Network-constructed energy storage transient stability optimization control method and system considering reactive power degradation

Abstract

The application discloses a network-constructed energy storage transient stability optimization control method and system considering reactive power degradation, and belongs to the field of power system transient stability control. The method constructs a network-constructed energy storage grid-connected system model, analyzes the reactive power degradation effect caused by the dynamic of the reactive power control loop, and establishes an active loop optimization control equation accordingly. On this basis, an adaptive torque adjustment module is embedded in the active control module, when the internal voltage of the inverter is monitored to be reduced to 50% of the rated value, the reference torque is automatically dynamically corrected to improve the power angle transient stability margin of the system. The simulation results show that the method can effectively suppress the power angle instability of the network-constructed energy storage, significantly enhance the transient stability of the system, and guarantee the safe and reliable operation of the power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system transient stability control, in particular to a network-forming energy storage transient stability optimization control method and system considering reactive power degradation. BACKGROUND

[0002] With the high proportion of new energy power generation equipment connected to the power grid and the formation of the power system, the key role of network-forming energy storage devices in maintaining the dynamic stability of the power system is increasingly prominent. However, traditional network-forming energy storage has significant challenges in transient synchronous stability. For example, in the fault state of the network-forming energy storage system, the internal voltage drop of the inverter caused by the reactive power regulation mechanism will exacerbate the imbalance between active power supply and demand, significantly weakening the transient stability margin of the system. However, traditional methods rely on idealized network models or single control dimensions, and do not fully consider the negative effects of the reactive power control loop on transient characteristics. Therefore, a new network-forming energy storage control method is needed that takes into account the degradation effects of network-forming energy storage reactive power control.

[0003] Currently, there is little research on the degradation effects of the reactive power control loop of network-forming energy storage systems. Patent CN119171479A provides a control method for network-forming energy storage systems based on virtual inertia and virtual damping, which can reduce the demand for energy storage, active power oscillation, and control frequency oscillation. Patent CN118432136A proposes a network-forming energy storage frequency control method suitable for weak grids, which builds a frequency and power cascade control structure for frequency regulation and power distribution control, improving the dynamic characteristics of the system and improving the power quality of new power systems. As can be seen, there is a lack of research on the degradation effects of the reactive power control loop of network-forming energy storage systems in existing technology. Therefore, a method is needed that takes into account the degradation effects of the reactive power control loop on network-forming energy storage transient stability control. SUMMARY

[0004] To address the shortcomings of the prior art, the present application aims to provide a network-forming energy storage transient stability optimization control method and system that considers reactive power degradation. This method embeds an adaptive torque adjustment module in the active power control loop of traditional network-forming energy storage control under the premise of considering the degradation effects of the reactive power control loop of network-forming energy storage systems, dynamically correcting the reference torque to ensure the stability of the power angle during system faults and improve the transient stability of network-forming energy storage systems.

[0005] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows:

[0006] In a first aspect, the present application provides a network-forming energy storage transient stability optimization control method that considers reactive power degradation effects. The method specifically includes the following steps:

[0007] S1: Modeling of grid-connected system of network-constructed energy storage power station.

[0008] According to the actual grid parameters, the grid-connected system model is constructed, which contains active power control module, governor module, reactive power control module, virtual impedance control module, abc / dq coordinate transformation module, double closed-loop control module, dq / abc coordinate transformation module, PWM module, DC power supply, three-phase full-bridge inverter circuit, filter inductor, filter capacitor, the sum of transformer equivalent inductance and line inductance, the sum of equivalent resistance, and the grid-connected system model of AC power grid.

[0009] Based on the analysis of system dynamic characteristics by multi-time scale decomposition and singular perturbation theory: the voltage and current double closed-loop control system is equivalent to an ideal transfer link, so that the output voltage amplitude and phase of the inverter are approximately equal to the control command value; the fast changing state variables of inductor current and capacitor voltage in LC filter link are ignored, and the algebraic expressions of system output active power P e , reactive power Q e , swing equation of network-constructed control, and mathematical equation of reactive control loop are derived.

