Comprehensive harmonic control method and device for distribution network based on photovoltaic local control

Abstract

The present invention discloses a method and device for comprehensive harmonic control of a distribution network based on photovoltaic local control. The proposed method combines two local controls, namely harmonic current compensation control and harmonic virtual conductance control, of a converter. By simulating the comprehensive harmonic control of typical operating scenarios of the distribution network, a harmonic control scheme for a photovoltaic converter is configured. In real-time applications, the harmonic state estimation results of an online power quality monitoring system every 3 minutes are utilized, and the control instructions of each converter are optimized and solved through a centralized controller and sent to the corresponding photovoltaic converter. The photovoltaic converters participating in the harmonic control, based on the received control instructions and the actual operating conditions of the photovoltaic converter, maximize the use of the remaining capacity of the converter for harmonic control while maximizing the use of the converter's remaining capacity for harmonic control, thereby improving the power quality of the distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of power quality compensation and distributed photovoltaic inverter control, and relates to a method and device for comprehensive harmonic control of a distribution network based on photovoltaic local control. Background Art

[0002] In power system operation, the quality of power is directly related to the normal operation of power equipment and the user's electricity experience. Traditional power quality management methods focus on local compensation of power quality at a specific point. This approach typically involves installing corresponding compensation devices, such as capacitors and reactors, at the specific location where power quality problems occur to improve parameters such as voltage and current at that point, thereby enhancing local power quality. This approach has the advantages of simple operation, low cost, and rapid effectiveness. In systems dominated by individual large harmonic sources, it can better meet the needs of power quality management.

[0003] However, with the rapid development of modern distribution networks, the limitations of traditional governance methods are becoming increasingly apparent. Modern distribution networks feature a high density of micro-harmonic sources, along with the widespread use of distributed power sources and power electronic equipment. This results in numerous and widely distributed sources of power quality pollution. Furthermore, the phenomenon of cross-coupling of harmonic flows is significant, with harmonics at different locations influencing each other. This can lead to localized power quality issues potentially being caused by harmonics from multiple sources. In this scenario, relying solely on local compensation at a single point is no longer sufficient to effectively address power quality issues across the entire substation, and it struggles to address multi-source pollution scenarios.

[0004] Therefore, to meet the new challenges of modern distribution networks, collaborative approaches to managing power quality across the entire substation area have become a research hotspot. Existing technologies use high-precision monitoring devices to collect real-time power quality data, such as harmonic voltage and current, from each node. Leveraging high-speed, reliable communication technologies, these data are uploaded to a centralized controller or shared between devices. The centralized controller then uses control algorithms to enable each device to adjust its output current based on this global information, working collaboratively to achieve optimal harmonic mitigation.

[0005] Although the collaborative management of multiple converters has achieved certain research results, it still faces some challenges, such as communication delay, implementation complexity, and coordination between converters. This is because the implementation of existing methods relies on real-time acquisition of the phase of the harmonic voltage and current of each node, so GPS is required for high-precision time synchronization. However, relevant research shows that the operation of GPS is often subject to interference from various aspects, and the time error can reach 2.3ms. Complex on-site environment and equipment fluctuations will affect the real-time harmonic phasor measurement, and a large number of optimization calculations need to be performed in a short time. This will make it difficult for the method of adjusting the harmonic current output of the converter in real time through a centralized controller to achieve the performance expected in theory. Summary of the Invention

[0006] In view of the limitations of existing centralized control, such as low efficiency in large-scale data processing and high requirements for real-time control, the present invention provides a method and device for comprehensive harmonic control of distribution networks based on photovoltaic local control. The method combines two local control methods, namely harmonic current compensation control and harmonic virtual conductance control of the converter, and simulates the comprehensive harmonic control of typical operating scenarios of the distribution network to configure the harmonic control scheme of the photovoltaic converter. In real-time applications, the harmonic state estimation results of the power quality online monitoring system every 3 minutes are used to optimize and solve the control instructions of each converter through a centralized controller and send the control instructions to the corresponding photovoltaic converter. The photovoltaic converter participating in the harmonic control, based on the received control instructions and the actual operating conditions of the photovoltaic converter, maximizes the use of the remaining capacity of the converter for harmonic control while maximizing the use of the converter's capacity for harmonic control, thereby improving the power quality of the distribution network.

[0007] The present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a method for comprehensive harmonic control of distribution network based on photovoltaic local control, comprising the following steps:

[0008] S1: Cluster the operating status according to the power system scenario to construct a typical operating scenario; for the photovoltaic converters involved in harmonic control, configure the harmonic control solution based on the typical operating scenario;

[0009] S2: The power quality online monitoring system (PQMS) detects the node's harmonic voltage and current vectors and performs harmonic state estimation. Based on the harmonic state estimation results, the centralized controller optimizes and solves the control instructions for each converter and sends the control instructions to the corresponding PV converter through one-way communication.

[0010] S3, based on the control instruction obtained in step S2 and the actual operation of the photovoltaic converter involved in harmonic control, ensures that the photovoltaic converter outputs the maximum available power while utilizing the remaining capacity of the converter for harmonic control according to the received control instruction.

