Networked energy storage and static synchronous compensator coordinated control method considering frequency-voltage coupling
Patent Information
- Application Number
- CN202611299357.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-26
- Publication Date
- 2026-09-25
AI Technical Summary
[0005]本发明的目的在于提供一种计及频压耦合的构网型储能与静止同步调相机协同控制方法，以解决现有技术在弱电网条件下因频压交叉耦合导致的控制竞争、装置容量利用不充分以及刚性恢复易引发过流和振荡的技术问题
[0045]（1）本发明通过建立电网强度参数化的频压全耦合模型并计算控制有效度矩阵，实现了对弱电网下有功-电压、无功-频率交叉耦合影响的精准量化评估，从而为协同控制分配提供了科学的数学依据，避免了传统解耦控制在低短路比下失效引发的控制竞争问题，有效降低频压控制偏差的均方根误差。
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of power system control and new energy grid connection technology, specifically to a method for coordinated control of grid-connected energy storage and static synchronous condensers that takes into account frequency-voltage coupling. Background Technology
[0002] With the increasing proportion of new energy power sources and power electronic equipment in the sending-end power grid, the system exhibits significant characteristics of "low inertia and low short-circuit capacity." Particularly in the new energy sending-end power grid, the capacity of synchronous power sources and inherent electromagnetic damping continue to decline, seriously threatening the frequency and voltage stability of the system. To address these issues, grid-based energy storage and static synchronous condensers (SSCs) are widely used as two important flexible AC devices. Grid-based energy storage can actively establish voltage phase and frequency references, providing virtual inertia and primary frequency regulation support through active power regulation; static synchronous condensers feature fast voltage response, a large reactive power regulation range, and strong short-time overload capacity. The two have significant complementarity in dynamic performance, making them suitable for forming a joint frequency and voltage support unit for weak power grids.
[0003] Existing methods for coordinated control of grid-based energy storage and static synchronizing transformers (SMTs) are typically based on an approximate decoupling assumption, meaning that grid-based energy storage is always responsible for active-frequency control, while SMTs are responsible for reactive-voltage control. However, under actual weak grid operating conditions, when the grid short-circuit ratio is low or the line impedance angle deviates from the typical value of high-voltage transmission networks, the cross-coupling terms in the power transfer equations cannot be ignored: the active-frequency regulation actions of grid-based energy storage may cause significant fluctuations in the point of common coupling voltage, and the reactive-voltage regulation actions of SMTs may also alter active-frequency dynamics.
[0004] If traditional fixed droop coefficients and fixed power allocation ratios are still used under weak grid conditions, the following technical problems will arise: First, due to the lack of consideration for frequency-voltage cross-coupling, the control objectives of the two devices interfere with each other, easily leading to control competition, resulting in a decrease in the damping of the system's frequency-voltage oscillation mode, and even inducing system instability; Second, due to the lack of awareness of the actual available capacity of the equipment and the grid strength, rigidly tracking the rated frequency and rated voltage will force the converter to output extremely high power in a short period of time, which can easily lead to converter overcurrent, rapid consumption of DC-side energy, and equipment thermal overload; Third, in dynamic processes, the converter capacity utilization is uneven, and the dynamic transfer of responsibilities cannot be performed according to the physical characteristics of the devices, resulting in a waste of overall control resources and making it difficult to fully utilize the combined supporting potential of grid-type energy storage and static synchronous condensers. Therefore, there is an urgent need for a collaborative control method that can accurately quantify the impact of frequency-voltage coupling, dynamically adapt to changes in grid strength, and achieve optimized capacity allocation of multiple devices. Summary of the Invention
[0005] The purpose of this invention is to provide a coordinated control method for grid-type energy storage and static synchronous condensers that takes into account frequency-voltage coupling, so as to solve the technical problems of control competition, insufficient utilization of device capacity, and overcurrent and oscillation caused by frequency-voltage cross-coupling in the existing technology under weak grid conditions.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0007] A method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling includes the following steps:
[0008] S10. Collect electrical quantities at the point of common coupling and state quantities of grid-type energy storage and static synchronous condensers, identify the equivalent impedance and generalized short-circuit ratio of the external power grid, and determine the power grid strength state vector.
[0009] S20. Based on the pre-constructed frequency-voltage full coupling model with parameterized grid strength, calculate and update the frequency-voltage coupling coefficient and control effectiveness matrix to characterize the actual frequency and voltage regulation capabilities of the two types of devices: grid-type energy storage and static synchronous condenser.
[0010] S30. Based on the electrical quantities at the common connection point and the output power of the two types of devices, the equivalent active and reactive disturbances of the system are estimated using an extended state observer.
[0011] S40. Based on the grid strength state vector and the equivalent active and reactive disturbances, the frequency reference trajectory and voltage reference trajectory jointly tracked by the two types of devices are generated through the virtual frequency-voltage guide of grid strength perception.
