Engineering measurement and calculation method adaptive to influence of flexible voltage regulating device on stable state of transformer area

Abstract

The invention relates to the technical field of steady-state analysis of a power system, in particular to an engineering measurement and calculation method adaptive to the influence of a flexible voltage regulating device on the steady state of a distribution transformer district, which comprises the following steps: S1, acquiring data information of the distribution transformer district and related equipment; s2, constructing a directed line segment topology model, and measuring and calculating an initial power flow index of the distribution transformer district by adopting a forward-backward substitution method; s3, measuring and calculating direct-current loss after the FVR devices are connected in parallel, wherein the direct-current loss comprises converter loss and direct-current wire loss; s4, constructing a direct-current influence boundary, and calculating alternating-current loss by adopting a two-stage power flow calculation method based on the boundary condition; and S5, integrating the direct-current loss and the alternating-current loss after the FVR devices are connected in parallel, and evaluating the steady-state index of the distribution transformer district. The method can accurately evaluate the influence of the access of the flexible voltage regulation device on stable state indexes such as transformer area voltage distribution, network loss, equipment load rate and the like, and provides a theoretical basis for device model selection, parameter configuration and engineering application.

Description

Technical Field

[0001] This invention relates to the field of power system steady-state analysis technology, specifically to an engineering calculation method for adapting flexible voltage regulation devices to the steady-state impact on distribution transformer areas. Background Technology

[0002] Conventional AC power flow calculation methods are based on a complete AC circuit model, considering voltage amplitude and phase angle, as well as the interaction between active and reactive power. However, the solution process for the nonlinear equations involved in this method is quite complex, especially in large-scale power grids, where the computational load increases exponentially. In the application scenario of transformer substations, although the scale of the substation is relatively small compared to the overall power grid, as the structure of the substation gradually becomes more complex, it may contain various types of electrical equipment and load characteristics. Some substations may have a large number of single-phase loads, leading to prominent three-phase imbalance problems. When dealing with three-phase imbalance problems, conventional AC power flow calculation methods often require complex transformations and adjustments to the model, increasing the difficulty and uncertainty of the calculation. In addition, there may be some special electrical equipment in the substation, such as power electronic devices. The nonlinear characteristics of these devices make it difficult for traditional AC power flow calculation methods to accurately simulate their impact on the voltage, power, and losses of the substation.

[0003] Flexible voltage regulators (FVRs), a new type of power equipment, offer rapid, flexible, and precise voltage regulation capabilities. They can monitor operating parameters such as voltage and current in the distribution area in real time and quickly adjust the output voltage according to preset control strategies, effectively solving problems such as voltage fluctuations, voltage deviations, and three-phase imbalances. Simultaneously, FVRs can improve the power factor and reduce line losses through flexible control of reactive power. Compared with traditional voltage regulating equipment, FVRs offer advantages such as fast response speed, wide adjustment range, high adjustment accuracy, and the ability to achieve independent three-phase adjustment, making them better suited to the complex and changing operating conditions of distribution areas.

[0004] Traditional AC / DC power flow methods suffer from limitations in terms of technical parameters and algorithm convergence in AC / DC hybrid distribution areas with flexible voltage regulators, failing to meet engineering calculation requirements. To fully leverage the role of flexible voltage regulators in distribution areas and achieve effective control and optimization of steady-state voltage, power, and losses, a suitable engineering calculation method is needed. This method can accurately assess the impact of flexible voltage regulators on various operating indicators of the distribution area under different operating conditions, providing a scientific basis for the selection of flexible voltage regulators, determination of installation locations, and formulation of control strategies. This ultimately improves the operating efficiency and power quality of the distribution area, reduces operating costs, and ensures the safe, stable, and economical operation of the power system. Summary of the Invention

[0005] To address the technical problem that traditional AC / DC power flow methods cannot meet the requirements for calculating steady-state indicators of distribution transformer areas connected to flexible voltage regulators, this invention provides an engineering calculation method adapted to the steady-state impact of flexible voltage regulators on distribution transformer areas. This method can accurately assess the impact of flexible voltage regulator connection on steady-state indicators such as voltage distribution, network loss, and equipment load rate in distribution transformer areas, providing a theoretical basis for device selection, parameter configuration, and engineering applications.

[0006] The technical solution adopted in this invention is to provide an engineering calculation method for adapting the impact of flexible voltage regulating devices on the steady-state of a distribution area, including the following steps:

[0007] S1. Obtain data information of the distribution transformer area and related equipment;

[0008] S2. Construct a directed line segment topology model, use the forward-backward substitution method to calculate the initial power flow index of the distribution transformer area, and analyze the voltage status of all nodes, including the host and slave access nodes, at different times.

[0009] Calculate DC losses after S3 and FVR devices are connected in parallel, including converter losses and DC conductor losses.

[0010] S4. Construct the DC influence boundary and calculate the AC loss based on the two-stage power flow calculation method based on the boundary conditions.

[0011] S5. Evaluate the steady-state indicators of the distribution transformer area by considering the DC and AC losses after the integrated FVR devices are connected in parallel.

[0012] The specific process of analyzing the voltage situation in step S2 includes:

[0013] S21. The initial voltage of each node and the input active / reactive power are calculated using the PV mode full-phase power flow method.

[0014] S22. Using the initial power flow index calculation results, construct the node voltage matrix at different time points.

[0015] The specific process of calculating the total phase current flow method in step S21 includes:

[0016] S211. By superimposing the branch currents of the terminal meter box onto the transformer substation outlet, the current of each branch is calculated using the following expression:

[0017]

[0018] In the formula, Let represent the current in a certain phase of the branch from the i-th node to the s-th node, where phase represents phase A, phase B, and phase C; represents the phase current injected into the power grid at node s; n represents the number of all lower-level branches directly connected to node s; m represents the numbers of all lower-level branches connected to node s. This represents the current in the m-th branch that is directly connected to node s;

[0019] S212. Using the A, B, and C phase currents of each branch, calculate the N-phase current. The expression is as follows.

