High-proportion new energy sending end power grid stability cooperative control method

Abstract

The invention discloses a high-proportion new energy sending end power grid stability cooperative control method, and relates to the technical field of power system stability control, and the method comprises the steps: S1, building an AC / DC sending end power grid temporary overvoltage model; s2, establishing a transient voltage stability model of the alternating-current and direct-current sending-end power grid; s3, establishing a transient stability model of the phase modifier; s4, constructing a multi-dimensional stability collaborative improvement objective function; s5, establishing a multi-dimensional stability collaborative improvement constraint condition; and S6, solving based on the multi-objective optimization function constructed in the step S4 and the constraint conditions constructed in the step S5. According to the method, a multi-dimensional analysis model of'temporary overvoltage-transient voltage stability-phase modifier power angle stability 'is constructed, so that the functions of unified modeling and collaborative optimization are realized, and multiple stability risks and dominant factors thereof faced by a power grid in different fault scenes can be accurately and quantitatively evaluated; and a clear theoretical basis and target are provided for implementing cooperative control.

Description

Technical Field

[0001] This invention relates to the field of power system stability control technology, specifically a method for coordinated control of the stability of a power grid with a high proportion of new energy sources. Background Technology

[0002] Driven by the "dual carbon" goal, my country's power grid has formed a typical pattern of "high proportion of new energy + ultra-high voltage DC transmission". As of 2023, the installed capacity of new energy has reached 47.3%. Its power electronic access characteristics and the high voltage DC system of grid commutation converter have complex dynamic interactions, which have led to three types of core stability problems: 1. Prominent risk of temporary overvoltage: When AC faults are recovered or DC commutation fails, the new energy power station cannot withdraw reactive power support in time due to control delay, while the reactive power demand of LCC-HVDC drops sharply, resulting in the accumulation of surplus reactive power and triggering equipment disconnection; 2. Unclear mechanism of transient voltage instability: With As the proportion of synchronous condensers decreases, the dominant factor for voltage stability shifts to the dynamic control of new energy converters. The unbalanced power caused by faults will drive the DC voltage to rise, forcing the active current to increase, which in turn leads to a drop in AC voltage, forming a new unstable pattern of "voltage-current" positive feedback, which is intertwined with synchronous instability. 3. Transient instability risks of synchronous condensers: Synchronous condensers lack prime movers, and their active power balance depends entirely on the exchange with the grid. Under metallic or high-resistance faults, the drastic fluctuations in new energy power can easily cause the rotor of the synchronous condenser to accelerate or decelerate excessively, and the accumulated kinetic energy will cause power angle instability. Its disconnection from the grid will further deteriorate the system voltage safety. Existing technologies have obvious limitations: overvoltage suppression, voltage stabilization control, and synchronous condenser stabilization control are often designed in isolation and lack coordination; the analysis methods fail to deeply integrate the dynamic characteristics of the three, resulting in insufficient model accuracy; and the control strategies focus more on safety and fail to achieve optimized coordination with the economic efficiency of new energy consumption and equipment operation and maintenance costs.

[0003] Patent document CN115208195B discloses a control method for improving grid stability in a hybrid energy storage system. The patent improves the dynamic response speed of the system by using an outer loop voltage control based on droop characteristics and an inner loop power control based on improved MPC to form a dual closed-loop control structure to control the energy storage converter.

[0004] The aforementioned patent proposes multi-step predictive MPC control for hybrid energy storage systems to address the prediction bias caused by large disturbances or modeling errors, ensuring that the selected output state is optimal within the control cycle, improving the dynamic response speed of the system, and thus enhancing the stability of the system after grid connection of new energy sources. However, it fails to implement multi-dimensional stability control covering overvoltage suppression, voltage stabilization, and synchronous condenser stabilization.

[0005] Therefore, this application proposes a method for coordinated control of the stability of a high-proportion renewable energy power grid at the sending end, which can cover overvoltage suppression, voltage stabilization, and synchronous condenser stabilization. Summary of the Invention

[0006] The purpose of this invention is to provide a method for coordinated control of grid stability at the high-proportion renewable energy sending end, in order to solve the technical problems mentioned in the background art, such as prominent temporary overvoltage risk, unclear transient voltage instability mechanism, and potential transient instability of synchronous condensers.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for coordinated control of grid stability at the high-proportion renewable energy transmission end, the method comprising the following steps: S1. Considering both AC and DC fault scenarios, establish an overvoltage analytical model that takes into account the dynamic interaction between new energy sources and DC. S2. Establish a transient voltage stability model for the AC / DC power grid at the sending end, taking into account the dynamics of the DC voltage outer loop control of the new energy voltage source converter. S3. Establish a transient stability model for synchronous condensers that equates new energy sources and synchronous condensers to "equivalent synchronous machines"; S4. Based on the models established in S1, S2 and S3, construct a multi-objective optimization function; S5. Establish a multi-dimensional set of stability synergistic improvement constraint conditions, including overvoltage suppression constraints, transient voltage stability constraints, synchronous condenser stability constraints, UHVDC system operation constraints, and new energy power station operation constraints; S6, based on the multi-objective optimization function constructed by S4 and the constraint condition set constructed by S5, forms a multi-dimensional stability collaborative improvement optimization model, and uses the interior point method for numerical solution to obtain the optimized control parameter set of new energy power stations, high voltage DC systems and synchronous condensers.

