Parallel operation control method of hybrid energy storage system and grid-connected system

Abstract

The application discloses a kind of parallel operation control method of hybrid energy storage system and grid-connected system, hybrid energy storage system and grid-connected system are controlled independently, the input side of hybrid energy storage inverter of hybrid energy storage system is connected with first photovoltaic component and battery, the output side of hybrid energy storage inverter is connected to power grid through switch S1;The input side of grid-connected inverter of grid-connected system is connected with second photovoltaic component, and the output side of grid-connected inverter is sequentially connected to power grid through intermediate switch group, switch S1;In the state of power grid failure, switch S1 is disconnected, and the electric energy output by grid-connected inverter is supplied to hybrid energy storage system or off-grid load through intermediate switch group, and the electric energy output by hybrid energy storage system is supplied to off-grid load;In the state of normal power grid, switch S1 is closed, and hybrid energy storage inverter controls the output power of grid-connected system by control command or by controlling the opening and closing of intermediate switch group.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and more particularly to a method for parallel operation control of a hybrid energy storage system and a grid-connected system. Background Technology

[0002] Photovoltaic (PV) power generation is widely used as a clean and renewable energy source, but its output power is unpredictable and volatile. As the proportion of PV power generation in traditional power grids continues to increase, its high penetration rate will bring a series of problems to grid voltage stability, power quality, and operation control. By adding energy storage devices to PV power generation systems and utilizing their charging and discharging characteristics, the power fluctuation problem caused by uneven sunlight can be effectively alleviated, while reducing curtailment, promoting large-scale consumption of PV power, and improving overall power generation revenue. However, with technological development and increasing electricity demand, hybrid energy storage systems consisting of inverters and energy storage batteries are no longer sufficient to meet current needs. Users typically expand capacity and power by connecting multiple hybrid energy storage systems and grid-connected systems in parallel.

[0003] In related technologies, during grid faults, both the hybrid energy storage system and the grid-connected system disconnect from the grid, rendering the grid-connected system's energy unusable and making curtailment of solar power difficult to avoid. This is especially problematic in areas with weak grids or frequent power outages, potentially failing to meet the power demands of large loads when off-grid. During normal grid operation, the hybrid energy storage system and the grid-connected system are controlled independently. In areas with reverse power limitations, the lack of coordination between the two can easily lead to overfeeding, causing grid faults or even grid paralysis. Summary of the Invention

[0004] One objective of this invention is to provide a parallel operation control method for a hybrid energy storage system and a grid-connected system, so as to effectively utilize the energy of the grid-connected system under grid fault conditions and to avoid overfeeding to the grid under normal grid conditions.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a parallel operation control method for a hybrid energy storage system and a grid-connected system, wherein the hybrid energy storage system and the grid-connected system are controlled independently. The input side of the hybrid energy storage inverter of the hybrid energy storage system is connected to a first photovoltaic module and a battery, and the output side of the hybrid energy storage inverter is connected to the grid via switch S1. The input side of the grid-connected inverter of the grid-connected system is connected to a second photovoltaic module, and the output side of the grid-connected inverter is connected to the grid sequentially via an intermediate switch group and switch S1. In the event of a grid fault, switch S1 is opened, and the electrical energy output by the grid-connected inverter is supplied to the hybrid energy storage system or an off-grid load via the intermediate switch group. The electrical energy output by the hybrid energy storage system is supplied to the off-grid load. In the event of a normal grid condition, switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system through control commands or by controlling the opening and closing of the intermediate switch group.

[0006] As a preferred embodiment, in the event of a grid fault, when the power of the first and second photovoltaic modules cannot be absorbed, the hybrid energy storage inverter reduces its output power and increases the voltage frequency output from the off-grid port to reduce the output power of the grid-connected inverter.

[0007] As a preferred embodiment, the bus voltage of the hybrid energy storage inverter is monitored. When the bus voltage of the hybrid energy storage inverter rises, it is determined that the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic module.

[0008] As a preferred embodiment, the battery absorption capacity of the hybrid energy storage system is monitored. When the battery absorption capacity decreases, it is determined that the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic module.

