Flexible grid connection method for industrial and commercial optical storage power generation system

Abstract

The invention relates to the technical field of optical storage power generation systems, and discloses a flexible grid connection method for industrial and commercial optical storage power generation systems. The flexible grid connection method for the industrial and commercial optical storage power generation system comprises the following steps: after the optical storage power generation system starts to operate, information about whether a grid connection condition is met is obtained through communication with an inverter, the maximum power point of a photovoltaic array is tracked, and energy scheduling strategies under various working conditions are judged in real time; the power flow of each power generation unit of the system is coordinated and controlled, the efficient and stable operation of the system is maintained, the working mode of the energy storage controller is divided into a photovoltaic grid-connected mode and a photovoltaic energy storage grid-connected mode, and the modes can be switched through a change-over switch; according to the invention, the grid-connected converter is controlled to carry out flexible grid-connected power generation according to the photovoltaic output power curve, the advantages of the optical storage power generation system are fully exerted, and the expandability is high; the charging and discharging times of the energy storage battery are effectively reduced, and the power output capability of the system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation systems, and specifically relates to a flexible grid-connected method for industrial and commercial photovoltaic power generation systems. Background Art

[0002] With the rapid development of the industrial and commercial economy, energy consumption has increased dramatically, fossil energy is becoming increasingly depleted, and the increasing environmental pollution caused by the burning of fossil fuels has brought serious threats to the ecological balance of the earth and human life. Therefore, building large-scale photovoltaic power stations to meet the energy needs of industry and commerce is the current development trend. Since photovoltaic power generation is affected by solar radiation intensity, battery component temperature, weather, clouds and some random factors, the system operation process is an unbalanced random process. Its power generation and output power are highly random, fluctuating and uncontrollable, which is particularly prominent when the weather changes suddenly. China vigorously develops flexible photovoltaic storage power generation, including various types of energy storage batteries such as lithium-ion batteries, sodium-sulfur batteries, flow batteries, and supercapacitors, but the current photovoltaic storage power generation system is difficult to fully meet the operating requirements of smart grids to accept distributed energy. Therefore, this power generation method will inevitably bring a series of problems to the safety of the power grid after being incorporated into the power grid; therefore, in view of the current situation, it needs to be improved. Summary of the invention

[0003] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a flexible grid-connected method for industrial and commercial photovoltaic power generation systems, which effectively solves the problem that the current photovoltaic power generation systems are difficult to fully meet the operating requirements of the smart grid to accept distributed energy, and have a negative impact on the security of the power grid after being connected to the power grid.

[0004] To achieve the above object, the present invention provides the following technical solution: a flexible grid-connected method for an industrial and commercial photovoltaic power generation system, characterized in that it comprises the following steps:

[0005] Step 1: After the photovoltaic power generation system starts to operate, it communicates with the inverter to obtain information on whether it is grid-connected, tracks the maximum power point of the photovoltaic array, determines the energy scheduling strategy under various working conditions in real time, coordinates the power flow of each power generation unit of the system, maintains efficient and stable operation of the system, and divides the working mode of the energy storage controller into photovoltaic grid-connected mode and photovoltaic energy storage grid-connected mode. The mode can be switched through the conversion switch;

[0006] Step 2: When the photovoltaic grid-connected mode is in progress, the inverter works in the MPPT mode to generate electricity and the energy storage system is disconnected. This mode is run when the energy storage system needs to be repaired or has special needs.

[0007] Step 3: The photovoltaic energy storage grid-connected mode is the main working mode of the system. In this mode, the energy storage controller controls the operation of the core control system. The system operates in two modes: automatic and manual. In the automatic mode, the system adjusts the inverter grid-connected power by tracking the input energy of the photovoltaic components. The supercapacitor performs the filtering function and the energy storage battery performs the energy storage function. The manual mode is mainly used in special situations where there is no sunlight, relying on the energy storage battery to supply electricity to the grid at a constant power during its discharge cycle.

