Grid-connected control method and device suitable for distributed photovoltaic, terminal equipment and storage medium

Abstract

The invention discloses a distributed photovoltaic grid-connected control method and device, terminal equipment and a storage medium, which not only considers the maximum grid-connected capacity and the minimum network loss, but also introduces a third model for minimizing the line power factor of a power distribution network. The line power factor of the power distribution network after photovoltaic grid connection can be calculated based on the reactive power data of each photovoltaic grid-connected node and the voltage data in the power distribution network, so that the voltage change of each node of the system can be quantified, and the voltage fluctuation of the power distribution network can be reduced by minimizing the line power factor; and the change of the node voltage can be limited by constructing the node voltage out-of-limit constraint corresponding to the third model, so that the reduction of the stability of the power distribution network caused by large voltage fluctuation can be effectively prevented. Compared with the prior art, the power optimization scheme provided by the invention meets the requirement of voltage stability while maximizing the grid-connected capacity, minimizing the network loss and minimizing the line power factor.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed photovoltaic output control, and in particular to a grid-connected control method, device, terminal equipment and storage medium suitable for distributed photovoltaic. Background Art

[0002] Connecting distributed photovoltaic power generation systems to the distribution network can achieve the interconnection between photovoltaic power generation and the power grid, making the power flow distribution in the power grid more reasonable, reducing unnecessary network losses, and improving the operation efficiency of the power grid. However, the access of distributed photovoltaics changes the grid structure of the distribution network, making the power flow operation of the power grid more complicated. For example, the access of distributed photovoltaics will cause the power flow of the distribution network to change, resulting in losses in distribution transformers and lines. In addition, the access of distributed photovoltaics will also cause changes in the voltage of each node of the distribution network, resulting in high and low voltage phenomena at the nodes of the distribution network.

[0003] In order to enhance the stability of the distribution network, by optimizing and controlling the power of photovoltaic grid-connected, the network loss and voltage fluctuation in the power grid can be reduced, and the grid fluctuation caused by photovoltaic access can be prevented from having an adverse effect on the system. In the construction process of the traditional photovoltaic grid-connected power optimization model, one or more planning models are usually established, but they only solve the optimal active power of photovoltaic grid-connected by minimizing network loss or maximizing economic benefits, and do not consider the voltage fluctuation of the distribution network after the distributed photovoltaic grid-connected. It is impossible to limit the voltage change of the node after the distributed photovoltaic access, and the power optimization scheme obtained may perform poorly in actual operation, such as causing large voltage fluctuations in the distribution network, making the stability of the distribution network low. Summary of the invention

[0004] The embodiments of the present invention provide a grid-connected control method, apparatus, terminal equipment and storage medium applicable to distributed photovoltaics, which not only considers maximizing the grid-connected capacity and minimizing the network loss, but also introduces a third model for minimizing the line power factor of the distribution network. The voltage changes of each node in the system can be quantified based on the line power factor between the two, which can effectively solve the problem that the voltage fluctuation of the distribution network after the grid-connection of distributed photovoltaics is not considered in the prior art, and the voltage changes of the nodes after the distributed photovoltaics are connected cannot be limited, thereby causing large voltage fluctuations in the distribution network.

[0005] An embodiment of the present invention provides a grid-connected control method applicable to distributed photovoltaics, comprising:

[0006] According to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node, a first model for maximizing the grid-connected capacity is constructed; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network;

[0007] According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint;

[0008] According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint;

[0009] Under various constraints, the first model, the second model and the third model are solved simultaneously to generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum;

[0010] According to the target active power of each photovoltaic grid-connected node, the output of each photovoltaic grid-connected node in the distribution network is controlled separately.

[0011] Preferably, the power balance constraint includes: active power constraint and reactive power constraint;

[0012] The generation of the power balance constraint comprises:

[0013] Acquire the input active power of each inflow node and the input reactive power of each inflow node in the distribution network; wherein the inflow node is a node for receiving the active power input from an external power source and the reactive power input from an external power source;

[0014] Generate the active power injection amount of each node in the distribution network according to the active power of each photovoltaic grid-connected node and the input active power of each inflow node;

[0015] Generate reactive power injection amount of each node in the distribution network according to reactive power of each photovoltaic grid-connected node and input reactive power of each inflow node;

[0016] Generate active power constraints based on the active power injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch;

[0017] Reactive power constraints are generated based on the reactive injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch.