[0009] As a preferred embodiment, the battery's absorption capacity is calculated by monitoring the battery voltage and SOC of the hybrid energy storage system, combined with the battery's BMS charging current limit value.

[0010] As a preferred embodiment, under normal grid conditions, when the power of the first and second photovoltaic modules cannot be absorbed, the hybrid energy storage inverter sends a control command to the grid-connected inverter to adjust the output power of the grid-connected inverter.

[0011] As a preferred embodiment, the intermediate switch group includes a switch S2, which is controlled by the internal circuit of the hybrid energy storage inverter. Under normal grid conditions, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the grid-connected inverter is disconnected from the grid by opening the switch S2.

[0012] As a preferred embodiment, the intermediate switch group further includes switch S3, which is connected in series with switch S2. Switch S3 is controlled by the dry node on / off signal of the hybrid energy storage inverter. Under normal grid conditions, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the grid-connected inverter is disconnected from the grid by disconnecting switch S3.

[0013] As a preferred embodiment, when the grid power of the hybrid energy storage inverter and the grid-connected inverter exceeds a preset threshold and continues for a preset time, the switch S2 and / or the switch S3 are disconnected; when the battery capacity of the hybrid energy storage system decreases and is within a preset hysteresis range, the switch S2 and the switch S3 are closed.

[0014] As a preferred embodiment, under grid fault conditions, when the power of the first and second photovoltaic modules can be absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the off-grid load, and the excess electrical energy is stored in the battery of the hybrid energy storage system; under normal grid conditions, when the power of the first and second photovoltaic modules can be absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the grid, and the excess electrical energy is stored in the battery of the hybrid energy storage system.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) When the grid is in a fault state, switch S1 is open, and the electrical energy output by the grid-connected inverter is supplied to the hybrid energy storage system or off-grid load through the intermediate switch group. The electrical energy output by the hybrid energy storage system is supplied to the off-grid load. This allows the electrical energy of the grid-connected system to be fully utilized, which is beneficial to avoid curtailment of solar power and to meet the application needs of high-power off-grid loads.

[0017] (2) Under normal grid conditions, when switch S1 is closed, the hybrid energy storage inverter controls the output power of the grid-connected system by means of control commands or by controlling the opening and closing of intermediate switch groups. This helps to avoid the hybrid energy storage system and the grid-connected system from generating excess grid feed, thereby reducing the risk of grid failure or paralysis. Attached Figure Description

[0018] Figure 1 This is a wiring diagram showing the parallel operation of a hybrid energy storage inverter and a grid-connected inverter in related technologies.

[0019] Figure 2 This is a wiring diagram of a hybrid energy storage inverter and a grid-connected inverter operating in parallel, according to some embodiments of this application.

[0020] Figure 3 This is a logic diagram of a parallel operation control method for a hybrid energy storage system and a grid-connected system according to some embodiments of this application.

[0021] Figure 4 This is a schematic diagram of the current flow of a hybrid energy storage inverter and a grid-connected inverter under grid fault conditions, according to some embodiments of this application.

[0022] Figure 5 This is a schematic diagram of the current flow of a hybrid energy storage inverter and a grid-connected inverter under grid fault conditions, which are embodiments of this application.

[0023] Figure 6 This is a graph showing the relationship between the output power and frequency of a grid-connected inverter according to some embodiments of this application.

[0024] Figure 7 This is a graph showing the relationship between the bus voltage and frequency of a hybrid energy storage inverter according to some embodiments of this application.

[0025] Figure 8 This is a graph showing the relationship between the battery absorption capacity and frequency of a hybrid energy storage inverter according to some embodiments of this application. Detailed Implementation

[0026] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0027] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0028] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0029] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection, a contact connection, or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0030] To facilitate understanding of the following scheme, this application will describe it as a multi-machine system in which a hybrid energy storage system and a grid-connected system operate in parallel. For example... Figure 1 As shown, the input side of the hybrid energy storage inverter in the hybrid energy storage system is connected to the first photovoltaic module and the battery, and the output side of the hybrid energy storage inverter is connected to the power grid; the input side of the grid-connected inverter in the grid-connected system is connected to the second photovoltaic module, and the output side of the grid-connected inverter is connected to the power grid.

