Impedance modeling method and system of grid-connected energy storage system considering ac-dc coupling

Abstract

The application belongs to the technical field of energy storage grid-connected modeling, and provides an impedance modeling method and system for a grid-connected energy storage system considering AC-DC coupling, which comprises the following steps: solving a steady-state equilibrium point according to the main circuit topology, control architecture and operating condition of the grid-connected energy storage system to be modeled; establishing a small-signal deviation relationship between a control coordinate system and a system coordinate system based on the steady-state equilibrium point, and obtaining a mapping relationship of a duty cycle disturbance with respect to a voltage disturbance and a current disturbance in the system coordinate system; establishing a small-signal model of an AC side filter main circuit and a DC side small-signal model containing a DC bus capacitor and a battery equivalent circuit, combining the mapping relationship, and constructing an AC-DC coupling small-signal model; eliminating the AC-DC coupling small-signal model to obtain an output impedance matrix of the grid-connected energy storage system. The application can improve the accuracy of impedance analysis of the grid-connected energy storage system, and make it more truly reflect the influence of parameter changes of the DC side energy storage unit on the impedance characteristics of the AC side.

Description

Technical Field

[0001] This invention belongs to the field of energy storage grid-connected modeling technology, and specifically relates to an impedance modeling method and system for grid-connected energy storage systems that take into account AC / DC coupling. Background Technology

[0002] The large-scale grid-connected application of new energy and electrochemical energy storage, with grid-connected energy storage having better adaptability than traditional grid-connected energy storage, is a core supporting equipment for the stable operation of new power systems.

[0003] When grid-connected energy storage is in operation, the dynamic interaction between multiple devices and the power grid can easily cause grid stability faults such as multi-frequency oscillations and resonances.

[0004] Currently, the industry mainly uses the impedance method to conduct small-signal stability analysis of grid-connected converters. This method transforms the dynamic interaction between the converter and the grid into a source-grid impedance matching problem, which has the core advantage of clear physical meaning. At the same time, it can efficiently carry out parameter sensitivity analysis and construct engineering criteria, making it the mainstream technical means for grid-connected stability analysis of energy storage.

[0005] Existing impedance modeling methods are mostly adapted to grid-based energy storage. However, the impedance model for VSG-controlled grid-based energy storage is incomplete and has several shortcomings: it fails to consider the impact of angular deviations in the grid control coordinate system on impedance characteristics; it simplifies the DC side to an ideal constant voltage source, neglecting AC-DC dynamic coupling; it does not incorporate the battery equivalent model, making it unsuitable for different battery operating states; and there is insufficient connection between steady-state solution and modeling processes. This leads to distortion of the model's impedance amplitude and phase characteristics, easily causing deviations in grid stability boundaries and oscillation risk assessments, and fails to meet the needs of grid-based energy storage engineering analysis and control design. Summary of the Invention

[0006] The purpose of this invention is to provide an impedance modeling method and system for grid-type energy storage systems that takes into account AC / DC coupling, so as to solve the problem that the impedance amplitude and phase characteristics of existing technology models are distorted, which can easily cause deviations in the assessment of grid stability boundaries and oscillation risks.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an impedance modeling method for a grid-type energy storage system considering AC / DC coupling, comprising: Based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled, the steady-state equilibrium point is determined. Based on the steady-state equilibrium point, a small-signal deviation relationship between the control coordinate system and the system coordinate system is established. Based on the deviation relationship, small-signal models of the power outer loop, voltage amplitude outer loop, and inner loop control are derived, and the mapping relationship between duty cycle disturbance and voltage disturbance and current disturbance in the system coordinate system is obtained. A small-signal model of the AC-side filter main circuit and a DC-side small-signal model including the DC bus capacitor and the battery equivalent circuit are established. Based on the mapping relationship, an AC-DC coupled small-signal model is constructed. Elimination is performed on the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

[0008] Furthermore, the step of solving for the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled includes: The main circuit topology of the grid-type energy storage system to be modeled, including the grid connection interface, filtering stage, DC bus, and equivalent battery structure, is determined. The control architecture of the grid-type energy storage system, including the VSG outer loop parameters and the simplified inner loop PI control parameters, is determined. Based on the operating conditions and network parameters, the steady-state equilibrium point of the grid-type energy storage system is solved according to the steady-state circuit relationship, power balance relationship, and DC side steady-state relationship, and the steady-state voltage, current, internal potential, duty cycle, and DC side voltage are obtained.

[0009] Furthermore, the steady-state equilibrium point includes the main circuit steady-state equilibrium point and the DC side steady-state equilibrium point; The solution for the steady-state equilibrium point of the main loop includes: Establish a steady-state circuit relationship between the internal potential, PCC voltage, and current on the AC side, and denote the internal potential of the grid-type energy storage. The complex vector is:

[0010] For the complex vector of the internal potential of a grid-type energy storage system, , For the real and imaginary steady-state components of the internal potential of grid-type energy storage, Let the imaginary operator be denoted as ; and let the steady-state admittances of the filter branch, the power grid branch, and the parallel branch be denoted as . , , Then the steady-state voltage of PCC is uniformly expressed as:

[0011] in, The steady-state voltage of PCC Let be the steady-state value of the equivalent voltage source of the power grid; when there are no parallel branches, let =0; Further obtain PCC current and physical filter branch current They are respectively:

[0012] Based on the steady-state operation target, active and reactive power are expressed as follows:

[0013] superscript Indicates a conjugate relationship. To perform the operation of taking the real part, For the imaginary part calculation; the reference values ​​for active and reactive power of the grid-type energy storage are denoted as follows: P ref , Q ref United P 0= P ref Q0=Q ref The steady-state component of the internal potential is obtained. E d0 , E rq0 This leads to the d-axis steady-state component of the voltage. U d0 steady-state component of voltage q-axis U q0 d-axis steady-state component of current I d0 steady-state component of current q-axis I q0 and the steady-state component of the d-axis current of the filter branch I fd0 q-axis steady-state component of filter branch current I fq0 ; The solution for the steady-state equilibrium point on the DC side includes: On the DC side, based on the steady-state modulation relationship of the two-level converter and the steady-state power balance relationship of the battery, the following is established:

[0014] in, This is the battery open-circuit voltage. This is the steady-state voltage of the DC bus. Let be the ohmic internal resistance of the battery; solve the simultaneous equations to obtain the steady-state operating point on the DC side.

[0015] Furthermore, establishing the small-signal deviation relationship between the control coordinate system and the system coordinate system based on the steady-state equilibrium point includes: The voltage, current, and duty cycle in the system coordinate system are u s i s d s The corresponding quantities in the control coordinate system are u c i c d c Then, all electrical quantities satisfy a unified rotational transformation relationship between the two coordinate systems. Under linearization conditions, the rotational transformation relationship can be written as the sum of the steady-state rotation term and the phase angle disturbance-introduced term:

[0016] in, To control small disturbance components of electrical quantities in the coordinate system, This refers to the small disturbance component of the electrical quantity in the system coordinate system. The superscript ~ uniformly indicates the small disturbance component of this parameter. Let be the rotation matrix determined by the steady-state angle. Let θ be its first-order partial derivative matrix with respect to angle, and let θ be the phase angle disturbance generated by the network control. For the steady-state value of the corresponding electrical quantity, for different physical quantities, The unified representation is:

[0017] in, , These represent the steady-state components of the voltage along the d and q axes, respectively. , These represent the steady-state components of the current along the d and q axes, respectively. , Let d and q represent the steady-state components of the duty cycle, respectively; let φ be the steady-state angle between the control coordinate system and the system coordinate system, where φ represents the difference between the steady-state voltage phase angle and the internal potential phase angle of the PCC; then the rotation matrix... Its first-order partial derivative matrix They are represented as follows:

[0018]

[0019] The small-signal transformation relationships of voltage, current, and duty cycle between the control coordinate system and the system coordinate system are obtained respectively.

[0020] Furthermore, the small-signal models for the power outer loop, voltage amplitude outer loop, and inner loop control, derived based on the deviation relationship, yield the mapping relationship between the duty cycle disturbance and the voltage and current disturbances in the system coordinate system, including: The small-signal models of the power outer loop and the voltage amplitude outer loop are derived, including: Linearizing the instantaneous power in the dq coordinate system at the steady-state equilibrium point yields the relationship between active power disturbance and reactive power disturbance and voltage disturbance and current disturbance; The power disturbance is input into the transfer functions of the active phase angle loop and the reactive voltage amplitude loop, respectively, to obtain the phase angle disturbance and the internal potential amplitude disturbance generated by the VSG outer loop; The small-signal model of the inner-loop control is derived, and the mapping relationship between duty cycle disturbance and voltage and current disturbances in the system coordinate system is obtained, specifically including: The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combining the phase angle disturbance obtained from the outer loop and the internal potential amplitude disturbance, through the voltage regulation and current regulation links, the mapping relationship in the system coordinate system can be derived, which can be represented by a linear combination of voltage disturbance and current disturbance.