[0018] Preferably, the generation of the node voltage limit constraint includes:

[0019] According to the active power injection amount of each node in the distribution network, the active power injection change amount of each node within a preset time period is generated;

[0020] According to the reactive power injection amount of each node in the distribution network, a reactive power injection change amount of each node within a preset time period is generated;

[0021] The node voltage over-limit constraint is generated according to the active power injection change of each node, the reactive power injection change of each node, the voltage change of each node in the distribution network, the line resistance of the distribution network and the rated voltage of the distribution network.

[0022] Preferably, the constraint conditions corresponding to the first model further include: broadband oscillation constraint;

[0023] The generation of the broadband oscillation constraint comprises:

[0024] A broadband oscillation constraint is generated according to a frequency deviation threshold of the photovoltaic power generation system, a damping coefficient of the photovoltaic power generation system, an active power of each photovoltaic grid-connected node, and a reference power of each photovoltaic grid-connected node.

[0025] Preferably, the constraint conditions corresponding to the first model further include: relay protection constraints; the relay protection constraints include: first-segment current protection constraints, second-segment current protection constraints, and third-segment current protection constraints;

[0026] Among them, the first-stage current protection constraint is used to characterize the first-stage current protection when the fault occurs in the downstream line of the grid connection point; the second-stage current protection constraint is used to characterize the second-stage current protection when the fault occurs in the downstream line of the grid connection point, and the action current setting value of the second-stage current protection is greater than the action current setting value of the first-stage current protection; the third-stage current protection constraint is used to characterize the third-stage current protection when the fault occurs in the adjacent feeder; the action current setting value is used to characterize the minimum current value required for the current protection device to trip;

[0027] The first current protection constraint includes:

[0028]

[0029] In the formula, I set.1 is the action current setting value of the first stage current protection, K′ rel1 is the reliability factor of the first stage current protection, E s is the system phase potential, U N is the rated voltage of the photovoltaic grid-connected node, P pv,i is the active power of the ith photovoltaic grid-connected node, Z AB is the impedance of the line without fault, Z S is the system equivalent impedance, Z f is the impedance of the line between the fault point and the photovoltaic grid-connected node;

[0030] The second section current protection constraint includes:

[0031]

[0032] In the formula, I set.2 is the action current setting value of the second stage current protection, K′ rel2 is the reliability factor of the second stage current protection, Z BC The impedance of the standby line corresponding to the second stage current protection;

[0033] The third section current protection constraint includes:

[0034]

[0035] In the formula, I set.3 It is the action current setting value of the third stage current protection.

[0036] Preferably, the constraint conditions corresponding to both the first model and the second model further include: a reverse load rate constraint;

[0037] The generation of the reverse load rate constraint includes:

[0038] The reverse load rate constraint is generated according to the preset reverse load rate, the active power of each photovoltaic grid-connected node, the power data of each load node and the rated capacity of the transformer.

[0039] Preferably, the first model comprises:

[0040] max f 1 =P pv,i ,P pv ≤P pvs ;

[0041] Among them, f 1 is the functional form of the first model, f 1 Represents the grid-connected capacity, P pv,i is the active power of the ith photovoltaic grid-connected node, P pvs is the distributed photovoltaic installed capacity corresponding to the i-th photovoltaic grid-connected node;

[0042] The second model comprises:

[0043]

[0044] Among them, f 2 is the functional form of the second model, f 2 Represents the network loss value, P Gi is the active power generated by the ith power source, P Li is the active power consumption of the i-th load node, N is the number of power sources, and M is the number of load nodes;

[0045] The third model comprises:

[0046]

[0047] Among them, f 3 is the functional form of the third model, f 3 Indicates the power factor of the line, ΔV j is the voltage change of node j in the distribution network within a preset time period, ΔQ i is the reactive power change of PV grid-connected node i within a preset time period, node j is connected to PV grid-connected node i by a line, node j is a PV grid-connected node, load node or power source node in the distribution network, n is the total number of nodes in the distribution network, and m is the total number of PV grid-connected nodes.

[0048] Based on the above method embodiments, the present invention provides corresponding device embodiments.

[0049] An embodiment of the present invention provides a grid-connected control device applicable to distributed photovoltaics, comprising: a model building module, a model solving module, and an output control module;

[0050] The model building module is used to build a first model to maximize the grid-connected capacity according to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network;

[0051] According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint;

[0052] According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint;

[0053] The model solving module is used to solve the first model, the second model and the third model simultaneously under various constraint conditions, and generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum;

[0054] The output control module is used to control the output of each photovoltaic grid-connected node in the distribution network according to the target active power of each photovoltaic grid-connected node.