[0031] In related technologies, such as Figure 1 As shown, the hybrid energy storage inverter and the grid-connected inverter are connected to the grid independently. Their power transfer to the grid is independent and does not affect each other. In other words, the hybrid energy storage system and the grid-connected system are independently controlled. The hybrid energy storage system is the main system, while the grid-connected system is an independent power generation system that cannot be controlled by the hybrid energy storage system. For example, adding a hybrid energy storage system when a grid-connected system is already installed, or vice versa, would make it difficult to control the two systems through the same communication mechanism.

[0032] Furthermore, during grid faults, both the hybrid energy storage system and the grid-connected system disconnect from the grid. The hybrid energy storage system connects to the off-grid load, providing power to it, while the grid-connected system disconnects, rendering its energy unusable and resulting in curtailment. This is particularly problematic in areas with weak grids or frequent power outages, potentially failing to meet the power demands of large off-grid loads. During normal grid operation, the hybrid energy storage system and the grid-connected system are independently controlled. In areas with reverse power limitations, the lack of coordination between them can easily lead to overfeeding, potentially causing grid faults or even grid paralysis. It should be understood that the first and second photovoltaic modules can also be implemented as other power sources, such as wind turbines, wave generators, or hydroelectric generators; this application does not impose specific limitations on this.

[0033] Based on the above, in order to solve or at least partially alleviate the curtailment of solar power and the problem of excessive grid feeding that occur when hybrid energy storage systems and grid-connected systems, which are originally independently controlled, operate in parallel, this application provides a parallel operation control method for hybrid energy storage systems and grid-connected systems, such as... Figures 2-8 As shown, the input side of the hybrid energy storage inverter in the hybrid energy storage system is connected to the first photovoltaic module and the battery, and the output side of the hybrid energy storage inverter is connected to the grid via switch S1; the input side of the grid-connected inverter in the grid-connected system is connected to the second photovoltaic module, and the output side of the grid-connected inverter is connected to the grid via intermediate switch group and switch S1 in sequence; in the case of grid fault, switch S1 is open, and the power output of the grid-connected inverter is supplied to the hybrid energy storage system or off-grid load through the intermediate switch group, and the power output of the hybrid energy storage system is supplied to the off-grid load; in the case of normal grid conditions, switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system through control commands or by controlling the opening and closing of the intermediate switch group.

[0034] This should be understandable, such as Figure 3 As shown, under grid fault conditions, the off-grid logic operates: switch S1 is open, and the electrical energy output by the grid-connected inverter is supplied to the hybrid energy storage system or off-grid loads via the intermediate switch group. The electrical energy output by the hybrid energy storage system is supplied to the off-grid loads. This ensures full utilization of the grid-connected system's electrical energy, which helps avoid curtailment of solar power and meets the application needs of high-power off-grid loads. Under normal grid conditions, the grid-connected logic operates: switch S1 is closed. If there are no grid feed restrictions, the hybrid energy storage inverter operates according to the preset energy storage mode, without limiting its own or the grid-connected inverter's excess grid feed power. If there are grid feed restrictions, the hybrid energy storage inverter generates power according to the preset limit for the first photovoltaic module. Simultaneously, the hybrid energy storage inverter controls the output power of the grid-connected system through control commands or by controlling the opening and closing of the intermediate switch group. This helps avoid excessive grid feed by the hybrid energy storage system and the grid-connected system, thereby reducing the risk of grid faults or grid paralysis.

[0035] In some embodiments, such as Figure 4As shown, when the sum of the power of the first photovoltaic module and the second photovoltaic module is less than the off-grid load power, that is, when the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter is less than the off-grid load power, the first photovoltaic module and battery of the hybrid energy storage system, as well as the second photovoltaic module of the grid-connected system, all supply power to the off-grid load. This helps to avoid the curtailment of the second photovoltaic module and can also provide a continuous and stable power supply for high-power industrial equipment such as large motors and frequency conversion drive systems, or centralized power facilities such as data centers and manufacturing lines, meeting the application needs of high-power off-grid loads. Specifically, when switch S1 and the intermediate switch group are both closed, the current flow of the hybrid energy storage inverter system and the grid-connected system is as follows: Figure 4 As shown by the arrow in the image.

