Control method and device of energy storage system

Abstract

The invention discloses a control method and device of an energy storage system, and belongs to the field of control of the energy storage system. By acquiring the voltage and frequency information of the grid-connected point, the power grid state can be monitored in real time, and the working mode of the energy storage system is determined accordingly. In the network construction mode, the voltage and frequency signals of the output end of the inverter are further obtained, the active power or reactive power output value of the grid-connected point is dynamically calculated in combination with a preset droop coefficient, the output of the inverter is adjusted accordingly, and it is ensured that the voltage and frequency of the grid-connected point are stabilized within a preset first numerical range. And in the network following mode, the power amplitude limiting value of the inverter is calculated according to the current residual capacity of the battery and a preset formula, and the charging and discharging power of the battery is adjusted according to the power amplitude limiting value of the inverter, so that the battery operates safely within a preset second numerical range. The problem that the energy storage system cannot be accurately and efficiently controlled in the prior art is effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of control of energy storage systems, and particularly to a control method and device for an energy storage system. Background Art

[0002] With the continuous development and application of distributed generation and microgrid technologies as well as intelligent power distribution and utilization technologies, the distribution network has gradually changed from a traditional passive radial network to a multi-source complex network. Various distributed power sources (such as solar energy, wind energy), energy storage systems, microgrids, electric vehicles, and diverse load demands of users have made the equipment composition of the power distribution system more complex, the dynamic process more abundant, and the control means more diverse. These changes have put forward higher requirements for the stability and reliability of the power system.

[0003] Due to its unique advantages such as economy, flexibility, and repeatability, the digital simulation technology of power systems has become one of the most effective means in power system research. As an important part of the digital simulation of power systems, electromagnetic transient simulation aims to finely model the target system and obtain detailed time-domain waveforms of various transient responses. Initially, electromagnetic transient simulation was mainly used for the research of problems such as overvoltage processes and subsynchronous resonance in power generation and transmission systems. In recent years, with the continuous development of distributed generation and microgrid technologies, the operating mechanism and dynamic characteristics of the distribution network have become more complex, and in-depth research using electromagnetic transient simulation technology is required.

[0004] However, the functions of the existing control modules for microgrid energy storage systems are relatively monotonous, and there are the following main problems:

[0005] Inflexible mode switching: Traditional energy storage systems rely on manual intervention or fixed logic during the grid-connected / off-grid state switching, with slow dynamic response, which is likely to cause voltage / frequency instability and is inconsistent with the actual situation.

[0006] Insufficient simulation accuracy of energy storage batteries: The energy storage system module lacks a comprehensive protection strategy for low voltage and overload of energy storage batteries. When the battery is overcharged or over-discharged, it is inconsistent with the actual situation.

[0007] Coarse battery protection mechanism: Battery protection relies on fixed thresholds (such as cutting off when SOC < 10%), without considering factors such as battery aging and temperature, which is likely to cause misoperation or protection failure.

[0008] These problems lead to the inability of the existing technology to accurately and efficiently control the energy storage system. Summary of the Invention

[0009] The present invention provides a control method and device for an energy storage system to solve the problem that the existing technology cannot accurately and efficiently control the energy storage system.

[0010] In a first aspect, the present application provides a control method for an energy storage system, including:

[0011] Obtain the voltage and frequency of the grid connection point;

[0012] Determine the working mode of the energy storage system according to the voltage and frequency of the grid connection point;

[0013] If the working mode is the grid-forming mode, obtain the voltage and frequency signals at the output end of the inverter in the energy storage system;

[0014] According to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, calculate the output value of the active power or reactive power at the grid connection point;

[0015] Adjust the output of the inverter according to the output value of the active power or reactive power, so that the voltage and frequency at the grid connection point are maintained within a preset first numerical range;

[0016] If the working mode is the grid-following mode, calculate the power limit value of the inverter according to the remaining capacity of the current battery in the energy storage system and a preset formula;

[0017] Adjust the charge and discharge power of the battery according to the power limit value, so that the battery is charged or discharged within a preset second numerical value.

[0018] By obtaining the voltage and frequency information of the grid connection point, the present application can monitor the grid state in real time and determine the working mode of the energy storage system accordingly. In the grid-forming mode, further obtain the voltage and frequency signals at the output end of the inverter, combined with a preset droop coefficient, dynamically calculate the output value of the active power or reactive power at the grid connection point, so as to accurately adjust the output of the inverter and ensure that the voltage and frequency at the grid connection point are stable within a preset first numerical range. This dynamic adjustment mechanism effectively improves the voltage and frequency stability of the energy storage system during independent operation and enhances the system's independent regulation ability. In the grid-following mode, calculate the power limit value based on the remaining capacity of the battery and a preset formula, and then adjust the charge and discharge power of the battery, so that the charge and discharge process of the battery is always within a preset second numerical range, effectively avoiding overcharging or over-discharging of the battery, extending the service life of the battery, and improving the flexibility and safety of the energy storage system during grid-connected operation. In summary, through mode switching and dynamic regulation, the present application significantly improves the operation efficiency and stability of the energy storage system, and effectively solves the problem that the prior art cannot accurately and efficiently control the energy storage system.

[0019] As a preferred embodiment of the first aspect, the step of determining the working mode of the energy storage system according to the voltage and frequency of the grid connection point is specifically:

[0020] If the voltage at the grid connection point is within the preset rated voltage range and the deviation of the frequency is less than a preset first threshold within a preset time period, determine that the operating mode is the grid-forming mode;

[0021] If the voltage at the grid connection point is lower than the preset lower limit value or the deviation of the frequency is greater than a preset second threshold within a preset time period, determine that the operating mode is the grid-following mode.

