Rural power distribution station distinguishing phase voltage control method based on inverter correlation degree

Abstract

The invention particularly relates to a rural power distribution station differentiated phase voltage control method based on inverter correlation degree, which comprises the following steps of: performing three-phase unbalanced load flow calculation, and analyzing a voltage out-of-limit condition of a power distribution station area; calculating a total active / reactive power-voltage correlation degree proportion index of the photovoltaic inverters, selecting the photovoltaic inverters participating in voltage regulation on the basis of the total active / reactive power-voltage correlation degree proportion index, and optimizing a regulation sequence; carrying out reactive power-voltage regulation by adopting a reactive power-split phase voltage control strategy until the photovoltaic inverters with high proportions of total reactive power-voltage correlation do not have the reactive power regulation capability or all node voltages do not exceed the limit any more; performing active-voltage regulation by adopting an active-split-phase voltage control strategy until the photovoltaic inverters with high proportion of total active-voltage correlation cannot continue to reduce the active output or all node voltages are no longer out of limit; and after reactive power and active power regulation, if a voltage out-of-limit condition still exists in the power distribution area, regulating the gear of the on-load voltage regulating transformer until all nodes do not exceed the limit.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology, specifically relating to a phase voltage control method for rural distribution stations based on inverter correlation. Background Technology

[0002] The global energy structure is rapidly transitioning towards cleaner and lower-carbon energy sources, and distributed photovoltaic (PV) systems, as a crucial component of renewable energy, are facing unprecedented development opportunities. Rural residential PV systems, connected to low-voltage distribution substations at 380V, offer advantages such as proximity to users and low transmission losses, making them a key development scenario for distributed PV and leading to their rapid growth.

[0003] Rural distribution substations in my country typically employ a mixed single-phase and three-phase power supply mode, with single-phase loads being the primary component. Uneven temporal and spatial load distribution leads to significant three-phase imbalance. Large-scale integration of distributed photovoltaic (PV) systems into these substations may exacerbate this imbalance, as the single-phase PV units may further contribute to it. Furthermore, the integration of PV systems can cause voltage increases at and near the PV connection point, potentially leading to voltage limits being exceeded. Therefore, high penetration rates of PV systems in rural distribution substations result in deteriorated power quality, primarily manifested in three-phase imbalance and voltage limit violations.

[0004] Household photovoltaic inverters are an important regulation resource in new power systems. They have flexible and fast three-phase independent active / reactive decoupling regulation capabilities. If, under the premise of considering voltage sensitivity, a photovoltaic inverter with strong regulation capability is selected for phase-by-phase voltage control, the problem of voltage exceeding limits in rural distribution substations can be solved while alleviating three-phase voltage imbalance.

[0005] Reference 1, "Low Voltage Management in Distribution Substations Using On-Load Capacity and Voltage Regulating Transformers and MPC Technology" (Power Construction, Vol. 44, No. 10, pp. 117-126), considers both day-ahead dispatch and intraday correction, proposing a model predictive control (MPC)-based strategy for optimizing low voltage management and economic operation in distribution substations, but primarily through adjusting on-load capacity and voltage regulating transformers. Reference 2, "Three-Phase Imbalance Management Strategy for Distribution Network Substations Based on Dynamic Region Division" (Power Automation Equipment, Vol. 45, No. 8, pp. 208-216), uses an improved Louvain community detection algorithm to achieve efficient partitioning, and proposes a two-layer optimization model to quickly solve the voltage optimization problem. The upper layer uses a genetic algorithm based on a cloud model to avoid local optima, while the lower layer constructs a second-order cone programming (SOCP) optimal power flow model to quickly solve the voltage optimization problem. Reference 3, "Second-Order Cone Optimization Modeling and Simulation of Three-Phase Unbalanced Active Distribution Network" (Journal of System Simulation, published online), establishes a dynamic optimal power flow model for a three-phase unbalanced active distribution network based on mixed-integer second-order cone programming, aiming to minimize active power losses in the distribution network by comprehensively applying active management and demand response strategies, thus achieving coordinated and optimized active-reactive power scheduling. Existing literature proposes voltage over-limit control methods for low-voltage distribution transformer areas, but these methods often rely on reactive power equipment for regulation and fail to consider the characteristics of three-phase imbalance in low-voltage distribution transformer areas, resulting in high costs and poor transformer area profitability. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a phase-by-phase voltage control method for rural distribution stations based on inverter correlation. This method selects a photovoltaic inverter with stronger regulation capability based on the static ratio of total active / reactive power to voltage correlation for phase-by-phase voltage control. This allows for more accurate calculation of the required regulation amount for each phase's active / reactive power, reduces the number of regulation cycles, and more quickly controls the voltage within the specified range, thus efficiently completing the regulation task.