[0011] Furthermore, the specific process of step S1 is:

[0012] S1.1, for the harmonic sources existing in the nodes of the distribution network, the harmonic Norton equivalent circuit HNM is used to represent them;

[0013] S1.2, pre-processing the power system operation status data and clustering the distribution network operation status data to construct typical operation scenarios;

[0014] S1.3, configure harmonic control schemes for typical operating scenarios; for PV converters involved in harmonic control, there are two local harmonic control methods: (1) detecting the grid-connected point harmonic voltage and adopting harmonic virtual conductance control; (2) detecting the local load harmonic current and adopting harmonic current compensation control; in different typical operating scenarios, each PV converter is respectively configured to adopt the above two local control schemes to form different PV converter configuration schemes;

[0015] S1.4, for the configuration scheme of photovoltaic converters in the distribution network, some photovoltaic converters adopt harmonic virtual conductance control, while other photovoltaic converters adopt harmonic current compensation control. Then, voltage / current sensors suitable for harmonic control are installed at the corresponding nodes, and the control strategy of the photovoltaic converter is modified so that it has the corresponding ability to receive control instructions to realize the harmonic control function.

[0016] Furthermore, the specific process of step S2 is:

[0017] S2.1, the power quality online monitoring system measures the harmonic voltage and current vectors of the distribution network nodes online, performs Fourier harmonic analysis and calculation, and transmits the average, maximum and minimum values ​​of the statistical data to the centralized controller for harmonic state estimation;

[0018] S2.2, based on the harmonic state estimation results and the harmonic source and line models, establish an optimization problem. This optimization problem takes the comprehensive optimization of the harmonic voltage of the entire distribution network node as the optimization objective, and uses the harmonic virtual conductance or harmonic current compensation coefficient of each PV converter participating in harmonic control as the variable;

[0019] S2.3, the centralized controller optimizes and solves the control instructions of each converter, converts the optimization problem into a mixed integer programming problem, and finally finds the optimal solution by combining branch and bound and heuristic algorithms; then the obtained harmonic virtual conductance or harmonic current compensation coefficient is sent as a control instruction to each photovoltaic converter participating in harmonic management.

[0020] Furthermore, the specific process of step S3 is:

[0021] S3.1. The PV converter involved in harmonic control consists of two parts: a DC-DC converter and a DC-AC converter. The DC-DC converter is located on the PV side and uses MPPT control to maximize the PV array's power output. The DC-AC converter is located on the grid side and is used to transmit power to the grid and perform harmonic compensation.

[0022] S3.2, the DC-AC part receives control instructions from the centralized controller, generates an initial reference value for the harmonic compensation current based on the received harmonic virtual conductance or harmonic current compensation coefficient, and then performs converter current limiting correction based on the actual operating conditions of the PV converter to obtain a corrected reference value for the harmonic compensation current;

[0023] S3.3, the reference value of the corrected harmonic compensation current is added to the reference value of the fundamental active and reactive current, and the grid-connected current tracking control is performed through the multi-PR controller in the fundamental and harmonic domains, so that the photovoltaic converter outputs the corresponding fundamental and harmonic currents, realizing comprehensive harmonic control of photovoltaic power generation and distribution network.

[0024] Furthermore, in step S1.1, the parameters of the Norton equivalent circuit are calculated using the wave quantity method, that is, when the power of the harmonic source remains unchanged for a period of time, at least two different node harmonic voltages are selected or two harmonic voltages are constructed by harmonic compensation through photovoltaic converters, and the difference between different harmonic voltages is sufficient to cause a significant change in the harmonic current injected by the harmonic source, the harmonic current source and harmonic impedance of the Norton equivalent circuit are calculated.

[0025] Furthermore, in step S1.3, the control scheme of the photovoltaic converter involved in harmonic control is:

[0026] (1) Detect the harmonic voltage at the grid connection point and adopt harmonic virtual conductance control, (2) detect the local load harmonic current and adopt harmonic current compensation control; then the photovoltaic converter generates the corresponding initial harmonic current reference value according to the virtual conductance or harmonic current compensation coefficient.

[0027] Furthermore, the optimization problem in step S2.2 is specifically expressed as:

[0028] The optimization objective of this optimization problem is to minimize the sum of the total harmonic distortion rates of all node voltages. The constraints of this optimization problem include harmonic power flow constraints, PV converter harmonic compensation capacity constraints, and virtual conductance control stability constraints.

[0029] Harmonic power flow constraints: This refers to the node voltage equation corresponding to the node admittance matrix in the harmonic domain. A control strategy for harmonic control is developed by combining two photovoltaic converters, where the wave virtual conductance is considered as part of the node self-admittance, and the harmonic current compensation coefficient is considered as the node injection current that offsets the harmonic source.

[0030] PV converter three-phase current limit constraint: During operation, the effective value of the three-phase current of the PV converter cannot exceed the maximum limit of the converter;

[0031] Virtual conductance control stability constraint: When the hth harmonic voltage at a node is less than the minimum value allowed by virtual conductance control, the PV converter at that node either does not use virtual conductance control for the hth harmonic or uses virtual conductance control for the hth harmonic. In this case, the hth harmonic voltage at the node after control should be greater than or equal to the minimum value allowed by virtual conductance control.