[0022] In this preferred embodiment, the present application realizes precise control of the operating state of the energy storage system by monitoring the voltage and frequency at the grid connection point in real time and determining the operating mode of the energy storage system based on whether they are within the preset normal range. When the voltage and frequency deviations at the grid connection point meet specific conditions, the system automatically switches to the grid-forming mode or the grid-following mode, ensuring stable operation under different grid conditions. This mode switching mechanism not only improves the flexibility and adaptability of the energy storage system but also enhances the stability of the power grid, effectively avoiding operation anomalies caused by grid fluctuations, thereby improving the reliability and operating efficiency of the entire power system.

[0023] As a preferred embodiment of the first aspect, calculating the output value of the active power or reactive power at the grid connection point according to the voltage or frequency signal at the output end of the inverter and in combination with a preset droop coefficient specifically includes:

[0024] Calculating the reactive power at the grid connection point according to the voltage at the output end of the inverter, the preset reference voltage, and the reference reactive power, and according to a preset first droop coefficient;

[0025] Wherein, the formula for calculating the reactive power at the grid connection point is:

[0026] Q = Q ref -k q ×(V - V ref )

[0027] In the formula, Q is the reactive power at the grid connection point, Q ref is the preset reference reactive power, V ref is the preset reference voltage, V is the voltage at the output end of the inverter, and k q is the preset first droop coefficient.

[0028] In this preferred embodiment, the present application accurately calculates the reactive power output value of the grid connection point by combining the voltage signal at the output end of the inverter with a preset reference voltage, reference reactive power, and first droop coefficient. The present application can dynamically adjust the output of the inverter to maintain the stability of the grid connection point voltage. This reactive power regulation mechanism based on droop control enables the energy storage system to automatically and accurately provide or absorb reactive power when the grid voltage fluctuates, thereby effectively maintaining the grid connection point voltage within a preset range. This not only enhances the adaptability and response ability of the energy storage system to grid voltage changes but also improves the voltage stability of the entire power grid, reduces equipment failures and energy losses that may be caused by voltage fluctuations, and thus improves the overall operating efficiency and reliability of the power system.

[0029] As a preferred embodiment of the first aspect, calculating the active power or reactive power output value of the grid connection point according to the voltage or frequency signal at the output end of the inverter and in combination with a preset droop coefficient specifically includes:

[0030] Calculating the active power of the grid connection point according to the frequency signal at the output end of the inverter, a preset rated frequency, and a preset first power, and according to a droop coefficient adjusted based on the remaining capacity of the current battery and the remaining capacity of the current battery;

[0031] Wherein, the formula for calculating the active power of the grid connection point is:

[0032] P = P ref -k p (SOC)×(f - f ref )

[0033] In the formula, P is the active power of the grid connection point, P ref is the preset first power, f ref is the preset rated frequency, SOC is the remaining capacity of the current battery, and k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery.

[0034] The preset droop coefficient adjusted based on the remaining capacity of the current battery specifically includes:

[0035] The calculation formula for the droop coefficient adjusted based on the remaining capacity of the current battery is:

[0036]

[0037] In the formula, k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery, β is a preset adjustment factor, SOC is the remaining capacity of the current battery, and k p0 is the preset second droop coefficient.

[0038] In this preferred embodiment, the present application accurately calculates the active power output value of the grid connection point by combining the frequency signal at the output end of the inverter, the preset rated frequency and the first power, and the droop coefficient adjusted based on the current remaining battery capacity. The present application realizes the dynamic regulation of the output power of the energy storage system. This dynamic regulation mechanism can flexibly adjust the active power output of the energy storage system according to the actual state of the battery (such as the remaining capacity) and the real-time frequency change of the power grid. This not only improves the adaptability and response ability of the energy storage system to the power grid frequency change, but also ensures the stability of the grid connection point frequency under different working conditions. In addition, by considering the remaining capacity of the battery, this method can effectively extend the service life of the battery, while improving the overall operation efficiency and reliability of the energy storage system.

[0039] As a preferred embodiment of the first aspect, if the working mode is the grid-following mode, the power limit value of the inverter is calculated according to the remaining capacity of the current battery in the energy storage system and a preset formula, specifically:

[0040] If the working mode is the grid-following mode, the power limit value of the inverter is calculated according to the remaining capacity of the current battery, the preset output power of the battery, the preset capacity attenuation coefficient and a preset formula.

[0041] The calculation formula for the power limit value of the inverter is:

[0042] P max =μ×C set ×(1 - e -γ×SOC )

[0043] In the formula, P max is the power limit value of the inverter, μ is the measured converter efficiency, C set is the preset output power of the battery, γ is the preset capacity attenuation coefficient, and SOC is the remaining capacity of the current battery.

[0044] In this preferred embodiment, in the grid-following mode, the present application calculates the power limit value of the inverter by using a specific formula considering the remaining capacity (SOC) of the current battery, the preset output power of the battery, the preset capacity attenuation coefficient and the measured converter efficiency. This dynamic adjustment mechanism can optimize the charging and discharging power limit of the inverter in real time according to the actual remaining capacity of the battery and the system efficiency. This not only effectively avoids overcharging or over-discharging of the battery during the charging and discharging process, extends the service life of the battery, but also improves the flexibility and safety of the energy storage system during grid-connected operation, ensuring that the energy storage system can operate stably under different grid conditions, thereby improving the reliability and operation efficiency of the entire power system.

[0045] As a preferred embodiment of the first aspect, it further includes:

[0046] Real-time monitor the remaining capacity and temperature of the battery in the energy storage system, and perform low-capacity classification protection and overload protection on the battery according to the monitoring results.

[0047] The low-capacity classification protection of the battery according to the monitoring results is specifically:

[0048] If the remaining capacity of the current battery in the energy storage system is lower than the preset first capacity threshold, cut off the battery output according to the preset first delay time;

[0049] If the remaining capacity of the current battery in the energy storage system is lower than the preset second capacity threshold, adjust the maximum output power of the battery within the preset second power range.