[0055] Based on the above method embodiments, the present invention provides corresponding terminal equipment embodiments.

[0056] Another embodiment of the present invention provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and when the processor executes the computer program, a grid-connected control method suitable for distributed photovoltaics described in the above-mentioned embodiment of the invention is implemented.

[0057] Based on the above method embodiments, the present invention provides corresponding storage medium item embodiments.

[0058] Another embodiment of the present invention provides a storage medium, wherein the computer-readable storage medium includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a grid-connected control method applicable to distributed photovoltaics as described in the above-mentioned embodiment of the invention.

[0059] The following beneficial effects are achieved by implementing the present invention:

[0060] The embodiments of the present invention provide a grid-connected control method, apparatus, terminal equipment and storage medium applicable to distributed photovoltaics. The present invention not only considers maximizing the grid-connected capacity and minimizing the network loss, but also introduces a third model for minimizing the line power factor of the distribution network. Specifically, when constructing the third model, the line power factor of the distribution network after photovoltaic grid-connection can be calculated based on the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network. Since the reactive power injected by the distributed photovoltaics will cause the voltage of each node of the distribution network to change, the present invention quantifies the voltage change of each node of the system based on the line power factor between the two. By minimizing the line power factor, the voltage fluctuation of the distribution network can be reduced. And by constructing the node voltage over-limit constraint corresponding to the third model, the node voltage change can be limited, which can effectively prevent the stability of the distribution network from being reduced due to large voltage fluctuations. Compared with the prior art, the present invention solves three models simultaneously under various constraints to ensure that the obtained power optimization solution meets the requirements of maximizing grid-connected capacity, minimizing network losses and minimizing line power factor, while also meeting the requirements of voltage stability. It can accurately control the output of each photovoltaic grid-connected node in the distribution network, reduce network losses and voltage fluctuations in the power grid, and improve the operating stability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a flow chart of a grid-connected control method applicable to distributed photovoltaics provided by an embodiment of the present invention.

[0062] Figure 2It is a structural schematic diagram of a grid-connected control device applicable to distributed photovoltaics provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] like Figure 1 FIG. 1 is a flow chart of a grid-connected control method applicable to distributed photovoltaics provided by an embodiment of the present invention. The grid-connected control method applicable to distributed photovoltaics includes:

[0065] Step S1: constructing a first model to maximize the grid-connected capacity according to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network;

[0066] According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint;

[0067] According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint;

[0068] Step S2: Under various constraints, the first model, the second model and the third model are solved simultaneously, and the target active power corresponding to each photovoltaic grid-connected node is generated when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum;

[0069] Step S3: According to the target active power of each photovoltaic grid-connected node, the output of each photovoltaic grid-connected node in the distribution network is controlled respectively.

[0070] For step S1, the optimization model of the distributed photovoltaic access to the distribution network of the present invention may include three aspects, such as: grid-connected capacity, network loss and voltage sensitivity;

[0071] The present invention can quantify the grid-connected capacity by constructing a first model, quantify the network loss by constructing a second model, and quantify the voltage sensitivity by constructing a third model.

[0072] Specifically, firstly, based on the active power data of each photovoltaic grid-connected node after connecting to the distribution network and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node, a first model for maximizing the grid-connected capacity can be constructed; it can be understood that the distributed photovoltaic of the present invention is grid-connected with a unity power factor, ignoring the influence of photovoltaic reactive power, and the objective function of the first model is:

[0073] max f 1 =P pv,i ,P pv ≤P pvs ;

[0074] Among them, f 1 is the functional form of the first model, f 1 Represents the grid-connected capacity, P pv,i is the active power of the ith photovoltaic grid-connected node, P pvs is the distributed photovoltaic installed capacity corresponding to the i-th photovoltaic grid-connected node. Indicatively, the influence of photovoltaic reactive power is ignored when photovoltaic grid-connected. Then, the present invention solves the P that satisfies the installed capacity through the constraint between the active power of the photovoltaic grid-connected node and its corresponding grid-connected capacity. pv,i .

[0075] Next, based on the power data of other conventional power sources in the distribution network and the power data of each load node, a second model is constructed to minimize network loss. It can be understood that the access of distributed photovoltaics will cause changes in the power flow of the original distribution network, resulting in changes in the distribution transformer and line losses. The power data of each load node (such as active power) and the power data of the power source (such as active power) can be used to obtain the network loss of the power grid system. The objective function of the second model is:

[0076]

[0077] Among them, f 2 is the functional form of the second model, f 2 Represents the network loss value, P Gi is the active power generated by the ith power source, P Li is the active power consumption of the i-th load node, N is the number of power sources, and M is the number of load nodes. By rationally planning the active power emitted by the power source, the network loss of the system can be reduced and the economy can be improved.