[0008] Step 4: In automatic mode, each DC / DC module of the energy storage controller enters a pre-set working mode, the photovoltaic module works in the maximum power tracking state, the supercapacitor module works in the constant voltage state, which is used to absorb short-term photovoltaic input energy fluctuations, and the energy storage battery module works in the constant current state, which is used to absorb long-term photovoltaic input energy fluctuations. In this state, the energy storage controller will calculate the average input power of the previous time period, and make the photovoltaic inverter connect to the grid to generate electricity at this constant power value, thereby ensuring the basic balance of system input and output power over a long period of time. Short-term light drops will be absorbed by the supercapacitor module, and the fluctuations in each time period can be basically filtered out due to the calculation of average power. This strategy effectively reduces the frequent charging and discharging of the energy storage battery module. Only when the energy difference accumulates over time and exceeds the adjustment range of the supercapacitor, the energy storage battery module is started, which greatly extends the life of the energy storage battery.

[0009] Step 5: In manual mode, the pre-set working mode of each module of the energy storage controller is: the photovoltaic module is shut down, the supercapacitor module is shut down, and the energy storage battery module works in a constant voltage state to provide a stable power supply for the inverter. The inverter power command is equal to the required output power command. When setting the output power, a system can run time is fed back according to the SOC state for the operator's reference. When the battery SOC value is too low, the system alarms, automatically shuts down and notifies the host computer.

[0010] Preferably, the photovoltaic energy storage grid connection proposed in step 1 is that the electric energy generated by the photovoltaic module is converted into stable electric energy for charging the energy storage system through the energy storage controller, or is sent to the power grid on demand with controllable power through the coordination of energy storage media. The energy storage controller is the control core of the energy storage system. The energy storage controller coordinates and controls all energy storage media in a unified manner, and sends energy to the power grid through the grid-connected converter. The energy storage medium adopts a combination of lithium batteries and supercapacitors, which are connected to the photovoltaic module and the energy storage controller. The energy storage controller communicates with the battery management system to grasp the operation or fault status of the battery in real time, and communicates with the grid-connected converter and the background monitoring system to exchange grid-connected information and power instructions, and display and save key data in real time.

[0011] Preferably, the photovoltaic modules are matched with the voltage of the energy storage system and the series-parallel design of the photovoltaic array. According to the design requirements of the photovoltaic modules, the voltage level of the photovoltaic array is designed to be approximately 1.4 times the nominal voltage of the energy storage battery to ensure that when the battery is fully charged, the voltage will not be higher than the design voltage of the photovoltaic modules to cause current backflow. The number of photovoltaic modules in series can be determined according to the power level of the system and the voltage and current parameters of the photovoltaic modules themselves, and the number of photovoltaic modules in parallel can be determined according to the installed capacity of the system.

[0012] Preferably, the design of the energy storage system includes the design calculation of the energy storage medium capacity and the series-parallel design of the energy storage medium. The selection of the energy storage medium capacity needs to be based on the installed capacity of the photovoltaic system and the full power generation time of the system, while fully considering the available discharge depth of the battery and the current that the photovoltaic module can provide. The number of energy storage media connected in series depends on the nominal voltage of the energy storage medium monomer, and the number of energy storage media that need to be connected in series is equal to the nominal voltage of the energy storage system divided by the nominal voltage of the energy storage medium monomer.

[0013] Preferably, the nominal voltage of the energy storage system is determined by the working voltage of the photovoltaic module and the rated voltage of the energy storage controller, ensuring that the energy storage system is reliably charged while meeting the voltage level standard of the controller. The nominal voltages of the energy storage media within the energy storage system should be as similar as possible, and the capacity of each energy storage medium should be designed according to the different operating times of each energy storage medium. The matching form of lithium-ion batteries and supercapacitors, the supercapacitor is configured based on the maximum power drop and drop time of the sunshine curve, as an instantaneous power supplement for the system, configured at 15 to 30 seconds per second, and the capacity does not exceed 1 / 20 of the rated capacity of the lithium battery. The design of the lithium battery requires capacity to take into account the average daily power consumption, discharge depth, and charge and discharge efficiency factors, and compare the investment and benefits of the lithium battery. The configuration capacity is the system peak power value, and the maximum continuous full-power operation time is 4 hours.

