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

Abstract

The invention discloses a parallel operation control method for a hybrid energy storage system and a grid-connected system, the hybrid energy storage system and the grid-connected system are controlled independently, the input side of a hybrid energy storage inverter of the hybrid energy storage system is connected with a first photovoltaic module and a battery, and the output side of the hybrid energy storage inverter is connected with a power grid through a switch S1; the input side of a grid-connected inverter of the grid-connected system is connected with the second photovoltaic module, and the output side of the grid-connected inverter is connected to a power grid through an intermediate switch group and a switch S1 in sequence; in a power grid fault state, the switch S1 is switched off, the electric energy 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 electric energy output by the hybrid energy storage system is supplied to the off-grid load; when the power grid is in a normal state, the switch S1 is switched on, and the hybrid energy storage inverter controls the output power of the grid-connected system through a control instruction or by controlling the switching-off and switching-on of the intermediate switch group.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and particularly to a parallel operation control method for a hybrid energy storage system and a grid-connected system. Background Art

[0002] Photovoltaic power generation is widely used as a clean and renewable energy source, but its output power is unpredictable and volatile. As the proportion of photovoltaic power generation in the traditional power grid continues to increase, its high penetration rate will bring a series of problems to the stability of the grid voltage, power quality, and operation control. By adding an energy storage device to the photovoltaic power generation system and utilizing its charge and discharge characteristics, the problem of power fluctuation caused by uneven illumination can be effectively alleviated. At the same time, the phenomenon of light abandonment can be reduced, the large-scale consumption of photovoltaic power generation can be promoted, and the overall power generation revenue can be increased. However, with the development of technology and the growth of electricity demand, the hybrid energy storage system composed of an inverter and an energy storage battery has been difficult to meet the current needs. Users usually adopt the method of multi-machine parallel connection of the hybrid energy storage system and the grid-connected system to expand the capacity and power.

[0003] In the related art, during a grid fault, both the hybrid energy storage system and the grid-connected system will disconnect from the grid, resulting in the inability to utilize the energy of the grid-connected system and making it difficult to avoid the phenomenon of light abandonment. Especially in weak grids or areas with frequent power outages, it may not be possible to meet the power demand of large loads during off-grid operation. During normal grid operation, the hybrid energy storage system and the grid-connected system are independently controlled. In areas with reverse power flow limitations, the lack of coordination and cooperation between the two is likely to lead to the problem of overfeeding the grid, triggering grid faults or even paralysis. Summary of the Invention

[0004] An object of the present 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 the grid fault state and avoid overfeeding the grid under the normal grid state.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A parallel operation control method for a hybrid energy storage system and a grid-connected system. 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 to the first photovoltaic module 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 to the second photovoltaic module, 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 case of a grid fault, the switch S1 is disconnected, and the electric energy 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 electric energy output by the hybrid energy storage system is supplied to the off-grid load. In the case of a normal grid state, the switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system by a control command or by controlling the opening and closing of the intermediate switch group.

[0006] As a preference, in the case of a grid fault, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the hybrid energy storage inverter reduces the output power and increases the voltage frequency at the off-grid port to reduce the output power of the grid-connected inverter.

[0007] As a preference, 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 preference, the absorption capacity of the battery of the hybrid energy storage system is monitored. When the absorption capacity of the battery 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 preference, the absorption 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.

[0010] As a preference, in the case of a normal grid state, when the power of the first photovoltaic module and the second photovoltaic module 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 preference, the intermediate switch group includes a switch S2, and the switch S2 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 switch S2 is disconnected to cut off the grid-connected inverter from the grid.

[0012] As a preference, the intermediate switch group further includes a switch S3. The switch S3 is connected in series with the switch S2, and the switch S3 is controlled by the on-off signal of the dry contact 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 switch S3 is disconnected to cut off the grid-connected inverter from the grid.

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

[0014] As a preference, under grid fault conditions, when the power of the first photovoltaic module and the second photovoltaic module can be absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the off-grid load, and the excess electric energy is stored in the battery of the hybrid energy storage system; under normal grid conditions, when the power of the first photovoltaic module and the second photovoltaic module can be absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the grid, and the excess electric 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: (1) Under grid fault conditions, the switch S1 is disconnected, and the electric energy 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 electric energy output by the hybrid energy storage system is supplied to the off-grid load, so that the electric energy of the grid-connected system can be fully utilized, which is beneficial to avoiding the phenomenon of light abandonment and meeting the application requirements of high-power off-grid loads.

