Energy storage virtual inertia calculation method and terminal based on frequency safety rise and fall time

Abstract

The present invention discloses a method and a terminal for calculating virtual inertia of energy storage based on frequency safety rise and fall time, establishes a frequency rise and fall time calculation model of a new energy grid-connected system containing energy storage, and calculates the frequency safety rise and fall time according to a system safety frequency threshold; calculates the virtual inertia size of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the charge state of the energy storage within the frequency safety rise and fall time; when a load disturbance occurs in the system and causes a frequency change, the present invention establishes a frequency rise and fall time calculation model for a new energy grid-connected system containing energy storage, thereby accurately calculating the frequency safety rise and fall time, and evaluating the virtual inertia size of the energy storage according to the change in the charge state of the energy storage within the obtained frequency safety rise and fall time, thereby better providing inertia support for the system.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation system control, and in particular to a method and terminal for calculating energy storage virtual inertia based on frequency safety rise and fall time. Background Art

[0002] With the continuous integration of various renewable energy sources, the proportion of traditional synchronous generators has continued to decline. This has led to a decrease in the system's inertia, reducing its ability to withstand frequency fluctuations and posing challenges to power system stability. Currently, many control strategies employ virtual inertia control for wind turbines, releasing rotor kinetic energy to provide a certain level of inertia support for the system. However, this control scheme conflicts with maximum power point tracking (MPPT) control and can also cause a secondary frequency drop during speed recovery, preventing maximum utilization of wind energy. Alternatively, energy storage can be configured for wind turbines. In theory, energy storage can provide inertia support for the system by storing and releasing stored energy, thereby reducing the rate of frequency fluctuation. Therefore, calculating the virtual inertia of energy storage during frequency fluctuations to better provide inertia support is a key issue in ensuring system frequency stability under high renewable energy penetration. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method and terminal for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time, which can calculate the size of the virtual inertia provided by the energy storage, thereby better providing inertia support for the system.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] The method for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time includes the following steps:

[0006] S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold;

[0007] S2. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time.

[0008] In order to solve the above technical problems, another technical solution adopted by the present invention is:

[0009] An energy storage virtual inertia calculation terminal based on frequency safety rise and fall time includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are implemented:

[0010] S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold;

[0011] S2. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time.

[0012] The beneficial effects of the present invention are as follows: the energy storage virtual inertia calculation method based on the frequency safety rise and fall time of the present invention establishes a frequency rise and fall time calculation model for the new energy grid-connected system containing energy storage based on the frequency response process of a high-penetration multi-machine system containing energy storage when the system undergoes a load disturbance and causes a frequency change. The frequency rise and fall time calculation model of the new energy grid-connected system containing energy storage is used to characterize the frequency response process of the entire system, thereby accurately calculating the frequency safety rise and fall time, and evaluating the size of the energy storage virtual inertia according to the change in the energy storage charge state within the obtained frequency safety rise and fall time, thereby better providing inertia support for the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Flowchart of a method for calculating energy storage virtual inertia based on frequency safety rise and fall time according to an embodiment of the present invention;

[0014] Figure 2 This is a structural diagram of an energy storage virtual inertia calculation terminal based on frequency safety rise and fall time according to an embodiment of the present invention;

[0015] Figure 3 Schematic diagram of frequency response curves at different wind power penetration rates according to a method for calculating virtual inertia of energy storage based on frequency safety rise and fall time according to an embodiment of the present invention;

[0016] Figure 4 A schematic diagram of the relationship between energy storage output power and state of charge in a method for calculating energy storage virtual inertia based on frequency safety rise and fall time according to an embodiment of the present invention;

[0017] Figure 5 A topological structure diagram of a three-machine system simulation according to a method for calculating virtual inertia of energy storage based on frequency safety rise and fall time according to an embodiment of the present invention;

[0018] Figure 6 Schematic diagram of simulation results of frequency response curves at different wind power penetration rates according to a method for calculating virtual inertia of energy storage based on frequency safety rise and fall time according to an embodiment of the present invention;

[0019] Figure 7 A schematic diagram of a frequency response curve of an energy storage virtual inertia calculation method based on frequency safety rise and fall time according to an embodiment of the present invention with or without additional virtual inertia control;

[0020] Figure 8 A schematic diagram of a curve showing a change in energy storage charge state according to a method for calculating energy storage virtual inertia based on frequency safety rise and fall time according to an embodiment of the present invention;

[0021] Figure 9 This is a block diagram of the primary frequency modulation transfer function of a new energy grid-connected system according to an embodiment of the present invention, using a method for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time.