[0008] Preferably, the temporary overvoltage analytical model in S1 includes a first sub-model constructed for AC fault scenarios. The first sub-model is based on the quasi-steady-state phasor method, which equates the new energy power station to a decoupled model of "constant current source + virtual reactance", and defines the generalized short-circuit ratio G. ov The overvoltage risk of a multi-feed system is quantified by the following expression: ; Among them, R kk M represents the self-impedance of the new energy grid connection point. kl For the generalized overvoltage multi-feed interaction factor, Q el For the equivalent transient capacity of new energy, Q el Taking current saturation effect into account and Q el The expression is: V cutTo determine the critical terminal voltage value for initiating the current limiting circuit of the converter, and to quickly locate the most severe overvoltage condition, a weighted sensitivity matrix is ​​introduced: ; Among them, Y LK This is the Kronen simplified form of the load node admittance matrix. The corrected impedance matrix is ​​used to account for the virtual reactance of new energy sources and the stator reactance of the synchronous condenser.

[0009] Preferably, the temporary overvoltage analytical model in S1 includes a second sub-model constructed for DC fault scenarios. The second sub-model divides the transient process of LCC-HVDC commutation failure into five stages: fault triggering, new energy LVRT startup, DC current overshoot, new energy HVRT startup, and system recovery to steady state, and derives the time-domain relationship between DC current and AC voltage. ; Among them, R gs For the equivalent reactance of the sending-end system, R C I is the equivalent reactance of the filter. aD and I aQ These are the d-axis and q-axis components of the LCC-HVDC AC current, respectively, and Q. V For the per-unit capacity of new energy power plants, the critical short-circuit ratio C for DC fault overvoltage is defined. OV for: ; When the actual short-circuit ratio of the system S cr <C OV When an overvoltage risk is identified, the overvoltage safety margin expression is: .

[0010] Preferably, the transient voltage stability model established in S2 reveals the transient voltage instability mechanism of the renewable energy grid-connected system: the unbalanced power caused by the fault will drive the DC voltage of the renewable energy source to rise, resulting in an increase in the active current Iad, which in turn will cause the AC voltage V to rise. b The decline forms a positive feedback loop, defining the dominant factor for transient stability. To distinguish the types of stable boundaries: ; Where m is the reactive power gain coefficient of the energy LVRT, U S R is the infinite bus voltage. S For the line reactance, P in For the DC input power of new energy sources, when <0 (weak grid scenario, corresponding to S) cr <3.78), transient voltage stability plays a dominant role, and the active current I corresponding to the unstable equilibrium point is... admax1 The expression is: ;in, , , ;when When I > 0, transient synchronous stability dominates, and the active current I corresponding to the singular point of the phase-locked loop is... admax2 The expression is: .

[0011] Preferably, in step S3, the new energy-synchronous condenser system is equivalent to an "equivalent synchronous condenser ESG", where the new energy source is the equivalent prime mover and the synchronous condenser is the rotor system. The power angle characteristics of the synchronous condenser under metallic faults are derived as follows: ; in, E cam To adjust the transient internal potential of the camera, R cam To account for the transient reactance of the synchronous condenser; and to address high-resistance grounding faults, to take into account the influence of line resistance and correct the power angle characteristics of the synchronous condenser: ; Among them, U seq R seq R res These represent the equivalent voltage, reactance, and resistance of the power grid under a high-resistance fault. The equivalent voltage phase; define the transient stability critical short-circuit ratio C of the synchronous condenser. cam : ; in, D is the system's rated angular frequency. t To adjust the camera damping coefficient, T is the fault duration, T in To adjust the camera's inertia time constant, The critical resection angle, The power angle before the fault; the expression for the system transient stability margin is: .

[0012] Preferably, the model built in S4 based on S1, S2, and S3 aims to achieve optimal overall stability of the sending-end power grid (minimizing overvoltage, maximizing voltage stability margin, and minimizing synchronous condenser power angle oscillation) and lowest economic cost (minimizing renewable energy curtailment cost and synchronous condenser operation and maintenance cost), and constructs a multi-objective optimization function:

[0013] ; in: The system's maximum temporary overvoltage, weighted by a coefficient. 1 = 0.3; Transient voltage stability margin Weighting coefficient 2 = 0.25; To adjust the maximum angle deviation of the camera, the weighting coefficient is... 3 = 0.2; The cost of curtailing renewable energy is calculated as follows: Weighting coefficient 4 = 0.15, where ; Contribute to the development of new energy sources To contribute practically, For time step; To adjust the camera's operation and maintenance costs, a weighting coefficient is used. 5 = 0.1, where ; For fixed costs, For unit power operation and maintenance cost, To adjust the average output of the camera.