[0016] (2) Under normal grid conditions, the switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system by control instructions or by controlling the disconnection and closing of the intermediate switch group, which is beneficial to avoiding overfeeding of the hybrid energy storage system and the grid-connected system, thereby reducing the risk of grid faults or paralysis. Description of the Drawings

[0017] Figure 1 is a wiring schematic diagram of the parallel operation of a hybrid energy storage inverter and a grid-connected inverter in the related art.

[0018] Figure 2 It is a wiring schematic diagram of the parallel operation of a hybrid energy storage inverter and a grid-connected inverter in some embodiments of the present application.

[0019] Figure 3 It is a logic diagram of a control method for the parallel operation of a hybrid energy storage system and a grid-connected system in some embodiments of the present application.

[0020] Figure 4 It is a schematic diagram of the current flow direction of a hybrid energy storage inverter and a grid-connected inverter in the grid fault state in some embodiments of the present application.

[0021] Figure 5 It is a schematic diagram of the current flow direction of a hybrid energy storage inverter and a grid-connected inverter in the grid fault state in some other embodiments of the present application.

[0022] Figure 6 It is a relationship diagram between the output power and frequency of a grid-connected inverter in some embodiments of the present application.

[0023] Figure 7 It is a relationship diagram between the bus voltage and frequency of a hybrid energy storage inverter in some embodiments of the present application.

[0024] Figure 8 It is a relationship diagram between the battery consumption capacity and frequency of a hybrid energy storage inverter in some embodiments of the present application. Detailed Embodiments

[0025] Next, in combination with the detailed embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0026] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects and do not necessarily describe a specific order or sequence.

[0027] The terms "including" and "having" in the specification and claims of the present application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0028] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or connected by contact or indirectly through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] For the convenience of understanding the following solutions, the present application will be described by a multi-machine system in which a hybrid energy storage system and a grid-connected system operate in parallel. As Figure 1 shown, the input side of the hybrid energy storage inverter of 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; the input side of the grid-connected inverter of 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.

[0030] In the related art, as Figure 1 shown, the hybrid energy storage inverter and the grid-connected inverter are independently connected to the grid, and the power transmission of the hybrid energy storage inverter and the grid-connected inverter to the grid is independent of each other and does not affect each other. That is to say, the hybrid energy storage system and the grid-connected system are independently controlled. The hybrid energy storage system is the main system, and the grid-connected system is an independent power generation system that cannot be controlled by the hybrid energy storage system. For example, in the case where a grid-connected system has been installed, a hybrid energy storage system is newly installed; or in the case where a hybrid energy storage system has been installed, a grid-connected system is newly installed; this will make it difficult to control the two systems through the same communication mechanism.

[0031] Furthermore, when a grid fault occurs, both the hybrid energy storage system and the grid-connected system will disconnect from the grid. Among them, the hybrid energy storage system is connected to the off-grid load and can provide electric energy to the off-grid load, while the grid-connected system is disconnected from the off-grid load, resulting in the energy of the grid-connected system not being utilized, thus causing a phenomenon of light abandonment; especially in weak grids or areas with frequent power outages, it may not be possible to meet the power demand of large loads during off-grid operation. When the grid is operating normally, the hybrid energy storage system and the grid-connected system are independently controlled. In areas with reverse power flow limitations, there is a lack of coordination and cooperation between the hybrid energy storage system and the grid-connected system, which is likely to cause problems of excessive power feeding into the grid, and further lead to grid faults or even paralysis. It should be understood that the first photovoltaic module and the second photovoltaic module can also be implemented as other power sources, such as wind turbines, wave generators, hydro generators, etc., and the present application does not make specific limitations on this.