[0022] Description of labels:

[0023] 1. Energy storage virtual inertia calculation terminal based on frequency safety rise and fall time; 2. Processor; 3. Memory. DETAILED DESCRIPTION

[0024] To illustrate the technical content, achieved objectives and effects of the present invention in detail, the following description is given in conjunction with the embodiments and accompanying drawings.

[0025] Please refer to Figure 1 as well as Figure 2 The method for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time includes the following steps:

[0026] S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold;

[0027] S2. Establish a relationship between the output power and state of charge of the energy storage, and calculate the change in the state of charge of the energy storage within the safe frequency rise and fall time;

[0028] S3. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time based on the definition of virtual inertia, the relationship, and the change in the state of charge of the energy storage within the frequency safety rise and fall time.

[0029] From the above description, it can be seen that the beneficial effects of the present invention are: the energy storage virtual inertia calculation method based on the frequency safety rise and fall time of the present invention establishes a frequency rise and fall time calculation model for the new energy grid-connected system containing energy storage based on the frequency response process of the high-penetration multi-machine system containing energy storage when the system undergoes a load disturbance and causes a frequency change. The frequency rise and fall time calculation model of the new energy grid-connected system containing energy storage is used to characterize the frequency response process of the entire system, thereby accurately calculating the frequency safety rise and fall time, and evaluating the size of the energy storage virtual inertia according to the change in the energy storage charge state within the obtained frequency safety rise and fall time, thereby better providing inertia support for the system.

[0030] Furthermore, the frequency rise and fall time calculation model in step S1 is specifically:

[0031] The frequency response dynamic equation of the system is:

[0032]

[0033] When the wind turbine is operating in the maximum power tracking state, its output power is affected by wind speed and has no response to changes in system frequency. The output power of the energy storage is affected by the state of charge and also has no response to changes in system frequency when no virtual inertia control is added. Simplifying the frequency response dynamic equation, the relationship between frequency deviation Δf and time t can be obtained:

[0034]

[0035] Among them, K S =K G +K L , assuming that the system experiences a load disturbance at time t = 0, the initial condition is:

[0036]

[0037] Then the analytical solution of Δf is:

[0038]

[0039] Where:

[0040]

[0041] Among them, K L is the system load frequency regulation effect coefficient, K G K is the generator power-frequency static characteristic coefficient, G =1 / R,T s is the system inertia time constant, T G is the generator primary frequency response coefficient, where T s =2H sys , ΔP L is the initial load disturbance of the system, ΔP G , ΔP wind , ΔP bess are the response powers of synchronous machine, wind turbine and energy storage respectively;

[0042] The calculation of the frequency safety rise and fall time according to the system safety frequency threshold is specifically as follows:

[0043] Substitute the system safety frequency threshold into Δf to calculate the frequency safety rise and fall time.

[0044] From the above description, it can be seen that the relationship between the frequency deviation and time during the system frequency increase or decrease process is established, and the frequency safety increase or decrease time is calculated by substituting the frequency safety threshold into the frequency deviation.

[0045] Furthermore, the step S2 is specifically as follows:

[0046] According to the definition of virtual inertia, the above relationship, and the change in the state of charge of the energy storage within the frequency safety rise and fall time, the virtual inertia of the energy storage during discharge is expressed as:

[0047]

[0048] The virtual inertia of the energy storage during charging is expressed as:

[0049]

[0050] Among them, ω e is the electrical angular velocity of the synchronous machine, Δω e is the change in electrical angular velocity of the synchronous machine, Δω e =2πΔf,p n is the number of pole pairs of the synchronous machine, J vir_B is the virtual inertia of the battery, J s is the moment of inertia of the synchronous generator with equal capacity, ΔSOC is the change in the state of charge of the battery during the frequency rise and fall time, SOC0 is the initial state of charge, SOC represents the current state of charge of the energy storage, E K It is the energy possessed by a synchronous generator of equal capacity.

[0051] From the above description, it can be seen that there are two cases: charging and discharging. Through the above formula, the virtual inertia of the energy storage is calculated according to the change in the state of charge.

[0052] Furthermore, the system inertia time constant T s The value is 2H sys , H sys The value range is 3-9s, and the system load regulation effect coefficient K L The value range of is 0-2, the value range of generator adjustment coefficient R is 0.04-0.1, and the value range of generator primary frequency response coefficient T g The value range is 0-3, the system initial load disturbance ΔP L The value is 0-10%.

[0053] It can be seen from the above description that the value ranges of some parameters are as above as a specific embodiment of the present invention.

[0054] Furthermore, the minimum value of the energy storage state of charge SOC min The value is 0.1, the smaller the value SOC low The value is 0.2, the larger value SOC high The value is 0.8, the maximum SOC maxThe value of is 0.9, the critical state of charge SOC1 when the output power starts to decrease from the rated power during the energy storage discharge process is 0.3, and the critical state of charge SOC2 when the output power starts to decrease from the rated power during the energy storage charging process is 0.7.

