Off-grid optical storage system, control method, charging and discharging method and circuit

Abstract

The invention relates to the field of photovoltaic technology, in particular to an off-grid optical storage system, a control method, a charging and discharging method and a circuit. An off-grid optical storage system comprises an energy storage cabinet, an electric energy management module, an energy storage battery module B, a charging and discharging module PCS, an MPPT photovoltaic controller and a photovoltaic string, wherein the electric energy management module, the energy storage battery module B and the charging and discharging module PCS are arranged in the energy storage cabinet, and the MPPT photovoltaic controller and the photovoltaic string are arranged outside the energy storage cabinet. According to the scheme, the independent MPPT adjusting capacity of the multi-path photovoltaic string is kept, the internal wiring structure of the energy storage cabinet is simplified, the overall power generation efficiency is improved, and therefore the reliability and efficiency of the system are improved.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to an off-grid photovoltaic storage system, a control method, a charging and discharging method and a circuit. Background Art

[0002] In current off-grid photovoltaic and energy storage applications, as the system power continues to increase, traditional photovoltaic and energy storage integrated solutions usually integrate the MPPT photovoltaic controller (maximum power point tracker) with the energy storage battery and inverter (charging and discharging) module in the same cabinet (energy storage cabinet). This layout can still cope with low-power scenarios, but when the power increases and the number of photovoltaic strings increases, the large number of photovoltaic DC cables that need to be connected inside the system will significantly increase the complexity of wiring and engineering difficulty. The easiest way to think of this is as follows Figure 1 The solution (hereinafter referred to as Document 1) generally adds a combiner box at the front end. The function of the combiner box is to collect the current of multiple photovoltaic panels together and then connect them to the MPPT controller of the inverter through fewer cables. The purpose is to make the wiring inside the system simpler. However, the design of introducing the combiner box will cause the connection between the photovoltaic module and the MPPT controller to be transferred, increase cable loss and construction costs, and make it difficult to perform maximum power point tracking (MPPT) on multiple photovoltaic strings, that is, it is difficult to maintain independent control and optimization of multiple MPPTs, thereby reducing power generation efficiency.

[0003] Therefore, how to develop an off-grid photovoltaic storage system that maintains the independent MPPT regulation capability of multiple photovoltaic strings, simplifies the internal wiring structure of the energy storage cabinet, and improves the overall power generation efficiency has become a topic to be studied by technical personnel in this field. Summary of the invention

[0004] The purpose of the present invention is to provide an off-grid photovoltaic storage system, a control method, a charging and discharging method and a circuit to address the deficiencies in the prior art, aiming to maintain the independent MPPT regulation capability of multiple photovoltaic strings, simplify the internal wiring structure of the energy storage cabinet, and improve the overall power generation efficiency, thereby improving the reliability and efficiency of the system.

[0005] The present invention achieves the above-mentioned purpose through the following technical solutions: an off-grid photovoltaic storage system, including an energy storage cabinet, an electric energy management module arranged inside the energy storage cabinet, an energy storage battery module B, a charge and discharge module PCS, and an MPPT photovoltaic controller and a photovoltaic string external to the energy storage cabinet; wherein: Energy storage battery module B, including energy storage batteries for storing photovoltaic power generation energy; The charging and discharging module PCS is connected to the energy storage battery module B and is used for bidirectional conversion of DC and AC electric energy, so as to convert the DC power of the energy storage battery into AC output and / or store the electric energy generated by photovoltaic power in the energy storage battery module; The MPPT photovoltaic controller is independently installed outside the energy storage cabinet and is connected to the photovoltaic strings and the charging and discharging module PCS respectively. It is used to output photovoltaic power generation energy to the DC bus of the system after performing maximum power point tracking (MPPT) on multiple photovoltaic strings, and share the DC bus with the charging and discharging module PCS and the energy storage battery module B, thereby maintaining the multi-channel MPPT regulation capability under high-power conditions of the system, simplifying internal wiring and improving overall power generation efficiency; The power management module is communicatively connected to the MPPT photovoltaic controller, and the power management module includes but is not limited to the EMS module and / or the BMS module. Specifically, the electric energy output by the MPPT photovoltaic controller enters the DC bus, and is simultaneously connected to the DC bus by the energy storage battery module B and the charge and discharge module PCS. The BMS module is responsible for monitoring and protecting the energy storage battery, and the power management module will schedule the energy flow of the system. When the battery needs to be charged, the charge and discharge module PCS achieves this by transferring the electric energy on the DC bus to the energy storage battery module B. When the battery needs to discharge to support the load, it is also fed back to the charge and discharge module PCS through the DC bus, and then converted into AC power by the charge and discharge module PCS to the load.

[0006] As a further solution of the present invention: the MPPT photovoltaic controller is connected to the photovoltaic string and is separated from the energy storage cabinet or independently arranged outdoors; The power management module includes but is not limited to an EMS module and / or a BMS module. Specifically, an EMS module or a BMS module or other existing power management modules may be used to strategically control photovoltaic access according to the real-time operating status of the energy storage battery module B (including status information fed back by the BMS module). When the charging demand is met, the photovoltaic input path is closed to charge the energy storage battery. When the energy storage battery is close to full charge or an abnormality occurs, the MPPT photovoltaic controller is instructed to reduce or stop the photovoltaic input, or the photovoltaic access is disconnected to protect the energy storage battery, thereby achieving safe and efficient operation of the off-grid photovoltaic storage system.

[0007] As a further solution of the present invention: the energy storage cabinet is also provided with: Photovoltaic input connector G, connected to the MPPT photovoltaic controller; The photovoltaic switch (H) is connected to the photovoltaic input connection port G and the charging and discharging module PCS respectively, and is used to control the access and exit of the MPPT photovoltaic controller; Load output connector F, used to connect load equipment; AC power connection port E, used to connect an external AC power source; and The off-grid and grid-connected switching module (STS) is respectively connected to the load output connection port F, the AC power connection port E and the charging and discharging module PCS, and is used for switching the off-grid photovoltaic storage system between the off-grid mode and the grid-connected mode; The power management module is used to close the photovoltaic switch (H) when the operating conditions are met, so that the photovoltaic energy is used to charge the energy storage battery energy module B or to supply power to the outside through the charge and discharge module PCS; when the access conditions are not met, the power management module is used to disconnect the photovoltaic switch H and stop the access of photovoltaic power. The power management module includes but is not limited to the EMS module and / or the BMS module.