[0021] Furthermore, the small-signal models for the power outer loop and the voltage amplitude outer loop specifically include: A VSG outer loop control structure is adopted, in which the active power-phase angle loop is used to establish synchronous power angle dynamics, and the reactive power-voltage amplitude loop is used to adjust the internal potential amplitude. First, based on the instantaneous power relationship in the dq coordinate system, at the steady-state operating point... U d0 , U q0 , I d0 , I q0 Performing small-signal linearization in the vicinity, we get:

[0022] in, For small disturbance components of active power, For small disturbance components of reactive power, , The static relationship matrix between active and reactive power with respect to voltage and current is:

[0023]

[0024] The outer loop of the VSG satisfies the following relationship: the active power deviation, after passing through the inertia and damping elements, results in phase angle disturbance; the reactive power deviation, after passing through the voltage amplitude regulation element, results in internal potential amplitude disturbance, which can be uniformly expressed as:

[0025] in, For phase angle perturbation, This is an internal potential amplitude disturbance. The outer loop transfer function matrix for VSG control; for the VSG control structure, the following general form is adopted:

[0026] in, For virtual inertia coefficient, The damping coefficient is... The rated angular frequency, This is the voltage amplitude adjustment coefficient; For the Laplace operator; Substituting the power-signal relationship into the outer-loop control equation, we get:

[0027] The phase angle disturbance and internal potential amplitude disturbance generated by the VSG outer loop are both represented as a linear combination of voltage disturbance and current disturbance in the system coordinate system, and embedded in the inner loop and main circuit model; The derived small-signal model of the inner-loop control includes: The following simplified inner-loop control structure is adopted:

[0028] in, For voltage regulation, For current regulation; Rewrite the two PI components in diagonal matrix form:

[0029]

[0030] in, , These are the proportional coefficient and integral coefficient of the voltage regulation stage, respectively. , These are the proportional coefficient and integral coefficient of the current regulation element, respectively; The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combined with the θ and E expressions obtained from the outer loop, the small-signal expressions of the inner loop error signal, voltage regulation output, and duty cycle command are obtained step by step:

[0031] in, and These represent the transmission matrices of voltage and current disturbances to duty cycle disturbances in the system coordinate system, respectively.

[0032] Furthermore, the establishment of a small-signal model of the AC-side filter main circuit and a DC-side small-signal model including the DC bus capacitor and the battery equivalent circuit, combined with the mapping relationship, to construct an AC / DC coupled small-signal model, includes: The AC side filter impedance matrix is:

[0033] in and These are the filter inductor and the filter resistor, respectively. For the Laplace operator, This is the rated angular frequency; If there is a parallel filter branch on the AC side, its small-signal admittance is uniformly expressed as the dq admittance matrix:

[0034] in, For dd channel admittance components, For the dq channel admittance component, For the qd channel admittance component, The admittance component of the qq channel is determined by the branch structure parameters; based on the dq circuit relationship of the two-level converter, the small-signal equation of the AC side main circuit is written as:

[0035] Where M is the identity matrix, This is the steady-state voltage on the DC side. For steady-state duty cycle column vectors, This is the AC side filter impedance matrix; For small disturbances in DC side voltage; This is a column vector representing the steady-state duty cycle. Consider the battery and DC bus capacitance on the DC side. C dc The effect of this is that the DC-side equivalent admittance is expressed as:

[0036] in, For DC bus capacitors, This is the equivalent impedance of the battery; The relationship between small DC-side voltage perturbations and AC-side variables can be written as follows:

[0037] in, and These represent the effects of AC-side voltage disturbances and current disturbances on DC-side voltage disturbances after coupling through duty cycle, current, DC-side admittance, and battery impedance, respectively. Substituting into the AC-side main circuit equations, a unified AC / DC coupling relationship is obtained:

[0038] Where A and B are system matrices that comprehensively consider outer loop control, inner loop control, AC side main circuit, DC bus dynamics, and battery impedance dynamics; thus, the dq output impedance matrix of the grid-type energy storage system is obtained:

[0039] in For the dd channel impedance component, For the dq channel impedance components, For the qd channel impedance component, For the qq channel impedance components; Eliminating variables from the above equations yields the dq impedance matrix Z of the grid-type energy storage system. ESS ( s Based on different battery parameters, different operating points and different grid strengths, impedance curves of grid-type energy storage systems under corresponding operating conditions are generated for impedance scanning analysis and small-disturbance stability assessment.

[0040] Secondly, the present invention provides an impedance modeling system for a grid-type energy storage system considering AC / DC coupling, comprising: The steady-state equilibrium point solution module is used to solve the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled. The mapping module is used to establish the small-signal deviation relationship between the control coordinate system and the system coordinate system based on the steady-state equilibrium point, and to derive the small-signal models of the power outer loop, voltage amplitude outer loop and inner loop control based on the deviation relationship, so as to obtain the mapping relationship between the duty cycle disturbance and the voltage disturbance and the current disturbance in the system coordinate system. The coupling construction module is used to establish a small-signal model of the AC-side filter main circuit and a DC-side small-signal model that includes the DC bus capacitor and the battery equivalent circuit. Combined with the mapping relationship, an AC-DC coupled small-signal model is constructed. The output module is used to eliminate elements in the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

[0041] Furthermore, the steady-state equilibrium point solution module is specifically used for: The main circuit topology of the grid-type energy storage system to be modeled, including the grid connection interface, filtering stage, DC bus, and equivalent battery structure, is determined. The control architecture of the grid-type energy storage system, including the VSG outer loop parameters and the simplified inner loop PI control parameters, is determined. Based on the operating conditions and network parameters, the steady-state equilibrium point of the grid-type energy storage system is solved according to the steady-state circuit relationship, power balance relationship, and DC side steady-state relationship, and the steady-state voltage, current, internal potential, duty cycle, and DC side voltage are obtained.

[0042] Furthermore, the steady-state equilibrium point includes the main circuit steady-state equilibrium point and the DC side steady-state equilibrium point; The solution for the steady-state equilibrium point of the main loop includes: Establish a steady-state circuit relationship between the internal potential, PCC voltage, and current on the AC side, and denote the internal potential of the grid-type energy storage. The complex vector is:

[0043] For the complex vector of the internal potential of a grid-type energy storage system, , For the real and imaginary steady-state components of the internal potential of grid-type energy storage, Let the imaginary operator be denoted as ; and let the steady-state admittances of the filter branch, the power grid branch, and the parallel branch be denoted as . , , Then the steady-state voltage of PCC is uniformly expressed as:

[0044] in, The steady-state voltage of PCC Let be the steady-state value of the equivalent voltage source of the power grid; when there are no parallel branches, let =0; Further obtain PCC current and physical filter branch current They are respectively:

[0045] Based on the steady-state operation target, active and reactive power are expressed as follows:

[0046] superscript Indicates a conjugate relationship. To perform the operation of taking the real part, For the imaginary part calculation; the reference values ​​for active and reactive power of the grid-type energy storage are denoted as follows: P ref , Q ref United P 0= P ref Q0=Q ref The steady-state component of the internal potential is obtained. E d0 , E rq0 This leads to the d-axis steady-state component of the voltage. U d0 steady-state component of voltage q-axis U q0 d-axis steady-state component of current I d0 steady-state component of current q-axis I q0 and the steady-state component of the d-axis current of the filter branch I fd0 q-axis steady-state component of filter branch current I fq0 ; The solution for the steady-state equilibrium point on the DC side includes: On the DC side, based on the steady-state modulation relationship of the two-level converter and the steady-state power balance relationship of the battery, the following is established:

[0047] in, This is the battery open-circuit voltage. This is the steady-state voltage of the DC bus. Let be the ohmic internal resistance of the battery; solve the simultaneous equations to obtain the steady-state operating point on the DC side.

