perform simulation calculations. The result of the calculation showed that the power loss between the photovoltaic module and the centralized inverter booster was 12.81%. Based on this data, it can be inferred that the minimum power required by the DC side energy storage controller should be 0.241MW. In order to ensure the stable operation of the system and reserve a certain margin, P was finally determined. DCi The value of is 0.25MW;

[0099] S5.2. Under normal circumstances, during the period from 10:30 to 14:20, the lighting conditions are ideal, and the input power of the DC side of the centralized inverter booster often exceeds the maximum input power allowed on the AC side. If the DC side is not equipped with an energy storage device, this excess energy will be wasted. With the help of PVsyst simulation software, it can be accurately calculated that the excess power generated during this period is approximately 0.49MW.h. Based on this, the capacity of the energy storage battery on the DC side of each array can be set to 0.5MW.h. The following are the specific configuration details of the energy storage on the DC side of the photovoltaic array:

[0100]

[0101] Taking into account the requirements of the local power grid for energy storage and primary frequency regulation, the requirements for energy storage devices on the AC side of the photovoltaic power station can be determined as follows:

[0102]

[0103] Based on the above requirements, after comprehensive and integrated consideration and analysis, the specific configuration details of the AC and DC side energy storage device of the photovoltaic power station are as follows:

[0104]

[0105] In the selection of energy storage equipment on the DC side, lithium iron phosphate batteries with higher energy density were used; by comparing the power generation of the photovoltaic power station before and after the configuration of the energy storage device (see Figure 3 ), it can be clearly seen that after the energy storage device is equipped on the DC side, the power generation of the photovoltaic power station has been significantly improved; especially in months with good lighting conditions, the photovoltaic power station can effectively avoid power loss caused by over-allocation; when the energy storage device is not yet configured on the DC side, the average annual power generation of the photovoltaic power station during the 25-year period is about 147,400 MW.h; after the energy storage device is configured on both the AC and DC sides, its 25-year average annual grid-connected power generation reaches about 151,500 MW.h, and the power generation has increased by about 2.79%; taking this 100MW agricultural-photovoltaic complementary photovoltaic power generation project as an example, it shows the increase in the power generation of the photovoltaic power station by configuring the AC and DC side energy storage device under different capacity ratios (see Figure 4 ); It can be clearly seen that the proportion of the DC side energy storage device in increasing the overall power generation of the photovoltaic power station will continue to increase with the increase of the capacity ratio;

[0106] S5.3. The photovoltaic power station model was successfully constructed with the help of MATLAB. For details, please refer to Figure 5At the same time, based on the simulation results, a detailed comparison was made between the number of times the photovoltaic power station energy storage battery participated in the primary frequency regulation under the AC side energy storage configuration strategy and the AC / DC side hybrid energy storage configuration strategy. The specific comparison can be viewed in Figure 6 .

[0107] The present invention can achieve the optimal configuration effect of the DC side and AC side energy storage devices according to the operating conditions of the photovoltaic power station and the relevant regulations of the local power grid. The core contributions of the present invention are mainly reflected in the following two aspects:

[0108] (1) The DC side energy storage device can effectively solve the problem of loss of photovoltaic module over-generation due to inverter power limitation, thereby helping to increase the overall power generation of photovoltaic power stations and improve the optimal capacity ratio of photovoltaic power stations. At the same time, the DC side energy storage device and photovoltaic power generation unit use a centralized inverter and booster, which can not only save the engineering workload of inverters, transformers, cables, etc., but also reduce the investment cost required for photovoltaic project energy storage configuration.

[0109] (2) A design scheme for AC / DC coupled energy storage for large photovoltaic power stations is proposed. The AC side uses energy storage batteries with high power density and long cycle life as energy storage devices. Their main function is to undertake the primary frequency regulation task of the system and play a role in assisting the DC side energy storage device in the storage and release of energy. The DC side uses energy storage batteries with higher energy density to construct energy storage devices. Their core purpose is to be responsible for the energy storage and release of photovoltaic power stations. They only participate in the primary frequency regulation of the system when the primary frequency regulation capacity of the AC side energy storage device cannot meet the demand. In this way, the operating time of the DC side energy storage device can be greatly reduced, thereby extending its service life.

[0110] The present invention provides more possibilities for promoting the research on energy storage configuration of large-scale photovoltaic power stations. Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments, and there may be many variations. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention shall be deemed to fall within the scope of protection of the present invention.

