A low-frequency oscillation suppression method considering energy storage soc

Abstract

The present application belongs to the technical field of stability control of power system after new energy access, and particularly relates to a low-frequency oscillation suppression method considering energy storage SOC. The method comprises the following steps: a virtual synchronous generator control strategy is adopted for the energy storage inverter to simulate a synchronous generator to provide inertia and damping support for the system; on the basis of the energy storage inverter control strategy, an oscillation cycle is divided into four stages; according to the swing limit of the synchronous generator, the maximum change of the electromagnetic power output by the synchronous generator is calculated, and an energy storage inverter control strategy for suppressing low-frequency oscillation of the system is established; the capacity of the energy storage battery is calculated; and the power value that can be output by the energy storage battery under a certain state of charge is calculated. The present application verifies the suppression effect of a certain capacity of energy storage battery on the same small disturbance of the system under different SOC, improves the reliability and dynamic response effect of the energy storage for suppressing low-frequency oscillation of the system, and prolongs the service life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of stability control technology for systems after new energy sources are connected to the power system, and particularly relates to a method for suppressing low-frequency oscillations considering the state of energy storage (SOC). Background Technology

[0002] With the increase in installed capacity of new energy sources, the rotational inertia and damping of the power system are gradually decreasing, which poses certain risks to the stable control of the system. The intermittent nature of photovoltaic and wind power generation requires the configuration of corresponding energy storage systems to smooth and suppress the impact of power generation fluctuations on the power grid, but these systems cannot effectively improve the stability of the system itself when subjected to small disturbances. Energy storage batteries play an important role in the stable regulation and control of the power system.

[0003] Different control algorithms for energy storage converters have different effects on system stability. Simple droop control and virtual inertia control can provide a certain amount of inertia and damping support, but the control effect is limited. In addition, the power characteristics of the energy storage battery are not fully considered in the control strategy. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a low-frequency oscillation suppression method considering the state of charge (SOC) of the energy storage system. The purpose is to improve the reliability of the low-frequency oscillation suppression system, enhance dynamic response, and extend battery life.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A method for suppressing low-frequency oscillations considering the state of energy storage (SOC) includes:

[0007] Step 1. The energy storage inverter adopts a virtual synchronous generator control strategy to simulate a synchronous generator to provide inertia and damping support for the system;

[0008] Step 2. Based on the energy storage inverter control strategy, one oscillation cycle is divided into four stages;

[0009] Step 3. In the case of synchronous generator and energy storage operating in parallel, calculate the maximum change in electromagnetic power output by synchronous generator based on the power angle oscillation limit of synchronous generator, and establish a control strategy for energy storage inverter to suppress low-frequency oscillation of system.

[0010] Step 4. Calculate the capacity of the energy storage battery based on the energy storage inverter control strategy used to suppress low-frequency oscillations in the system;

[0011] Step 5. Based on the capacity of the energy storage battery, calculate the power output value of the energy storage battery under a certain state of charge, which is used to suppress low-frequency oscillations of the system.

[0012] Furthermore, the control strategy for the synchronous generator includes an active and reactive power control loop and a dual closed-loop control of output voltage and current.

[0013] The active power loop input signal is the real-time sampled value of the three-phase voltage and current output from the grid-connected energy storage inverter. The electromagnetic power is obtained through the instantaneous power calculation method, as shown in the following formula:

[0014]

[0015] The active power control loop simulates the rotor motion equation of a synchronous generator as follows:

[0016]

[0017] In the above formula, P and Q are the active and reactive power output values ​​of the energy storage inverter, respectively, and u a ,u b ,u c and i a i b i c These represent the output three-phase voltage and current values, respectively; J is the moment of inertia, and P... refM The reference value for the active power output of the energy storage is ω, where ω is the angular frequency. n Where ω is the rated angular frequency, δ is the power angle, and D is the damping coefficient.

[0018] The reactive power control adopts the reactive voltage droop control method, which synthesizes the output voltage vector based on the voltage phase output by the active power control loop and the voltage amplitude output by the reactive power loop.