[0008] As a further solution of the present invention: at least two MPPT photovoltaic controllers and photovoltaic strings are provided, at least one MPPT photovoltaic controller is provided with at least one MPPT, at least one MPPT photovoltaic controller is connected to at least one photovoltaic string in a one-to-one correspondence, and each photovoltaic string is tracked by the MPPT photovoltaic controller for maximum power point to optimize photovoltaic power generation efficiency; The power management module is connected to the external MPPT photovoltaic controller through a communication protocol (such as RS485 or CAN bus) to perform real-time regulation and power limit control on the photovoltaic power output.

[0009] As a further solution of the present invention: the power management module is used to control the photovoltaic switch H to close when the battery charge SOC state of the energy storage battery module is lower than a preset threshold value (e.g., 80%) of the battery charge SOC state, and to control the photovoltaic switch H to open when the battery charge SOC state is higher than the preset threshold value or an alarm occurs in the energy storage battery module; The MPPT photovoltaic controller includes a multi-channel PV input interface, a PV input switch, an input lightning protection circuit, a plurality of DC / DC boost circuits, and an output bus and lightning protection unit. The plurality of DC / DC boost circuits respectively perform maximum power point tracking on different photovoltaic strings, so as to maintain a sufficient number of MPPTs under high power conditions and improve power generation efficiency. Specifically, when the system power is expanded, each photovoltaic string can still maintain independent MPPT regulation, that is, the MPPT photovoltaic controller contains multiple MPPTs to be sufficient to perform maximum power point tracking on each photovoltaic string. The photovoltaic switch H is a semiconductor switch device or a mechanical switch. The semiconductor switch device includes an IGBT or a MOS tube, and the mechanical switch includes a contactor or a relay.

[0010] A photovoltaic access and exit control method comprises the following steps: Power monitoring step: The power management module is specifically the EMS module that monitors the battery charge SOC state of the energy storage battery module B in real time; Access judgment step: judging whether the battery charge SOC state of the energy storage battery module B is lower than the first preset threshold value, if so, entering the photovoltaic access step; if not, entering the exit judgment step; Photovoltaic access steps: control the photovoltaic switch H to close, connect the photovoltaic power generation energy, and the photovoltaic power generation energy is optimized by the MPPT photovoltaic controller externally placed in the energy storage cabinet and then input into the energy storage battery module B for charging, or output to the external load through the charge and discharge module PCS; Exit judgment step: judge whether the battery charge SOC state of the energy storage battery module B is higher than the second preset threshold, or whether a secondary alarm occurs, including overvoltage, overcurrent or high temperature state. If so, enter the photovoltaic exit step; if not, continue to maintain the photovoltaic connection state; Photovoltaic exit steps: control the photovoltaic switch H to disconnect and stop the photovoltaic power generation from being input into the energy storage battery module B.

[0011] As a further solution of the present invention: it also includes an abnormal protection step: when it is detected that the communication of the MPPT photovoltaic controller is interrupted or the power limit adjustment fails, the photovoltaic switch H is controlled to be disconnected, and the photovoltaic power generation input is stopped to protect the safety of the energy storage battery module; The access determination step also includes: when the battery charge SOC state is lower than the first preset threshold, first determining whether the temperature of the energy storage battery module B is lower than the upper limit of the safety range, if so, entering the photovoltaic access step; if not, stopping the photovoltaic access (or stopping the photovoltaic power generation access); The exit judgment steps are as follows: determine whether the battery charge SOC state is higher than the second preset threshold; determine whether the energy storage battery module B has a first-level alarm state, and if so, alleviate the abnormality by adjusting the photovoltaic input power or reducing the charging rate; determine whether a second-level alarm state occurs, and if so, enter the photovoltaic exit step; if none of the above conditions are triggered, continue to maintain the photovoltaic connection state.

[0012] As a further solution of the present invention: the abnormal protection step includes: when the secondary alarm signal of the energy storage battery module B is overvoltage and / or overcurrent and / or high temperature of the battery cell, disconnecting the photovoltaic switch H; when the MPPT photovoltaic controller fails to limit the power and causes the power input to be greater than the preset power value, disconnecting the photovoltaic switch H; The exit judgment step also includes: judging whether the photovoltaic input power meets the current load demand, and when the load cannot fully absorb the photovoltaic power generation power, controlling the MPPT photovoltaic controller to limit the power; if the power limit fails or the load power demand is zero, disconnecting the photovoltaic switch H; The first-level alarm state includes that the cell voltage or temperature of the energy storage battery is close to the set upper limit, but has not exceeded the safety range; it refers to the slight abnormal state of the energy storage battery module B, such as the cell voltage or temperature is close to the set upper limit, but has not exceeded the safety range. The power management module will handle it by adjusting the photovoltaic power, reducing the charging rate, etc. when the first-level alarm is triggered; Level 2 alarm status includes overvoltage, overcurrent or high temperature of the battery cell; it means that the energy storage battery module B has a serious abnormal state, such as overvoltage, overcurrent or high temperature of the battery cell, which exceeds the safety range and requires immediate protection measures, including disconnecting the photovoltaic input; The first preset threshold is that the battery SOC state of charge of the energy storage battery module B is lower than 80%, and the second preset threshold is that the battery SOC state of charge is higher than 95%.