[0020]

[0021] In the formula, This represents the N-phase current in the branch from the i-th node to the s-th node. This represents the A-phase current in the branch from the i-th node to the s-th node. This represents the B-phase current in the branch from the i-th node to the s-th node. Let C represent the C-phase current in the branch from the i-th node to the s-th node;

[0022] S213. Calculate the phase voltage of each node using the voltage at the outlet side of the transformer area and the branch current. The expression is as follows.

[0023]

[0024] In the formula, This represents the phase voltage of the s-th node; This represents the phase voltage of the i-th node; This represents the branch impedance from node i to node s, with phases A, B, and C having the same impedance; except for the first node, the initial voltage of all other nodes is set to U. A0 =0.22∠0°、U B0 =0.22∠-120°, U C0 =0.22∠120°;

[0025]

[0026] In the formula, U represents the node voltage calculated in the k-th iteration for the i-th node; i (k-1) Calculate the node voltage for the (k-1)th iteration of the i-th node; ε is the allowable error.

[0027] The specific process for calculating DC loss in step S3 includes:

[0028] S31. Based on the voltage regulation parameters set by the FVR device, calculate the DC power flow of the parallel line of the FVR device, and the main unit terminal voltage V. 主 Slave terminal voltage V 从 The details are as follows:

[0029] DCLoss = loss Fvr +loss DCLine

[0030] In the formula, DCLoss represents DC loss, and loss Fvr This represents the overall loss of the FVR device. DCLine Indicates DC conductor loss;

[0031]

[0032] In the formula, loss Fvr S represents the overall loss of the FVR device, η represents the conversion efficiency of the FVR device, and S represents the overall loss of the FVR device. Fvr Indicates the capacity of the FVR device, sf out The value of m represents the standby power consumption of the FVR device, m represents the frequency of the FVR device starting voltage regulation, and t represents the current time.

[0033]

[0034] In the formula, loss DCLine Indicates DC conductor loss; Sign indicates whether the FVR device is in voltage regulation mode; R dc Represents the impedance of a DC conductor, Long dc P is the length of the DC conductor. Fvr_out For output power, I dc The current flowing through the DC conductor is represented by m, the frequency of the FVR device starting voltage regulation is represented by t, and the current time is represented by t.

[0035] R dc =2*Long dc *R dc.base

[0036] In the formula, R dc Represents the impedance of a DC conductor, Long dc R is the length of the DC conductor. dc.base The resistance is a DC unit resistance.

[0037]

[0038] In the formula, I dc U represents the current flowing through a DC conductor. dc P represents DC voltage. Fvr_out Output power, typically equal to S Fvr ;

[0039]

[0040] In the formula, Sign indicates whether the FVR device is in voltage regulation mode, and V out V is the voltage at the node connected to the inverter slave unit. set_lowSet the voltage for the FVR device. When the mains voltage is lower than this set value, the FVR device will start voltage regulation.

[0041] S32, when the slave terminal voltage V 从 >Host terminal voltage V 主 At this time, the rectifier and inverter function modes switch, the correction device starts, and the voltage V at the node connected to the inverter slave unit changes. out ≥V set_high At that time, Sign = 1, and the current reverses; V set_high This indicates the highest value of the voltage threshold set by the FVR device.

[0042] The two-stage power flow calculation method in step S4 specifically includes:

[0043] S41. Power flow calculation, voltage at the node connected to the inverter slave unit. Device set voltage V set_low The measurement range includes the conductors and users between the low-voltage outlet of the distribution transformer and the node connected to the inverter slave unit. The AC output current of the slave unit is...

[0044]

[0045] In the formula, U0 represents the rated three-phase AC line voltage of 380 volts; I Fvr.out Indicates the AC output current of the FVR device; S Fvr Indicates the capacity of the FVR device;

[0046] S42. Based on the node current connected to the inverter slave in the initial power flow specifications. Output current I on the AC side of the slave terminal Fvr.out The magnitude of the relationship is used to calculate the impact on AC losses when the FVR device is in operation at time t.

[0047] when At that time, the original AC loss remains unchanged, and the residual current and residual power are calculated.

[0048]

[0049] In the formula, For residual current, I is the initial current at the slave terminal. Fvr.out To output current from the AC side of the generator terminal, For the remaining power, V set_low Set the voltage value for the FVR device;

[0050] S43. Based on the FVR device settings, considering the voltage reactive power regulation limit and the impact of PV mode on power flow, the details are as follows.

[0051] The reactive power regulation range of the FVR device is:

[0052]

[0053] In the formula, Q Fvr S indicates the reactive power regulation range of the FVR device. Fvr Let Cos represent the capacity of the FVR device, where Cos∈[-0.9,0.9].

[0054] The reactive power adjustment constraints are ≤Qmax and ≥Qmin, and the maximum and minimum values ​​are determined based on the reactive power adjustment range of the FVR device.

[0055] S44. The first forward push process, the initial iteration value is the initial node voltage of phase A in PV mode at the grid connection point, which is V. set_low ∠0°, phase B is V set_low ∠-120°, C phase is V set_low ∠120°, active power is The reactive power is 0; the initial values ​​of the phase voltages of other nodes A, B, and C are 0.22∠0°, 0.22∠-120°, and 0.22∠120°, respectively; at this time, the PV node is calculated by superimposing the forward current to the previous stage.

[0056] S45. In the first reverse calculation process, the voltage at the transformer substation outlet and the current from the first forward calculation are used to recalculate the voltage at each node, as detailed below.

