Quantitative evaluation method and system for quiescent voltage supporting capability of network construction type single-feed-in system

Abstract

The invention relates to the technical field of new energy, in particular to a network construction type single-feed-in system static voltage supporting capacity quantitative evaluation method and system.The method comprises the steps that a power flow model is constructed according to reactive voltage response characteristics in a network construction type power supply steady state, the model is iteratively solved through a power iteration power flow algorithm, a system jacobian matrix is constructed, and the static voltage supporting capacity of a network construction type single-feed-in system is evaluated. The method solves the problems that the static voltage stability limit boundary of the system cannot be accurately evaluated and safe and stable operation of the novel power system cannot be ensured in the prior art, and has the technical effects of accurately evaluating the static voltage stability limit boundary of the system and ensuring safe and stable operation of the novel power system.

Description

Technical Field

[0001] The present invention relates to the field of new energy technologies, and in particular to a method and system for quantitatively evaluating the static voltage support capability of a grid-type single-feedback system. Background Art

[0002] In recent years, grid-type converters with voltage source characteristics have been applied to engineering practice because they can be used as supporting power sources to connect to weak power grids to enhance the system's stable operation capabilities. At present, most of the research on grid-type converters focuses on the implementation of different control methods, proposes various control strategies and parameter optimization schemes, or analyzes the impact of converter access in new energy sites dominated by grid-type converters. The analysis of the output voltage characteristics of grid-type converters and the static voltage stability mechanism of grid-type converters is relatively lacking, and the research on the factors affecting the static voltage stability of grid-type converter systems is still insufficient. How to explain the specific impact of grid-type converter access on the static voltage stability of the system from a quantitative perspective still needs further research; the existing technology lacks quantitative analysis of the voltage stability margin of the new energy system connected to the grid through the grid-type converter due to the lack of consideration of the voltage support capability of the grid-type converter, which makes it impossible to accurately evaluate the static voltage stability limit boundary of the system and ensure the safe and stable operation of the new power system. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a method and system for quantitatively evaluating the static voltage support capability of a grid-type single-feedback system;

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: a quantitative evaluation method for the static voltage support capability of a grid-type single-feedback system, comprising:

[0005] Based on the grid-connected equivalent circuit of the grid-type power supply, and according to the relationship between the output power of the grid-type power supply and the voltage amplitude and phase angle of the grid-connected point, the grid-connected point voltage effective value model is constructed to provide system voltage support;

[0006] Based on the grid-connected point voltage effective value model, a power flow model is constructed according to the reactive voltage response characteristics of the grid-connected power supply in steady state. The system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iterative power flow algorithm to obtain the system voltage collapse point through the power flow change process.

[0007] Based on the system Jacobian matrix, through the analysis of the operating boundaries of the voltage support capability boundary analysis and the power delivery capability boundary analysis, the quantitative calculation analytical expression of the operating boundary of the single-feed system and the operating boundary diagram of the grid-type power supply are obtained, so as to provide the static voltage support capability evaluation of the system through the changes of system parameters in the operating boundary diagram.

[0008] Preferably, the relationship between the output power of the grid-connected power supply and the voltage amplitude and phase angle at the grid connection point includes:

[0009]

[0010] Among them, the P S , active power of grid-type power supply; the Q S The reactive power of the grid-type power supply; S is the voltage on the AC side of the VSC; S is the voltage phase angle; the X T is the equivalent reactance of the grid-connected line including the connecting transformer;

[0011] The grid connection point voltage effective value model includes:

[0012]

[0013] Preferably, the process of constructing a power flow model according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and iteratively solving the model through a power iterative power flow algorithm to construct a system Jacobian matrix includes:

[0014] In the first stage of reactive power response:

[0015] Based on the active power sub-model of the grid-connected point voltage effective value model, the active power reference value output by the grid-connected power source is gradually increased from the initial working point, the AC side current of the voltage source converter VSC is gradually increased, and the actual active power value and reactive power actual value fed into the controller are obtained based on the gradually increased VSC AC side current and voltage;

[0016] Based on the actual value of active power and reactive power fed into the controller and the equivalent impedance parameters, the grid point bus voltage is maintained at the rated value by increasing the reactive power output of the grid-type power supply according to the grid point voltage effective value model;

[0017] Based on the controller model of the grid-type power supply, through each control link of the model, the potential and current inside the AC side of the VSC are brought to the upper limit of modulation, and the potential inside the AC side of the VSC is constrained;

[0018] Based on the q-axis component of the potential inside the VSC AC side after modulation upper limit, the active power output model of the grid-type power supply is output through the dominant variable control of the reactive voltage control loop.

[0019] Preferably, the grid-type power source active power output model includes:

[0020]

[0021] Wherein, R is the equivalent resistance of the converter loss; L is the equivalent reactance of the converter loss, and isd is the simplified analysis coefficient of the d-axis component of the converter output AC current, Vq is the constant value of the converter output AC voltage after reaching the upper limit; ω is the angular frequency; u sd is the grid connection point voltage; sq It is the q-axis component of the inverter output AC current.

[0022] Preferably, the process of constructing a power flow model according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and iteratively solving the model through a power iterative power flow algorithm to construct a system Jacobian matrix includes:

[0023] In the second stage of reactive power response:

[0024] The reactive power sub-model based on the grid-connected point voltage effective value model gradually increases the reactive power reference value output by the grid-connected power source, gradually reduces the AC side voltage of the voltage source converter VSC, and outputs the VSC AC side voltage and the grid-connected power source reactive power output model through the control of the external system to which the grid-connected power source is connected.