[0032] Furthermore, the control principle for the current limit correction of the photovoltaic converter using harmonic virtual conductance control in step S3.2 is:

[0033] a. When the harmonic voltages of all nodes requiring compensation are greater than or equal to the minimum value allowed by virtual conductance control, the harmonic adjustment coefficient is equal to the effective value of the sum of the maximum allowable current of the converter divided by the initial reference values ​​of the harmonic compensation currents;

[0034] b. When only the hth node harmonic voltage that needs to be compensated is less than the minimum value allowed by virtual conductance control, the integral control is used to adjust the harmonic adjustment coefficient , so that the hth harmonic is greater than or equal to the minimum value allowed by the virtual conductance control or the corresponding harmonic virtual conductance is equal to 0; When, if satisfied ,in, For the jth harmonic whose harmonic voltage is greater than or equal to the minimum value allowed by virtual conductance control, then the hth harmonic is adjusted according to the previous rule a so that , and follow Adjust all the items that meet the requirements from largest to smallest. If the hth harmonic voltage is less than the minimum value allowed by the virtual conductance control, then adjust according to the integral control ;

[0035] c. If all harmonics that need to be compensated are less than the minimum value allowed by virtual conductance control, use integral control to adjust the harmonic adjustment coefficient , by adjusting the integral control If the effective value of each harmonic superposition is greater than the maximum allowable current of the converter, for the maximum value The corresponding jth harmonic, Equal to the maximum allowable current of the converter and adjusted by integral control The difference between the effective values ​​of all harmonics of the current order is divided by the effective value of the superposition of the initial reference values ​​of the compensation current of each harmonic, and then the rules in b are used to adjust the harmonics of other orders.

[0036] Furthermore, in step S3.2, the control principle for the current limit correction of the photovoltaic converter using harmonic current compensation control is:

[0037] Calculate the effective value of the initial reference value of each harmonic compensation current after superposition, compare it with the maximum allowable current of the converter, and proportionally reduce or expand the compensation coefficient of each harmonic current , so that the reference value of the corrected harmonic compensation current is equal to the maximum allowable current of the converter. , then let , and then recalculate Up to all harmonics Or the reference value of the corrected harmonic compensation current is equal to the maximum allowable current of the converter.

[0038] In a second aspect, the present invention also provides a device for comprehensive harmonic control of a distribution network based on photovoltaic local control, comprising a memory and one or more processors, wherein the memory stores executable code, and when the processor executes the executable code, it implements the method for comprehensive harmonic control of a distribution network based on photovoltaic local control.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention can overcome the limitations of existing centralized control systems, such as low efficiency in large-scale data processing and high real-time control requirements. It only requires the use of the harmonic state estimation results of the existing power quality online monitoring system in the distribution network every 3 minutes, and the one-way communication link between the centralized controller and the photovoltaic power generation system, to achieve harmonic control through two local control schemes: harmonic current compensation control or harmonic virtual conductance control, thereby avoiding the problems caused by communication delays, insufficient computing power, and converter coordination.

[0041] (2) The present invention does not require additional energy storage equipment. While ensuring that the photovoltaic system generates the maximum available power, it distributes compensation instructions according to the remaining capacity of different photovoltaic converters to achieve a comprehensive improvement in the power quality of the distribution network.

[0042] (3) The present invention controls the current of each phase below the maximum allowable current of the photovoltaic converter, maximizes the use of the remaining capacity of the photovoltaic converter, achieves better comprehensive harmonic control effects, and avoids system instability during the harmonic compensation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 Schematic diagram of the hth harmonic Norton equivalent circuit of the harmonic source.

[0045] Figure 2 This is a cluster diagram of typical operation scenarios of distribution networks.

[0046] Figure 3 This is the structure diagram of the local harmonic control strategy of the photovoltaic converter involved in harmonic management.

[0047] Figure 4 This is a flow chart of the proposed comprehensive harmonic control method for distribution network based on photovoltaic local control.

[0048] Figure 5 This is the topology diagram of the IEEE13-node distribution network in the application example.

[0049] Figure 6 is the magnitude of the harmonic current injected by the nonlinear load in the application example.

[0050] Figure 7 is the voltage amplitude of each node before and after harmonic control in the application example.

[0051] Figure 8 This shows the changes in the amplitude of each harmonic voltage at node 3 under all operating conditions in the application example.

[0052] Figure 9 The three-phase current waveforms output by the photovoltaic converter at node 3 in the application example before and after comprehensive harmonic control.

[0053] Figure 10 is the THD of each node after adopting different control strategies in the application example.

[0054] Figure 11 This is the simulation result of the converter current limit correction based on the actual operation of the photovoltaic converter when the photovoltaic converter only compensates the 17th and 19th voltages in the application example.

[0055] Figure 12 This is a structural schematic diagram of a distribution network harmonic comprehensive control device based on photovoltaic local control provided by the present invention. DETAILED DESCRIPTION

[0056] The following is an explanation and description of the technical solutions of the embodiments of the present invention in conjunction with the drawings of the embodiments of the present invention, but the following embodiments are only preferred embodiments of the present invention and are not exhaustive. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0057] Example 1: This example provides a method for comprehensive harmonic control of a distribution network based on photovoltaic local control, comprising the following steps:

[0058] S1, based on the characteristics of the multi-scenario operating status of the power system, clusters the multi-scenario operating status of the power system, which can effectively reduce the computational complexity, retain representative scenarios, configure harmonic control solutions based on typical operating scenarios, and transform the photovoltaic converters involved in harmonic control. The specific process is as follows:

[0059] S1.1, for the harmonic source existing in the node numbered i (subscript i) in the distribution network, considering the modeling accuracy and the difficulty of obtaining model parameters, the harmonic Norton model (HNM) is used to represent it, as shown in Figure 1 As shown, represents the harmonic impedance of the hth harmonic, The parameters of the Norton equivalent circuit are calculated using the wave quantity method, that is, when the power of the harmonic source remains constant for a period of time, at least two different node harmonic voltages are selected or two harmonic voltages are constructed by harmonic compensation through photovoltaic converters, and different harmonic voltages are obtained. The difference between the two is sufficient to cause the harmonic current injected by the harmonic source When a significant change occurs, the Norton equivalent circuit of the hth harmonic can be obtained by the following formula: and :

[0060]

[0061]

[0062] S1.2: Normalize or standardize the power system operating status data (power of nodes within the distribution network, photovoltaic output, harmonic voltages, injected harmonic currents, and system background harmonics). Each sample point represents a power quality management operation scenario. A distance-based K-Means clustering algorithm is used, with the objective function being to minimize the sum of squared distances (WCSS) from the cluster samples to the centroid:

[0063]

[0064] Where K represents the number of clusters, represents the samples of the i-th cluster, each cluster is represented by a centroid, Represents the centroid set of the i-th cluster. The samples are divided into K clusters through iterative optimization. The algorithm achieves clustering by minimizing the distance between the sample and the centroid of the cluster to which it belongs. The specific steps are:

[0065] a. Randomly initialize K centroids.