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

[0008] A method for phase voltage control of rural distribution stations based on inverter correlation includes the following steps:

[0009] S1: Perform three-phase unbalanced power flow calculations and analyze voltage over-limit situations in distribution substations;

[0010] S2: Calculate the total active / reactive power-voltage correlation ratio of the photovoltaic inverter, and select the photovoltaic inverters to participate in voltage regulation based on this, and optimize the regulation order.

[0011] S3: Use a reactive-phase voltage control strategy to regulate reactive-voltage until photovoltaic inverters with a high proportion of total reactive-voltage correlation no longer have reactive regulation capabilities or all node voltages no longer exceed limits.

[0012] S4: Use the active-phase voltage control strategy to regulate active-voltage until photovoltaic inverters with a high proportion of total active-voltage correlation can no longer reduce active power output or all node voltages no longer exceed the limit.

[0013] S5: After reactive and active power regulation, if the voltage in the distribution area still exceeds the limit, adjust the on-load tap changer (OLTC) setting until all nodes are within the limit.

[0014] Furthermore, as a preferred embodiment of the present invention, step S1 includes the following steps:

[0015] S1-1. For a low-voltage distribution substation with N nodes (excluding the slack node), the node admittance matrix is ​​established as shown below using Kirchhoff's current law:

[0016] ;

[0017] In the formula: matrix Y is the nodal admittance matrix; , Let the voltage and injected current be at node i;

[0018] S1-2. Utilize the PQ decomposition method to perform power flow calculations on N nodes of the distribution system, excluding the slack node, i.e.:

[0019] ;

[0020] In the formula: ΔP and ΔQ are the changes in active and reactive power at the node; Δθ and ΔU are the changes in phase angle and magnitude of the node voltage. , , , represents the elements in the Jacobian matrix;

[0021] S1-3. Set the upper and lower limits of the voltage of each node to 1.07pu and 0.93pu respectively. If the node voltage is lower than 0.93pu, the node exceeds the lower limit. If the node voltage is higher than 1.07pu, the node exceeds the upper limit.

[0022] Furthermore, as a preferred embodiment of the present invention, step S2 includes the following steps:

[0023] S2-1. Perform inverse operation on the Jacobian matrix to obtain the sensitivity matrix;

[0024] ;

[0025] In the formula: It is an Nth-order active-voltage sensitivity matrix. Let be an N-order reactive-voltage sensitivity matrix, representing the change in node voltage amplitude when active and reactive power injections change by a unit; It is an Nth-order active-phase sensitivity matrix. The four sensitivity matrices are of order N, representing the changes in node voltage phase angle when active and reactive power injections change by a unit rate. After large-scale distributed photovoltaic (PV) grid integration into the distribution system, node voltage exceeding limits is a major factor restricting the absorption of distributed PV power. Therefore, among the four sensitivity matrices given, and Play a leading role;

[0026] S2-2. Based on the reactive power-voltage sensitivity matrix and the active power-voltage sensitivity matrix, calculate the active power / reactive power-voltage correlation degree, as shown below:

[0027] ;

[0028] ;

[0029] In the formula: This indicates the active power-voltage correlation between nodes i and j. The larger the value, the greater the impact of the active power change at any node on the voltage amplitude at the other node. This indicates the reactive power-voltage correlation between nodes i and j. The larger the value, the greater the impact of reactive power changes at any node on the voltage amplitude at the other node. Represents the active-voltage sensitivity matrix The element in the i-th row and j-th column; Represents the reactive power-voltage sensitivity matrix The element in the i-th row and j-th column;

[0030] S2-3. Calculate the active / reactive power-voltage correlation degree for each phase, as shown below:

[0031] ;

[0032] ;

[0033] In the formula: O represents the phase sequence, which can refer to phases A, B, or C respectively; This represents the active power-voltage correlation degree between corresponding phases at nodes i and j; This represents the reactive power-voltage correlation degree between corresponding phases of nodes i and j; Represents the active-voltage sensitivity matrix of the corresponding phase. The element in the i-th row and j-th column; Represents the corresponding phase reactive-voltage sensitivity matrix The element in the i-th row and j-th column;

[0034] S2-4. Calculate the total active / reactive power-voltage correlation degree for each photovoltaic inverter. Assuming that node k is connected to a photovoltaic inverter, its total active / reactive power-voltage correlation degree can be expressed by the following formula:

[0035] ;

[0036] ;

[0037] In the formula: k represents a node connected to a photovoltaic inverter; g represents a node not connected to a photovoltaic inverter; This refers to the set of nodes connected to photovoltaic inverters in a distribution network. This refers to the set of nodes that are not connected to a photovoltaic inverter. , These represent the active-voltage correlation and reactive-voltage correlation of phase O (O can refer to phase A, B or C) between nodes k and g, respectively. , These represent the total active voltage correlation and the total reactive voltage correlation of the photovoltaic inverter connected to node k, respectively.