[0019] The phase of the grid voltage is obtained by using a phase-locked loop. The collected three-phase voltage and the voltage vector synthesized by the active and reactive power loops are transformed into the voltage components of the dq axis of the synchronous rotating coordinate system through coordinate transformation. The reference value of the dq axis current of the output current loop is controlled by a PI controller.

[0020] The collected three-phase current is transformed by coordinates and then used as the modulation signal of the inverter by PI control, along with the current reference value output from the previous stage.

[0021] Furthermore, based on the energy storage inverter control strategy, one oscillation cycle is divided into four stages. According to the dynamic motion process of the synchronous generator during a small disturbance in the system, using the synchronous generator's state variables angular frequency and angular frequency acceleration as judgment conditions, and the steady-state operating point as the equilibrium point, one oscillation cycle is divided into four stages:

[0022] Phase 1: (P) m <P e ,ω>1,a ω <0);

[0023] Phase Two: (P) m <Pe ,ω<1,a ω <0);

[0024] Phase Two: (P) m >P e ,ω<1,a ω >0);

[0025] Phase Three: (P) m >P e ,ω>1,a ω >0);

[0026] Where P m P is the mechanical power of the synchronous generator. e For the electromagnetic power of the synchronous generator, a ω The acceleration is measured at angular frequency; the instantaneous values ​​of the angular frequency and angular velocity of the synchronous generator are collected to determine the stage of oscillation and adjust the active power reference value of the energy storage inverter.

[0027] The calculation method for the adjustment value of the active power reference value of the energy storage inverter is as follows:

[0028] ΔP refM =K P ω-1| (3)

[0029] Where: ΔP refM K represents the change in the active power reference value of the energy storage inverter. P K is the gain coefficient for power regulation; during the oscillation in the first and second stages, K P When K takes a negative value, the oscillation occurs in the third and fourth stages. P The value of is negative; the adjustment method for the rotational inertia J, a control parameter of the virtual synchronous generator of the energy storage inverter, is as follows: when K J When <|ω-1|, J takes the value J / 10, and when K J When J > |ω-1|, J remains constant, where K J This is the allowable threshold for angular frequency oscillation of a synchronous generator.

[0030] Furthermore, the criterion for determining that an oscillation cycle is divided into four stages is: combining the synchronous generator angular frequency to adaptively modify the active power reference value of the energy storage inverter, and modifying the virtual rotational inertia of the energy storage inverter to improve dynamic response capability.

[0031] Furthermore, the method for approximately calculating the maximum change in electromagnetic power output by the synchronous generator is as follows:

[0032]

[0033] Where: ΔP e maxLet E be the maximum change in electromagnetic power of the synchronous generator, E be the generator terminal voltage, U be the infinite bus voltage, and δ0 and δ1 be the maximum change in electromagnetic power of the synchronous generator. m These represent the power angle of the synchronous generator during steady-state operation and the maximum allowable value when the power angle of the synchronous generator oscillates, respectively.

[0034] Furthermore, the method for calculating the capacity of the energy storage battery is as follows:

[0035] The moment of inertia in the virtual synchronous generator control strategy of the energy storage inverter is calculated using the following formula:

[0036]

[0037] The required capacity of the energy storage battery is calculated using the following formula:

[0038]

[0039] Where: T is the inertial time constant of the virtual synchronous generator control strategy, C max S represents the maximum discharge rate of the energy storage battery. Battery This refers to the capacity of the energy storage battery.

[0040] Furthermore, based on the energy storage battery capacity, the power output value of the energy storage battery under a certain state of charge is calculated, and the dynamic characteristics of the energy storage battery are described using a 1-RCs dynamic model, with circuit parameters R0, R1, C1, and V. oc All are related to the state of charge (SOC) of the energy storage battery, and their relationship is fitted based on experimental measurement data of the energy storage battery.

[0041] The maximum discharge current of the energy storage battery is given by the following formula:

[0042]

[0043] The formula for calculating the discharge power of an energy storage battery is as follows:

[0044] P d max =V off ·I d max (8);

[0045] Where: R0, R1, C1 and V oc These are the internal resistance, polarization resistance, polarization capacitance, and open-circuit voltage of the energy storage battery, respectively. d max V is the maximum discharge current of the energy storage battery. off P is the discharge cutoff voltage of the energy storage battery. d max This refers to the maximum discharge power of the energy storage battery under a certain state of charge.