[0066] b. Assign each sample to the cluster to which the nearest centroid belongs.

[0067] c. Update the centroid of each cluster to the mean of all samples in that cluster.

[0068] d. Repeat steps b and c until the centroid no longer changes or the maximum number of iterations is reached.

[0069] The above method is used to cluster different K values, and the elbow method, Gap Statistic, and Calinski-Harabasz index are used to select the optimal K value. When the K value is small, the similarity of samples within the cluster is high and the similarity between clusters is low. By clustering the distribution network operation status data for one year, a typical operation scenario is constructed, and finally the typical operation scenario of the distribution network and its operation status are obtained. Figure 2 shown.

[0070] S1.3, further configure harmonic control solutions for these typical operating scenarios. For photovoltaic converters involved in harmonic control, their local harmonic control strategies include two types: (1) Detecting the harmonic voltage at the grid connection point And adopt harmonic virtual conductance control, (2) detect local load harmonic current And adopt harmonic current compensation control, the specific control strategy structure diagram is as follows Figure 3 Then the PV converter is based on the virtual conductance Or harmonic current compensation coefficient Generate the corresponding initial harmonic current reference values, the expressions are:

[0071]

[0072]

[0073] In different typical operating scenarios, each PV converter is instructed to adopt the two local control schemes described above to form different PV converter configuration schemes. Harmonic control is then performed in combination with the control instructions of the centralized controller in step S2. The control effect of each PV converter configuration scheme is recorded.

[0074] S1.4. Select the solution with the best comprehensive treatment effect as the configuration solution for the photovoltaic converters in the distribution network (some photovoltaics use harmonic virtual conductance control, and other photovoltaics use harmonic current compensation control). Then, install voltage / current sensors with an accuracy level of less than 0.5% suitable for harmonic treatment at the corresponding nodes, and modify the control strategy of the photovoltaic converter to enable it to have the corresponding harmonic treatment function; at the same time, enable the photovoltaic converter to receive control instructions from the distribution network centralized controller every 3 minutes.

[0075] In S2, the power quality online monitoring system (PQMS) detects the node's harmonic voltage and current vectors and performs harmonic state estimation every 3 minutes. Based on the harmonic state estimation results, the centralized controller optimizes and solves the control instructions for each converter and sends these control instructions to the corresponding PV converter every 3 minutes through one-way communication. The specific process is as follows:

[0076] S2.1. According to the IEC 61000-4-7:2002 standard, the online power quality monitoring system measures the harmonic voltage and current vectors at the distribution network nodes online, performs Fourier harmonic analysis and calculations every 10 grid cycles (0.2s), calculates the average, maximum and minimum values ​​of 900 data points every 3 minutes, and transmits these data to the centralized controller every 3 minutes for harmonic state estimation in accordance with the IEEE 1159.3-2019 power quality data exchange format.

[0077] S2.2, based on the harmonic state estimation results and the harmonic source and line models, an optimization problem is established. The optimization problem takes the comprehensive optimization of the harmonic voltage of the entire distribution network node as the optimization goal, and the harmonic virtual conductance of each photovoltaic converter participating in harmonic control is used as the optimization target. Or harmonic current compensation coefficient As a variable, the centralized controller optimizes and solves the control instructions of each converter. The optimization objective of this optimization problem can be expressed as:

[0078]

[0079] in is the weighted sum of the total harmonic distortion (THD) of the node voltage, is the weight coefficient of node i, is the total harmonic distortion rate of the voltage at node i, is the fundamental voltage of node i. Considering that most of the harmonics in the power grid are Second-rate, It can be expressed as:

[0080]

[0081] The constraints of this optimization problem include harmonic power flow constraints, photovoltaic converter harmonic compensation capacity constraints, and virtual conductance control stability constraints.

[0082] Harmonic power flow constraint: that is, the node voltage equation corresponding to the node admittance matrix in the harmonic domain. For the hth harmonic, we have:

[0083]

[0084] Where, is the column vector of the hth harmonic current injected into the node, is the column vector of node h harmonic voltage, is a The hth harmonic node admittance matrix, including the node self-admittance of node i , and the node mutual admittance between node i and node j The control strategy of combining two photovoltaic converters for harmonic control is presented, in which the wave virtual conductance It can be regarded as part of the node self-admittance, harmonic current compensation coefficient It can be regarded as offsetting the node injection current of the harmonic source, so the above formula can be expressed as:

[0085]

[0086] PV converter three-phase current limit constraint: The effective value of the three-phase current of the PV converter during operation cannot exceed the maximum limit of the converter, that is, the amplitude of the harmonic current injected by the PV converter , fundamental active current , fundamental reactive current The effective value of the superimposed current should be less than the maximum allowable current of the converter ,Right now:

[0087]

[0088] For the photovoltaic converter using harmonic virtual conductance control, the injected harmonic current amplitude is ; For photovoltaic converters using harmonic current compensation control, the injected harmonic current amplitude .