[0055] It can be seen from the above description that the values ​​of some partitions of SOC are as above as a specific embodiment of the present invention.

[0056] An energy storage virtual inertia calculation terminal based on frequency safety rise and fall time includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are implemented:

[0057] S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold;

[0058] S2. Establish a relationship between the output power and state of charge of the energy storage, and calculate the change in the state of charge of the energy storage within the safe frequency rise and fall time;

[0059] S3. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time based on the definition of virtual inertia, the relationship, and the change in the state of charge of the energy storage within the frequency safety rise and fall time.

[0060] From the above description, it can be seen that the beneficial effect of the present invention is that: when the system undergoes load disturbance and causes frequency change, the present invention establishes a frequency rise and fall time calculation model for the new energy grid-connected system containing energy storage based on the frequency response process of the high-penetration multi-machine system containing energy storage, and uses the frequency rise and fall time calculation model of the new energy grid-connected system containing energy storage to characterize the frequency response process of the entire system, thereby accurately calculating the frequency safety rise and fall time, and evaluating the size of the energy storage virtual inertia according to the change in the energy storage charge state within the obtained frequency safety rise and fall time, thereby better providing inertia support for the system.

[0061] Furthermore, the frequency rise and fall time calculation model in step S1 is specifically:

[0062] The frequency response dynamic equation of the system is:

[0063]

[0064] When the wind turbine is operating in the maximum power tracking state, its output power is affected by wind speed and has no response to changes in system frequency. The output power of the energy storage is affected by the state of charge and also has no response to changes in system frequency when no virtual inertia control is added. Simplifying the frequency response dynamic equation, the relationship between frequency deviation Δf and time t can be obtained:

[0065]

[0066] Among them, K S =K G +K L , assuming that the system experiences a load disturbance at time t = 0, the initial condition is:

[0067]

[0068] Then the analytical solution of Δf is:

[0069]

[0070] Where:

[0071]

[0072] Among them, K L is the system load frequency regulation effect coefficient, K G K is the generator power-frequency static characteristic coefficient, G =1 / R,T s is the system inertia time constant, T G is the generator primary frequency response coefficient, where T s =2H sys , ΔP L is the initial load disturbance of the system, ΔP G , ΔP wind , ΔP bess are the response powers of synchronous machine, wind turbine and energy storage respectively;

[0073] The calculation of the frequency safety rise and fall time according to the system safety frequency threshold is specifically as follows:

[0074] Substitute the system safety frequency threshold into Δf to calculate the frequency safety rise and fall time.

[0075] From the above description, it can be seen that the relationship between the frequency deviation and time during the system frequency increase or decrease process is established, and the frequency safety increase or decrease time is calculated by substituting the frequency safety threshold into the frequency deviation.

[0076] Furthermore, the step S2 is specifically as follows:

[0077] According to the definition of virtual inertia, the above relationship, and the change in the state of charge of the energy storage within the frequency safety rise and fall time, the virtual inertia of the energy storage during discharge is expressed as:

[0078]

[0079] The virtual inertia of the energy storage during charging is expressed as:

[0080]

[0081] Among them, ω e is the electrical angular velocity of the synchronous machine, Δω e is the change in electrical angular velocity of the synchronous machine, Δω e =2πΔf,p n is the number of pole pairs of the synchronous machine, J vir_B is the virtual inertia of the battery, J s is the moment of inertia of the synchronous generator with equal capacity, ΔSOC is the change in the state of charge of the battery during the frequency rise and fall time, SOC0 is the initial state of charge, SOC represents the current state of charge of the energy storage, E K It is the energy possessed by a synchronous generator of equal capacity.

[0082] From the above description, it can be seen that there are two situations: charging and discharging. Through the above formula, the virtual inertia of the energy storage is calculated according to the change in the state of charge.

[0083] Furthermore, the system inertia time constant T s The value is 2H sys , H sys The value range is 3-9s, and the system load regulation effect coefficient K L The value range of is 0-2, the value range of generator adjustment coefficient R is 0.04-0.1, and the value range of generator primary frequency response coefficient T g The value range is 0-3, the system initial load disturbance ΔP L The value is 0-10%.

[0084] It can be seen from the above description that the value ranges of some parameters are as above as a specific embodiment of the present invention.