[0036] In some embodiments, such as Figure 5 As shown, when the sum of the power of the first photovoltaic module and the second photovoltaic module is greater than the off-grid load power (i.e., the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter is greater than the off-grid load power), and the battery of the hybrid energy storage system can absorb the excess energy, the first photovoltaic module of the hybrid energy storage system and the second photovoltaic module of the grid-connected system prioritize supplying power to the off-grid load, and the excess energy is supplied to the battery of the hybrid energy storage system. Specifically, when both switch S1 and the intermediate switch group are closed, the current flow directions of the hybrid energy storage system and the grid-connected system are as follows: Figure 5 As shown by the arrow in the image.

[0037] In summary, under grid fault conditions, when the power of the first and second photovoltaic modules can be absorbed by the hybrid energy storage system and the grid-connected system, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the off-grid load, and the excess electrical energy is stored in the battery of the hybrid energy storage system, which helps to avoid the curtailment of solar power in the grid-connected system.

[0038] In some embodiments, under grid fault conditions, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, that is, when the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter is greater than the off-grid load power, and the battery of the hybrid energy storage system cannot absorb the excess electrical energy, the hybrid energy storage inverter limits the power generation of the first photovoltaic module to reduce its own output power, and reduces the output power of the grid-connected inverter by increasing the voltage frequency output at the off-grid port.

[0039] Specifically, when the sum of the power of the first photovoltaic module and the power input to the hybrid energy storage inverter from the second photovoltaic module exceeds the off-grid load power, and the batteries in the hybrid energy storage system cannot absorb the excess energy, the hybrid energy storage inverter will actively increase its output voltage frequency. For example, the hybrid energy storage inverter can actively adjust its output AC frequency by actively modifying the frequency setpoint, through frequency-power droop control, or through power device drive adjustment. These are all existing technologies and will not be elaborated here. Furthermore, utilizing the safety regulations regarding frequency-watt control in various regions, when the voltage frequency output from the off-grid port increases, the grid-connected inverter can reduce its output power through its own hardware control architecture and software algorithms.

[0040] It is understandable that due to safety certification requirements—most grid-connected inverters must pass official certification tests, such as CSA certification—to ensure that they can reduce load according to standards when frequency limits are exceeded, the hybrid energy storage inverter actively increases its output voltage frequency, i.e., increases the off-grid output voltage frequency, enabling most grid-connected inverters to reduce output power. Furthermore, if the grid-connected inverter does not have the function of reducing load according to standards when frequency limits are exceeded, then the overfrequency protection of the grid-connected system—that is, the output power of the grid-connected inverter directly drops to 0—also helps to avoid adverse effects on the normal operation of the hybrid energy storage system and the power grid.

[0041] In at least one embodiment, such as Figure 6 As shown, the G99 safety standard requires that the grid-connected power P = P m -(P ref *Δf) / (f n *droop), where P is the target active power value that the inverter is currently allowed to output, P m P represents the maximum available power that current photovoltaic modules can provide. ref Let f be the rated active power of the inverter, and Δf be the offset of the system frequency relative to the rated frequency. n Here, droop is the rated frequency of the power grid. For example, when the energy storage inverter in a hybrid energy storage system actively increases its output voltage frequency from the standard 50Hz to 50.5Hz, 51Hz, 51.5Hz or higher, the grid-connected inverter will reduce its output voltage frequency according to its own set droop factor droop. In other words, the hybrid energy storage inverter can indirectly control the output power of the grid-connected system by controlling the voltage frequency output from the off-grid port.

[0042] In some embodiments, the bus voltage of the hybrid energy storage inverter is monitored. When the bus voltage of the hybrid energy storage inverter rises, it is determined that the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic module. Specifically, such as... Figure 7 As shown, when the hybrid energy storage inverter cannot absorb the electrical energy input from the first photovoltaic module and the grid-connected inverter, the bus voltage of the hybrid energy storage inverter will rise. Therefore, by monitoring the bus voltage of the hybrid energy storage inverter, it can be determined whether the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed.