[0089] Stability constraint of virtual conductance control: The larger the virtual harmonic conductance of the photovoltaic converter, the better the harmonic control effect. However, if it is not restricted, when the node h-order harmonic voltage approaches 0, the h-order harmonic virtual conductance may approach infinity, and when the node h-order harmonic voltage is extremely small, it is difficult to accurately measure its amplitude and phase angle, which may easily lead to inaccurate harmonic compensation or even system instability. Therefore, when the h-order harmonic voltage at a certain node is less than the minimum value allowed by virtual conductance control, When the PV converter at this node does not use virtual conductance control for the hth harmonic (for example, 0.2% pu), and if virtual conductance control is used for the hth harmonic, the node hth harmonic voltage after control should be greater than or equal to , the formula corresponding to this constraint can be expressed as:

[0090]

[0091] S2.3, the optimization problem consists of quadratic constraints and bilinear constraints, which is a non-convex quadratic programming problem. Gurobi is used to transform the non-convex quadratic programming into a mixed integer programming problem. By combining branch and bound and heuristic algorithms, after preprocessing and simplifying the model, multi-threading is used to accelerate the search, and the optimal solution is finally found in a short time (usually a few seconds). Then the harmonic virtual conductance obtained is used as the Or harmonic current compensation coefficient As a control instruction, it is sent to each photovoltaic converter involved in harmonic control through one-way communication.

[0092] S3, based on the control instructions obtained in step S2 and the actual operating conditions of the photovoltaic converter involved in harmonic control, ensures that the photovoltaic converter outputs the maximum available power while using the remaining capacity of the converter to control harmonics according to the control instructions received every 3 minutes. The specific process is as follows:

[0093] S3.1. The PV converter involved in harmonic control consists of two parts: a DC-DC converter and a DC-AC converter. The converter uses an LCL filter to suppress harmonics in the switching frequency band and a capacitor branch with a series resistor to suppress the resonant peak of the LCL filter. The DC-DC part is located on the PV side and uses MPPT control to maximize the output power of the PV array. The DC-AC part is located on the grid side and is used to transmit power to the grid and perform harmonic compensation. In addition to the traditional phase-locked loop unit and DC bus voltage control module, this part also includes a harmonic compensation current generation module.

[0094] S3.2, the harmonic compensation current generation module receives the control instruction from the centralized controller through one-way communication, and generates the harmonic compensation current according to the received virtual conductance. Or harmonic current compensation coefficient Generates the initial reference value for harmonic compensation current Then, according to the actual operation of the photovoltaic converter, the converter current limit is corrected to obtain the reference value of the harmonic compensation current. ;

[0095] S3.3, The fundamental active and reactive current reference values ​​obtained by the DC bus voltage control module are added together, and the grid-connected current tracking control is performed through a multi-PR controller in the fundamental and harmonic domains, so that the photovoltaic converter outputs the corresponding fundamental and harmonic currents, realizing comprehensive harmonic control of photovoltaic power generation and distribution network.

[0096] The flow chart of the method for comprehensive control of distribution network harmonics based on photovoltaic local control proposed by the present invention is as follows: Figure 4 As shown, the three parts in the figure correspond to the implementation steps S1, S2, and S3 respectively: S1 realizes the comprehensive harmonic control configuration of the photovoltaic converter, which is a necessary preparation before harmonic control, that is, by clustering the historical data of the distribution network into different typical operation scenarios, and then configuring harmonic control schemes for different typical scenarios, and selecting the scheme with the best comprehensive control effect in each scenario as the configuration scheme of the photovoltaic converter in the distribution network; S2 realizes the state estimation and the optimization solution of the converter control instruction in the centralized controller, which runs once every 3 minutes, that is, through the PQMD monitoring node harmonic voltage and current vector, the monitored data is used to perform harmonic state estimation every 3 minutes, and the harmonic conductance of each photovoltaic converter is optimized. and current compensation coefficient , and send it as a control instruction to each photovoltaic converter participating in harmonic control; S3 implements local control in each photovoltaic converter, and makes real-time adjustments according to the current operating status of the converter. The converter corrects the converter current limit according to the control instruction received every 3 minutes and the actual operating conditions of the photovoltaic converter, generates harmonic current instructions for the converter output, avoids overcurrent while maximizing the use of the remaining capacity of the photovoltaic converter, and then realizes current tracking through PR control. In summary, through the above-mentioned control scheme configuration, centralized optimization solution, and local control correction, the present invention can overcome the limitations of the existing centralized control of low efficiency in large-scale data processing and high requirements for real-time control. While ensuring that the photovoltaic system emits the maximum available power, the compensation instructions are distributed according to the remaining capacity of different photovoltaic converters to achieve a comprehensive improvement in the power quality of the distribution network.

[0097] Example 2: A photovoltaic converter for harmonic control, comprising:

[0098] The DC-DC converter is located on the PV side and uses MPPT control to maximize the power output of the PV array.

[0099] DC-AC converter, located on the grid side, is used to deliver power to the grid and control harmonics;

[0100] The data sampling unit includes an AC voltage and current sensor at the output port of the DC-AC converter and a DC voltage and current sensor at the PV port. The AC voltage and current sensors at the output port of the DC-AC converter are used to sample the current voltage and current at the point of grid connection (PCC) and the current output current. The DC voltage and current sensors at the PV port are used to sample the current port voltage and current of the photovoltaic array.