[0010]

[0011] In the formula: G = R s / ( R s 2 + X s 2 ), B =- X s / ( R s 2 + X s 2 ), R s +j X s =( R g + R v )+j( X g + X v ), R g is the line resistance, R v is the virtual resistance, Xg is the reactance corresponding to the line inductance, X v is the reactance corresponding to the virtual inductance; V g is the phase angle of the grid voltage (with the grid voltage phase angle as the reference phase angle), E is the amplitude of the internal voltage of the inverter, and the grid voltage phase angle is set according to the setting convention of the grid synchronous coordinate system V g is regarded as the reference phase angle, and the power angle δ is regarded as the internal voltage of the inverter E and the phase angle difference between the grid-side voltage V g satisfies the following mathematical expression:

[0012]

[0013] In the formula: ω 0 is the rated synchronous angular velocity of the grid, ω 1 is the angular velocity of the grid-connected energy storage system of the grid-forming type.

[0014] The swing equation of the grid-forming control is:

[0015]

[0016] In the formula: J v1 is the virtual inertia; D v1 is the virtual damping coefficient; T em is the output torque, which can be calculated by T em P e ω 0, the reference active power P ref is generated by the speed regulator, and the calculation method is as follows:

[0017]

[0018] In combination, the following can be obtained:

[0019]

[0020] In the formula: D p D v1 K f ω 0, D p is the equivalent damping; T 0=​​​​​P 0 / ω 0.

[0021] The mathematical equation of the reactive power control loop is:

[0022]

[0023] In the formula: K =1 / K i , K i is the voltage integral coefficient; D q is Q - V the droop coefficient; E 0, Q 0respectively the reference voltage and the reference reactive power.

[0024] S2: Analysis of reactive power degradation effect and establishment of active power loop optimization control equation.

[0025] The derivative equation of the internal voltage of the inverter E is converted into a quasi-steady-state equation, and the network-forming control model obtained in step S1 is simplified into the form of "second-order derivative equation + quasi-steady-state equation".

[0026] Taking E as a parameter variable, the derivative equation of the internal voltage of the inverter E can be converted into a quasi-steady-state equation. The network-forming control model in formula (4)-(6) is simplified into a second-order derivative equation plus a quasi-steady-state equation, as shown below:

[0027]

[0028] The transient equivalent circuit (including the equivalent circuit without considering reactive power control and the equivalent circuit considering reactive power control) of the network-forming energy storage grid-connected and the active power P power angle δ curve diagram are constructed, and the coordinate translation improvement method is adopted to make the power angle related equation satisfy the odd function characteristics, so as to accurately analyze the transient power angle problem.

[0029] The improved method of coordinate translation is adopted, so that formula (9) is an odd function:

[0030]

[0031] In the formula: δ t = δ + - π / 2 , Z s and These are the line impedance and the impedance angle, respectively.

[0032] Combining transient equivalent circuit and P - δ Curve analysis of reactive power degradation effect: During grid faults, the voltage difference between grid-connected energy storage and the grid voltage causes a sudden increase in its output reactive power, and the internal voltage of the inverter... E Reduce; after the fault is cleared, E Unable to recover immediately, making P - δ maximum value of the curve P max The reduction in size leads to an increase in the acceleration zone area during a fault and a decrease in the deceleration zone area after the fault is cleared, which may result in a decrease in the maximum power angle. δ max Exceeding the unstable equilibrium point δ u This can lead to transient instability of the work angle.

[0033] Based on the quasi-steady-state equation, a reference torque characterizing the fault is established. T ref With internal voltage E The active power control optimization equation for the relationship:

[0034]

[0035] In the formula: δ t0 The initial power angle, V g1 This represents the grid-side voltage after the fault.

[0036] S3: Optimization of the active power control module.

[0037] An adaptive torque regulation module is embedded in the active power control module of the grid-type energy storage system. This module has two operating states: "optimization control not started" and "optimization control started".

[0038] Optimized control not started: reference torque T ref Reference active power output by the speed controller P ref After 1 / ω Generate by 0 operation; T ref With actual electromagnetic torque T e The deviation values ​​are input sequentially into the equivalent damping. D p Components (simulating system damping characteristics to suppress power oscillations), virtual inertia J v1Integral element (simulating the inertia of the rotor of the analog synchronous generator, delaying the rate of change of frequency), 1 / S integral element, and finally the phase angle of the grid-connected energy storage θ g participate in the power angle stability control.