[0014] Preferably, the voltage suppression constraint in S5 is: Equivalent transient capacity constraints of new energy sources under AC fault conditions: ,in, For the maximum allowable current of new energy sources, This refers to the reactive current prior to the fault. Control parameter constraints under DC faults: Proportional coefficient of DC constant current controller: The lower limit of the VDCOL voltage in the low-voltage current limiting circuit is: ; Reactive power gain coefficient of new energy LVRT: ; DC blocking time constraints: ,in, This is the peak value of the overvoltage. The delay for new energy control is set to [0.02, 0.04] s.

[0015] Preferably, the transient voltage stability constraint in S5 is: Active current limiting constraints for new energy sources: ; Dynamic adjustment constraint for current limiting: ,in, This is the upper limit of the current change rate, with a value of 0.5 pu / s; Reactive current constraints of new energy sources: And it satisfies the reactive current priority limiting principle. .

[0016] Preferably, the camera stabilization constraint in S5 is: Adjusting camera angle constraints: ,in, The critical cut angle is obtained through calculation using the equal area rule; Adjusting camera frequency constraints: The angular frequency deviation is controlled within ±2%. New energy - LVRT collaborative constraints: ,in, The control law for the power injected into the grid into the combined system is: ,in, .

[0017] Preferably, the operating constraints of the UHVDC system and the operating constraints of the new energy power station in S5 are as follows: UHVDC system constraints: DC power modulation range constraints: ,in, The rated power of the DC system is used, and the modulation range is ±10% of the rated power. Commutation failure recovery constraints: ,in, The inverter-side turn-off angle is set to ensure stable commutation. DC current constraint: ; Constraints on new energy power stations: Wind power load shedding reserve constraints: ,in, This is the wind power load reduction factor, with a value range of [0.05, 0.2], which is reserved for backup through overspeed or pitch control; Energy storage charge / discharge constraints: Power constraints: ,in, This is the maximum charging power for energy storage. This represents the maximum discharge power of the energy storage. Capacity constraints: ,in ; , These are the energy storage charging and discharging efficiencies, respectively. =0.2, =0.8.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs a multi-dimensional analysis model of "temporary overvoltage - transient voltage stability - synchronous condenser power angle stability", realizing the functions of unified modeling and collaborative optimization. It can accurately and quantitatively assess the multiple stability risks and their dominant factors faced by the power grid under different fault scenarios, providing a clear theoretical basis and objective for implementing collaborative control. 2. This invention, through the established analytical model, enables rapid identification and location of stability risks, reveals the dynamic coupling mechanism between new energy sources, DC systems, and synchronous condensers, and, in conjunction with tools such as weighted sensitivity matrices and critical short-circuit ratio criteria, greatly improves the efficiency of online assessment and early warning of power grid safety; 3. This invention improves the dynamic response characteristics of the system by optimizing the control parameters of the new energy power station, LCC-HVDC system and synchronous condenser. It forms an economic improvement path with "parameter optimization" as the main approach and "hardware switching" as the auxiliary approach. By utilizing the control redundancy of existing equipment, it significantly improves stability while greatly saving hardware investment costs and subsequent operation and maintenance expenses. 4. This invention achieves highly practical engineering functions through upgrades in software algorithms and control strategies. It can be directly embedded into existing power grid energy management systems, new energy power station controllers, and DC control and protection systems without requiring large-scale modifications to the existing power grid structure. It is convenient to implement, low in cost, and provides a solution for high-proportion new energy access to new power systems, with broad application prospects. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: Please refer to Figure 1 A method for coordinated control of grid stability at the high-proportion renewable energy sending end, the method comprising the following steps, wherein the temporary overvoltage analytical model in step S1 includes a first sub-model constructed for AC fault scenarios, the first sub-model being based on the quasi-steady-state phasor method, which equates renewable energy power stations to a decoupled model of "constant current source + virtual reactance", and defines the generalized short-circuit ratio G. ov To quantify the overvoltage risk of multi-infeed systems and quickly locate the most severe overvoltage conditions, a weighted sensitivity matrix is ​​introduced. The temporary overvoltage analytical model in S1 includes a second sub-model constructed for DC fault scenarios. The second sub-model divides the transient process of LCC-HVDC commutation failure into five stages: fault triggering, new energy LVRT startup, DC current overshoot, new energy HVRT startup, and system recovery to steady state, and derives the time-domain relationship between DC current and AC voltage. Furthermore, this embodiment illustrates the process of establishing the temporary overvoltage analytical model for AC and DC fault scenarios in the grid stability collaborative control method. First, considering the AC fault scenario, a first sub-model is constructed. Based on the quasi-steady-state phasor method, the new energy power station is equivalent to a decoupled model of "constant current source + virtual reactance." This is achieved by introducing the generalized short-circuit ratio G. OV To quantify the overvoltage risk of multi-infeed systems, the calculation of the generalized short-circuit ratio involves the self-impedance R at the grid connection point of new energy sources. kk and generalized overvoltage multi-feed interaction factor M kl And the equivalent transient capacity Q of new energy el Q el The calculation specifically takes into account the current saturation effect, and its expression is related to the critical terminal voltage V at which the converter current limiting circuit starts. cut Closely related to the actual fault conditions, the model is accurate under real-world fault conditions. To quickly locate the most severe overvoltage condition in the system, a weighted sensitivity matrix is ​​further introduced into the model. This weighted sensitivity matrix is ​​based on the Kronen simplification of the load node admittance matrix Y. LK and the corrected impedance matrix The constructed and modified impedance matrix fully considers the influence of virtual reactance of new energy sources and stator reactance of synchronous condensers. The first sub-model can clearly reveal the physical process by which excess reactive power accumulates in the system and causes temporary overvoltage during the clearing or restoration of AC faults due to the dynamic mismatch between the control response delay of new energy power plants and the sudden change in reactive power demand of LCC-HVDC system. Through the first sub-model, operators can identify nodes or areas with high overvoltage risk in the power grid in advance, assess the overvoltage level under different new energy penetration rates, power grid structures and control parameters, and provide quantitative basis for the formulation of subsequent suppression strategies. For DC fault scenarios, especially the commutation failure process of LCC-HVDC, a second sub-model was constructed. This sub-model finely divides the complex transient process into five stages: fault triggering, low-voltage ride-through startup of new energy sources, DC current overshoot, high-voltage ride-through startup of new energy sources, and system recovery to steady state. By deriving the analytical relationship between DC current and AC voltage in the time domain, the second sub-model characterizes the equivalent reactance R of the sending-end system. gs Filter equivalent reactance R C The d-axis and q-axis components of the LCC-HVDC AC current. aD with I aQand the per-unit capacity Q of new energy power stations V The interaction of factors such as [missing information] during the overvoltage generation process defines the critical short-circuit ratio C for overvoltage under DC faults. OV The critical short-circuit ratio of overvoltage is compared with the actual short-circuit ratio S. cr By comparing the data, it is possible to clearly determine whether there is an overvoltage risk, and further calculate the overvoltage safety margin ξ. ov By quantifying the degree of risk, the DC fault overvoltage model can accurately predict the transient rise trajectory of the grid voltage at the sending end when a serious fault such as commutation failure occurs in the DC system, identify the dominant factors causing overvoltage, and thus provide theoretical guidance for optimizing DC control system parameters and coordinating the LVRT / HVRT strategies of new energy power plants, avoiding large-scale grid disconnection of new energy due to overvoltage, and ensuring the rapid recovery capability of the system after a fault.

