Method and system for improving voltage supporting capability of network-forming converter

Abstract

The invention discloses a method and a system for improving the voltage supporting capability of a network construction type converter, relates to a technology for improving the voltage supporting capability of the converter, and analyzes the influence of main control parameters of the converter on the voltage supporting capability of the converter by providing a dynamic evaluation index for the voltage supporting capability. Meanwhile, a parameter sensitivity analysis method is used for analyzing the influence rule of main control parameters on the impedance characteristics of the converter, a main control parameter adjusting method is given, and key support is provided for the small disturbance stability of the system while the voltage supporting capacity is guaranteed. And finally, optimal parameter setting is obtained through a particle swarm optimization algorithm, and a network construction type converter control strategy considering the voltage supporting capability and the small disturbance stability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of power transmission and distribution technology, specifically relating to a method and system for improving the voltage support capability of grid-type converters. Background Technology

[0002] With the increasing penetration rate of new energy sources, the reactive power and voltage problems of new power systems with "high" and "high" characteristics are becoming increasingly prominent. How to effectively provide voltage support during system faults has become a hot research topic. Traditional grid-following (GFL) converters, due to their inherently limited reactive power regulation capabilities, often experience a decline in overall system voltage support after the integration of a large number of distributed energy sources. In contrast, grid-forming (GFM) converters not only exhibit better stability under weak grid conditions but also possess the ability to provide voltage and frequency support to the grid; however, the influencing factors on their voltage support capability remain unclear. Furthermore, in practice, the connection / disconnection of large-capacity power sources / loads causes significant fluctuations in grid strength, posing a small-disturbance stability problem for grid-forming converters. Therefore, to address the ever-increasing reactive power and voltage challenges in new power systems, developing effective grid-forming converter control strategies that balance small-disturbance stability and voltage support capability is crucial.

[0003] At present, some literature has studied the voltage support function of grid-type converters, mainly focusing on reactive power control strategies.

[0004] Scholars such as Shang Lei have modeled virtual synchronous generators under symmetrical grid fault conditions and proposed a method to improve reactive power output capability by locking the reactive power regulator. Scholars such as Wang Xuemei have improved reactive power voltage control based on the third-order model of the synchronous machine, thereby improving the reactive power voltage support capability of the unit. Scholars such as Zhang Yuyu have improved the power loop of VSG control and improved the reactive power characteristics during faults by setting the voltage reference value according to the power angle. Scholars such as Fu Yang have adopted reactive power priority control and provided voltage support for the system by injecting dynamic reactive current.

[0005] New power systems based on power electronic converters offer high flexibility and controllability, and voltage support can be achieved by controlling the reactive power output of the converters. However, it is worth noting that the aforementioned research on the voltage support capability of grid-connected converters focuses on control strategy improvements and does not consider the impact of control parameters on their voltage support capability. Furthermore, there is relatively little research on whether adjustments to control parameters affect the converter's stability margin. Therefore, there is an urgent need for a method to improve the voltage support capability of grid-connected converters while also considering stability under small disturbances. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a method and system for improving the voltage support capability of grid-type converters while taking into account stability under small disturbances.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] First, a method for improving the voltage support capability of grid-type converters that takes into account small disturbance stability is provided, including the following steps:

[0009] Based on the dynamic evaluation index of voltage support capability of grid-type converters, the impact of key control parameters on voltage support capability is determined.

[0010] By employing optimization algorithms and coordinating the optimization of key control parameters, a control strategy for grid-type energy storage converters that balances voltage support and stability under small disturbances is obtained.

[0011] A control strategy that balances voltage support and stability under small disturbances is adopted to control the grid-type energy storage converter.

[0012] Preferably, the dynamic evaluation index of the voltage support capability of a grid-type converter is expressed as follows:

[0013]

[0014] in, This represents the reactive power output of the grid-connected converter. Represents the grid connection point voltage, K represents the reactive power loop integral coefficient, and D... q Q represents the voltage droop factor. ref U represents the reference command value for reactive power output of a given grid-connected converter. ref This represents the given grid connection point voltage reference command value. Indicates the voltage phase angle. x2 represents the virtual power angle of the grid-connected converter, and x2 represents the grid connection distance.