[0032] Based on the above, to solve or at least partially alleviate the problem of light curtailment and excessive power feeding that occur when the originally independently controlled hybrid energy storage system and grid-connected system operate in parallel. The present application provides a method for controlling the parallel operation of a hybrid energy storage system and a grid-connected system, as Figures 2 - 8 shown, the input side of the hybrid energy storage inverter of 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 through switch S1; the input side of the grid-connected inverter of the grid-connected system is connected to the second photovoltaic module, and the output side of the grid-connected inverter is sequentially connected to the grid through the intermediate switch group and switch S1; in the event of a grid fault, switch S1 is disconnected, and the electric energy output by the grid-connected inverter is supplied to the hybrid energy storage system or off-grid load through the intermediate switch group, and the electric energy output by the hybrid energy storage system is supplied to the off-grid load; in the normal state of the grid, switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system by control instructions or by controlling the opening and closing of the intermediate switch group.

[0033] It should be understood that, as Figure 3 shown, in the event of a grid fault, the off-grid logic is run, that is: switch S1 is disconnected, and the electric energy output by the grid-connected inverter is supplied to the hybrid energy storage system or off-grid load through the intermediate switch group, and the electric energy output by the hybrid energy storage system is supplied to the off-grid load, so that the electric energy of the grid-connected system can be fully utilized, which is beneficial to avoiding light curtailment and meeting the application requirements of high-power off-grid loads. In the normal state of the grid, the grid-connected logic is run, that is: switch S1 is closed. If there is no grid power feeding limit, the hybrid energy storage inverter operates according to the preset energy storage mode without restricting the excess grid power feeding of itself and the grid-connected inverter; if there is a grid power feeding limit, the hybrid energy storage inverter restricts the power generation of the first photovoltaic module according to the preset, and at the same time, the hybrid energy storage inverter controls the output power of the grid-connected system by control instructions or by controlling the opening and closing of the intermediate switch group, which is beneficial to avoiding excessive grid power feeding of the hybrid energy storage system and the grid-connected system, thereby reducing the risk of grid faults or paralysis.

[0034] In some embodiments, as Figure 4As shown, when the sum of the powers 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 input from the second photovoltaic module to the hybrid energy storage inverter is less than the off-grid load power, the first photovoltaic module, the battery of the hybrid energy storage system, and the second photovoltaic module of the grid-connected system all supply power to the off-grid load. This is beneficial for avoiding the phenomenon of light curtailment in the second photovoltaic module and can also provide continuous and stable power supply for high-power industrial equipment such as large motors and variable-frequency drive systems, or centralized power-consuming facilities such as data centers and manufacturing production lines, meeting the application requirements of high-power off-grid loads. Specifically, switch S1 and the intermediate switch group are both closed, and the current flow directions of the hybrid energy storage system and the grid-connected system are as Figure 4 shown by the arrows in

[0035] In some embodiments, as Figure 5 shown, when the sum of the powers of the first photovoltaic module and the second photovoltaic module is greater than the off-grid load power, that is, when the sum of the power of the first photovoltaic module and the power input from the second photovoltaic module 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 electrical energy, the first photovoltaic module of the hybrid energy storage system and the second photovoltaic module of the grid-connected system preferentially supply power to the off-grid load, and the excess electrical energy is supplied to the battery of the hybrid energy storage system. Specifically, switch S1 and the intermediate switch group are both closed, and the current flow directions of the hybrid energy storage system and the grid-connected system are as Figure 5 shown by the arrows in

[0036] In summary, in the grid fault state, when the powers of the first photovoltaic module and the second photovoltaic module 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 is beneficial for avoiding the phenomenon of light curtailment in the grid-connected system.

[0037] In some embodiments, in the grid fault state, when the powers 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 input from the second photovoltaic module 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 restricts the power generation of the first photovoltaic module to reduce its own output power and increases the voltage frequency at the off-grid port to reduce the output power of the grid-connected inverter.

[0038] Specifically, when the sum of the power of the first photovoltaic module and the power input to the hybrid energy storage inverter by the second photovoltaic module 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 will actively increase the voltage frequency of its output. For example, the hybrid energy storage inverter can actively adjust the alternating current frequency of its output by actively modifying the frequency setting value, or through frequency-power droop control, or through power device drive adjustment, etc. These are all existing technologies and will not be elaborated here. Further, using the safety regulations requirements for frequency-watt control in each region, when the voltage frequency of the off-grid port output increases, the grid-connected inverter can reduce its output power through its own hardware control architecture and software algorithm.