[0039] Optimized control start state: when the internal voltage of the inverter is monitored to be reduced to 50% of the rated value, this state is started. First, the difference between the reference voltage E 0 and the grid-side voltage V g is adjusted by a proportional element, and then added to the difference between the reference reactive power V 0 and the actual reactive power K v , and the obtained signal is accumulated and operated by a voltage integral element, and then added to the reference voltage Q 0 to generate the internal voltage Q e ; subsequently, the initial power angle K i is calculated by substituting E and the real-time monitored post-fault grid-side voltage E g1 into the active power expression of step S1; then, the corrected reference torque E V t0 is obtained by substituting δ t0 , δ g1 , E ref into the active control optimization equation; the subsequent signal processing process is consistent with the "optimized control non-start state", and the initial power angle is stabilized and the power angle out-of-step is suppressed by dynamically correcting V ref . T T e

[0040] In a second aspect, the present application provides a grid-connected energy storage transient stability optimization control system considering the effect of reactive power degradation. The system comprises a grid-connected system modeling module, a reactive power degradation analysis and optimization equation construction module, and an active control optimization module, and the functions of each module are as follows:

[0041] Grid-connected system modeling module: according to the actual grid parameters, a grid-connected energy storage power station grid-connected system model is constructed, based on multi-time scale decomposition and singular perturbation theory, the voltage and current double closed loop control system is equivalent to an ideal transfer element, the fast changing state quantity in the LC filter link is ignored, and the system output active power P e , reactive power Q e ​​The algebraic expression of the control, as well as the swing equation of the network control and the mathematical equation of the reactive power control loop.

[0042] Reactive power degradation analysis and optimization equation construction module: This module constructs the inverter's internal voltage... E The derivative equation is transformed into a quasi-steady-state equation, simplifying the network control model; through transient equivalent circuit and P - δ The curve analysis shows the deteriorating effect of the reactive power control loop on transient angular stability (the area of ​​the acceleration zone increases during a fault, and the area of ​​the deceleration zone decreases after the fault is cleared). The coordinate translation improvement method is used to handle the power angle correlation equation, and the active power control optimization equation is established based on the quasi-steady-state equation.

[0043] Active power control optimization module: Includes an adaptive torque regulation unit for real-time monitoring of the inverter's internal voltage. E ;when E When the power output drops to 50% of the rated value, optimized control is initiated, based on the active power control optimization equation and combined with real-time monitoring. E Voltage on the grid side after the fault V g1 Calculate the initial power angle δ t0 and dynamically correct the reference torque. T ref This improves the system's transient stability margin.

[0044] Thirdly, this invention provides a transient stability optimization control method for grid-connected energy storage that considers reactive power degradation effects, or an application of the aforementioned transient stability optimization control system for grid-connected energy storage that considers reactive power degradation effects in power systems with a high proportion of renewable energy integration. This method is used to address the transient power angle instability problem caused by three-phase short-circuit faults in the power grid during the operation of grid-connected energy storage in the power system, enabling online monitoring and optimized regulation of the power system, enhancing the transient stability of the grid-connected energy storage system, and thus improving the overall reliability of the power system.

[0045] Advantages and beneficial effects of the present invention:

[0046] The application is aimed at the transient power angle instability problem caused by the dynamic of reactive power control loop during the power grid fault, fully considers the influence of the reactive power control loop on the transient angle stability, and proposes a method for optimizing the active control module of the traditional grid-forming energy storage control, through real-time monitoring of the voltage after the grid side fault and the internal voltage of the inverter, when the internal voltage of the inverter is reduced to half of the rated value, the optimized control is started to dynamically reduce the reference torque of the system, so as to improve the transient stability margin of the power angle, thereby achieving the purpose of improving the transient stability of the grid-forming energy storage system. The scheme is suitable for online monitoring and optimal regulation and control of the power system, can effectively enhance the transient stability of the grid-forming energy storage system, thereby improving the overall reliability and stability of the power system, and building a strong protection for the safe operation of the power grid. Specifically:

[0047] 1. The application first considers the deterioration effect of the reactive power control loop of the grid-forming energy storage system, breaks through the limitation of the traditional control method which relies on idealized model and ignores the negative influence of reactive power control on transient characteristics, and accurately captures the transient power angle instability risk caused by the internal voltage drop of the inverter during the fault.

[0048] 2. The application embeds an adaptive torque adjustment module in the active control module, takes the internal voltage of the inverter E = 50% of the rated value as the starting threshold, and dynamically corrects the reference torque T ref , which can effectively suppress the power angle instability during the transient period and significantly improve the transient stability margin of the grid-forming energy storage system.