[0085] Furthermore, the minimum value of the energy storage state of charge SOC min The value is 0.1, the smaller the value SOC low The value is 0.2, the larger value SOC high The value is 0.8, the maximum SOC max The value of is 0.9, the critical state of charge SOC1 when the output power starts to decrease from the rated power during the energy storage discharge process is 0.3, and the critical state of charge SOC2 when the output power starts to decrease from the rated power during the energy storage charging process is 0.7.

[0086] It can be seen from the above description that the values ​​of some partitions of SOC are as above as a specific embodiment of the present invention.

[0087] The energy storage virtual inertia calculation method based on frequency safety rise and fall time of the present invention is applicable to a scenario in which energy storage absorbs and stores / releases energy in a grid-connected power generation system to provide inertia support for the system.

[0088] Please refer to Figure 1 , embodiment 1 of the present invention is:

[0089] The method for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time includes the following steps:

[0090] S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold;

[0091] The frequency rise and fall time calculation model in step S1 is specifically:

[0092] The frequency response dynamic equation of the system is:

[0093]

[0094] When the wind turbine is operating in the maximum power tracking state, its output power is affected by wind speed and has no response to changes in system frequency. The output power of the energy storage is affected by the state of charge and also has no response to changes in system frequency when no virtual inertia control is added. Simplifying the frequency response dynamic equation, the relationship between frequency deviation Δf and time t can be obtained:

[0095]

[0096] Among them, K S =K G +K L , assuming that the system experiences a load disturbance at time t = 0, the initial condition is:

[0097]

[0098] Then the analytical solution of Δf is:

[0099]

[0100] Where:

[0101]

[0102] Among them, K L is the system load frequency regulation effect coefficient, K G K is the generator power-frequency static characteristic coefficient, G =1 / R,T s is the system inertia time constant, T G is the generator primary frequency response coefficient, where T s =2H sys , ΔP L is the initial load disturbance of the system, ΔP G , ΔP wind , ΔPbess are the response powers of synchronous machine, wind turbine and energy storage respectively;

[0103] The calculation of the frequency safety rise and fall time according to the system safety frequency threshold is specifically as follows:

[0104] Substitute the system safety frequency threshold into Δf to calculate the frequency safety rise and fall time.

[0105] S2. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time.

[0106] The step S2 is specifically as follows:

[0107] According to the definition of virtual inertia, the frequency safety ramp time, and the change in state of charge of the energy storage within the frequency safety ramp time, the virtual inertia of the energy storage during discharge is calculated as follows:

[0108]

[0109] The calculation of the virtual inertia of energy storage during charging is as follows:

[0110]

[0111] Among them, t is the frequency safety rise and fall time, ω e is the electrical angular velocity of the synchronous machine, Δω e is the change in electrical angular velocity of the synchronous machine, Δω e =2πΔf,p n is the number of pole pairs of the synchronous machine, J vir_B is the virtual inertia of the battery, J s is the moment of inertia of the synchronous generator with equal capacity, ΔSOC is the change in the state of charge of the battery during the frequency rise and fall time, SOC0 is the initial state of charge, SOC represents the current state of charge of the energy storage, E K is the energy of a synchronous generator of equal capacity, P rated Indicates the rated power during energy storage charging and discharging, SOC min , SOC low , SOC high and SOC max The SOCs represent the minimum, minimum, maximum, and maximum states of charge for the energy storage system, respectively. SOC1 and SOC2 represent the critical states of charge at which the output power begins to decrease from the rated power during the energy storage discharge and charging processes, respectively. Except for the safe frequency ramp time, all other parameters are known or obtained through measurement.

[0112] According to the calculated virtual inertia size of the energy storage within the frequency safety rise and fall time, the energy storage is further controlled by virtual inertia.

[0113] Please refer to Figure 3 and Figure 4 , the second embodiment of the present invention is:

[0114] The method for calculating the virtual inertia of energy storage based on the frequency safety rise and fall time includes the following steps:

[0115] Step 1: Analyze the system frequency characteristics after load disturbances and establish a frequency rise and fall time calculation model for the grid-connected system with energy storage and renewable energy.

[0116] Step 2: Calculate the time required for the frequency to rise and fall to the safety threshold based on the frequency rise and fall time calculation model for the grid-connected renewable energy system with energy storage.

[0117] Step 3: Obtain the relationship between energy storage output power and state of charge according to the energy storage operation status;

[0118] Step 4: During the frequency rise and fall period, calculate the change in energy storage energy based on the state of charge and output of the energy storage;

[0119] Step 5: Considering the state of charge and based on the definition of energy storage virtual inertia, estimate the virtual inertia of the energy storage during the frequency rise and fall period.