[0015] A value less than zero indicates that the grid-type converter can provide reactive power support when the voltage drops, and The larger the value, the more reactive power the grid-type converter outputs when the voltage changes, and the stronger its voltage support capability. or When it increases, It will decrease, reduce voltage support capacity, and reduce grid connection distance. It can improve the voltage support capability of grid-type converters;

[0016] The key control parameters include the voltage loop proportional coefficient k. vpVoltage loop integral coefficient k vi Reactive power loop integral coefficient K, voltage droop coefficient D q .

[0017] Preferably, by setting the grid impedance to pure inductance, the reactive power output equation of the grid-type converter is obtained:

[0018]

[0019] The actual internal potential of the grid-type converter, and These are the voltage amplitude and phase angle at the grid connection point, respectively. For virtual power angles of grid-type converters; For grid connection distance;

[0020] The electromotive force of a grid-type converter using power synchronous control is:

[0021]

[0022] Substituting the converter electromotive force into the reactive power equation yields the composite function of the reactive power output of the grid-connected converter with respect to the grid connection point voltage:

[0023]

[0024] Where K represents the reactive power loop integral coefficient, Q ref Q represents the given reactive power reference command value for a grid-type converter. s D represents the reactive power of a grid-connected converter. q U represents the voltage droop factor. ref This represents the given grid connection point voltage reference command value. Indicates the voltage at the grid connection point. Indicates the voltage phase angle. This represents the virtual power angle of a grid-type converter;

[0025] Composite function Take the partial derivative with respect to the grid connection point voltage:

[0026]

[0027] Composite function Substituting the specific expression into the above formula, we obtain the evaluation index of the voltage support capability of the grid-type converter.

[0028] Preferably, a multi-objective optimization problem is constructed using the particle swarm optimization algorithm, which integrates the reactive power loop integral coefficient K and the droop coefficient. Voltage loop proportionality coefficient k vp And the integral coefficient k of the voltage loop viFour parameters to be optimized are used as particle position vectors. The parameter range and stability are constrained according to the actual engineering situation. Through iterative optimization, the optimal solution of the key control parameters is obtained, which maximizes the voltage support capability while taking into account the stability of the system under small disturbances.

[0029] Preferably, the following steps are also included:

[0030] S1: Based on the topology and control block diagram of the grid converter, an analytical impedance model of the grid converter is established using the dq domain impedance modeling method.

[0031] S2: Based on the impedance model of the grid-type converter, the influence of key control parameters on the impedance characteristics of the converter is analyzed using the parameter sensitivity analysis method.

[0032] Preferably, in step S1, the phase sequence impedance Z of the grid-type converter is obtained by using a coordinate transformation formula. pn-psc :

[0033] .

[0034] Preferably, in step S2, the full-order impedance model of the grid-type converter is first reduced in order to obtain a simplified positive-sequence impedance model Zsimp dq-psc in the phase sequence domain of the converter.

[0035]

[0036] By using coordinate transformation formulas to transform the dq domain impedance to the phase sequence domain, a simplified positive sequence impedance model Zsimp pn-psc for the converter in the phase sequence domain is obtained.

[0037]

[0038] in,

[0039] s=jω dq =j2πf dq ;f dq For the system frequency in the dq domain, , These are the d-axis steady-state components of the grid-connected point voltage, current, and current in the actual coordinate system, where J represents the inertia constant and D... q H represents the voltage droop factor, K represents the reactive power loop integral factor, and H represents the voltage droop factor. v Let be the transfer function of the voltage loop.

[0040] Based on the analysis of the simplified positive-sequence impedance model Zsimp pn-psc in the phase sequence domain of the converter, the key parameters affecting the impedance characteristics are the voltage loop proportionality coefficient k. vp Integral coefficient k viReactive power loop integral coefficient K, voltage droop coefficient D q .

[0041] Preferably, in step S2, the calculation formula for the sensitivity analysis of key control parameters of the converter is expressed as follows:

[0042]

[0043] Where, σ ρ This represents the effect of any adjustable control parameter ρ on the system impedance characteristics, and σ ρ It is a complex number containing a real part and an imaginary part, where the real part σ ρR This represents the effect of parameter ρ on the equivalent resistance R of the system, with its imaginary part σ. ρX This indicates the effect of parameter ρ on the system's equivalent reactance X.