[0025] Preferably, the grid-type power supply reactive power output model includes:

[0026]

[0027] Among them, K is the growth coefficient of the grid-side AC current as the active power output of the VSC changes, wherein K=IS / (R+SL), wherein S is the differential in the Laplace transform; it is constrained by the amplitude limit of the modulation link; and cosθ is the cosine value of the voltage phase angle output by the active power control link. When the DC voltage is constant, the change amplitude is small and it is treated as a constant.

[0028] Preferably, the process of constructing a power flow model according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and iteratively solving the model through a power iterative power flow algorithm to construct a system Jacobian matrix includes:

[0029] Flow model building phase:

[0030] Based on the active power output model and reactive power output model of the grid-forming power source, and according to the controller model of the grid-forming power source, a VSC output power model is constructed;

[0031] Based on the VSC output power model and the grid-connected point voltage effective value model, the nonlinear equation of the grid-connected power single-feed system is constructed.

[0032] Based on the nonlinear equation, the Jacobian matrix of the first element of the system is constructed;

[0033] Based on the voltage sampling value of the grid connection point of the single-feed system, according to the power flow change process model, the reactive power, active power and AC side voltage of the VSC are iteratively calculated through the power iterative power flow algorithm;

[0034] Based on the reactive power, active power of the grid-connected power source and the AC side voltage of the VSC in each iterative solution, the Jacobian matrix of the first element of the system is modified to the system Jacobian matrix, and the singular point of the system Jacobian matrix is ​​set to the system voltage collapse point.

[0035] Preferably, the VSC output power model includes:

[0036]

[0037] The nonlinear equations include:

[0038]

[0039] Among them, the ΔP S is the active power variation; the ΔQ S is the reactive power variation;

[0040] The Jacobian matrix of the first element of the system is:

[0041]

[0042] Among them, the H 11 is the Jacobian matrix self-feedback term; is the partial derivative of active power with respect to phase angle;

[0043] The power flow change process model:

[0044]

[0045] The i is the i-th step of the power flow calculation;

[0046] The system Jacobian matrix:

[0047]

[0048] Among them, the is the Jacobian matrix.

[0049] Preferably, the voltage support capability boundary analysis includes:

[0050] Based on the system Jacobian matrix and the constraints that characterize the voltage support capability boundary, the voltage support capability boundary model of the analytical model with quantitative calculation of the single-feedback system operation boundary is used to derive the maximum value of the VSC AC side voltage that can be reached when the grid-connected point voltage provides voltage support.

[0051] The constraints characterizing the voltage support capability boundary are:

[0052]

[0053] Among them, the is the partial derivative of reactive power to current growth coefficient;

[0054] The voltage support capability boundary model:

[0055]

[0056] The power delivery capability boundary analysis includes:

[0057] Based on the system Jacobian matrix and the singular conditions of the Jacobian matrix, the power delivery capacity boundary model of the analytical model is quantitatively calculated at the operating boundary of the single-feed system, and the grid connection point breakdown voltage is derived when the Jacobian matrix singular conditions are met.

[0058] Based on the power delivery capability boundary model, the operation boundary diagram of the grid-forming power source is obtained through the iterative solution process of the VSC output power model, so as to realize that the grid-forming power source will also be converted from a PV node to a PQ node after reaching the potential constraint condition in the VSC;

[0059] The conditions under which the Jacobian matrix is ​​singular are:

[0060] det(J)=0

[0061] Among them, the ( is the Jacobian matrix;

[0062] The power delivery capability boundary model:

[0063]

[0064] The internal potential constraints in the iterative solution process of the VSC output power model are:

[0065]

[0066] Among them, the is the partial derivative of active power with respect to the current growth coefficient.

[0067] On the other hand, the present invention also provides a quantitative evaluation system for the static voltage support capability of a grid-type single-feed system, comprising:

[0068] Based on the above quantitative evaluation method, the quantitative evaluation system includes:

[0069] Voltage effective value construction module: It is used to construct the grid connection point voltage effective value model based on the grid-connected equivalent circuit of the grid-connected power source and the relationship between the grid-connected power source output power and the grid connection point voltage amplitude and phase angle to provide system voltage support;

[0070] Jacobian matrix construction module: It is used to build a power flow model based on the grid-connected point voltage effective value model and the reactive voltage response characteristics of the grid-connected power supply in a steady state. The system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iterative power flow algorithm to obtain the system voltage collapse point through the power flow change process.

[0071] Voltage support capability assessment module: Based on the system Jacobian matrix, it is used to obtain the quantitative calculation formula of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply through the analysis of the operating boundary of the voltage support capability boundary analysis and the power delivery capability boundary analysis, so as to provide the static voltage support capability assessment of the system through the changes of system parameters in the operating boundary diagram.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] The invention content of this case can be summarized as follows: through the quantitative calculation method of the static voltage stability boundary of the single-feed system of the grid-type power supply voltage support capacity, a power flow mathematical model is constructed according to the reactive voltage response characteristics of the grid-type power supply under steady state, and the quantitative calculation analytical expression of the single-feed system operation boundary is obtained. This case first analyzes the main circuit structure and control strategy of the grid-type converter, derives the normalized mathematical model of the grid-type converter control system in the rotating coordinate system, and establishes the corresponding electromechanical transient model based on this; by analyzing the evolution law of the grid-connected point voltage of the grid-type converter as the output power of the converter changes, the mechanism of the grid-type converter providing voltage support for the system is revealed, and combined with the line power transmission constraints The phasor relationship satisfied by the bus voltage at the grid-connected point of the converter is obtained; the analytical expressions of the output power and voltage of the grid-connected converter are further derived, and the PV curve of the converter output active power and the grid-connected point voltage is constructed. Then, the static voltage stability mechanism of the grid-connected converter single-feed system is analyzed from a quantitative perspective, and a calculation method for the static stability limit boundary of the converter single-feed system is proposed. The factors affecting the static voltage stability of the system are quantitatively analyzed, and the effectiveness of the proposed algorithm is verified through simulation. By taking into account the voltage support capacity of the grid-connected converter, the voltage stability margin of the new energy system connected to the grid through the grid-connected converter is quantitatively analyzed, and the static voltage stability limit boundary of the system is accurately evaluated to ensure the safe and stable operation of the new power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 is a flow chart of a method for constructing a system Jacobian matrix by constructing a power flow model according to an embodiment of the present invention;