[0120] According to the frequency response process of the power system after being disturbed by load, a frequency response model of the new energy grid-connected system with energy storage is established, that is, a frequency rise and fall time calculation model of the new energy grid-connected system with energy storage. Figure 9 The frequency response model of a new energy grid-connected system with energy storage is a frequency response model of a multi-machine system that is aggregated into a frequency response model of a single synchronous generator through parameter aggregation. This model can calculate the frequency rise and fall time and transient frequency deviation extremes of the system during the frequency response process while ensuring a small error.

[0121] According to the frequency response model of the grid-connected renewable energy system with energy storage, the frequency response dynamic equation of the system can be obtained as shown below:

[0122]

[0123] Where K L is the system load frequency regulation effect coefficient, K G K is the generator power-frequency static characteristic coefficient, G =1 / R,T s is the system inertia time constant, T G is the generator primary frequency response coefficient, where T s =2H sys , ΔPL is the initial overload of the system. s The rest are per-unit values.

[0124] When the wind turbine is operating in maximum power tracking mode, its output power is affected by wind speed and does not respond to changes in system frequency. The output power of the energy storage is affected by the state of charge and is also unresponsive to changes in system frequency when virtual inertia control is not added. Simplifying the above equation, the relationship between frequency deviation Δf and time t is shown below:

[0125]

[0126] Where: K S =K G +K L , assuming that the system experiences a load disturbance at time t = 0, the initial condition is:

[0127]

[0128] Combining the above two equations, we can get the analytical solution of Δf:

[0129]

[0130] Where:

[0131]

[0132] From the above formula, we can see that the frequency deviation Δf is a function of time t. The moment when the derivative of Δf is 0 with respect to t is the moment corresponding to the extreme value of the transient frequency deviation. The moment t corresponding to the extreme value of the transient frequency deviation can be obtained by calculation. lim and the transient frequency deviation extreme value Δf lim As shown in formula (6):

[0133]

[0134] The values ​​of the parameters in the formula are shown in Table 1:

[0135] Table 1 System frequency response model parameter values

[0136]

[0137] As wind power penetration increases, the system's inertia time constant and equivalent regulation coefficient change proportionally, and the system's frequency response also changes accordingly. While the penetration rate is a known quantity and not directly involved in the calculation, its magnitude indirectly affects the magnitude of the system's inertia time constant, Hsys. Given a system disturbance of a 10% load surge, equations (5) and (6), along with the parameters in Table 1, yield the frequency drop time during the system's frequency response for different wind power penetration rates.

[0138] Figure 3 It is the frequency response curve of sudden load increase under different wind power penetration rates. The inertia time constant of the system decreases proportionally with the increase of wind power penetration rate, and the equivalent regulation coefficient of the system increases proportionally with the increase of wind power penetration rate. Figure 3 It can be seen that the impact of the increase in wind power penetration on the system frequency response process is that the system frequency drops faster and the transient frequency deviation extreme value becomes larger.

[0139] Therefore, the increase in wind power penetration will affect the system's ability to operate safely and stably. It is necessary to configure corresponding energy storage for wind turbines to provide virtual inertia support for the system and improve the system's inertia level.

[0140] The size of the virtual inertia of energy storage depends on the operating status of the energy storage, which is mainly reflected in the output power and charge state of the energy storage.

[0141] Figure 4 It shows the relationship between the output power and state of charge of energy storage. Figure 4 The relationship between the output power and state of charge of energy storage can be divided into two situations: discharging and charging.

[0142] When discharging:

[0143]

[0144] While charging:

[0145]

[0146] Where, P bess ,P rated Respectively represent the actual power and rated power during energy storage charging and discharging, SOC min , SOC low , SOC high , SOC max They represent the minimum, minimum, maximum, and maximum state of charge of the energy storage, respectively. SOC1 and SOC2 are the critical state of charge at which the output power begins to decrease from the rated power during the energy storage discharge and charging process. The values ​​of the various parameters are shown in Table 2:

[0147] Table 2 SOC partition values

[0148]

[0149] During the system frequency change, the battery energy can be expressed as:

[0150]

[0151] Where u B、i B are the voltage and current of the battery respectively, ω e is the electrical angular velocity of the synchronous machine, p n is the number of pole pairs of the synchronous machine, Q N is the rated capacity of the battery, J vir_B is the virtual inertia of the battery, which can be expressed as follows when discharging:

[0152]

[0153] When charging, it can be expressed as:

[0154]

[0155] Where J s is the moment of inertia of the synchronous generator with equal capacity, ΔSOC is the change in the state of charge of the battery during the frequency rise and fall time, SOC0 is the initial state of charge, E K = is the energy possessed by a synchronous generator of equal capacity. It can be seen that the battery's virtual inertia is related to its capacity and state of charge. If the rate of change of the battery's state of charge is much greater than the rate of change of the generator's speed, then through short-term energy regulation of the battery, a greater virtual moment of inertia than that of the synchronous generator can be generated.