[0050] The overload protection of the battery according to the monitoring results is specifically:

[0051] Perform overload protection on the battery according to the preset short-term overload derating curve and the remaining capacity of the current battery in the energy storage system;

[0052] Among them, the preset short-term overload derating curve is:

[0053]

[0054] In the formula, τ is the preset time constant, P over is the maximum short-term overload power of the converter, P t is the instantaneous overload power of the converter, and t is the time.

[0055] In this preferred embodiment, the present application significantly improves the safety and service life of the battery by real-time monitoring the remaining capacity (SOC) and temperature of the battery in the energy storage system and implementing low-capacity classification protection and overload protection according to the monitoring results. Specifically, when the remaining capacity of the battery is lower than the preset first capacity threshold, the system will cut off the battery output after the preset first delay time to prevent the battery from over-discharging; when the remaining capacity is lower than the preset second capacity threshold, the system will limit the maximum output power of the battery within the preset second power range, thereby reducing its output power when the battery power is low and avoiding damage to the battery caused by over-discharging. In addition, based on the preset short-term overload derating curve, the system can dynamically adjust its instantaneous overload power according to the remaining capacity of the battery to ensure that the battery will not be damaged due to exceeding its tolerance in the case of overload. This refined protection strategy not only effectively avoids the potential risks of the battery in low-power and overload states, but also improves the reliability and stability of the energy storage system under various operating conditions, providing a strong guarantee for the safe operation of the power system.

[0056] Second aspect, the present application provides a control device for an energy storage system. The control of the energy storage system includes an acquisition module, a mode switching module, a grid-forming operation mode module, and a grid-following operation mode module;

[0057] The acquisition module is used to acquire the voltage and frequency of the grid connection point;

[0058] The mode switching module is used to determine the operation mode of the energy storage system according to the voltage and frequency of the grid connection point;

[0059] The grid-forming operation mode module is used to, if the operation mode is the grid-forming mode, acquire the voltage and frequency signals at the output end of the inverter in the energy storage system;

[0060] According to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, calculate the output value of the active power or reactive power of the grid connection point;

[0061] According to the output value of the active power or reactive power, adjust the output of the inverter so that the voltage and frequency of the grid connection point are maintained within a preset first numerical range;

[0062] The grid-following operation mode module is used to, if the operation mode is the grid-following mode, calculate the power limit value of the inverter according to the remaining capacity of the battery in the current energy storage system and a preset formula;

[0063] According to the power limit value, adjust the charge and discharge power of the battery so that the battery is charged or discharged within a preset second numerical value.

[0064] This device uses four modules to work in division and coordination, which can control the energy storage system more accurately and efficiently. By acquiring the voltage and frequency information of the grid connection point, the present application can monitor the grid state in real time and determine the operation mode of the energy storage system accordingly. In the grid-forming mode, further acquire the voltage and frequency signals at the output end of the inverter, combined with a preset droop coefficient, dynamically calculate the output value of the active power or reactive power of the grid connection point, so as to accurately adjust the output of the inverter and ensure that the voltage and frequency of the grid connection point are stable within a preset first numerical range. This dynamic adjustment mechanism effectively improves the voltage and frequency stability of the energy storage system during independent operation and enhances the system's independent regulation ability. In the grid-following mode, calculate the power limit value based on the remaining capacity of the battery and a preset formula, and then adjust the charge and discharge power of the battery, so that the charge and discharge process of the battery is always within a preset second numerical range, effectively avoiding the phenomenon of overcharging or over-discharging of the battery, prolonging the service life of the battery, and improving the flexibility and safety of the energy storage system during grid-connected operation. In summary, through mode switching and dynamic regulation, the present application significantly improves the operation efficiency and stability of the energy storage system, and effectively solves the problem that the prior art cannot accurately and efficiently control the energy storage system. Description of the Drawings

[0065] Figure 1 : Schematic flow diagram of an embodiment of the control method for the energy storage system provided in this application;

[0066] Figure 2 : Schematic structural diagram of an embodiment of the hardware control strategy for the energy storage system provided in this application;

[0067] Figure 3 : Schematic structural diagram of an embodiment of the charge and discharge system for the energy storage system provided in this application;

[0068] Figure 4 : Schematic structural diagram of an embodiment of the control device for the energy storage system provided in this application. Detailed implementation manners

[0069] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0070] Embodiment 1

[0071] Please refer to Figure 1 , to solve the problem that the prior art cannot accurately and efficiently control the energy storage system, an energy storage system control method provided by an embodiment of the present invention.

[0072] In this embodiment, the process of the control method for the energy storage system in this application is described in detail through steps S01 - S07.

[0073] As Figure 2 and Figure 3 shown, this application realizes the adaptive switching of the converter state through dynamic droop coefficient optimization and dynamic amplitude limiting algorithm, and constructs a complete battery protection strategy to improve the performance of the energy storage battery converter module.

[0074] S01: Obtain the voltage and frequency of the grid connection point.

[0075] S02: Determine the working mode of the energy storage system according to the voltage and frequency of the grid connection point.

[0076] As a preferred embodiment of Embodiment 1, the determining the working mode of the energy storage system according to the voltage and frequency of the grid connection point is specifically:

[0077] If the voltage at the grid connection point is within the preset rated voltage range and the deviation of the frequency is less than a preset first threshold within a preset time period, determine that the operating mode is the grid-forming mode;

[0078] If the voltage at the grid connection point is lower than the preset lower limit value or the deviation of the frequency is greater than a preset second threshold within a preset time period, determine that the operating mode is the grid-following mode.