Claims

1. A design method for AC / DC coupled energy storage in a large photovoltaic power station, characterized in that The design method comprises: S1. Establish an AC / DC side coupled energy storage system and topological structure; the centralized photovoltaic power generation system is mainly composed of photovoltaic strings, DC combiner boxes, and centralized inverter and booster equipment; S1.

1. The DC side energy storage device includes a DC side energy storage battery and a DC side energy storage controller; the DC side energy storage device is connected to the DC side of the centralized inverter and booster by means of a dedicated photovoltaic DC cable; S1.2, the AC side energy storage device consists of an AC side energy storage battery and an AC side energy storage controller, which are connected to the booster station energy storage switch cabinet via cables; S2. Configuration of hybrid energy storage on the DC side. When the lighting conditions are good and the capacity ratio is high, the input power on the DC side of the photovoltaic power station will exceed the maximum input power allowed by the inverter. The photovoltaic power station will then generate power loss due to the limited power generation on the DC side. S3, configuration of AC side hybrid energy storage; the AC side energy storage device is composed of an AC side energy storage battery and an AC side energy storage controller, wherein the AC side energy storage controller is responsible for controlling the energy storage and release of the AC side energy storage battery, and the AC side energy storage device is connected to the energy storage incoming cabinet via an AC cable; S4, AC / DC hybrid energy storage configuration; the specific process is as follows: S4.

1. Ensure that the over-generated energy of the photovoltaic modules will not be lost due to the limited power of the inverter; and only participate in the primary frequency regulation of the system when the primary frequency regulation capacity of the AC side energy storage device cannot meet the demand; S4.

2. The configuration of the AC side energy storage device shall follow the following principle: its capacity shall be at least half of the primary frequency regulation capacity required by the system, and after being integrated with the DC side energy storage device, it shall be able to meet the minimum standards for energy storage configuration of photovoltaic power stations in various regions; S4.

3. Rationally optimize the system capacity ratio to further reduce the system's cost per kilowatt-hour. The capacity ratio of a photovoltaic system is the ratio of the photovoltaic module power to the inverter rated power.

2. A verification analysis of a large-scale photovoltaic power station AC / DC coupled energy storage design method, characterized by The validation analysis: S5. In this experimental verification and analysis, a 100MW agricultural photovoltaic power generation project in Shanxi Province was selected as a typical case to further explain the joint design method of AC and DC hybrid energy storage on large photovoltaic power stations; S5.

1. During the experiment, PVsyst software was used to perform simulation calculations. The result of the calculation showed that the power loss between the photovoltaic module and the centralized inverter-boosting integrated machine was 12.81%. Based on this data, it can be inferred that the minimum power required by the DC side energy storage controller should be 0.241MW. In order to ensure the stable operation of the system and reserve a certain margin, P was finally determined. DCi The value of is 0.25MW; S5.

2. Under normal circumstances, during the period from 10:30 to 14:20, the lighting conditions are ideal, and the input power on the DC side of the centralized inverter-boosting machine often exceeds the maximum input power allowed on the AC side. If the DC side is not equipped with an energy storage device, this excess energy will be wasted. The following are the specific configuration details of the energy storage on the DC side of the photovoltaic array: Formula (7): Taking into account the requirements of the local power grid for energy storage and primary frequency regulation, the requirements for energy storage devices on the AC side of the photovoltaic power station can be determined as follows: Formula (8): Based on the above requirements, after comprehensive and integrated consideration and analysis, the specific configuration details of the AC and DC side energy storage device of the photovoltaic power station are as follows: Formula (9): In the selection of energy storage equipment on the DC side, lithium iron phosphate batteries with higher energy density were used. A comparative analysis was conducted on the power generation of the photovoltaic power station before and after the configuration of the energy storage device. Taking this 100MW agricultural-photovoltaic complementary photovoltaic power generation project as an example, it was demonstrated that under the conditions of different capacity ratios, the configuration of AC and DC side energy storage devices can increase the power generation of the photovoltaic power station. S5.

3. A photovoltaic power station model was successfully constructed with the help of MATLAB. At the same time, based on the simulation results, a detailed comparison was made on the number of times the photovoltaic power station energy storage battery participated in a frequency modulation under the AC side energy storage configuration strategy and the AC / DC side hybrid energy storage configuration strategy.

3. The AC / DC coupled energy storage design method for a large photovoltaic power station according to claim 1 is characterized in that In the S1.1, on the DC side, a storage battery with a high energy density is selected to store and release energy, while also having a primary frequency regulation auxiliary function.