[0014] Preferably, the energy storage controller is a key component connecting the photovoltaic module, energy storage medium and grid-connected converter, and has an expandable bidirectional DC / DC module, which can be flexibly configured according to the system level. The energy storage controller communicates with other parts of the system through coordinated control and protection between various power sources to ensure safe and stable operation of the system.

[0015] Preferably, the energy storage controller is configured with three groups of DC / DC modules. The photovoltaic control module tracks the maximum power of the photovoltaic module through the MPPT control strategy, and the DC / DC modules of the lithium battery and supercapacitor provide power on demand through unified coordinated control. The three groups of modules are each DC / DC converted and connected to the DC bus. Since the voltage level of the photovoltaic module is higher than the voltage level of the energy storage system, the voltage level on the input side of the energy storage controller is higher than the open-circuit voltage of the photovoltaic module. The input side power meets the maximum working power of the system. The input side of the grid-connected converter is connected to the DC bus of the energy storage controller. The power command is issued to the grid-connected converter through the short-term power prediction strategy of the energy storage controller. The DC bus voltage of the energy storage controller must strictly meet the DC side voltage range of the inverter to prevent the system from starting and stopping frequently.

[0016] Preferably, the grid-connected converter is located between the power grid and the energy storage controller. On the premise of meeting the charging and discharging characteristics of the energy storage system, it can adjust the output active power and reactive power according to the grid dispatching instructions, realize the control of the active power and reactive power of the grid, communicate with the battery management system and the energy storage controller in real time, and provide grid status information and system protection control.

[0017] Preferably, the output side of the grid-connected converter is connected to the distribution network directly or via a transformer according to different application scenarios, and the input side is connected to the energy storage controller, whose power level is determined by the installed capacity of the system, and the input voltage range should match the charging and discharging voltage range of the energy storage system. The minimum voltage of the energy storage system should be greater than the grid-connected starting voltage of the inverter to ensure the normal operation of the system and avoid power failure without reason.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention configures lithium batteries and supercapacitors as energy storage media, and the energy storage controller serves as the system control core, which completes the communication with the monitoring system and accepts its scheduling, manages the energy distribution between the battery pack and the photovoltaic array, and coordinates the DC source to provide stable power support for the inverter, thereby providing stable electricity for industry and commerce.

[0019] 2. The present invention tracks the photovoltaic cell module working in the maximum power state, controls the grid-connected converter according to the photovoltaic output power curve to perform flexible grid-connected power generation, and the energy storage battery block receives the information of the battery management system to stabilize the DC bus voltage. By controlling the current of the supercapacitor module and the battery module, the DC bus presents a constant voltage source characteristic to the outside. The supercapacitor performs the filtering function, effectively absorbs the short-term power fluctuation of the photovoltaic module, avoids the frequent charging and discharging of the lithium battery, and gives full play to the advantages of the photovoltaic storage power generation system, with strong scalability. It effectively reduces the number of charge and discharge times of the energy storage battery, reduces the equipment redundancy, and improves the power output capacity of the system.

[0020] 3. The present invention can grasp the operation or fault status of the battery in real time, and communicate with the grid-connected converter and the background monitoring system at the same time, exchange grid-connected information and power instructions, and display and save key data in real time. The battery capacity required by this system is relatively low, and no complex control is required. The system is economical and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0022] In the attached picture:

[0023] Figure 1 It is a flowchart of the flexible grid-connected method of the industrial and commercial photovoltaic power generation system of the present invention; DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] See also Figure 1 The present invention provides a flexible grid-connected method for an industrial and commercial photovoltaic power generation system, comprising the following steps:

[0026] Step 1: After the photovoltaic power generation system starts to operate, it communicates with the inverter to obtain information on whether it is grid-connected, tracks the maximum power point of the photovoltaic array, determines the energy scheduling strategy under various working conditions in real time, coordinates the power flow of each power generation unit of the system, maintains efficient and stable operation of the system, and divides the working mode of the energy storage controller into photovoltaic grid-connected mode and photovoltaic energy storage grid-connected mode. The mode can be switched through the conversion switch;

[0027] Step 2: When the photovoltaic grid-connected mode is in progress, the inverter works in the MPPT mode to generate electricity and the energy storage system is disconnected. This mode is run when the energy storage system needs to be repaired or has special needs.