[0057] The voltage at the PV node of the slave parallel connection point is Voltage difference is

[0058] Based on the resistance R and reactance X of the branch where the slave parallel connection point is located, calculate the set voltage V of the FVR device. set_low The required reactive power support is calculated as follows:

[0059]

[0060] Reactive power required here Determine ΔQ t Does it satisfy the condition between Qmin and Qmax? Where, Indicates reactive power. This represents the reactive power of the slave parallel node after the back-substitution. This represents the active power of the slave parallel node after the back-substitution.

[0061] When ΔQ t >0, and ΔQ t ≤Qmax or ΔQ t <0, and ΔQ t When Qmin is ≥,

[0062] At the second iteration, the PV node parameters are adjusted to an active power of and a reactive power adjusted to In subsequent iterations, the voltage V at the PV node set_low remains unchanged before and after iteration, as long as the voltage difference between two consecutive iterations at other nodes satisfies |V k -V k-1 |< 0.001, then the power flow is determined to have converged;

[0063] In the formula, V k represents the voltage value at the K-th iteration, and V k-1 represents the voltage value at the (K - 1)-th iteration;

[0064] When the reactive power support margin cannot meet the reactive power support threshold required by the grid voltage, the PV node needs to be converted to a PQ node, that is,

[0065] When ΔQ t > 0, and ΔQ t > Qmax, the reactive power is adjusted to Qmax;

[0066] When ΔQ t < 0, and ΔQ t < Qmin, the reactive power is adjusted to Qmin;

[0067] At the second iteration, the PV node parameters are adjusted to an active power of and a reactive power adjusted to Qmax or Qmin; in subsequent iterations, the PV node is processed in the conventional PQ node manner, and the voltage difference between two consecutive iterations at the node satisfies |V k -V k-1 |< 0.001, then the power flow is determined to have converged;

[0068] S46. Two-stage power flow calculation, the calculation range is between the node connected to the slave inverter and the backend power supply users, and the voltage of the node connected to the slave inverter is the set voltage V set_low of the device. The node connected to the slave inverter is used as a new power source point, and the voltage is set to V set_low at this time. The backward-forward sweep method is used again to calculate the power flow in the lower section. If the voltage difference between two consecutive iterations at each node satisfies |V k -V k-1 |< 0.001, then the power flow is determined to have converged.

[0069] S47. When the photovoltaic power generation is large, the voltage V 从 at the slave machine end is > the voltage V 主 at the master machine end, the power flow is reversed and flows from the slave machine end to the master machine end. The photovoltaic power generation causes the voltage at the slave machine end to rise.

[0070] When the FVR device switches from voltage boost mode to power feedback mode, the surplus photovoltaic power from the slave end is transmitted to the host end through the internal DC bus and finally fed back to the upstream grid.

[0071]

[0072] In the formula, This represents the grid-connected power of the photovoltaic (PV) node at time t. This represents the load power at time t. I represents the input power of the FVR device at time t. dc P represents the current flowing through a DC conductor. Fvr_out U represents the DC output power, η represents the conversion efficiency of the FVR device, and U represents the DC output power. dc Indicates DC voltage;

[0073] when And the master and slave voltages meet the requirements. When the power flow reverses, the buck mode is activated, at which point the slave node injects power. DC output power is P Fvr_out =S Fvr_out .

[0074] The data information of the distribution transformer area and related equipment in step S1 includes cable topology information, meter box / low-voltage user information, photovoltaic equipment information, time-series acquisition information, and flexible voltage regulation device information.

[0075] The cable topology information includes the name of the overhead line / cable, the connection relationship of the topology nodes, the cable length, and the model of the overhead line or cable. The meter box / low-voltage user information includes the name of the meter box / user, the meter box to which the user belongs, and the phase information of the low-voltage user. The photovoltaic equipment information includes the equipment name, capacity, access location, and PV / PQ node settings. The time-series acquisition information includes the three-phase current and three-phase voltage of the A / B / C outlet of the distribution transformer area, the photovoltaic output power, and the active power of the low-voltage user. The flexible voltage regulating device information includes the equipment model, capacity, DC output voltage, rated AC output voltage, voltage regulation range, device loss rate, and standby loss.

[0076] The beneficial effects of this invention are:

[0077] 1. Fundamentally improves the efficiency and automation level of analysis work. Traditional methods rely on general simulation software or manual calculations, requiring professionals to manually construct data files, a tedious and error-prone process. This invention, through simple data encapsulation and automatic topology identification technology, can directly convert transformer, cable, meter box, and user data of a distribution area into accurate models required for full-phase power flow calculations. It achieves one-click automatic generation from raw data to calculation models, shortening the time required for preliminary preparation and greatly freeing up manpower.

[0078] 2. A two-stage refined calculation framework of "DC steady-state analysis - boundary construction - AC correction" is adopted. Existing AC power flow algorithms cannot effectively assess the impact of flexible voltage regulators on the DC side. The calculation framework of this invention first independently calculates the voltage fluctuations and losses on the DC side of the device, and then feeds them back as precise boundary conditions to the AC power flow correction process. This achieves decoupling and re-integration of AC and DC systems at the algorithm level, ensuring the accuracy and reliability of power flow calculation for new transformer substations that include flexible voltage regulators.

