Photovoltaic energy storage system, control method thereof, program product and readable storage medium
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FOXESS CO LTD
- Filing Date
- 2026-03-12
- Publication Date
- 2026-06-19
Smart Images
Figure CN122246816A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of photovoltaic energy storage technology, and in particular relates to a photovoltaic energy storage system and its control method, program product and readable storage medium. Background Technology
[0002] When adding an energy storage system to an existing pure photovoltaic inverter system, the photovoltaic inverter is typically connected to the load side of the energy storage system. When the grid is abnormal and the energy storage inverter is in off-grid operation, the photovoltaic inverter can still continuously charge the battery in the energy storage inverter.
[0003] However, the magnitude and fluctuation of the output power of the photovoltaic inverter will affect the operational stability of the energy storage system. If its output power exceeds the real-time absorption capacity of the energy storage system, the energy storage inverter will have difficulty maintaining the stability of the AC bus voltage, which will lead to the instability or even collapse of the energy storage system. Summary of the Invention
[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a photovoltaic energy storage system and its control method, program product, and readable storage medium, which shuts down the photovoltaic inverter due to over-frequency operation when the output power of the photovoltaic inverter continuously exceeds the maximum charging power of the energy storage unit, thereby maintaining the power balance of the energy storage system and the stability of the AC bus voltage.
[0005] In a first aspect, this application provides a control method for a photovoltaic energy storage system. The photovoltaic energy storage system includes an energy storage inverter, an energy storage unit, and a photovoltaic inverter. The energy storage unit is electrically connected to the DC side of the energy storage inverter, and the AC side of the energy storage inverter is electrically connected to both the AC side of the photovoltaic inverter and the power grid. The control method includes: When the energy storage inverter is in off-grid operation mode and the photovoltaic inverter outputs power to the energy storage inverter, obtain the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit. If the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit, and the duration reaches a preset time threshold, the output frequency of the photovoltaic inverter is adjusted to the over-frequency protection value, causing the photovoltaic inverter to shut down due to over-frequency.
[0006] According to the control method of the photovoltaic energy storage system of this application, when the output power of the photovoltaic inverter is detected to be continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset threshold, the photovoltaic inverter is actively shut down due to overfrequency. When the photovoltaic power is excessive, the photovoltaic power supply is cut off to maintain the power balance of the energy storage system and the stability of the AC bus voltage.
[0007] According to one embodiment of this application, the method for obtaining the maximum charging power of the energy storage unit includes: Obtain the maximum AC input power of the energy storage inverter and the maximum allowable charging power of the energy storage unit; The minimum of the maximum input power and the maximum allowable charging power is taken as the maximum charging power of the energy storage unit.
[0008] According to one embodiment of this application, adjusting the output frequency of a photovoltaic inverter to an over-frequency protection value to shut down the photovoltaic inverter due to over-frequency operation includes: The AC bus frequency of the energy storage inverter is controlled to operate at a value greater than or equal to the over-frequency protection value, so that the output frequency of the photovoltaic inverter follows the AC side operating frequency of the energy storage inverter to achieve the over-frequency protection value.
[0009] According to one embodiment of this application, before controlling the energy storage inverter to operate at a value greater than or equal to the overfrequency protection value, the method further includes: Obtain the current power derating percentage of the photovoltaic inverter; The desired AC bus frequency of the energy storage inverter is determined based on the preset frequency-power derating mapping relationship and the current power derating percentage. Control the energy storage inverter to operate at the desired AC bus frequency to regulate the output power of the photovoltaic inverter.
[0010] According to one embodiment of this application, obtaining the current power derating percentage of a photovoltaic inverter includes: The ratio of the maximum charging power of the energy storage unit to the maximum output power of the photovoltaic inverter is used as the current power derating percentage.
[0011] According to one embodiment of this application, when the output power of the photovoltaic inverter continuously exceeds the maximum charging power of the energy storage unit, the control method further includes: The output power of the photovoltaic inverter and the instantaneous charging power of the energy storage unit are continuously monitored within a preset time threshold. Within a preset time threshold, the output power of the photovoltaic inverter and the instantaneous charging power of the energy storage unit both drop to less than or equal to the maximum charging power, and the energy storage inverter is controlled to return to rated frequency operation.
[0012] According to one embodiment of this application, after obtaining the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit, the method further includes: Obtain the output power of the photovoltaic inverter; When the output power of the photovoltaic inverter is less than the maximum charging power of the energy storage unit, the charging power limit of the energy storage unit is set to the maximum charging power.
[0013] Secondly, this application provides a computer program product, comprising: The acquisition module is used to acquire the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit when the energy storage inverter is in off-grid operation mode and the photovoltaic inverter is outputting electrical energy to the energy storage inverter. The adjustment module is used to adjust the output frequency of the photovoltaic inverter to the over-frequency protection value when the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset time threshold, so that the photovoltaic inverter shuts down due to over-frequency.