[0044] Preferably, the optimization algorithm is to construct a multi-objective optimization problem using a particle swarm optimization algorithm, or to balance two optimization objectives using a weighted single-objective function with weight coefficients.

[0045] In addition, a system for improving the voltage support capability of a grid-connected converter that balances small disturbance stability is provided, for implementing the aforementioned method for improving the voltage support capability of a grid-connected converter that balances small disturbance stability, including:

[0046] The module for constructing the impedance analytical model of a grid-type converter establishes an impedance analytical model of the grid-type converter based on the topology and control block diagram of the grid-type converter using the dq domain impedance modeling method.

[0047] The key control parameter analysis module analyzes the influence of key control parameters on the impedance characteristics of the converter based on the impedance model of the grid-type converter and using parameter sensitivity analysis.

[0048] The module for dynamic evaluation of voltage support capability of grid-type converters analyzes the dynamic evaluation index of voltage support capability of grid-type converters and determines the impact of key control parameters on voltage support capability.

[0049] The multi-objective optimization module uses the particle swarm optimization algorithm to construct a multi-objective optimization problem, or uses a weighted single-objective function to balance two optimization objectives through weight coefficients, thereby synergistically optimizing key control parameters and obtaining a grid-type energy storage converter control strategy that takes into account both voltage support and small disturbance stability.

[0050] The present invention, employing the above-mentioned technical solution, has the following beneficial effects: The present invention proposes a dynamic evaluation index for voltage support capability and analyzes the influence of the main control parameters of the converter on its voltage support capability. Simultaneously, using parameter sensitivity analysis, it analyzes the influence law of the main control parameters on the impedance characteristics of the converter and provides a method for adjusting the main control parameters, providing crucial support for the system's small-disturbance stability while ensuring voltage support capability. Finally, the optimal parameter settings are obtained through particle swarm optimization algorithm, resulting in a grid-type converter control strategy that balances voltage support capability and small-disturbance stability. Therefore, a grid-type energy storage converter control strategy that balances voltage support and small-disturbance stability can be used to control the grid-type converter.

[0051] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. Attached Figure Description

[0052] The invention will be further described below with reference to the accompanying drawings: Figure 1a This is the main circuit diagram of a grid-type converter; Figure 1b A control block diagram of the control loop for a grid-type converter; Figure 2a Control block diagram of active power control loop in grid converter; Figure 2b Control block diagram of reactive power control in a grid converter; Figure 3a This is a control block diagram of the voltage control loop for a grid-type converter. Figure 3b The control block diagram of the current control loop for a grid-type converter; Figure 4 The graph shows the results of the sensitivity analysis of the main control parameters; Figure 5 A circuit model diagram of a grid-connected system for a grid-connected converter; Figure 6 The grid connection point voltage fluctuation diagram is shown under different reactive voltage integral coefficients. Figure 7 The impedance characteristics of a grid-type converter are shown in the figure based on parameter sensitivity analysis. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0054] This embodiment proposes a method for improving the voltage support capability of grid-type converters that takes into account stability under small disturbances, including the following steps:

[0055] S1: Based on the topology and control block diagram of the grid-type converter, an analytical model of the dq-domain impedance of the grid-type converter based on power synchronous control is established using the dq-domain impedance modeling method. The analytical model of the phase sequence domain impedance is then obtained using the coordinate system transformation formula. The system topology and control block diagram are as follows: Figure 1a and 1b As shown.

[0056] Among them, u abc and i abc These are the three-phase voltage and current at point PCC; e abc and i iabc These are the three-phase voltage and current output from the converter, respectively; L f For the filter inductor, C f and R f These are the filter capacitor and its parasitic resistance, respectively; L g and R g These are the equivalent inductance and resistance of the power grid transmission line, V. g V is the mains voltage; dc DC bus voltage; g 1-6 This represents the modulation trigger signal; P and Q represent active power and reactive power, respectively; U is the voltage amplitude at the PCC point; E and θ are the reference voltage amplitude and coordinate transformation angle within the grid converter, respectively; u d u q and i d i q These are the d-axis and q-axis components of the grid connection point voltage and current, respectively; e d e q and i id i iq These are the d-axis and q-axis components of the voltage and current at the converter output port, respectively; i dq =[i d i q ]; i idq =[i id i iq ]; u dq =[u d u q ]; e dq =[e d e q J, D p D q K and represent the inertia constant, damping coefficient, voltage droop coefficient, and voltage integral coefficient, respectively; 1 / s represents the integrator; the subscript "ref" indicates the given reference command value; and ω1 is the rated angular frequency. H vand H i These are the transfer functions for the voltage loop and current loop, respectively, with the superscript "r" indicating the modulation reference value of the previous stage output.