[0078] Finally, since the reactive power injected by distributed photovoltaics will cause changes in the voltage of each node in the distribution network, the voltage changes of each node in the system are measured based on voltage sensitivity. Specifically, the power factor change of the line can be used to characterize the sensitivity of voltage. The reactive power change of the distributed photovoltaic access node and the voltage change of other nodes can be used to construct a third model to obtain the power factor of each connecting line (such as a branch). The objective function of the third model is:

[0079]

[0080] Among them, f 3 is the functional form of the third model, f 3 Indicates the power factor of the line, ΔV j is the voltage change of node j in the distribution network within a preset time period, ΔQ i is the reactive power change of PV grid-connected node i within a preset time period, node j is connected to PV grid-connected node i by a line, node j is a PV grid-connected node, load node or power source node in the distribution network, n is the total number of nodes in the distribution network, and m is the total number of PV grid-connected nodes.

[0081] In schematic form, by constructing the first model to quantify the grid-connected capacity, the present invention can clearly understand the actual grid-connected capacity of each photovoltaic grid-connected node, so that when the optimal target active power of the photovoltaic grid-connected node is finally solved, it can ensure that the access of the photovoltaic system will not cause excessive pressure on the distribution network, and at the same time, it can also optimize the layout and capacity configuration of the photovoltaic system to achieve the maximum grid-connected benefit.

[0082] By constructing a second model to quantify network losses, we can accurately evaluate the impact of distributed photovoltaic access on the distribution network flow and the resulting changes in distribution transformer and line losses. The second model can then be used to rationally plan the active power generated by the power source, significantly reduce the system's network losses, and improve the economy and efficiency of the distribution network.

[0083] Furthermore, distributed photovoltaic grid-connected will cause voltage fluctuations in the distribution network. The third model of the present invention calculates the line power factor of the distribution network after photovoltaic grid-connected based on the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network. The voltage sensitivity of each node can be quantified, thereby minimizing the line power factor and reducing the impact of the reactive power injected by distributed photovoltaics on the voltage of each node in the distribution network, that is, reducing the voltage fluctuation of the distribution network and ensuring the safe and stable operation of the distribution network.

[0084] Therefore, the three models of the present invention together constitute a comprehensive evaluation system for the access of distributed photovoltaic power generation to the distribution network. By comprehensively considering multiple aspects such as grid-connected capacity, network loss and voltage sensitivity, it can be ensured that the power optimization solution ultimately obtained based on the simultaneous solution of the three models can meet the requirements of maximizing grid-connected capacity, minimizing network loss and minimizing line power factor while also meeting the requirements of voltage stability.

[0085] For step S2, in a preferred embodiment, the first model, the second model and the third model all correspond to power balance constraints and node voltage over-limit constraints; and the power balance constraints include: active power constraints and reactive power constraints;

[0086] The generation of the power balance constraint includes:

[0087] Acquire the input active power of each inflow node and the input reactive power of each inflow node in the distribution network; wherein the inflow node is a node for receiving the active power input from an external power source and the reactive power input from an external power source;

[0088] Generate the active power injection amount of each node in the distribution network according to the active power of each photovoltaic grid-connected node and the input active power of each inflow node;

[0089] Generate reactive power injection amount of each node in the distribution network according to reactive power of each photovoltaic grid-connected node and input reactive power of each inflow node;

[0090] Generate active power constraints based on the active power injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch;

[0091] Reactive power constraints are generated based on the reactive injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch.

[0092] Specifically, the formula for the active power constraint is as follows:

[0093]

[0094] P is =P pv,i +P i ;

[0095] Among them, P is is the active power injection amount of node is, node is the photovoltaic grid-connected node, load node or power source node in the distribution network, P pv,i is the active power of the ith photovoltaic grid-connected node, P i is the input active power flowing into the ith node, Ui is the voltage amplitude flowing into the ith node, U j is the voltage amplitude of node j connected to the i-th inflow node, G ij , B ij are the real and imaginary parts of the node admittance matrix, θ ij is the phase difference between the inflow nodes i and j at both ends of the branch.

[0096] The formula for the reactive power constraint is as follows:

[0097]

[0098] Q is =Q pv,i +Q i ;

[0099] Among them, Q is is the reactive power injection amount of node is, Q pv,i is the reactive power of the ith photovoltaic grid-connected node, Q i is the input reactive power flowing into the i-th node.