[0048] Furthermore, the mapping module is specifically used for: The voltage, current, and duty cycle in the system coordinate system are u s i s d s The corresponding quantities in the control coordinate system are u c i c d c Then, all electrical quantities satisfy a unified rotational transformation relationship between the two coordinate systems. Under linearization conditions, the rotational transformation relationship can be written as the sum of the steady-state rotation term and the phase angle disturbance-introduced term:

[0049] in, To control small disturbance components of electrical quantities in the coordinate system, This refers to the small disturbance component of the electrical quantity in the system coordinate system. The superscript ~ uniformly indicates the small disturbance component of this parameter. Let be the rotation matrix determined by the steady-state angle. Let θ be its first-order partial derivative matrix with respect to angle, and let θ be the phase angle disturbance generated by the network control. For the steady-state value of the corresponding electrical quantity, for different physical quantities, The unified representation is:

[0050] in, , These represent the steady-state components of the voltage along the d and q axes, respectively. , These represent the steady-state components of the current along the d and q axes, respectively. , Let d and q represent the steady-state components of the duty cycle, respectively; let φ be the steady-state angle between the control coordinate system and the system coordinate system, where φ represents the difference between the steady-state voltage phase angle and the internal potential phase angle of the PCC; then the rotation matrix... Its first-order partial derivative matrix They are represented as follows:

[0051]

[0052] The small-signal transformation relationships of voltage, current, and duty cycle between the control coordinate system and the system coordinate system are obtained respectively.

[0053] Furthermore, the mapping module is also used for: The small-signal models of the power outer loop and the voltage amplitude outer loop are derived, including: Linearizing the instantaneous power in the dq coordinate system at the steady-state equilibrium point yields the relationship between active power disturbance and reactive power disturbance and voltage disturbance and current disturbance; The power disturbance is input into the transfer functions of the active phase angle loop and the reactive voltage amplitude loop, respectively, to obtain the phase angle disturbance and the internal potential amplitude disturbance generated by the VSG outer loop; The small-signal model of the inner-loop control is derived, and the mapping relationship between duty cycle disturbance and voltage and current disturbances in the system coordinate system is obtained, specifically including: The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combining the phase angle disturbance obtained from the outer loop and the internal potential amplitude disturbance, through the voltage regulation and current regulation links, the mapping relationship in the system coordinate system can be derived, which can be represented by a linear combination of voltage disturbance and current disturbance.

[0054] Furthermore, the small-signal models for the power outer loop and the voltage amplitude outer loop specifically include: A VSG outer loop control structure is adopted, in which the active power-phase angle loop is used to establish synchronous power angle dynamics, and the reactive power-voltage amplitude loop is used to adjust the internal potential amplitude. First, based on the instantaneous power relationship in the dq coordinate system, at the steady-state operating point... U d0 , U q0 , I d0 , I q0 Performing small-signal linearization in the vicinity, we get:

[0055] in, For small disturbance components of active power, For small disturbance components of reactive power, , The static relationship matrix between active and reactive power with respect to voltage and current is:

[0056]

[0057] The outer loop of the VSG satisfies the following relationship: the active power deviation, after passing through the inertia and damping elements, results in phase angle disturbance; the reactive power deviation, after passing through the voltage amplitude regulation element, results in internal potential amplitude disturbance, which can be uniformly expressed as:

[0058] in, For phase angle perturbation, This is an internal potential amplitude disturbance. The outer loop transfer function matrix for VSG control; for the VSG control structure, the following general form is adopted:

[0059] in, For virtual inertia coefficient, The damping coefficient is... The rated angular frequency, This is the voltage amplitude adjustment coefficient; For the Laplace operator; Substituting the power-signal relationship into the outer-loop control equation, we get:

[0060] The phase angle disturbance and internal potential amplitude disturbance generated by the VSG outer loop are both represented as a linear combination of voltage disturbance and current disturbance in the system coordinate system, and embedded in the inner loop and main circuit model; The derived small-signal model of the inner-loop control includes: The following simplified inner-loop control structure is adopted:

[0061] in, For voltage regulation, For current regulation; Rewrite the two PI components in diagonal matrix form:

[0062]

[0063] in, , These are the proportional coefficient and integral coefficient of the voltage regulation stage, respectively. , These are the proportional coefficient and integral coefficient of the current regulation element, respectively; The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combined with the θ and E expressions obtained from the outer loop, the small-signal expressions of the inner loop error signal, voltage regulation output, and duty cycle command are obtained step by step:

[0064] in, and These represent the transmission matrices of voltage and current disturbances to duty cycle disturbances in the system coordinate system, respectively.

[0065] Furthermore, the coupling building module is specifically used for: The AC side filter impedance matrix is:

[0066] in and These are the filter inductor and the filter resistor, respectively. For the Laplace operator, This is the rated angular frequency; If there is a parallel filter branch on the AC side, its small-signal admittance is uniformly expressed as the dq admittance matrix:

[0067] in, For dd channel admittance components, For the dq channel admittance component, For the qd channel admittance component, The admittance component of the qq channel is determined by the branch structure parameters; based on the dq circuit relationship of the two-level converter, the small-signal equation of the AC side main circuit is written as:

[0068] Where M is the identity matrix, This is the steady-state voltage on the DC side. For steady-state duty cycle column vectors, This is the AC side filter impedance matrix; For small disturbances in DC side voltage; This is a column vector representing the steady-state duty cycle. Consider the battery and DC bus capacitance on the DC side. C dc The effect of this is that the DC-side equivalent admittance is expressed as:

[0069] in, For DC bus capacitors, This is the equivalent impedance of the battery; The relationship between small DC-side voltage perturbations and AC-side variables can be written as follows:

[0070] in, and These represent the effects of AC-side voltage disturbances and current disturbances on DC-side voltage disturbances after coupling through duty cycle, current, DC-side admittance, and battery impedance, respectively. Substituting into the AC-side main circuit equations, a unified AC / DC coupling relationship is obtained:

[0071] Where A and B are system matrices that comprehensively consider outer loop control, inner loop control, AC side main circuit, DC bus dynamics, and battery impedance dynamics; thus, the dq output impedance matrix of the grid-type energy storage system is obtained:

[0072] in For the dd channel impedance component, For the dq channel impedance components, For the qd channel impedance component, For the qq channel impedance components; Eliminating variables from the above equations yields the dq impedance matrix Z of the grid-type energy storage system. ESS ( s Based on different battery parameters, different operating points, and different grid strengths, impedance curves of grid-type energy storage systems under corresponding operating conditions are generated for impedance scanning analysis and small-disturbance stability assessment.

[0073] Thirdly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the impedance modeling method for a grid-type energy storage system considering AC / DC coupling.

[0074] Fourthly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the impedance modeling method for a grid-type energy storage system considering AC / DC coupling.

[0075] Compared with the prior art, the present invention has the following technical effects: This invention addresses the problem of insufficient characterization of the deviation between the control coordinate system and the system coordinate system under network control. Starting from the internal phase angle disturbance generated by the VSG outer loop, it constructs a unified rotational transformation relationship for voltage, current, and duty cycle between the two coordinate systems. It dynamically introduces the power angle into the linearized expression of all dq quantities, fundamentally changing the approach of relying on phase-locked loops to establish coordinate system relationships in network models. This allows the unique synchronization mechanism of network-type equipment to be accurately characterized in the impedance model.

[0076] To address the issue of oversimplifying the DC side to an ideal constant voltage source, a DC bus voltage disturbance term is directly embedded into the AC side filter main circuit equations. Furthermore, by leveraging the power balance relationship of the two-level converter, a coupling path is established between the AC side voltage and current disturbances and the DC bus voltage via duty cycle and DC side equivalent admittance. Additionally, to address the lack of dynamic battery information, the battery equivalent circuit and DC bus capacitance are merged into the DC side equivalent admittance. Battery parameters such as open-circuit voltage, ohmic internal resistance, polarization resistance, and polarization capacitance are all incorporated into a unified small-signal framework, enabling the model to reflect changes in the energy storage system's impedance characteristics under different states of charge or aging conditions.

[0077] To address the issue of loose connections in the modeling process, a parameterized and streamlined modeling procedure is presented, from solving for the steady-state equilibrium point of the main circuit and DC side to linearization of each stage and then to overall matrix elimination. The operating point is determined first, followed by the construction of the small-signal model. Simulation verification shows that under both extremely low and extremely high battery energy states, the theoretical impedance curve calculated by this method highly overlaps with the Bode plot obtained from electromagnetic transient simulation scanning over a wide frequency band. The impedance amplitude variation trend, resonance peak position, and phase change inflection point are all consistent, and no mid-frequency impedance characteristic distortion occurs due to neglecting battery dynamics or AC / DC coupling. This provides a more reliable analytical tool for weak grid stability assessment, control parameter tuning, and resonance risk identification of grid-type energy storage systems. Attached Figure Description

[0078] Figure 1 A schematic diagram of the topology for connecting a grid-type energy storage system to the power grid.