[0014] According to the computer program product of this application, when it is detected that the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset threshold, the photovoltaic inverter is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance of the energy storage system and the stability of the AC bus voltage.
[0015] Thirdly, this application provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the aforementioned control method for a photovoltaic energy storage system.
[0016] According to the computer-readable storage medium of this application, when the output power of the photovoltaic inverter is detected to be continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset threshold, the photovoltaic inverter is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance of the energy storage system and the stability of the AC bus voltage.
[0017] Fourthly, this application provides a photovoltaic energy storage system, which includes: A photovoltaic system includes a photovoltaic inverter, the DC side of which is used for electrical connection with photovoltaic modules; An energy storage system includes an energy storage unit, an energy storage inverter, and a controller. The DC side of the energy storage inverter is electrically connected to the energy storage unit, and the AC side of the energy storage inverter is electrically connected to the AC side of the photovoltaic inverter. The controller is configured to execute the aforementioned control method for the photovoltaic energy storage system.
[0018] According to the photovoltaic energy storage system of this application, when the output power of the photovoltaic inverter is detected to be continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset threshold, the photovoltaic inverter is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance of the energy storage system and the stability of the AC bus voltage.
[0019] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description
[0020] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is one of the flowcharts of the control method for the photovoltaic energy storage system provided in the embodiments of this application; Figure 2 This is a structural block diagram of the photovoltaic energy storage system provided in the embodiments of this application; Figure 3 This is the second flowchart of the control method for the photovoltaic energy storage system provided in the embodiments of this application; Figure 4 This is a structural block diagram of the computer program product provided in the embodiments of this application.
[0021] Figure label: Photovoltaic system 10, photovoltaic inverter 11, energy storage system 20, energy storage unit 21, energy storage inverter 22, first photovoltaic module 31, second photovoltaic module 32, first load 41, second load 42, power grid 50, computer program product 60, acquisition module 61, regulation module 62. Detailed Implementation
[0022] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.
[0023] In the following description, a "circuit" refers to a conductive loop consisting of at least one element or sub-circuit connected by an electrical or electromagnetic link. When an element or circuit is said to be "coupled to" or "connected to" another element, or when an element / circuit is said to be "coupled at" or "connected at" two nodes, it can be directly coupled to or connected to the other element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there are no intermediate elements between them.
[0024] In the description, the terms "first," "second," etc., are used to distinguish similar objects, not to describe a specific order or sequence. It should be understood that such numerical descriptors can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.
[0025] Furthermore, the use of terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0026] Figure 1 A flowchart illustrating the control method for a photovoltaic energy storage system provided in an embodiment of this application is shown. (Refer to...) Figure 1 One embodiment of this application proposes a control method for a photovoltaic energy storage system. The photovoltaic energy storage system includes an energy storage inverter 22, an energy storage unit 21, and a photovoltaic inverter 11. The energy storage unit 21 is electrically connected to the DC side of the energy storage inverter 22, and the AC side of the photovoltaic inverter 11 is electrically connected to the AC side of the energy storage inverter 22. The control method includes steps 10 and 20.
[0027] Step 10: When the energy storage inverter 22 is in off-grid operation mode and the photovoltaic inverter 11 is outputting electrical energy to the energy storage inverter 22, obtain the output power of the photovoltaic inverter 11 and the maximum charging power P of the energy storage unit 21. bat_char_max ; Step 20: When the output power of the photovoltaic inverter 11 is continuously greater than the maximum charging power P of the energy storage unit 21 bat_char_max If the duration reaches the preset time threshold, the output frequency of the photovoltaic inverter 11 is adjusted to the over-frequency protection value, causing the photovoltaic inverter 11 to shut down due to over-frequency.
[0028] Figure 2 A structural block diagram of a photovoltaic energy storage system provided in an embodiment of this application is shown. (Refer to...) Figure 2 To more clearly illustrate the control method proposed in this embodiment, one embodiment of this application proposes a photovoltaic energy storage system. In this embodiment, the photovoltaic energy storage system includes a photovoltaic system 10 and an energy storage system 20. The photovoltaic system 10 includes a photovoltaic inverter 11, the DC side of which is electrically connected to a first photovoltaic module 31; the energy storage system 20 includes an energy storage unit 21, an energy storage inverter 22, and a controller. The DC side of the energy storage inverter 22 is electrically connected to the energy storage unit 21, the AC side of the energy storage inverter 22 is electrically connected to the AC side of the photovoltaic inverter 11, and the controller is electrically connected to the energy storage inverter 22 and can send drive signals to the switching transistors in the energy storage inverter 22.
[0029] The energy storage unit 21 is electrically connected to the DC side of the energy storage inverter 22. The energy storage inverter 22 typically has the function of bidirectional energy conversion. During charging, the energy storage inverter 22 rectifies the AC power from the AC side to charge the energy storage unit 21; during discharging, the energy storage unit 21 provides DC power to the energy storage inverter 22.