[0022] Example 2: Please refer to Figure 1 A method for coordinated control of grid stability at the high-proportion renewable energy sending end, the method comprising the following steps, wherein the transient voltage stability model established in step S2 reveals the transient voltage instability mechanism of the renewable energy grid-connected system: the unbalanced power caused by the fault will drive the DC voltage of the renewable energy to rise, resulting in the active current I ad Increase, thereby increasing the AC voltage V b The decline forms a positive feedback loop, defining the dominant factor for transient stability. To distinguish the types of stable boundaries, when When < 0, transient voltage stability plays a dominant role; when When >0, transient synchronization and stability dominate; Furthermore, this embodiment involves the establishment of a transient voltage stability model in the grid stability collaborative control method, revealing the mechanism of transient voltage instability dominated by renewable energy voltage source converters. The transient voltage stability model takes into account the dynamic process of the outer loop control of the DC voltage of the renewable energy converter. In traditional synchronous machine-dominated systems, voltage stability is mainly affected by reactive power balance. However, in weak grids with a high proportion of renewable energy, the unbalanced power caused by faults will first act on the DC side of the renewable energy converter, leading to an increase in DC voltage. The transient voltage stability model accurately describes this process: the increase in DC voltage forces the converter control to increase its output active current I. ad The aim is to restore power balance; however, under weak grid conditions, the increased active current flowing through the grid impedance will cause the AC bus voltage V to drop. bFurther voltage drops, which in turn can trigger further fluctuations in DC voltage through control loop feedback, create a vicious cycle of positive feedback: "DC voltage increases → active current increases → AC voltage decreases," ultimately leading to transient voltage instability. To quantitatively analyze this instability risk, the transient voltage stability model defines a transient stability dominant factor ψ, which is the reactive power gain coefficient m of the new energy LVRT and the infinite bus voltage U. S Line reactance R S and the DC input power P of new energy in The sign and magnitude of the function ψ become key criteria for distinguishing the type of stability boundary: when ψ is less than zero, it corresponds to a weak power grid scenario with low short-circuit ratio, where transient voltage stability plays a dominant role; the transient voltage stability model further derives the maximum active current I corresponding to the unstable equilibrium point of the system under this scenario. admax1 The analytical expression, which includes grid parameters, new energy control parameters, and fault information, can be used to calculate the transient voltage stability limit of the system. When ψ is greater than zero, the system exhibits a transient synchronization stability problem dominated by phase-locked loop dynamics. The transient voltage stability model also gives the active current limit I corresponding to the phase-locked loop singularity point. admax2 ; The transient voltage stability model plays a crucial role, elucidating two different forms of instability mechanisms that may occur in renewable energy grid-connected systems under fault conditions and their transition conditions. It breaks through the limitations of previous analyses that isolated voltage stability and synchronization stability. Based on this transient voltage stability model, the impact of different grid strengths, renewable energy control modes, and LVRT strategy parameters on transient voltage stability margin can be quantitatively evaluated. This guides renewable energy power plants to optimize their converter control parameters, suppress the occurrence of positive feedback instability cycles from the source, and enhance the grid's ability to withstand severe faults.