[0079] 3. This invention achieves visualization, intelligentization, and decision support-oriented analysis of the process and results. The core algorithm is encapsulated in a graphical user interface, allowing users to easily complete device access, parameter settings, and scenario simulations through intuitive operations such as clicking and selecting. Analysis results are presented in various formats, including topology coloring diagrams, trend curves, and multi-scheme comparison reports, making key indicators such as voltage exceedances, power flow distribution, and network loss changes readily apparent. This not only significantly lowers the technical barrier but also enables maintenance personnel to quickly assess the mitigation effects of different access locations and device capacities, providing efficient and accurate quantitative decision-making basis for equipment selection and mitigation scheme formulation, thus powerfully promoting the development of intelligent distribution network management and proactive voltage mitigation. Attached Figure Description

[0080] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0081] like Figure 1 As shown, this invention provides an engineering calculation method for adapting flexible voltage regulating devices to the steady-state impact of transformer substations, including the following steps:

[0082] S1. Obtain data information from the distribution transformer area and related equipment; including,

[0083] Cable topology information: name of overhead line / cable, connection relationship of topology nodes, cable length, overhead line or cable model;

[0084] Meter box / low-voltage user information collection: Meter box / user name, meter box to which the user belongs, and low-voltage user phase information;

[0085] Photovoltaic model information: device name, capacity, access location, PV / PQ node settings;

[0086] Time-series data acquisition: three-phase current and three-phase voltage at the A / B / C outlets of the distribution transformer area, as well as photovoltaic power output and active power of low-voltage users;

[0087] Parameters of flexible integrated voltage regulator: model, capacity, DC output voltage, rated AC output voltage, voltage regulation range, device loss rate, and standby loss.

[0088] S2. Construct a directed line segment topology model, use the forward-backward substitution method to calculate the initial power flow index of the distribution transformer area, and analyze the voltage status of all nodes, including the host and slave access nodes, at different times.

[0089] The specific method for calculating the initial power flow index is as follows:

[0090] (1) Power loss in the transformer area

[0091] AC line time-sharing and phase-sharing losses,

[0092]

[0093] DC line loss,

[0094]

[0095] Total time-of-use loss for the station.

[0096]

[0097] In the formula, The AC line phase loss power at time t; The input and output power of the phase-separated AC line at time t; ΔDcLoss t DC line loss at time t; DCLoss is the DC component loss; Sigh indicates whether the FVR device is in voltage regulation mode; ΔTqLoss t Let t be the total power loss of the transformer area at time t.

[0098] (2) Overall line loss rate of transformer area

[0099] AC line time-sharing and phase-sharing loss rate

[0100]

[0101] Time-of-use line loss rate of Taiwan

[0102]

[0103] in,

[0104]

[0105] Comprehensive line loss rate of the transformer area

[0106]

[0107] In the formula, The AC line phase loss power at time t; The input power of the phase-separated AC line at time t; The phase-separated AC line loss rate at time t;

[0108] ΔTqLoss t TqLoss represents the total power loss of the transformer area at time t. t Let t be the total power supply of the transformer area at time t;

[0109] TqLoss t δTqLoss is the line loss rate of the transformer area at time t; δTqLoss is the comprehensive line loss rate of the transformer area, which is the comprehensive line loss rate after considering the superposition of losses and power supply at 24 time points. This represents the user power at time t. This represents the grid-connected power of the photovoltaic (PV) node at time t;

[0110] (3) Branch load rate

[0111]

[0112] In the formula, Let t be the branch load rate; Let I be the current in branch i at time t; i_e_line The rated current carrying capacity of the conductor containing branch line i.

[0113] (4) Node voltage deviation rate

[0114]

[0115] In the formula, Let i be the voltage deviation rate at node i at time t; U is the calculated voltage of phases A / B / C at node i at time t; e The rated AC phase voltage is taken as 220 volts.

[0116] (5) User voltage qualification rate

[0117]

[0118] In the formula, δV user To meet the user's operating voltage qualification requirements; U i Calculate the voltage at node i; U e Rated AC phase voltage; AllNum user This refers to the total number of low-voltage users in the transformer area.

[0119] Definition of the judgment function: I(·) is a logical judgment function. If the condition in the parentheses is true, then I = 1; otherwise, I = 0.

[0120] (6) Percentage of heavy overload on branch roads

[0121]

[0122] In the formula, δF line The percentage of branches experiencing severe overload during operation; Let AllNum be the branch load rate at time t; line represents the total number of branch lines in the transformer area; I(·) is the logical judgment function.

[0123] S21. The initial voltage of each node and the input active / reactive power are calculated using the PV mode full-phase power flow method.

[0124] S211. By superimposing the branch currents of the terminal meter box onto the transformer substation outlet, the current of each branch is calculated using the following expression:

[0125]

[0126] In the formula, Let represent the current in a certain phase of the branch from the i-th node to the s-th node, where phase represents phase A, phase B, and phase C; represents the phase current injected into the power grid at node s; n represents the number of all lower-level branches directly connected to node s; m represents the numbers of all lower-level branches connected to node s. This represents the current in the m-th branch that is directly connected to node s;

[0127] S212. Using the A, B, and C phase currents of each branch, calculate the N-phase current. The expression is as follows.

[0128]

[0129] In the formula, This represents the N-phase current in the branch from the i-th node to the s-th node. This represents the A-phase current in the branch from the i-th node to the s-th node. This represents the B-phase current in the branch from the i-th node to the s-th node. Let C represent the C-phase current in the branch from the i-th node to the s-th node;

[0130] S213. Calculate the phase voltage of each node using the voltage at the outlet side of the transformer area and the branch current. The expression is as follows.

[0131]

[0132] In the formula, This represents the phase voltage of the s-th node; This represents the phase voltage of the i-th node; This represents the branch impedance from node i to node s, with phases A, B, and C having the same impedance; except for the first node, the initial voltage of all other nodes is set to U. A0 =0.22∠0°、U B0=0.22∠-120°, U C0 =0.22∠120°;

[0133]

[0134] In the formula, U represents the node voltage calculated in the k-th iteration for the i-th node; i (k-1) Calculate the node voltage for the (k-1)th iteration of the i-th node; ε is the allowable error.

[0135] S22. Using the initial power flow index calculation results, construct the node voltage matrix at different time points.