[0030] The specific type of energy storage unit 21 can be selected according to the actual application scenario, and is not limited here. For example, energy storage unit 21 can be a battery pack composed of lithium-ion batteries or lead-acid batteries.
[0031] In addition to the interface of the energy storage unit 21, the DC side of the energy storage inverter 22 usually also integrates a photovoltaic module input interface for electrical connection with the second photovoltaic module 32. Photovoltaic power generation can be directly used for local loads, power the energy storage unit 21, or feed into the grid 50 when connected to the grid.
[0032] The AC output side of the photovoltaic inverter 11 and the AC output side of the energy storage inverter 22 are connected in parallel to the same AC bus via AC cables. The first load 41 can be directly connected to this AC bus to obtain electrical energy from the bus.
[0033] It should be noted that, in addition to being electrically connected to the AC side of the photovoltaic inverter 11, the AC side of the energy storage inverter 22 is also typically electrically connected to the power grid 50. A second load 42 can be connected to the line connecting the AC side of the energy storage inverter 22 to the power grid 50.
[0034] When the grid 50 is normal, the energy storage inverter 22 can operate in grid-connected mode, following the voltage and frequency commands of the grid 50. Photovoltaic power generation prioritizes supplying local loads, with the remainder charging the energy storage unit 21 or feeding back into the grid 50 via the energy storage inverter 22. When photovoltaic power generation is insufficient to meet load demand, the energy storage unit 21 can discharge or supplement from the grid 50. In off-grid mode, the energy storage inverter 22 switches to off-grid operation mode, acting as a voltage source to maintain the voltage and frequency stability of the AC bus and supply power to local loads. The photovoltaic inverter 11 is electrically connected to the AC side of the energy storage inverter 22 via the AC bus. A portion of the output power of the photovoltaic inverter 11 can supply local loads, with the remainder charging the energy storage unit 21 via the energy storage inverter 22. However, photovoltaic module power generation is volatile and intermittent. When the output power of the photovoltaic inverter 11 continuously exceeds the real-time maximum charging power P of the energy storage unit 21... bat_char_max At this time, the excess power cannot be absorbed. Without control, the energy storage inverter 22 will be forced to deviate from its rated operating point in order to absorb the excess power, and eventually it will be difficult to maintain the stability of the AC bus voltage, leading to system voltage collapse.
[0035] This application proposes a control method for a photovoltaic energy storage system, wherein the output power of the photovoltaic inverter 11 is continuously greater than the maximum charging power P of the energy storage unit 21.bat_char_max When the frequency is too high, the photovoltaic inverter 11 is shut down to maintain the power balance and AC bus voltage stability of the energy storage system 20.
[0036] The execution subject of the control method for the photovoltaic energy storage system provided in the embodiments of this application can be the aforementioned controller or a functional module or functional entity in the controller that can implement the control method. The control method for the photovoltaic energy storage system provided in the embodiments of this application will be described below with the controller as the execution subject as an example.
[0037] When the energy storage inverter 22 is in off-grid operation mode and the photovoltaic inverter 11 outputs electrical energy to the energy storage inverter 22 to charge the energy storage unit 21, the controller obtains the output power of the photovoltaic inverter 11 and the maximum charging power P of the energy storage unit 21. bat_char_max .
[0038] The controller of the energy storage system 20 compares in real time the actual output power of the photovoltaic inverter 11 with the real-time updated maximum charging power P of the energy storage unit 21. bat_char_max When the actual output power of the photovoltaic inverter 11 is greater than the maximum charging power P of the energy storage unit 21 bat_char_max If the time exceeds the preset time threshold, the controller will issue a command to control the photovoltaic inverter 11 to shut down due to over-frequency.
[0039] The preset time threshold refers to the maximum observation and waiting time allowed from the moment the system first detects that the output power of the photovoltaic inverter is greater than the maximum charging power of the energy storage unit, until the final decision is made on whether to trigger the over-frequency protection shutdown action.
[0040] The specific value of the preset time threshold can be selected according to the actual application scenario, and is not limited here. For example, the preset time threshold can be 8 seconds or 10 seconds.
[0041] Understandably, the controller of the energy storage system 20 can collect the output current and output voltage of the photovoltaic inverter 11 in real time, and the actual output power of the photovoltaic inverter 11 can be obtained by calculating the product of the output current and output voltage of the photovoltaic inverter 11.
[0042] Upon detecting an abnormally high frequency, photovoltaic inverter 11 will trigger its hardware protection mechanism and immediately shut down. For energy storage inverter 22, the shutdown of photovoltaic inverter 11 cuts off the excess power source, restoring the power balance of the photovoltaic energy storage system (leaving only energy storage inverter 22 supplying power to the load), thereby protecting energy storage system 20 and preventing a complete system collapse.