[0046] Based on the maximum change in electromagnetic power ΔP of the synchronous generatore max Energy storage battery capacity S Battery The fitting relationship between the experimental parameters of the 1-RCs dynamic model of the energy storage battery and the battery SOC was determined, and the state of charge of a certain capacity battery was determined when the virtual synchronous generator control strategy of the energy storage inverter was used to suppress the low-frequency oscillation of the system.

[0047] Furthermore, the energy storage inverter adopts a virtual synchronous generator control strategy, simulating a synchronous generator to provide inertia and damping support for the system. The parallel operation system of the synchronous generator and energy storage inverter consists of the #1 unit synchronous generator connected to line 1, and the #2 new energy storage system unit connected to the bus via filter inductor L and line 2, then connected to the 110kV power grid via line 3. The synchronous generator has a rated capacity of 60MVA, a terminal voltage of 10.5kV, an energy storage capacity of 1MW, and an output voltage of 220V, which is stepped up to 10.5kV by a transformer. After 5 seconds of system operation, a small disturbance is applied to the system to compare the suppression effect of the two energy storage battery charging states on the synchronous generator rotor angular frequency oscillation.

[0048] A computer device includes a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, wherein the processor, when executing the computer program, implements the steps of any of the methods for suppressing low-frequency oscillations in consideration of a storage-based system-of-charge (SOC).

[0049] A computer storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the steps of any of the methods for suppressing low-frequency oscillations in an energy storage SOC.

[0050] The present invention has the following beneficial effects and advantages:

[0051] This invention takes into account the state of charge of the energy storage battery, which can improve the reliability of the low-frequency oscillation suppression system. The energy storage inverter adopts an improved virtual synchronous generator control strategy, which can improve the dynamic response and extend the battery life by changing the output size instead of frequent charging and discharging.

[0052] This invention employs a virtual synchronous generator control strategy, fully considering the different relationships between the state of charge (SOC) and power characteristics of the energy storage battery during charging and discharging. Specifically, considering the SOC constraint of the energy storage battery, the control algorithm suppresses low-frequency oscillations caused by system power imbalance while providing sufficient rotational inertia and damping for the system. This invention can also be used for the inertia and damping allocation planning and design of multi-energy generating units and synchronous generator systems. Attached Figure Description

[0053] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0054] Figure 1 This is a diagram of the grid-connected operation system of the energy storage battery and synchronous generator of the present invention;

[0055] Figure 2 This is a comparison chart showing the effect of different states of charge of the energy storage battery of the present invention on the suppression of angular frequency oscillation of synchronous generator. Detailed Implementation

[0056] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0057] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0058] The following reference Figure 1 and Figure 2 The technical solutions of some embodiments of the present invention are described below.

[0059] Example 1

[0060] This invention provides an embodiment of a low-frequency oscillation suppression method considering the state of charge (SOC) of energy storage. Especially when distributed energy sources such as wind, solar, and energy storage are integrated into systems, the energy storage converter control strategy needs to fully consider the impact of the actual operating state of charge (SOC) of the energy storage battery on its power characteristics. This invention first employs a virtual synchronous generator control strategy in the energy storage inverter to simulate a synchronous generator providing inertia and damping support for the system. Second, it analyzes the phased mechanism of the synchronous generator within one oscillation cycle during a small disturbance in the system. Based on the oscillation suppression target, the active power reference value in the virtual synchronous generator control of the energy storage inverter is improved at different stages. The change in the active power reference value is calculated by multiplying the absolute value of the change in the synchronous generator's angular frequency by the gain coefficient of each stage. Referring to the rotational inertia of the virtual synchronous generator control parameters, the required energy storage battery capacity is obtained through the calculation method of the equivalent inertial time constant of the energy storage battery and the formula for calculating the energy storage battery capacity. Based on the dynamic model of the energy storage battery, the state of charge (SOC) of the energy storage battery corresponding to the instantaneous discharge power when the energy storage battery can meet the power oscillation suppression target is obtained. Based on a grid-connected system of the synchronous generator and energy storage battery, the suppression effect of a certain capacity energy storage battery on the same small disturbance in the system under different SOCs is verified.