[0136] Time Node t1 t2 ... t24 Node 1 V11 V12 ... V124 Node 2 V21 V22 ... V224 ... ... ... ... ... Node host Vin1 Vin2 ... Vin24 Node slave Vout1 Vout2 ... Vout24 ... ... ... ... ... Node n Vn1 Vn2 ... Vn24

[0137] Among them, the voltages of the master and slave access nodes at time t are marked using the power flow results. and The main steady-state indicators of the transformer area include voltage qualification rate, branch load rate, comprehensive line loss rate, and branch loss rate. The initial power flow marker active power at node t where the slave unit is located is... Mark reactive power as The marked current value is

[0138] The DC loss is calculated after the S3 and FVR devices are connected in parallel, including converter loss and DC conductor loss; converter loss includes IGBT switching loss and conduction loss, and converter loss is related to the device conversion efficiency μ.

[0139] S31. Based on the voltage regulation parameters set by the FVR device, calculate the DC power flow of the parallel lines of the FVR device, as follows.

[0140] Host terminal voltage V 主 Slave terminal voltage V 从 ,

[0141] DCLoss = loss Fvr +loss DCLine

[0142] In the formula, DCLoss represents DC loss, and loss Fvr This represents the overall loss of the FVR device. DCLine Indicates DC conductor loss;

[0143]

[0144] In the formula, loss Fvr S represents the overall loss of the FVR device, η represents the conversion efficiency of the FVR device, and S represents the overall loss of the FVR device. FvrIndicates the capacity of the FVR device, sf out The value m represents the standby power consumption of the FVR device, and m represents the frequency of the FVR device starting voltage regulation. For example, if it starts at time t, time t+1, and time t+2, then m = 3; t represents the current time.

[0145]

[0146] In the formula, loss DCLine Indicates DC conductor loss; Sign indicates whether the FVR device is in voltage regulation mode; R dc Represents the impedance of a DC conductor, Long dc P is the length of the DC conductor. Fvr_out For output power, I dc The current flowing through the DC-guided circuit is represented by m, which represents the frequency of the FVR device's voltage regulation operation; t represents the current moment.

[0147] R dc =2*Long dc *R dc.base

[0148] In the formula, R dc Represents the impedance of a DC conductor, Long dc R is the length of the DC conductor. dc.base The resistance is a DC unit resistance.

[0149]

[0150] In the formula, I dc U represents the current flowing through a DC conductor. dc P represents DC voltage. Fvr_out Output power, typically equal to S Fvr ;

[0151]

[0152] In the formula, Sign indicates whether the FVR device is in voltage regulation mode, and V out V is the voltage at the node connected to the inverter slave unit. set_low Set the voltage for the FVR device. When the mains voltage is lower than this set value, the FVR device will start voltage regulation.

[0153] S32. When a large amount of photovoltaic backfeed occurs, the voltage V at the slave terminal... 从 >Host terminal voltage V 主 At this time, the rectifier and inverter function modes switch, the correction device starts, and the voltage V at the node connected to the inverter slave unit changes. out ≥V set_high At that time, Sign = 1, and the current reverses; V set_highThis indicates the highest value of the voltage threshold set by the FVR device.

[0154] S4. Construct the DC influence boundary, and based on this boundary condition, calculate and optimize the two-stage power flow calculation method used in the AC section.

[0155] The engineering calculations mainly involve the following four working conditions:

[0156] ① Traditional transformer substations have no photovoltaic power, low voltage, V 主 >V 从 ;

[0157] ② Contains a small amount of photovoltaic power, but still exhibits low voltage, V 主 >V 从 ;

[0158] ③ Contains a high proportion of photovoltaic power, reverse power transmission from the distribution area, overvoltage, V 主 <V 从 ;

[0159] ④ The voltage problem occurs at different times of the day, with overvoltage during the day and low voltage at night. Therefore, it is necessary to consider both voltage levels simultaneously. 主 >V 从 and V 主 <V 从 The two-way flow of current.

[0160] Based on the above working condition analysis, the main focus is on V. 主 >V 从 and V 主 <V 从 Two states.

[0161] (1) Under normal circumstances, there is no photovoltaic power or little photovoltaic power generation, and the voltage at the main unit terminal V is... 主 Slave terminal voltage V 从 In traditional power supply mode, power flows from the master unit to the slave unit. In contrast, FVR devices draw power from the AC grid and actively boost the slave unit voltage through AC / DC and DC / AC conversion to supply power to remote users.

[0162] The method for calculating the AC power flow from the distribution transformer to the slave unit is as follows.

[0163] S41, Voltage of the node connected to the inverter slave unit Device set voltage V set_low The measurement range includes the conductors and users between the low-voltage side outlet of the distribution transformer and the node connected to the inverter slave unit. The AC output current of the slave unit is...

[0164]

[0165] In the formula, U0 represents the rated three-phase AC line voltage of 380 volts; I Fvr.outIndicates the AC output current of the FVR device; S Fvr Indicates the capacity of the FVR device;

[0166] S42. Based on the node current connected to the inverter slave in the initial power flow specifications. Output current I on the AC side of the slave terminal Fvr.out The magnitude of the relationship is used to calculate the impact on AC losses when the FVR device is in operation at time t.

[0167] when At that time, the original AC loss remains unchanged, and the residual current and residual power are calculated.

[0168]

[0169] In the formula, For residual current, I is the initial current at the slave terminal. Fvr.out To output current from the AC side of the generator terminal, For the remaining power, V set_low Set the voltage value for the FVR device;

[0170] S43. Based on the FVR device settings, considering the voltage reactive power regulation limit and the impact of PV mode on power flow, the details are as follows.

[0171] The reactive power regulation range of the FVR device is:

[0172]

[0173] In the formula, Q Fvr S indicates the reactive power regulation range of the FVR device. Fvr Let Cos represent the capacity of the FVR device, where Cos∈[-0.9,0.9].

[0174] The reactive power adjustment constraints are ≤Qmax and ≥Qmin, and the maximum and minimum values ​​are determined based on the reactive power adjustment range of the FVR device.