[0100] The present invention ensures that the power injection and outflow of each node in the power grid are within a reasonable range through active power constraints, thereby avoiding the instability of the power grid caused by excessive or insufficient power. Through active power constraints, the optimized distribution of power grid trends can be achieved, and the power injection amount of each node can be adjusted to make the distribution of trends in the power grid more balanced, thereby reducing power grid losses and voltage fluctuations.

[0101] Through reactive power constraints, the reactive power injection amount of each node can be adjusted to achieve effective control of the grid voltage, thereby avoiding equipment damage and grid instability caused by voltage fluctuations.

[0102] In a preferred embodiment, the generation of the node voltage limit constraint includes:

[0103] According to the active power injection amount of each node in the distribution network, the active power injection change amount of each node within a preset time period is generated;

[0104] According to the reactive power injection amount of each node in the distribution network, a reactive power injection change amount of each node within a preset time period is generated;

[0105] The node voltage over-limit constraint is generated according to the active power injection change of each node, the reactive power injection change of each node, the voltage change of each node in the distribution network, the line resistance of the distribution network and the rated voltage of the distribution network.

[0106] Then the formula for the node voltage over-limit constraint is:

[0107]

[0108] Among them, ΔU is is the voltage change at node is, R and X are the different line resistances in the distribution network, and U is the rated voltage of the distribution network.

[0109] Therefore, the active and reactive injection amounts of each node can be adjusted through node voltage over-limit constraints, so that the voltage of each node in the power grid fluctuates within the allowed range, thereby avoiding serious problems such as equipment damage and power grid collapse caused by excessively high or low voltage.

[0110] In a preferred embodiment, the constraint conditions corresponding to the first model further include: broadband oscillation constraint;

[0111] The generation of the broadband oscillation constraint comprises:

[0112] A broadband oscillation constraint is generated according to a frequency deviation threshold of the photovoltaic power generation system, a damping coefficient of the photovoltaic power generation system, an active power of each photovoltaic grid-connected node, and a reference power of each photovoltaic grid-connected node.

[0113] In schematic form, since the inertia of photovoltaic power generation is smaller than that of generators, and the photovoltaic inverter responds quickly during the process of being connected to the grid and off-grid, the damping effect of the photovoltaic power generation system is insufficient, and broadband oscillation is prone to occur. In order to suppress the oscillation, a suitable control strategy needs to be adopted to improve the frequency stability of the system. The present invention not only considers the overall stability of the photovoltaic power generation system through broadband oscillation constraints, but also pays attention to the power distribution of each photovoltaic grid-connected node. By reasonably setting the active power of the photovoltaic grid-connected node and combining the frequency deviation threshold of the photovoltaic power generation system, the power distribution of each node can be optimized to avoid oscillations caused by excessive or insufficient power in some nodes.

[0114] In a preferred embodiment, the constraint conditions corresponding to the first model further include: relay protection constraints; the relay protection constraints include: first-segment current protection constraints, second-segment current protection constraints, and third-segment current protection constraints;

[0115] Among them, the first-stage current protection constraint is used to characterize the first-stage current protection when the fault occurs in the downstream line of the grid connection point; the second-stage current protection constraint is used to characterize the second-stage current protection when the fault occurs in the downstream line of the grid connection point, and the action current setting value of the second-stage current protection is greater than the action current setting value of the first-stage current protection; the third-stage current protection constraint is used to characterize the third-stage current protection when the fault occurs in the adjacent feeder; the action current setting value is used to characterize the minimum current value required for the current protection device to trip;

[0116] The first current protection constraint includes:

[0117]

[0118] In the formula, I set.1 is the action current setting value of the first stage current protection, K′ rel1 is the reliability factor of the first stage current protection, E s is the system phase potential, U N is the rated voltage of the photovoltaic grid-connected node, P pv,i is the active power of the ith photovoltaic grid-connected node, Z AB is the impedance of the line without fault, Z S is the system equivalent impedance, Z f is the impedance of the line between the fault point and the photovoltaic grid-connected node;

[0119] The second section current protection constraint includes:

[0120]

[0121] In the formula, I set.2 is the action current setting value of the second stage current protection, K′ rel2 is the reliability factor of the second stage current protection, Z BC The impedance of the standby line corresponding to the second stage current protection;

[0122] The third section current protection constraint includes:

[0123]

[0124] In the formula, I set.3 It is the action current setting value of the third stage current protection.