[0061] like Figure 1 As shown, Figure 1This is a schematic diagram of the structure of the energy storage battery and synchronous generator grid-connected operation system of the present invention.

[0062] This invention proposes a control method for applying energy storage systems to high-proportion new energy power systems. This method provides inertia and damping to the system while suppressing the power angle oscillation of synchronous generators. The key focus is on providing a method for calculating the energy storage state of charge and battery capacity, specifically including the following steps:

[0063] Step 1. The energy storage inverter adopts a virtual synchronous generator control strategy to simulate a synchronous generator to provide inertia and damping support for the system. The control loop of the synchronous generator includes active and reactive power control loops and output voltage and current dual closed-loop control. First, the active loop needs to input the real-time sampled values ​​of the three-phase voltage and current output by the grid-connected energy storage inverter. The electromagnetic power is obtained by instantaneous power calculation method as shown in equation (1). The active control loop simulates the rotor motion equation of the synchronous generator as shown in equation (2). The reactive power control adopts the reactive voltage droop control method. The output voltage vector is synthesized based on the voltage phase output by the active control loop and the voltage amplitude output by the reactive power loop. Next, the phase-locked loop is used to obtain the grid voltage phase. Then, the collected three-phase voltage and the voltage vector synthesized by the active and reactive power loops are transformed into the dq axis voltage components of the synchronous rotating coordinate system through coordinate transformation. The dq axis current reference value of the output current loop is controlled by PI. Finally, the collected three-phase current is transformed by coordinate transformation and then controlled by PI to serve as the modulation signal of the inverter.

[0064]

[0065]

[0066] In the above formula, P and Q are the active and reactive power output values ​​of the energy storage inverter, respectively, and u a ,u b ,u c and i a i b i c These represent the output three-phase voltage and current values, respectively; J is the moment of inertia, and P... refM The reference value for the active power output of the energy storage is ω, where ω is the angular frequency. n δ is the rated angular frequency, δ is the power angle, and D is the damping coefficient.

[0067] Step 2. Based on the energy storage inverter control strategy in Step 1, and considering the dynamic motion of the synchronous generator during a small disturbance in the system, using the synchronous generator's state variables angular frequency and angular frequency acceleration as judgment conditions, and taking the steady-state operating point as the equilibrium point, one oscillation cycle is divided into four stages, namely:

[0068] Phase 1: (P) m <Pe ,ω>1,a ω <0);

[0069] Phase Two: (P) m <P e ,ω<1,a ω <0);

[0070] Phase Two: (P) m >P e ,ω<1,a ω >0);

[0071] Phase Three: (P) m >P e ,ω>1,a ω >0);

[0072] Where P m P is the mechanical power of the synchronous generator. e For the electromagnetic power of the synchronous generator, a ω The acceleration is the angular frequency. The instantaneous values ​​of the angular frequency and angular velocity of the synchronous generator are collected to determine the stage of oscillation, and then the active power reference value of the energy storage inverter is adjusted. The calculation method of the adjustment value of the active power reference value of the energy storage inverter is shown in the following formula (3);

[0073] ΔP refM =K P ω-1| (3)

[0074] Where: ΔP refM K represents the change in the active power reference value of the energy storage inverter. P K is the gain coefficient for power regulation; during the oscillation in the first and second stages, K P When K takes a negative value, the oscillation occurs in the third and fourth stages. P The value of is negative; the adjustment method for the rotational inertia J, a control parameter of the virtual synchronous generator of the energy storage inverter, is as follows: when K J When <|ω-1|, J takes the value J / 10, and when K J When J > |ω-1|, J remains constant, where K J This is the allowable threshold for angular frequency oscillation of a synchronous generator.

[0075] In step 2, based on the judgment criteria of four stages within one oscillation cycle, the active power reference value of the energy storage inverter is adaptively modified in combination with the synchronous generator angular frequency, and the virtual rotational inertia of the energy storage inverter is modified to improve the dynamic response capability.