[0012] S50. Calculate the generalized frequency-voltage control quantity based on the frequency reference trajectory and voltage reference trajectory, and perform constraint optimization allocation based on the control effectiveness matrix, joint frequency-voltage stability margin and equipment constraints to obtain the active power command and reactive power command of the grid-type energy storage and static synchronous condenser.
[0013] S60. The optimized active power command and reactive power command are respectively sent to the local grid controller of the grid-type energy storage and static synchronous condenser for closed-loop control.
[0014] Specifically, in step S10, the process of determining the power grid strength state vector includes:
[0015] Identify the equivalent impedance, impedance angle, and generalized short-circuit ratio of the external power grid based on the voltage / current changes at the point of common coupling.
[0016] The generalized short-circuit ratio is used to characterize the short-circuit capacity of the power grid. Combined with the preset thresholds for weak and strong grids, the normalized grid strength is calculated.
[0017] The power grid strength state vector is constructed by combining the external power grid's fundamental frequency equivalent impedance and impedance angle with the normalized power grid strength.
[0018] Specifically, in step S20, the process of calculating and updating the frequency-voltage coupling coefficient and the control effectiveness matrix includes:
[0019] Small-signal linearization is performed at the rated operating point to extract the main channel matrix and cross channel matrix in the frequency-voltage fully coupled model;
[0020] The frequency-voltage coupling coefficient is calculated based on the ratio of the Frobenius norm of the main channel matrix to the cross channel matrix.
[0021] By combining the state base value matrix and available power capacity matrix of the grid-type energy storage and the static synchronous condenser, the frequency-voltage fully coupled model is normalized to obtain the normalized control effectiveness matrix.
[0022] Specifically, in step S30, the extended state observer is configured with the common coupling point frequency deviation and voltage amplitude deviation as states, and the equivalent active and reactive disturbances as extended states. The observer gain is determined by pole placement or linear matrix inequalities to keep the observation error system stable within the allowable range of the power grid strength.
[0023] Specifically, in step S40, the process of generating a frequency reference trajectory and a voltage reference trajectory jointly tracked by the two types of devices through a virtual frequency-voltage guide that senses power grid strength includes:
[0024] A second-order virtual frequency-voltage guidance model is constructed, which includes a virtual inertia matrix, a damping matrix, and a restitution coefficient matrix.
[0025] A leakage integral prediction state is introduced, and a mapping matrix from disturbance to frequency voltage reference is designed. The feedforward compensation of equivalent active disturbance and equivalent reactive disturbance is embedded in the second-order virtual frequency voltage guidance model.
[0026] The virtual inertia matrix, damping matrix, and integral gain matrix are adaptively adjusted based on the power grid strength state vector. The lower the power grid strength, the greater the virtual inertia and damping. The frequency reference trajectory and voltage reference trajectory are obtained by solving the second-order virtual frequency-voltage guidance model.
[0027] Specifically, in step S50, the process of calculating the generalized frequency voltage control quantity includes:
[0028] Obtain the frequency tracking error and its derivative, and the voltage tracking error and its derivative;
[0029] By combining the frequency-voltage collaborative feedback gain with the equivalent active and reactive disturbances, the equivalent frequency control action and voltage control action required at the current moment are calculated and combined into a generalized frequency-voltage control quantity.
[0030] Specifically, before performing the constraint optimization allocation in step S50, the method further includes constructing a priori power allocation vector:
[0031] The total active power demand and total reactive power demand are calculated in reverse based on the generalized frequency voltage control quantity.
[0032] The active power load ratio and reactive power load ratio of the static synchronous condenser are set, and adaptive adjustment is performed in combination with its short-term energy storage available energy margin, current margin and normalized thermal state to form an a priori power allocation vector. The a priori power allocation vector is dominated by the grid-type energy storage frequency and the static synchronous condenser voltage, and the two are cross-assisted.
[0033] Specifically, the constraint optimization assignment in step S50 involves solving the following quadratic programming problem:
[0034] The objective function includes: a term for fulfilling frequency-voltage control requirements, a term for maintaining the prior power allocation vector, and a term for suppressing the decrease in the joint frequency-voltage stability margin;
[0035] The joint frequency voltage stability margin is defined based on the joint frequency voltage energy function. When the joint frequency voltage energy matrix is positive, the joint frequency voltage stability margin is determined to meet the condition.
[0036] The constraints of the optimization process include apparent power limitations of grid-type energy storage and static synchronous condensers, state of charge constraints of grid-type energy storage, short-term energy storage constraints of static synchronous condensers, and thermal overload constraints.
[0037] Specifically, in step S50, when the quadratic programming problem becomes infeasible due to an extreme failure, a current priority projection strategy is adopted:
[0038] When the voltage drops significantly, increase the reactive power priority of the static synchronous condenser.
[0039] When the frequency deviation and frequency change rate exceed the limit, the active power priority of the grid-type energy storage is increased to achieve a smooth transfer of control tasks.