[0028] Step 3: The photovoltaic energy storage grid-connected mode is the main working mode of the system. In this mode, the energy storage controller controls the operation of the core control system. The system operates in two modes: automatic and manual. In the automatic mode, the system adjusts the inverter grid-connected power by tracking the input energy of the photovoltaic components. The supercapacitor performs the filtering function and the energy storage battery performs the energy storage function. The manual mode is mainly used in special situations where there is no sunlight, relying on the energy storage battery to supply electricity to the grid at a constant power during its discharge cycle.

[0029] Step 4: In automatic mode, each DC / DC module of the energy storage controller enters a pre-set working mode, the photovoltaic module works in the maximum power tracking state, the supercapacitor module works in the constant voltage state, which is used to absorb short-term photovoltaic input energy fluctuations, and the energy storage battery module works in the constant current state, which is used to absorb long-term photovoltaic input energy fluctuations. In this state, the energy storage controller will calculate the average input power of the previous time period, and make the photovoltaic inverter connect to the grid to generate electricity at this constant power value, thereby ensuring the basic balance of system input and output power over a long period of time. Short-term light drops will be absorbed by the supercapacitor module, and the fluctuations in each time period can be basically filtered out due to the calculation of average power. This strategy effectively reduces the frequent charging and discharging of the energy storage battery module. Only when the energy difference accumulates over time and exceeds the adjustment range of the supercapacitor, the energy storage battery module is started, which greatly extends the life of the energy storage battery.

[0030] Step 5: In manual mode, the pre-set working mode of each module of the energy storage controller is: the photovoltaic module is shut down, the supercapacitor module is shut down, and the energy storage battery module works in a constant voltage state to provide a stable power supply for the inverter. The inverter power command is equal to the required output power command. When setting the output power, a system can run time is fed back according to the SOC state for the operator's reference. When the battery SOC value is too low, the system alarms, automatically shuts down and notifies the host computer.