[0049] 3. MATLAB / Simulink simulation verification: in the scenario of three-phase short-circuit fault of the power grid (the voltage on the grid side is reduced to 20% of the rated value, and the fault is cleared), the internal voltage of the system using the control method of the application can gradually recover to the steady state before the fault, and the power angle returns to the steady state value before the fault within 13s; while the internal voltage of the system using the traditional control method oscillates and loses stability, and the power angle seriously loses step.

[0050] 4. The application is suitable for online monitoring and optimal regulation and control of the power system, can effectively enhance the transient stability of the grid-forming energy storage in the power system with high proportion of new energy access, and further improve the overall reliability of the power system, thereby providing protection for the safe operation of the power grid. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a grid-connected topology structure diagram of the grid-forming energy storage power station;

[0052] Figure 2 is an equivalent circuit diagram of grid-connected grid-forming energy storage;

[0053] Figure 3 is a power angle diagram of the grid-forming energy storage during the transient period; P -δ Graphs;

[0054] Figure 4 is the optimization control block diagram of the grid-connected energy storage transient stability of the application;

[0055] Figure 5 is the simulation voltage waveform diagram of the grid-connected energy storage system;

[0056] Figure 6 is the simulation power angle waveform diagram of the grid-connected energy storage system.

[0057] In the figure: 1, active power control module; 2, speed regulator module; 3, reactive power control module; 4, virtual impedance control module; 5, abc / dq coordinate transformation; 6, double closed-loop control; dq / abc coordinate transformation; 8, PWM module; 9, DC power supply; 10, three-phase full-bridge inverter circuit; 11, filter inductance; 12, filter capacitance; 13, the sum of transformer equivalent inductance and line inductance; 14, the sum of equivalent resistance; 15, AC power grid. DETAILED DESCRIPTION

[0058] The technical solutions of the application will be further described in detail below in combination with the drawings and specific embodiments.

[0059] It should be noted that the embodiments described herein are only used to illustrate the core idea of the application and do not constitute any limitation on the protection scope of the application.

[0060] Embodiment 1

[0061] The grid-connected energy storage transient stability optimization control method and system considering reactive power degradation proposed by the application are specifically divided into the following three steps:

[0062] Step S1: According to the actual power grid situation, the grid-connected energy storage power station system modeling is carried out.

[0063] Figure 1 is the grid-connected topology structure diagram of the grid-connected energy storage system of the application. The grid-connected energy storage system is composed of the following modules: active power control module 1, speed regulator module 2, reactive power control module 3, virtual impedance control module 4, abc / dq coordinate transformation 5, double closed-loop control 6, dq / abc coordinate transformation 7, PWM module 8, DC power supply 9, three-phase full-bridge inverter circuit 10, filter inductance 11, filter capacitance 12, the sum of transformer equivalent inductance and line inductance 13, the sum of equivalent resistance 14, AC power grid 15.

[0064] In the study of the dynamic characteristics of the above-mentioned grid-connected system model of the network-structured energy storage power station, an analysis method based on multi-time scale decomposition and singular perturbation theory is used, that is, in the analysis of the slow dynamic process of the system, the fast-changing state variables are considered to have converged to the quasi-steady state. Therefore, the voltage and current double-loop control system of the model can be equivalent to an ideal transfer link, so that the amplitude and phase of the inverter output voltage are approximately equal to the control command value. At the same time, by ignoring the fast-changing state variables of the inductance current and the capacitance voltage in the LC filter link, the active power P e and reactive power Q e output by the system can be represented by algebraic equations as follows:

[0065]

[0066] wherein: G = R s / ( R s 2 + X s 2 ), B =- X s / ( R s 2 + X s 2 ), R s +j X s =( R g + R v )+j( X g + X v )。According to the setting convention of the grid synchronous coordinate system, the phase angle of the grid voltage V g is regarded as the reference phase angle, and the power angle δ is regarded as the phase angle difference between the internal voltage E of the inverter and the grid-side voltage V g , which satisfies the following mathematical expression:

[0067]

[0068] wherein: ω 0 is the rated synchronous angular velocity of the grid, ω 1 is the angular velocity of the network-structured energy storage grid-connected system.

[0069] The swing equation of the network-constructing type control is:

[0070]

[0071] In the formula: J v1 is the virtual inertia; D v1 is the virtual damping coefficient; T em is the output torque, which can be calculated by T em = P e / ω 0, the reference active power P ref is generated by the speed governor, and the calculation method is as follows:

[0072]

[0073] In combination, the following can be obtained:

[0074]

[0075] In the formula: D p = D v1 + K f / ω 0, D p is the equivalent damping; T 0= P 0 / ω 0.