[0023] Example 3: Please refer to Figure 1 A method for coordinated control of grid stability at the high-proportion renewable energy sending end, comprising the following steps: In step S3, the renewable energy-synchronous condenser system is equivalent to an "equivalent synchronous condenser (ESG)," with renewable energy as the equivalent prime mover and the synchronous condenser as the rotor system. The power angle characteristics of the synchronous condenser under metallic faults are derived. For high-resistance grounding faults, the influence of line resistance is taken into account to correct the power angle characteristics of the synchronous condenser. The transient stability critical short-circuit ratio C of the synchronous condenser is defined. cam ; Furthermore, this embodiment illustrates the establishment of the transient stability model of the synchronous condenser in the grid stability collaborative control method. The hybrid system composed of new energy sources and synchronous condensers is equivalent to an "equivalent synchronous machine." Under this equivalent framework, the new energy power generation unit is considered as an equivalent prime mover, responsible for providing mechanical power input, while the synchronous condenser is equivalent to a rotor system, whose dynamics are described by the classical rotor motion equations. This equivalent method can utilize mature synchronous machine stability theory to analyze the power angle behavior of the synchronous condenser, which originally lacked a prime mover, under system disturbances. The transient stability model of the synchronous condenser first derives the time-domain characteristic equation of the power angle swing of the synchronous condenser for metallic short-circuit faults. The equation includes the transient internal potential E of the synchronous condenser. cam Transient reactance R cam In addition to the equivalent system voltage and impedance determined by the renewable energy source and grid parameters, the equation clearly shows that the power fluctuations output by the renewable energy source during a fault will be directly converted into acceleration or deceleration power acting on the equivalent rotor. If the fluctuations are severe or last for a long time, it may cause the synchronous condenser rotor to accumulate excessive kinetic energy deviation, leading to power angle instability or even loss of synchronization. For the more complex high-resistance grounding fault, the transient stability model of the synchronous condenser further incorporates the influence of line resistance, modifies the power angle characteristic equation, and introduces the equivalent grid voltage U under high-resistance fault conditions. seq Equivalent reactance R seq and equivalent resistance R res These parameters enable the transient stability model of the synchronous condenser to more accurately reflect the influence of resistance on damping characteristics and stability boundary. Based on this transient stability model, this invention defines the critical short-circuit ratio C for transient stability of the synchronous condenser. cam This criterion takes into account the system's rated angular frequency ω. N Adjust the camera damping coefficient D t Fault duration T, synchronous condenser inertia time constant T in Critical cut-off angle θ lim and the power angle θ before the fault cam0 Multiple factors, such as the actual short-circuit ratio of the system, were considered by comparing it with C. cam It can quickly determine whether a camera faces transient instability risk under specific fault conditions and calculate its stability margin ξ. cam ; This transient stability model for synchronous condensers provides a precise analytical tool for solving the stability problem of synchronous condensers in "high proportion of new energy + synchronous condensers" systems. It reveals how rapid and random fluctuations in new energy power threaten the rotor angle stability of the synchronous condenser through electrical connections. Based on this transient stability model, the excitation control parameters of the synchronous condenser can be optimized, the necessity of adding a power system stabilizer can be evaluated, and control strategies coordinated with new energy power generation can be designed. For example, when a fault or severe power fluctuation is detected, the active power output rate of the new energy can be temporarily adjusted or energy storage devices can be used for power smoothing, providing virtual inertial support for the synchronous condenser, thereby jointly maintaining the power angle stability of the hybrid system and preventing system voltage collapse caused by the instability of the synchronous condenser.