[0079] Figure 2 This is a block diagram of the impedance transfer function of a grid-type energy storage system.

[0080] Figure 3 Flowchart for impedance modeling of grid-type energy storage systems.

[0081] Figure 4 The results show the comparison between the theoretical and simulated values ​​of the impedance model of the grid-type energy storage system under different battery energy states, where (a) SOE=1% condition; (b) SOE=99% condition.

[0082] Figure 5 This is a flowchart of the present invention. Detailed Implementation

[0083] The present invention will be further described below with reference to the accompanying drawings: Example 1: This invention provides an impedance modeling method for a grid-type energy storage system considering AC / DC coupling, comprising: S1. Solve for the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled. S2, with the steady-state equilibrium point as the reference, establish the small-signal deviation relationship between the control coordinate system and the system coordinate system, and derive the small-signal models of the power outer loop, voltage amplitude outer loop and inner loop control based on the deviation relationship, and obtain the mapping relationship between the duty cycle disturbance and the voltage disturbance and the current disturbance in the system coordinate system. S3. Establish a small-signal model of the AC-side filter main circuit and a DC-side small-signal model including the DC bus capacitor and the battery equivalent circuit. Combine the mapping relationship to construct an AC / DC coupled small-signal model. S4 eliminates elements in the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

[0084] This invention considers the power-phase angle, reactive power-voltage outer loop, and simplified voltage-current double inner loop under grid-based control on the AC side. On the DC side, it considers the DC bus capacitor and the equivalent circuit of the battery, and establishes a dynamic mapping relationship between duty cycle, current, voltage, and DC-side voltage disturbance through power balance. By uniformly considering the deviation between the control coordinate system and the system coordinate system, the dynamics of the outer loop control, the dynamics of the inner loop control, the dynamics of the main circuit, and the dynamics of the battery, this invention can derive a complete dq impedance matrix expression for a grid-based energy storage system.

[0085] The modeling method constructed in this invention can, on the one hand, improve the accuracy of impedance analysis of grid-type energy storage systems, making it more realistically reflect the impact of changes in DC-side energy storage unit parameters on AC-side impedance characteristics; on the other hand, it can form a programmable and process-deployable modeling method, providing a unified model foundation for impedance scanning of grid-type energy storage systems, weak grid stability assessment, control parameter tuning, and power plant-level grid-connected performance analysis.

[0086] Example 2: This invention provides an impedance modeling method for a grid-type energy storage system considering AC / DC coupling, including: (1) Determine the main circuit topology of the grid-type energy storage system to be modeled, including the grid connection interface, filtering stage, DC bus and battery equivalent structure; (2) Determine the control architecture of the grid-type energy storage system, including the VSG outer loop parameters and the simplified inner loop PI control parameters; (3) Based on the operating conditions and network parameters, the steady-state equilibrium point of the grid-type energy storage system is determined by formulas (steady-state circuit relationship), (power balance relationship) and (DC side steady-state relationship), and the steady-state voltage, current, internal potential, duty cycle and DC side voltage are obtained. (4) Establish the small-signal deviation relationship between the control coordinate system and the system coordinate system, and derive the small-signal models of the power outer loop and the voltage amplitude outer loop; (5) Establish a simplified small-signal model for inner-loop control and obtain the mapping relationship between duty cycle disturbance and voltage and current disturbance in the system coordinate system; (6) Establish the small-signal model of the AC side filter main circuit, the first-order RC model of the DC side battery, and the DC bus capacitor model; (7) Establish the coupling equation between the AC side and the DC side through the power balance relationship, and construct a unified AC / DC coupling small-signal model; (8) Eliminate the above equations to obtain the dq impedance matrix ZESS(s) of the grid-type energy storage system; (9) Based on different battery parameters, different operating points and different grid strengths, generate impedance curves of the grid-type energy storage system under corresponding operating conditions for impedance scanning analysis and small disturbance stability assessment.

[0087] The modeling object of this invention is a grid-type energy storage system employing a VSG control strategy. Its main circuit includes: grid equivalent impedance, AC-side filtering stage of the energy storage converter, power conversion bridge, DC bus capacitor, and battery equivalent circuit, as shown in the appendix. Figure 1 As shown. The battery adopts a first-order RC equivalent model, and its impedance is expressed as: (1) in, The internal resistance of the battery is in ohms. and These are the polarization resistance and polarization capacitance, respectively. This model can reflect the impact of battery voltage dynamics and polarization processes on the DC-side impedance.

[0088] This invention establishes a dq small-signal model of a grid-type energy storage system based on the PCC voltage, current, and duty cycle in the system coordinate system. Unlike existing modeling methods that mainly target grid-type energy storage, this invention does not use a PLL as the angle source. Instead, it uses the internal phase angle disturbance generated by the VSG outer loop as the source of deviation between the control coordinate system and the system coordinate system. By explicitly constructing coordinate transformation relationships, the grid control dynamics, main circuit dynamics, and battery dynamics are unified and incorporated into the impedance modeling framework.

[0089] The modeling process proposed in this invention includes: establishing the deviation relationship between the control coordinate system and the system coordinate system; establishing small-signal models of the power outer loop and the voltage amplitude outer loop; establishing a simplified inner loop control model; establishing dynamic models of the AC side filter main circuit and the DC side battery-bus; solving for the steady-state equilibrium point; and finally eliminating variables to obtain the output impedance matrix of the grid-type energy storage system in the dq coordinate system.

[0090] Small signal deviation relationship between control coordinate system and system coordinate system In steady-state operation, the internal potential phase angle of a grid-type energy storage system (VSGS) exists at a fixed angle with the system's synchronous rotating coordinate system. Under small disturbance conditions, a small angular deviation exists between the control coordinate system and the system coordinate system due to phase angle disturbances generated by the VSG outer loop. Let the voltage, current, and duty cycle in the system coordinate system be u, respectively. s i s d s The corresponding quantities in the control coordinate system are u c i c d c Then, all electrical quantities satisfy a unified rotational transformation relationship between the two coordinate systems. Under linearization conditions, the above relationship can be written as the sum of the steady-state rotation term and the phase angle disturbance-introduced term, that is: (2) in, To control small disturbance components of electrical quantities in the coordinate system, This refers to the small disturbance component of the electrical quantity in the system coordinate system. The superscript ~ uniformly indicates the small disturbance component of this parameter. Let be the rotation matrix determined by the steady-state angle. Let θ be its first-order partial derivative matrix with respect to angle, and let θ be the phase angle disturbance generated by the network control. For the steady-state value of the corresponding electrical quantity, for different physical quantities, The unified representation is: (3) in, , These represent the steady-state components of the voltage along the d and q axes, respectively. , These represent the steady-state components of the current along the d and q axes, respectively. , Let d and q represent the steady-state components of the duty cycle, respectively; let φ be the steady-state angle between the control coordinate system and the system coordinate system, where φ represents the difference between the steady-state voltage phase angle and the internal potential phase angle of the PCC; then the rotation matrix... Its first-order partial derivative matrix They are represented as follows: (4) (5) Based on the above relationships, the small-signal transformation relationships of voltage, current, and duty cycle between the control coordinate system and the system coordinate system can be obtained respectively. This step is the foundation for constructing the network-type energy storage impedance model. Its function is to explicitly introduce the phase angle dynamics caused by the outer loop into the linearized expression of the dq quantity, so that the subsequent control system and main circuit equations can be analyzed simultaneously within a unified framework.

[0091] Small-signal model of outer loop control This invention employs a VSG outer loop control structure. The active power-phase angle loop is used to establish dynamic synchronous power angle, and the reactive power-voltage amplitude loop is used to adjust the internal potential amplitude. First, based on the instantaneous power relationship in the dq coordinate system, at the steady-state operating point... U d0 , U q0 , I d0 , I q0 By performing small-signal linearization on the surrounding area, we obtain: (6) in, , The static relationship matrix between active and reactive power with respect to voltage and current is: (7) (8) Based on this, the outer loop of the VSG satisfies the following relationship: the active power deviation, after passing through the inertia and damping elements, results in phase angle disturbance; the reactive power deviation, after passing through the voltage amplitude regulation element, results in internal potential amplitude disturbance. This can be uniformly expressed as: (9) in, This represents the transfer function matrix of the VSG control outer loop. The VSG control structure described in this invention can adopt the following general form: (10) in, For virtual inertia coefficient, The damping coefficient is... The rated angular frequency, This is the voltage amplitude adjustment coefficient; This is the Laplace operator. The above expression shows that the phase angle channel reflects the inertia-damping dynamics of the VSG, and the voltage amplitude channel reflects the influence of reactive power regulation on the internal potential amplitude.