[0075] Figure 2 This is the grid-connected equivalent circuit of the grid-forming power supply of an embodiment of the present invention;

[0076] Figure 3 is a controller model of a grid-connected power supply according to an embodiment of the present invention;

[0077] Figure 4 is a curve showing a change in the controller output parameter with active power according to an embodiment of the present invention;

[0078] Figure 5 is a schematic diagram of the operation boundary of a grid-type power supply according to an embodiment of the present invention; DETAILED DESCRIPTION

[0079] It is worth noting that the methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products, and their sources are not specifically limited unless otherwise specified.

[0080] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0081] like Figure 1 As shown, the embodiment of the present invention includes a method for quantitatively evaluating the static voltage support capability of a grid-type single-feedback system, including:

[0082] Based on the grid-connected equivalent circuit of the grid-type power supply, according to the relationship between the output power of the grid-type power supply and the voltage amplitude and phase angle of the grid-connected point, a grid-connected point voltage effective value model is constructed to provide system voltage support S101;

[0083] Based on the grid-connected point voltage effective value model, a power flow model is constructed according to the reactive voltage response characteristics of the grid-connected power supply in steady state. The system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iterative power flow algorithm to obtain the system voltage collapse point S102 through the power flow change process.

[0084] Based on the system Jacobian matrix, through the analysis of the operating boundaries of the voltage support capability boundary analysis and the power delivery capability boundary analysis, the quantitative calculation analytical expression of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply are obtained, so as to provide the system static voltage support capability evaluation S103 through the system parameter changes of the operating boundary diagram.

[0085] According to one embodiment of the present invention, Figure 1 As shown, the relationship between the output power of the grid-connected power supply and the voltage amplitude and phase angle at the grid connection point includes:

[0086]

[0087] Among them, the P S , active power of grid-type power supply; the QS The reactive power of the grid-type power supply; S is the voltage on the AC side of the VSC; S is the voltage phase angle; the X T is the equivalent reactance of the grid-connected line including the connecting transformer;

[0088] The grid connection point voltage effective value model includes:

[0089]

[0090] According to one embodiment of the present invention, Figure 1 As shown, the power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iteration power flow algorithm, including:

[0091] In the first stage of reactive power response:

[0092] Based on the active power sub-model of the grid-connected point voltage effective value model, the active power reference value output by the grid-connected power source is gradually increased from the initial working point, the AC side current of the voltage source converter VSC is gradually increased, and the actual active power value and reactive power actual value fed into the controller are obtained based on the gradually increased VSC AC side current and voltage S201;

[0093] Based on the actual value of active power and reactive power fed into the controller and the equivalent impedance parameters, according to the grid voltage effective value model, the grid bus voltage is maintained at the rated value S202 by increasing the reactive power output of the grid-type power supply;

[0094] Based on the controller model of the grid-type power supply, through each control link of the model, the potential and current in the AC side of the VSC are brought to the upper limit of modulation, and the potential in the AC side of the VSC is constrained S203;

[0095] Based on the q-axis component of the potential inside the VSC AC side after the modulation upper limit, the active power output model S204 of the grid-type power supply is output through the dominant variable control of the reactive voltage control loop.

[0096] According to one embodiment of the present invention, Figure 1 As shown, the active power output model of the grid-type power supply includes:

[0097]

[0098] Wherein, R is the equivalent resistance of the converter loss; L is the equivalent reactance of the converter loss, and i sd is the simplified analysis coefficient of the d-axis component of the converter output AC current, Vq is the constant value of the converter output AC voltage after reaching the upper limit; ω is the angular frequency; usd is the grid connection point voltage; sq It is the q-axis component of the inverter output AC current.

[0099] According to one embodiment of the present invention, Figure 1 As shown, the power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iteration power flow algorithm, including:

[0100] In the second stage of reactive power response:

[0101] The reactive power sub-model based on the grid-connected point voltage effective value model gradually reduces the voltage on the AC side of the voltage source converter VSC by gradually increasing the reactive power reference value output by the grid-connected power source, and outputs the VSC AC side voltage and the grid-connected power source reactive power output model S205 through the control of the external system to which the grid-connected power source is connected.

[0102] According to one embodiment of the present invention, Figure 1 As shown, the grid-type power supply reactive power output model includes:

[0103]

[0104] Among them, K is the growth coefficient of the grid-side AC current as the active power output of the VSC changes, wherein K=IS / (R+SL), wherein S is the differential in the Laplace transform; Vq is the potential in the q-axis of the converter, which is constrained by the amplitude limit of the modulation link; cosθ is the cosine value of the voltage phase angle output by the active power control link, and when the DC voltage is constant, the change amplitude is small and it is treated as a constant.

[0105] According to one embodiment of the present invention, Figure 1 As shown, the power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iteration power flow algorithm, including:

[0106] Flow model building phase:

[0107] Based on the active power output model of the grid-type power source and the reactive power output model of the grid-type power source, and according to the controller model of the grid-type power source, a VSC output power model is constructed S206;

[0108] Based on the VSC output power model and the grid-connected point voltage effective value model, the nonlinear equation S207 of the grid-connected power supply single-feed system is constructed;

[0109] Based on the nonlinear equation, the Jacobian matrix S208 of the first element of the system is constructed;

[0110] Based on the voltage sampling value of the grid connection point of the single-feed system, according to the power flow change process model, the reactive power, active power and AC side voltage of the VSC S209 of the grid-connected power source are iteratively calculated through the power iteration power flow algorithm;

[0111] Based on the reactive power, active power and AC side voltage of the grid-forming power source in each iterative solution, the system first element Jacobian matrix is ​​modified to the system Jacobian matrix, and the singular point of the system Jacobian matrix is ​​set to the system voltage collapse point S210.