[0013] As a further solution of the present invention: also include: Charge and discharge monitoring steps: real-time monitoring of the battery charge SOC state of the energy storage battery module B and the power demand of the external load; Charging control step: when the battery charge SOC state is lower than the first charging threshold, the charging and discharging module PCS is controlled to enter the charging mode, and the photovoltaic power generation energy is used to charge the energy storage battery through the charging and discharging module PCS; Charging exit step: when the battery charge SOC state reaches the second charging threshold or the energy storage battery module B triggers an overvoltage alarm, the charging operation is stopped; Discharge control step: when the power demand of the external load is greater than zero and the battery charge SOC state is higher than the minimum discharge threshold, the charge and discharge module PCS is controlled to enter the discharge mode to output the power of the energy storage battery to the external load; Discharge exit step: When the load demand is zero or the battery SOC state is lower than the minimum discharge threshold, the discharge operation is stopped; Among them: the first charging threshold is that the battery SOC state is lower than 30%, the second charging threshold is that the battery SOC state is higher than 95%, and the minimum discharge threshold is that the battery SOC state is lower than 20%; The charging control step also includes: before entering the charging mode, checking whether the photovoltaic input power meets the charging demand of the energy storage battery. When the power is insufficient, the MPPT photovoltaic controller is used to give priority to adjusting the photovoltaic power generation so that the photovoltaic string operates in the maximum power tracking mode; The discharge control step also includes: when the load demand is insufficient, controlling the charge and discharge module PCS to enter a low-power discharge mode to reduce the discharge rate of the energy storage battery; when the load demand increases suddenly, giving priority to outputting the electric energy of the energy storage battery module B to the critical load.

[0014] A photovoltaic access and exit control method comprises the following steps: Battery status monitoring step: The power management module, specifically the BMS module, obtains the battery charge SOC state and determines whether it is lower than a preset SOC threshold; Access condition evaluation step: if the battery charge SOC state is lower than the preset SOC threshold, it is determined that the photovoltaic access condition is met; Photovoltaic access steps: When the photovoltaic access conditions are met, the photovoltaic switch H is closed, and the photovoltaic power processed by the MPPT photovoltaic controller (i.e., outdoor MPPT photovoltaic controller) outside the energy storage cabinet is connected to the system, so that the photovoltaic power can charge the energy storage battery module B or supply power to the outside through the charging and discharging module PCS; Power limit instruction step: When the energy storage battery module B is close to full charge and cannot further transmit power to the outside, a power limit instruction is sent to the MPPT photovoltaic controller through the power management module to reduce the photovoltaic power input; Communication abnormality handling steps: If the MPPT photovoltaic controller fails to execute the power limit instruction due to communication abnormality, the power management module stops the input of photovoltaic power by disconnecting the photovoltaic switch H to protect the energy storage battery module B; Reconnection determination step: After the photovoltaic switch H is disconnected, if the battery charge SOC state of the energy storage battery module B drops below a predetermined recovery threshold, the power management module allows the photovoltaic switch H to be closed again to restore photovoltaic power access, thereby realizing dynamic access and exit control of photovoltaic energy.

[0015] As a further solution of the present invention, the following charging and discharging steps of the off-grid photovoltaic storage system are also included: Charging control step: when the battery charge SOC state of the energy storage battery module B is lower than the first set threshold, the energy storage battery module B is charged with photovoltaic power in priority until the battery charge SOC state reaches the second set threshold or it is no longer possible to obtain excess photovoltaic power generation; Discharge control step: in an off-grid state, when the external power supply is unavailable and the load has power demand, according to the battery charge SOC state and the load power demand, the charge and discharge module PCS is controlled to discharge from the energy storage battery module B to the load until the battery charge SOC state drops to a third set threshold or the load demand decreases; Safety protection steps: During the above-mentioned charging control and discharging control process, if the BMS module detects that the battery has a level 2 alarm state or above, the power management module will reduce or stop the charging power, limit the discharging power, or disconnect the photovoltaic access to ensure the safety of the battery and the smooth operation of the system.

[0016] A charging and discharging method for an off-grid photovoltaic storage system, characterized in that it comprises the following steps: Charging monitoring step: The power management module, specifically the EMS module, monitors the battery charge SOC state of the energy storage battery module B in real time to determine whether the energy storage battery needs to be charged; Charging control step: when the battery charge SOC state is lower than the first charging threshold, the charging and discharging module PCS is controlled to enter the charging mode, and the photovoltaic power generation energy charges the energy storage battery module B through the charging and discharging module PCS; Charging exit step: when the battery charge SOC state reaches the second charging threshold or the energy storage battery module B triggers an overvoltage alarm, the charging operation is stopped; Discharge monitoring step: real-time detection of the power demand of the external load and the battery charge SOC state of the energy storage battery module B; Discharge control step: when the load power demand is greater than zero and the battery charge SOC state of the energy storage battery is higher than the minimum discharge threshold, the charge and discharge module PCS is controlled to enter the discharge mode, and the power of the energy storage battery module B is output to the load; Discharge exit step: When the load demand is zero or the battery charge SOC state of the energy storage battery is lower than the minimum discharge threshold, the discharge operation is stopped.

[0017] As a further solution of the present invention: the first charging threshold is that the SOC state of charge of the energy storage battery module B is lower than 30%, and the second charging threshold is that the SOC state of charge of the battery is higher than 95%; the minimum discharge threshold is that the SOC state of charge of the energy storage battery module B is lower than 20%; The charging control step also includes: before entering the charging mode, checking whether the photovoltaic input power meets the charging requirements of the energy storage battery. When the power is insufficient, the MPPT photovoltaic controller external to the energy storage cabinet prioritizes photovoltaic power generation so that the photovoltaic string operates in maximum power tracking; The discharge control step also includes: when the load demand is insufficient, controlling the charge and discharge module PCS to enter a low-power discharge mode to reduce the discharge rate of the energy storage battery; when the load demand increases suddenly, giving priority to outputting the electric energy of the energy storage battery module B to the critical load.

[0018] An off-grid photovoltaic storage circuit is applied to any of the above-mentioned off-grid photovoltaic storage systems.

[0019] In this solution, the MPPT photovoltaic controller is independently installed outside the energy storage cabinet, and shares the power channel with the charging and discharging module PCS and the energy storage battery module B through the DC bus. The power management module is connected to the MPPT photovoltaic controller in communication, thereby achieving the following beneficial effects: 1. Simplify internal wiring and reduce the difficulty of construction and maintenance: The MPPT photovoltaic controller gathers multiple photovoltaic strings outside the energy storage cabinet, eliminating the need for a large number of DC cables to penetrate deep into the energy storage cabinet. This significantly reduces the number and length of cables inside the cabinet, reduces wiring complexity and installation costs, and allows the system to maintain a neat and orderly cable layout under high-power conditions, which is conducive to later maintenance and expansion.