[0079] More specifically, the switching method is as follows:

[0080] Grid-forming → Grid-following: Grid voltage V grid ∈[0.95V N , 1.05V N and the frequency deviation Δf < 0.05 Hz lasts for 100 ms;

[0081] Grid-following → Grid-forming: V grid <0.8V N or Δf > 0.05 Hz lasts for 20 ms;

[0082] The deviation is the difference between the current actual frequency and the system rated frequency (for example, the rated frequency in China is 50 Hz and the rated frequency in the United States is 60 Hz).

[0083] In this preferred embodiment, the present application determines the operating mode of the energy storage system by real-time monitoring of the voltage and frequency at the grid connection point and based on whether they are within the preset normal range. The present application realizes precise control of the operating state of the energy storage system. When the voltage and frequency deviations at the grid connection point meet specific conditions, the system automatically switches to the grid-forming mode or the grid-following mode, ensuring stable operation under different grid conditions. This mode switching mechanism not only improves the flexibility and adaptability of the energy storage system but also enhances the stability of the power grid, effectively avoiding operating abnormalities caused by grid fluctuations, thereby improving the reliability and operating efficiency of the entire power system.

[0084] S03: If the operating mode is the grid-forming mode, obtain the voltage and frequency signals at the output end of the inverter in the energy storage system.

[0085] S04: According to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, calculate the output value of the active power or reactive power at the grid connection point.

[0086] As a preferred embodiment of Embodiment 1, the calculating the output value of the active power or reactive power at the grid connection point according to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, is specifically as follows:

[0087] Traditional generators in the power system all have droop characteristics, that is, when the grid connection point frequency is higher than the rated frequency, the traditional generator will reduce the active power output. When the grid connection point voltage is higher than the rated voltage, the reactive power output will be reduced.

[0088] By setting a strategy similar to that of a traditional motor in the converter, when the grid connection point voltage is detected to be higher than the rated voltage, the output reactive power is reduced, and when the grid connection point voltage frequency is detected to be higher than the rated frequency, the output active power is reduced to determine the system voltage stability.

[0089] According to the voltage at the output end of the inverter, the preset reference voltage and reference reactive power, and according to the preset first droop coefficient, the reactive power at the grid connection point is calculated;

[0090] Among them, the formula for calculating the reactive power at the grid connection point is:

[0091] Q = Q ref -k q ×(V - V ref )

[0092] In the formula, Q is the reactive power at the grid connection point, Q ref is the preset reference reactive power, V ref is the preset reference voltage, V is the voltage at the output end of the inverter, k q is the preset first droop coefficient, calculated according to the rated capacity S rated of the converter, k q is default set to 0.03 kVAR / V and can be flexibly set according to user needs.

[0093] In this preferred embodiment, the present application accurately calculates the reactive power output value at the grid connection point by combining the voltage signal at the output end of the inverter with the preset reference voltage, reference reactive power, and first droop coefficient. The present application can dynamically adjust the output of the inverter to maintain the stability of the grid connection point voltage. This reactive power regulation mechanism based on droop control enables the energy storage system to automatically and accurately provide or absorb reactive power when the grid voltage fluctuates, thereby effectively maintaining the grid connection point voltage within the preset range. This not only enhances the adaptability and response ability of the energy storage system to grid voltage changes, but also improves the voltage stability of the entire power grid, reduces equipment failures and energy losses that may be caused by voltage fluctuations, and thus improves the overall operation efficiency and reliability of the power system.

[0094] The calculation of the active power or reactive power output value at the grid connection point according to the voltage or frequency signal at the output end of the inverter, combined with the preset droop coefficient, is specifically as follows:

[0095] Calculate the active power of the grid connection point according to the frequency signal at the output end of the inverter, the preset rated frequency and the preset first power, and according to the preset droop coefficient adjusted based on the remaining capacity of the current battery and the remaining capacity of the current battery.

[0096] Among them, the formula for calculating the active power of the grid connection point is:

[0097] P = P ref -k p (SOC)×(f - f ref )

[0098] In the formula, P is the active power of the grid connection point, P ref is the preset first power, f ref is the preset rated frequency, SOC is the remaining capacity of the current battery, k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery.

[0099] The preset droop coefficient adjusted based on the remaining capacity of the current battery is specifically:

[0100] The calculation formula for the droop coefficient adjusted based on the remaining capacity of the current battery is:

[0101]

[0102] In the formula, k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery, β is the preset adjustment factor, and the default setting value is 0.2, which is used to balance the power response speed at different SOCs and can be flexibly set according to user needs; SOC is the remaining capacity of the current battery, k p0 is the preset second droop coefficient, that is, the reference droop coefficient, which is default set to kW / 0.05Hz and can be flexibly set according to user needs.

[0103] This application accurately calculates the output value of the active power of the grid connection point by combining the frequency signal at the output end of the inverter, the preset rated frequency and the first power, and the droop coefficient adjusted based on the remaining capacity of the current battery. This application realizes the dynamic adjustment of the output power of the energy storage system. This dynamic adjustment mechanism can flexibly adjust the active power output of the energy storage system according to the actual state of the battery (such as the remaining capacity) and the real-time frequency change of the power grid. This not only improves the adaptability and response ability of the energy storage system to the power grid frequency change, but also ensures the stability of the grid connection point frequency under different working conditions. In addition, by considering the remaining capacity of the battery, this method can effectively extend the service life of the battery, while improving the overall operation efficiency and reliability of the energy storage system.

[0104] S05: Adjust the output of the inverter according to the active power or reactive power output value, so as to maintain the voltage and frequency at the grid connection point within a preset first numerical range.

[0105] S06: If the working mode is the grid-following mode, calculate the power limit value of the inverter according to the remaining capacity of the current battery in the energy storage system and a preset formula.

[0106] As a preferred embodiment of Embodiment 1, the step of calculating the power limit value of the inverter according to the remaining capacity of the current battery in the energy storage system and a preset formula when the working mode is the grid-following mode is specifically: if the working mode is the grid-following mode, calculate the power limit value of the inverter according to the remaining capacity of the current battery, the preset output power of the battery, a preset capacity attenuation coefficient and a preset formula.