[0038] S2-5. Calculate the total active / reactive power-voltage correlation ratio of each photovoltaic inverter in the distribution substation area to comprehensively measure the voltage regulation capability of each photovoltaic inverter, as shown in the following formula:

[0039]

[0040]

[0041] In the formula: and The total active-voltage correlation ratio and the total reactive-voltage correlation ratio of the photovoltaic inverter connected to node k are the two values. or The larger the value, the better the voltage quality in the distribution area can be improved by adjusting the active or reactive power output of the inverter.

[0042] Furthermore, as a preferred embodiment of the present invention, step S3 includes the following steps:

[0043] S3-1. Based on the calculation results of step S1-3, obtain the node i0 with the most severe voltage over-limit in reactive phase O (O represents phase A, B or C).

[0044] S3-2. Sort each photovoltaic inverter according to the proportion of total reactive power-voltage correlation from large to small, select photovoltaic inverters with a proportion higher than 1 / M to participate in reactive power-voltage regulation, and give priority to regulating inverters with a large proportion of total reactive power-voltage correlation. M is the total number of photovoltaic inverter nodes connected.

[0045] S3-3. Determine whether the photovoltaic inverter intended to participate in reactive power-voltage regulation has zero-phase reactive power-voltage regulation capability based on the following formula:

[0046] ;

[0047] In the formula: n represents the node connected to the photovoltaic inverter; This indicates the injected reactive power of the photovoltaic inverter connected to node n in phase O. Indicates the reactive power adjustment step size of phase O, when At that time, the maximum reactive power regulation value of the photovoltaic inverter can be calculated. ; This represents the injected active power at node n connected to phase O of the photovoltaic inverter; This indicates the maximum capacity of the photovoltaic inverter connected to node m in phase O;

[0048] S3-4. If the photovoltaic inverter to be involved in reactive power-voltage regulation has reactive power regulation capability, then... The step size is used to adjust the reactive power output of the O-phase of the photovoltaic inverter. The specific adjustment method is as follows:

[0049] ;

[0050] In the formula: n is the access node of the photovoltaic inverter with the largest reactive power regulation capability in the reactive power O phase. This represents the reactive power output of the photovoltaic inverter connected to node n after phase O regulation. This indicates the reactive power output before adjustment;

[0051] S3-5. Determine whether the over-limit issue of phase O voltage at node i0 has been resolved. If not, continue with... The step size is used to adjust the reactive power output of the current photovoltaic inverter. If the current photovoltaic inverter no longer has reactive power regulation capability, other photovoltaic inverters with reactive power regulation capability are selected sequentially according to the total reactive power-voltage correlation ratio for regulation. If all photovoltaic inverters with a total reactive power-voltage correlation ratio higher than 1 / M no longer have reactive power regulation capability, then step S4 is performed to carry out active power-phase voltage control.

[0052] Furthermore, as a preferred embodiment of the present invention, step S4 includes the following steps:

[0053] S4-1. Based on the calculation results and reactive power regulation results of step S1-3, obtain the node i1 with the most severe voltage over-limit in the active phase O.

[0054] S4-2. Sort all photovoltaic inverters according to their proportion of total active power-voltage correlation from largest to smallest, select photovoltaic inverters with a proportion higher than 1 / M to participate in active power-voltage regulation, and prioritize regulating inverters with a large proportion of total active power-voltage correlation.

[0055] S4-3. Determine whether the photovoltaic inverter to be involved in active power-voltage regulation has 0-phase active power-voltage regulation capability based on the formula. The specific determination method is as follows:

[0056] ;

[0057] In the formula: r represents the node connected to the photovoltaic inverter; This indicates the injected active power at node r connected to phase O of the photovoltaic inverter; This indicates the active power adjustment step size for phase O, which can be preset. This indicates the injected reactive power at node r connected to phase O of the photovoltaic inverter; This represents the maximum capacity of the photovoltaic inverter O phase connected to node r. If the photovoltaic inverter O phase connected to node r satisfies the constraints given by the formula, it means that the inverter has active power regulation capability.