[0031] Among them, the photovoltaic energy storage grid connection proposed in step one is that the electric energy generated by the photovoltaic components is converted into stable electric energy for charging the energy storage system through the energy storage controller, or it is sent to the power grid on demand with controllable power through the coordination of energy storage media. The energy storage controller is the control core of the energy storage system. The energy storage controller coordinates and controls all energy storage media in a unified manner, and sends energy to the power grid through the grid-connected converter. The energy storage medium is a combination of lithium batteries and supercapacitors, which are connected to the photovoltaic components and the energy storage controller. The energy storage controller communicates with the battery management system to grasp the operation or fault status of the battery in real time, and communicates with the grid-connected converter and the background monitoring system to exchange and The network information and power instructions are displayed and saved in real time. The photovoltaic module is matched with the voltage of the energy storage system and the series-parallel design of the photovoltaic array. According to the design requirements of the photovoltaic module, the voltage level of the photovoltaic array is designed to be about 1.4 times the nominal voltage of the energy storage battery, ensuring that the voltage will not be higher than the design voltage of the photovoltaic module when the battery is fully charged, causing the current to flow back. The number of photovoltaic modules in series can be determined according to the power level of the system and the voltage and current parameters of the photovoltaic module itself, and the number of photovoltaic modules in parallel can be determined according to the installed capacity of the system. The design of the energy storage system includes the design calculation of the energy storage medium capacity and the series-parallel design of the energy storage medium. The selection of the energy storage medium capacity needs to be based on the installed capacity of the photovoltaic system and the full-time time of the system, while fully considering the available discharge depth of the battery and the current that the photovoltaic module can provide. The number of energy storage media in series depends on the nominal voltage of the energy storage medium monomer. The number of energy storage media that need to be connected in series is equal to the nominal voltage of the energy storage system divided by the nominal voltage of the energy storage medium monomer. The nominal voltage of the energy storage system is determined by the working voltage of the photovoltaic module and the rated voltage of the energy storage controller, ensuring that the energy storage system is reliably charged while meeting the voltage level standard of the controller. The nominal voltage of each energy storage medium in the energy storage system should be as similar as possible, and the capacity of each energy storage medium should be designed according to the different operating time of each energy storage medium. The matching form of lithium-ion batteries and supercapacitors is that the supercapacitor is configured based on the maximum power drop and drop time of the sunshine curve. As the instantaneous power supplement of the system, it is configured for 15 to 30 seconds at the second level, and the capacity does not exceed 1 / 20 of the rated capacity of the lithium battery. The design of the lithium battery requires the capacity to consider the daily average power consumption, discharge depth, and charge and discharge efficiency factors, and compare the investment and benefits of the lithium battery. The configuration capacity is the peak power value of the system, and the maximum continuous full-power operation time is 4 hours. The energy storage controller is a key component connecting photovoltaic modules, energy storage media and grid-connected converters. It has an expandable bidirectional DC / DC module and can be flexibly configured according to the system level. The energy storage controller communicates with other parts of the system through coordinated control and protection between various power sources to ensure the safe and stable operation of the system. The energy storage controller is equipped with three groups of DC / DC modules.The photovoltaic control module tracks the maximum power of the photovoltaic module through the MPPT control strategy. The DC / DC modules of the lithium battery and supercapacitor provide power on demand through unified coordinated control. The three groups of modules are each DC / DC converted and connected to the DC bus. Since the voltage level of the photovoltaic module is higher than the voltage level of the energy storage system, the voltage level on the input side of the energy storage controller is higher than the open-circuit voltage of the photovoltaic module. The input side power meets the maximum working power of the system. The input side of the grid-connected converter is connected to the DC bus of the energy storage controller. The power command is issued to the grid-connected converter through the short-term power prediction strategy of the energy storage controller. The DC bus voltage of the energy storage controller must strictly meet the DC side voltage range of the inverter to prevent the system from frequently starting. Stop, the grid-connected converter is located between the power grid and the energy storage controller. Under the premise of meeting the charging and discharging characteristics of the energy storage system, it can adjust the output active power and reactive power according to the grid dispatching instructions to realize the control of the active power and reactive power of the power grid, communicate with the battery management system and the energy storage controller in real time, provide grid status information and system protection control, and the output side of the grid-connected converter is directly or through a transformer to connect to the distribution network according to different application scenarios. The input side is connected to the energy storage controller, and its power level is determined by the installed capacity of the system. The input voltage range should match the charging and discharging voltage range of the energy storage system, and the minimum voltage of the energy storage system should be greater than the grid-connected starting voltage of the inverter to ensure the normal operation of the system and avoid power failure without reason.

[0032] By configuring lithium batteries and supercapacitors as energy storage media, the energy storage controller as the system control core completes the communication with the monitoring system and accepts its dispatch, manages the energy distribution between the battery group and the photovoltaic array, and coordinates the DC source to provide stable power support for the inverter, thereby providing stable electricity for industry and commerce; by tracking the photovoltaic battery module working in the maximum power state, the grid-connected converter is controlled according to the photovoltaic output power curve to perform flexible grid-connected power generation, and the energy storage battery block receives the information of the battery management system to stabilize the DC bus voltage. By controlling the current of the supercapacitor module and the battery module, the DC bus presents a constant voltage source characteristic to the outside. The supercapacitor assumes the filtering function, effectively absorbs the short-term power fluctuation of the photovoltaic module, avoids the frequent charging and discharging of the lithium battery, and gives full play to the advantages of the photovoltaic storage power generation system, with strong scalability. It effectively reduces the number of charge and discharge times of the energy storage battery, reduces the equipment redundancy, improves the power output capacity of the system, and grasps the operation or fault status of the battery in real time. At the same time, it communicates with the grid-connected converter and the background monitoring system to exchange grid-connected information and power instructions, and displays and saves key data in real time. The capacity of the battery required for this system is low, and no complex control is required. The system is economical and easy to implement.