[0043] In at least one embodiment, a bus voltage threshold is set. When the monitored bus voltage exceeds the preset bus voltage threshold and remains so for a preset time, it is determined that the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed. As a result, the energy storage inverter reduces its own output power and increases the voltage frequency output from the off-grid port. This is beneficial to improving the reliability of the parallel operation of the hybrid energy storage system and the grid-connected system.

[0044] In some embodiments, the battery absorption capacity of the hybrid energy storage system is monitored. When the battery absorption capacity decreases, it is determined that the power of the first and second photovoltaic modules cannot be absorbed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic module. Specifically, such as... Figure 8 As shown, when the hybrid energy storage inverter cannot absorb the electrical energy input from the first photovoltaic module and the grid-connected inverter, the absorption capacity of the battery will decrease. Therefore, by monitoring the absorption capacity of the battery in the hybrid energy storage system, it can be determined whether the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed.

[0045] In some embodiments, the battery's absorption capacity is calculated by monitoring the battery voltage and SOC (State of Charge) of the hybrid energy storage system, combined with the battery's BMS (Battery Management System) charging current limit value. It should be understood that by combining the voltage and SOC curve gradient, the charging current limit value can be dynamically adjusted, which helps avoid problems such as lithium deposition and thermal runaway. Furthermore, combining the battery's BMS charging current limit value can enhance battery safety redundancy, thereby ensuring the normal operation of the hybrid energy storage system and the grid-connected system while reducing solar power curtailment.

[0046] In some embodiments, when the grid does not restrict the grid-connected power, the sum of the power of the first photovoltaic module and the second photovoltaic module, that is, the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter, can be absorbed by the grid, thus eliminating the need to control the output power of the hybrid energy storage inverter and the grid-connected inverter.

[0047] In some embodiments, when the grid limits the power connected to the grid, if the sum of the power of the first photovoltaic module and the second photovoltaic module (i.e., the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter) is greater than the grid limit on the power connected to the grid, and the battery of the hybrid energy storage system can absorb the excess power, the first photovoltaic module of the hybrid energy storage system and the second photovoltaic module of the grid-connected system will prioritize supplying power to the grid, and the excess power will be supplied to the battery of the hybrid energy storage system. This is beneficial to reducing the impact of the intermittency and volatility of photovoltaic power generation on the grid, especially in high-penetration areas, thereby improving the stability, security and power quality of grid operation.

[0048] In summary, under normal grid conditions, when the power of the first and second photovoltaic modules is absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the grid, and the excess electrical energy is stored in the battery of the hybrid energy storage system.

[0049] In some embodiments, under normal grid conditions, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, that is, when the grid limits the grid-connected power, the sum of the power of the first photovoltaic module and the second photovoltaic module (i.e., the sum of the power of the first photovoltaic module and the power of the second photovoltaic module input to the hybrid energy storage inverter) exceeds the grid limit on the grid-connected power, and the battery of the hybrid energy storage system cannot absorb the excess electrical energy, the hybrid energy storage inverter sends a control command to the grid-connected inverter to adjust the output power of the grid-connected inverter. This helps to avoid the hybrid energy storage system and the grid-connected system from generating excess grid feed, reducing the risk of grid failure or paralysis.

[0050] It is worth mentioning that, under normal grid conditions, the power of the first and second photovoltaic modules can be determined by monitoring the bus voltage of the hybrid energy storage inverter or by monitoring the absorption capacity of the batteries in the hybrid energy storage system. This will not be elaborated on here.

[0051] In some embodiments, communication is established between the hybrid energy storage inverter and the grid-connected inverter. The hybrid energy storage inverter determines the maximum grid-feed power of the grid-connected inverter and further sends control commands to the grid-connected inverter, causing the grid-connected inverter to adjust its output power in accordance with the control commands. This allows the grid-feed power of the hybrid energy storage inverter and the grid-connected inverter to be more accurately matched with the grid's grid-connected power limit, which helps reduce curtailment of solar power and improves the dynamic adjustment performance of the grid-connected inverter. Especially when the hybrid energy storage inverter and the grid-connected inverter are products from the same manufacturer or have compatible communication protocols, it is easier to establish communication between them to achieve control of the output power of the grid-connected inverter by the hybrid energy storage inverter.