[0112] According to one embodiment of the present invention, Figure 1 As shown, the VSC output power model includes:

[0113]

[0114] The nonlinear equations include:

[0115]

[0116] Among them, the ΔP S is the active power variation; the ΔQ S is the reactive power variation;

[0117] The Jacobian matrix of the first element of the system:

[0118]

[0119] Among them, the H 11 is the Jacobian matrix self-feedback term; is the partial derivative of active power with respect to phase angle;

[0120] The power flow change process model:

[0121]

[0122] The i is the i-th step of the power flow calculation;

[0123] The system Jacobian matrix:

[0124]

[0125] Among them, the is the Jacobian matrix.

[0126] According to one embodiment of the present invention, Figure 1 As shown, the voltage support capability boundary analysis includes:

[0127] Based on the system Jacobian matrix and the constraints that characterize the voltage support capability boundary, the voltage support capability boundary model of the analytical model with quantitative calculation of the single-feedback system operation boundary is used to derive the maximum value of the VSC AC side voltage that can be reached when the grid-connected point voltage provides voltage support.

[0128] The constraints characterizing the voltage support capability boundary are:

[0129]

[0130] Among them, the is the partial derivative of reactive power to current growth coefficient;

[0131] The voltage support capability boundary model:

[0132]

[0133] The power delivery capability boundary analysis includes:

[0134] Based on the system Jacobian matrix and the singular conditions of the Jacobian matrix, the power delivery capacity boundary model of the analytical model is quantitatively calculated at the operating boundary of the single-feed system, and the grid connection point breakdown voltage is derived when the Jacobian matrix singular conditions are met.

[0135] Based on the power delivery capability boundary model, the operation boundary diagram of the grid-forming power source is obtained through the iterative solution process of the VSC output power model, so as to realize that the grid-forming power source will also be converted from a PV node to a PQ node after reaching the potential constraint condition in the VSC;

[0136] The conditions under which the Jacobian matrix is ​​singular are:

[0137] det(J)=0

[0138] Among them, the ( is the Jacobian matrix;

[0139] The power delivery capability boundary model:

[0140]

[0141] The internal potential constraints in the iterative solution process of the VSC output power model are:

[0142]

[0143] Among them, the is the partial derivative of active power with respect to the current growth coefficient.

[0144] At the same time, the present invention also embodies a quantitative evaluation system for static voltage support capability of a grid-type single-feedback system, comprising:

[0145] Based on the above quantitative evaluation method, the quantitative evaluation system includes:

[0146] Voltage effective value construction module: used to construct a grid connection point voltage effective value model based on the grid-connected equivalent circuit of the grid-connected power source and the relationship between the grid-connected power source output power and the grid connection point voltage amplitude and phase angle to provide system voltage support S101;

[0147] Jacobian matrix construction module: used to construct a power flow model based on the grid-connected point voltage effective value model and the reactive voltage response characteristics under steady-state grid-type power supply, and to construct a system Jacobian matrix through the iterative solution process of the model through the power iterative power flow algorithm, so as to obtain the system voltage collapse point S102 through the power flow change process;

[0148] Voltage support capability assessment module: used to obtain the quantitative calculation formula of the single-feed system operating boundary and the operating boundary diagram of the grid-type power source through the analysis of the operating boundary of the voltage support capability boundary analysis and the power delivery capability boundary analysis based on the system Jacobian matrix, so as to provide the system static voltage support capability assessment S103 through the system parameter changes of the operating boundary diagram.

[0149] The working principle of the quantitative evaluation method shown in the second embodiment is described below.

[0150] As shown in 2, this quantitative evaluation method includes the steps of constructing a voltage effective value model, constructing a power flow model, constructing a system Jacobian matrix, and analyzing the operating boundary. Among them, the voltage effective value model is constructed based on the grid-connected equivalent circuit of the grid-connected power source, and the grid-connected point voltage effective value model is constructed according to the relationship between the grid-connected power source output power and the grid-connected point voltage amplitude and phase angle. Among them, constructing the power flow model and constructing the system Jacobian matrix include constructing a power flow model based on the grid-connected point voltage effective value model according to the reactive voltage response characteristics of the grid-connected power source under steady state, and constructing the system Jacobian matrix through the iterative solution process of the model through the power iterative power flow algorithm. Among them, the analysis of the operating boundary includes the analysis of the operating boundary based on the system Jacobian matrix, through the voltage support capability boundary analysis and the power delivery capability boundary analysis, to obtain the quantitative calculation analytical expression of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply; through the above three steps, the following purposes are achieved in sequence: providing system voltage support, obtaining the system voltage collapse point through the power flow change process, and providing the system static voltage support capability evaluation through the system parameter changes of the operating boundary diagram. Through the above three steps, the invention content of this case can be summarized as: through the quantitative calculation of the static voltage stability boundary of the single-feed system of the grid-type power supply voltage support capability The calculation method is used to build a power flow mathematical model according to the reactive voltage response characteristics of the grid-type power supply in steady state, and the quantitative calculation analytical expression of the single-feed system operation boundary is obtained. This case first analyzes the main circuit structure and control strategy of the grid-type converter, derives the normalized mathematical model of the grid-type converter control system in the rotating coordinate system, and establishes the corresponding electromechanical transient model based on this; by analyzing the evolution law of the grid-connected point voltage of the grid-type converter as the output power of the converter changes, the mechanism of the grid-type converter providing voltage support for the system is revealed, and the phasor relationship satisfied by the bus voltage at the grid-connected point of the converter is obtained in combination with the line power transmission constraints; further The analytical expressions of the output power and voltage of the grid-connected converter are derived step by step, and the PV curve of the converter output active power and the grid-connected point voltage is constructed. Then, the static voltage stability mechanism of the grid-connected converter single-feed system is analyzed from a quantitative perspective, and a calculation method for the static stability limit boundary of the converter single-feed system is proposed. The factors affecting the static voltage stability of the system are quantitatively analyzed, and the effectiveness of the proposed algorithm is verified through simulation. By taking into account the voltage support capacity of the grid-connected converter, the voltage stability margin of the new energy system connected to the grid through the grid-connected converter is quantitatively analyzed, and the static voltage stability limit boundary of the system is accurately evaluated to ensure the safe and stable operation of the new power system.