[0040] Specifically, in step S60, the closed-loop control process of the local grid controller of the grid-type energy storage and the static synchronous condenser includes:
[0041] Grid-based energy storage adopts frequency-driven virtual synchronous control, which adjusts the phase angle and frequency dynamics according to the allocated active power command to maintain strong frequency stiffness.
[0042] The static synchronous condenser adopts voltage-dominated grid control, which adjusts the internal potential amplitude dynamically according to the allocated reactive power command to maintain strong voltage stiffness.
[0043] A current-limiting smoothing function is introduced into the local control to prevent overcurrent in the converter.
[0044] Compared with the prior art, the present invention has the following beneficial effects:
[0045] (1) This invention establishes a frequency-voltage full coupling model with power grid strength parameterization and calculates the control effectiveness matrix, thereby achieving accurate quantitative evaluation of the cross-coupling effects of active power-voltage and reactive power-frequency under weak power grids. This provides a scientific mathematical basis for coordinated control allocation, avoids the control competition problem caused by the failure of traditional decoupling control under low short-circuit ratio, and effectively reduces the root mean square error of frequency-voltage control deviation.
[0046] (2) By introducing a virtual frequency-voltage prediction guide with grid strength perception, this invention realizes feedforward compensation that embeds power imbalance and cross-coupling effects into the reference trajectory, thereby effectively avoiding the problem of converter overcurrent and rapid energy consumption on the DC side caused by rigid recovery command under weak grid conditions, and suppressing transient current peak under extreme fault conditions.
[0047] (3) By constructing a quadratic planning optimization allocation method based on joint frequency and voltage stability margin and multi-device constraints, this invention realizes the dynamic responsibility transfer of "networked energy storage frequency dominance, static synchronous condenser voltage dominance, and cross-assistance between the two", thereby fully exploring the complementary advantages of continuous energy storage and short-term overload of synchronous condenser and improving the overall capacity utilization of converter.
[0048] (4) This invention addresses the infeasible optimization conditions by designing a current priority projection strategy, thereby achieving smooth degradation and priority protection of control tasks under extreme faults, thus enhancing the system's survivability and frequency-voltage collaborative support resilience under severe disturbances. Attached Figure Description
[0049] Figure 1 This is a schematic diagram of the collaborative control process of an embodiment of the present invention. Detailed Implementation
[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.
[0051] Example
[0052] like Figure 1As shown, this embodiment provides a coordinated control method for grid-connected energy storage and static synchronous condensers that considers frequency-voltage coupling. The system consists of an equivalent renewable energy source, a battery energy storage system (BESS) using grid-connected control, a static synchronous condenser (SSC), a point of common coupling (PCC), and an external AC power grid. Both the BESS and SSC employ voltage source grid-connected control and are connected in parallel to the PCC. The BESS has continuous active power regulation capability, while the SSC is equipped with supercapacitors or equivalent short-time DC energy storage units to provide millisecond to second-level transient active power and rapid reactive power support. The static synchronous condenser (SSC) used in this invention is a static synchronous phase-changing device based on a voltage source converter, unlike traditional rotating synchronous condensers.
[0053] The method includes the following steps:
[0054] Step S10: Collect electrical quantities at the point of common coupling and state quantities of grid-type energy storage and static synchronous condensers, identify the equivalent impedance and generalized short-circuit ratio of the external power grid, and determine the power grid strength state vector.
[0055] Specifically, the voltage, frequency, current, and active and reactive power of the PCC are collected, while the state of charge and available capacity of the BESS, and the short-time energy storage capacity, current margin, and thermal state of the SSC are also obtained. The online identification process employs a recursive least squares method, extracting the fundamental frequency positive sequence component to obtain the equivalent impedance and impedance angle of the external power grid at its fundamental frequency. The equivalent impedance of the external power grid at its fundamental frequency is denoted as... The impedance angle is , where R g X represents the equivalent resistance of the power grid. g This represents the inductive reactance of the power grid. The equivalent short-circuit capacity at PCC is denoted as S. sc The calculation is as follows:
[0056]
[0057] In the above formula, U N This refers to the rated voltage of the PCC. The generalized short-circuit ratio is defined as the ratio of the equivalent short-circuit capacity of the PCC to the total apparent power of the grid-connected power electronic devices, expressed as...
[0058]
[0059] In the above formula, and These represent the rated apparent power of grid-connected energy storage and static synchronous condensers, respectively. A larger gSCR indicates a stronger external AC grid capacity relative to the parallel device capacity of the PCC, while a smaller gSCR indicates a weaker grid. The generalized short-circuit ratio gSCR characterizes the grid's short-circuit capacity, and combined with preset weak and strong grid judgment thresholds, the normalized grid strength is calculated. , can be represented as:
[0060]
[0061] In the above formula, gSCR w The threshold for weak network detection, gSCR s The threshold for determining a strong network is 'sat', where 'sat' is a saturation function. The smaller the value, the weaker the power grid. This indicates a weak network connection.