[0020] 2. Maintain multi-channel MPPT regulation capability and improve power generation efficiency: Multiple photovoltaic strings can independently track the maximum power point at the outdoor MPPT controller, without excessive current convergence to reduce cables. This ensures that each group of photovoltaic components can operate at its own optimal working point, improves the overall power generation and system efficiency, and meets the high power generation performance requirements under high-power applications.

[0021] 3. Flexibly control photovoltaic access and exit, protect energy storage batteries and improve system reliability: Through the communication between the power management module and the MPPT photovoltaic controller, the system can adjust the photovoltaic access in real time according to the battery status feedback from the BMS module. When the battery is close to full charge or an abnormal alarm occurs, the power management module can quickly instruct the MPPT photovoltaic controller to reduce the photovoltaic output or disconnect the access, thereby avoiding battery overcharging and potential damage, and improving system safety and operational stability.

[0022] 4. Efficient energy flow and intelligent scheduling: The MPPT photovoltaic controller shares photovoltaic power with the charging and discharging module PCS and the energy storage battery module B through the DC bus, so that the charging and discharging module PCS can flexibly choose to supply photovoltaic power to the load or store it in the energy storage battery. When the load is reduced or the battery is fully charged, the photovoltaic input can be timely controlled to reduce, which helps to achieve efficient energy utilization and intelligent scheduling, and improve the overall performance of the off-grid photovoltaic storage system.

[0023] In summary, this solution beneficially solves the technical problems of complex cables, limited MPPT capacity and lack of flexible adjustment means in traditional off-grid photovoltaic storage systems, so as to achieve a safer, more efficient, easy-to-maintain and scalable off-grid photovoltaic storage system architecture. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the circuit connection structure of a traditional high-power photovoltaic storage off-grid system using a combiner box.

[0025] Figure 2 This is a schematic block diagram of the circuit structure connection of the off-grid photovoltaic storage system of this solution.

[0026] Figure 3 This is the electrical diagram of the off-grid photovoltaic storage system of this solution.

[0027] Figure 4 This is the electrical system schematic diagram of the MPPT photovoltaic controller of this solution.

[0028] Figure 5 This is an example diagram of a single DC / DC circuit in the MPPT photovoltaic controller of this solution.

[0029] Figure 6 This is a control flow chart of part of the photovoltaic access and exit control method of this scheme.

[0030] Figure 7 This is another part of the control flow chart of the photovoltaic access and exit control method of this scheme. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It is understood that the drawings are only provided for reference and illustration, and are not used to limit the present invention. The connection relationship shown in the drawings is only for the convenience of clear description and does not limit the connection method.

[0032] In the related technologies, most of the current industrial and commercial off-grid photovoltaic storage systems have gradually developed from small-power household energy storage systems. This means that the early designs were mainly aimed at small, low-power applications, with relatively simple structures, suitable for fewer photovoltaic cables and lower power requirements. In these traditional systems, the photovoltaic MPPT (maximum power point tracking) controller module is located inside the inverter or charge and discharge module PCS (charge and discharge control module) cabinet. The function of the MPPT controller is to optimize the power generation of the photovoltaic panel to the maximum value, so that the system can obtain as much electricity as possible.

[0033] However, as the demand for system power increases, the demand for photovoltaic power generation also increases, so more photovoltaic panels need to be connected in parallel. This means that more PV module source (i.e. photovoltaic) DC cables need to be connected to the MPPT controller inside the inverter. Because these cables have to be connected to one place when connected to the inverter, the internal wiring becomes more and more numerous and messy, which increases the complexity and maintenance difficulty of the project.

[0034] In order to reduce the number of cables in the system, the easiest way to think of is Figure 1 The solution (hereinafter referred to as Document 1) generally adds a combiner box at the front end. The combiner box is used to collect the current of multiple photovoltaic panels together and then connect them to the MPPT controller of the inverter through fewer cables, in order to make the wiring inside the system simpler.

[0035] However, after repeated research, the inventors found that although the combiner box simplifies the wiring, it brings a new problem: the number of MPPTs is reduced. Specifically: without using a combiner box, each group of photovoltaic panels can be equipped with an independent MPPT controller to achieve maximum power tracking and fully utilize the power generation potential of each group of photovoltaic cells. Once a combiner box is used to concentrate the current of multiple photovoltaic panels, only a few MPPT controllers can be used in the system. This means that the maximum power tracking cannot be performed independently between photovoltaic panels, resulting in a decrease in the overall power generation of the photovoltaic system.

[0036] In detail, the function of the combiner box is to converge the currents of multiple photovoltaic panels or strings together and output a total current to supply the back-end equipment (such as MPPT controller, inverter). This centralized convergence design allows the subsequent equipment to receive the "synthetic current" of multiple photovoltaic strings instead of the individual current of each string. Each MPPT controller is designed to independently optimize the power generation for a photovoltaic string (or a group of photovoltaic panels with a specific configuration). It needs to measure the voltage and current in real time and dynamically adjust the working state of the photovoltaic components to maximize the power generation. If the currents of multiple photovoltaic strings are concentrated together, the MPPT controller will lose the ability to optimize each string independently and can only manage the "synthetic current" as a whole. In the absence of a combiner box, the system can configure an MPPT controller for each photovoltaic string separately to maximize the power generation efficiency of each string. Once the combiner box is used, the currents of multiple photovoltaic strings are concentrated, which is equivalent to the multiple strings being "merged" into one input. At this time, only one MPPT controller is needed to manage these strings as a whole. In this way, the number of MPPT controllers in the system will be reduced because the number of strings each controller is responsible for has increased. The working conditions of different photovoltaic strings are usually inconsistent (for example, different light intensity, temperature, dust shielding and other conditions), and their optimal working points will be different. After converging, the MPPT controller can only optimize an average power point for the "overall current" and cannot adjust it according to the actual situation of each string. This will cause some strings to not operate in the optimal state, reducing the power generation efficiency.

[0037] To this end, an embodiment of the present application provides an off-grid photovoltaic storage system, which can reduce the wiring complexity and retain sufficient MPPT controller paths under high-power conditions of the system, ensuring that each photovoltaic panel independently performs maximum power tracking to improve power generation efficiency, and flexibly control photovoltaic access and exit through the photovoltaic switch H, thereby ensuring the safe operation of the energy storage battery.