[0151] Combine the following Figure 1 , 3 The working principle of the quantitative evaluation method shown in the embodiment is explained.

[0152] like Figure 1 , 3As shown, the first step is to construct a voltage effective value model, that is, based on the grid-connected equivalent circuit of the grid-type power supply, according to the relationship between the output power of the grid-type power supply and the voltage amplitude and phase angle of the grid-connected point, to construct a grid-connected point voltage effective value model to provide system voltage support. In the first step, there are three elements. First, based on the grid-connected equivalent circuit of the grid-type power supply, as shown Figure 2 As shown in the figure, this circuit goes from the photovoltaic wind turbine to the grid-connected converter VSC, then to the bus voltage at the PCC grid-connected point, and then outputs to the AC system through the reactance. The active power and reactive power injected into the AC system by the grid-connected power supply are P S , Q S , expressed in complex power form; U S is the bus voltage amplitude at the PCC grid connection point, δ S is the voltage phase angle; X T The equivalent reactance of the grid-connected line including the connecting transformer is taken, and the line resistance and ground capacitance are ignored. The relationship between the output power and the voltage amplitude and phase angle of the grid-connected point when the grid-type power source is connected to the infinite AC system is obtained:

[0153]

[0154] Eliminate phase angle δ S , we can get the effective value of the grid connection point voltage as:

[0155]

[0156] Combine the following Figure 1 , 4 , 5. The working principle of the quantitative evaluation method shown in the embodiment is explained.

[0157] like Figure 1 , 4, 5, the second step: constructing a power flow model and a system Jacobian matrix, that is, based on the grid-connected point voltage effective value model, constructing a power flow model according to the reactive voltage response characteristics of the grid-connected power supply in a steady state, and iterating the model through the power iteration power flow algorithm to construct a system Jacobian matrix to obtain the system voltage collapse point through the power flow change process, wherein, the second step includes three stages, wherein the first stage: the reactive response first stage; the second stage: the reactive response second stage; the third stage: the power flow model construction stage, wherein the reactive response first stage includes four sub-steps, the first sub-step: based on the active power sub-model of the grid-connected point voltage effective value model, gradually increase the active power reference value output by the grid-connected power supply from the initial working point, and increase the voltage source converter VSC AC side power The current gradually increases, and the actual value of active power and reactive power fed into the controller are obtained based on the gradually increasing VSC AC side current and voltage; the second sub-step: based on the actual value of active power and reactive power fed into the controller and the equivalent impedance parameters, according to the grid voltage effective value model, by increasing the reactive power output of the grid-forming power supply, the grid bus voltage is maintained at the rated value; the third sub-step: based on the controller model of the grid-forming power supply, through each control link of the model, the potential and current inside the VSC AC side reach the modulation upper limit, and the potential inside the VSC AC side is constrained; the fourth sub-step: based on the q-axis component of the potential inside the VSC AC side after the modulation upper limit, the active power output model of the grid-forming power supply is output through the dominant variable control of the reactive voltage control loop; starting from the initial working point (U S =1p.u.) gradually increases the active power reference value of the grid-type power supply output, the VSC AC side current increases, and the actual active and reactive values ​​fed into the controller are calculated from the grid side AC voltage and current, such as Figure 3 As shown, the equivalent impedance parameter in the per-unit system is smaller in magnitude, according to the following formula:

[0158]

[0159] The reactive power output of the grid-connected power source increases, providing support for the system voltage, so the bus voltage at the grid connection point can be temporarily maintained near the rated value; under the action of various control links, the converter will eventually reach the upper limit of modulation, such as Figure 4 As shown, the potential in its dq axis is constrained, and the q axis component is directly affected by the reactive voltage control loop and will become the dominant variable; at the same time, as a voltage source converter, there is an approximately linear relationship between the AC current output by VSC and the potential inside VSC. The converter is connected to the AC system through a converter transformer and a connecting reactor, so the reactive power Q injected into the AC system by the converter S It can be expressed as follows:

[0160]

[0161] Where R and L represent the converter loss equivalent resistance and connection reactance respectively. sd The increase is relatively small and can be used as a coefficient to simplify the analysis. After Vq reaches the upper limit, it becomes a constant value. After that, the reactive power output of the grid-connected power supply changes with the grid connection point voltage. From the initial operating point to the limit state, the grid-connected power supply outputs reactive power Q S Determined by the controller and the grid-connected point voltage, the output reactive power continues to increase, thus forming the first stage in the reactive voltage change curve.