[0175] S44. The first forward push process, the initial iteration value is the initial node voltage of phase A in PV mode at the grid connection point, which is V. set_low ∠0°, phase B is V set_low ∠-120°, C phase is V set_low ∠120°, active power is The reactive power is 0; the initial values ​​of the phase voltages of other nodes A, B, and C are 0.22∠0°, 0.22∠-120°, and 0.22∠120°, respectively; at this time, the PV node is calculated by superimposing the forward current to the previous stage.

[0176] S45. In the first reverse calculation process, the voltage at the transformer substation outlet and the current from the first forward calculation are used to recalculate the voltage at each node, as detailed below.

[0177] The voltage at the PV node of the slave parallel connection point is Voltage difference is

[0178] Based on the resistance R and reactance X of the branch where the slave parallel connection point is located, calculate the set voltage V of the FVR device. set_low The required reactive power support is calculated as follows:

[0179]

[0180] Reactive power required here Determine ΔQ t Does it satisfy the condition between Qmin and Qmax? Where, Indicates reactive power. This represents the reactive power of the slave parallel node after the back-substitution. This represents the active power of the slave parallel node after the back-substitution.

[0181] When ΔQ t >0, and ΔQ t ≤Qmax or ΔQ t <0, and ΔQ t When Qmin is ≥,

[0182] In the second iteration, the PV node parameters were adjusted to have the active power as follows: Reactive power adjusted to In subsequent iterations, the voltage V at the PV node set_low The iterations remain unchanged, as long as the voltage difference between the two iterations at other nodes satisfies |V k -V k-1 If | < 0.001, then the power flow is considered to be converging;

[0183] In the formula, V k V represents the voltage value at the Kth iteration. k-1 This represents the voltage value in the (K-1)th iteration, i.e., the previous value;

[0184] When the reactive power support margin cannot meet the reactive power support threshold required by the grid voltage, the PV node needs to be converted into a PQ node, that is,

[0185] When ΔQ t >0, and ΔQ t When the value is greater than Qmax, the reactive power is adjusted to Qmax.

[0186] When ΔQ t <0, and ΔQt When Q is less than or equal to Qmin, the reactive power is adjusted to Qmin;

[0187] At the second iteration, the parameters of the PV node are adjusted such that the active power is The reactive power is adjusted to Qmax or Qmin; in subsequent iterations, the PV node is processed in the conventional PQ node mode, and the voltage differences between the two consecutive times at the node both satisfy |V k - V k-1 | < 0.001, then the power flow is determined to have converged;

[0188] S46. Calculate the two-stage power flow. The calculation range is between the node connected to the slave inverter and the backend power supply users. The voltage of the node connected to the slave inverter The device sets the voltage V set_low , and the node connected to the slave inverter is used as the new power source point. At this time, the set voltage is V set_low , and the backward-forward sweep method is used again to calculate the lower-stage power flow. The voltage differences between the two consecutive times at each node both satisfy |V k - V k-1 | < 0.001, then the power flow is determined to have converged.

[0189] S47. When the photovoltaic power generation is abundant, the voltage at the slave machine end V 从 > the voltage at the master machine end V 主 , the power flow is reversed and flows from the slave machine end to the master machine end. The photovoltaic power generation causes the voltage at the slave machine end to increase.

[0190] The FVR device switches from the voltage boost mode to the power reverse mode, and conveys the remaining photovoltaic power at the slave machine end through the internal DC bus to the master machine end and finally returns it to the superior power grid;

[0191]

[0192] In the formula, represents the grid-connected power of the photovoltaic PV node at time t, represents the load power at time t, represents the input power of the FVR device at time t, I dc represents the current flowing through the DC wire, P Fvr_out represents the DC output power, η represents the conversion efficiency of the FVR device, U dc represents the DC voltage;

[0193] When and the voltages of the master and slave machines satisfy the power flow is reversed and the buck mode is started. At this time, the slave machine node is the injected power The DC output power is P Fvr_out = S fvr_out .

[0194] S5. Evaluate the steady-state indicators of the distribution transformer area by considering the DC and AC losses after the integrated FVR devices are connected in parallel.

[0195] Steady-state performance improvement indicators after FVR device connection:

[0196] (1) Overall loss reduction rate of the transformer area

[0197] ΔδTqLoss=δTqLoss fvr -δTqLoss default

[0198] Where ΔδTqLoss is the overall loss reduction rate of the transformer area; δTqLoss default The initial state of the overall line loss rate of the transformer area; δTqLoss fvr The overall line loss rate after the FVR device is connected to the distribution area.

[0199] (2) Reduction rate of transformer area loss

[0200]

[0201] Among them, δFLoss is the reduction rate of transformer area loss, which mainly analyzes the reduction of total loss before and after FVR access within 24 hours. The initial state of the transformer area at time t represents the total power loss. Let t be the total power loss after the FVR is connected to the distribution area.

[0202] (3) User voltage boost rate

[0203]

[0204] ΔδV user =δV fvr_user -δV default_user

[0205] In the formula, ΔδV user For the improvement rate of user voltage qualification rate; δV default_user This represents the percentage of users in the initial state of the distribution area who meet the operating voltage requirements; δV fvr_user The percentage of users meeting the operating voltage requirements after FVR is connected to the distribution area is analyzed.

[0206] (4) Voltage drop for key users

[0207]

[0208] This aligns with the definition of user voltage qualification rate, focusing on the voltage drop of key users after FVR connection. Specifically, For voltage drop of key users (such as end users); The voltage at time t for key end users.

[0209] This invention also provides a steady-state impact analysis system for a flexible voltage regulator access area based on graphical simulation, comprising:

[0210] The basic digital model management module is used to maintain the basic model of the transformer substation, such as conductor parameters and types, topology association information, user power / electricity information; and to maintain the technical parameters of the flexible DC voltage regulator.