[0052] In some embodiments, such as Figure 2 As shown, the intermediate switch group includes switch S2, which is an internal device of the hybrid energy storage inverter and is controlled by the internal circuit of the hybrid energy storage inverter. Under normal grid conditions, when the power of the first and second photovoltaic modules cannot be absorbed, switch S2 is disconnected to disconnect the grid-connected inverter from the grid. It is worth mentioning that switch S2 can be implemented as a thyristor, relay, or other components capable of circuit connection and disconnection; this application does not impose specific limitations on this.

[0053] In some embodiments, such as Figure 2 The intermediate switch group also includes switch S3, which is connected in series with switch S2. Switch S3 is controlled by the dry node on / off signal of the hybrid energy storage inverter. Under normal grid conditions, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, switch S3 is disconnected to disconnect the grid-connected inverter from the grid.

[0054] Specifically, the hybrid energy storage inverter has an internal dry contact DO signal circuit, which outputs a passive dry contact on / off signal. This signal controls switch S3 to open or close. Controlling S3 via the dry contact on / off signal facilitates electrical isolation and reduces electromagnetic noise interference, thus improving safety. It also ensures compatibility with most contactors, increasing compatibility and reducing the cost of retrofitting the inverter. Furthermore, in the event of a fault in the hybrid energy storage inverter, the dry contact on / off signal defaults to disconnecting switch S3, forcibly disconnecting both the grid-connected inverter and the hybrid energy storage inverter, thus improving reliability.

[0055] In at least one embodiment, the hybrid energy storage inverter first controls the switch S3 to disconnect via the dry node on / off signal to achieve physical isolation, and then controls the switch S2 to disconnect. This helps to avoid the risk of electric arc, improve safety and reliability, and extend the hardware life of the hybrid energy storage inverter.

[0056] In at least one embodiment, switch S3 is implemented as a contactor, which improves response speed and facilitates frequent operation. It is worth noting that, in this case, the on / off control of the grid-connected inverter by the hybrid energy storage inverter is primarily accomplished by switch S3.

[0057] In at least one embodiment, switch S3 is implemented as a circuit breaker, providing automatic protection and exhibiting good arc-extinguishing capability and high breaking capacity, thereby improving safety. It is worth noting that in this case, the on / off control of the grid-connected inverter by the hybrid energy storage inverter is primarily accomplished by switch S2. It should be understood that the grid-connected inverter is preferentially disconnected from the grid by opening switch S3; if switch S3 is not available, then the grid-connected inverter is disconnected from the grid by opening switch S2.

[0058] It should be understood that the implementation of switch S3 as a contactor or circuit breaker may be determined as appropriate, for example, by comprehensively considering whether the power grid is a single-phase or three-phase system, as well as the power of the grid-connected inverter and the load power, etc., in order to select the appropriate type of switch S3. This application does not impose specific restrictions in this regard.

[0059] In some embodiments, when the grid-feed power of the hybrid energy storage inverter and the grid-connected inverter exceeds a preset threshold and persists for a preset time, switches S2 and / or S3 are disconnected. This helps to prevent instantaneous fluctuations in grid-feed power from erroneously triggering the disconnection of switches S2 and S3. Furthermore, when the battery capacity of the hybrid energy storage system decreases—that is, when the current battery capacity is lower than the battery capacity when switches S2 and S3 are disconnected—and this occurs within a preset hysteresis interval, switches S2 and S3 are closed. This helps to prevent the hybrid energy storage inverter from frequently controlling the operation of switches S2 and S3, improving reliability by introducing a "delayed recovery" mechanism. In at least one embodiment, the hybrid energy storage inverter monitors the grid-feed power of the hybrid energy storage inverter and the grid-connected inverter in real time using a meter or a current transformer (CT).