[0092] Substituting the power-signal relationship into the outer-loop control equation, we get: (11) The above results show that the phase angle disturbance and the internal potential amplitude disturbance generated by the VSG outer loop can both be expressed as a linear combination of voltage disturbance and current disturbance in the system coordinate system, and thus can be directly embedded into the inner loop and main circuit model.

[0093] Small-signal model of inner-loop control This invention adopts the following simplified inner-loop control structure for grid-type energy storage systems: (12) in, For voltage regulation, As a current regulation element, this structure omits some decoupling compensation terms, making it easier to form a clearly defined impedance model with well-defined parameters.

[0094] To maintain consistency, the two PI stages can be written as diagonal matrix forms: (13) (14) in, , These are the proportional coefficient and integral coefficient of the voltage regulation stage, respectively. , These are the proportional coefficient and integral coefficient of the current regulation element, respectively; Based on the established coordinate transformation relationship, the voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combining this with the θ and E expressions obtained from the outer loop, the small-signal expressions for the inner loop error signal, voltage regulation output, and duty cycle command can be obtained step-by-step. After simplification, the small-signal expression for the duty cycle in the system coordinate system can be written as: (15) in, and These represent the transmission relationship matrices of voltage disturbance and current disturbance to duty cycle disturbance in the system coordinate system, respectively. This equation shows that the inner loop control of the grid-type energy storage can be equivalent to a dynamic duty cycle element jointly determined by voltage disturbance and current disturbance under small-signal conditions, and it already comprehensively reflects the influence of the VSG outer loop, coordinate deviation, and PI controller parameters.

[0095] Small-signal model of AC / DC coupling between main circuit and battery On the AC side, the main circuit of the grid-type energy storage system is determined by the converter output voltage, the filter inductor and resistor, and the PCC voltage. Let the AC side filter impedance matrix be: (16) in and These are the filter inductor and the filter resistor, respectively. For the Laplace operator, This is the rated angular frequency; If there is a parallel filter branch on the AC side, its small-signal admittance can be uniformly expressed as the dq admittance matrix: (17) in, For dd channel admittance components, For the dq channel admittance component, For the qd channel admittance component, The admittance component of the qq channel is determined by the branch structure parameters; when this branch is ignored, it is only necessary to let Y... c =0. Based on the dq circuit relationship of the two-level converter, the small-signal equation of the AC main circuit can be written as: (18) Where M is the identity matrix, This is the steady-state voltage on the DC side. For steady-state duty cycle column vectors, This is the AC side filter impedance matrix; For small disturbances in DC side voltage; This is a column vector representing the steady-state duty cycle. Considering the effects of the battery and DC bus capacitance Cdc on the DC side, the equivalent admittance on the DC side can be expressed as: (19) For DC bus capacitors, This is the equivalent impedance of the battery; Further considering the power balance relationship of a two-level converter, the relationship between a small DC-side voltage disturbance and an AC-side variable can be written as: (20) in, and These represent the effects of AC-side voltage disturbances and current disturbances on DC-side voltage disturbances after coupling through duty cycle, current, DC-side admittance, and battery impedance, respectively.

[0096] Substituting the above equation into the AC-side main circuit equation, we can obtain a unified AC / DC coupling relationship: (twenty one) Where A and B are the system matrices that comprehensively consider outer loop control, inner loop control, AC side main circuit, DC bus dynamics, and battery impedance dynamics. From this, the dq output impedance matrix of the grid-type energy storage system can be obtained: (twenty two) in For the dd channel impedance component, For the dq channel impedance components, For the qd channel impedance component, For the qq channel impedance components; Appendix Figure 2 The transfer function for the above steps is given.

[0097] Through the above derivation, this invention realizes the unified incorporation of grid control dynamics, AC main circuit dynamics, and battery first-order RC dynamics into the dq impedance model, forming an impedance modeling method for grid-type energy storage systems that takes into account AC-DC coupling relationships.

[0098] Methods for finding steady-state equilibrium points To enable the impedance model to be accurately evaluated at a given operating point, this invention further provides a method for solving the steady-state equilibrium point.

[0099] (1) Method for solving the steady-state equilibrium point of the main circuit First, establish the steady-state circuit relationship between the internal potential, PCC voltage, and current on the AC side. The complex vector of the internal potential Em in the grid-type energy storage is denoted as: (twenty three) For the complex vector of the internal potential of a grid-type energy storage system, , For the real and imaginary steady-state components of the internal potential of grid-type energy storage, Let the imaginary operator be denoted as ; and let the steady-state admittances of the filter branch, the power grid branch, and the parallel branch be denoted as . , , Then the steady-state voltage of PCC is uniformly expressed as: (twenty four) in, The steady-state voltage of PCC Let be the steady-state value of the equivalent voltage source of the power grid; when there are no parallel branches, let =0; Further, the PCC current and the physical filter branch current can be obtained. They are respectively: (25) Based on the steady-state operation target, active and reactive power are expressed as follows: (26) superscript Indicates a conjugate relationship. To perform the operation of taking the real part, For the imaginary part calculation; the reference values ​​for active and reactive power of the grid-type energy storage are denoted as follows: P ref , Q ref , United P 0= P ref Q0=Q ref The steady-state component of the internal potential is obtained. E d0 ,E rq0 This leads to the d-axis steady-state component of the voltage. U d0 steady-state component of voltage q-axis U q0 d-axis steady-state component of current I d0 steady-state component of current q-axis I q0 and the d-axis steady-state component of the filter branch current I fd0 q-axis steady-state component of filter branch current I fq0 ; (2) Method for solving the steady-state equilibrium point on the DC side On the DC side, based on the steady-state modulation relationship of the two-level converter and the steady-state power balance relationship of the battery, the following can be established: (26) in, This is the battery open-circuit voltage. This is the steady-state voltage of the DC bus. Let be the ohmic internal resistance of the battery; solve the simultaneous equations to obtain the steady-state operating point on the DC side.

[0100] The purpose of this step is to provide a unified and clear operating point for small-signal linearization. Since the impedance characteristics of a grid-type energy storage system are closely related to the operating power, grid parameters, internal potential, and battery parameters, the approach of "first finding the steady-state equilibrium point and then constructing the small-signal impedance model" ensures that the model has clear physical meaning and good engineering applicability.

[0101] To verify the effectiveness of the proposed impedance modeling method for grid-type energy storage systems considering AC / DC coupling, a comparative analysis was conducted between theoretical impedance calculation results and electromagnetic transient simulation impedance scanning results. The simulation model was built based on the aforementioned main circuit and VSG control structure of the grid-type energy storage system. Following the modeling process described in Part 4, the steady-state equilibrium point was obtained, a dq impedance model was established, and a theoretical impedance curve was generated. This theoretical impedance curve was then compared with the impedance curve obtained from the simulation scan. By comparing the theoretical and scanned values ​​under different battery charge states, the impedance model established in this invention can be verified to characterize the AC / DC coupling dynamics of the grid-type energy storage system.

[0102] The verification conditions used in this invention are as follows: (1) The rated voltage of the grid-type energy storage system is 380 V, the rated capacity is 150 kW, and the rated frequency is 50 Hz; the rated angular frequency of the system is 100π rad / s; the equivalent grid parameters at the grid connection point are set according to the grid strength of 10, and the equivalent resistance and inductance on the grid side can be calculated based on the grid strength; the energy storage converter adopts a two-level topology structure, and the AC side adopts a filter inductor-capacitor branch structure.

[0103] (2) The parameters of the AC side main circuit of the energy storage system are set as follows: filter inductance L f =500 μH, parallel branch capacitor C f =100μF; DC bus capacitance is taken as C. dc =1000 μF.

[0104] (3) The VSG outer loop control parameters are set as follows: virtual inertia coefficient J=7.6, damping coefficient D=200, and voltage amplitude adjustment coefficient k. q =0.001. The inner loop control adopts the simplified PI structure described in Part 4, where the proportional coefficient and integral coefficient of the voltage regulation element are k and k, respectively. pu =10、k iu =500, the proportional coefficient and integral coefficient of the current regulation link are respectively k pi =0.1, k ii =500. The active power command for the energy storage system is P. ref =150 kW.