[0076] Step 3. Based on Step 1 and Step 2, in the case of synchronous generator and energy storage operating in parallel, the maximum change in electromagnetic power output by synchronous generator is approximately calculated according to the power angle oscillation limit of synchronous generator, and an energy storage inverter control strategy for suppressing low-frequency oscillation of system is established.

[0077] The method for approximating the maximum change in electromagnetic power output by the synchronous generator is shown in the following formula (4);

[0078]

[0079] Where: ΔP e max Let E be the maximum change in electromagnetic power of the synchronous generator, E be the generator terminal voltage, U be the infinite bus voltage, and δ0 and δ1 be the maximum change in electromagnetic power of the synchronous generator. m These represent the power angle of the synchronous generator during steady-state operation and the maximum allowable value when the power angle of the synchronous generator oscillates, respectively.

[0080] Step 4. Based on the energy storage inverter control strategy established in Step 1 and Step 2 for suppressing low-frequency oscillations of the system, the capacity of the energy storage battery is calculated as follows: First, the moment of inertia in the virtual synchronous generator control strategy of the energy storage inverter is used to calculate the inertial time constant of the energy storage inverter, and the calculation formula is shown in Equation (5) below; then, the required capacity of the energy storage battery is calculated, and the calculation formula is shown in Equation (6).

[0081]

[0082]

[0083] Where: T is the inertial time constant of the virtual synchronous generator control strategy, C max S represents the maximum discharge rate of the energy storage battery. Battery This refers to the capacity of the energy storage battery.

[0084] Step 5. Based on the energy storage battery capacity determined in Step 4, describe the dynamic characteristics of the energy storage battery using a 1-RCs dynamic model, where the circuit parameters R0, R1, C1, and V... oc All are related to the state of charge (SOC) of the energy storage battery, and their relationship can be fitted based on the experimental measurement data of the energy storage battery; finally, the power value that the energy storage battery can output under a certain state of charge is calculated, that is, the state of charge of the energy storage battery is determined under the virtual synchronous generator control strategy of the energy storage inverter to suppress the low-frequency oscillation of the system. The maximum discharge current value of the energy storage battery is calculated as shown in the following formula (7); the discharge power of the energy storage battery is calculated as shown in the following formula (8).

[0085]

[0086] P d max =Voff ·I d max (8)

[0087] Where: R0, R1, C1 and V oc These are the internal resistance, polarization resistance, polarization capacitance, and open-circuit voltage of the energy storage battery, respectively. d max V is the maximum discharge current of the energy storage battery. off P is the discharge cutoff voltage of the energy storage battery. d max This represents the maximum discharge power of the energy storage battery under a certain state of charge.

[0088] Finally, based on the maximum change in electromagnetic power ΔP of the synchronous generator calculated in step 3... e max The energy storage battery capacity S calculated in step 4 Battery The fitting relationship between the experimental parameters of the 1-RCs dynamic model of the energy storage battery and the battery SOC was determined, and the conditions that the state of charge of a certain capacity battery needs to meet when the energy storage inverter adopts the virtual synchronous generator control strategy to suppress the low-frequency oscillation of the system were determined.

[0089] Step 5, by combining the correspondence between the dynamic circuit model parameters of the energy storage battery and the SOC, gives the maximum discharge power of the energy storage battery under a certain SOC. Therefore, the SOC setting value of the energy storage inverter for suppressing low-frequency oscillations under the improved virtual synchronous generator control strategy can be determined.

[0090] Example 2

[0091] The present invention provides another embodiment, which is a method for suppressing low-frequency oscillations considering energy storage SOC.

[0092] like Figure 1 As shown, Figure 1 This is a diagram illustrating the parallel operation system of a synchronous generator and an energy storage inverter as described in this invention. The #1 synchronous generator unit is connected to line 1, and the #2 new energy storage system unit is connected in parallel to line 2 via a filter inductor L, then to the bus, and finally connected to the 110kV power grid via line 3. The synchronous generator has a rated capacity of 60MVA and a terminal voltage of 10.5kV; the energy storage capacity is 1MW, and the output voltage is 220V, which is stepped up to 10.5kV by a transformer.