[0060] In some embodiments, the detection circuit is located near switch S2, enabling more reliable and accurate monitoring of the voltage, current, and power information output from the grid-connected inverter under grid fault conditions. That is, the voltage, current, and power information output by the grid-connected inverter can be obtained through the detection circuit inside the hybrid energy storage inverter, which helps avoid the need for additional detection circuitry, thus reducing costs and improving reliability. In other embodiments, an additional detection circuit may be provided, and the detection information may be fed back to the hybrid energy storage inverter; this application does not impose specific limitations on this.

[0061] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. A parallel operation control method of a hybrid energy storage system and a grid-connected system, characterized by, The hybrid energy storage system and the grid-connected system are independently controlled, the input side of the hybrid energy storage inverter of the hybrid energy storage system is connected with the first photovoltaic assembly and the battery, and the output side of the hybrid energy storage inverter is connected to the grid through the switch S1; the input side of the grid-connected inverter of the grid-connected system is connected with the second photovoltaic assembly, and the output side of the grid-connected inverter is connected to the grid through the intermediate switch group and the switch S1 in sequence; In the grid fault state, the switch S1 is disconnected, the power output by the grid-connected inverter is supplied to the hybrid energy storage system or the off-grid load through the intermediate switch group, and the power output by the hybrid energy storage system is supplied to the off-grid load; when the power of the first photovoltaic assembly and the second photovoltaic assembly cannot be consumed, the hybrid energy storage inverter reduces the output power and reduces the output power of the grid-connected inverter by increasing the voltage frequency of the output of the off-grid port; In the grid normal state, the switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system through a control instruction or by controlling the opening and closing of the intermediate switch group.

2. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to claim 1, characterized in that, The bus voltage of the hybrid energy storage inverter is monitored, when the bus voltage of the hybrid energy storage inverter rises, it is determined that the power of the first photovoltaic assembly and the second photovoltaic assembly cannot be consumed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic assembly.

3. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to claim 1, characterized in that, The consumption capacity of the battery of the hybrid energy storage system is monitored, when the consumption capacity of the battery decreases, it is determined that the power of the first photovoltaic assembly and the second photovoltaic assembly cannot be consumed, and the hybrid energy storage inverter reduces the input power of the first photovoltaic assembly.

4. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to claim 3, characterized in that, The consumption capacity of the battery is calculated by monitoring the voltage of the battery of the hybrid energy storage system, the SOC of the battery of the hybrid energy storage system, and combining the BMS charging current limiting value of the battery.

5. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to claim 1, characterized in that, In the grid normal state, when the power of the first photovoltaic assembly and the second photovoltaic assembly cannot be consumed, the hybrid energy storage inverter sends a control instruction to the grid-connected inverter to adjust the output power of the grid-connected inverter.

6. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to claim 1, characterized in that, The intermediate switch group includes a switch S2 and a switch S3, the switch S2 is controlled by the internal circuit of the hybrid energy storage inverter, and the switch S3 is controlled by the dry node on-off signal of the hybrid energy storage inverter; in the grid normal state, when the power of the first photovoltaic assembly and the second photovoltaic assembly cannot be consumed, the switch S2 and / or the switch S3 are disconnected to disconnect the grid-connected inverter from the grid.

7. The method for parallel operation control of the hybrid energy storage system and grid-connected system according to claim 6, characterized in that, When the grid power of the hybrid energy storage inverter and the grid-connected inverter exceeds the preset threshold value and lasts for a preset time, the switch S2 and / or the switch S3 are disconnected; When the battery capacity of the hybrid energy storage system decreases and in a preset hysteresis interval, the switch S2 and the switch S3 are closed.

8. The method for parallel operation control of the hybrid energy storage system and grid-connected system according to claim 6, characterized in that, The switch S3 is a contactor or a circuit breaker.

9. The method for parallel operation control of a hybrid energy storage system and grid-connected system according to any one of claims 1-8, characterized in that, In the grid fault state, when the power of the first photovoltaic assembly and the second photovoltaic assembly can be consumed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the off-grid load, and the excess power is stored in the battery of the hybrid energy storage system; in the grid normal state, when the power of the first photovoltaic assembly and the second photovoltaic assembly can be consumed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the grid, and the excess power is stored in the battery of the hybrid energy storage system.

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