[0125] In the embodiment of the present invention, a three-stage current protection can be used. When a fault occurs in the downstream line of the grid-connected point, the photovoltaic effect on the downstream short-circuit current is to increase the current, which will cause the fault line circuit breaker current protection stage I and stage II to malfunction. Then, the active power of the photovoltaic grid-connected node under the original setting value can be constrained, and the sensitivity requirements of the current stage II must be met while satisfying the protection range constraint of the current stage I. When the fault occurs in the adjacent feeder, the photovoltaic effect on the short-circuit current is reverse, and the reverse current may cause the upstream line protection to malfunction; therefore, the maximum reverse short-circuit current provided by the photovoltaic energy is less than the minimum protection setting value of the three-stage protection of the upstream line of the grid-connected point, that is, the active power of the photovoltaic grid-connected node is constrained by the set value of the current stage III protection.

[0126] Therefore, the present invention can ensure that when a serious fault occurs in the downstream line of the grid-connected point, the fault circuit can be quickly cut off to prevent the fault current from causing damage to the photovoltaic grid-connected node and downstream equipment through the action current setting value of the first-stage current protection constraint. And the maximum allowable injection power of the photovoltaic grid-connected node under fault conditions can be determined, thereby ensuring that the protection will not be rejected or malfunctioned due to excessive power during protection action.

[0127] The second-stage current protection constraint serves as a backup for the first-stage current protection. Its action current setting value and time delay setting can ensure that when a fault occurs, the faulty circuit is selectively cut off while avoiding unnecessary power outages on adjacent lines, thereby further reasonably allocating the active power of the photovoltaic grid-connected nodes within the protection range and ensuring the stable operation of the power grid.

[0128] The third-stage current protection constraint serves as the backup protection for the entire relay protection system. Its action current setting value is set to avoid the maximum load current. It can ensure reliable protection action when a slight overload or fault occurs in the power grid. Therefore, the active power of the photovoltaic grid-connected node can be dynamically adjusted according to the load changes during the operation of the power grid to ensure the safe and stable operation of the power grid.

[0129] The embodiment of the present invention can suppress the power oscillation phenomenon in the power grid by setting the relay protection constraint, and ensure that the photovoltaic grid-connected nodes will not cause adverse effects on the power grid due to excessive power fluctuations during the grid-connected process.

[0130] In a preferred embodiment, the constraint conditions corresponding to both the first model and the second model further include: a reverse load rate constraint;

[0131] The generation of the reverse load rate constraint includes:

[0132] The reverse load rate constraint is generated according to the preset reverse load rate, the active power of each photovoltaic grid-connected node, the power data of each load node and the rated capacity of the transformer.

[0133] Among them, the formula for the constraint condition of the reverse load rate is:

[0134]

[0135] Where λ is the reverse load rate, P pv,i is the active power of the ith photovoltaic grid-connected node, P L is the total power of the load node, S e is the rated capacity of the transformer.

[0136] Since excessive reverse power flow may cause grid instability or even grid failure, the reverse load rate constraint can limit the active power output of photovoltaic grid-connected nodes, thereby preventing excessive reverse power flow in the grid. Through the reverse load rate constraint, it can ensure that the grid is in a stable operating state and fully utilizes the output power of the photovoltaic power generation system, while avoiding adverse effects on the grid.

[0137] Therefore, the present invention can solve the first model, the second model and the third model at the same time under the power balance constraint, the node voltage over-limit constraint, the wide-band oscillation constraint, the first-segment current protection constraint, the second-segment current protection constraint, the third-segment current protection constraint and the reverse load rate constraint, so as to generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum.

[0138] Under the premise of meeting various constraints, the grid-connected capacity can be maximized, thereby making full use of the output power of the photovoltaic power generation system and improving the economy and efficiency of the power grid. It is also possible to find a photovoltaic grid-connected node power configuration scheme that minimizes network loss, thereby reducing the operating cost of the power grid. Furthermore, the influence of the line power factor is also considered in the solution process, which can ultimately reduce the flow and loss of reactive power and improve the power quality of the power grid.

[0139] For step S3, in a preferred embodiment, after the control system of each photovoltaic grid-connected node receives the target active power, it controls the output of the photovoltaic grid-connected node by adjusting the output power of the inverter. Since the target active power finally obtained satisfies the maximum grid-connected capacity, the minimum network loss and the minimum line power factor, the network loss and voltage fluctuation in the power grid can be reduced, and the operation stability of the power grid can be improved.