[0043] According to the control method of the photovoltaic energy storage system of this application, when the output power of the photovoltaic inverter 11 is detected to be continuously greater than the maximum charging power of the energy storage unit 21 and the duration reaches a preset threshold, the photovoltaic inverter 11 is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance and AC bus voltage stability of the energy storage system 20.
[0044] In some embodiments, the maximum charging power P of the energy storage unit 21 bat_char_max The methods for obtaining this include: obtaining the maximum AC input power P of the energy storage inverter 22. ac_in The maximum allowable charging power of the energy storage unit 21; the minimum value between the maximum input power and the maximum allowable charging power is taken as the maximum charging power of the energy storage unit 21.
[0045] The maximum charging power P of energy storage unit 21 bat_char_max The determination of the energy storage unit 21 requires consideration of its battery-based characteristics, such as its rated voltage and maximum allowable charging current. It also requires consideration of the energy storage inverter 22's ability to convert energy from the AC side to the DC side, i.e., its maximum input power on the AC side. The maximum charging power P of the energy storage unit 21... bat_char_max The actual value is the smaller of the inverter's maximum AC input power and the energy storage unit 21's maximum allowable charging power.
[0046] Energy storage inverter 22 AC maximum input power P ac_in This refers to the maximum active power that the energy storage inverter 22 can receive and process from the AC bus side in off-grid operation. This power limit is usually a default value set by the program and mainly depends on the current thermal limit of the power devices inside the energy storage inverter 22, the capacity of the heat dissipation system, and the withstand voltage rating of the DC bus capacitor. When the power processed by the inverter approaches this limit, its internal temperature will rise, and long-term operation beyond the limit will lead to overheating and damage to the devices.
[0047] The maximum permissible charging power of energy storage unit 21 refers to its safe charging acceptance capability under the current state. This limit is to prevent safety issues such as overheating caused by excessive charging current. This limit can be dynamically adjusted according to the battery's state of charge, temperature, and health condition.
[0048] The maximum allowable charging power of the energy storage unit 21 can usually be calculated directly from the product of the rated voltage of the energy storage unit 21 and its maximum rechargeable current.
[0049] Rated voltage refers to the terminal voltage of energy storage unit 21 (usually a battery pack) under nominal or standard operating conditions. The rated voltage value specified by the manufacturer can be used in calculations. The maximum rechargeable current of energy storage unit 21 is a dynamic safety parameter. It is not a fixed value, but rather an upper limit calculated and published in real time by the battery management system based on the real-time status of energy storage unit 21 (mainly including current state of charge, cell temperature, health status, and historical operating data). Its fundamental purpose is to prevent the battery from being subjected to excessive charging current surges at any time.
[0050] Because the maximum rechargeable current is dynamically updated, the calculated maximum allowable charging power of the energy storage unit 21 is also a real-time changing value. For example, when the state of charge of the energy storage unit 21 is close to full charge, the battery management system will reduce the allowable charging current, thereby automatically reducing the system's charging power limit.
[0051] Because the actual capacity of the entire charging circuit depends on the weakest link. If the maximum AC input power P of the energy storage inverter 22... ac_in If the energy storage unit 21 can currently only safely accept 4kW, the system should limit charging to 4kW; otherwise, the battery will be damaged. Conversely, if the energy storage unit 21 can accept 5kW, but the energy storage inverter 22 can only handle 4.5kW due to overheating limitations, then the charging power should be capped at 4.5kW to protect the hardware of the energy storage inverter 22. Therefore, the controller of the energy storage system 20 sets the maximum AC input power P of the energy storage inverter 22 to... ac_in The maximum allowable charging power of the energy storage unit 21 is compared in real time with the minimum value, and the minimum value is taken as the final maximum charging power P of the energy storage unit 21. bat_char_max This ensures that, under any operating condition, the system's charging power will not exceed the physical processing limit of the energy storage inverter 22, nor violate the electrochemical safety guidelines of the energy storage unit 21 itself, thereby maximizing equipment safety and operational reliability at the system level.
[0052] In some embodiments, adjusting the output frequency of the photovoltaic inverter 11 to the over-frequency protection value to shut down the photovoltaic inverter 11 due to over-frequency includes: controlling the AC bus frequency of the energy storage inverter 22 to operate at a value greater than or equal to the over-frequency protection value, so that the output frequency of the photovoltaic inverter 11 follows the AC side operating frequency of the energy storage inverter 22 to reach the over-frequency protection value.
[0053] In the off-grid microgrid 50 established by the energy storage inverter 22, the energy storage inverter 22 acts as the sole voltage source, actively establishing and maintaining the voltage amplitude and frequency of the AC bus. The frequency of the voltage signal output by the energy storage inverter 22 serves as the frequency reference for the entire system.
[0054] The photovoltaic inverter 11 is connected to the microgrid 50 as a current source, primarily for outputting specified power. To accurately inject current into the grid 50, the photovoltaic inverter 11 typically synchronizes the frequency of its output current with the frequency of the AC bus voltage it is connected to. Therefore, the output frequency of the photovoltaic inverter 11 essentially passively follows the AC bus frequency.