[0057] Based on the topology of the grid-type converter shown in the diagram, taking the voltage at point PCC as an example, the voltage in the actual coordinate system and the voltage in the control coordinate system have the following relationship:

[0058]

[0059] In this context, the superscript "c" indicates a variable in the control coordinate system, the superscript "s" indicates a variable in the actual coordinate system, and T is the transformation matrix between the control coordinate system and the actual coordinate system.

[0060] The transformation matrix T can be represented as:

[0061]

[0062] Where θ is the voltage angle at the grid connection point, and the superscript "~" indicates the small-signal disturbance component.

[0063] If the system is in steady state, the transformation matrix T is a second-order identity matrix, and uc dq = us dq; if there is a disturbance signal in the system, it can be expressed as:

[0064]

[0065] After simplification and discarding the second-order small-signal terms, we obtain:

[0066]

[0067] Similarly, the small-signal model of the coordinate transformation link for the grid connection point current and the output port current can be obtained:

[0068]

[0069]

[0070] Wherein, Us d, Us q, Is d, Is q and Is id, Is iq are the d-axis and q-axis steady-state components of the voltage, current and output port current of the PCC point in the actual coordinate system, respectively.

[0071] Grid-type converter control based on power synchronization requires modulating the grid voltage phase and amplitude using active and reactive power at the grid connection point. To ensure that the phase obtained from active power modulation accurately tracks the grid voltage phase, the calculation of active and reactive power should use the grid connection point voltage and current in the actual coordinate system, as shown below:

[0072]

[0073] Among them, P s and Q s These are the active power and reactive power at point PCC, respectively.

[0074] Adding small perturbations to the above equation and rearranging it, we obtain the small-signal model for the power calculation stage:

[0075]

[0076] Among them, G i and G u These are the transfer function matrices from voltage and current at point PCC to active power and reactive power, respectively, in the actual coordinate system.

[0077]

[0078]

[0079] according to Figure 2a and Figure 2b The transfer functions of the active power control and reactive power control links are shown in the following equations:

[0080]

[0081]

[0082] Where s=jω dq =j2πf dq ;f dq Let f be the system frequency in the dq domain, and f dq =f pn -f1; f pn The system frequency in the phase sequence domain is given by the voltage amplitude U at the PCC point, which is calculated from the dq-axis voltage at the PCC point. Therefore, the disturbance component introduced by the calculated U must also be considered when performing small-signal modeling.

[0083] By superimposing small disturbances onto the above equation and rearranging it, we obtain the small-signal model of the power control loop.

[0084]

[0085] Among them, G PQ and G v These are the transfer function matrices from power and voltage to the reference phase and reference voltage amplitude, respectively.

[0086]

[0087]

[0088] according to Figure 3a and Figure 3bThe voltage control element consists of a proportional-integral (PI) controller and a dq-axis voltage decoupling term. Its small-signal model can be expressed as follows:

[0089]

[0090] Among them, G Hv and G ωC These are the transfer function matrix and the decoupling term of the voltage control, respectively.

[0091]

[0092]

[0093] Where k vp and k vi These are the proportional and integral coefficients of the voltage loop, respectively.

[0094] The current control loop consists of a PI controller, a dq-axis current decoupling term, and a voltage feedforward term. Its small-signal model can be expressed as follows:

[0095]

[0096] Among them, K u G is the voltage feedforward coefficient. Hi and G ωL These are the transfer function matrix for current control and the decoupling term for voltage control, respectively.

[0097]

[0098]

[0099] Where k ip and k ii These are the proportional and integral coefficients of the current loop, respectively.