[0062] The external power grid's fundamental frequency equivalent impedance and impedance angle are combined with the normalized power grid strength to construct a power grid strength state vector. , can be represented as: .
[0063] Step S20: Based on the pre-constructed frequency-voltage full coupling model with parameterized grid strength, calculate and update the frequency-voltage coupling coefficient and control effectiveness matrix to characterize the actual frequency and voltage regulation capabilities of the two types of devices: grid-type energy storage and static synchronous condenser.
[0064] Specifically, small-signal linearization is performed at the rated operating point. The PCC frequency deviation and voltage amplitude deviation are selected as the state vector, and the active and reactive power increments of the grid-type energy storage and SSC are used as the control input vectors. This can be expressed as follows:
[0065]
[0066] In the above formula, Represents the state vector. The PCC bus angular frequency deviation is obtained by subtracting the rated power frequency from the current actual angular frequency. The deviation of the PCC bus voltage amplitude is obtained by subtracting the rated voltage amplitude from the actual bus voltage amplitude. The superscript T indicates transposition. Represents the control input vector. For grid-type energy storage, the active power regulation increment, For incremental reactive power regulation of grid-type energy storage, For SSC active power adjustment increment, This is the reactive power adjustment increment for SSC.
[0067] The frequency-voltage fully coupled model can be expressed as:
[0068]
[0069] In the above formula, the load disturbance vector middle For equivalent active power disturbance, For equivalent reactive power disturbance, This represents the perturbation input matrix, which is generally a constant matrix; Represents the power grid state matrix; To control the input matrix, it can be represented as
[0070]
[0071] In a matrix, row index and These represent the effects on the dynamic deviations of PCC angular frequency and voltage amplitude, respectively, indicated by column headings. , , and These eight elements represent the BESS active power, BESS reactive power, SSC active power, and SSC reactive power control channels, respectively. They characterize the linearization control effect of the corresponding power channel on the PCC frequency or voltage dynamics. Specifically, The linearization control coefficient for the BESS active power regulation increment on the PCC angular frequency deviation dynamics. The linearization control coefficient of the BESS reactive power regulation increment on the PCC angular frequency deviation dynamics. The linearization control coefficient for the SSC active power regulation increment on the PCC angular frequency deviation dynamics. The linearization control coefficient of the SSC reactive power regulation increment on the PCC angular frequency deviation dynamics. The linearization control coefficient of the BESS active power regulation increment on the PCC voltage amplitude deviation dynamics. The linearization control coefficient of the BESS reactive power regulation increment on the dynamics of the PCC voltage amplitude deviation is given. The linearization control coefficient for the SSC active power regulation increment on the PCC voltage amplitude deviation dynamics. This represents the linearized control coefficient of the reactive power regulation increment of the SSC on the dynamic voltage amplitude deviation of the PCC. Based on the definitions of the main channel matrix and the cross-channel matrix, the active-frequency and reactive-voltage terms are assigned to the main channel, and the reactive-frequency and active-voltage terms are assigned to the cross-channel. The BESS primarily uses active-frequency regulation, while the SSC primarily uses reactive-voltage regulation. The cross-term is relatively small under strong grid conditions, and its proportion increases with increasing frequency under weak grid conditions. Increase and Improvement comes with change.
[0072] Extracting the main channel matrix from the frequency-voltage fully coupled model With cross-channel matrix The degree of frequency-voltage coupling can be quantitatively characterized as follows:
[0073]
[0074] The frequency-voltage coupling coefficient is calculated based on the ratio of the Frobenius norm of the main channel matrix to the cross channel matrix. , can be represented as
[0075]
[0076] In the above formula, It is the Frobenius norm. To prevent extremely small positive numbers with a denominator of zero; The larger the size, the more traditional it is. – , – The less valid the decoupling assumption is.
[0077] By combining the state base matrix and available power capacity matrix of the grid-type energy storage and the static synchronous condenser, the frequency-voltage fully coupled model is normalized to obtain the normalized control effectiveness matrix. , can be represented as
[0078]
[0079] In the above formula, The state basis value matrix, This is the reference value for angular frequency. The reference value for the PCC bus voltage is given, and diag represents a diagonal matrix. This is the available power capacity matrix. This represents the maximum available capacity currently available for grid-based energy storage. This represents the maximum available power capacity of the SSC. Each column reflects the unitized control effect of the corresponding power channel on frequency and voltage under the current grid strength and equipment capacity, and is the core basis for subsequent coordinated allocation.
[0080] Step S30: Based on the electrical quantities at the common connection point and the output power of the two types of devices, estimate the equivalent active and reactive disturbances of the system using an extended state observer.