[0055] The controller sends a command to the energy storage inverter 22, which is in voltage source mode, requesting it to actively adjust the frequency of the output AC voltage from the current operating value to a preset over-frequency protection value. The over-frequency protection value is greater than or equal to the over-frequency shutdown protection threshold defined in the photovoltaic inverter 11 product standard (for example, if the standard requires the photovoltaic inverter 11 to shut down within a specified time when the frequency is higher than 51.5Hz, then the over-frequency protection value can be set to 51.8Hz).
[0056] This embodiment utilizes the characteristic that the frequency of the photovoltaic inverter 11 follows the frequency change of the AC bus, eliminating the need to establish any dedicated real-time communication link between the energy storage inverter 22 and the photovoltaic inverter 11. By adjusting the single variable of frequency through the energy storage inverter 22, indirect control of the power of the photovoltaic inverter 11 can be achieved, simplifying the system architecture and reducing costs and potential points of failure.
[0057] In some embodiments, before controlling the energy storage inverter 22 to operate at a value greater than or equal to the overfrequency protection value, the method further includes: obtaining the current power derating percentage of the photovoltaic inverter 11; determining the desired AC bus frequency of the energy storage inverter 22 based on a preset frequency-power derating mapping relationship and the current power derating percentage; and controlling the energy storage inverter 22 to operate at the desired AC bus frequency to adjust the output power of the photovoltaic inverter 11.
[0058] The current power derating percentage of photovoltaic inverter 11 is mainly used to characterize the relative relationship between the theoretical upper limit of the output power of photovoltaic inverter 11 and the current absorption limit of energy storage inverter 22.
[0059] The frequency-power derating mapping relationship refers to the pre-set correspondence table or function curve in the control logic of the energy storage inverter 22. The frequency-power curve specifies the percentage of power derating that different output frequency values should correspond to the expected power derating percentage of the photovoltaic inverter 11. This curve is usually set to an inverse relationship; when the energy storage system 20 has a weak absorption capacity and needs to be significantly drated, the corresponding frequency setpoint is higher; conversely, when the energy storage system 20 has a strong absorption capacity, the corresponding frequency setpoint is close to the rated frequency.
[0060] The energy storage inverter 22 controller, based on the obtained current photovoltaic derating percentage, queries the frequency-power derating mapping relationship to calculate the required frequency, which is the desired AC bus frequency. Subsequently, through its internal phase-locked loop and pulse width modulation control, it stabilizes the frequency of its output voltage at this desired AC bus frequency.
[0061] It should be noted that the frequency-power derating mapping relationship is essentially pre-set based on the frequency-power characteristics commonly used in grid connection standards. In this control strategy, the energy storage inverter 22 actively stabilizes the frequency of its output voltage at the desired AC bus frequency, thereby dominating the frequency of the entire AC bus. The photovoltaic inverter 11 detects and tracks this target frequency in real time and automatically reduces its output power proportionally according to its built-in frequency-power curve, ultimately ensuring that the actual power derating percentage of the photovoltaic system matches the system's expected value.
[0062] In some embodiments, obtaining the current power derating percentage of the photovoltaic inverter 11 includes: setting the maximum charging power P of the energy storage unit 21 as the current power derating percentage. bat_char_max With the maximum output power P of photovoltaic inverter 11 pv_max The ratio is used as the current power derating percentage.
[0063] The current power derating percentage of the photovoltaic inverter 11 can be determined by the maximum charging power P of the energy storage unit 21. bat_char_max The maximum output power P of the photovoltaic inverter 11 pv_max The ratio is calculated. The current power derating percentage K is calculated using the following formula: The current power derating percentage K reflects the theoretically required percentage of maximum output of the photovoltaic inverter 11 to prevent overcharging of the energy storage unit 21 under the current system conditions. For example, if the calculated result is 60%, it means that under the current system conditions, the photovoltaic inverter 11 should limit its output to within 60% of its maximum potential output to ensure that all generated power can be safely absorbed by the energy storage unit 21, thereby maintaining the stability of the off-grid AC bus.
[0064] In some embodiments, when the output power of the photovoltaic inverter 11 is continuously greater than the maximum charging power P of the energy storage unit 21 bat_char_max The control method also includes: continuously monitoring the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21 within a preset time threshold; and controlling the energy storage inverter 22 to resume operation at the rated frequency when the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21 both drop to less than or equal to the maximum charging power within the preset time threshold.
[0065] The output power of the photovoltaic inverter 11 is greater than or equal to the maximum charging power P of the energy storage unit 21. bat_char_maxWhen this occurs, it indicates that the output power of the photovoltaic inverter 11 has reached or even exceeded the maximum value that the energy storage system 20 can currently safely accept, and the energy storage system 20 is in a state of power surplus.