[0107] The calculation formula for the power limit value of the inverter is:

[0108] P max =μ×C set ×(1 - e -γ×SOC )

[0109] In the formula, P max is the power limit value of the inverter, μ is the measured converter efficiency, which is a measured value with a typical range of 95% - 98%, C set is the preset output power of the battery, γ is the preset capacity attenuation coefficient, which is fitted according to the cycle life curve provided by the battery manufacturer, with a typical value of 0.02, and SOC is the remaining capacity of the current battery.

[0110] In this preferred embodiment, in the grid-following mode, by considering the remaining capacity (SOC) of the current battery, the preset output power of the battery, the preset capacity attenuation coefficient and the measured converter efficiency, the power limit value of the inverter is calculated using a specific formula. This dynamic adjustment mechanism can optimize the charging and discharging power limits of the inverter in real time according to the actual remaining capacity of the battery and the system efficiency. This not only effectively avoids overcharging or over-discharging of the battery during the charging and discharging process, extends the service life of the battery, but also improves the flexibility and safety of the energy storage system during grid-connected operation, ensuring that the energy storage system can operate stably under different grid conditions, thereby enhancing the reliability and operating efficiency of the entire power system.

[0111] S07: Adjust the charging and discharging power of the battery according to the power limit value, so that the battery is charged or discharged within a preset second numerical value.

[0112] As a preferred embodiment of Embodiment 1, it further includes:

[0113] The remaining capacity and temperature of the battery in the energy storage system are monitored in real time, and low-capacity grading protection and overload protection are performed on the battery according to the monitoring results.

[0114] The low-capacity grading protection is specifically as follows:

[0115] Low-capacity grading protection:

[0116] First-level protection (SOC < 20%):

[0117] When SOC < 20%, the maximum output power of the battery is limited within the range of 50% of the rated power. That is: when SOC < 20%, the power output limit value < 0.5.

[0118] Second-level protection (SOC < 10%):

[0119] When SOC < 10%, the battery output is cut off after a delay. Delay cut-off time: adjustable from 1 to 300 s, default 30 s.

[0120] The overload protection is specifically as follows:

[0121] Short-term overload derating curve:

[0122]

[0123] Among them: τ: is the time constant, set according to the test results of the converter heat capacity to ensure that the junction temperature rise < 30 °C, default 30 s, and can be flexibly set according to user needs; P over : the maximum short-term overload power of the converter, default 1 M, and can be flexibly set according to user needs, P t : the instantaneous overload power of the converter.

[0124] In this preferred embodiment, the present application significantly improves the safety and service life of the battery by monitoring the remaining capacity (SOC) and temperature of the battery in the energy storage system in real time and implementing low-capacity grading protection and overload protection according to the monitoring results. Specifically, when the remaining capacity of the battery is lower than the preset first capacity threshold, the system will cut off the battery output after the preset first delay time to prevent the battery from over-discharging; when the remaining capacity is lower than the preset second capacity threshold, the system will limit the maximum output power of the battery within the preset second power range, thereby reducing its output power when the battery power is low and avoiding damage to the battery caused by over-discharging. In addition, based on the preset short-term overload derating curve, the system can dynamically adjust its instantaneous overload power according to the remaining capacity of the battery to ensure that the battery will not be damaged due to exceeding its tolerance in the case of overload. This fine protection strategy not only effectively avoids the potential risks of the battery in the low-power and overload states, but also improves the reliability and stability of the energy storage system under various operating conditions, providing a strong guarantee for the safe operation of the power system.

[0125] By obtaining the voltage and frequency information of the grid connection point, this application can monitor the grid status in real time and determine the working mode of the energy storage system accordingly. In the grid-forming mode, the voltage and frequency signals at the output end of the inverter are further obtained, and combined with the preset droop coefficient, the active power or reactive power output value of the grid connection point is dynamically calculated, so as to accurately adjust the output of the inverter and ensure that the voltage and frequency of the grid connection point are stable within the preset first numerical range. This dynamic adjustment mechanism effectively improves the voltage and frequency stability of the energy storage system during independent operation and enhances the system's independent regulation ability. In the grid-following mode, the power limit value is calculated based on the remaining capacity of the battery and a preset formula, and then the charging and discharging power of the battery is adjusted, so that the charging and discharging process of the battery is always within the preset second numerical range, effectively avoiding the phenomenon of overcharging or over-discharging of the battery, extending the service life of the battery, and improving the flexibility and safety of the energy storage system during grid-connected operation. In summary, through mode switching and dynamic regulation, this application significantly improves the operation efficiency and stability of the energy storage system, and effectively solves the problem that the prior art cannot accurately and efficiently control the energy storage system.

[0126] Embodiment 2

[0127] Please refer to Figure 4 , a control device for an energy storage system provided by an embodiment of this application.

[0128] In this embodiment, the control device of the energy storage system includes an acquisition module 10, a mode switching module 20, a grid-forming working mode module 30, and a grid-following working mode module 40.

[0129] As Figure 2 and Figure 3 shown, this application realizes the adaptive switching of the converter state through dynamic droop coefficient optimization and dynamic limiting algorithm, and constructs a complete battery protection strategy to improve the performance of the energy storage battery converter module.

[0130] The acquisition module 10 is used to acquire the voltage and frequency of the grid connection point.

[0131] The mode switching module 20 is used to determine the working mode of the energy storage system according to the voltage and frequency of the grid connection point.

[0132] As a preferred embodiment of Embodiment 2, the determining the working mode of the energy storage system according to the voltage and frequency of the grid connection point is specifically:

[0133] If the voltage of the grid connection point is within the preset rated voltage range and the deviation of the frequency is less than a preset first threshold within a preset time period, it is determined that the working mode is the grid-forming mode;

[0134] If the voltage at the grid connection point is lower than a preset lower limit value or the deviation of the frequency is greater than a preset second threshold within a preset time period, determine that the operating mode is the grid-following mode.