[0058] S4-4. If the photovoltaic inverter to be involved in active power-voltage regulation has active power regulation capability, then... The active power output of the O phase of the photovoltaic inverter is adjusted in steps, as shown below:

[0059] ;

[0060] In the formula: r represents the access node of the photovoltaic inverter with the largest active power regulation capability in the active phase O; This represents the active power output of the photovoltaic inverter connected to node r after phase O-phase adjustment. This indicates the active power output before adjustment;

[0061] S4-5. Determine whether the voltage over-limit problem of node i1 in phase O has been resolved. If not, continue with... The active power output of the current photovoltaic inverter is adjusted according to the step size. If the current photovoltaic inverter no longer has active power regulation capability, other photovoltaic inverters with active power regulation capability are selected in turn according to the proportion of total active power-voltage correlation until the voltage limit of node i1 is resolved. If all photovoltaic inverters with a total active power-voltage correlation ratio higher than 1 / M no longer have active power regulation capability, then step S5 is performed.

[0062] The present invention provides a phase voltage control method for rural distribution stations based on inverter correlation. Compared with existing technologies, the above technical solution has the following technical advantages:

[0063] (1) This invention calculates sensitivity in an offline state and establishes an index, which is used to select a photovoltaic inverter with a higher total active / reactive power-voltage correlation for three-phase voltage control. From the perspective of correlation, the higher the three-phase correlation of the photovoltaic inverter, the less active / reactive power regulation is required, and the better the voltage regulation effect. At the same time, it avoids occupying a lot of computing resources and reduces redundant steps.

[0064] (2) Individual control of the three phases of the photovoltaic inverter. When adjusting the three-phase balanced voltage regulation, all photovoltaic inverters need to be traversed, and the adjustment will only stop after the node with the most severe voltage over-limit is improved. It is easy to have situations where the voltage values ​​of other phases have returned to normal but voltage regulation is still being performed. Compared with the three-phase balanced voltage regulation, the phase-by-phase voltage regulation can more accurately calculate the required adjustment amount of active / reactive power of each phase, reduce the number of adjustments, alleviate the problem of three-phase imbalance in the distribution area, and efficiently complete the adjustment task. Attached Figure Description

[0065] Figure 1 This is a flowchart of a method according to an embodiment of the present invention;

[0066] Figure 2 This is a node voltage diagram of the power distribution system in an embodiment of the present invention;

[0067] Figure 3 This is a voltage diagram of each node in the power distribution system after reactive power-phase voltage control in an embodiment of the present invention;

[0068] Figure 4 This is a voltage diagram of each node in the power distribution system after active phase voltage control in an embodiment of the present invention. Detailed Implementation

[0069] The present invention will be further explained in detail below with reference to the accompanying drawings, so that those skilled in the art can better understand and implement the present invention. However, the following examples are only used to explain the present invention and are not intended to limit the present invention.

[0070] like Figure 1 As shown, a method for phase voltage control of rural distribution stations based on inverter correlation includes the following steps:

[0071] S1: Perform three-phase unbalanced power flow calculations and analyze voltage over-limit situations in distribution substations;

[0072] S1-1. For a low-voltage distribution substation with N nodes (excluding the slack node), the node admittance matrix is ​​established as shown below using Kirchhoff's current law:

[0073]

[0074] In the formula: matrix Y is the nodal admittance matrix; , Here are the voltage and injected current at node i. N is not explained.

[0075] In this embodiment, N is 36.

[0076] S1-2. Utilize the PQ decomposition method to perform power flow calculations on N nodes of the distribution system, excluding the slack node, i.e.:

[0077]

[0078] In the formula: ΔP and ΔQ are the changes in active and reactive power at the node; Δθ and ΔU are the changes in phase angle and magnitude of the node voltage. , , , are elements in the Jacobian matrix.

[0079] S1-3. Set the upper and lower limits of the voltage of each node to 1.07pu and 0.93pu respectively. If the node voltage is lower than 0.93pu, the node is above the lower limit. If the node voltage is higher than 1.07pu, the node is above the upper limit.

[0080] S2: Calculate the total active / reactive power-voltage correlation ratio of the photovoltaic inverter, and select the photovoltaic inverters to participate in voltage regulation based on this, and optimize the regulation order.

[0081] S2-1. Perform inverse operation on the Jacobian matrix to obtain the sensitivity matrix;

[0082]

[0083] In the formula: It is an Nth-order active-voltage sensitivity matrix. Let be an N-order reactive-voltage sensitivity matrix, representing the change in node voltage amplitude when active and reactive power injections change by a unit; It is an Nth-order active-phase sensitivity matrix. These are N-order reactive power-phase angle sensitivity matrices, representing the change in node voltage phase angle when there is a unit change in injected active and reactive power, respectively. After large-scale distributed photovoltaic (PV) grid integration into the distribution system, node voltage exceeding limits is the main factor restricting the absorption of distributed PV power. Therefore, among the four sensitivity matrices given, and It plays a leading role.