[0024] Example 4: Please refer to Figure 1 A method for coordinated control of grid stability at the sending end of a high proportion of renewable energy sources, the method includes the following steps: in step S4, based on the model constructed by S1, S2, and S3, a multi-objective optimization function is constructed with the objectives of achieving optimal comprehensive grid stability at the sending end (minimizing overvoltage, maximizing voltage stability margin, and minimizing synchronous condenser power angle oscillation) and minimum economic cost (minimizing renewable energy curtailment cost and synchronous condenser operation and maintenance cost). Furthermore, this embodiment describes the role of the multi-dimensional stability synergistic improvement objective function constructed in the power grid stability synergistic control method in terms of the comprehensive stability and economy of the sending-end power grid. In terms of stability, the objective function incorporates three key indicators: firstly, the system's maximum temporary overvoltage V. tmax The first requirement is to minimize it to protect the insulation safety of electrical equipment; the second is the transient voltage stability margin ξ. v , defined as the distance between the actual operating point and the stability boundary, is required to be maximized to enhance the system's ability to withstand voltage collapse; the third is the maximum power angle deviation Δθ of the synchronous condenser. camax The objective function requires minimizing these parameters to ensure that the power angle oscillation amplitude of the synchronous condenser remains within a safe range during faults. These three indicators correspond to the analytical outputs of the three core stability models established in claims S1, S2, and S3, respectively, achieving a unified quantitative description of the multi-dimensional stability state of "overvoltage-voltage stability-power angle stability." In terms of economics, the objective function simultaneously considers the cost of renewable energy consumption and equipment operation and maintenance costs: renewable energy curtailment cost C... loss By calculating the actual power output P of new energy sources vact (h) relative to the reference output P vref The deviation of (h) is represented by multiplying it by the unit curtailment cost factor. Minimizing this factor means absorbing as much renewable energy as possible while ensuring stability; the operation and maintenance cost C of the synchronous condenser. camop This includes fixed costs and average output P. camavgThe related operating costs, which are minimized, help improve the economic efficiency of asset utilization. To balance the importance and dimensional differences between different objectives, the function assigns empirical weight coefficients to each sub-objective. These weights can be adjusted according to the actual operating needs and risk preferences of the power grid. This multi-objective optimization function establishes a clear collaborative optimization framework, placing technically coupled and potentially conflicting stability requirements and operational economic objectives on the same decision-making platform. By solving this optimization problem, decision-makers no longer need to handle individual stability issues in isolation and sequentially, but can obtain a coordinated control scheme that can simultaneously improve multiple stability issues while taking into account economic efficiency. This provides a direct and quantifiable objective guide for the subsequent formation of specific optimized control instruction sets, such as adjusting the power reference value of new energy power plants, modifying the power modulation instructions of DC systems, and optimizing the reactive power output setpoint of synchronous condensers.

[0025] Example 5: Please refer to Figure 1 A method for coordinated control of grid stability at high-proportion renewable energy transmission ends, the method includes the following steps, S5: establishing a multi-dimensional set of stability coordination and improvement constraints, including overvoltage suppression constraints, transient voltage stability constraints, synchronous condenser stability constraints, ultra-high voltage DC system operation constraints, and renewable energy power station operation constraints; Furthermore, the systematic constraint set established in this invention defines a safe and feasible decision space for solving the multi-objective optimization model, which is crucial to ensuring the practicality of the optimization results. The constraint set comprehensively covers the operational limitations of all major components of the sending-end power grid. Regarding overvoltage suppression, for AC faults, it constrains the equivalent transient capacity of new energy sources to ensure that the reactive current output during the fault does not exceed the maximum allowable current I of the equipment. maxj And consider the reactive current I before the fault. aq0j For DC faults, upper and lower limits were set for key control parameters, including the proportional coefficient K of the DC constant current controller. pcc The lower voltage limit V of the low-voltage current limiting circuit dcolmin The reactive power gain factor *m* of the new energy LVRT directly affects the dynamics of reactive power exchange and overvoltage peaks during faults; it also constrains the timing of the DC blocking command, requiring it to avoid the overvoltage peak time *t*. peak And consider the control delay τ of new energy sources d To avoid improper operation exacerbating voltage surges; Regarding transient voltage stability, the constraints mainly focus on the current control of the renewable energy converter: an active current limit value I is set. adlim To prevent excessive active current from causing voltage positive feedback instability, an upper limit k for the rate of change of current was set. rate To avoid power surges causing impacts on the power grid; the output range I of reactive current was clearly defined.aqmin to I aqmax It also emphasized the principle of "reactive current priority limiting", that is, when the current reaches the total limit, priority should be given to ensuring reactive power support capacity, which is crucial for maintaining voltage stability during faults. In terms of camera stabilization, its power angle θ was constrained. cam It must be less than the critical resection angle θ, which can be calculated using the equal area rule. lim This is the fundamental condition for ensuring transient power angle stability; it also constrains the frequency deviation of the synchronous condenser to within ±2% to ensure its synchronous operation; furthermore, it proposes a coordinated constraint between new energy sources and the synchronous condenser during LVRT, requiring that the power P jointly injected into the grid by both be... grid (t) satisfies a certain control law, which aims to smooth out power fluctuations and provide a stable operating environment for the synchronous condenser; For ultra-high voltage direct current systems, the power modulation range is constrained to ensure adjustment flexibility without affecting the main transmission function; the inverter-side turn-off angle γ is also constrained. inv This is to prevent commutation failure; and to constrain the DC current within a safe range. For new energy power plants, a wind power load shedding reserve constraint is introduced, using a load shedding coefficient d. w A portion of active power is reserved for frequency or power support during fault periods; for the supporting energy storage system, strict constraints are imposed on both power and capacity to ensure its safe operation when participating in optimized regulation. The multi-dimensional constraint set transforms all the physical laws of the power system, equipment safety operation procedures, technical standards, and actual engineering limitations into inequalities or equality constraints in the mathematical model. This ensures that the set of control parameters obtained through the optimization algorithm is not only optimal or superior in performance, but more importantly, feasible and safe in engineering. This makes it possible for the collaborative control method of this invention to move from theoretical model to engineering application. The optimization results can directly guide the adjustment of setpoints in various stations and control systems, forming a complete, reliable, and economical stability improvement scheme.