[0156] Given frequency safety threshold Δf s =0.5Hz, calculate the frequency safety rise and fall time t according to steps 1 and 2 s Then, according to steps 3 and 4, the changes in battery energy and state of charge within the frequency safety rise and fall time are obtained. Finally, according to step 5, the virtual inertia of the battery can be calculated.

[0157] This invention provides a method for evaluating the virtual inertia of energy storage based on the frequency safety ramp time. First, an equivalent model of a grid-connected renewable energy system containing energy storage is established. The frequency safety ramp time is calculated through frequency response. During this time, the energy storage can provide a certain amount of virtual inertia support to the system by releasing its own energy, compensating for the insufficient system inertia support under high renewable energy penetration. Therefore, the virtual inertia of energy storage is defined, expressed in a manner analogous to that of wind turbines. The virtual inertia provided by the energy storage is then evaluated within the frequency safety ramp time to quantify its support capacity for the system.

[0158] Please refer to Figures 5 to 8 , the third embodiment of the present invention is:

[0159] A method for calculating the virtual inertia of energy storage based on the safe frequency rise and fall time adds virtual inertia control to the energy storage in the new energy system containing energy storage according to the calculated frequency rise and fall time, so that the energy storage can provide inertia support for the system through inertial response when the system load fluctuates. Figure 5 This is a three-machine system simulation topology diagram of the third embodiment of the present invention, as shown in FIG. Figure 5 The illustrated high-wind-power-penetration power system with energy storage includes an equivalent synchronous generator SG1, an equivalent synchronous generator SG2, a wind farm equipped with energy storage, a grid-connected converter, transformers T1, T2, T3, and T4, and a total system load L. The equivalent generator SG1 is connected to bus B4 via transformer T1, the equivalent generator SG2 is connected to bus B4 via transformer T4, the doubly-fed wind turbines are connected to bus B4 via the grid-connected converter and transformers T2 and T3, and the system load is directly connected to bus B4. When the system load changes, the energy storage system responds inertially based on the system frequency signal.

[0160] This example builds a three-machine simulation system for wind farm integration based on the DIGSILENT / Power Factory simulation platform. The simulation system includes two 900MVA synchronous generators and 600 2MW doubly-fed wind turbines (DFIGs). It is equipped with an energy storage system that accounts for 10% of the wind turbine capacity. The initial wind turbine penetration rate is 40%, and the number of wind turbines connected in parallel is adjustable. The wind turbine penetration rate is changed by changing the number of wind turbines and the capacity of the synchronous generators.

[0161] The following two control schemes are set up: control scheme 1 is used to verify the influence of system inertia on the frequency response process, and control scheme 2 is used to verify the effectiveness of the method proposed in this invention for evaluating the virtual inertia of energy storage within the frequency safety rise and fall time.

[0162] Control Scheme 1: Without virtual inertia control, the energy storage in the system changes the number of wind turbines in parallel and the capacity of the synchronous generator to change the penetration rate. The correctness of the frequency rise and fall time calculation method proposed in this invention is verified by observing the frequency response process.

[0163] Control Scheme 2: Energy storage in the system is supplemented with virtual inertia control to control the state of charge change within the frequency safety rise and fall time, verifying the correctness of the energy storage virtual inertia evaluation method based on the frequency safety rise and fall time proposed in this invention.

[0164] A system disturbance with a sudden load increase of 10% is set to occur at 3 seconds. Figure 6 This is the frequency response curve for the system in Control Scheme 1. As renewable energy penetration increases, the inertial time constant of the power system decreases and the equivalent regulation coefficient increases when energy storage does not respond inertially. This causes the system frequency to drop faster and the transient frequency deviation to increase during a sudden load increase. However, the time it takes for the frequency to drop to its lowest point remains almost unchanged. The simulation results are close to the calculated results, verifying the accuracy of the proposed method for calculating the safe frequency rise and fall times.

[0165] In control scheme 2, the frequency calculation model of the wind power grid-connected system established according to steps (1) and (2) shows that under a load disturbance of 10% and a wind power penetration rate of 40%, the system frequency drops to the safety threshold of 0.5Hz after 2.03s. Assuming that the rated capacity of the battery is 120MW×4s and the initial state of charge is SOC0=0.9, the battery is charged at the rated power P rated Discharge, the charge state change is ΔSOC = 0.5. According to the data, the moment of inertia of the synchronous generator with the same capacity is 8220kg*m 2 According to step (5), it can be calculated that the virtual inertia provided by the battery during the time when the system frequency drops to the safety threshold is 16.68Js.