[0084] S2-2. Based on the reactive power-voltage sensitivity matrix and the active power-voltage sensitivity matrix, calculate the active power / reactive power-voltage correlation degree, as shown below:

[0085]

[0086]

[0087] In the formula: This indicates the active power-voltage correlation between nodes i and j. The larger the value, the greater the impact of the active power change at any node on the voltage amplitude at the other node. This indicates the reactive power-voltage correlation between nodes i and j. The larger the value, the greater the impact of reactive power changes at any node on the voltage amplitude at the other node. Represents the active-voltage sensitivity matrix The element in the i-th row and j-th column; Represents the reactive power-voltage sensitivity matrix The element in the i-th row and j-th column.

[0088] S2-3. Calculate the active / reactive power-voltage correlation degree for each phase, as shown below:

[0089]

[0090]

[0091] In the formula: O represents the phase sequence, which can refer to phases A, B, or C respectively; This represents the active power-voltage correlation degree between corresponding phases at nodes i and j; This represents the reactive power-voltage correlation degree between corresponding phases of nodes i and j; Represents the active-voltage sensitivity matrix of the corresponding phase. The element in the i-th row and j-th column; Represents the corresponding phase reactive-voltage sensitivity matrix The element in the i-th row and j-th column.

[0092] S2-4. Calculate the total active / reactive power-voltage correlation degree for each photovoltaic inverter. For ease of expression, assume that node k is connected to a photovoltaic inverter, and its total active / reactive power-voltage correlation degree can be expressed by the following formula:

[0093]

[0094]

[0095] In the formula: k represents a node connected to a photovoltaic inverter; g represents a node not connected to a photovoltaic inverter; This refers to the set of nodes connected to photovoltaic inverters in a distribution network. This refers to the set of nodes that are not connected to a photovoltaic inverter. , These represent the active-voltage correlation and reactive-voltage correlation of phase O (O can refer to phase A, B or C) between nodes k and g, respectively. , These represent the total active voltage correlation and the total reactive voltage correlation of the photovoltaic inverter connected to node k, respectively.

[0096] S2-5. Calculate the total active / reactive power-voltage correlation ratio of each photovoltaic inverter in the distribution substation area to comprehensively measure the voltage regulation capability of each photovoltaic inverter, as shown in the following formula:

[0097]

[0098]

[0099] In the formula: and The total active-voltage correlation ratio and the total reactive-voltage correlation ratio of the photovoltaic inverter connected to node k are the two values. or The larger the value, the better the voltage quality in the distribution area can be improved by adjusting the active or reactive power output of the inverter.

[0100] S3: Use a reactive-phase voltage control strategy to regulate reactive-voltage until photovoltaic inverters with a high proportion of total reactive-voltage correlation no longer have reactive regulation capabilities or all node voltages no longer exceed limits.

[0101] S3-1. Based on the calculation results of step S1-3, obtain the node i0 with the most severe voltage over-limit in reactive phase O (O represents phase A, B or C);

[0102] S3-2. Sort each photovoltaic inverter according to the proportion of total reactive power-voltage correlation from large to small, select photovoltaic inverters with a proportion higher than 1 / M to participate in reactive power-voltage regulation, and give priority to regulating inverters with a large proportion of total reactive power-voltage correlation (M is the total number of photovoltaic inverter nodes connected).

[0103] In this embodiment, M is 17.

[0104] S3-3. Determine whether the photovoltaic inverter intended to participate in reactive power-voltage regulation has zero-phase reactive power-voltage regulation capability based on the following formula:

[0105]

[0106] In the formula: n represents the node connected to the photovoltaic inverter; This indicates the injected reactive power of the photovoltaic inverter connected to node n in phase O. Indicates the reactive power adjustment step size of phase O, when At that time, the maximum reactive power regulation value of the photovoltaic inverter can be calculated. ; This represents the injected active power at node n connected to phase O of the photovoltaic inverter; This indicates the maximum capacity of the photovoltaic inverter connected to node m in phase O.

[0107] S3-4. If the photovoltaic inverter to be involved in reactive power-voltage regulation has reactive power regulation capability, then... The step size is used to adjust the reactive power output of the O-phase of the photovoltaic inverter. The specific adjustment method is as follows:

[0108]

[0109] In the formula: n is the access node of the photovoltaic inverter with the largest reactive power regulation capability in the reactive power O phase. This represents the reactive power output of the photovoltaic inverter connected to node n after phase O regulation. This indicates the reactive power output before adjustment.