[0033] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0034] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system, characterized by: The following steps are involved: Step 1: After the photovoltaic power generation system starts to operate, it communicates with the inverter to obtain information on whether it is grid-connected, tracks the maximum power point of the photovoltaic array, determines the energy scheduling strategy under various working conditions in real time, coordinates the power flow of each power generation unit of the system, maintains efficient and stable operation of the system, and divides the working mode of the energy storage controller into photovoltaic grid-connected mode and photovoltaic energy storage grid-connected mode. The mode can be switched through the conversion switch; Step 2: When the photovoltaic grid-connected mode is in progress, the inverter works in the MPPT mode to generate electricity and the energy storage system is disconnected. This mode is run when the energy storage system needs to be repaired or has special needs. Step 3: The photovoltaic energy storage grid-connected mode is the main working mode of the system. In this mode, the energy storage controller controls the operation of the core control system. The system operates in two modes: automatic and manual. In the automatic mode, the system adjusts the inverter grid-connected power by tracking the input energy of the photovoltaic components. The supercapacitor performs the filtering function and the energy storage battery performs the energy storage function. The manual mode is mainly used in special situations where there is no sunlight, relying on the energy storage battery to supply electricity to the grid at a constant power during its discharge cycle. Step 4: In automatic mode, each DC / DC module of the energy storage controller enters a pre-set working mode, the photovoltaic module works in the maximum power tracking state, the supercapacitor module works in the constant voltage state, which is used to absorb short-term photovoltaic input energy fluctuations, and the energy storage battery module works in the constant current state, which is used to absorb long-term photovoltaic input energy fluctuations. In this state, the energy storage controller will calculate the average input power of the previous time period, and make the photovoltaic inverter connect to the grid to generate electricity at this constant power value, thereby ensuring the basic balance of system input and output power over a long period of time. Short-term light drops will be absorbed by the supercapacitor module, and the fluctuations in each time period can be basically filtered out due to the calculation of average power. This strategy effectively reduces the frequent charging and discharging of the energy storage battery module. Only when the energy difference accumulates over time and exceeds the adjustment range of the supercapacitor, the energy storage battery module is started, which greatly extends the life of the energy storage battery. Step 5: In manual mode, the pre-set working mode of each module of the energy storage controller is: the photovoltaic module is shut down, the supercapacitor module is shut down, and the energy storage battery module works in a constant voltage state to provide a stable power supply for the inverter. The inverter power command is equal to the required output power command. When setting the output power, a system can run time is fed back according to the SOC state for the operator's reference. When the battery SOC value is too low, the system alarms, automatically shuts down and notifies the host computer.

2. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 1, characterized in that: The photovoltaic energy storage grid connection proposed in step 1 is that the electric energy generated by the photovoltaic module is converted into stable electric energy for charging the energy storage system through the energy storage controller, or is sent to the power grid on demand with controllable power through the coordination of energy storage media. The energy storage controller is the control core of the energy storage system. The energy storage controller coordinates and controls all energy storage media in a unified manner, and sends energy to the power grid through the grid-connected converter. The energy storage medium adopts a combination of lithium batteries and supercapacitors, which are connected to the photovoltaic module and the energy storage controller. The energy storage controller communicates with the battery management system to grasp the operation or fault status of the battery in real time, and communicates with the grid-connected converter and the background monitoring system to exchange grid-connected information and power instructions, and display and save key data in real time.

3. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 2, characterized in that: The photovoltaic modules are designed to match the voltage of the energy storage system and the series-parallel connection of the photovoltaic array. According to the design requirements of the photovoltaic modules, the voltage level of the photovoltaic array is designed to be approximately 1.4 times the nominal voltage of the energy storage battery to ensure that the voltage will not be higher than the design voltage of the photovoltaic modules when the battery is fully charged, causing current backflow. The number of photovoltaic modules in series can be determined according to the power level of the system and the voltage and current parameters of the photovoltaic modules themselves, and the number of photovoltaic modules in parallel can be determined according to the installed capacity of the system.

4. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 3, characterized in that: The design of the energy storage system includes the design calculation of the energy storage medium capacity and the series-parallel design of the energy storage medium. The selection of the energy storage medium capacity needs to be based on the installed capacity of the photovoltaic system and the full power time of the system, while fully considering the available discharge depth of the battery and the current that the photovoltaic module can provide. The number of energy storage media connected in series depends on the nominal voltage of the energy storage medium monomer. The number of energy storage media that need to be connected in series is equal to the nominal voltage of the energy storage system divided by the nominal voltage of the energy storage medium monomer.

5. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 4, characterized in that: The nominal voltage of the energy storage system is determined by the working voltage of the photovoltaic module and the rated voltage of the energy storage controller, ensuring that the energy storage system can be reliably charged while meeting the voltage level standard of the controller. The nominal voltages of the energy storage media within the energy storage system should be as similar as possible, and the capacity of each energy storage medium should be designed according to the different operating times of each energy storage medium. The matching form of lithium-ion batteries and supercapacitors, supercapacitors are configured based on the maximum power drop and drop time of the sunshine curve. As an instantaneous power supplement for the system, it is configured for 15 to 30 seconds at the second level, and the capacity does not exceed 1 / 20 of the rated capacity of the lithium battery. The design of the lithium battery requires capacity to take into account the average daily power consumption, discharge depth, and charge and discharge efficiency factors, and compare the investment and benefits of the lithium battery. The configuration capacity is the system peak power value, and the maximum continuous full-power operation time is 4 hours.

6. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 5, characterized in that: The energy storage controller is a key component that connects photovoltaic modules, energy storage media and grid-connected converters. It has an expandable bidirectional DC / DC module and can be flexibly configured according to the system level. The energy storage controller communicates with other parts of the system through coordinated control and protection between various power sources to ensure safe and stable operation of the system.

7. A method for flexible grid connection of an industrial and commercial photovoltaic power generation system according to claim 6, characterized in that: The energy storage controller is equipped with three groups of DC / DC modules. The photovoltaic control module tracks the maximum power of the photovoltaic module through the MPPT control strategy. The DC / DC modules of the lithium battery and supercapacitor provide power on demand through unified coordinated control. The three groups of modules are each DC / DC converted and connected to the DC bus. Since the voltage level of the photovoltaic module is higher than the voltage level of the energy storage system, the voltage level on the input side of the energy storage controller is higher than the open-circuit voltage of the photovoltaic module. The input side power meets the maximum working power of the system. The input side of the grid-connected converter is connected to the DC bus of the energy storage controller. The power command is issued to the grid-connected converter through the short-term power prediction strategy of the energy storage controller. The DC bus voltage of the energy storage controller must strictly meet the DC side voltage range of the inverter to prevent the system from starting and stopping frequently.

8. The method for flexible grid connection of an industrial and commercial photovoltaic power generation system according to claim 7, characterized in that: The grid-connected converter is located between the power grid and the energy storage controller. On the premise of meeting the charging and discharging characteristics of the energy storage system, it can adjust the output active power and reactive power according to the grid dispatching instructions to achieve control of the active power and reactive power of the grid, communicate with the battery management system and the energy storage controller in real time, and provide grid status information and system protection control.

9. A flexible grid-connected method for an industrial and commercial photovoltaic power generation system according to claim 8, characterized in that: The output side of the grid-connected converter is connected to the distribution network directly or through a transformer according to different application scenarios, and the input side is connected to the energy storage controller, whose power level is determined by the installed capacity of the system. The input voltage range should match the charging and discharging voltage range of the energy storage system, and the minimum voltage of the energy storage system should be greater than the grid-connected starting voltage of the inverter to ensure the normal operation of the system and avoid power failure without reason.

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