[0081] Specifically, an extended state observer is designed, with the frequency deviation and voltage amplitude deviation at the point of common coupling as the states, and equivalent active and reactive disturbances as the extended states, which can be represented as follows:
[0082]
[0083]
[0084] In the above formula, and These are the state estimate and the disturbance estimate, respectively. The state observation gain matrix is... This is the observation gain matrix for disturbances. The observer gain is determined by pole placement or linear matrix inequalities to ensure that the observation error system remains stable within the allowable range of grid strength.
[0085] Step S40: Based on the grid strength state vector and the equivalent active and reactive disturbances, generate the frequency reference trajectory and voltage reference trajectory jointly tracked by the two types of devices through the virtual frequency-voltage guide of grid strength perception.
[0086] Specifically, under weak grid conditions, a rigid rated reference forces the converter to output large amounts of active and reactive power in a short period of time, leading to conflicts between overcurrent, rapid DC-side energy consumption, and the frequency-voltage recovery process. Therefore, a virtual frequency-voltage state is defined. , For virtual frequency deviation, To simulate the voltage amplitude deviation, a second-order virtual frequency-voltage guidance model is constructed, which includes a virtual inertia matrix, a damping matrix, and a restitution coefficient matrix. The leakage integral prediction state and the mapping matrix from the disturbance to the frequency-voltage reference are introduced, and the feedforward compensation of the equivalent active disturbance and the equivalent reactive disturbance are embedded in the virtual frequency-voltage guidance model.
[0087] The second-order virtual frequency voltage guidance model can be expressed as:
[0088]
[0089] In the above formula, , , These are the virtual inertia matrix, damping matrix, and restitution coefficient matrix, respectively. The mapping matrix from the perturbation to the frequency voltage reference. Here is the integral gain matrix. The leakage integral prediction state has the following dynamics:
[0090]
[0091] In the above formula, It is a positive definite diagonal gain matrix;
[0092] matrix In a fully coupled form, it can be represented as
[0093]
[0094] In the above formula, For active-virtual frequency channel gain, For reactive-virtual frequency cross-coupling gain, For active-virtual voltage cross-coupling gain, For reactive power-virtual voltage path gain; and Based on frequency-voltage coupling coefficient Online adjustments enable feedforward compensation of the effects of reactive power disturbances on frequency and active power disturbances on voltage during the reference trajectory generation stage.
[0095] The weaker the power grid, the easier it is for rapid frequency and voltage recovery to induce current saturation and cross-oscillations. Therefore, the virtual reference model should appropriately increase inertia and damping, while enhancing disturbance feedforward compensation. The virtual inertia matrix, damping matrix, and integral gain matrix are adaptively adjusted based on the aforementioned power grid strength state vector, where the lower the power grid strength, the greater the virtual inertia and damping. The adaptive adjustment strategy can be expressed as:
[0096]
[0097]
[0098] In the above formula, and These are the foundation inertia matrix and foundation damping matrix under a strong power grid, respectively. and These are the additional inertia matrix and the additional damping matrix for the weak network, respectively. This is the basic integral gain matrix under a strong power grid. Add a correction gain matrix to the weak network. For the base cross-coupling gain under strong power grid conditions, A fixed correction factor is applied to this channel. For the active power-voltage coupling gain of the foundation under a strong power grid, A fixed correction factor is applied to this gain. This adaptive adjustment strategy separates "recovery speed" and "support strength": the virtual frequency voltage bootstrap is responsible for generating a smooth, achievable frequency voltage trajectory; the power control layers of BESS and SSC are responsible for rapid support, thereby avoiding slow response caused by simply increasing virtual inertia, or network instability caused by simply increasing control bandwidth.
[0099] Solving the second-order virtual frequency-voltage guidance model yields the virtual frequency-voltage state, which serves as the frequency reference trajectory and voltage reference trajectory.
[0100] Step S50: Calculate the generalized frequency-voltage control quantity based on the frequency reference trajectory and voltage reference trajectory, and perform constraint optimization allocation based on the control effectiveness matrix, joint frequency-voltage stability margin and equipment constraints to obtain the active power command and reactive power command of the grid-type energy storage and static synchronous condenser.
[0101] Specifically, in the process of calculating the generalized frequency-voltage control quantity, the frequency-voltage tracking error and its derivative are defined as follows:
[0102]
[0103] In the above formula, The tracking error vector is given by the frequency tracking error vector. The voltage tracking error corresponds to .
[0104] By combining the frequency-voltage coordinated feedback gain with the equivalent active and reactive power disturbances, the required equivalent frequency control action and voltage control action at the current moment are calculated and combined into a generalized frequency-voltage control quantity. , can be represented as
[0105]
[0106] In the above formula, , For frequency-voltage collaborative feedback gain; These represent the equivalent frequency control and voltage control required at the current moment, rather than directly specifying the power of a particular device.