[0038] like Figure 2~Figure 7As shown, this embodiment is based on an off-grid photovoltaic storage system, which includes an energy storage cabinet and various functional modules configured inside and outside the energy storage cabinet. Through a reasonable system architecture and control strategy, efficient coordination of photovoltaic (PV) power and energy storage battery energy module B is achieved, and stable, safe and efficient operation is ensured under off-grid conditions.

[0039] Overall structure and layout of the system: The off-grid photovoltaic storage system of this embodiment includes an energy storage cabinet, an energy storage battery module B, a charge and discharge module PCS, an electric energy management module, an MPPT photovoltaic controller and a photovoltaic string.

[0040] The energy storage cabinet integrates an energy management module, an energy storage battery module B, and a charge and discharge module PCS. The energy management module includes but is not limited to an EMS module and / or a BMS module.

[0041] The energy storage battery module B includes energy storage batteries for storing photovoltaic power generation. The BMS module continuously monitors the voltage, current, temperature and state of charge SOC of the battery cells and generates an alarm signal when an abnormality (such as overvoltage, overcurrent or high temperature) occurs.

[0042] As a bidirectional power conversion unit, the charge and discharge module PCS can convert the DC power in the energy storage battery module B into AC power and output it to the load, and can also convert the AC power of photovoltaic power or external power supply into DC power to charge the energy storage battery module B.

[0043] The MPPT photovoltaic controller is independently installed outside the energy storage cabinet, close to the photovoltaic string, and is responsible for the maximum power point tracking (MPPT) control of multiple photovoltaic modules. It outputs optimized DC power to the DC bus of the system, and shares the DC bus with the charging and discharging module PCS and the energy storage battery module B to achieve energy distribution and allocation.

[0044] The power management module is connected to the MPPT photovoltaic controller through communication, and strategically controls the photovoltaic access and exit according to the battery charge SOC state of the energy storage battery module B and the BMS alarm information. The power management module includes but is not limited to the EMS module and / or the BMS module.

[0045] Connection and control of photovoltaic power generation and energy storage modules: In this embodiment, if Figure 4The MPPT photovoltaic controller contains multiple maximum power point tracking (MPPT). The MPPT photovoltaic controller is connected to multiple photovoltaic strings through its multiple PV input interfaces. For each photovoltaic string, the internal DC / DC boost circuit of the MPPT photovoltaic controller can independently perform maximum power point tracking, so as to continuously obtain the maximum possible power generation under different light irradiance conditions. When the system scale or power increases and the number of photovoltaic strings increases, a sufficient number of MPPTs can still be maintained without reducing the number of independent channels, thereby avoiding a decrease in power generation efficiency and simplifying the internal wiring structure of the cabinet.

[0046] The photovoltaic power optimized by the MPPT photovoltaic controller is transmitted to the energy storage battery module B and the charging and discharging module PCS through the DC bus. When the battery charge SOC of the energy storage battery module B is low, the power management module controls the photovoltaic switch H to close, and the photovoltaic power charges the energy storage battery module B; when the energy storage battery module B is close to full charge or an abnormal alarm (such as a level 2 alarm) occurs, the power management module can instruct the MPPT photovoltaic controller to reduce the power generation. If the power limit fails due to communication interruption, the photovoltaic access is immediately cut off by disconnecting the photovoltaic switch H to protect the battery safety.

[0047] Switching between off-grid and on-grid modes: This embodiment may also include an off-grid switching module (STS), which is connected to the load output connection port F, the AC power connection port E, and the charging and discharging module PCS. When the grid is unavailable or the user expects to operate completely off-grid, the off-grid switching module (STS) switches to off-grid mode, so that the energy storage battery module B and photovoltaic power generation can independently power the load. When the grid-connected power supply is available, grid-connected operation or auxiliary power supply supplement can be achieved in the grid-connected mode. When the grid is interrupted or the voltage is unstable, the system can quickly switch to off-grid mode to maintain reliable power supply to the load.

[0048] PV access and exit control strategy: (1) Photovoltaic access conditions: The power management module determines whether photovoltaic access is required based on the SOC of the energy storage battery module B. When the SOC is lower than the first preset threshold (such as 30%), the power management module controls the photovoltaic switch H to close, inputs photovoltaic power into the system DC bus, charges the energy storage battery module B or supplies power to the load through the PCS.

[0049] (2) Photovoltaic exit conditions: When the BSOC of the energy storage battery module is higher than the second preset threshold (such as 95%) or a secondary alarm occurs (such as battery cell overvoltage, overcurrent, high temperature) and the MPPT photovoltaic controller cannot reduce the power output in time, the power management module controls the photovoltaic switch H to disconnect and stop the photovoltaic power input. This can prevent the energy storage battery module B from overcharging, thereby ensuring the safety and stability of the system.

[0050] (3) Abnormal protection: When the MPPT photovoltaic controller fails to execute the power limit instruction due to communication interruption, resulting in the input power being unable to be controlled and endangering the battery safety, the power management module will immediately disconnect the photovoltaic switch H to achieve emergency protection.

[0051] Charge and discharge control: When the external power supply is unavailable and the load has power demand, the PCS discharges from the energy storage battery module B to supply energy to the load; when the BSOC of the energy storage battery module is insufficient, it is supplemented by photovoltaic power generation. If the battery is fully charged and the load still has demand, the system can adjust the power output of the MPPT photovoltaic controller so that the photovoltaic power can directly supply the load.

[0052] Under a specific threshold, the power management module controls the charging and discharging mode switching of the PCS to charge or discharge the energy storage battery module B in a timely manner to meet the load demand and battery maintenance strategy (such as ensuring battery life and avoiding over-discharge).

[0053] For multi-channel MPPT control and optimization under high power conditions: This implementation mode configures at least one MPPT photovoltaic controller corresponding to one or more photovoltaic strings to ensure that each photovoltaic string obtains MPPT control. In this way, even in high-power scenarios, high parallelism and high flexibility of MPPT regulation can be maintained, thereby maximizing the utilization of photovoltaic energy and improving overall power generation efficiency.