[0093] After 5 seconds of system operation, a small disturbance was applied to the system to compare the suppression effects of two different energy storage battery charging states on the rotor angular frequency oscillation of the synchronous generator. For example... Figure 2 As shown, Figure 2 This is a comparison diagram showing the effect of different states of charge (SOCs) of the energy storage battery of this invention on suppressing the angular frequency oscillation of the synchronous generator. The SOCs corresponding to the solid lines are greater than those corresponding to the dashed lines.

[0094] Example 3

[0095] Based on the same inventive concept, embodiments of the present invention also provide a computer device, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the computer program, it implements the steps of any of the low-frequency oscillation suppression methods for energy storage SOCs described in Embodiment 1 or 2.

[0096] Example 4

[0097] Based on the same inventive concept, embodiments of the present invention also provide a computer storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of any of the low-frequency oscillation suppression methods considering energy storage SOC described in Embodiment 1 or 2.

[0098] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0099] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0100] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0101] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0102] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for suppressing low-frequency oscillations considering the state of energy storage (SOC), characterized by comprising: Step 1. The energy storage inverter adopts a virtual synchronous generator control strategy to simulate a synchronous generator to provide inertia and damping support for the system; Step 2. Based on the energy storage inverter control strategy, one oscillation cycle is divided into four stages. According to the dynamic motion process of the synchronous generator during a small disturbance in the system, using the synchronous generator's state variables angular frequency and angular frequency acceleration as judgment conditions, and the steady-state operating point as the equilibrium point, one oscillation cycle is divided into four stages: Stage 1: Phase Two: Phase Two: Phase Three: ;in For the mechanical power of the synchronous generator, The electromagnetic power of the synchronous generator, The angular frequency is the acceleration; the instantaneous values ​​of the angular frequency and angular velocity of the synchronous generator are collected to determine the stage of oscillation and adjust the active power reference value of the energy storage inverter; the calculation method for the adjustment value of the active power reference value of the energy storage inverter is as follows: (3); where: This represents the change in the active power reference value of the energy storage inverter. The gain coefficient for power regulation; oscillations occur in the first and second stages. When the value is negative, the oscillation occurs in the third and fourth stages. The value of is negative; the adjustment method for the rotational inertia J, a control parameter of the virtual synchronous generator of the energy storage inverter, is as follows: when When J takes the value J / 10, At that time, J remains unchanged, where This is the allowable threshold for the angular frequency oscillation of a synchronous generator; Step 3. In the case of synchronous generator and energy storage operating in parallel, calculate the maximum change in electromagnetic power output by synchronous generator based on the power angle oscillation limit of synchronous generator, and establish a control strategy for energy storage inverter to suppress low-frequency oscillation of system. Step 4. Calculate the capacity of the energy storage battery based on the energy storage inverter control strategy used to suppress low-frequency oscillations in the system; Step 5. Based on the capacity of the energy storage battery, calculate the power output value of the energy storage battery under a certain state of charge, which is used to suppress low-frequency oscillations of the system.

2. The low-frequency oscillation suppression method considering energy storage SOC according to claim 1, characterized in that: The control strategy of the synchronous generator includes an active and reactive power control loop and a dual closed-loop control of output voltage and current. The active power loop input signal is the real-time sampled value of the three-phase voltage and current output from the grid-connected energy storage inverter. The electromagnetic power is obtained through the instantaneous power calculation method, as shown in the following formula: （1）； The active power control loop simulates the rotor motion equation of a synchronous generator as follows: （2） In the above formula, These represent the active and reactive power outputs of the energy storage inverter, respectively. and These represent the output three-phase voltage and current values, respectively; J is the moment of inertia. This is a reference value for the active power output of energy storage. Angular frequency, The rated angular frequency, For power angle, The damping coefficient; The reactive power control adopts the reactive voltage droop control method, which synthesizes the output voltage vector based on the voltage phase output by the active power control loop and the voltage amplitude output by the reactive power loop. The phase of the grid voltage is obtained by using a phase-locked loop. The collected three-phase voltage and the voltage vector synthesized by the active and reactive power loops are transformed into the voltage components of the dq axis of the synchronous rotating coordinate system through coordinate transformation. The reference value of the dq axis current of the output current loop is controlled by a PI controller. The collected three-phase current is transformed by coordinates and then used as the modulation signal of the inverter by PI control, along with the current reference value output from the previous stage.