[0107] To maintain a clear physical division of labor, a priori power allocation vector is constructed before performing constrained optimization allocation, which can be represented as follows:
[0108]
[0109] In the above formula, and These are respectively generalized frequency voltage control quantities The total active power demand and total reactive power demand are obtained by reverse calculation; The active power contribution ratio of the stationary synchronous condenser. This represents the reactive power load ratio of the stationary synchronous condenser. It meets the following requirements during normal operation. This establishes a basic hierarchy with BESS frequency dominance, SSC voltage dominance, and cross-assistance between the two. Its adaptive adjustment strategy can be configured as follows:
[0110]
[0111]
[0112] In the above formula, For the available energy margin of SSC short-term energy storage, For SSC current margin, Normalization heat state, This indicates the upper limit of the proportion of contribution borne. This indicates the lower limit of the proportion of reactive power contribution. The active power contribution ratio of the SSC base under a strong power grid. Adjusting the gain for weak networks, Adjust the gain to allow for energy margin adjustment. The reactive power bearing ratio of SSC under a strong power grid. To adaptively adjust the gain for weak networks, To adaptively adjust the gain for current margin, The gain is adaptively adjusted for thermal conditions.
[0113] Specifically, during the constraint optimization allocation process based on the control effectiveness matrix, joint frequency-voltage stability margin, and equipment constraints, the following quadratic programming problem is solved in each coordinated control cycle:
[0114] The objective function is expressed as
[0115]
[0116] In the above formula, the weighted 2-norm , This is a positive definite weight matrix; the first term is the frequency and voltage control requirement fulfillment term, ensuring that the frequency and voltage control requirements are met. The first term is the frequency-voltage tracking error weight matrix; the second term is the prior power allocation vector term, maintaining the prior responsibility of "dual dominance and cross-assistance". The prior power reference penalty coefficient, The first term is the weighting matrix for the output deviation of the two types of devices; the second term is the term for suppressing the decrease in the joint frequency-voltage stability margin. The stability margin penalty coefficient, This is a joint frequency voltage stability margin penalty term.
[0117] Define the joint frequency-voltage energy function , represented as
[0118]
[0119] In the above formula, The equivalent inertia coefficient, The equivalent recovery coefficient, This represents the frequency-voltage cross-coupling coefficient.
[0120] And define the joint frequency-voltage stability margin , represented as
[0121]
[0122] In the above formula, To preset the minimum expected stability margin reference threshold, The real-time estimated joint frequency-voltage stability margin obtained from online identification can be updated by the online small-signal model or recursive identification results, so that the cooperative allocation not only tracks the frequency and voltage, but also actively avoids entering the strongly coupled low-damping region.
[0123] when When the joint frequency-voltage energy matrix is positive definite, it is determined that the joint frequency-voltage stability margin meets the condition.
[0124] The constraints of the optimization process include apparent power limitations of grid-type energy storage and static synchronous condensers, state of charge constraints of grid-type energy storage, short-term energy storage constraints of static synchronous condensers, and thermal overload constraints.
[0125] The apparent power limitation of grid-type energy storage and static synchronous condenser is expressed as:
[0126]
[0127] In the above formula, i=b represents a BESS device, i=s represents an SSC device, Pi is the current total active power output of device i, and Qi is the current total reactive power output of device i. The current available apparent power limit for device i.
[0128] The state-of-charge constraint of grid-based energy storage is expressed as:
[0129]
[0130] In the above formula, This refers to the real-time state of charge of the BESS. and These are the minimum and maximum charge thresholds allowed by BESS, respectively.
[0131] The short-time energy storage constraint of a stationary synchronous condenser is expressed as:
[0132]
[0133] In the above formula, The current stored energy for SSC short-term energy storage. and These represent the lower and upper limits of available energy for SSC short-term energy storage, respectively.
[0134] Thermal overload constraint is expressed as
[0135]
[0136] In the above formula, This represents the rate of temperature change of the SSC power device over time. Where is the heat gain coefficient, and Is is the SSC output operating current. For heat dissipation coefficient, This refers to the current temperature of the SSC power device. For ambient temperature, This refers to the maximum permissible operating temperature for SSC power devices.
[0137] Since the objective function is a convex quadratic form and the above capacity constraints can be processed by second-order cone or conservative linearization, the proposed power allocation can be solved in real time within the control cycle.
[0138] When the quadratic programming problem becomes infeasible due to extreme failures, a current priority projection strategy is adopted:
[0139] When the voltage drops significantly, increase the reactive power priority of the static synchronous condenser.
[0140] When the frequency deviation and frequency change rate exceed the limit, the active power priority of the grid-type energy storage is increased to achieve a smooth transfer of control tasks.
[0141] Step S60: The optimized active power command and reactive power command are sent to the local grid controller of the grid-type energy storage and static synchronous condenser for closed-loop control.
[0142] Specifically, grid-based energy storage employs frequency-driven virtual synchronous control, adjusting phase angle and frequency dynamics according to allocated active power commands to maintain strong frequency stiffness. This can be expressed as...