[0110] S3-5. Determine whether the over-limit issue of phase O voltage at node i0 has been resolved. If not, continue with... The step size is used to adjust the reactive power output of the current photovoltaic inverter. If the current photovoltaic inverter no longer has reactive power regulation capability, other photovoltaic inverters with reactive power regulation capability are selected sequentially according to the total reactive power-voltage correlation ratio for regulation. If all photovoltaic inverters with a total reactive power-voltage correlation ratio higher than 1 / M no longer have reactive power regulation capability, then step S4 is performed to carry out active power-phase voltage control.

[0111] In the embodiments, Take 0.1Kvar.

[0112] S4: Use the active-phase voltage control strategy to regulate active-voltage until photovoltaic inverters with a high proportion of total active-voltage correlation can no longer reduce active power output or all node voltages no longer exceed the limit.

[0113] S4-1. Based on the calculation results and reactive power regulation results of step S1-3, obtain the node i1 with the most severe voltage over-limit in the active phase O.

[0114] S4-2. Sort all photovoltaic inverters according to their proportion of total active power-voltage correlation from largest to smallest, select photovoltaic inverters with a proportion higher than 1 / M to participate in active power-voltage regulation, and prioritize regulating inverters with a large proportion of total active power-voltage correlation.

[0115] S4-3. Determine whether the photovoltaic inverter to be involved in active power-voltage regulation has 0-phase active power-voltage regulation capability based on the formula. The specific determination method is as follows:

[0116]

[0117] In the formula: r represents the node connected to the photovoltaic inverter; This indicates the injected active power at node r connected to phase O of the photovoltaic inverter; This indicates the active power adjustment step size for phase O, which can be preset. This indicates the injected reactive power at node r connected to phase O of the photovoltaic inverter; This represents the maximum capacity of the O phase of the photovoltaic inverter connected to node r. If the O phase of the photovoltaic inverter connected to node r satisfies the constraints given by the formula, it means that the inverter has active power regulation capability.

[0118] S4-4. If the photovoltaic inverter to be involved in active power-voltage regulation has active power regulation capability, then... The active power output of the O phase of the photovoltaic inverter is adjusted in steps, as shown below:

[0119]

[0120] In the formula: r represents the access node of the photovoltaic inverter with the largest active power regulation capability in the active phase O; This represents the active power output of the photovoltaic inverter connected to node r after phase O-phase adjustment. This indicates the active power output before adjustment.

[0121] S4-5. Determine whether the voltage over-limit problem of node i1 in phase O has been resolved. If not, continue with... The active power output of the current photovoltaic inverter is adjusted according to the step size. If the current photovoltaic inverter no longer has active power regulation capability, other photovoltaic inverters with active power regulation capability are selected in turn according to the proportion of total active power-voltage correlation until the voltage limit of node i1 is resolved. If all photovoltaic inverters with a total active power-voltage correlation ratio higher than 1 / M no longer have active power regulation capability, then step S5 is performed.

[0122] In the embodiments, Take 0.1kW.

[0123] S5: After adjusting the reactive and active power, if the voltage in the distribution area still exceeds the limit, adjust the OLTC setting until all nodes no longer exceed the limit.

[0124] To verify the effectiveness of the phase-by-phase voltage control strategy described in this invention, a simulation was constructed based on actual data from a rural distribution transformer area in Jiangsu Province. This distribution transformer area has 37 nodes, of which 17 nodes are connected to photovoltaic inverters. Figure 2The voltage data for each node in the distribution substation area before voltage regulation is shown. After reactive power regulation using the phase-by-phase voltage control strategy described in this invention, the voltage data for each node are as follows: Figure 3 As shown in the figure, reactive power regulation alone can solve the voltage over-limit problem of most nodes in phase A, but it is difficult to completely solve the voltage over-limit problem of phases B and C in nodes 11 to 19. Next, the phase-by-phase voltage control strategy described in this invention is applied for active power regulation, and the voltage data of each node are as follows: Figure 4 As shown in the figure, after active power regulation, the voltage at each node no longer exceeds the limit. In other words, the phase-by-phase voltage control strategy described in this invention effectively solves the voltage limit exceeding problem.