[0101] Phase-locked loop unit, which determines the angle of the grid connection point voltage through a phase-locked loop (PLL) to keep the converter synchronized with the grid;

[0102] The DC bus voltage control module keeps the voltage on the DC capacitor constant through PI control;

[0103] The grid-connected current tracking control module tracks the reference current through a proportional resonant (PR) controller;

[0104] Photovoltaic power conditioning module, which uses the perturbation and observation method to perform maximum power point tracking (MPPT) and generate the voltage reference value of the photovoltaic array;

[0105] The photovoltaic voltage control module adjusts the voltage of the photovoltaic array to its reference value through voltage and current dual closed-loop control;

[0106] The harmonic compensation current generation module receives control instructions from the centralized controller through one-way communication and generates reference values ​​for the corresponding harmonic compensation currents. ;

[0107] The structure diagram of the local harmonic control strategy of the photovoltaic converter involved in harmonic control is as follows: Figure 3 As shown, the photovoltaic converter is connected to the PCC point through an LCL filter. The DC-DC converter is used to adjust the output of the photovoltaic array, and the perturbation observation method is used to maximize the available power of the photovoltaic output. The DC-AC converter is used to deliver power to the grid while performing harmonic control. In addition to traditional phase locking, DC bus voltage and grid-connected current control, the core of the control strategy involved in this invention is the harmonic compensation current generation module, which generates a reference value of the harmonic compensation current according to the control instructions received from the centralized controller. .

[0108] According to the actual operation of the photovoltaic converter, the converter current limit correction needs to be performed. The specific control strategy is as follows:

[0109] 1) For PV converters using harmonic virtual conductance control:

[0110] a. When the harmonic voltages of all nodes to be compensated are greater than or equal to hour, Compared to Should be returned to the original times, where the harmonic adjustment coefficient equal Divide by each Effective value after superposition;

[0111] b. When the harmonic voltage of some nodes to be compensated is less than , and the harmonic voltages of other orders are greater than or equal to When the harmonic voltage is less than The hth harmonic is adjusted by integral control , so that the hth harmonic is greater than or equal to Or let the corresponding harmonic virtual conductance be equal to 0; for harmonic voltage greater than The jth harmonic, equal Adjust with integral control The difference between the effective values ​​of all harmonics of The effective value after superposition; when adjusted by integral control When, if satisfied , then the hth harmonic should be adjusted according to the previous rule so that , and according to this rule Adjust all the items that meet the requirements from largest to smallest. harmonics of order h, then if the harmonic voltage is less than Then adjust according to the integral control ;

[0112] c. If all harmonics to be compensated are less than , using integral control to adjust , by adjusting the integral control When the effective value of each harmonic superposition is greater than , for the largest value The corresponding jth harmonic, equal Adjust with other integral control The difference between the effective values ​​of all harmonics of The effective value after superposition, and then use the last rule in b to adjust the harmonics of other orders.

[0113] 2) For photovoltaic converters using harmonic current compensation control:

[0114] Calculate each time The effective value after superposition, if it is greater than , then reduce each time in equal proportion Make equal If it is less than , then the proportion of each Make equal In this process, if the hth harmonic corresponds to , then let , and then recalculate according to the above rules Up to all harmonics or equal .

[0115] Application example: In order to verify the effectiveness of the proposed control strategy, an IEEE13-node distribution network consisting of three photovoltaic converters, seven nonlinear loads and linear loads at each node was selected, such as Figure 5As shown in Figure 1, node 1 is the low-voltage side node of the transformer. The rated frequency of the power grid is 50Hz, and the transmission network consists of 50km of three-phase overhead lines and a 10kV / 400V transformer with a short-circuit impedance of 6%. The calculation is evenly proportionally converted to the low-voltage side. The voltage level in the distribution network is 230 / 400V, and the line is a 150-300m YJV cable. The distribution network line parameters are shown in Table 1. The nonlinear loads in the distribution network are all six-pulse rectifiers, connected to nodes 3, 4, 5, 8, 10, 12, and 14, with power of 12kW, 4kW, 7kW, 10kW, 7kW, 10kW, and 7kW respectively. The magnitude of the injected harmonic current is shown in Table 1. Figure 6 As shown in the figure, the three photovoltaic converters involved in harmonic compensation are common household three-phase photovoltaic converters with a rated power of 10kW, a switching frequency of 20kHz, LCL converter parameters of 2mH / 3uF / 0.2mH, and a maximum allowable current of each phase of 1.1 times the current corresponding to the maximum photovoltaic power.

[0116] The application example was simulated and tested using MATLAB / Similink. After configuring harmonic control solutions for different typical scenarios with sufficient sunlight, the solution with the best comprehensive control effect in each scenario was selected as the configuration solution for the photovoltaic converters in the distribution network. That is, the photovoltaic converter at node 14 uses harmonic virtual conductance control, and the photovoltaic converters at nodes 3 and 12 use harmonic current compensation control. The system's initial state does not contain any harmonic control measures. Through harmonic state estimation, the harmonic conductance of each photovoltaic converter is optimized and solved. and current compensation coefficient At the first second, it is sent as a control instruction to each photovoltaic converter participating in harmonic control and comprehensive harmonic control is performed. At 1.4 seconds, the harmonic compensation capacity of the photovoltaic converter is reduced by 20% due to light fluctuations. At 1.7 seconds, the harmonic source of node 8 is cut off.