[0135] More specifically, the switching method is as follows:

[0136] Grid-forming → Grid-following: Grid voltage V grid ∈[0.95V N , 1.05V N and the frequency deviation Δf < 0.05 Hz lasts for 100 ms;

[0137] Grid-following → Grid-forming: V grid <0.8V N or Δf > 0.05 Hz lasts for 20 ms;

[0138] The deviation is the difference between the current actual frequency and the system rated frequency (e.g., the rated frequency in China is 50 Hz and the rated frequency in the United States is 60 Hz).

[0139] In this preferred embodiment, the present application determines the operating mode of the energy storage system by real-time monitoring of the voltage and frequency at the grid connection point and based on whether they are within a preset normal range. The present application realizes precise control of the operating state of the energy storage system. When the voltage and frequency deviations at the grid connection point meet specific conditions, the system automatically switches to the grid-forming mode or the grid-following mode, ensuring stable operation under different grid conditions. This mode switching mechanism not only improves the flexibility and adaptability of the energy storage system but also enhances the stability of the power grid, effectively avoiding operating abnormalities caused by grid fluctuations, thereby improving the reliability and operating efficiency of the entire power system.

[0140] The grid-forming operating mode module 30 is used to obtain the voltage and frequency signals at the output end of the inverter in the energy storage system if the operating mode is the grid-forming mode.

[0141] The grid-forming operating mode module 30 is also used to calculate the output value of the active power or reactive power at the grid connection point according to the voltage or frequency signal at the output end of the inverter and in combination with a preset droop coefficient.

[0142] As a preferred embodiment of the second embodiment, the calculating the output value of the active power or reactive power at the grid connection point according to the voltage or frequency signal at the output end of the inverter and in combination with a preset droop coefficient is specifically as follows:

[0143] Traditional generators in power systems all have a droop characteristic, that is, when the grid connection point frequency is higher than the rated frequency, traditional generators will reduce the active power output. When the grid connection point voltage is higher than the rated voltage, the reactive power output will be reduced.

[0144] The energy storage converter determines the system voltage stability by setting a strategy similar to that of a traditional motor in the converter. When the grid connection point voltage is detected to be higher than the rated voltage, the reactive power output is reduced. When the grid connection point voltage frequency is detected to be higher than the rated frequency, the active power output is reduced.

[0145] Calculate the reactive power of the grid connection point according to the voltage at the output end of the inverter, the preset reference voltage and reference reactive power, and according to the preset first droop coefficient.

[0146] Among them, the formula for calculating the reactive power of the grid connection point is:

[0147] Q = Q ref -k q ×(V - V ref )

[0148] In the formula, Q is the reactive power of the grid connection point, Q ref is the preset reference reactive power, V ref is the preset reference voltage, V is the voltage at the output end of the inverter, k q is the preset first droop coefficient, calculated according to the rated capacity S rated of the converter, k q is default set to 0.03 kVAR / V and can be flexibly set according to user requirements.

[0149] In this preferred embodiment, the present application accurately calculates the reactive power output value of the grid connection point by combining the voltage signal at the output end of the inverter with the preset reference voltage, reference reactive power and first droop coefficient. The present application can dynamically adjust the output of the inverter to maintain the stability of the grid connection point voltage. This reactive power regulation mechanism based on droop control enables the energy storage system to automatically and accurately provide or absorb reactive power when the grid voltage fluctuates, thereby effectively maintaining the grid connection point voltage within the preset range. This not only enhances the adaptability and response ability of the energy storage system to grid voltage changes, but also improves the voltage stability of the entire grid, reduces equipment failures and energy losses that may be caused by voltage fluctuations, and thus improves the overall operation efficiency and reliability of the power system.

[0150] The calculation of the active power or reactive power output value of the grid connection point according to the voltage or frequency signal at the output end of the inverter, combined with the preset droop coefficient, is specifically as follows:

[0151] Calculate the active power of the grid connection point according to the frequency signal at the output end of the inverter, the preset rated frequency and preset first power, and according to the droop coefficient adjusted based on the remaining capacity of the current battery and the remaining capacity of the current battery.

[0152] Among them, the formula for calculating the active power at the grid connection point is as follows:

[0153] P = P ref -k p (SOC)×(f - f ref )

[0154] In the formula, P is the active power at the grid connection point, P ref is the preset first power, f ref is the preset rated frequency, SOC is the remaining capacity of the current battery, and k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery.

[0155] The preset droop coefficient adjusted based on the remaining capacity of the current battery is specifically:

[0156] The calculation formula for the droop coefficient adjusted based on the remaining capacity of the current battery is:

[0157]

[0158] In the formula, k p (SOC) is the droop coefficient adjusted based on the remaining capacity of the current battery, β is the preset adjustment factor, and the default setting value is 0.2, which is used to balance the power response speed at different SOCs and can be flexibly set according to user requirements; SOC is the remaining capacity of the current battery, and k p0 is the preset second droop coefficient, that is, the reference droop coefficient, and the default setting is kW / 0.05Hz, which can be flexibly set according to user requirements.

[0159] This application accurately calculates the active power output value at the grid connection point by combining the frequency signal at the output end of the inverter, the preset rated frequency and the first power, and the droop coefficient adjusted based on the remaining capacity of the current battery. This application realizes the dynamic adjustment of the output power of the energy storage system. This dynamic adjustment mechanism can flexibly adjust the active power output of the energy storage system according to the actual state of the battery (such as the remaining capacity) and the real-time frequency change of the power grid. This not only improves the adaptability and response ability of the energy storage system to the power grid frequency change, but also ensures the stability of the grid connection point frequency under different working conditions. In addition, by considering the remaining capacity of the battery, this method can effectively extend the service life of the battery, while improving the overall operation efficiency and reliability of the energy storage system.