[0054] This solution can solve the following technical problems and achieve corresponding beneficial effects: Technical issues solved: Complex wiring and difficult maintenance: The traditional solution is to build the MPPT controller inside the energy storage cabinet, resulting in numerous cables and complex engineering. By installing the MPPT photovoltaic controller independently outside the energy storage cabinet, the convergence of the photovoltaic strings and the MPPT control are completed outdoors, which greatly reduces the number of DC cables entering the energy storage cabinet and reduces the complexity and engineering difficulty of the system.

[0055] Reduced power generation efficiency due to reduced number of MPPTs: Traditional solutions usually use centralized MPPT or Figure 1 The combiner box is used for confluence, reducing the number of MPPTs. The implementation method of this solution maintains a high number of MPPT channels through multiple independent MPPT photovoltaic controllers, and each photovoltaic string is independently tuned, thereby avoiding a sharp drop in the number of MPPTs due to excessive confluence and ensuring maximum photovoltaic power generation efficiency.

[0056] Uncontrollable photovoltaic access leads to battery overcharging and safety risks: When the battery is close to full charge or in an abnormal state, if the photovoltaic input cannot be quickly disconnected or reduced, the battery will be overcharged or damaged. In this embodiment, the power management module communicates with the MPPT photovoltaic controller and forcibly cuts off the photovoltaic access by disconnecting the photovoltaic switch H when necessary, thereby achieving rapid and effective protection of battery safety.

[0057] Beneficial effects achieved: Simplify wiring and improve maintainability: The MPPT photovoltaic controller is independently installed outside the energy storage cabinet, which effectively reduces the burden of cables inside the cabinet, facilitates engineering installation and subsequent maintenance, and enhances system scalability and reliability.

[0058] Improve power generation efficiency and flexibility: Each photovoltaic string is independently maximized by its corresponding MPPT photovoltaic controller, maintaining high power generation efficiency even in high-power application scenarios. Multiple MPPTs work in parallel, without the need for excessive convergence in the cabinet, without sacrificing power generation performance.

[0059] Enhanced safety and rapid response capability: The power management module dynamically regulates the photovoltaic input by real-time monitoring of the SOC and BMS alarm information of the energy storage battery module B. When the battery is fully charged or an alarm occurs, the power management module can instruct the MPPT photovoltaic controller to reduce power. If it fails, the photovoltaic switch H is immediately disconnected to ensure that the battery is not overcharged, thereby improving system safety and operational stability.

[0060] Intelligent scheduling and efficient use of energy: Under off-grid conditions, the power management module and PCS work together to flexibly allocate photovoltaic power and energy storage battery power to the load. When the load demand changes or the battery status changes, the system can flexibly adjust the photovoltaic access and power output through the power management module instructions to achieve efficient energy utilization.

[0061] In summary, the technical information disclosed in this solution, by independently installing the MPPT photovoltaic controller, realizing independent control of multiple MPPTs, configuring the power management module, the energy storage battery module B and the charging and discharging module PCS in the energy storage cabinet, and introducing the photovoltaic switch H and the corresponding photovoltaic access and exit control method, effectively solves the technical problems of the traditional off-grid photovoltaic storage system under high-power conditions, the difficulty in maintaining the power generation efficiency, and the inability to quickly reduce or cut off the photovoltaic input when the battery is close to full charge, thereby achieving the beneficial effects of simplifying engineering wiring, maintaining the adjustment capability of multiple MPPTs, enhancing system safety, improving power generation efficiency and realizing intelligent energy scheduling.

[0062] In detail: like Figure 2As shown in the figure, the off-grid photovoltaic storage system circuit block diagram of this scheme is connected in a schematic diagram. After the photovoltaic PV components are converged and boosted by the outdoor MPPT photovoltaic controller (i.e., the MPPT photovoltaic controller external to the energy storage cabinet), they are sent to the photovoltaic interface G of the off-grid photovoltaic storage integrated machine (i.e., the energy storage cabinet), and then to the charging and discharging module PCS and the energy storage battery module B through the series photovoltaic switch H. The outdoor MPPT photovoltaic controller is no longer installed in the off-grid photovoltaic storage integrated machine. When power limiting is required, the outdoor MPPT photovoltaic controller is connected to the power management module through communication (usually RS485).

[0063] like Figure 3 The figure shows the electrical diagram of the off-grid photovoltaic storage system of this scheme, which includes an off-grid photovoltaic storage integrated machine and a photovoltaic MPPT controller. After the three-phase AC voltage passes through the grid switch circuit breaker, it enters the off-grid switching module (STS) to achieve off-grid switching, and then outputs to the input end of the charging and discharging module PCS, and is transmitted to the load through the load switch circuit breaker. At the same time, a maintenance bypass switch is added between the grid and the load, so that the load power supply can be manually guaranteed in the event of a failure of the off-grid switching module (STS) for off-grid switching. The three-phase voltage at the input end of the charging and discharging module PCS is converted by AC / DC by the charging and discharging module PCS and output to the P+ and P- ends of the DC bus. On the one hand, the DC bus at the P+ and P- ends is connected to the energy storage battery group through the high-voltage box, which includes a soft start circuit, a fuse and a circuit breaker protection circuit, and a loop current detection circuit; on the other hand, the DC bus at the P+ and P- ends is connected to the external MPPT photovoltaic controller through the series photovoltaic switch H. Since photovoltaic PV modules have the characteristic of current limitation, that is, the current will not be much larger than the rated current after the output is short-circuited, the protection effect of circuit breaker is not great. Therefore, the photovoltaic switch H generally uses a switch that can be automatically controlled by software, typically a contactor or a high-power relay. The battery cluster is the energy storage battery module B.

[0064] like Figure 4 The electrical system diagram of the MPPT photovoltaic controller of this solution is shown. The positive and negative of 16 pairs of PV strings are connected separately, and after passing through the photovoltaic input switch and input lightning protection circuit, they are divided into multiple DC / DC circuits for MPPT control. At the same time, the outputs of multiple groups of DC / DC circuits are unified and lightning-protected to form positive and negative BUS outputs.