[0125] The specific implementation schemes described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific implementation schemes of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for phase voltage control of rural distribution stations based on inverter correlation, characterized in that, Includes the following steps: S1: Perform three-phase unbalanced power flow calculations and analyze voltage over-limit situations in distribution substations; S2: Calculate the total active / reactive power-voltage correlation ratio of the photovoltaic inverter, and select the photovoltaic inverters to participate in voltage regulation based on this, and optimize the regulation order. S3: Use a reactive-phase voltage control strategy to regulate reactive-voltage until photovoltaic inverters with a high proportion of total reactive-voltage correlation no longer have reactive regulation capabilities or all node voltages no longer exceed limits. S4: Use the active-phase voltage control strategy to regulate active-voltage until photovoltaic inverters with a high proportion of total active-voltage correlation can no longer reduce active power output or all node voltages no longer exceed the limit. S5: After reactive and active power regulation, if the voltage in the distribution area still exceeds the limit, adjust the OLTC tap of the on-load tap changer until all nodes no longer exceed the limit.

2. The method for phase voltage control of rural distribution stations based on inverter correlation as described in claim 1, characterized in that, Step S1 includes the following steps: S1-1. For a low-voltage distribution substation with N nodes (excluding the slack node), the node admittance matrix is ​​established as shown below using Kirchhoff's current law: ； In the formula: matrix Y is the nodal admittance matrix; , Let the voltage and injected current be at node i; S1-2. Utilize the PQ decomposition method to perform power flow calculations on N nodes of the distribution system, excluding the slack node, i.e.: ； In the formula: ΔP and ΔQ are the changes in active and reactive power at the node; Δθ and ΔU are the changes in phase angle and magnitude of the node voltage. , , , represents the elements in the Jacobian matrix; S1-3. Set the upper and lower limits of the voltage of each node to 1.07pu and 0.93pu respectively. If the node voltage is lower than 0.93pu, the node exceeds the lower limit. If the node voltage is higher than 1.07pu, the node exceeds the upper limit.

3. The method for phase voltage control of rural distribution stations based on inverter correlation as described in claim 2, characterized in that, Step S2 includes the following steps: S2-1. Perform inverse operation on the Jacobian matrix to obtain the sensitivity matrix; ； In the formula: It is an Nth-order active-voltage sensitivity matrix. Let be an N-order reactive-voltage sensitivity matrix, representing the change in node voltage amplitude when active and reactive power injections change by a unit; It is an Nth-order active-phase sensitivity matrix. The four sensitivity matrices are of order N, representing the changes in node voltage phase angle when active and reactive power injections change by a unit rate. After large-scale distributed photovoltaic (PV) grid integration into the distribution system, node voltage exceeding limits is a major factor restricting the absorption of distributed PV power. Therefore, among the four sensitivity matrices given, and Play a leading role; S2-2. Based on the reactive power-voltage sensitivity matrix and the active power-voltage sensitivity matrix, calculate the active power / reactive power-voltage correlation degree, as shown below: ； ； In the formula: This indicates the active power-voltage correlation between nodes i and j. The larger the value, the greater the impact of the active power change at any node on the voltage amplitude at the other node. This indicates the reactive power-voltage correlation between nodes i and j. The larger the value, the greater the impact of reactive power changes at any node on the voltage amplitude at the other node. Represents the active-voltage sensitivity matrix The element in the i-th row and j-th column; Represents the reactive power-voltage sensitivity matrix The element in the i-th row and j-th column; S2-3. Calculate the active / reactive power-voltage correlation degree for each phase, as shown below: ； ； In the formula: O represents the phase sequence, which can refer to phases A, B, or C respectively; This represents the active power-voltage correlation degree between corresponding phases at nodes i and j; This represents the reactive power-voltage correlation degree between corresponding phases of nodes i and j; Represents the active-voltage sensitivity matrix of the corresponding phase. The element in the i-th row and j-th column; Represents the corresponding phase reactive-voltage sensitivity matrix The element in the i-th row and j-th column; S2-4. Calculate the total active / reactive power-voltage correlation degree for each photovoltaic inverter. Assuming that node k is connected to a photovoltaic inverter, its total active / reactive power-voltage correlation degree can be expressed by the following formula: ； ； In the formula: k represents a node connected to a photovoltaic inverter; g represents a node not connected to a photovoltaic inverter; This refers to the set of nodes connected to photovoltaic inverters in a distribution network. This refers to the set of nodes that are not connected to a photovoltaic inverter. , These represent phase O between nodes k and g, respectively, with O representing the active-voltage correlation and reactive-voltage correlation of phases A, B, or C. , These represent the total active voltage correlation and the total reactive voltage correlation of the photovoltaic inverter connected to node k, respectively. S2-5. Calculate the total active / reactive power-voltage correlation ratio of each photovoltaic inverter in the distribution substation area to comprehensively measure the voltage regulation capability of each photovoltaic inverter, as shown in the following formula: ； ； In the formula: and The total active-voltage correlation ratio and the total reactive-voltage correlation ratio of the photovoltaic inverter connected to node k are the two values. or The larger the value, the better the voltage quality in the distribution area can be improved by adjusting the active or reactive power output of the inverter.