[0066] When the system detects that the photovoltaic output power is too high, the energy storage inverter 22 will increase its output frequency according to the frequency-power derating mapping relationship. The photovoltaic inverter 11 tracks this bus frequency in real time and follows its built-in frequency-power characteristics. When it detects that the frequency is higher than the rated value, it will actively reduce its active power output according to a preset ratio. Under the above circumstances, the controller continuously monitors the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21.
[0067] The preset time threshold represents the maximum allowable duration for the energy storage system 20 to cope with power surges. Within the preset time threshold, if the output power of the photovoltaic inverter 11 drops to less than or equal to the maximum charging power P... bat_char_max Furthermore, the instantaneous charging power of the energy storage unit 21 also decreases synchronously to less than or equal to the maximum charging power P. bat_char_max If this happens, the power limit violation can be determined as a short-lived, recoverable event. At this time, the energy storage system 20 resets the charging power limit of the energy storage unit 21 to the maximum charging power P. bat_char_max This signifies that the system has exited the high-risk warning state and resumed normal safe power management, allowing the energy storage unit 21 to charge flexibly within the safe limit. This avoids frequent and unnecessary protective shutdowns of the photovoltaic inverter 11 due to momentary disturbances or fluctuations, improving the operational continuity and availability of the off-grid system.
[0068] In some embodiments, after obtaining the output power of the photovoltaic inverter 11 and the maximum charging power of the energy storage unit 21, the method further includes: obtaining the output power of the photovoltaic inverter 11; when the output power of the photovoltaic inverter 11 is less than the maximum charging power P of the energy storage unit 21... bat_char_max At that time, the charging power limit value of energy storage unit 21 is set to the maximum charging power P. bat_char_max .
[0069] The energy storage system 20 can continuously measure the real-time voltage and current flowing into the DC terminal of the energy storage unit 21 using high-precision sensors (such as Hall current sensors and voltage sampling circuits), and calculate the instantaneous charging power of the energy storage unit 21 accordingly.
[0070] After obtaining the instantaneous charging power of the energy storage unit 21, the controller compares it with the preset maximum charging power P of the energy storage unit 21. bat_char_max Real-time comparison is performed, and the preset maximum charging power P of energy storage unit 21 is determined. bat_char_max The value is usually calculated dynamically based on factors such as battery chemical safety, temperature, and health status.
[0071] When the instantaneous charging power of energy storage unit 21 is detected to be greater than the maximum charging power P of energy storage unit 21 bat_char_max This indicates that the current actual charging power of energy storage unit 21 has not reached its safe upper limit, and there is a certain power safety margin between the two. In this case, the energy storage system 20 will set the charging power limit of the energy storage unit 21 to be the same as the maximum charging power P. bat_char_max Equal. After confirming the instantaneous safety of the system, the energy storage unit 21 is allowed to charge at the highest possible safe power, which enables faster storage of excess photovoltaic energy, improves the immediate absorption capacity of fluctuating photovoltaic output in off-grid conditions, reduces energy waste, and thus optimizes the overall operating economy of the system.
[0072] The instantaneous charging power is greater than or equal to the maximum charging power P. bat_char_max When the output power of the photovoltaic inverter 11 is less than the maximum charging power P of the energy storage unit 21, the controller can obtain the output power of the photovoltaic inverter 11; when the output power of the photovoltaic inverter 11 is less than the maximum charging power P of the energy storage unit 21, the controller can obtain the output power of the photovoltaic inverter 11. bat_char_max At that time, the charging power limit value of energy storage unit 21 is set to the maximum charging power P. bat_char_max .
[0073] The instantaneous charging power of energy storage unit 21 is greater than or equal to the maximum charging power P. bat_char_max When the energy storage unit 21 is at or has exceeded its safe charging boundary, this indicates that the output power of the photovoltaic inverter 11 exceeds the absorption capacity of the energy storage system 20. Further analysis of the source composition of the power is required.
[0074] The output power of the photovoltaic inverter 11 can be calculated by multiplying its output current and output voltage. The instantaneous charging power of the energy storage unit 21 is greater than or equal to the maximum charging power P. bat_char_max Under the premise that the output power of photovoltaic inverter 11 is less than the maximum charging power P bat_char_max This indicates that although the total charging power of the energy storage unit 21 is too high, the electrical energy output by the photovoltaic inverter 11 does not exceed the absorption capacity of the energy storage unit 21. This means that the total charging power is greater than or equal to the maximum charging power P. bat_char_max This may be due to a sudden decrease in load demand, which causes the residual power of the photovoltaic inverter 11 after supplying the load to increase instantaneously.
[0075] In the above case, the charging power limit of the energy storage unit 21 is set to be equal to its maximum charging power P. bat_char_max This prevents the system from mistakenly triggering over-frequency shutdown of photovoltaic inverters when transient imbalances occur due to non-photovoltaic factors such as sudden load changes, thus ensuring the continuity of photovoltaic power generation.