[0162] like Figure 1 , 4 As shown in Figure 5, the second stage of reactive response includes a sub-step, namely, a reactive power sub-model based on the grid-connected point voltage effective value model. By gradually increasing the reactive power reference value output by the grid-connected power source, the voltage on the AC side of the voltage source converter VSC is gradually reduced, and the VSC AC side voltage and the grid-connected power source reactive power output model are output through the external system control connected to the grid-connected power source. The voltage change trend of the grid-connected point will be determined by the external circuit after the controller reaches the limiting state. Considering the power flow on the transmission line between the grid-connected point and the AC system, it is determined by:

[0163]

[0164] It can be seen that after passing the turning point of the first stage of operation, it continues to increase and then drops sharply, in the same direction of change. Therefore, the grid-type power supply can play a certain role in voltage support for the system, but its voltage support capacity is affected by the constraints of the converter modulation link. After the constraints are met, the grid-side voltage and output reactive power will be determined by the external system to which the grid-type power supply is connected.

[0165] like Figure 1 , 5As shown, the analysis of the operating boundary includes five sub-steps. The first sub-step is to construct a VSC output power model based on the active power output model of the grid-type power supply and the reactive power output model of the grid-type power supply according to the controller model of the grid-type power supply; the second sub-step is to construct a nonlinear equation of the single-feed system of the grid-type power supply based on the VSC output power model and the grid-connected point voltage effective value model; the third sub-step is to construct the Jacobian matrix of the first element of the system based on the nonlinear equation; the fourth sub-step is to iteratively solve the reactive power, active power and AC side voltage of the grid-type power supply through the power iteration power flow algorithm based on the grid-connected point voltage sampling value of the single-feed system according to the power flow change process model; the fifth sub-step is to modify the Jacobian matrix of the first element of the system to the system Jacobian matrix based on the reactive power, active power and AC side voltage of the VSC in each iterative solution, and set the singular point of the system Jacobian matrix to the system voltage collapse point, and ignore the high-frequency harmonic components generated by the switching action in the steady state, and only consider the fundamental component under the three-phase symmetry of the AC system, that is, the d-axis component u of the AC bus voltage sd Coincident with the positive sequence fundamental component of the AC bus voltage, the q-axis component u sq is 0. According to Figure 1 The controller structure shown can obtain the VSC output power expressed by the control parameters in the dq coordinate system:

[0166]

[0167] Among them, K = IS / (R+SL) (R, L are the resistance and inductance parameters of the converter), which is the growth coefficient of the grid-side AC current as the VSC output active power changes; Vq is the potential in the q axis of the converter, which is constrained by the amplitude limit of the modulation link; cosθ is the cosine value of the voltage phase angle output by the active control link. When the DC voltage is constant, the change amplitude of cosθ is small, so it is treated as a constant and simplified to:

[0168]

[0169] The grid-type power source has voltage source characteristics under rated working conditions. Therefore, in the single-feed system shown, the PCC point is regarded as a PV node, and the infinite AC system is a balanced node. The power equation in polar coordinate form for the PCC point is:

[0170]

[0171] The nonlinear equation describing the grid-type power supply single-feed system is:

[0172]

[0173] At this time, the Jacobian matrix of the single-feed system has only one element, namely:

[0174]

[0175] If the active output of the grid-type power source continues to increase or an external circuit fault causes an overcurrent, the converter will reach the upper modulation limit. Medium V q becomes a constant, and the grid-type power supply outputs reactive power Q S Determined by the grid-connected point voltage, the power flow change process is actually the process of feeding the grid-connected point voltage sampling value into the control system to achieve the iterative solution of the power, which can be specifically expressed by the following formula:

[0176]

[0177] Therefore, when the power flow calculation is performed in step i, the given quantity at the PCC point is the active power P S and reactive power Q S That is, the node type of the PCC point is converted from a PV node to a PQ node, and the system Jacobian matrix is ​​modified to:

[0178]

[0179] In the renewable energy collection system, the increase in the power transmitted from the renewable energy station will cause the bus voltage at the grid connection point to decrease until it reaches the critical point of static voltage stability, which is also the singular point of the system Jacobian matrix. When it approaches the critical point, it may cause voltage collapse in the system. The critical point corresponds to the maximum output power of the station.

[0180] Combine the following Figure 1 The working principle of the quantitative evaluation method shown in the embodiment is explained.

[0181] like Figure 1As shown, the third step: analysis of the operating boundary, that is, based on the system Jacobian matrix, through the analysis of the operating boundary of the voltage support capability boundary and the power delivery capability boundary analysis, the quantitative calculation analytical expression of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply are obtained, so as to provide the static voltage support capability evaluation of the system through the system parameter changes of the operating boundary diagram, wherein the third step includes two elements, first, voltage support capability boundary analysis; second, power delivery capability boundary analysis; wherein, voltage support capability boundary analysis: based on the system Jacobian matrix, according to the approximate characterization of the voltage support capability boundary The voltage support capability boundary model of the analytical model of the quantitative calculation of the single-feedback system operation boundary is derived, and the maximum value of the VSC AC side voltage that can be achieved when the grid-connected point voltage provides voltage support is derived. The reactive power output of the grid-connected power source is affected by the constraints of the controller. There is an inflection point that increases first and then decreases with the change of power, and the node type will also change. The analysis of its operation boundary will consist of two parts: the voltage support capability boundary and the power delivery capability boundary. From the above analysis, it can be obtained that when the internal potential reaches the amplitude, the grid-connected point voltage drops rapidly, and at this time it runs to the voltage support capability boundary, and the internal potential V q becomes a constant, Q S The change curve has an inflection point, and the condition that characterizes the voltage support capacity boundary is obtained as follows:

[0182]

[0183] Depend on have:

[0184]

[0185] Will Substitution And derive it to get:

[0186]

[0187] Substituting the above expression into Let the expression be 0. The maximum value that the grid connection point voltage can reach when the grid-connected power source provides voltage support can be deduced from the above expression:

[0188]