[0076] The mathematical equation of the reactive power control loop is:

[0077]

[0078] In the formula: K =1 / K i , K i is the voltage integral coefficient; D q is the Q - V droop coefficient; E 0, Q 0 are the reference voltage and the reference reactive power respectively.

[0079] Step S2: analyze the reactive power degradation effect of the network-constructing type energy storage and establish the active loop optimization control equation.

[0080] As the parameter variable, the derivative equation of the inverter internal voltage E can be transformed into the quasi-steady-state equation. The grid-forming control model in equations (4)-(6) is simplified into a second-order derivative equation plus a quasi-steady-state equation, as shown below: E

[0081]

[0082] In order to study the transient characteristics of the grid-forming energy storage system and construct the active power control optimization equation, equation (7) needs to be further processed to obtain equation (9). In the transient state, the grid-forming converter can be represented by a voltage source to establish the transient equivalent circuit of the system. As shown in Figure 2 , where Figure 2 (a) is the grid-connected equivalent circuit without considering reactive power control, Figure 2 (b) is the grid-connected equivalent circuit considering the influence of the reactive power control loop, V g is the grid phase voltage amplitude, Z is the equivalent line impedance. At the same time, the active power P -power angle δ curve needs to be constructed to analyze the transient power angle problem in the distribution network, as shown in Figure 3 , where Figure 3 (a) is the P - δ curve with constant inverter internal voltage, Figure 3 (b) is the P - δ curve considering the influence of the reactive power control loop. Because the resistance in the distribution network cannot be ignored, otherwise it will lead to the active power no longer being an odd function of the power angle. Therefore, the improved method of coordinate translation is adopted here, so that equation (9) is an odd function:

[0083]

[0084] In the formula: δ t = δ + - π / 2 , Z s and are the line impedance and impedance angle, respectively.

[0085] Based on the coordinate translation, Figure 2 (a) the relationship between the active power P and the power angle δ of the model is shown in Figure 3 (a). Curve I is the P - δ relationship before and after the fault, and curve II is the​P - δ The curve has a stable equilibrium point. δ s and unstable equilibrium points δ u The Extended Equal Area Criterion (EEAC) can intuitively explain the transient angular stability criterion: before the fault, the system... δ s During operation, if a fault occurs, the operating point jumps to curve II, causing an imbalance in active power. δ Acceleration; at the critical work angle δ c Clear the fault and return the running point to curve I. δ slow down. δ max Given the maximum power angle after the fault, and ignoring damping losses, the transient angular stability criterion is calculated based on the acceleration area S1 equaling the deceleration area S2. δ max < δ u .

[0086] When considering the impact of reactive power control loops, use Figure 2 (b) shows the equivalent circuit of grid-connected energy storage. Due to the voltage amplitude difference between the grid-connected energy storage and the grid, a ground fault causes a sudden increase in reactive power output from the grid-connected energy storage, and the internal voltage of the inverter... E Reduced. After the fault is cleared, E Unable to recover immediately, making P - δ Maximum values ​​of curves I and II P max1 and P max2 They will be reduced to P max1 and P max2 This results in an increased acceleration zone area during fault detection and a decreased deceleration zone area after fault clearance. This could lead to a decrease in the maximum power angle within the same fault clearance time. δ max Greater than δ u This is known as the degradation effect of the reactive power control loop on transient angular stability. Therefore, it is essential to consider the degradation effect of the reactive power control loop when controlling grid-type energy storage systems.

[0087] Internal voltage E After the derivative equation can be regarded as the quasi-steady-state equation, it can be seen from equations (8) and (9) that the reference torque after the fault is T ref With internal voltage E The relationship between them can be described by equation (10), which is the active power control optimization equation of this invention:

[0088]

[0089] In the formula: δ t0 The initial power angle, V g1 This represents the grid-side voltage after the fault.

[0090] Step S3: Optimize the active power control module of the grid-type energy storage system using the control method of the present invention.

[0091] Figure 4 This is a block diagram for optimizing the transient stability of grid-type energy storage according to the present invention. The operations included in this block diagram are as follows: Operation one is 1 / ω 0, Operation 2 is the damping coefficient D p In the third step, the calculation is for virtual inertia. J v1 The integration stage, operation four is the integration stage of 1 / S, operation five is... K v The proportional step, the operation of six is K i The voltage integral stage is used to calculate the optimized control stage of formula (10).