[0065] like Figure 5The figure shows a single DC / DC circuit example in the MPPT photovoltaic controller of this solution. The input voltage is connected to the inductor L after being filtered by the capacitor. During the on-phase of the IGBT (T), the inductor current increases. During the off-phase of the IGBT (T), the inductor current charges the output capacitor through the diode D. As the inductor current decreases, the energy stored in the inductor in the early stage is transferred to the output capacitor at the rear end, realizing the step-up conversion from input voltage to output voltage. Under normal circumstances, the DC / DC circuit performs MPPT (Max Power Point Tracking), that is, controlling the input voltage change to maximize the output power of the PV.

[0066] like Figure 6 The figure shows a control flow chart of part of the photovoltaic access and exit control method of this scheme, specifically, the BMS alarm detection flow chart of the energy storage battery module B of the off-grid photovoltaic storage integrated machine. The control system of the battery management module reads the voltage and temperature data of all cells of the energy storage battery and the cluster current data in real time to determine whether the above data exceeds the first-level alarm threshold. If not, it returns; if exceeded, it further determines whether it exceeds the second-level alarm threshold. At this time, if the first-level alarm threshold is exceeded but the second-level alarm threshold is not exceeded, the BMS first-level alarm flag is set. If the second-level alarm is exceeded, it is further determined whether the third-level alarm threshold is exceeded. At this time, if the second-level alarm threshold is exceeded but the third-level alarm threshold is not exceeded, the BMS second-level alarm flag is set, and if the third-level alarm threshold is exceeded, the BMS third-level alarm flag is set. The first, second and third level alarm thresholds for cell voltage, temperature and current are set relative to their respective rated values. The normal cell voltage is 3.2V, but 3.5V, 3.55V and 3.6V are the first, second and third level alarm thresholds for cell voltage being too high, and 3.0V, 2.95V and 2.85V are the first, second and third level alarm thresholds for cell voltage being too low. The same is true for current and temperature.

[0067] like Figure 7The figure shows another part of the control flow chart of the photovoltaic access and exit control method of this scheme. The system reads the SOC status of the energy storage battery module B in real time. If the SOC is less than 80%, the photovoltaic switch H connected in series is closed to charge the energy storage battery module B, or the photovoltaic energy is released to the outside through the charging and discharging module C (charging and discharging module PCS). When the SOC is less than 80% and the photovoltaic switch H connected in series is closed, it is further determined whether the power management module, specifically the BMS module, reaches the second-level alarm. If the second-level alarm is reached, the specific information of the second-level alarm is read. If it is the second-level overvoltage of the battery cell voltage or the second-level charging overcurrent of the battery current, the photovoltaic switch H connected in series is disconnected to stop the access of photovoltaic energy. The power management module, specifically the BMS module, is generally divided into three levels of protection. When the first-level alarm occurs, the charging and discharging target power is reduced. When the second-level alarm occurs, the charging and discharging target power is set to 0. When the third-level alarm occurs, the contactor switch of the battery controller is tripped to stop charging and discharging. When the battery is fully charged and the battery voltage reaches the second-level alarm, the target power is set to 0. However, due to the long distance of the MPPT, the power limit may fail. In order to prevent the battery from having the third-level alarm protection, it is necessary to disconnect the photovoltaic input energy in time, that is, disconnect the series photovoltaic switch H. Or when the number of photovoltaic PV component sources configured in the system is too large, resulting in too high voltage and too much power, even if the MPPT photovoltaic controller stops boosting, the current is still relatively large, and when it exceeds the second-level protection of the energy storage battery module B, the series photovoltaic switch H must also be disconnected.

[0068] The battery SOC state of charge of lithium-ion batteries can be calculated by a variety of methods, including methods based on the number of cycles, methods based on voltage and current, methods based on battery models, methods based on laboratory test data, as well as chemical methods, voltage methods, electrochemical impedance methods, current integration methods, Kalman filtering methods, neural network methods, etc. The method based on the number of cycles is based on the number of cycles of the battery and the power loss after the cycle. The battery SOC state of charge of the battery is determined by calculating the energy loss of the battery after multiple cycles. The advantage is that the capacity decay of the battery can be accurately calculated, and the disadvantage is that a large amount of testing and calculation corrections are required for the battery.

[0069] Finally, it should be noted that: those skilled in the art cross-reference or superimpose the various embodiments of the present solution, which still fall within the original disclosure scope of the present solution. In addition, the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments, or perform equivalent replacements on some of the technical features therein. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An off-grid solar storage system, characterized in that: It includes an energy storage cabinet, an energy management module, an energy storage battery module (B), a charge and discharge module (PCS) arranged inside the energy storage cabinet, and an MPPT photovoltaic controller and photovoltaic strings external to the energy storage cabinet; wherein: An energy storage battery module (B), comprising an energy storage battery for storing photovoltaically generated electrical energy; The charging and discharging module (PCS) is connected to the energy storage battery module (B) and is used for bidirectional conversion of DC and AC power; The MPPT photovoltaic controller is independently installed outside the energy storage cabinet and is connected to the photovoltaic strings and the charging and discharging module (PCS) respectively. It is used to output photovoltaic power generation energy to the DC bus of the system after performing maximum power point tracking (MPPT) on multiple photovoltaic strings, and shares the DC bus with the charging and discharging module (PCS) and the energy storage battery module (B); The power management module is connected to the MPPT photovoltaic controller for communication.

2. The off-grid solar energy storage system according to claim 1, characterized in that: The MPPT photovoltaic controller is connected to the photovoltaic string and is separated from the energy storage cabinet or independently set outdoors. The power management module is used to control the photovoltaic access according to the real-time operating status of the energy storage battery module (B). When the charging demand is met, the photovoltaic input path is closed to charge the energy storage battery. When the energy storage battery is close to full charge or an abnormality occurs, the MPPT photovoltaic controller is instructed to reduce or stop the photovoltaic input, or disconnect the photovoltaic access.