[0166] Figure 7 The system frequency response curves before and after applying virtual inertia control to the energy storage system. Applying virtual inertia control reduces the rate of change of the system frequency, providing effective inertia support for the system. Simultaneously, due to the influence of the inertia support, the frequency recovery rate also decreases, but the steady-state frequency deviation remains unchanged, verifying the effectiveness of virtual inertia control for the energy storage system. Figure 8 The state of charge change curve of the energy storage can be seen from the curve. The initial state of charge of the energy storage SOC0 = 0.88, ΔSOC = 0.507. Therefore, according to formula (10), the virtual inertia provided by the energy storage during the frequency safety rise and fall time is calculated to be 17.29Js.

[0167] The simulation results verify the correctness of the proposed energy storage virtual inertia evaluation method based on frequency safety rise and fall time.

[0168] Please refer to Figure 2 , the fourth embodiment of the present invention is:

[0169] The energy storage virtual inertia calculation terminal 1 based on the frequency safety rise and fall time includes a processor 2, a memory 3, and a computer program stored in the memory 3 and executable on the processor 2. When the processor 2 executes the computer program, the steps of the energy storage virtual inertia calculation method based on the frequency safety rise and fall time of the above embodiments 1 to 3 are implemented.

[0170] In summary, the energy storage virtual inertia calculation method based on the frequency safety rise and fall time provided by the present invention, compared with the traditional method, the present invention establishes a new energy grid-connected system model containing energy storage based on the frequency response process of the system, and equates the inertial response of the new energy grid-connected system model containing energy storage and the primary frequency modulation process to a first-order inertial response link, obtains an equivalent transfer function block diagram of the frequency response process, and then calculates the time taken for the frequency to rise and fall to the safety threshold when the system is subjected to load disturbance based on the transfer function block diagram. The size of the virtual inertia of the energy storage is evaluated based on the change in the energy storage charge state during this time. The energy storage virtual inertia evaluation method based on the frequency safety rise and fall time provided by the present invention calculates the size of the energy storage virtual inertia by the change in the energy storage charge state during the frequency safety rise and fall time, quantifies the energy storage virtual inertia within the frequency time, and obtains the supporting capacity of the energy storage during the inertial response.

[0171] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for calculating virtual inertia of energy storage based on frequency safety rise and fall time, characterized in that: Includes steps: S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold; S2. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time; The frequency rise and fall time calculation model in step S1 is specifically: The frequency response dynamic equation of the system is: ； The wind turbine is running in the maximum power tracking state, and the output power is affected by the wind speed and has no response to the system frequency change. The output power of the energy storage is affected by the charge state and has no response to the system frequency change when no virtual inertia control is added. The frequency response dynamic equation is simplified to obtain the frequency deviation Δ f With time t The relationship is: ； in, K S = K G + K L , assuming that the system has a load disturbance at time t=0, the initial condition is: ； Then Δ f The analytical solution is: ； Where: ； in, K L is the system load frequency regulation effect coefficient, K G is the generator power-frequency static characteristic coefficient, K G =1 / R , T s is the system inertia time constant, T G is the generator primary frequency regulation response coefficient, where: T s = 2 H sys , Δ P L is the initial load disturbance of the system, Δ P G , Δ P wind , Δ P bess are the response powers of synchronous machine, fan and energy storage respectively; The calculation of the frequency safety rise and fall time according to the system safety frequency threshold is specifically as follows: Substitute the system safety frequency threshold into Δ f , calculate the frequency safety rise and fall time; The step S2 is specifically as follows: According to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time, the calculation of the virtual inertia of the energy storage during discharge is specifically as follows: ； The calculation of the virtual inertia of energy storage during charging is as follows: ； Among them, t is the frequency safety rise and fall time, ω e is the electrical angular velocity of the synchronous machine, Δ ω e is the change in electrical angular velocity of the synchronous machine, Δ ω e =2πΔ f , p n is the number of pole pairs of the synchronous machine, J vir_B is the virtual inertia of the battery, J s is the moment of inertia of synchronous generators of equal capacity, Δ SOC is the change in the battery's state of charge during the frequency rise and fall time, SOC 0 is the initial state of charge, SOC represents the current state of charge of the energy storage, E K is the energy of a synchronous generator of equal capacity, P rated Indicates the rated power during energy storage charging and discharging. SOC min , SOC low , SOC high and SOC max Respectively represent the minimum, minimum, maximum and maximum values ​​of the preset energy storage charge state, SOC 1 and SOC 2 are the critical charge states where the output power starts to decrease from the rated power during the energy storage discharge and charging processes.