[0076] Figure 3A flowchart illustrating the control method for a photovoltaic energy storage system provided in an embodiment of this application is shown. (Refer to...) Figure 3 The specific process of the control method for the photovoltaic energy storage system in this application is as follows: The controller controls the energy storage inverter 22 to operate at a target AC output frequency. For example, the controller of the energy storage system 20 obtains the current power derating percentage of the photovoltaic inverter 11, and determines the target AC output frequency of the energy storage inverter 22 based on a preset frequency-power derating mapping relationship and the current power derating percentage.
[0077] During operation, the controller determines whether the instantaneous charging power of the energy storage unit 21 is less than the maximum charging power of the energy storage unit 21. The controller obtains the instantaneous charging power of the energy storage unit 21 and compares it with the determined maximum charging power.
[0078] When the instantaneous charging power is less than the maximum charging power of the energy storage unit 21, the controller sets the charging power limit of the energy storage unit 21 to the maximum charging power. When the instantaneous charging power is greater than or equal to the maximum charging power, the controller obtains the output power of the photovoltaic inverter 11 and determines whether the output power is less than the maximum charging power of the energy storage unit 21.
[0079] When the output power of the photovoltaic inverter 11 is less than the maximum charging power of the energy storage unit 21, the controller sets the charging power limit of the energy storage unit 21 to the maximum charging power. When the output power of the photovoltaic inverter 11 is greater than or equal to the maximum charging power of the energy storage unit 21, it is determined whether the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21 both decrease to less than or equal to the maximum charging power within a preset time threshold.
[0080] The controller can determine the desired AC bus frequency of the energy storage inverter based on a preset frequency-power derating mapping relationship and the current power derating percentage; and control the energy storage inverter to operate at the desired AC bus frequency to adjust the output power of the photovoltaic inverter. The controller can continuously monitor the relationship between the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21 and the maximum charging power.
[0081] If, within a preset time threshold, both the output power of the photovoltaic inverter 11 and the instantaneous charging power of the energy storage unit 21 decrease to less than or equal to the maximum charging power, the charging power limit of the energy storage unit 21 can be set to the maximum charging power according to the aforementioned steps. If the output power of the photovoltaic inverter 11 continues to exceed the maximum charging power of the energy storage unit 21, and the duration reaches the preset time threshold, the output frequency of the energy storage inverter 22 is adjusted to the over-frequency protection value, causing the photovoltaic inverter 11 to shut down due to over-frequency operation.
[0082] Figure 4 A structural block diagram of a computer program product 60 provided in an embodiment of this application is shown. (Refer to...) Figure 4 One embodiment of this application proposes a computer program product 60, including: an acquisition module 61 and an adjustment module 62. The acquisition module 61 is used to acquire the output power of the photovoltaic inverter 11 and the maximum charging power of the energy storage unit 21 when the energy storage inverter 22 is in off-grid operation mode and the photovoltaic inverter 11 outputs electrical energy to the energy storage inverter 22; the adjustment module 62 is used to adjust the output frequency of the photovoltaic inverter 11 to an over-frequency protection value when the output power of the photovoltaic inverter 11 is continuously greater than the maximum charging power of the energy storage unit 21 and the duration reaches a preset time threshold, so that the photovoltaic inverter 11 shuts down due to over-frequency.
[0083] For a description of the features in the embodiments corresponding to the computer program product 60, please refer to the relevant descriptions of the embodiments corresponding to the photovoltaic energy storage system and the control method of the photovoltaic energy storage system, which will not be repeated here.
[0084] According to the computer program product 60 of this application, when it is detected that the output power of the photovoltaic inverter 11 is continuously greater than the maximum charging power of the energy storage unit 21 and the duration reaches a preset threshold, the photovoltaic inverter 11 is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance and AC bus voltage stability of the energy storage system 20.
[0085] One embodiment of this application proposes a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the aforementioned control method for a photovoltaic energy storage system.
[0086] For a description of the features in the embodiments corresponding to the computer-readable storage medium, please refer to the relevant description of the embodiments corresponding to the control method of the photovoltaic energy storage system, which will not be repeated here.
[0087] According to the computer-readable storage medium of this application, when the output power of the photovoltaic inverter 11 is detected to be continuously greater than the maximum charging power of the energy storage unit 21 for a period of time reaching a preset threshold, the photovoltaic inverter 11 is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance and AC bus voltage stability of the energy storage system 20.
[0088] One embodiment of this application proposes a photovoltaic energy storage system, which includes a photovoltaic system 10 and an energy storage system 20. The photovoltaic system 10 includes a photovoltaic inverter 11, the DC side of which is electrically connected to photovoltaic modules; the energy storage system 20 includes an energy storage unit 21, an energy storage inverter 22, and a controller. The DC side of the energy storage inverter 22 is electrically connected to the energy storage unit 21, and the AC side of the energy storage inverter 22 is electrically connected to the AC side of the photovoltaic inverter 11. The controller is configured to execute the aforementioned control method of the photovoltaic energy storage system.