4. The AC / DC coupled energy storage design method for a large photovoltaic power station according to claim 1 is characterized in that In the above-mentioned S1.2, the AC side uses energy storage batteries with large power density and long cycle life, with primary frequency regulation function as the main function and energy storage and release as the auxiliary function.

5. The AC / DC coupled energy storage design method for a large photovoltaic power station according to claim 1 is characterized in that In S2, an energy storage device is installed on the DC side of the photovoltaic power station. This can fully utilize the efficiency of the centralized inverter and booster in the photovoltaic array. On the other hand, it can store energy when the DC side is fully powered to prevent power loss, and release energy when the DC side is weak to ensure the stability of photovoltaic power generation. The specific process is as follows: S2.1, Assume that the power of the centralized inverter-boosting integrated machine on the AC side of the i-th photovoltaic power generation unit is P 0i , the power generated by the PV module on the DC side is P ri , the design volume ratio is set to r i , the power loss from the photovoltaic module to the centralized inverter booster is recorded as η i , this loss covers the loss of the centralized inverter-boosting machine itself; To prevent the DC side from losing power due to over-distribution, the power P of the energy storage battery on the DC side of each centralized inverter booster is DCi The configuration should meet the following requirements: Formula (1): In view of the fact that the inverter and box-type transformer have an overload capacity of 1.1 times in the long-term operation, the power of the DC-side energy storage controller should not be less than the difference between the maximum power of the DC-side of the centralized inverter-boost integrated machine and the maximum allowable power of the AC-side, which helps to maintain the stable operation of the entire system and the effective regulation of electric energy; S2.2, select the day with the best power generation efficiency of the photovoltaic power station in a year, and calculate the DC side power generation power P of the photovoltaic module in the i-th photovoltaic power generation unit centralized inverter booster ri Exceeds the maximum allowable output power on the AC side by 1.1 P0i The excess power generated during this period is calculated; then, the DC side energy storage battery capacity E of the array DCi The following conditions should be met: Formula (2): S2.

3. Select the DC side energy storage controller and DC side energy storage battery according to the energy storage configuration power and capacity requirements of each photovoltaic power generation unit on the DC side; the total power P of the DC side energy storage device DC With total capacity E DC The expression is as follows: Formula (3): In order to prevent the loss of the electric energy generated by the photovoltaic modules due to the limitation of the inverter or box transformer, the capacity ratio of the photovoltaic power station is usually set at 1.1 / (1-η), so as to ensure that the electric energy generated by the photovoltaic modules can be smoothly transmitted through the inverter. If the capacity ratio is further increased, although the cost of electricity of the photovoltaic power station can be reduced to a certain extent, the electric energy generated by the photovoltaic modules will be limited by the inverter, resulting in electric energy loss. According to formula (1), it can be deduced that there is a relationship between the capacity ratio of the photovoltaic power generation unit and the DC side energy storage as shown in formula (4): Formula (4):

6. The AC / DC coupled energy storage design method for a large photovoltaic power station according to claim 1 is characterized in that When configuring the AC side energy storage device in S3, the following principle must be followed: its capacity must be at least half of the primary frequency regulation capacity required by the system, and after working in conjunction with the DC side energy storage device, it must be able to meet the minimum standards set by various regions for photovoltaic power station energy storage configuration; the specific implementation steps are as follows: S3.

1. Meet the minimum energy storage configuration requirements of photovoltaic power stations. Generally, each region has put forward specific requirements for the energy storage configuration of photovoltaic power stations. Taking Jiangxi Province as an example, it stipulates that new energy must be equipped with energy storage devices that are not less than 10% of the installed capacity and have a duration of 1 hour. Based on the total installed capacity data of photovoltaic power stations, the minimum configuration power P of energy storage can be calculated. C And capacity E C ; From this, we can know that the AC side energy storage power of the photovoltaic power station P AC and capacity E AC The following conditions should be met: Formula (5): S3.2, meet the system's primary frequency regulation requirements; if the maximum power of the photovoltaic power station required by the system is P f , the maximum capacity is E f , then the AC side energy storage power P of the photovoltaic power station can be derived AC and capacity E AC The following conditions must be met: Formula (6): According to formula (6), the AC side energy storage controller and the AC side energy storage battery can be screened; generally speaking, in daily operation, the energy storage battery can participate in the primary frequency modulation action thousands of times, while the deep frequency modulation is only about a hundred times; because the AC side energy storage device preferentially participates in the primary frequency modulation, it can greatly reduce the charging and discharging frequency of the DC side energy storage battery, thereby effectively extending the service life of the DC side energy storage device.

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