[0092] The optimization control module aims to achieve the same steady-state operating point as before the fault. This module operates in two states: optimization control not started (state 1) and optimization control started (state 2). State 2 occurs when the system detects the internal voltage of the inverter. E Start when the torque is reduced to half of the rated value. In state 1, the reference torque... T ref The speed controller will set the reference active power. P ref The input is fed into the active power optimization control module to generate the first calculation. Then the reference torque is... T ref With actual electromagnetic torque T e The difference is calculated, and the deviation value is introduced into the second calculation stage. This stage is used to simulate the system's damping characteristics and suppress power oscillations during transient processes. The processed signal is then input to the third calculation stage, where virtual inertia is used to simulate the inertial characteristics of the synchronous generator rotor, thus slowing down the rate of change of the system frequency. Finally, the phase angle of the grid-type energy storage is obtained through the fourth integration calculation. θ g It participates in the power angle stability control of the system.

[0093] The optimized control module, in state 2, reference torque T ref The control method consists of the following two steps:

[0094] Step 1: The reactive power control module will use the reference voltage. V 0 and grid-side voltage V g The difference, after adjustment by calculation five, is compared with the reference reactive power. Q 0 and actual reactive power Q e The differences are added together, and the resulting signal is used for a six-integration operation. The integrated output signal is then compared with the reference voltage. E The zeros are added together to generate the internal voltage. E .

[0095] Step 2: The reactive power control module controls the internal voltage of the inverter. E The input is given to the computational optimization control module, first setting the internal voltage... E and measured grid-side voltage after fault V g1 Substituting into equation (10), the initial power angle is calculated. δ t0 Then calculate the result δ t0 and known E , V g1 Substituting into the following equation (10), the reference torque can be obtained. T ref In State 2 mode, the subsequent operation of the active power optimization control module is the same as in State 1.

[0096] As can be seen from the above analysis, when the optimization control module is in state 2, the reference torque is adjusted using the above method. T ref Real-time adjustments are made to ensure the stability of the initial power angle of the system, thereby achieving the optimized control objective, suppressing the power angle loss phenomenon, solving the transient power angle stability problem of grid-type control, and improving the transient stability of grid-type energy storage control power systems.

[0097] This invention optimizes the active power control loop of traditional grid-type energy storage control by considering the influence of the reactive power control loop, using a dynamic torque optimization method. When the system detects that the inverter's internal voltage drops to 50% of its rated value, the optimized control of this invention reduces the input reference torque to suppress the risk of power angle instability during transient periods, thereby improving the transient power angle stability of the grid-type control. A grid-type energy storage control system connected to an infinite three-phase voltage source was established as the research system in MATLAB / Simulink simulation. For the three-phase short-circuit fault scenario, the grid-side voltage... V gAt 10s, the voltage is reduced to 20% of the rated value, and the system is set to clear the fault at 10.3s. At the same time, the internal voltage of the inverter under permanent fault of the system is monitored in real time E At 10s, the voltage is reduced to 20% of the rated value, and the system is set to clear the fault at 10.3s. At the same time, the internal voltage of the inverter under permanent fault of the system is monitored in real time E When the internal voltage of the inverter is reduced to half of the rated value, the optimized control link of the application is enabled to reduce the input reference torque. The internal voltage and the fault power angle of the grid-forming energy storage system are monitored. The simulation results are shown in Figure 5 and Figure 6 , wherein Figure 5 is the fault internal voltage waveform, Figure 6 is the fault power angle waveform. In Figure 5 , it can be seen that when the grid-forming energy storage system uses the traditional control method, the fault internal voltage will oscillate and become unstable after the fault is cleared. When the system uses the optimized control method of the application, the internal voltage of the system will gradually return to the steady state before the fault after the system fault is cleared at 10.3s. The fault power angle waveform is shown in Figure 6 , when the grid-forming energy storage system uses the traditional control method, the power angle will have a serious instability phenomenon. However, when the optimized control method of the application is used, the power angle of the system will return to the steady state value of the power angle before the fault at 13s. From the simulation, it can be seen that the optimization effect of the optimized control method of the application is remarkable.