[0211] The automatic mapping module generates planar topological graphics based on the maintained topology using digital twin technology;

[0212] The calculation engine module incorporates the steady-state AC / DC measurement method of this invention, which is used to perform power flow calculations based on network topology data and device parameter data.

[0213] The graphical analysis module allows for the graphical setup of the FVR master and slave connection locations. It supports interactive input of information such as the connection location and capacity parameters of the flexible voltage regulator, automatically calculates the DC line length between the master and slave, and can automatically simulate the steady-state operating conditions such as voltage distribution and power flow in the background area where the device is connected. It also displays the steady-state impact results in an intuitive graphical way, such as voltage curves and power dynamic flow diagrams, which helps technicians quickly understand the effect of the device on the steady-state operation of the distribution area and compare the changes in key steady-state indicators before and after the installation of the FVR.

[0214] This system, by combining the different access locations of flexible integrated voltage regulators, provides automatic analysis of the steady-state impact on distribution areas, efficiently assisting in equipment selection and voltage mitigation. Based on the different nodes of the distribution area where the flexible integrated voltage regulator is connected, such as the distribution area's incoming line, load concentration points, and voltage-weak points, it can generate analysis reports including the magnitude of voltage improvement, changes in equipment load rate, and the effect of network loss optimization, providing accurate and efficient decision support for equipment selection and voltage mitigation scheme formulation.

Claims

1. An engineering calculation method for adapting the steady-state influence of a flexible voltage regulating device on a transformer area, characterized in that: The method comprises the following steps, S1, obtaining data information of the distribution transformer area and related equipment; S2, constructing a directed line segment topology model, using the forward-back substitution method to measure the initial power flow index of the distribution transformer area, and analyzing the voltage conditions of all nodes at different time points, including the master and slave access nodes; S3, measuring the DC loss after the FVR device is connected in parallel, including converter loss and DC conductor loss; S4, constructing a DC influence boundary, and using a two-section power flow measurement method to measure the AC loss based on the boundary condition; S5, comprehensively evaluating the steady-state index of the distribution transformer area by combining the DC loss and AC loss after the FVR device is connected in parallel.

2. The method according to claim 1, wherein the method is characterized in that: The specific process of analyzing the voltage condition in step S2 comprises, S21, using the PV mode full-phase power flow method to measure the initial voltage of each node, input active / reactive power condition; S22, using the initial power flow index measurement result to construct a node voltage matrix at different time points.

3. The method according to claim 2, characterized in that: The specific process of the full-phase power flow method in step S21 comprises, S211, using the end metering box branch current to be superimposed to the outlet of the transformer area, calculating the current of each branch, and the expression is as follows, wherein, represents the certain phase current of the i-th node to the s-th node branch, and phase represents A phase, B phase, and C phase; represents the certain phase current injected by the power grid into the s-th node; n represents the number of all lower-layer branch bars directly connected to the node s; and m represents the number of all lower-layer branches connected to the node s; represents the m-th branch current directly connected to the s-th node. S212, using the A, B, C phase currents of each branch to calculate the N phase current, and the expression is as follows, wherein represents the N-phase current of the branch from the i-th node to the s-th node, represents the A-phase current of the branch from the i-th node to the s-th node, represents the B-phase current of the branch from the i-th node to the s-th node, represents the C-phase current of the branch from the i-th node to the s-th node; S213, using the outlet side voltage of the transformer area and the branch current to measure the voltage of each node, and the expression is as follows, In the formula, Vsi represents the voltage of a certain phase of the s-th node; Vsi represents the voltage of a certain phase of the i-th node; Zsi represents the branch impedance from the i-th node to the s-th node, and the A / B / C phase impedances are consistent; the initial voltage of each node except the first node is set to U A0 = 0.22 ∠0 0 , U B0 = 0.22 ∠-120 0 , U C0 = 0.22 ∠120 0 ; In the formula, Uik represents the kth iteration calculation of the node voltage of the ith node; i (k-1) Uik-1 represents the k-1th iteration calculation of the node voltage of the ith node; ε is the allowable error.

4. The method according to claim 1, wherein the method is characterized in that: The specific process of measuring the DC loss in step S3 comprises, S31, according to the voltage regulation parameter set by the FVR device, measure the DC power flow of the FVR device parallel line, the host end voltage V 主 > the slave end voltage V 从 , as follows, DCLoss = loss Fvr + loss DCLine where DCLoss represents the DC loss, Loss Fvr represents the FVR device total loss, loss DCLine represents the DC conductor loss; In the formula, loss Fvr represents the comprehensive loss of the FVR device, η represents the conversion efficiency of the FVR device, S Fvr represents the capacity of the FVR device, sf out represents the standby loss of the FVR device, m represents the action frequency of starting the voltage regulation work of the FVR device, and t represents the current time. wherein, loss DCLine represents the DC wire loss, Sign represents the identification of whether the FVR device is in the voltage regulation state, R dc represents the DC wire impedance, Long dc is the DC wire length, P Fvr_out is the output power, I dc represents the current flowing through the DC wire, m represents the action frequency of the FVR device starting the voltage regulation work, and t represents the current time. R dc = 2 * Long dc R dc.base where R dc represents the DC wire impedance, Long dc is the DC wire length, R dc.base is the DC unit resistance; where I dc represents the current flowing through the DC conductor, U dc represents the DC voltage, P Fvr_out is the output power, generally equal to S Fvr ; wherein Sign represents an indication of whether the FVR device is in voltage regulating state, V out V is the voltage at the node to which the inverter slave is connected set_low V is the set voltage for the FVR device, below which the FVR device will initiate voltage regulation S32, when the slave end voltage V 从 the host end voltage V 主 , the rectifier and inverter function mode conversion, correction device start identification, inverter slave node voltage V out ≥ V set_high , Sign = 1, the flow reversal; V set_high represent the highest value of the FVR device set voltage threshold.