[0189] Power delivery capability boundary analysis: Based on the system Jacobian matrix, according to the singular conditions of the Jacobian matrix, the power delivery capability boundary model of the analytical model of the single-feed system operation boundary is quantitatively calculated to derive the grid connection point collapse voltage when the Jacobian matrix singular conditions are met; Based on the power delivery capability boundary model, through the iterative solution process of the VSC output power model, the operation boundary diagram of the grid-forming power source is obtained to realize that the grid-forming power source will also be converted from a PV node to a PQ node after reaching the potential constraint conditions in the VSC; Analyze the power transmission capability boundary, according to:

[0190]

[0191] The condition for the system power flow Jacobian matrix to be singular is:

[0192] det(J)=0

[0193] Will Middle Q S Substitute the analytical expression into det(J) = 0 and solve it to obtain the grid connection point voltage when the Jacobian matrix singular condition is satisfied:

[0194]

[0195] During the iteration process, Substitution Solve the power flow and when the system reaches the power delivery limit, the following equation is satisfied:

[0196]

[0197] Corresponding to the characteristics of synchronous machines converting from PV nodes to PQ nodes after reactive power exceeds the limit, the grid-forming power source will also be converted from PV nodes to PQ nodes after reaching the potential constraint conditions in the VSC. Therefore, the operation boundary diagram of the grid-forming power source is obtained:

[0198] Among them U S represents the voltage vector at the grid-connected point of the grid-type power supply. The angle δ formed by the voltage vector and the horizontal axis represents the phase difference between the AC voltage and current. S represents the current vector of the system. The dashed lines of different colors represent the operating limits of the system under different active output conditions. As the output power of the grid-type power source changes, the operating point changes from U S Change to U S , in the reactive response rising stage, the phase angle changes from δ to δ', and the operating boundary shifts from the black dotted line to the red dotted line; when the voltage support capacity boundary is reached, as the active power increases, the system will operate in the reactive response falling stage, and the operating point changes from U S Change to U S, the phase angle changes from δ' to δ", and the operating boundary becomes a green dotted line. The power limit curve in the figure depicts the power transmission capacity of the grid-type power supply at different operating stages, where the red dotted line represents the voltage support boundary, the green dotted line represents the power transmission boundary, and the blue solid line part obtained by considering the whole process of the power change of the grid-type power supply represents the overall operating boundary.

[0199] At the same time, the present invention also provides a quantitative evaluation system for the static voltage support capability of a grid-type single-feed system to support the above-mentioned quantitative evaluation method. The quantitative evaluation system includes three main modules: a first module: a voltage effective value construction module; a second module: a Jacobian matrix construction module; a third module: a voltage support capability evaluation module; the voltage effective value construction module: used to construct a grid-connected point voltage effective value model based on the grid-connected equivalent circuit of the grid-type power supply, according to the relationship between the grid-type power supply output power and the grid-connected point voltage amplitude and phase angle, so as to provide system voltage support; the Jacobian matrix construction module: used to construct a grid-connected point voltage effective value model based on the grid-connected point voltage effective value model, according to the relationship between the grid-type power supply output power and the grid-connected point voltage amplitude and phase angle, so as to provide system voltage support. The reactive voltage response characteristics under steady state are used to construct a power flow model, and the system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iteration power flow algorithm, so as to obtain the system voltage collapse point through the power flow change process; the voltage support capability evaluation module is used to obtain the quantitative calculation analytical expression of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply through the analysis of the operating boundary of the voltage support capability boundary analysis and the power delivery capability boundary analysis based on the system Jacobian matrix, so as to provide the system static voltage support capability evaluation through the system parameter changes of the operating boundary diagram, accurately evaluate the system static voltage stability limit boundary, and ensure the safe and stable operation of the new power system.

[0200] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A quantitative evaluation method for the static voltage support capability of a grid-type single-feed system, characterized by: include: Based on the grid-connected equivalent circuit of the grid-type power supply, and according to the relationship between the output power of the grid-type power supply and the voltage amplitude and phase angle of the grid-connected point, the grid-connected point voltage effective value model is constructed to provide system voltage support; Based on the grid-connected point voltage effective value model, a power flow model is constructed according to the reactive voltage response characteristics of the grid-connected power supply in steady state. The system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iterative power flow algorithm to obtain the system voltage collapse point through the power flow change process. Based on the system Jacobian matrix, through the analysis of the operating boundaries of the voltage support capability boundary analysis and the power delivery capability boundary analysis, the quantitative calculation analytical expression of the operating boundary of the single-feed system and the operating boundary diagram of the grid-type power supply are obtained, so as to provide the static voltage support capability evaluation of the system through the changes of system parameters in the operating boundary diagram.

2. The quantitative evaluation method according to claim 1, characterized in that: The relationship between the output power of the grid-connected power source and the voltage amplitude and phase angle at the grid connection point includes: Among them, the P S , active power of grid-type power supply; the Q S The reactive power of the grid-type power supply; S is the voltage on the AC side of the VSC; S is the voltage phase angle; the X T is the equivalent reactance of the grid-connected line including the connecting transformer; The grid connection point voltage effective value model includes:

3. The quantitative evaluation method according to claim 1, characterized in that: The power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iterative power flow algorithm, including: In the first stage of reactive power response: Based on the active power sub-model of the grid-connected point voltage effective value model, the active power reference value output by the grid-connected power source is gradually increased from the initial working point, the AC side current of the voltage source converter VSC is gradually increased, and the actual active power value and reactive power actual value fed into the controller are obtained based on the gradually increased VSC AC side current and voltage; Based on the actual value of active power and reactive power fed into the controller and the equivalent impedance parameters, the grid point bus voltage is maintained at the rated value by increasing the reactive power output of the grid-type power supply according to the grid point voltage effective value model; Based on the controller model of the grid-type power supply, through each control link of the model, the potential and current inside the AC side of the VSC are brought to the upper limit of modulation, and the potential inside the AC side of the VSC is constrained; Based on the q-axis component of the potential inside the VSC AC side after modulation upper limit, the active power output model of the grid-type power supply is output through the dominant variable control of the reactive voltage control loop.