Claims

1. A transient stability optimization control method for grid-type energy storage considering reactive power degradation effects, characterized in that: Includes the following steps: S1: Based on actual grid parameters, construct a grid-connected system model for a grid-connected energy storage power station. This model includes an active power control module, a speed governor module, a reactive power control module, a virtual impedance control module, a coordinate transformation module, a dual-loop control module, a PWM module, a DC power supply, a three-phase full-bridge inverter circuit, filter components, and equivalent grid components. Based on multi-timescale decomposition and singular perturbation theory, the voltage and current dual-loop control system in the grid-connected system model is equivalent to an ideal transmission link. Ignoring rapidly changing state variables in the LC filter link, the system output active power is derived. P e reactive power Q e The algebraic expressions of the network control system and the swing equation and mathematical equation of the reactive power control loop; S2: Analyze the reactive power degradation effect of grid-type energy storage, transforming the derivative equation of the inverter's internal voltage E into a quasi-steady-state equation; simplify the grid-type control model obtained in step S1, employing a coordinate translation improvement method to handle the power angle-related equations, and combining the transient equivalent circuit with... P - δ The influence of the reactive power control loop on transient angular stability is analyzed using curve analysis. Based on the quasi-steady-state equation, an active power control optimization equation is established, which characterizes the reference torque after a fault. T ref Relationship with internal voltage E; S3: Embed an adaptive torque regulation module in the active power control module of the grid-type energy storage system: The adaptive torque regulation module has two states: optimized control not started and started. When the inverter internal voltage E is detected to drop to 50% of the rated value, the optimized control state is started. Based on the active power control optimization equation obtained in step S2, combined with the real-time monitoring of the internal voltage... E Voltage on the grid side after the fault V g1 Calculate the initial power angle δ t0 And dynamically correct the reference torque T ref This helps to suppress power angle instability during transient periods.

2. The transient stability optimization control method for grid-type energy storage considering reactive power degradation effect according to claim 1, characterized in that: In step S1, the active power P e reactive power Q e The algebraic expression satisfies: In the formula: G = R s / ( R s 2 + X s 2 ), B =- X s / ( R s 2 + X s 2 ), R s +j X s =( R g + R v )+j( X g + X v ), R g For line resistance, R v For virtual resistance, X g The reactance corresponding to the line inductance. X v The reactance corresponding to the virtual inductance; V g The voltage amplitude of the power grid. E This refers to the internal voltage amplitude of the inverter. δ For the angle of attack, and δ =∠ E -∠ V g ,∠ E The internal voltage phase angle of the inverter, ∠ V g Phase angle of grid voltage; power angle δ Considered as the internal voltage of the inverter E With grid-side voltage V g The phase angle difference satisfies the following mathematical expression: In the formula: ω 0 represents the rated synchronous angular velocity of the power grid. ω 1 represents the angular velocity of the grid-connected energy storage system.

3. The transient stability optimization control method for grid-type energy storage considering reactive power degradation effect according to claim 2, characterized in that: In step S1, the swing equation of the network control satisfies: In the formula: J v1 This is virtual inertia; D v1 This is the virtual damping coefficient; T em For output torque, T ref For reference torque T em = P e / ω 0 calculation, reference active power P ref Generated by the speed controller, its calculation method is as follows: Combining these, we get: In the formula: D p = D v1 + K f / ω 0, D p For equivalent damping; T 0= P 0 / ω 0.

4. The transient stability optimization control method for grid-type energy storage considering reactive power degradation effect according to claim 3, characterized in that: In step S1, the mathematical equation of the reactive power control loop satisfies: In the formula: K =1 / K i , K i The voltage integral coefficient; D q for Q - V Sag coefficient; E 0、 Q 0 represents the reference voltage and reference reactive power, respectively.

5. The transient stability optimization control method for grid-type energy storage considering reactive power degradation effect according to claim 4, characterized in that: In step S2, the improved coordinate translation method defines... δ t = δ + - π / 2 , Z s and Let the line impedance and impedance angle be the line impedance and the impedance angle, respectively, so that the power angle related equation satisfies the odd function property: Will E As a parameter variable, the internal voltage of the inverter E The derivative equation is transformed into a quasi-steady-state equation; the network control model in equations (4)-(6) is simplified to a second-order derivative equation plus a quasi-steady-state equation, as shown below: Further processing of formula (7) yields formula (9); an improved method of coordinate translation is adopted, making formula (9) an odd function: In the formula: δ t = δ + - π / 2 , Z s and These are the line impedance and the impedance angle, respectively.