[0039] It should be understood that due to safety regulations certification requirements, that is, most grid-connected inverters must pass official certification tests, such as CSA certification, to ensure that the grid-connected inverter can reduce the load according to the standard when the frequency exceeds the limit. Therefore, by actively increasing the voltage frequency of the output of the hybrid energy storage inverter, that is, increasing the voltage frequency of the off-grid port output, most grid-connected inverters can achieve the effect of reducing the output power. Further, if the grid-connected inverter does not have the function of reducing the load according to the standard when the frequency exceeds the limit, then through the over-frequency protection of the grid-connected system, that is, the output power of the grid-connected inverter is directly reduced to 0, which is also beneficial to avoiding adverse effects on the normal operation of the hybrid energy storage system and the power grid.

[0040] In at least one embodiment, as Figure 6 shown, the G99 safety regulation requires that the grid-connected power P = P m -(P ref *Δf) / (f n *droop), where P is the target active power value currently allowed to be output by the inverter, P m is the maximum available power that the current photovoltaic module can provide, P ref is the rated active power of the inverter, Δf is the offset of the system frequency relative to the rated frequency, f n is the rated frequency of the power grid, and droop is the droop coefficient. For example, when the energy storage inverter in the hybrid energy storage system actively increases the voltage frequency of its output from the standard 50 Hz to 50.5 Hz, 51 Hz, 51.5 Hz or higher, the grid-connected inverter will reduce the output voltage frequency according to the droop coefficient droop set by itself. That is to say, the hybrid energy storage inverter can indirectly control the output power of the grid-connected system by controlling the voltage frequency of the off-grid port output.

[0041] 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, as Figure 7 shown, when the hybrid energy storage inverter cannot absorb the electrical energy input by the first photovoltaic module and the grid-connected inverter, it will cause the bus voltage of the hybrid energy storage inverter to rise. Therefore, by monitoring the bus voltage of the hybrid energy storage inverter, it is possible to determine whether the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed.

[0042] In at least one embodiment, a bus voltage threshold is set. When the monitored bus voltage exceeds the preset bus voltage threshold and remains for a preset time, it is determined that the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed. Then, the energy storage inverter reduces its own output power and increases the voltage frequency of the off-grid output, which is beneficial to improving the reliability of the parallel operation of the hybrid energy storage system and the grid-connected system.

[0043] In some embodiments, the absorption capacity of the battery of the hybrid energy storage system is monitored. When the absorption capacity of the battery 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. Specifically, as Figure 8 shown, when the hybrid energy storage inverter cannot absorb the electrical energy input by the first photovoltaic module and the grid-connected inverter, it will cause the absorption capacity of the battery to decrease. Therefore, by monitoring the absorption capacity of the battery of the hybrid energy storage system, it is possible to determine whether the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed.

[0044] In some embodiments, the absorption capacity of the battery is calculated by monitoring the voltage of the battery of the hybrid energy storage system, the SOC (State of Charge) of the battery of the hybrid energy storage system, and combining the charging current limiting value of the BMS (Battery Management System) of the battery. It should be understood that by combining the voltage and the SOC curve gradient, the charging current limiting value can be dynamically adjusted downward, which is beneficial to avoiding problems such as lithium precipitation and thermal runaway of the battery; further, combining the charging current limiting value of the BMS of the battery can play a role in improving the safety redundancy of the battery, so as to ensure the normal operation of the hybrid energy storage system and the grid-connected system on the basis of reducing the phenomenon of light abandonment.

[0045] In some embodiments, when the grid has no limit on the grid-connected power, the sum of the powers 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 input by the second photovoltaic module to the hybrid energy storage inverter, can be absorbed by the grid, and then there is no need to control the output powers of the hybrid energy storage inverter and the grid-connected inverter.

[0046] In some embodiments, when the grid has restrictions on the grid-connected power, the sum of the powers 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, is greater than the grid's restrictions on the grid-connected power, and when the battery of the hybrid energy storage system can absorb the excess electric energy, the first photovoltaic module of the hybrid energy storage system and the second photovoltaic module of the grid-connected system preferentially supply power to the grid, and the excess electric energy is supplied to the battery of the hybrid energy storage system, which is beneficial to reducing the impact of the intermittency and volatility of photovoltaic power generation on the grid. Especially in high-penetration areas, the stability, security, and power quality of the grid operation can be improved.