[0026] Working Principle: First, for both AC and DC fault scenarios, a precise analytical model for temporary overvoltage, taking into account the dynamic interaction between renewable energy and the DC system, is established. Second, a voltage stability model is constructed to reveal a new mechanism for transient voltage instability caused by the dynamic control of renewable energy converters. Then, a power angle stability model is established that equates renewable energy and synchronous condensers to "equivalent synchronous machines" to analyze the transient behavior of synchronous condensers under renewable energy power fluctuations. Based on these three core models, a multi-objective optimization function is further constructed that comprehensively considers minimizing overvoltage, maximizing voltage stability margin, minimizing power angle oscillation, and minimizing renewable energy curtailment and synchronous condenser operation and maintenance costs. Simultaneously, multi-dimensional constraints such as overvoltage suppression, transient voltage stability, synchronous condenser stability, DC system operation, and renewable energy plant operation are systematically integrated to form a complete set of synergistic improvement constraints. Finally, based on the constructed multi-objective function and constraint set, a multi-dimensional stability synergistic improvement optimization model is formed and solved using numerical methods such as the interior-point method. This yields a set of strategies that can coordinate and optimize the control parameters of renewable energy plants, high-voltage DC systems, and synchronous condensers, achieving a comprehensive improvement in grid safety, stability, and economic operation.

[0027] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for coordinated control of grid stability at the high-proportion renewable energy transmission end, characterized in that: The method includes the following steps: S1. Considering both AC and DC fault scenarios, establish an overvoltage analytical model that takes into account the dynamic interaction between new energy sources and DC. S2. Establish a transient voltage stability model for the AC / DC power grid at the sending end, taking into account the dynamics of the DC voltage outer loop control of the new energy voltage source converter. S3. Establish a transient stability model for synchronous condensers that equates new energy sources and synchronous condensers to "equivalent synchronous machines"; S4. Based on the models established in S1, S2 and S3, construct a multi-objective optimization function; S5. Establish a multi-dimensional set of stability synergistic improvement constraint conditions, including overvoltage suppression constraints, transient voltage stability constraints, synchronous condenser stability constraints, UHVDC system operation constraints, and new energy power station operation constraints; S6, based on the multi-objective optimization function constructed by S4 and the constraint condition set constructed by S5, forms a multi-dimensional stability collaborative improvement optimization model, and uses the interior point method for numerical solution to obtain the optimized control parameter set of new energy power stations, high voltage DC systems and synchronous condensers.

2. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The temporary overvoltage analytical model in S1 includes a first sub-model constructed for AC fault scenarios. The first sub-model is based on the quasi-steady-state phasor method, which equates the new energy power station to a decoupled model of "constant current source + virtual reactance", and defines the generalized short-circuit ratio G. ov The overvoltage risk of a multi-feed system is quantified by the following expression: ; Among them, R kk M represents the self-impedance of the new energy grid connection point. kl For the generalized overvoltage multi-feed interaction factor, Q el For the equivalent transient capacity of new energy, Q el Taking current saturation effect into account and Q el The expression is: V cut The critical terminal voltage value for initiating the current limiting circuit of the converter; a weighted sensitivity matrix is ​​introduced to quickly locate the most severe overvoltage condition: ; Among them, Y LK This is the Kronen simplified form of the load node admittance matrix. The corrected impedance matrix is ​​used to account for the virtual reactance of new energy sources and the stator reactance of the synchronous condenser.

3. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The temporary overvoltage analytical model in S1 includes a second sub-model constructed for DC fault scenarios. The second sub-model divides the transient process of LCC-HVDC commutation failure into five stages: fault triggering, new energy LVRT startup, DC current overshoot, new energy HVRT startup, and system recovery to steady state. The time-domain relationship between DC current and AC voltage is derived as follows: ; Among them, R gs For the equivalent reactance of the sending-end system, R C I is the equivalent reactance of the filter. aD and I aQ These are the d-axis and q-axis components of the LCC-HVDC AC current, respectively, and Q. V For the per-unit capacity of new energy power plants, the critical short-circuit ratio C for DC fault overvoltage is defined. OV for: ; When the actual short-circuit ratio of the system S cr <C OV When an overvoltage risk is identified, the overvoltage safety margin expression is: .

4. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The transient voltage stability model established in S2 reveals the transient voltage instability mechanism of the renewable energy grid-connected system: the unbalanced power caused by the fault will drive up the DC voltage of the renewable energy, resulting in an increase in the active current I. ad Increase, thereby increasing the AC voltage V b The decline forms a positive feedback loop, defining the dominant factor for transient stability. To distinguish the types of stable boundaries: ； Where m is the reactive power gain coefficient of the energy LVRT, U S R is the infinite bus voltage. S For line reactance, P in For the DC input power of new energy sources, when <0 (weak grid scenario, corresponding to S) cr <3.78), transient voltage stability plays a dominant role, and the active current I corresponding to the unstable equilibrium point is... admax1 The expression is: ; in, , , ;when When I > 0, transient synchronous stability dominates, and the active current I corresponding to the singular point of the phase-locked loop is... admax2 The expression is: .

5. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: In S3, the new energy-synchronous condenser system is equivalent to an "equivalent synchronous machine ESG", with the new energy source being the equivalent prime mover and the synchronous condenser being the rotor system. The power angle characteristics of the synchronous condenser under metallic faults are derived as follows: ; in, E cam To adjust the transient internal potential of the camera, R cam To account for the transient reactance of the synchronous condenser; and to address high-resistance grounding faults, to take into account the influence of line resistance and correct the power angle characteristics of the synchronous condenser: ； Among them, U seq R seq R res These represent the equivalent voltage, reactance, and resistance of the power grid under a high-resistance fault. The equivalent voltage phase; define the transient stability critical short-circuit ratio C of the synchronous condenser. cam : ； in, D is the system's rated angular frequency. t To adjust the camera damping coefficient, T is the fault duration, T in To adjust the camera's inertia time constant, The critical resection angle, The power angle before the fault; the expression for the system transient stability margin is: .

6. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The model in S4, based on S1, S2, and S3, aims to achieve optimal overall stability of the sending-end power grid (minimizing overvoltage, maximizing voltage stability margin, and minimizing synchronous condenser power angle oscillation) and lowest economic cost (minimizing renewable energy curtailment cost and synchronous condenser operation and maintenance cost). A multi-objective optimization function is constructed as follows: ； ； in: The system's maximum temporary overvoltage, weighted by a coefficient. 1 = 0.3; Transient voltage stability margin Weighting coefficient 2 = 0.25; To adjust the maximum angle deviation of the camera, the weighting coefficient is... 3 = 0.2; The cost of curtailing renewable energy is calculated as follows: Weighting coefficient 4 = 0.15, where ; Contribute to the development of new energy sources To contribute practically, For time step; To adjust the camera's operation and maintenance costs, a weighting coefficient is used. 5 = 0.1, where ； For fixed costs, For unit power operation and maintenance cost, To adjust the average output of the camera.

7. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The voltage suppression constraint in S5 is: Equivalent transient capacity constraints of new energy sources under AC fault conditions: ,in, For the maximum allowable current of new energy sources, This refers to the reactive current prior to the fault. Control parameter constraints under DC faults: Proportional coefficient of DC constant current controller: The lower limit of the VDCOL voltage in the low-voltage current limiting circuit is: ; Reactive power gain coefficient of new energy LVRT: ; DC blocking time constraints: ,in, At the peak of the overvoltage, The delay for new energy control is set to [0.02, 0.04] s.

8. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The transient voltage stability constraint in S5: Active current limiting constraints for new energy sources: ; Dynamic adjustment constraint for current limiting: ,in, This is the upper limit of the current change rate, with a value of 0.5 pu / s; Reactive current constraints of new energy sources: And it satisfies the reactive current priority limiting principle. .

9. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The camera stabilization constraint in S5 is as follows: Adjusting camera angle constraints: ,in, The critical cut angle is obtained through calculation using the equal area rule; Adjusting camera frequency constraints: The angular frequency deviation is controlled within ±2%. New energy - LVRT collaborative constraints: ,in, The control law for the power injected into the grid into the combined system is: ,in, .

10. The method for coordinated control of grid stability at a high proportion of renewable energy transmission terminals according to claim 1, characterized in that: The following are the operational constraints of the ultra-high voltage direct current system and the operational constraints of new energy power plants in S5: UHVDC system constraints: DC power modulation range constraints: ,in, The rated power of the DC system is used, and the modulation range is ±10% of the rated power. Commutation failure recovery constraints: ,in, The inverter-side turn-off angle is set to ensure stable commutation. DC current constraint: ; Constraints on new energy power stations: Wind power load shedding reserve constraints: ,in, This is the wind power load reduction factor, with a value range of [0.05, 0.2], which is reserved for backup through overspeed or pitch control; Energy storage charge / discharge constraints: Power constraints: ,in, This is the maximum charging power for energy storage. This represents the maximum discharge power of the energy storage. Capacity constraints: ,in ； , These are the energy storage charging and discharging efficiencies, respectively. =0.2, =0.8.

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