[0105] (4) According to the steady-state equilibrium point solution method, the system operating point is obtained under the rated active power output condition, and the PCC voltage, current, internal potential, duty cycle and DC side steady-state voltage corresponding to the operating point are substituted into the impedance model to generate the theoretical dq impedance curve of the grid-type energy storage system.

[0106] (5) The DC-side battery adopts a first-order RC equivalent circuit model, and two typical operating conditions, SOE=1% and SOE=99%, are selected for verification. For each SOE operating condition, the theoretical impedance model is established and the simulated impedance scan is carried out using the corresponding open-circuit voltage, ohmic internal resistance, polarization resistance and polarization capacitance parameter set.

[0107] (6) Under the above two SOE operating conditions, impedance scanning is performed on the grid-type energy storage system within the analyzed frequency band, and the impedance Bode plot obtained by the scanning is compared with the impedance Bode plot calculated by the model established in this invention, as shown in the appendix. Figure 4 As shown in the figures. One set of figures corresponds to the SOE=1% operating condition, and the other set corresponds to the SOE=99% operating condition.

[0108] Simulation comparison results show that, under the two operating conditions of SOE=1% and SOE=99%, the theoretical values ​​obtained from the impedance model of the grid-type energy storage system established in this invention can coincide well with the simulated scan values, maintaining good consistency in terms of impedance amplitude variation trends, resonance peak positions, and phase change inflection points. Especially in the mid-frequency impedance dip region, near the resonance peak, and in the high-frequency attenuation region, the model of this invention can accurately reflect the main characteristics presented by the scan results, indicating that the modeling method proposed in this invention can effectively describe the coupling relationship between the VSG outer loop, simplified inner loop, AC side filter network, DC bus dynamics, and battery equivalent impedance.

[0109] Compared to simplified modeling methods that neglect battery dynamics and fail to establish AC / DC coupling, this invention introduces a first-order RC equivalent element of the DC-side battery, DC bus dynamics, and the coupling relationship between power, voltage, and current on the AC side into the impedance model. This allows the theoretical model to more accurately reflect the impedance characteristics of the actual energy storage system and avoids impedance amplitude and phase deviations caused by oversimplification of the DC side. This demonstrates that this invention can provide a more reliable theoretical basis for impedance analysis, control parameter tuning, resonance risk identification, and small-disturbance stability assessment of grid-connected energy storage systems under weak grid conditions.

[0110] In summary, the impedance modeling method for grid-type energy storage systems considering AC / DC coupling proposed in this invention has advantages such as clear model structure, well-defined physical meaning of parameters, adaptability to different battery states and operating points, and good agreement between theoretical calculation results and simulation results. This method can effectively improve the accuracy of impedance characteristic analysis of grid-type energy storage systems, has good engineering application value, and can be widely used for modeling and analysis of grid-type energy storage equipment, grid-connected performance evaluation, and weak grid adaptability research.

[0111] This solution is applicable to impedance modeling, small-disturbance stability analysis, and instability risk assessment of grid-connected energy storage systems / energy storage power stations controlled by virtual synchronous generators (VSGs). Through this invention, the dq impedance characteristics of grid-connected energy storage systems can be accurately characterized under different battery states of charge, operating power, and grid strength conditions, thereby enabling the analysis and identification of their oscillation and instability risks under weak grid conditions. Simultaneously, it provides a reference for the tuning of control parameters, optimization of main circuit parameter design, and grid-connected performance evaluation of grid-connected energy storage systems, and offers technical support for grid dispatching and operation personnel to conduct grid-connected stability analysis and safe operation boundary assessment of grid-connected energy storage systems.

[0112] In another embodiment of the present invention, an impedance modeling system for a grid-type energy storage system considering AC / DC coupling is provided, which can be used to implement the above-mentioned impedance modeling method for a grid-type energy storage system considering AC / DC coupling. Specifically, the system includes: The steady-state equilibrium point solution module is used to solve the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled. The mapping module is used to establish the small-signal deviation relationship between the control coordinate system and the system coordinate system based on the steady-state equilibrium point, and to derive the small-signal models of the power outer loop, voltage amplitude outer loop and inner loop control based on the deviation relationship, so as to obtain the mapping relationship between the duty cycle disturbance and the voltage disturbance and the current disturbance in the system coordinate system. The coupling construction module is used to establish a small-signal model of the AC-side filter main circuit and a DC-side small-signal model that includes the DC bus capacitor and the battery equivalent circuit. Combined with the mapping relationship, an AC-DC coupled small-signal model is constructed. The output module is used to eliminate elements in the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

[0113] The module division in this embodiment of the invention is illustrative and represents only one logical functional division. In actual implementation, other division methods may be used. Furthermore, the functional modules in the various embodiments of the invention can be integrated into a single processor, exist as separate physical entities, or be integrated into a single module. The integrated modules described above can be implemented in hardware or as software functional modules.

[0114] In another embodiment of the present invention, a computer device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to achieve a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used for operating the impedance modeling method of AC / DC coupled grid-type energy storage systems.

[0115] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the impedance modeling method for grid-type energy storage systems considering AC / DC coupling in the above embodiments.

[0116] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0117] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0118] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0119] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An impedance modeling method for grid-type energy storage systems considering AC / DC coupling, characterized in that, include: Based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled, the steady-state equilibrium point is determined. Based on the steady-state equilibrium point, a small-signal deviation relationship between the control coordinate system and the system coordinate system is established. Based on the deviation relationship, small-signal models of the power outer loop, voltage amplitude outer loop, and inner loop control are derived, and the mapping relationship between duty cycle disturbance and voltage disturbance and current disturbance in the system coordinate system is obtained. A small-signal model of the AC-side filter main circuit and a DC-side small-signal model including the DC bus capacitor and the battery equivalent circuit are established. Based on the mapping relationship, an AC-DC coupled small-signal model is constructed. Elimination is performed on the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

2. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 1, characterized in that, The process of solving for the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled includes: The main circuit topology of the grid-type energy storage system to be modeled, including the grid connection interface, filtering stage, DC bus, and equivalent battery structure, is determined. The control architecture of the grid-type energy storage system, including the VSG outer loop parameters and the simplified inner loop PI control parameters, is determined. Based on the operating conditions and network parameters, the steady-state equilibrium point of the grid-type energy storage system is solved according to the steady-state circuit relationship, power balance relationship, and DC side steady-state relationship, and the steady-state voltage, current, internal potential, duty cycle, and DC side voltage are obtained.

3. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 2, characterized in that, The steady-state equilibrium point includes the main circuit steady-state equilibrium point and the DC side steady-state equilibrium point; The solution for the steady-state equilibrium point of the main loop includes: Establish a steady-state circuit relationship between the internal potential, PCC voltage, and current on the AC side, and denote the internal potential of the grid-type energy storage. The complex vector is: For the complex vector of the internal potential of a grid-type energy storage system, , For the real and imaginary steady-state components of the internal potential of grid-type energy storage, Let the imaginary operator be denoted as ; and let the steady-state admittances of the filter branch, the power grid branch, and the parallel branch be denoted as . , , Then the steady-state voltage of PCC is uniformly expressed as: in, The steady-state voltage of PCC Let be the steady-state value of the equivalent voltage source of the power grid; when there are no parallel branches, let =0; Further obtain PCC current and physical filter branch current They are respectively: Based on the steady-state operation target, active and reactive power are expressed as follows: superscript Indicates a conjugate relationship. To perform the operation of taking the real part, For the imaginary part calculation; the reference values ​​for active and reactive power of the grid-type energy storage are denoted as follows: P ref , Q ref United P 0= P ref Q0=Q ref The steady-state component of the internal potential is obtained. E d0 , E rq0 This leads to the d-axis steady-state component of the voltage. U d0 steady-state component of voltage q-axis U q0 d-axis steady-state component of current I d0 steady-state component of current q-axis I q0 and the steady-state component of the d-axis current of the filter branch I fd0 q-axis steady-state component of filter branch current I fq0 ; The solution for the steady-state equilibrium point on the DC side includes: On the DC side, based on the steady-state modulation relationship of the two-level converter and the steady-state power balance relationship of the battery, the following is established: in, This is the battery open-circuit voltage. This is the steady-state voltage of the DC bus. Let be the ohmic internal resistance of the battery; solve the simultaneous equations to obtain the steady-state operating point on the DC side.

4. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 1, characterized in that, The establishment of the small-signal deviation relationship between the control coordinate system and the system coordinate system, based on the steady-state equilibrium point, includes: The voltage, current, and duty cycle in the system coordinate system are u s i s d s The corresponding quantities in the control coordinate system are u c i c d c Then, all electrical quantities satisfy a unified rotational transformation relationship between the two coordinate systems. Under linearization conditions, the rotational transformation relationship can be written as the sum of the steady-state rotation term and the phase angle disturbance-introduced term: in, To control small disturbance components of electrical quantities in the coordinate system, This refers to the small disturbance component of the electrical quantity in the system coordinate system. The superscript ~ uniformly indicates the small disturbance component of this parameter. Let be the rotation matrix determined by the steady-state angle. Let θ be its first-order partial derivative matrix with respect to angle, and let θ be the phase angle disturbance generated by the network control. For the steady-state value of the corresponding electrical quantity, for different physical quantities, The unified representation is: in, , These represent the steady-state components of the voltage along the d and q axes, respectively. , These represent the steady-state components of the current along the d and q axes, respectively. , Let d and q represent the steady-state components of the duty cycle, respectively; let φ be the steady-state angle between the control coordinate system and the system coordinate system, where φ represents the difference between the steady-state voltage phase angle and the internal potential phase angle of the PCC; then the rotation matrix... Its first-order partial derivative matrix They are represented as follows: The small-signal transformation relationships of voltage, current, and duty cycle between the control coordinate system and the system coordinate system are obtained respectively.

5. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 4, characterized in that, The small-signal models for the power outer loop, voltage amplitude outer loop, and inner loop control, derived based on the deviation relationship, yield the mapping relationship between the duty cycle disturbance and the voltage and current disturbances in the system coordinate system, including: The small-signal models of the power outer loop and the voltage amplitude outer loop are derived, including: Linearizing the instantaneous power in the dq coordinate system at the steady-state equilibrium point yields the relationship between active power disturbance and reactive power disturbance and voltage disturbance and current disturbance; The power disturbance is input into the transfer functions of the active phase angle loop and the reactive voltage amplitude loop, respectively, to obtain the phase angle disturbance and the internal potential amplitude disturbance generated by the VSG outer loop; The small-signal model of the inner-loop control is derived, and the mapping relationship between duty cycle disturbance and voltage and current disturbances in the system coordinate system is obtained, specifically including: The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combining the phase angle disturbance obtained from the outer loop and the internal potential amplitude disturbance, through the voltage regulation and current regulation links, the mapping relationship in the system coordinate system can be derived, which can be represented by a linear combination of voltage disturbance and current disturbance.

6. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 5, characterized in that, The small-signal models for the power outer loop and the voltage amplitude outer loop specifically include: A VSG outer loop control structure is adopted, in which the active power-phase angle loop is used to establish synchronous power angle dynamics, and the reactive power-voltage amplitude loop is used to adjust the internal potential amplitude. First, based on the instantaneous power relationship in the dq coordinate system, at the steady-state operating point... U d0 , U q0 , I d0 , I q0 Performing small-signal linearization in the vicinity, we get: in, For small disturbance components of active power, For small disturbance components of reactive power, , The static relationship matrix between active and reactive power with respect to voltage and current is: The outer loop of the VSG satisfies the following relationship: the active power deviation, after passing through the inertia and damping elements, results in phase angle disturbance; the reactive power deviation, after passing through the voltage amplitude regulation element, results in internal potential amplitude disturbance, which can be uniformly expressed as: in, For phase angle perturbation, This is an internal potential amplitude disturbance. The outer loop transfer function matrix for VSG control; for the VSG control structure, the following general form is adopted: in, For virtual inertia coefficient, The damping coefficient is... The rated angular frequency, This is the voltage amplitude adjustment coefficient; For the Laplace operator; Substituting the power-signal relationship into the outer-loop control equation, we get: The phase angle disturbance and internal potential amplitude disturbance generated by the VSG outer loop are both represented as a linear combination of voltage disturbance and current disturbance in the system coordinate system, and embedded in the inner loop and main circuit model; The derived small-signal model of the inner-loop control includes: The following simplified inner-loop control structure is adopted: in, For voltage regulation, For current regulation; Rewrite the two PI components in diagonal matrix form: in, , These are the proportional coefficient and integral coefficient of the voltage regulation stage, respectively. , These are the proportional coefficient and integral coefficient of the current regulation element, respectively; The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combined with the θ and E expressions obtained from the outer loop, the small-signal expressions of the inner loop error signal, voltage regulation output, and duty cycle command are obtained step by step: in, and These represent the transmission relationship matrices of voltage disturbance and current disturbance to duty cycle disturbance in the system coordinate system, respectively.

7. The impedance modeling method for a grid-type energy storage system considering AC / DC coupling according to claim 1, characterized in that, The establishment of a small-signal model of the AC-side filter main circuit and a DC-side small-signal model including the DC bus capacitor and battery equivalent circuit, combined with the mapping relationship, constructs an AC / DC coupled small-signal model, including: The AC side filter impedance matrix is: in and These are the filter inductor and the filter resistor, respectively. For the Laplace operator, The rated angular frequency; If there is a parallel filter branch on the AC side, its small-signal admittance is uniformly expressed as the dq admittance matrix: in, For dd channel admittance components, For the dq channel admittance component, For the qd channel admittance component, The admittance component of the qq channel is determined by the branch structure parameters; based on the dq circuit relationship of the two-level converter, the small-signal equation of the AC side main circuit is written as: Where M is the identity matrix, This is the steady-state voltage on the DC side. For steady-state duty cycle column vectors, This is the AC side filter impedance matrix; For small disturbances in DC side voltage; This is a column vector representing the steady-state duty cycle. Consider the battery and DC bus capacitance on the DC side. C dc The effect of this is that the DC-side equivalent admittance is expressed as: in, For DC bus capacitors, This is the equivalent impedance of the battery. The relationship between small DC-side voltage perturbations and AC-side variables can be written as follows: in, and These represent the effects of AC-side voltage disturbances and current disturbances on DC-side voltage disturbances after coupling through duty cycle, current, DC-side admittance, and battery impedance, respectively. Substituting into the AC-side main circuit equations, we obtain a unified AC / DC coupling relationship: Where A and B are system matrices that comprehensively consider outer loop control, inner loop control, AC side main circuit, DC bus dynamics, and battery impedance dynamics; thus, the dq output impedance matrix of the grid-type energy storage system is obtained: in For the dd channel impedance component, For the dq channel impedance components, For the qd channel impedance component, For the qq channel impedance components; Eliminating variables from the above equations yields the dq impedance matrix Z of the grid-type energy storage system. ESS ( s Based on different battery parameters, different operating points, and different grid strengths, impedance curves of grid-type energy storage systems under corresponding operating conditions are generated for impedance scanning analysis and small-disturbance stability assessment.

8. An impedance modeling system for a grid-type energy storage system considering AC / DC coupling, characterized in that, include: The steady-state equilibrium point solution module is used to solve the steady-state equilibrium point based on the main circuit topology, control architecture, and operating conditions of the grid-type energy storage system to be modeled. The mapping module is used to establish the small-signal deviation relationship between the control coordinate system and the system coordinate system based on the steady-state equilibrium point, and to derive the small-signal models of the power outer loop, voltage amplitude outer loop and inner loop control based on the deviation relationship, so as to obtain the mapping relationship between the duty cycle disturbance and the voltage disturbance and the current disturbance in the system coordinate system. The coupling construction module is used to establish a small-signal model of the AC-side filter main circuit and a DC-side small-signal model that includes the DC bus capacitor and the battery equivalent circuit. Combined with the mapping relationship, an AC-DC coupled small-signal model is constructed. The output module is used to eliminate elements in the AC / DC coupled small-signal model to obtain the output impedance matrix of the grid-type energy storage system.

9. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 8, characterized in that, The steady-state equilibrium point solving module is specifically used for: The main circuit topology of the grid-type energy storage system to be modeled, including the grid connection interface, filtering stage, DC bus, and equivalent battery structure, is determined. The control architecture of the grid-type energy storage system, including the VSG outer loop parameters and the simplified inner loop PI control parameters, is determined. Based on the operating conditions and network parameters, the steady-state equilibrium point of the grid-type energy storage system is solved according to the steady-state circuit relationship, power balance relationship, and DC side steady-state relationship, and the steady-state voltage, current, internal potential, duty cycle, and DC side voltage are obtained.

10. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 9, characterized in that, The steady-state equilibrium point includes the main circuit steady-state equilibrium point and the DC side steady-state equilibrium point; The solution for the steady-state equilibrium point of the main loop includes: Establish a steady-state circuit relationship between the internal potential, PCC voltage, and current on the AC side, and denote the internal potential of the grid-type energy storage. The complex vector is: For the complex vector of the internal potential of a grid-type energy storage system, , For the real and imaginary steady-state components of the internal potential of grid-type energy storage, Let the imaginary operator be denoted as ; and let the steady-state admittances of the filter branch, the power grid branch, and the parallel branch be denoted as . , , Then the steady-state voltage of PCC is uniformly expressed as: in, The steady-state voltage of PCC Let be the steady-state value of the equivalent voltage source of the power grid; when there are no parallel branches, let =0; Further obtain PCC current and physical filter branch current They are respectively: Based on the steady-state operation target, active and reactive power are expressed as follows: superscript Indicates a conjugate relationship. To perform the operation of taking the real part, For the imaginary part calculation; the reference values ​​for active and reactive power of the grid-type energy storage are denoted as follows: P ref , Q ref United P 0= P ref Q0=Q ref The steady-state component of the internal potential is obtained. E d0 , E rq0 This leads to the d-axis steady-state component of the voltage. U d0 steady-state component of voltage q-axis U q0 d-axis steady-state component of current I d0 steady-state component of current q-axis I q0 and the steady-state component of the d-axis current of the filter branch I fd0 q-axis steady-state component of filter branch current I fq0 ; The solution for the steady-state equilibrium point on the DC side includes: On the DC side, based on the steady-state modulation relationship of the two-level converter and the steady-state power balance relationship of the battery, the following is established: in, This is the battery open-circuit voltage. This is the steady-state voltage of the DC bus. Let be the ohmic internal resistance of the battery; solve the simultaneous equations to obtain the steady-state operating point on the DC side.

11. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 8, characterized in that, The mapping module is specifically used for: The voltage, current, and duty cycle in the system coordinate system are u s i s d s The corresponding quantities in the control coordinate system are u c i c d c Then, all electrical quantities satisfy a unified rotational transformation relationship between the two coordinate systems. Under linearization conditions, the rotational transformation relationship can be written as the sum of the steady-state rotation term and the phase angle disturbance-introduced term: in, To control small disturbance components of electrical quantities in the coordinate system, This refers to the small disturbance component of the electrical quantity in the system coordinate system. The superscript ~ uniformly indicates the small disturbance component of this parameter. Let be the rotation matrix determined by the steady-state angle. Let θ be its first-order partial derivative matrix with respect to angle, and let θ be the phase angle disturbance generated by the network control. For the steady-state value of the corresponding electrical quantity, for different physical quantities, The unified representation is: in, , These represent the steady-state components of the voltage along the d and q axes, respectively. , These represent the steady-state components of the current along the d and q axes, respectively. , Let d and q represent the steady-state components of the duty cycle, respectively; let φ be the steady-state angle between the control coordinate system and the system coordinate system, where φ represents the difference between the steady-state voltage phase angle and the internal potential phase angle of the PCC; then the rotation matrix... Its first-order partial derivative matrix They are represented as follows: The small-signal transformation relationships of voltage, current, and duty cycle between the control coordinate system and the system coordinate system are obtained respectively.

12. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 11, characterized in that, The mapping module is also used for: The small-signal models of the power outer loop and the voltage amplitude outer loop are derived, including: Linearizing the instantaneous power in the dq coordinate system at the steady-state equilibrium point yields the relationship between active power disturbance and reactive power disturbance and voltage disturbance and current disturbance; The power disturbance is input into the transfer functions of the active phase angle loop and the reactive voltage amplitude loop, respectively, to obtain the phase angle disturbance and the internal potential amplitude disturbance generated by the VSG outer loop; The small-signal model of the inner-loop control is derived, and the mapping relationship between duty cycle disturbance and voltage and current disturbances in the system coordinate system is obtained, specifically including: The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combining the phase angle disturbance obtained from the outer loop and the internal potential amplitude disturbance, through the voltage regulation and current regulation links, the mapping relationship in the system coordinate system can be derived, which can be represented by a linear combination of voltage disturbance and current disturbance.

13. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 12, characterized in that, The small-signal models for the power outer loop and the voltage amplitude outer loop specifically include: A VSG outer loop control structure is adopted, in which the active power-phase angle loop is used to establish synchronous power angle dynamics, and the reactive power-voltage amplitude loop is used to adjust the internal potential amplitude. First, based on the instantaneous power relationship in the dq coordinate system, at the steady-state operating point... U d0 , U q0 , I d0 , I q0 Performing small-signal linearization in the vicinity, we get: in, For small disturbance components of active power, For small disturbance components of reactive power, , The static relationship matrix between active and reactive power with respect to voltage and current is: The outer loop of the VSG satisfies the following relationship: the active power deviation, after passing through the inertia and damping elements, results in phase angle disturbance; the reactive power deviation, after passing through the voltage amplitude regulation element, results in internal potential amplitude disturbance, which can be uniformly expressed as: in, For phase angle perturbation, This is an internal potential amplitude disturbance. The outer loop transfer function matrix for VSG control; for the VSG control structure, the following general form is adopted: in, For virtual inertia coefficient, The damping coefficient is... The rated angular frequency, This is the voltage amplitude adjustment coefficient; For the Laplace operator; Substituting the power-signal relationship into the outer-loop control equation, we get: The phase angle disturbance and internal potential amplitude disturbance generated by the VSG outer loop are both represented as a linear combination of voltage disturbance and current disturbance in the system coordinate system, and embedded in the inner loop and main circuit model; The derived small-signal model of the inner-loop control includes: The following simplified inner-loop control structure is adopted: in, For voltage regulation, For current regulation; Rewrite the two PI components in diagonal matrix form: in, , These are the proportional coefficient and integral coefficient of the voltage regulation stage, respectively. , These are the proportional coefficient and integral coefficient of the current regulation element, respectively; The voltage and current in the control coordinate system are expressed as functions of the voltage, current, and phase angle disturbance in the system coordinate system. Combined with the θ and E expressions obtained from the outer loop, the small-signal expressions of the inner loop error signal, voltage regulation output, and duty cycle command are obtained step by step: in, and These represent the transmission relationship matrices of voltage disturbance and current disturbance to duty cycle disturbance in the system coordinate system, respectively.

14. The impedance modeling system for a grid-type energy storage system considering AC / DC coupling according to claim 8, characterized in that, The coupling construction module is specifically used for: The AC side filter impedance matrix is: in and These are the filter inductor and the filter resistor, respectively. For the Laplace operator, The rated angular frequency; If there is a parallel filter branch on the AC side, its small-signal admittance is uniformly expressed as the dq admittance matrix: in, For dd channel admittance components, For the dq channel admittance component, For the qd channel admittance component, The admittance component of the qq channel is determined by the branch structure parameters; based on the dq circuit relationship of the two-level converter, the small-signal equation of the AC side main circuit is written as: Where M is the identity matrix, This is the steady-state voltage on the DC side. For steady-state duty cycle column vectors, This is the AC side filter impedance matrix; For small disturbances in DC side voltage; This is a column vector representing the steady-state duty cycle. Consider the battery and DC bus capacitance on the DC side. C dc The effect of this is that the DC-side equivalent admittance is expressed as: in, For DC bus capacitors, This is the equivalent impedance of the battery. The relationship between small DC-side voltage perturbations and AC-side variables can be written as follows: in, and These represent the effects of AC-side voltage disturbances and current disturbances on DC-side voltage disturbances after coupling through duty cycle, current, DC-side admittance, and battery impedance, respectively. Substituting into the AC-side main circuit equations, a unified AC / DC coupling relationship is obtained: Where A and B are system matrices that comprehensively consider outer loop control, inner loop control, AC side main circuit, DC bus dynamics, and battery impedance dynamics; thus, the dq output impedance matrix of the grid-type energy storage system is obtained: in For the dd channel impedance component, For the dq channel impedance components, For the qd channel impedance component, For the qq channel impedance components; Eliminating variables from the above equations yields the dq impedance matrix Z of the grid-type energy storage system. ESS ( s Based on different battery parameters, different operating points, and different grid strengths, impedance curves of grid-type energy storage systems under corresponding operating conditions are generated for impedance scanning analysis and small-disturbance stability assessment.

15. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the impedance modeling method for a grid-type energy storage system considering AC / DC coupling as described in any one of claims 1 to 7.

16. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the impedance modeling method for a grid-type energy storage system considering AC / DC coupling as described in any one of claims 1 to 7.

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