[0140] like Figure 2 As shown, based on the above-mentioned various embodiments of the grid-connected control method applicable to distributed photovoltaics, the present invention provides a corresponding device embodiment;

[0141] An embodiment of the present invention provides a grid-connected control device applicable to distributed photovoltaics, comprising: a model building module, a model solving module, and an output control module;

[0142] The model building module is used to build a first model to maximize the grid-connected capacity according to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network;

[0143] According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint;

[0144] According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint;

[0145] The model solving module is used to solve the first model, the second model and the third model simultaneously under various constraint conditions, and generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum;

[0146] The output control module is used to control the output of each photovoltaic grid-connected node in the distribution network according to the target active power of each photovoltaic grid-connected node.

[0147] It should be noted that the device embodiments described above are merely schematic, wherein the modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical modules, and may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the accompanying drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement it without paying creative labor.

[0148] Those skilled in the art can clearly understand that, for the sake of convenience and simplicity, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0149] Based on the above-mentioned various embodiments of the grid-connected control method applicable to distributed photovoltaics, the present invention provides corresponding embodiments of terminal equipment items.

[0150] An embodiment of the present invention provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, a grid-connected control method applicable to distributed photovoltaics as described in any method embodiment of the present invention is implemented.

[0151] The terminal device may be a computing terminal device such as a desktop computer, a notebook, a palm computer, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0152] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal device, and uses various interfaces and lines to connect various parts of the entire terminal device.

[0153] The memory can be used to store the computer program, and the processor realizes various functions of the terminal device by running or executing the computer program stored in the memory and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application required for a function, etc.; the data storage area can store data created according to the use of the mobile phone, etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device or other volatile solid-state storage device.

[0154] Based on the above-mentioned various embodiments of the grid-connected control method applicable to distributed photovoltaics, the present invention provides a corresponding storage medium item embodiment.

[0155] An embodiment of the present invention provides a storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a grid-connected control method applicable to distributed photovoltaics as described in any method embodiment of the present invention.

[0156] The storage medium is a computer-readable storage medium, and the computer program is stored in the computer-readable storage medium. When the computer program is executed by the processor, the steps of each method embodiment described above can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0157] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A grid-connected control method applicable to distributed photovoltaics, characterized in that: include: According to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node, a first model for maximizing the grid-connected capacity is constructed; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network; According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint; According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint; Under various constraints, the first model, the second model and the third model are solved simultaneously to generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum; According to the target active power of each photovoltaic grid-connected node, the output of each photovoltaic grid-connected node in the distribution network is controlled separately.

2. A grid-connected control method applicable to distributed photovoltaics according to claim 1, characterized in that: The power balance constraint includes: active power constraint and reactive power constraint; The generation of the power balance constraint comprises: Acquire the input active power of each inflow node and the input reactive power of each inflow node in the distribution network; wherein the inflow node is a node for receiving the active power input from an external power source and the reactive power input from an external power source; Generate the active power injection amount of each node in the distribution network according to the active power of each photovoltaic grid-connected node and the input active power of each inflow node; Generate reactive power injection amount of each node in the distribution network according to reactive power of each photovoltaic grid-connected node and input reactive power of each inflow node; Generate active power constraints based on the active power injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch; Reactive power constraints are generated based on the reactive injection amount of each node, the voltage amplitude of each node, the node admittance matrix, and the phase difference between the nodes at both ends of the branch.

3. A grid-connected control method applicable to distributed photovoltaics as claimed in claim 2, characterized in that: The generation of the node voltage limit constraint includes: According to the active power injection amount of each node in the distribution network, the active power injection change amount of each node within a preset time period is generated; According to the reactive power injection amount of each node in the distribution network, a reactive power injection change amount of each node within a preset time period is generated; The node voltage over-limit constraint is generated according to the active power injection change of each node, the reactive power injection change of each node, the voltage change of each node in the distribution network, the line resistance of the distribution network and the rated voltage of the distribution network.

4. A grid-connected control method applicable to distributed photovoltaics as claimed in claim 3, characterized in that: The constraints corresponding to the first model also include: broadband oscillation constraints; The generation of the broadband oscillation constraint comprises: A wideband oscillation constraint is generated according to a frequency deviation threshold of the photovoltaic power generation system, a damping coefficient of the photovoltaic power generation system, the active power of each photovoltaic grid-connected node, and a reference power of each photovoltaic grid-connected node.