[0100] In practical converter control, the modulation stage usually needs to pay attention to issues such as control delay, DC voltage dynamics, and coordinate transformation. However, the influence of control delay and switching model usually only affects the impedance in the higher frequency range (1k~2k Hz). In this implementation, we mainly focus on the stability issues within 1k Hz. Moreover, the DC side voltage of grid-type converters with power synchronous control is usually controlled by the front stage. Therefore, the modeling of the modulation stage only considers the small disturbance introduced by coordinate transformation. That is, it is assumed that there is only coordinate transformation disturbance between the voltage reference in the control coordinate system obtained by the current control stage and the voltage at the converter output port.

[0101] The transfer function of the modulation stage can be expressed as,

[0102]

[0103] After superimposing and organizing the small signals, the small-signal model of the modulation stage can be obtained.

[0104]

[0105] Where Ec d and Ec q are the d-axis steady-state components of the modulation reference voltage, respectively.

[0106] The control topology in this embodiment uses an LC filter. To simplify the derivation, the filter is decomposed into a filter inductor and a filter capacitor when modeling the filtering circuit. Its small-signal model is shown below.

[0107]

[0108]

[0109] Among them, G Lf and G Cf These are the transfer functions of the filter inductor and the filter capacitor, respectively.

[0110]

[0111]

[0112] Finally, by combining the above equations, we can obtain the ratio of the voltage and current along the dq axis at point PCC in the actual coordinate system, which is the converter's dq domain impedance Z. dq-psc ,

[0113]

[0114] Where, λ u and λ i These are the coefficient matrices before the voltage and current matrices of the PCC point along the dq axis in the actual coordinate system after processing.

[0115] λ u and λ i The specific expression is shown below.

[0116]

[0117]

[0118] Among them, G eθ G uθ and G iiθ G1 and G2 are the coordinate transformation transfer function matrices for the modulation voltage, grid connection point voltage, and output current, respectively. 01 G uc and G iiAll are 2×2 matrices, as shown below.

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] The phase sequence domain impedance and the dq domain impedance can be mutually converted through a transformation matrix to obtain the phase sequence domain impedance Z of the grid converter. pn-psc :

[0127]

[0128] S2: Reduce the order of the full-order impedance model of the grid-type converter obtained in the above steps to obtain a simplified impedance model. Use parameter sensitivity analysis to analyze the influence of the main control parameters on the impedance characteristics of the converter.

[0129] The basic principle of impedance order reduction is to preserve its impedance characteristics near the fundamental frequency, or more precisely, to preserve the phase spike of the converter impedance in the subsynchronous frequency band. Based on this principle, the following criteria for order reduction can be derived:

[0130] (1) Since the integral coefficient of the current loop is small when the parameters are selected, the current loop of proportional-integral (PI) control can be equivalent to a proportional element in the mid-frequency range.

[0131] (2) The impact of the output filtering stage is mainly reflected in the high frequency, so the filtering stage can be ignored.

[0132] (3) Due to the damping coefficient D p A larger value makes the transfer matrix G of the power control loop larger. PQ The first term in the equation can be approximated as zero in the low-to-mid frequency range, so it is directly set to zero during the order reduction process.

[0133] (4) Since the product of the parameters of the decoupling term is small, the decoupling term in the control loop can also be ignored.

[0134] Based on the above order reduction criteria, the reduced-order converter dq domain impedance model Zsimp dq-psc is expressed as:

[0135]

[0136] For ease of analysis, the dq-domain impedance is transformed to the phase sequence domain using coordinate transformation formulas, resulting in the simplified positive-sequence impedance model Zsimp pn-psc for the converter phase sequence domain.

[0137]

[0138] According to the simplified positive-sequence impedance model Zsimp pn-psc of the phase sequence domain for a grid-type converter based on power synchronous control, the main parameters affecting its impedance characteristics are the voltage loop proportionality coefficient k. vp Integral coefficient k vi The reactive power loop integral coefficient K and the droop coefficient D q Therefore, this implementation method will mainly focus on the above four parameters to conduct parameter sensitivity analysis and summarize the influence of these parameters on the impedance characteristics of the converter.

[0139] According to control system theory, when analyzing the influence of any adjustable control parameter ρ on the system impedance characteristics, parameter sensitivity analysis can be performed using the differential calculation shown in the following formula.

[0140]

[0141] Where, σ ρ This represents the effect of any adjustable control parameter ρ on the system impedance characteristics, and σ ρ It is a complex number containing a real part and an imaginary part, where the real part σ ρR This represents the effect of parameter ρ on the equivalent resistance R of the system, with its imaginary part σ. ρX This indicates the effect of parameter ρ on the system's equivalent reactance X.