3. The low-frequency oscillation suppression method considering energy storage SOC according to claim 1, characterized in that: The criterion for determining that an oscillation cycle is divided into four stages is: adaptively modifying the active power reference value of the energy storage inverter in conjunction with the synchronous generator angular frequency, and modifying the virtual rotational inertia of the energy storage inverter to improve dynamic response capability.

4. The low-frequency oscillation suppression method considering energy storage SOC according to claim 2, characterized in that: The method for calculating the maximum change in electromagnetic power output by the synchronous generator is as follows: （4） in: This represents the maximum change in the electromagnetic power of the synchronous generator. U is the terminal voltage of the synchronous generator, and U is the infinite bus voltage. , These represent the power angle of the synchronous generator during steady-state operation and the maximum allowable value when the power angle of the synchronous generator oscillates, respectively.

5. A method for suppressing low-frequency oscillations considering energy storage SOC according to claim 4, characterized in that: The method for calculating the capacity of the energy storage battery is as follows: The moment of inertia in the virtual synchronous generator control strategy of the energy storage inverter is calculated using the following formula: （5）； The required capacity of the energy storage battery is calculated using the following formula: （6） Where: T is the inertial time constant of the virtual synchronous generator control strategy. This represents the maximum discharge rate of the energy storage battery. This refers to the capacity of the energy storage battery.

6. The low-frequency oscillation suppression method considering energy storage SOC according to claim 1, characterized in that: Based on the energy storage battery capacity, the power output value of the energy storage battery under a certain state of charge is calculated, and the dynamic characteristics of the energy storage battery are described using a 1-RCs dynamic model, including circuit parameters. , , and All are related to the state of charge (SOC) of the energy storage battery, and their relationship is fitted based on experimental measurement data of the energy storage battery. The maximum discharge current of the energy storage battery is given by the following formula: （7）； The formula for calculating the discharge power of an energy storage battery is as follows: （8）； in: , , and These are the internal resistance, polarization resistance, polarization capacitance, and open-circuit voltage of the energy storage battery. This is the maximum discharge current of the energy storage battery. This is the discharge cutoff voltage of the energy storage battery. This refers to the maximum discharge power of the energy storage battery under a certain state of charge. Based on the maximum change in electromagnetic power of the synchronous generator Energy storage battery capacity The fitting relationship between the experimental parameters of the 1-RCs dynamic model of the energy storage battery and the battery SOC was determined, and the state of charge of a certain capacity battery was determined when the virtual synchronous generator control strategy of the energy storage inverter was used to suppress the low-frequency oscillation of the system.

7. The low-frequency oscillation suppression method considering energy storage SOC according to claim 1, characterized in that: The energy storage inverter adopts a virtual synchronous generator control strategy, simulating a synchronous generator to provide inertia and damping support for the system. The parallel operation system of the synchronous generator and energy storage inverter consists of the #1 unit synchronous generator connected to line 1, and the #2 new energy storage system unit connected to the bus via filter inductor L and line 2, then connected to the 110kV power grid via line 3. The synchronous generator has a rated capacity of 60MVA, a terminal voltage of 10.5kV, an energy storage capacity of 1MW, and an output voltage of 220V, which is stepped up to 10.5kV by a transformer. After 5 seconds of system operation, a small disturbance is applied to the system to compare the suppression effect of two different energy storage battery charging states on the synchronous generator rotor angular frequency oscillation.

8. A computer device, comprising a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of a low-frequency oscillation suppression method considering an energy storage SOC as described in any one of claims 1-7.

9. A computer storage medium, characterized in that: The computer storage medium contains a computer program, which, when executed by a processor, implements the steps of a low-frequency oscillation suppression method considering an energy storage SOC as described in any one of claims 1-7.

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