4. The method for phase voltage control of rural distribution stations based on inverter correlation as described in claim 3, characterized in that, Step S3 includes the following steps: S3-1. Based on the calculation results of step S1-3, obtain the reactive phase O, where O represents the node i0 with the most severe voltage over-limit in phases A, B, or C. S3-2. Sort each photovoltaic inverter according to the proportion of total reactive power-voltage correlation from large to small, select photovoltaic inverters with a proportion higher than 1 / M to participate in reactive power-voltage regulation, and give priority to regulating inverters with a large proportion of total reactive power-voltage correlation. M is the total number of photovoltaic inverter nodes connected. S3-3. Determine whether the photovoltaic inverter intended to participate in reactive power-voltage regulation has zero-phase reactive power-voltage regulation capability based on the following formula: ； In the formula: n represents the node connected to the photovoltaic inverter; This indicates the injected reactive power of the photovoltaic inverter connected to node n in phase O. Indicates the reactive power adjustment step size of phase O, when At that time, the maximum reactive power regulation value of the photovoltaic inverter can be calculated. ; This represents the injected active power at node n connected to phase O of the photovoltaic inverter; This indicates the maximum capacity of the photovoltaic inverter connected to node m in phase O; S3-4. If the photovoltaic inverter to be involved in reactive power-voltage regulation has reactive power regulation capability, then... The step size is used to adjust the reactive power output of the O-phase of the photovoltaic inverter. The specific adjustment method is as follows: ； In the formula: n is the access node of the photovoltaic inverter with the largest reactive power regulation capability in the reactive power O phase. This represents the reactive power output of the photovoltaic inverter connected to node n after phase O regulation. This indicates the reactive power output before adjustment; S3-5. Determine whether the over-limit issue of phase O voltage at node i0 has been resolved. If not, continue with... The step size is used to adjust the reactive power output of the current photovoltaic inverter. If the current photovoltaic inverter no longer has reactive power regulation capability, other photovoltaic inverters with reactive power regulation capability are selected sequentially according to the total reactive power-voltage correlation ratio for regulation. If all photovoltaic inverters with a total reactive power-voltage correlation ratio higher than 1 / M no longer have reactive power regulation capability, then step S4 is performed to carry out active power-phase voltage control.

5. The method for phase voltage control of rural distribution stations based on inverter correlation as described in claim 4, characterized in that, Step S4 includes the following steps: S4-1. Based on the calculation results and reactive power regulation results of step S1-3, obtain the node i1 with the most severe voltage over-limit in the active phase O. S4-2. Sort all photovoltaic inverters according to their proportion of total active power-voltage correlation from largest to smallest, select photovoltaic inverters with a proportion higher than 1 / M to participate in active power-voltage regulation, and prioritize regulating inverters with a large proportion of total active power-voltage correlation. S4-3. Determine whether the photovoltaic inverter to be involved in active power-voltage regulation has 0-phase active power-voltage regulation capability based on the formula. The specific determination method is as follows: ； In the formula: r represents the node connected to the photovoltaic inverter; This indicates the injected active power at node r connected to phase O of the photovoltaic inverter; This indicates the active power adjustment step size for phase O, which can be preset. This indicates the injected reactive power at node r connected to phase O of the photovoltaic inverter; This represents the maximum capacity of the photovoltaic inverter O phase connected to node r. If the photovoltaic inverter O phase connected to node r satisfies the constraints given by the formula, it means that the inverter has active power regulation capability. S4-4. If the photovoltaic inverter to be involved in active power-voltage regulation has active power regulation capability, then... The active power output of the O phase of the photovoltaic inverter is adjusted in steps, as shown below: ； In the formula: r represents the access node of the photovoltaic inverter with the largest active power regulation capability in the active phase O; This represents the active power output of the photovoltaic inverter connected to node r after phase O-phase adjustment. This indicates the active power output before adjustment; S4-5. Determine whether the voltage over-limit problem of node i1 in phase O has been resolved. If not, continue with... The active power output of the current photovoltaic inverter is adjusted according to the step size. If the current photovoltaic inverter no longer has active power regulation capability, other photovoltaic inverters with active power regulation capability are selected in turn according to the proportion of total active power-voltage correlation until the voltage limit of node i1 is resolved. If all photovoltaic inverters with a total active power-voltage correlation ratio higher than 1 / M no longer have active power regulation capability, then step S5 is performed.

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