[0142] Within the frequency band of 1~50 Hz, the voltage loop proportionality coefficient k vp Integral coefficient k vi The reactive power loop integral coefficient K and the droop coefficient D q The results of the parameter sensitivity analysis are as follows Figure 4 As shown.

[0143] according to Figure 4 Analysis results: In the frequency band of 1~50 Hz, compared to the voltage loop's scaling factor k vp Integral coefficient k vi The significant impact on impedance characteristics is due to the reactive power loop integral coefficient K and the droop coefficient D. q The impact on resistance and reactance is relatively small. Regarding the proportionality coefficient k of the voltage loop... vp In the frequency band below 50Hz, k vp It only has a significant effect on the resistance characteristics, that is, if k is increased... vpThis can enhance the resistive characteristics of this frequency band, while the effect on reactance is negligible. For the integral coefficient k of the voltage loop... vi In the frequency band below 50Hz, k vi It only has a significant effect on the reactance characteristics, that is, if k is increased... vi This can enhance the capacitive characteristics of this frequency band, while the effect on resistance is negligible. For the reactive power loop integral factor K, in the frequency band below 50Hz, increasing K will weaken the resistive characteristics while enhancing the inductive characteristics. For the reactive power loop droop factor D... q In the frequency band below 50Hz, increase D q This will weaken the resistive characteristics of that frequency band and also weaken the inductive characteristics of that frequency band.

[0144] Based on the above analysis, appropriately increasing k... vp Or appropriately reduce k vi、 D q Both can optimize the impedance characteristics of grid-type converters based on power synchronous control to a certain extent in the frequency range of 1~50 Hz.

[0145] S3: Based on the reactive power output equation of the grid-connected converter, a dynamic evaluation index for voltage support capability is constructed, and the influence of the converter's main control parameters on voltage support capability is analyzed. The control of the grid-connected converter is divided into an outer loop and an inner loop. The response speed of the inner loop is much higher than that of the outer loop, therefore the dynamics of the inner loop are ignored. Based on the grid-connected system circuit model of the grid-connected converter, such as... Figure 5 As shown, the reactive power output of the converter is:

[0146]

[0147] in

[0148]

[0149] and These are the voltage amplitude and phase angle at the grid connection point, respectively. and For grid-connected line resistance and reactance of grid-type converters; For virtual power angles of grid-type converters; For the actual internal potential of the grid-type converter, neglecting the inner loop and filtering stages, the converter port voltage phasor is E∠. .

[0150] Grid impedance is typically composed of the resistance and inductance of transmission lines. However, in this implementation scenario, the renewable energy generation grid-connected device is connected to the grid via a long-distance transmission line. Therefore, the grid impedance characteristics will be dominated by the line inductance. To simplify the analysis, this implementation sets the grid impedance as purely inductive, resulting in the reactive power equation for the grid-connected converter output:

[0151]

[0152] according to Figure 2a and Figure 2b The electromotive force of a grid-type converter using power synchronous control is:

[0153]

[0154] Substituting the converter electromotive force into the reactive power equation yields the composite function of the reactive power output of the grid-connected converter with respect to the grid connection point voltage:

[0155]

[0156] Composite function Take the partial derivative with respect to the grid connection point voltage:

[0157]

[0158] Composite function Substituting the specific expression into the above formula, we obtain the evaluation index for the voltage support capability of grid-type converters:

[0159]

[0160] The above voltage support capability indicators reflect the impact of grid-type converter control parameters on voltage support capability. A value less than zero indicates that the grid-type converter can provide reactive power support when the voltage drops. The larger the value, the more reactive power the grid-type converter outputs when the voltage changes, and the stronger its voltage support capability. When the reactive power loop integral coefficient... or droop coefficient When it increases, This will reduce voltage support capacity. Additionally, it will reduce grid connection distance. It can improve the voltage support capability of grid-type converters.

[0161] S4: Based on the particle swarm optimization algorithm, the above control parameters are optimized in a coordinated manner, and a control strategy for grid-type energy storage converter that takes into account both voltage support and small disturbance stability is proposed.