[0047] In summary, under normal grid conditions, when the powers of the first photovoltaic module and the second photovoltaic module can be absorbed, the hybrid energy storage inverter and the grid-connected inverter jointly supply power to the grid, and the excess electric energy is stored in the battery of the hybrid energy storage system.

[0048] In some embodiments, under normal grid conditions, when the powers of the first photovoltaic module and the second photovoltaic module cannot be absorbed, that is, when the grid has restrictions on the grid-connected power, the sum of the powers 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, is greater than the grid's restrictions on the grid-connected power, and when the battery of the hybrid energy storage system cannot absorb the excess electric energy, the hybrid energy storage inverter sends a control instruction to the grid-connected inverter to adjust the output power of the grid-connected inverter, which is beneficial to avoiding overfeeding of the hybrid energy storage system and the grid-connected system and reducing the risk of grid faults or paralysis.

[0049] It is worth mentioning that under normal grid conditions, it is also possible to determine whether the powers of the first photovoltaic module and the second photovoltaic module cannot be absorbed by monitoring the bus voltage of the hybrid energy storage inverter or by monitoring the absorption capacity of the battery of the hybrid energy storage system, which will not be elaborated here.

[0050] In some embodiments, communication is established between the hybrid energy storage inverter and the grid-connected inverter, and the hybrid energy storage inverter judges the maximum feed-in power of the grid-connected inverter. Further, a control instruction is sent from the hybrid energy storage inverter to the grid-connected inverter, so that the grid-connected inverter cooperates with the control instruction to adjust the output power. In this way, the feed-in powers of the hybrid energy storage inverter and the grid-connected inverter can be more accurately matched with the grid-connected limit power of the grid, which is beneficial to reducing the phenomenon of light abandonment and improving the dynamic regulation performance of the grid-connected inverter. Especially when the hybrid energy storage inverter and the grid-connected inverter are products of the same manufacturer or the communication protocols are adapted, it is more convenient to establish communication between the hybrid energy storage inverter and the grid-connected inverter to realize the control of the output power of the grid-connected inverter by the hybrid energy storage inverter.

[0051] In some embodiments, as Figure 2 shown, the intermediate switch group includes a switch S2. The switch S2 is an internal device of the hybrid energy storage inverter and is controlled by the internal circuit of the hybrid energy storage inverter. In the normal state of the power grid, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the switch S2 is disconnected to cut off the grid-connected inverter from the power grid. It is worth mentioning that the switch S2 can be implemented as a thyristor, a relay or other components that can realize the connection and disconnection of the circuit. The present application does not make specific limitations on this.

[0052] In some embodiments, as Figure 2 described, the intermediate switch group further includes a switch S3. The switch S3 is connected in series with the switch S2 and is controlled by the on-off signal of the dry contact of the hybrid energy storage inverter. In the normal state of the power grid, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the switch S3 is disconnected to cut off the grid-connected inverter from the power grid.

[0053] Specifically, the hybrid energy storage inverter has a dry contact DO signal circuit inside, which can output a passive on-off signal of the dry contact, and then control the switch S3 through the on-off signal of the dry contact to make the switch S3 disconnect or close. It should be understood that controlling S3 through the on-off signal of the dry contact is beneficial to achieving electrical isolation and reducing electromagnetic noise interference, thereby improving safety; it is also beneficial to be compatible with most contactors, thereby improving compatibility and reducing the cost of retrofitting the inverter later; in addition, if the hybrid energy storage inverter fails, the on-off signal of the dry contact defaults to disconnect the switch S3 to forcibly cut off the grid-connected inverter and the hybrid energy storage inverter, which is beneficial to improving reliability.

[0054] In at least one embodiment, the hybrid energy storage inverter first controls the switch S3 to disconnect through the on-off signal of the dry contact to achieve physical isolation, and then controls the switch S2 to disconnect. This is beneficial to avoiding the risk of electric arc, improving safety and reliability, and prolonging the hardware life of the hybrid energy storage inverter.

[0055] In at least one embodiment, the switch S3 is implemented as a contactor, which can improve the response speed and is beneficial to frequent operation. It is worth mentioning that at this time, the on-off control of the hybrid energy storage inverter on the grid-connected inverter is mainly completed by the switch S3.