[0160] The grid-forming working mode module 30 is also used to adjust the output of the inverter according to the active power or reactive power output value, so as to maintain the voltage and frequency at the grid connection point within a preset first numerical range.

[0161] The follow - the - grid working mode module 40 is used to calculate the power limit value of the inverter according to the remaining capacity of the current battery in the energy storage system and a preset formula if the working mode is the follow - the - grid mode.

[0162] As a preferred embodiment of the second embodiment, the step of calculating the power limit value of the inverter according to the remaining capacity of the current battery in the energy storage system and a preset formula if the working mode is the follow - the - grid mode is specifically as follows: if the working mode is the follow - the - grid mode, calculate the power limit value of the inverter according to the remaining capacity of the current battery, the preset output power of the battery, the preset capacity attenuation coefficient and a preset formula.

[0163] The calculation formula for the power limit value of the inverter is:

[0164] P max =μ×C set ×(1 - e -γ×SOC )

[0165] In the formula, P max is the power limit value of the inverter, μ is the measured converter efficiency, which is an actual measured value, and the typical range is 95% - 98%, C set is the preset output power of the battery, γ is the preset capacity attenuation coefficient, which is fitted according to the cycle life curve provided by the battery manufacturer, and the typical value is 0.02, and SOC is the remaining capacity of the current battery.

[0166] In this preferred embodiment, in the follow - the - grid mode, by considering the remaining capacity (SOC) of the current battery, the preset output power of the battery, the preset capacity attenuation coefficient and the measured converter efficiency, the power limit value of the inverter is calculated using a specific formula. This dynamic adjustment mechanism can optimize the charging and discharging power limits of the inverter in real - time according to the actual remaining capacity of the battery and the system efficiency. This not only effectively avoids over - charging or over - discharging of the battery during the charging and discharging process, extends the service life of the battery, but also improves the flexibility and safety of the energy storage system during grid - connected operation, ensuring that the energy storage system can operate stably under different grid conditions, thereby enhancing the reliability and operation efficiency of the entire power system.

[0167] The follow - the - grid working mode module 40 is also used to adjust the charging and discharging power of the battery according to the power limit value, so that the battery is charged or discharged within a preset second value.

[0168] As a preferred embodiment of the second embodiment, it further includes:

[0169] The remaining capacity and temperature of the battery in the energy storage system are monitored in real - time, and low - capacity grading protection and overload protection are performed on the battery according to the monitoring results.

[0170] The low-capacity hierarchical protection is specifically as follows:

[0171] Low-capacity hierarchical protection:

[0172] Primary protection (SOC < 20%):

[0173] When SOC < 20%, the maximum output power of the battery is limited within the range of 50% of the rated power. That is: when SOC < 20%, the power output limit value < 0.5.

[0174] Secondary protection (SOC < 10%):

[0175] When SOC < 10%, the battery output is cut off with a time delay. The time delay for cutting off: adjustable from 1 - 300 s, default 30 s.

[0176] The overload protection is specifically as follows:

[0177] Short-time overload derating curve:

[0178]

[0179] Where: τ: is the time constant, set according to the test results of the converter heat capacity to ensure that the junction temperature rise < 30°C, default 30 s, and can be flexibly set according to user requirements; P over : the maximum short-time overload power of the converter, default 1 M, and can be flexibly set according to user requirements, P t : the instantaneous overload power of the converter.

[0180] In this preferred embodiment, the present application significantly improves the safety and service life of the battery by real-time monitoring of the remaining capacity (SOC) and temperature of the battery in the energy storage system and implementing low-capacity hierarchical protection and overload protection according to the monitoring results. Specifically, when the remaining capacity of the battery is lower than the preset first capacity threshold, the system will cut off the battery output after a preset first delay time to prevent the battery from over-discharging; when the remaining capacity is lower than the preset second capacity threshold, the system will limit the maximum output power of the battery within the preset second power range, thereby reducing its output power when the battery power is low and avoiding damage to the battery caused by over-discharging. In addition, based on the preset short-time overload derating curve, the system can dynamically adjust its instantaneous overload power according to the remaining capacity of the battery to ensure that the battery will not be damaged due to exceeding its tolerance in the case of overload. This fine protection strategy not only effectively avoids the potential risks of the battery in the low-power and overload states, but also improves the reliability and stability of the energy storage system under various operating conditions, providing a strong guarantee for the safe operation of the power system.

[0181] The device uses four modules to divide the work and coordinate with each other to control the energy storage system more accurately and efficiently. By obtaining the voltage and frequency information of the grid connection point, this application can monitor the grid status in real time and determine the working mode of the energy storage system accordingly. In the grid-forming mode, the voltage and frequency signals at the output end of the inverter are further obtained, and combined with the preset droop coefficient, the active power or reactive power output value of the grid connection point is dynamically calculated, so as to accurately adjust the output of the inverter and ensure that the voltage and frequency at the grid connection point are stable within the preset first numerical range. This dynamic adjustment mechanism effectively improves the voltage and frequency stability of the energy storage system during independent operation and enhances the system's independent regulation ability. In the grid-following mode, the power limit value is calculated based on the remaining capacity of the battery and a preset formula, and then the charging and discharging power of the battery is adjusted, so that the charging and discharging process of the battery is always within the preset second numerical range, effectively avoiding overcharging or over-discharging of the battery, extending the service life of the battery, and improving the flexibility and safety of the energy storage system during grid-connected operation. In summary, through mode switching and dynamic regulation, this application significantly improves the operation efficiency and stability of the energy storage system, and effectively solves the problem that the prior art cannot accurately and efficiently control the energy storage system.