2. The energy storage virtual inertia calculation method based on frequency safety rise and fall time according to claim 1 is characterized in that: System inertia time constant T s The value of is 2 H sys , H sys The value range is 3-9s, and the system load regulation effect coefficient K L The value range is 0-2, the generator adjustment coefficient R The value range is 0.04-0.1, and the generator primary frequency response coefficient T g The value range is 0-3, the system initial load disturbance Δ P L The value is 0-10%.

3. The energy storage virtual inertia calculation method based on frequency safety rise and fall time according to claim 1 is characterized in that: Minimum value of energy storage state of charge SOC min The value is 0.1, and the smaller value SOC low The value is 0.2, the larger value SOC high The value is 0.8, the maximum value SOC max The value is 0.9, which is the critical charge state where the output power starts to decrease from the rated power during the energy storage discharge process. SOC The value of 1 is 0.3, which is the critical charge state where the output power starts to decrease from the rated power during the energy storage charging process. SOC The value of 2 is 0.

7.

4. A terminal for calculating energy storage virtual inertia based on frequency safety rise and fall time, comprising a processor, a memory, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the following steps are implemented: S1. Establish a frequency rise and fall time calculation model for a new energy grid-connected system with energy storage, and calculate the frequency safety rise and fall time based on the system safety frequency threshold; S2. Calculate the virtual inertia of the energy storage within the frequency safety rise and fall time according to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time; The frequency rise and fall time calculation model in step S1 is specifically: The frequency response dynamic equation of the system is: ； The wind turbine is running in the maximum power tracking state, and the output power is affected by the wind speed and has no response to the system frequency change. The output power of the energy storage is affected by the charge state and has no response to the system frequency change when no virtual inertia control is added. The frequency response dynamic equation is simplified to obtain the frequency deviation Δ f With time t The relationship is: ； in, K S = K G + K L , assuming that the system has a load disturbance at time t=0, the initial condition is: ； Then Δ f The analytical solution is: ； Where: ； in, K L is the system load frequency regulation effect coefficient, K G is the generator power-frequency static characteristic coefficient, K G =1 / R , T s is the system inertia time constant, T G is the generator primary frequency regulation response coefficient, where: T s = 2 H sys , Δ P L is the initial load disturbance of the system, Δ P G , Δ P wind , Δ P bess are the response powers of synchronous machine, fan and energy storage respectively; The calculation of the frequency safety rise and fall time according to the system safety frequency threshold is specifically as follows: Substitute the system safety frequency threshold into Δ f , calculate the frequency safety rise and fall time; The step S2 is specifically as follows: According to the definition of virtual inertia, the frequency safety rise and fall time, and the change in the state of charge of the energy storage within the frequency safety rise and fall time, the calculation of the virtual inertia of the energy storage during discharge is specifically as follows: ； The calculation of the virtual inertia of energy storage during charging is as follows: ； Among them, t is the frequency safety rise and fall time, ω e is the electrical angular velocity of the synchronous machine, Δ ω e is the change in electrical angular velocity of the synchronous machine, Δ ω e =2πΔ f , p n is the number of pole pairs of the synchronous machine, J vir_B is the virtual inertia of the battery, J s is the moment of inertia of synchronous generators of equal capacity, Δ SOC is the change in the battery's state of charge during the frequency rise and fall time, SOC 0 is the initial state of charge, SOC represents the current state of charge of the energy storage, E K is the energy of a synchronous generator of equal capacity, P rated Indicates the rated power during energy storage charging and discharging. SOC min , SOC low , SOC high and SOC max Respectively represent the minimum, minimum, maximum and maximum values ​​of the preset energy storage charge state, SOC 1 and SOC 2 are the critical charge states where the output power starts to decrease from the rated power during the energy storage discharge and charging processes.

5. The energy storage virtual inertia calculation terminal based on frequency safety rise and fall time according to claim 4 is characterized in that: System inertia time constant T s The value of is 2 H sys , H sys The value range is 3-9s, and the system load regulation effect coefficient K L The value range is 0-2, the generator adjustment coefficient R The value range is 0.04-0.1, and the generator primary frequency response coefficient T g The value range is 0-3, the system initial load disturbance Δ P L The value is 0-10%.

6. The energy storage virtual inertia calculation terminal based on frequency safety rise and fall time according to claim 4 is characterized in that: Minimum value of energy storage state of charge SOC min The value is 0.1, and the smaller value SOC low The value is 0.2, the larger value SOC high The value is 0.8, the maximum value SOC max The value is 0.9, which is the critical charge state where the output power starts to decrease from the rated power during the energy storage discharge process. SOC The value of 1 is 0.3, which is the critical charge state where the output power starts to decrease from the rated power during the energy storage charging process. SOC The value of 2 is 0.7.

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