[0143]
[0144] In the above formula, The derivative of the virtual phase angle of the output voltage of the BESS virtual synchronous machine. This is the local virtual angular frequency of BESS. This is the system's rated angular frequency; For the virtual rotational inertia of BESS, The rate of change of virtual angular frequency. This is a reference value for the active power of energy storage issued by the upper level. This represents the actual active power output of the BESS. This is the BESS frequency damping coefficient. This is the virtual reference angular frequency output by the upper-level model.
[0145] The static synchronous condenser employs voltage-dominated grid control, dynamically adjusting its internal potential amplitude according to the allocated reactive power command to maintain strong voltage stiffness. This can be expressed as...
[0146]
[0147] In the above formula, The time constant of the SSC potential loop is... The rate of change of the virtual internal potential amplitude in SSC network control. For SSC voltage proportional gain, This serves as the virtual voltage reference output by the upper-level model, where V is the measured voltage of the PCC bus. This refers to the reactive power droop factor for SSC. This represents the actual reactive power output of the SSC. This is the SSC reactive power reference value issued by the upper level. For current limiting feedback gain, For current-limited smoothing functions, This refers to the output current of the SSC.
[0148] Introducing a current-limiting smoothing function in local control This prevents overcurrent in the converter. Control parameters must meet [the specified requirements]. , , For SSC equivalent frequency damping, To improve the BESS voltage loop gain, the local control layer further ensures that the BESS has strong frequency stiffness and the SSC has strong voltage stiffness. Optimize the output distribution. , As the outer loop command for both types of devices, the local voltage and current inner loop are executed continuously at a high frequency.
[0149] Stability analysis
[0150] Assume power grid strength state Belongs to compact set The model matrix is continuous and bounded; the rate of change of the disturbance is bounded; the control effectiveness matrix has full row rank in the controllable frequency subspace; and the observer error system is exponentially stable.
[0151] Define the perturbation estimation error vector Choose the Lyapunov function
[0152]
[0153] Among them, the symmetric positive definite weighting matrix in the quadratic form of frequency voltage tracking error Symmetric positive definite weighting matrix in the quadratic form of the perturbation estimation error Positive weighting coefficients of the joint frequency-voltage energy term Substituting the generalized frequency-voltage control quantity and the optimized allocation error into the closed-loop system, we can obtain the following using Young's inequality:
[0154]
[0155] In the formula, , and All are positive values, corresponding to the frequency voltage tracking error, disturbance estimation error, and the attenuation term of the joint frequency voltage energy, respectively; The constant is obtained by estimating the upper bound of the relevant interaction terms using Young's inequality. The constant is obtained by applying Young's inequality to estimate the upper bound of the related terms of the rate of change of the disturbance; To allocate residuals to controls affected by capacity constraints and numerical solution errors, The optimal control input vector obtained from the constrained optimization problem in step S50 is derived from the BESS active power optimal increment. BESS optimal reactive power increment SSC active power optimal increment and SSC reactive power optimal increment Composition. If and If it is bounded, then there exist positive constants. and ,make
[0156]
[0157] Obtained from the comparison principle
[0158]
[0159] Therefore, frequency error, voltage error, disturbance observation error, and joint frequency-voltage energy consistency are eventually bounded; when the rate of change of the disturbance approaches zero and the optimization residual approaches zero, the frequency-voltage tracking error asymptotically converges. Parameter scheduling adopts continuous mapping and sets a rate of change limit, which can avoid the discontinuity of control parameters caused by sudden changes in grid strength.
[0160] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any changes made based on the design principles of the present invention, or any non-creative modifications made thereon, shall fall within the scope of protection of the present invention.
Claims
1. A method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling, characterized in that, Includes the following steps: S10. Collect electrical quantities at the point of common connection and state quantities of grid-type energy storage and static synchronous condensers, identify the equivalent impedance and generalized short-circuit ratio of the external power grid, and determine the power grid strength state vector. S20. Based on the pre-constructed frequency-voltage full coupling model with parameterized grid strength, calculate and update the frequency-voltage coupling coefficient and control effectiveness matrix to characterize the actual frequency and voltage regulation capabilities of the two types of devices: grid-type energy storage and static synchronous condenser. S30. Based on the electrical quantities at the common connection point and the output power of the two types of devices, the equivalent active and reactive disturbances of the system are estimated using an extended state observer. S40. Based on the grid strength state vector and the equivalent active and reactive disturbances, the frequency reference trajectory and voltage reference trajectory jointly tracked by the two types of devices are generated through the virtual frequency-voltage guide of grid strength perception. S50. Calculate the generalized frequency-voltage control quantity based on the frequency reference trajectory and voltage reference trajectory, and perform constraint optimization allocation based on the control effectiveness matrix, joint frequency-voltage stability margin and equipment constraints to obtain the active power command and reactive power command of the grid-type energy storage and static synchronous condenser. S60. The optimized active power command and reactive power command are respectively sent to the local grid controller of the grid-type energy storage and static synchronous condenser for closed-loop control.
2. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 1, characterized in that, In step S10, the process of determining the power grid strength state vector includes: Identify the equivalent impedance, impedance angle, and generalized short-circuit ratio of the external power grid based on the voltage / current changes at the point of common coupling. The generalized short-circuit ratio is used to characterize the short-circuit capacity of the power grid. Combined with the preset thresholds for weak and strong grids, the normalized grid strength is calculated. The power grid strength state vector is constructed by combining the external power grid's fundamental frequency equivalent impedance and impedance angle with the normalized power grid strength.
3. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 2, characterized in that, In step S20, the process of calculating and updating the frequency-voltage coupling coefficient and the control effectiveness matrix includes: Small-signal linearization is performed at the rated operating point to extract the main channel matrix and cross channel matrix in the frequency-voltage fully coupled model; The frequency-voltage coupling coefficient is calculated based on the ratio of the Frobenius norm of the main channel matrix to the cross channel matrix. By combining the state base value matrix and available power capacity matrix of the grid-type energy storage and the static synchronous condenser, the frequency-voltage fully coupled model is normalized to obtain the normalized control effectiveness matrix.
4. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 3, characterized in that, In step S30, the extended state observer is configured with the common coupling point frequency deviation and voltage amplitude deviation as states, and the equivalent active and reactive disturbances as extended states. The observer gain is determined by pole placement or linear matrix inequalities to keep the observation error system stable within the allowable range of the power grid strength.
5. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 4, characterized in that, In step S40, the process of generating a frequency reference trajectory and a voltage reference trajectory jointly tracked by the two types of devices through a virtual frequency-voltage guide that senses power grid strength includes: A second-order virtual frequency-voltage guidance model is constructed, which includes a virtual inertia matrix, a damping matrix, and a restitution coefficient matrix. A leakage integral prediction state is introduced, and a mapping matrix from disturbance to frequency voltage reference is designed. The feedforward compensation of equivalent active disturbance and equivalent reactive disturbance is embedded in the second-order virtual frequency voltage guidance model. The virtual inertia matrix, damping matrix, and integral gain matrix are adaptively adjusted based on the power grid strength state vector. The lower the power grid strength, the greater the virtual inertia and damping. The frequency reference trajectory and voltage reference trajectory are obtained by solving the second-order virtual frequency-voltage guidance model.
6. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 5, characterized in that, In step S50, the process of calculating the generalized frequency voltage control quantity includes: Obtain the frequency tracking error and its derivative, and the voltage tracking error and its derivative; By combining the frequency-voltage collaborative feedback gain with the equivalent active and reactive disturbances, the equivalent frequency control action and voltage control action required at the current moment are calculated and combined into a generalized frequency-voltage control quantity.
7. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 6, characterized in that, Before performing constraint optimization allocation in step S50, the method further includes the step of constructing a priori power allocation vector: The total active power demand and total reactive power demand are calculated in reverse based on the generalized frequency voltage control quantity. The active power load ratio and reactive power load ratio of the static synchronous condenser are set, and adaptive adjustment is performed in combination with its short-term energy storage available energy margin, current margin and normalized thermal state to form an a priori power allocation vector. The a priori power allocation vector is dominated by the grid-type energy storage frequency and the static synchronous condenser voltage, and the two are cross-assisted.
8. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 7, characterized in that, The constraint optimization assignment in step S50 involves solving the following quadratic programming problem: The objective function includes: a term for fulfilling frequency-voltage control requirements, a term for maintaining the prior power allocation vector, and a term for suppressing the decrease in the joint frequency-voltage stability margin; The joint frequency voltage stability margin is defined based on the joint frequency voltage energy function. When the joint frequency voltage energy matrix is positive, the joint frequency voltage stability margin is determined to meet the condition. The constraints of the optimization process include apparent power limitations of grid-type energy storage and static synchronous condensers, state of charge constraints of grid-type energy storage, short-term energy storage constraints of static synchronous condensers, and thermal overload constraints.
9. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 8, characterized in that, In step S50, when the quadratic programming problem becomes infeasible due to an extreme failure, a current priority projection strategy is adopted: When the voltage drops significantly, increase the reactive power priority of the static synchronous condenser. When the frequency deviation and frequency change rate exceed the limit, the active power priority of the grid-type energy storage is increased to achieve a smooth transfer of control tasks.
10. The method for coordinated control of grid-type energy storage and static synchronous condenser considering frequency-voltage coupling according to claim 9, characterized in that, In step S60, the closed-loop control process of the local grid controller for the grid-type energy storage and the static synchronous condenser includes: Grid-based energy storage adopts frequency-driven virtual synchronous control, which adjusts the phase angle and frequency dynamics according to the allocated active power command to maintain strong frequency stiffness. The static synchronous condenser adopts voltage-dominated grid control, which adjusts the internal potential amplitude dynamically according to the allocated reactive power command to maintain strong voltage stiffness. A current-limiting smoothing function is introduced into the local control to prevent overcurrent in the converter.