[0089] The specific structure and working principle of the photovoltaic energy storage system can be referred to in the aforementioned embodiments, and will not be repeated here.
[0090] According to the photovoltaic energy storage system of this application, when the output power of the photovoltaic inverter 11 is detected to be continuously greater than the maximum charging power of the energy storage unit 21 and the duration reaches a preset threshold, the photovoltaic inverter 11 is actively shut down due to over-frequency, and the photovoltaic power supply is cut off when the photovoltaic power is excessive, so as to maintain the power balance and AC bus voltage stability of the energy storage system 20.
[0091] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.
Claims
1. A control method for a photovoltaic energy storage system, characterized in that, The photovoltaic energy storage system includes an energy storage inverter, an energy storage unit, and a photovoltaic inverter. The energy storage unit is electrically connected to the DC side of the energy storage inverter, and the AC side of the energy storage inverter is electrically connected to the AC side of the photovoltaic inverter and the power grid, respectively. The control method includes: When the energy storage inverter is in off-grid operation mode and the photovoltaic inverter outputs electrical energy to the energy storage inverter, the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit are obtained. If the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit for a period of time that reaches a preset time threshold, the output frequency of the photovoltaic inverter is adjusted to the over-frequency protection value, causing the photovoltaic inverter to shut down due to over-frequency.
2. The control method for a photovoltaic energy storage system according to claim 1, characterized in that, The method for obtaining the maximum charging power of the energy storage unit includes: Obtain the maximum AC input power of the energy storage inverter and the maximum allowable charging power of the energy storage unit; The minimum value between the maximum input power and the maximum allowable charging power is taken as the maximum charging power of the energy storage unit.
3. The control method for a photovoltaic energy storage system according to claim 1, characterized in that, Adjusting the output frequency of the photovoltaic inverter to the over-frequency protection value to shut down the photovoltaic inverter due to over-frequency operation includes: The AC bus frequency of the energy storage inverter is controlled to operate at a value greater than or equal to the over-frequency protection value, so that the output frequency of the photovoltaic inverter follows the AC side operating frequency of the energy storage inverter to achieve the over-frequency protection value.
4. The control method for the photovoltaic energy storage system according to claim 3, characterized in that, Before controlling the energy storage inverter to operate at a value greater than or equal to the overfrequency protection value, the method further includes: Obtain the current power derating percentage of the photovoltaic inverter; The desired AC bus frequency of the energy storage inverter is determined based on the preset frequency-power derating mapping relationship and the current power derating percentage. The energy storage inverter is controlled to operate at the desired AC bus frequency to adjust the output power of the photovoltaic inverter.
5. The control method for a photovoltaic energy storage system according to claim 4, characterized in that, The step of obtaining the current power derating percentage of the photovoltaic inverter includes: The ratio of the maximum charging power of the energy storage unit to the maximum output power of the photovoltaic inverter is used as the current power derating percentage.
6. The control method for a photovoltaic energy storage system according to claim 1, characterized in that, When the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit, the control method further includes: The output power of the photovoltaic inverter and the instantaneous charging power of the energy storage unit are continuously monitored within the preset time threshold. Within the preset time threshold, if the output power of the photovoltaic inverter and the instantaneous charging power of the energy storage unit both decrease to less than or equal to the maximum charging power, the energy storage inverter is controlled to return to the rated frequency operation.
7. The control method for a photovoltaic energy storage system according to claim 1, characterized in that, After obtaining the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit, the method further includes: Obtain the output power of the photovoltaic inverter; When the output power of the photovoltaic inverter is less than the maximum charging power of the energy storage unit, the charging power limit value of the energy storage unit is set to the maximum charging power.
8. A computer program product, characterized in that, include: The acquisition module is used to acquire the output power of the photovoltaic inverter and the maximum charging power of the energy storage unit when the energy storage inverter is in off-grid operation mode and the photovoltaic inverter outputs electrical energy to the energy storage inverter. The adjustment module is used to adjust the output frequency of the photovoltaic inverter to the over-frequency protection value when the output power of the photovoltaic inverter is continuously greater than the maximum charging power of the energy storage unit and the duration reaches a preset time threshold, so that the photovoltaic inverter shuts down due to over-frequency.
9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein the computer program, when executed by a processor, implements the control method of the photovoltaic energy storage system according to any one of claims 1-7.
10. A photovoltaic energy storage system, characterized in that, include: A photovoltaic system includes a photovoltaic inverter, wherein the DC side of the photovoltaic inverter is used for electrical connection with photovoltaic modules; An energy storage system includes an energy storage unit, an energy storage inverter, and a controller. The DC side of the energy storage inverter is electrically connected to the energy storage unit, and the AC side of the energy storage inverter is electrically connected to the AC side of a photovoltaic inverter. The controller is configured to execute the control method of the photovoltaic energy storage system according to any one of claims 1-7.