5. A grid-connected control method applicable to distributed photovoltaics as claimed in claim 4, characterized in that: The constraint conditions corresponding to the first model also include: relay protection constraints; the relay protection constraints include: first-segment current protection constraints, second-segment current protection constraints, and third-segment current protection constraints; Among them, the first-stage current protection constraint is used to characterize the first-stage current protection when the fault occurs in the downstream line of the grid connection point; the second-stage current protection constraint is used to characterize the second-stage current protection when the fault occurs in the downstream line of the grid connection point, and the action current setting value of the second-stage current protection is greater than the action current setting value of the first-stage current protection; the third-stage current protection constraint is used to characterize the third-stage current protection when the fault occurs in the adjacent feeder; the action current setting value is used to characterize the minimum current value required for the current protection device to trip; The first current protection constraint includes: In the formula, I set.1 is the action current setting value of the first stage current protection, K′ rel1 is the reliability factor of the first stage current protection, E s is the system phase potential, U N is the rated voltage of the photovoltaic grid-connected node, P pv,i is the active power of the ith photovoltaic grid-connected node, Z AB is the impedance of the line without fault, Z S is the system equivalent impedance, Z f is the impedance of the line between the fault point and the photovoltaic grid-connected node; The second section current protection constraint includes: In the formula, I set.2 is the action current setting value of the second stage current protection, K′ rel2 is the reliability factor of the second stage current protection, Z BC The impedance of the standby line corresponding to the second stage current protection; The third section current protection constraint includes: In the formula, I set.3 It is the action current setting value of the third stage current protection.

6. A grid-connected control method applicable to distributed photovoltaics as claimed in claim 5, characterized in that: The constraint conditions corresponding to both the first model and the second model also include: a reverse load rate constraint; The generation of the reverse load rate constraint includes: The reverse load rate constraint is generated according to the preset reverse load rate, the active power of each photovoltaic grid-connected node, the power data of each load node and the rated capacity of the transformer.

7. A grid-connected control method applicable to distributed photovoltaics as claimed in claim 6, characterized in that: The first model comprises: max f1=P pv,i, P pv ≤P pvs ; Among them, f1 is the function of the first model, f1 represents the grid-connected capacity, P pv,i is the active power of the ith photovoltaic grid-connected node, P pvs is the distributed photovoltaic installed capacity corresponding to the i-th photovoltaic grid-connected node; The second model comprises: Among them, f2 is the function of the second model, f2 represents the network loss value, P Gi is the active power generated by the i-th power source, P Li is the active power consumption of the i-th load node, N is the number of power sources, and M is the number of load nodes; The third model comprises: Among them, f3 is the function of the third model, f3 represents the power factor of the line, ΔV j is the voltage change of node j in the distribution network within a preset time period, ΔQ i is the reactive power change of PV grid-connected node i within a preset time period, node j is connected to PV grid-connected node i by a line, node j is a PV grid-connected node, load node or power source node in the distribution network, n is the total number of nodes in the distribution network, and m is the total number of PV grid-connected nodes.

8. A grid-connected control device suitable for distributed photovoltaics, characterized in that: include: Model building module, model solving module and output control module; The model building module is used to build a first model to maximize the grid-connected capacity according to the active power data of each photovoltaic grid-connected node and the distributed photovoltaic installed capacity of each photovoltaic grid-connected node; wherein the photovoltaic grid-connected node is a node where the distributed photovoltaic is connected to the distribution network; According to the power data of each power source in the distribution network and the power data of each load node, a second model is constructed to minimize the network loss; wherein the constraint conditions corresponding to the first model and the second model are: power balance constraint; According to the reactive power data of each photovoltaic grid-connected node and the voltage data in the distribution network, a third model is constructed to minimize the line power factor of the distribution network; wherein the constraint condition corresponding to the third model is: node voltage over-limit constraint; The model solving module is used to solve the first model, the second model and the third model simultaneously under various constraint conditions, and generate the target active power corresponding to each photovoltaic grid-connected node when the grid-connected capacity is maximum, the network loss is minimum and the line power factor is minimum; The output control module is used to control the output of each photovoltaic grid-connected node in the distribution network according to the target active power of each photovoltaic grid-connected node.

9. A terminal device, characterized in that: The invention comprises a processor, a memory and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, a grid-connected control method applicable to distributed photovoltaics as described in any one of claims 1 to 7 is implemented.

10. A storage medium, characterized in that: The storage medium includes a stored computer program, wherein when the computer program is running, the device where the storage medium is located is controlled to execute a grid-connected control method applicable to distributed photovoltaics as described in any one of claims 1 to 7.

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