[0182] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. In particular, for those skilled in the art, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A control method for an energy storage system, characterized in that: include: Obtain the voltage and frequency of the grid connection point; Determining the working mode of the energy storage system according to the voltage and frequency of the grid connection point; If the working mode is a grid-building mode, obtaining voltage and frequency signals at the output end of the inverter in the energy storage system; According to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, the output value of the active power or reactive power of the grid connection point is calculated; According to the active power or reactive power output value, adjust the output of the inverter so that the voltage and frequency of the grid connection point are maintained within a preset first value range; If the working mode is the grid-following mode, the power limit value of the inverter is calculated according to the remaining capacity of the current battery in the energy storage system and a preset formula; According to the power limit value, the charging and discharging power of the battery is adjusted so that the battery is charged or discharged within a preset second value.

2. The control method of the energy storage system according to claim 1, characterized in that: The operation mode of the energy storage system is determined according to the voltage and frequency of the grid connection point, specifically: If the voltage of the grid connection point is within a preset rated voltage range, and the frequency deviation is less than a preset first threshold value within a preset time period, determining that the working mode is a networking mode; If the voltage of the grid-connected point is lower than a preset lower limit or the frequency deviation is greater than a preset second threshold within a preset time period, it is determined that the working mode is a grid-following mode.

3. The control method of the energy storage system according to claim 1, characterized in that: The output value of active power or reactive power of the grid connection point is calculated based on the voltage or frequency signal at the output end of the inverter in combination with a preset droop coefficient, specifically: The reactive power of the grid connection point is calculated according to the voltage at the output end of the inverter, the preset reference voltage and the reference reactive power, and according to the preset first droop coefficient; The formula for calculating the reactive power of the grid connection point is: Q=Q ref -k q ×(V-V ref ) In the formula, Q is the reactive power of the grid connection point, Q ref is the preset reference reactive power, V ref is the preset reference voltage, V is the voltage at the output of the inverter, k q is the preset first droop coefficient.

4. The control method of the energy storage system according to claim 1, characterized in that: The output value of active power or reactive power of the grid connection point is calculated based on the voltage or frequency signal at the output end of the inverter in combination with a preset droop coefficient, specifically: The active power of the grid connection point is calculated according to the frequency signal of the output end of the inverter, the preset rated frequency and the preset first power, and according to the preset droop coefficient adjusted based on the current remaining capacity of the battery and the current remaining capacity of the battery; The formula for calculating the active power of the grid connection point is: P=P ref -k p (SOC)×(ff ref ) Where P is the active power of the grid connection point, P ref is the preset first power, f ref is the preset rated frequency, SOC is the current remaining capacity of the battery, k p (SOC) is the droop coefficient adjusted based on the current remaining capacity of the battery.

5. The control method of the energy storage system according to claim 4, characterized in that: The preset droop coefficient adjusted based on the current remaining capacity of the battery is specifically: The calculation formula of the droop coefficient adjusted based on the current remaining capacity of the battery is: In the formula, k p (SOC) is the droop coefficient adjusted based on the current remaining capacity of the battery, β is the preset adjustment factor, SOC is the current remaining capacity of the battery, k p0 is the preset second droop coefficient.

6. The control method of the energy storage system according to claim 1, characterized in that: If the working mode is the grid-following mode, the power limit value of the inverter is calculated according to the remaining capacity of the current battery in the energy storage system and a preset formula, which is specifically: If the working mode is the grid-following mode, the power limit value of the inverter is calculated according to the current remaining capacity of the battery, the preset output power of the battery, the preset capacity attenuation coefficient and the preset formula, The calculation formula of the power limit value of the inverter is: P max =μ×C set ×(1-e -γ×SOC ) Where P max is the power limit value of the inverter, μ is the measured converter efficiency, C set is the preset output power of the battery, γ is the preset capacity attenuation coefficient, and SOC is the current remaining capacity of the battery.

7. The control method of the energy storage system according to any one of claims 1 to 6, characterized in that: Also includes: The remaining capacity and temperature of the batteries in the energy storage system are monitored in real time, and the batteries are protected against low capacity and overload according to the monitoring results.

8. The control method of the energy storage system according to claim 7, characterized in that: The low-capacity graded protection of the battery according to the monitoring results is specifically as follows: If the remaining capacity of the current battery in the energy storage system is lower than a preset first capacity threshold, cutting off the battery output according to a preset first delay time; If the remaining capacity of the current battery in the energy storage system is lower than a preset second capacity threshold, the maximum output power of the battery is adjusted to be within a preset second power range.

9. The control method of the energy storage system according to claim 7, characterized in that: The overload protection of the battery according to the monitoring result is specifically as follows: The battery is protected from overload according to the preset short-term overload reduction curve and the remaining capacity of the current battery in the energy storage system; Wherein, the preset short-time overload load reduction curve is: Where τ is the preset time constant, P over is the maximum short-time overload power of the converter, P t is the instantaneous overload power of the converter, and t is the time.

10. A control device for an energy storage system, characterized in that: It includes an acquisition module, a mode switching module, a network building working mode module and a network following working mode module; The acquisition module is used to obtain the voltage and frequency of the grid connection point; The mode switching module is used to determine the working mode of the energy storage system according to the voltage and frequency of the grid connection point; The networking working mode module is used to obtain the voltage and frequency signals of the output end of the inverter in the energy storage system if the working mode is the networking mode; According to the voltage or frequency signal at the output end of the inverter, combined with a preset droop coefficient, the output value of the active power or reactive power of the grid connection point is calculated; According to the active power or reactive power output value, adjust the output of the inverter so that the voltage and frequency of the grid connection point are maintained within a preset first value range; The grid-following working mode module is used to calculate the power limit value of the inverter according to the remaining capacity of the battery in the current energy storage system and a preset formula if the working mode is the grid-following mode; According to the power limit value, the charging and discharging power of the battery is adjusted so that the battery is charged or discharged within a preset second value.

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