3. The off-grid solar energy storage system according to claim 1, characterized in that: The energy storage cabinet is also equipped with: Photovoltaic input connector (G), connected to the MPPT photovoltaic controller; The photovoltaic switch (H) is connected to the photovoltaic input connection port (G) and the charging and discharging module (PCS) respectively, and is used to control the connection and exit of the MPPT photovoltaic controller; Load output connector (F), used to connect load equipment; AC power connector (E), used to connect to an external AC power source; and The off-grid and grid-connected switching module (STS) is respectively connected to the load output connection port (F), the AC power connection port (E) and the charging and discharging module (PCS) and is used for switching the off-grid photovoltaic storage system between the off-grid mode and the grid-connected mode; The power management module is used to close the photovoltaic switch (H) when the operating conditions are met, so that the photovoltaic energy is used to charge the energy storage battery energy module (B) or to supply power to the outside through the charge and discharge module (PCS); when the access conditions are not met, the power management module is used to disconnect the photovoltaic switch (H) and stop the access of photovoltaic power.

4. The off-grid solar energy storage system according to claim 1, characterized in that: There is at least one MPPT photovoltaic controller and one photovoltaic string, at least one MPPT photovoltaic controller is provided with at least one MPPT, at least one MPPT photovoltaic controller is connected to at least one photovoltaic string, and each photovoltaic string is tracked by the MPPT photovoltaic controller for maximum power point to optimize photovoltaic power generation efficiency; The power management module is connected to the external MPPT photovoltaic controller through a communication protocol to perform real-time regulation and power limit control on the photovoltaic power output.

5. The off-grid solar storage system according to claim 2, characterized in that: The power management module is used to control the photovoltaic switch (H) to close when the battery state of charge (SOC) of the energy storage battery module is lower than a preset threshold battery state of charge (SOC), and to control the photovoltaic switch (H) to open when the battery state of charge (SOC) is higher than the preset threshold or an alarm occurs in the energy storage battery module; The MPPT photovoltaic controller includes a multi-channel PV input interface, a PV input switch, an input lightning protection circuit, multiple DC / DC boost circuits, and an output bus and lightning protection unit. The multiple DC / DC boost circuits respectively perform maximum power point tracking on different photovoltaic strings. The photovoltaic switch (H) is a semiconductor switch device or a mechanical switch.

6. A photovoltaic access and exit control method, characterized in that: The steps include: Power monitoring steps: The power management module monitors the battery charge (SOC) state of the energy storage battery module (B) in real time; Access judgment step: judging whether the battery state of charge (SOC) is lower than a first preset threshold, if so, entering the photovoltaic access step; if not, entering the exit judgment step; Photovoltaic access steps: control the photovoltaic switch (H) to close, connect the photovoltaic power generation energy, and the photovoltaic power generation energy is optimized by the MPPT photovoltaic controller externally placed in the energy storage cabinet and then input into the energy storage battery module (B) for charging, or output to the external load through the charge and discharge module (PCS); Exit judgment step: judge whether the battery state of charge (SOC) is higher than the second preset threshold, or whether a second-level alarm occurs. If so, enter the photovoltaic exit step; if not, continue to maintain the photovoltaic connection state; Photovoltaic exit steps: control the photovoltaic switch (H) to disconnect and stop the photovoltaic power generation from being input into the energy storage battery module (B).

7. The photovoltaic access and exit control method according to claim 6, characterized in that: It also includes an abnormal protection step: when it is detected that the MPPT photovoltaic controller communication is interrupted or the power limit adjustment fails, the photovoltaic switch (H) is controlled to be disconnected to stop the photovoltaic power generation input; The access determination step further includes: when the battery state of charge (SOC) is lower than a first preset threshold, first determining whether the temperature of the energy storage battery module (B) is lower than the upper limit of the safety range, if so, entering the photovoltaic access step; if not, stopping the photovoltaic access; The exit judgment steps are as follows: judging whether the battery state of charge (SOC) is higher than a second preset threshold; judging whether the energy storage battery module (B) is in a first-level alarm state, and if so, alleviating the abnormality by adjusting the photovoltaic input power or reducing the charging rate; judging whether a second-level alarm state is present, and if so, entering the photovoltaic exit step; if none of the above conditions are triggered, continuing to maintain the photovoltaic access state.

8. The photovoltaic access and exit control method according to claim 7, characterized in that: The abnormal protection steps include: when the secondary alarm signal of the energy storage battery module (B) is overvoltage and / or overcurrent and / or high temperature of the battery cell, disconnecting the photovoltaic switch (H); when the MPPT photovoltaic controller fails to limit the power and causes the power input to be greater than the preset power value, disconnecting the photovoltaic switch (H); The exit judgment step also includes: judging whether the photovoltaic input power meets the current load demand, and when the load cannot fully absorb the photovoltaic power generation power, controlling the MPPT photovoltaic controller to limit the power; if the power limit fails or the load power demand is zero, disconnecting the photovoltaic switch (H); The first level warning state includes that the cell voltage or temperature of the energy storage battery is close to the set upper limit, but has not exceeded the safety range; Secondary alarm conditions include battery cell overvoltage, overcurrent or high temperature.

9. A photovoltaic access and exit control method, characterized in that: The steps include: Battery status monitoring steps: The power management module obtains the battery state of charge (SOC) and determines whether it is lower than the preset SOC threshold; Access condition evaluation step: if the battery state of charge (SOC) is lower than the preset SOC threshold, it is determined that the photovoltaic access condition is met; Photovoltaic access steps: When the photovoltaic access conditions are met, close the photovoltaic switch (H) and connect the photovoltaic power processed by the MPPT photovoltaic controller outside the energy storage cabinet to the system, so that the photovoltaic power can charge the energy storage battery module (B) or supply power to the outside through the charging and discharging module (PCS); Power limit instruction step: When the energy storage battery module (B) is close to full charge and cannot further transmit power to the outside, a power limit instruction is sent to the MPPT photovoltaic controller through the power management module to reduce the photovoltaic power input; Communication abnormality handling steps: If the MPPT photovoltaic controller fails to execute the power limit instruction due to communication abnormality, the power management module stops the input of photovoltaic power by disconnecting the photovoltaic switch (H); Reconnection determination steps: When the photovoltaic switch (H) is disconnected, if the battery state of charge (SOC) of the energy storage battery module (B) drops below a predetermined recovery threshold, the power management module allows the photovoltaic switch (H) to be closed again to restore photovoltaic power access.

10. An off-grid solar storage circuit, characterized in that: An off-grid solar storage system applied to any one of claims 1-5.

Images