5. The method according to claim 1, wherein the method is characterized in that: The two-section power flow measurement method in step S4 specifically comprises, S41, a section of the tidal current measurement, inverter from the node voltage Device set voltage V set_low , the measurement range is between the low voltage side outlet and the inverter slave node connected to the wire and the user, the slave AC side output current is wherein U0 represents a rated three-phase AC line voltage of 380 volts; I Fvr.out represents the AC side output current of the FVR device; S Fvr represents the capacity of the FVR device; S42, according to the initial flow index inverter slave node current The size of the relationship between the slave side of the alternating current output current I Fvr.out The size of the relationship between the slave side of the alternating current output current I The size of the relationship between the slave side of the alternating current output current I When the original AC loss remains unchanged, the residual current and residual power are calculated, wherein, is the residual current, is the slave-side initial current, I Fvr.out is the slave-side AC-side output current, is the residual power, V set_low is the voltage value set for the FVR device; S43, according to the FVR device setting, considering the voltage reactive power regulation limit and the influence of the PV mode on the power flow, and the specific process is as follows, The reactive power regulation range of the FVR device is, wherein Q Fvr represents the reactive regulation range of the FVR device, S Fvr represents the capacity of the FVR device, Cos ∈ [-0.9, 0.9], The reactive power adjustment constraint is ≤Qmax, ≥Qmin, and the maximum and minimum values are determined according to the reactive power regulation range of the FVR device; S44, the first time, the initial value of the iteration is the initial node voltage of the grid-connected point PV mode A phase V set_low ∠0°, B phase V set_low ∠-120°, C phase V set_low ∠120°, the active power is The reactive power is 0; the initial values of the A, B and C phase voltages of other nodes are 0.22∠0°, 0.22∠-120° and 0.22∠120°; at this time, the PV node is superimposed with a forward current to the previous level for forward calculation; S45, the first back substitution process, using the measured voltage of the outlet of the transformer area and the current of the first forward calculation to back substitute and recalculate the voltage of each node, and the specific process is as follows, The voltage difference is The voltage difference is According to the resistance R and reactance X of the branch where the slave machine parallel point is located, the required reactive support for maintaining the set voltage V of the FVR device is calculated as follows: set_low reactance X of the branch where the slave machine parallel point is located, the required reactive support for maintaining the set voltage V of the FVR device is calculated as follows: The required reactive support here Judging ΔQ t whether it is between Qmin and Qmax; where, Q represents the reactive power, Q represents the reactive power of the slave parallel node after substitution, Q represents the active power of the slave parallel node after substitution, When AQ t > 0, and AQ t ≤ Qmax or AQ t < 0, and AQ t ≥ Qmin, At the second iteration, the PV node parameter is adjusted to, and the active power is The reactive power is adjusted to In the subsequent iterations, the voltage V set_low The front and back iterations remain unchanged, as long as the voltage difference of other nodes between the front and back two times meets |V k -V k-1 |<0.001, it is determined that the power flow converges; wherein V k represents the voltage value of the Kth iteration, V k-1 represents the voltage value of the K-1th iteration; When the reactive power support margin cannot meet the threshold value between the required reactive power support of the power grid voltage, the PV node needs to be converted into a PQ node, that is, When ΔQ t > 0, and ΔQ t > Qmax, the reactive adjustment is Qmax; When ΔQ t <0, and ΔQ t Qmin; when Qmin At the second iteration, the PV node parameter is adjusted to, the active power is The reactive power is adjusted to Qmax or Qmin; in the subsequent iterations, the PV node is processed in the conventional PQ node mode, and the voltage difference before and after the node satisfies |V k -V k-1 | < 0.001, it is determined that the power flow converges; S46, two-stage power flow measurement, the measurement range is the inverter slave node and the back-end power supply users, inverter slave node voltage Device set voltage V set_low , the slave inverter node as a new power point, at this time the voltage is V set_low , reusing the forward substitution method to calculate the next section of the power flow, the voltage difference between the two times of each node meets |V k -V k-1 | <0.001, then determine the power flow convergence. S47, when photovoltaic power is large, from the slave end voltage V 从 > host end voltage V 主 , the flow of power is reversed, from the slave end to the host end, photovoltaic power causes the slave end voltage to rise, The FVR device switches from the voltage lifting mode to the power reverse sending mode, and the remaining power of the slave end photovoltaic device is sent to the master end through the internal DC bus, and finally returned to the upper power grid; wherein represents the grid power at the photovoltaic PV node at time t, represents the load power at time t, represents the input power of the FVR device at time t, I dc represents the current flowing through the DC conductor, P Fvr_out represents the DC output power, η represents the conversion efficiency of the FVR device, U dc represents the DC voltage; When And master-slave voltage meets Tidal flow reverses, starting the step-down mode, when the slave node is injected power DC output power is P Fvr_out = S Fvr_out .

6. The method according to claim 1, wherein the method is characterized in that: The data information of the distribution transformer area and related equipment in step S1 comprises cable topology information, meter box / low-voltage user information, photovoltaic equipment information, time sequence level acquisition information, and flexible voltage regulation device information.

7. The method according to claim 6, wherein the method is characterized in that: The cable topology information comprises overhead line / cable name, connection relationship of topology node, cable length, overhead line or cable type, the meter box / low-voltage user information comprises meter box / user name, user belonging meter box, low-voltage user phase information, the photovoltaic equipment information comprises equipment name, capacity, access position, PV / PQ node setting, the time sequence level acquisition information comprises distribution transformer area outlet A / B / C three-phase current and three-phase voltage, photovoltaic output power, low-voltage user active power, and the flexible voltage regulation device information comprises device model, capacity, DC output voltage, rated AC output voltage, voltage regulation range, device loss rate, standby loss.

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