[0056] In at least one embodiment, the switch S3 is implemented as a circuit breaker, which can play an automatic protection role, and has good arc extinguishing ability and high breaking ability, so as to improve safety. It is worth mentioning that at this time, the on-off control of the hybrid energy storage inverter on the grid-connected inverter is mainly completed by the switch S2. It should be understood that the grid-connected inverter is preferentially cut off from the power grid by disconnecting the switch S3; if the switch S3 is not available, the grid-connected inverter is cut off from the power grid by disconnecting the switch S2.

[0057] It should be understood that the switch S3 can be implemented as a contactor or a circuit breaker depending on the circumstances. For example, comprehensive considerations are made according to 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., so as to select a suitable type of switch S3. The present application does not make specific restrictions on this.

[0058] In some embodiments, when the feeding power of the hybrid energy storage inverter and the grid-connected inverter exceeds a preset threshold and lasts for a preset time, the switch S2 and / or the switch S3 is disconnected. This is beneficial to avoid false triggering of the disconnection of the switch S2 and the switch S3 due to instantaneous fluctuations in the feeding power. Further, when the battery capacity of the hybrid energy storage system decreases, that is, the current capacity of the battery is lower than the battery capacity when the switch S2 and the switch S3 are disconnected and within a preset hysteresis interval, the switch S2 and the switch S3 are closed. This is beneficial to avoid frequent control of the actions of the switch S2 and the switch S3 by the hybrid energy storage inverter, and to improve the reliability by introducing a "delayed recovery" mechanism. In at least one embodiment, the hybrid energy storage inverter monitors the feeding power of the hybrid energy storage inverter and the grid-connected inverter in real time through an electric meter or a CT (Current Transformer).

[0059] In some embodiments, the detection circuit is located near the switch S2, so as to more reliably and accurately monitor the voltage, current, and power information output from the grid-connected inverter in the case of a grid fault state. That is to say, the voltage, current, and power information output from the grid-connected inverter can be obtained through the detection circuit inside the hybrid energy storage inverter, which is beneficial to avoid setting up an additional detection circuit to reduce costs and improve reliability. In some other embodiments, an additional detection circuit can also be set up and the detection information can be fed back to the hybrid energy storage inverter. The present application does not make specific restrictions on this.

[0060] The basic principles, main features, and advantages of the present invention have been described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A parallel operation control method for a hybrid energy storage system and a grid-connected system, characterized in that 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 to the first photovoltaic module 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 to the second photovoltaic module, 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, and the electric energy 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 electric energy output by the hybrid energy storage system is supplied to the off-grid load. In the normal grid state, the switch S1 is closed, and the hybrid energy storage inverter controls the output power of the grid-connected system by a control command or by controlling the opening and closing of the intermediate switch group.

2. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 1, characterized in that In the grid fault state, when the power of the first photovoltaic module and the second photovoltaic module cannot be absorbed, the hybrid energy storage inverter reduces the output power and reduces the output power of the grid-connected inverter by increasing the voltage frequency at the off-grid port.

3. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 2, characterized in that, Monitor the bus voltage of the hybrid energy storage inverter. 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.

4. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 2, characterized in that, Monitor the absorption capacity of the battery of the hybrid energy storage system. When the absorption capacity of the battery 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.

5. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 4, characterized in that, Calculate the absorption capacity of the battery 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 charging current limiting value of the battery BMS.

6. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 1, characterized in that, In the normal grid state, when the power of the first photovoltaic module and the second photovoltaic module 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.

7. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 1, characterized in that, The intermediate switch group includes a switch S2, and the switch S2 is controlled by the internal circuit of the hybrid energy storage inverter. In the normal grid state, 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.

8. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 7, characterized in that, The intermediate switch group further includes a switch S3, and the switch S3 is connected in series with the switch S2. The switch S3 is controlled by the on-off signal of the dry contact of the hybrid energy storage inverter. In the normal grid state, 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 S3.

9. The parallel operation control method of the hybrid energy storage system and the grid-connected system according to claim 8, wherein When the feeding power of the hybrid energy storage inverter and the grid-connected inverter exceeds the preset threshold and lasts for the preset time, the switch S2 and / or the switch S3 is opened. When the battery capacity of the hybrid energy storage system decreases and is within the preset hysteresis interval, the switch S2 and the switch S3 are closed.

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

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