[0162] Based on the above analysis, the reactive power loop integral coefficient should be appropriately reduced. or droop coefficient This can improve the voltage support capability of grid-type converters. For example... Figure 6 As shown, reducing different integral coefficients The voltage fluctuation amplitude at the grid connection point gradually decreases. However, changing these parameters affects the system's impedance characteristics, thus impacting its stability margin. The critical phase margin of the grid-connected system impedance reflects the critical state between stability and instability. Its corresponding frequency range characterizes the frequency range at which the system is prone to instability in a given scenario. The smaller this range, the larger the system's stable operating range, indicating better system stability. Figure 7 It can be seen that when the proportional coefficient k of the voltage loop... vp When the voltage increases from 1 pu to 2 pu, the frequency range corresponding to the critical phase margin of the grid-connected system impedance changes from 9 Hz to 6 Hz; when the integral coefficient k of the voltage loop... vi When the impedance changes from 1 pu to 0.2 pu, the frequency range corresponding to the critical phase margin of the grid-connected system impedance changes from 9 Hz to 4 Hz. Therefore Figure 7 This not only demonstrates the effectiveness of parameter adjustment in improving system stability but also proves the accuracy of the parameter sensitivity analysis results. Following this approach, the optimization objective of this implementation method is to ensure that the system still has a certain stability margin while maximizing the voltage support capability of the grid-type converter, taking into account small disturbance stability. A multi-objective optimization problem is constructed using a particle swarm optimization algorithm, or a weighted single-objective function is used to balance the two optimization objectives through weight coefficients. The four parameters to be optimized are used as particle position vectors, and constraints on parameter range and stability (e.g., stability margin greater than 30°) are imposed according to engineering practice. Through iterative optimization, the optimal solution for the control parameters is obtained, maximizing voltage support capability while also considering the system's small disturbance stability.

[0163] Finally, the grid-type energy storage converter is controlled using the above-mentioned control strategy that balances voltage support and small disturbance stability, thereby balancing voltage support and small disturbance stability.

[0164] The above description is merely a specific embodiment of the invention, but the scope of protection of the invention is not limited thereto. Those skilled in the art should understand that the invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for improving the voltage support capability of grid-type converters while taking into account small disturbance stability, characterized in that, Includes the following steps: Based on the dynamic evaluation index of voltage support capability of grid-type converters, the impact of key control parameters on voltage support capability is determined. By employing optimization algorithms and coordinating the optimization of key control parameters, a control strategy for grid-type energy storage converters that balances voltage support and stability under small disturbances is obtained. A control strategy that balances voltage support and stability under small disturbances is adopted to control the grid-type energy storage converter.

2. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 1, characterized in that, The dynamic evaluation index of the voltage support capability of grid-type converters is expressed as follows: in, This represents the reactive power output of the grid-connected converter. Represents the grid connection point voltage, K represents the reactive power loop integral coefficient, and D... q Q represents the voltage droop factor. ref U represents the reference command value for reactive power output of a given grid-connected converter. ref This represents the given grid connection point voltage reference command value. Indicates the voltage phase angle. x2 represents the virtual power angle of the grid-connected converter, and x2 represents the grid connection distance. A value less than zero indicates that the grid-type converter can provide reactive power support when the voltage drops, and The larger the value, the more reactive power the grid-type converter outputs when the voltage changes, and the stronger its voltage support capability. or When it increases, It will decrease, reduce voltage support capacity, and reduce grid connection distance. It can improve the voltage support capability of grid-type converters; The key control parameters include the voltage loop proportional coefficient k. vp Voltage loop integral coefficient k vi Reactive power loop integral coefficient K, voltage droop coefficient D q .

3. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 2, characterized in that, By setting the grid impedance to pure inductance, the reactive power equation for the grid-connected converter is obtained: The actual internal potential of the grid-type converter, and These are the voltage amplitude and phase angle at the grid connection point, respectively. For virtual power angles of grid-type converters; For grid connection distance; The electromotive force of a grid-type converter using power synchronous control is: Substituting the converter electromotive force into the reactive power equation yields the composite function of the reactive power output of the grid-connected converter with respect to the grid connection point voltage: Where K represents the reactive power loop integral coefficient, Q ref Q represents the given reactive power reference command value for a grid-type converter. s D represents the reactive power of a grid-connected converter. q U represents the voltage droop factor. ref This represents the given grid connection point voltage reference command value. Indicates the voltage at the grid connection point. Indicates the voltage phase angle. This represents the virtual power angle of a grid-type converter; Composite function Take the partial derivative with respect to the grid connection point voltage: Composite function Substituting the specific expression into the above formula, we obtain the evaluation index of the voltage support capability of the grid-type converter.

4. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 2, characterized in that, A multi-objective optimization problem is constructed using the particle swarm optimization algorithm, which integrates the reactive power loop integral coefficient K and the droop coefficient. Voltage loop proportionality coefficient k vp And the integral coefficient k of the voltage loop vi Four parameters to be optimized are used as particle position vectors. The parameter range and stability are constrained according to the actual engineering situation. Through iterative optimization, the optimal solution of the key control parameters is obtained, which maximizes the voltage support capability while taking into account the stability of the system under small disturbances.

5. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 1, characterized in that, It also includes the following steps: S1: Based on the topology and control block diagram of the grid converter, an analytical impedance model of the grid converter is established using the dq domain impedance modeling method. S2: Based on the impedance model of the grid-type converter, the influence of key control parameters on the impedance characteristics of the converter is analyzed using the parameter sensitivity analysis method.

6. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 5, characterized in that, In step S1, the phase sequence impedance Z of the grid-type converter is obtained by using the coordinate transformation formula. pn-psc : 。 7. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 6, characterized in that, In step S2, the full-order impedance model of the grid-type converter is first reduced in order to obtain the simplified positive-sequence impedance model Zsimp dq-psc in the phase sequence domain of the converter. By using coordinate transformation formulas to transform the dq domain impedance to the phase sequence domain, a simplified positive sequence impedance model Zsimp pn-psc for the converter in the phase sequence domain is obtained. in, s=jω dq =j2πf dq ;f dq For the system frequency in the dq domain, , These are the d-axis steady-state components of the grid-connected point voltage, current, and current in the actual coordinate system, where J represents the inertia constant and D... q H represents the voltage droop factor, K represents the reactive power loop integral factor, and H represents the voltage droop factor. v Let be the transfer function of the voltage loop. Based on the analysis of the simplified positive-sequence impedance model Zsimp pn-psc in the phase sequence domain of the converter, the key parameters affecting the impedance characteristics are the voltage loop proportionality coefficient k. vp Integral coefficient k vi Reactive power loop integral coefficient K, voltage droop coefficient D q .

8. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 5, characterized in that, In S2, the calculation formula for the sensitivity analysis of key control parameters of the converter is expressed as follows: Where, σ ρ This represents the effect of any adjustable control parameter ρ on the system impedance characteristics, and σ ρ It is a complex number containing a real part and an imaginary part, where the real part σ ρR This represents the effect of parameter ρ on the equivalent resistance R of the system, with its imaginary part σ. ρX This indicates the effect of parameter ρ on the system's equivalent reactance X.

9. The method for improving the voltage support capability of a grid-type converter while taking into account small disturbance stability as described in claim 1, characterized in that, The optimization algorithm described is to construct a multi-objective optimization problem using particle swarm optimization, or to balance two optimization objectives using a weighted single-objective function with weight coefficients.

10. A system for enhancing the voltage support capability of a grid-type converter while considering small disturbance stability, used to implement the method for enhancing the voltage support capability of a grid-type converter while considering small disturbance stability as described in any one of claims 1 to 9, characterized in that, include: The module for constructing the impedance analytical model of a grid-type converter establishes an impedance analytical model of the grid-type converter based on the topology and control block diagram of the grid-type converter using the dq domain impedance modeling method. The key control parameter analysis module analyzes the influence of key control parameters on the impedance characteristics of the converter based on the impedance model of the grid-type converter and using parameter sensitivity analysis. The module for dynamic evaluation of voltage support capability of grid-type converters analyzes the dynamic evaluation index of voltage support capability of grid-type converters and determines the impact of key control parameters on voltage support capability. The multi-objective optimization module uses the particle swarm optimization algorithm to construct a multi-objective optimization problem, or uses a weighted single-objective function to balance two optimization objectives through weight coefficients, thereby synergistically optimizing key control parameters and obtaining a grid-type energy storage converter control strategy that takes into account both voltage support and small disturbance stability.

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