6. The transient stability optimization control method for grid-type energy storage considering reactive power degradation effect according to claim 5, characterized in that: The adaptive torque regulation module in step S3 includes two operating states: optimization control not started and optimization control started. The specific control method is as follows: Reference torque when optimized control is not activated T ref Reference active power output by the speed controller P ref After 1 / ω Generation of the 0-stage calculation; the reference torque T ref With actual electromagnetic torque T e The deviation value is successively passed through the equivalent damping. D p Links, virtual inertia J v1 After processing by the integration stage and the 1 / S integration operation stage, the phase angle of the grid-type energy storage is obtained. θ g ; In optimized control startup mode, the startup condition is that the system detects the internal voltage of the inverter. E Reduced to 50% of its rated value; in this state, the reactive power control module first generates the inverter's internal voltage. E The internal voltage of the inverter E Voltage on the grid side after the fault V g1 Substitute into the calculation to obtain the initial power angle δ t0 ; Then the initial power angle δ t0 Inverter internal voltage E and grid-side voltage after fault V g1 Substituting into the active power control optimization equation, the corrected reference torque is calculated. T ref The subsequent correction reference torque T ref With actual electromagnetic torque T e The process for handling deviation values ​​is the same as that for when optimization control is not activated, and it is achieved through dynamic correction. T ref To ensure initial power angle stability and suppress power angle loss of synchronization; in the active power control optimization equation, the reference torque T ref The value is determined by the initial power angle. δ t0 Inverter internal voltage E and grid-side voltage after fault V g1 It was jointly determined that, among which δ t0 The initial power angle, V g1 This refers to the voltage on the grid side after the fault. The active power control optimization equation is as follows: In the formula: δ t0 The initial power angle, V g1 This represents the grid-side voltage after the fault.

7. A grid-type energy storage transient stability optimization control system considering reactive power degradation effects, characterized in that: It includes a grid-connected system modeling module, a reactive power degradation analysis and optimization equation construction module, and an active power control optimization module; The grid-connected system modeling module is used to construct a grid-connected system model of the grid-connected energy storage power station based on actual grid parameters and derive the system's output active power. P e reactive power Q e The algebraic expressions of the network control system and the swing equation and mathematical equation of the reactive power control loop; The reactive power degradation analysis and optimization equation construction module is used to analyze the reactive power degradation effect of grid-type energy storage, simplify the grid-type control model, and establish active power control optimization equations. The active power control optimization module includes an adaptive torque regulation unit for monitoring the internal voltage of the inverter. E ,when E When the torque drops to 50% of its rated value, the reference torque is dynamically corrected based on the active power control optimization equation. T ref This improves the system's transient stability margin. The control system is implemented by any one of the control methods described in claims 1 to 6, wherein the grid-connected system modeling module performs the modeling and derivation process of step S1 in claim 1, the reactive power degradation analysis and optimization equation construction module performs the degradation analysis and equation establishment process of step S2 in claim 1, and the active power control optimization module performs the adaptive torque adjustment process of step S3 in claim 1. The three modules are sequentially advanced and interconnected, forming a closed-loop optimization system of "modeling-analysis-control" to improve the stability of the grid-type energy storage system under transient conditions.

8. The grid-type energy storage transient stability optimization control system considering reactive power degradation effect according to claim 7, characterized in that: The grid-connected system modeling module is based on multi-timescale decomposition and singular perturbation theory. It equates the voltage and current dual closed-loop control system in the grid-connected system model to an ideal transmission link and ignores the rapidly changing state variables in the LC filtering link.

9. The grid-type energy storage transient stability optimization control system considering reactive power degradation effect according to claim 8, characterized in that: The reactive power degradation analysis and optimization equation construction module uses transient equivalent circuits and... P - δ The curves are used to analyze the deterioration effect of the reactive power control loop on transient angular stability. The deterioration effect is manifested as an increase in the acceleration zone area during a fault and a decrease in the deceleration zone area after the fault is cleared.

10. The application of the grid-type energy storage transient stability optimization control method considering reactive power degradation effect as described in any one of claims 1-6, or the grid-type energy storage transient stability optimization control system considering reactive power degradation effect as described in any one of claims 7-9, in a power system with a high proportion of new energy access, characterized in that: This system is designed to address the transient power angle instability caused by three-phase short-circuit faults in the power grid during the operation of grid-connected energy storage in the power system. It aims to enable online monitoring and optimized control of the power system, enhance the transient stability of the grid-connected energy storage system, and improve the overall reliability of the power system.

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