4. The quantitative evaluation method according to claim 3, characterized in that: The active power output model of the grid-forming power supply includes: Wherein, R is the equivalent resistance of the converter loss; L is the equivalent reactance of the converter loss, and i sd is a simplified analysis coefficient of the d-axis component of the converter output AC current, and Vq is a constant value of the converter output AC voltage after reaching the upper limit; The ω is the angle frequency; the u sd is the grid connection point voltage; sq It is the q-axis component of the inverter output AC current.

5. The quantitative evaluation method according to claim 1, characterized in that: The power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iterative power flow algorithm, including: In the second stage of reactive power response: The reactive power sub-model based on the grid-connected point voltage effective value model gradually increases the reactive power reference value output by the grid-connected power source, gradually reduces the AC side voltage of the voltage source converter VSC, and outputs the VSC AC side voltage and the grid-connected power source reactive power output model through the control of the external system to which the grid-connected power source is connected.

6. The quantitative evaluation method according to claim 5, characterized in that: The grid-type power source reactive power output model includes: Among them, K is the growth coefficient of the grid-side AC current as the active power output of the VSC changes, wherein K=IS / (R+SL), wherein S is the differential in the Laplace transform; it is constrained by the amplitude limit of the modulation link; and cosθ is the cosine value of the voltage phase angle output by the active power control link. When the DC voltage is constant, the change amplitude is small and it is treated as a constant.

7. The quantitative evaluation method according to claim 1, characterized in that: The power flow model is constructed according to the reactive voltage response characteristics of the grid-type power supply in a steady state, and the system Jacobian matrix is ​​constructed by iteratively solving the model through a power iterative power flow algorithm, including: Flow model building phase: Based on the active power output model and reactive power output model of the grid-forming power source, and according to the controller model of the grid-forming power source, a VSC output power model is constructed; Based on the VSC output power model and the grid-connected point voltage effective value model, the nonlinear equation of the grid-connected power single-feed system is constructed. Based on the nonlinear equation, the Jacobian matrix of the first element of the system is constructed; Based on the voltage sampling value of the grid connection point of the single-feed system, according to the power flow change process model, the reactive power, active power and AC side voltage of the VSC are iteratively calculated through the power iterative power flow algorithm; Based on the reactive power, active power of the grid-connected power source and the AC side voltage of the VSC in each iterative solution, the Jacobian matrix of the first element of the system is modified to the system Jacobian matrix, and the singular point of the system Jacobian matrix is ​​set to the system voltage collapse point.

8. The quantitative evaluation method according to claim 7, characterized in that: The VSC output power model includes: The nonlinear equations include: Among them, the ΔP S is the active power variation; the ΔQ S is the reactive power variation; The Jacobian matrix of the first element of the system: Among them, the H 11 is the Jacobian matrix self-feedback term; is the partial derivative of active power with respect to phase angle; The power flow change process model: The i is the i-th step of the power flow calculation; The system Jacobian matrix: Among them, the is the Jacobian matrix.

9. The quantitative evaluation method according to claim 1, characterized in that: The voltage support capability boundary analysis includes: Based on the system Jacobian matrix and the constraints that characterize the voltage support capability boundary, the voltage support capability boundary model of the analytical model of the quantitative calculation of the single-feedback system operation boundary is used to derive the maximum value of the VSC AC side voltage that can be achieved when the grid-connected point voltage provides voltage support. The constraints characterizing the voltage support capability boundary are: Among them, the is the partial derivative of reactive power to current growth coefficient; The voltage support capability boundary model: The power delivery capability boundary analysis includes: Based on the system Jacobian matrix and the singular conditions of the Jacobian matrix, the power delivery capacity boundary model of the analytical model is quantitatively calculated at the operating boundary of the single-feed system, and the grid connection point breakdown voltage is derived when the Jacobian matrix singular conditions are met. Based on the power delivery capability boundary model, the operation boundary diagram of the grid-forming power source is obtained through the iterative solution process of the VSC output power model, so as to realize that the grid-forming power source will also be converted from a PV node to a PQ node after reaching the potential constraint condition in the VSC; The conditions under which the Jacobian matrix is ​​singular are: det(J)=0 Among them, the ( is the Jacobian matrix; The power delivery capability boundary model: The internal potential constraints in the iterative solution process of the VSC output power model are: Among them, the is the partial derivative of active power with respect to the current growth coefficient.

10. A quantitative evaluation system for the static voltage support capability of a grid-type single-feed system, characterized by: include: Based on the quantitative evaluation method according to claim 1 to claim 9, the quantitative evaluation system comprises: Voltage effective value construction module: It is used to construct the grid connection point voltage effective value model based on the grid-connected equivalent circuit of the grid-connected power source and the relationship between the grid-connected power source output power and the grid connection point voltage amplitude and phase angle to provide system voltage support; Jacobian matrix construction module: It is used to build a power flow model based on the grid-connected point voltage effective value model and the reactive voltage response characteristics of the grid-connected power supply in a steady state. The system Jacobian matrix is ​​constructed through the iterative solution process of the model through the power iterative power flow algorithm to obtain the system voltage collapse point through the power flow change process. Voltage support capability assessment module: Based on the system Jacobian matrix, it is used to obtain the quantitative calculation formula of the single-feed system operating boundary and the operating boundary diagram of the grid-type power supply through the analysis of the operating boundary of the voltage support capability boundary analysis and the power delivery capability boundary analysis, so as to provide the static voltage support capability assessment of the system through the changes of system parameters in the operating boundary diagram.

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