[0117] Table 1 Distribution network line parameters

[0118]

[0119] Figures 7 to 10 The simulation results of multiple operating conditions in the application example of the present invention are as follows: Figure 7 (a) and Figure 7 As shown in (b), Figure 8 is the change of each harmonic voltage amplitude of node 3 under all working conditions, Figure 7 and Figure 8It can be seen that after the harmonic comprehensive management control strategy proposed in this patent is adopted in the first second, the harmonic voltage of each node is managed to a certain extent, and the power quality in the distribution network is comprehensively improved. Moreover, after the occurrence of events such as the adoption of harmonic comprehensive management, the reduction of harmonic compensation capacity, and the switching out of harmonic sources, the harmonic voltage of node 3 changes accordingly under the harmonic comprehensive management control strategy and can transition to a steady state in a short time. Figure 9 The three-phase current waveforms output by the photovoltaic converter at node 3 before and after comprehensive harmonic control are shown. It can be seen that after adopting comprehensive harmonic control, the photovoltaic converter participating in unbalance compensation can respond quickly to control instructions and the three-phase current is maintained within the maximum allowable current.

[0120] Figure 10 The THD of each node after adopting different control strategies, among which the traditional distributed control is that the photovoltaic converter detects the current of the local harmonic source and compensates according to its own capacity. It is the most commonly used harmonic compensation strategy in engineering, and the control strategy does not require communication; the control algorithm of harmonic virtual conductance control is referenced in [1] Lijuan Lin, etal. Partitional Collaborative Mitigation Strategy of Distribution Network Harmonics Based on Distributed Model Predictive Control [J]. IEEE Trans. Smartgrid, 14(3), pp.1998-2009, 2023, and the harmonic virtual conductance values ​​of each node are listed in Table 2; the harmonic virtual conductance and harmonic current compensation coefficient of the method proposed in this patent are also listed in Table 2. Figure 10 It can be seen that the initial average THD of the voltage at each node in the distribution network is 6.945%. After adopting the traditional distributed control, the average THD is reduced to 4.766%. After adopting the harmonic virtual conductance control in the literature [1], the average THD is reduced to 4.059%. After adopting the harmonic comprehensive control control strategy proposed in this patent, the average THD of the voltage at each node is reduced to 3.863%, which has better harmonic control effect than the existing methods.

[0121] Table 2 Harmonic compensation configuration in different control methods

[0122]

[0123] Figure 11This is the simulation result of correcting the converter current limit according to the actual operation of the photovoltaic converter when the photovoltaic converter only compensates for the 17th and 19th voltages. In this simulation, only the harmonic source and photovoltaic converter at node 3 are retained in the distribution network to demonstrate the stability of the control strategy and the ability to compensate for harmonics in stages when the harmonic voltage is low. The photovoltaic converter adopts virtual conductance control and the harmonic capacity is set to 1A. Figure 11 (a) shows the minimum value allowed by virtual conductance control before and after harmonic control. The waveform of the voltage amplitude of node 3 at each time when it changes, Figure 11 (b) shows the changes in the harmonic adjustment coefficients corresponding to the 17th and 19th harmonics. Figure 11 (c) is the effective value of the harmonic current injected by the photovoltaic converter, which is given by Figure 11 It can be seen that when the operating conditions of the photovoltaic converter change, the harmonic current output by the converter can be adjusted according to the rules of the converter current limit correction, avoiding overcurrent while maximizing the use of the remaining capacity of the photovoltaic converter and avoiding the risk of system instability in harmonic virtual conductance control.

[0124] See also Figure 12 An embodiment of the present invention provides a distribution network harmonic comprehensive control device based on photovoltaic local control, including a memory and one or more processors. The memory stores executable code, and when the processor executes the executable code, it is used to implement a distribution network harmonic comprehensive control method based on photovoltaic local control in the above embodiment.

[0125] The embodiment of the comprehensive harmonic control device for distribution network based on photovoltaic local control provided by the present invention can be applied to any device with data processing capability, and the device with data processing capability can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capability in which it is located reading the corresponding computer program instructions in the non-volatile memory into the memory for execution. From the hardware level, if Figure 12 As shown in the figure, it is a hardware structure diagram of any device with data processing capability where a photovoltaic local control-based distribution network harmonic comprehensive treatment device is provided by the present invention, except Figure 12 In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities in which the apparatus in the embodiment is located may also include other hardware, generally based on the actual functions of the device with data processing capabilities, which will not be described in detail.

[0126] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0127] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present invention. A person of ordinary skill in the art can understand and implement the present invention without inventive work.

[0128] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, a method for comprehensive harmonic control of a distribution network based on photovoltaic local control in the above embodiment is implemented.

[0129] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the aforementioned embodiments, such as a hard disk or memory. The computer-readable storage medium may also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store data that has been output or is to be output.

[0130] The present invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the method for comprehensive harmonic control of distribution network based on photovoltaic local control.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for comprehensive harmonic control of distribution network based on photovoltaic local control, characterized in that: The steps include: S1: Cluster the operating status according to the power system scenario to construct a typical operating scenario; for the photovoltaic converters involved in harmonic control, configure the harmonic control solution based on the typical operating scenario; the specific process is as follows: S1.1, for the harmonic sources existing in the nodes of the distribution network, the harmonic Norton equivalent circuit HNM is used to represent them; S1.2, pre-processing the power system operation status data and clustering the distribution network operation status data to construct typical operation scenarios; S1.3, configure harmonic control solutions for typical operating scenarios; For PV converters involved in harmonic control, there are two local harmonic control methods: (1) detecting the grid-connected point harmonic voltage and adopting harmonic virtual conductance control; (2) detecting the local load harmonic current and adopting harmonic current compensation control. Under different typical operating scenarios, each PV converter is respectively configured to adopt the above two local control schemes to form different PV converter configuration schemes. S1.4: For the configuration of photovoltaic converters in the distribution network, some photovoltaic converters adopt harmonic virtual conductance control, while others adopt harmonic current compensation control. Then, voltage / current sensors suitable for harmonic control are installed at the corresponding nodes, and the control strategy of the photovoltaic converter is modified to enable it to receive corresponding control instructions to achieve harmonic control function. S2: The power quality online monitoring system (PQMS) detects the node's harmonic voltage and current vectors and performs harmonic state estimation. Based on the harmonic state estimation results, the centralized controller optimizes and solves the control instructions for each converter and sends the control instructions to the corresponding PV converter through one-way communication. S3, based on the control instruction obtained in step S2 and the actual operation of the photovoltaic converter involved in harmonic control, ensures that the photovoltaic converter outputs the maximum available power while utilizing the remaining capacity of the converter for harmonic control according to the received control instruction.

2. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 1 is characterized in that: The specific process of step S2 is: S2.1, the power quality online monitoring system measures the harmonic voltage and current vectors of the distribution network nodes online, performs Fourier harmonic analysis and calculation, and transmits the average, maximum and minimum values ​​of the statistical data to the centralized controller for harmonic state estimation; S2.2, based on the harmonic state estimation results and the harmonic source and line models, establish an optimization problem. This optimization problem takes the comprehensive optimization of the harmonic voltage of the entire distribution network node as the optimization objective, and uses the harmonic virtual conductance or harmonic current compensation coefficient of each PV converter participating in harmonic control as the variable; S2.3, the centralized controller optimizes and solves the control instructions of each converter, converts the optimization problem into a mixed integer programming problem, and finally finds the optimal solution by combining branch and bound and heuristic algorithms; then the obtained harmonic virtual conductance or harmonic current compensation coefficient is sent as a control instruction to each photovoltaic converter participating in harmonic management.

3. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 1 is characterized in that: The specific process of step S3 is: S3.

1. The PV converter involved in harmonic control consists of two parts: a DC-DC converter and a DC-AC converter. The DC-DC converter is located on the PV side and uses MPPT control to maximize the PV array's power output. The DC-AC converter is located on the grid side and is used to transmit power to the grid and perform harmonic compensation. S3.2, the DC-AC part receives control instructions from the centralized controller, generates an initial reference value for the harmonic compensation current based on the received harmonic virtual conductance or harmonic current compensation coefficient, and then performs converter current limiting correction based on the actual operating conditions of the PV converter to obtain a corrected reference value for the harmonic compensation current; S3.3, the reference value of the corrected harmonic compensation current is added to the reference value of the fundamental active and reactive current, and the grid-connected current tracking control is performed through the multi-PR controller in the fundamental and harmonic domains, so that the photovoltaic converter outputs the corresponding fundamental and harmonic currents, realizing comprehensive harmonic control of photovoltaic power generation and distribution network.

4. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 1 is characterized in that: In step S1.1, the parameters of the Norton equivalent circuit are calculated using the wave quantity method, that is, when the power of the harmonic source remains unchanged for a period of time, at least two different node harmonic voltages are selected or two harmonic voltages are constructed through harmonic compensation through photovoltaic converters, and the difference between different harmonic voltages is sufficient to cause a significant change in the harmonic current injected by the harmonic source, the harmonic current source and harmonic impedance of the Norton equivalent circuit are calculated.

5. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 1 is characterized in that: In step S1.3, the control scheme of the photovoltaic converter involved in harmonic control is: (1) Detect the harmonic voltage at the grid connection point and adopt harmonic virtual conductance control, (2) detect the local load harmonic current and adopt harmonic current compensation control; then the photovoltaic converter generates the corresponding initial harmonic current reference value according to the virtual conductance or harmonic current compensation coefficient.

6. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 2 is characterized in that: The optimization problem in step S2.2 is specifically expressed as: The optimization objective of this optimization problem is to minimize the sum of the total harmonic distortion rates of all node voltages. The constraints of this optimization problem include harmonic power flow constraints, PV converter harmonic compensation capacity constraints, and virtual conductance control stability constraints. Harmonic power flow constraints: This refers to the node voltage equation corresponding to the node admittance matrix in the harmonic domain. A control strategy for harmonic control is developed by combining two photovoltaic converters, where the wave virtual conductance is considered as part of the node self-admittance, and the harmonic current compensation coefficient is considered as the node injection current that offsets the harmonic source. PV converter three-phase current limit constraint: During operation, the effective value of the three-phase current of the PV converter cannot exceed the maximum limit of the converter; Virtual conductance control stability constraint: When the hth harmonic voltage at a node is less than the minimum value allowed by virtual conductance control, the PV converter at that node either does not use virtual conductance control for the hth harmonic or uses virtual conductance control for the hth harmonic. In this case, the hth harmonic voltage at the node after control should be greater than or equal to the minimum value allowed by virtual conductance control.

7. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 3 is characterized in that: The control principle for the current limit correction of the photovoltaic converter using harmonic virtual conductance control in step S3.2 is: a. When the harmonic voltages of all nodes requiring compensation are greater than or equal to the minimum value allowed by virtual conductance control, the harmonic adjustment coefficient is equal to the effective value of the sum of the maximum allowable current of the converter divided by the initial reference values ​​of the harmonic compensation currents; b. When only the hth node harmonic voltage that needs to be compensated is less than the minimum value allowed by virtual conductance control, the integral control is used to adjust the harmonic adjustment coefficient , so that the hth harmonic is greater than or equal to the minimum value allowed by the virtual conductance control or the corresponding harmonic virtual conductance is equal to 0; When, if satisfied ,in, For the jth harmonic whose harmonic voltage is greater than or equal to the minimum value allowed by virtual conductance control, then the hth harmonic is adjusted according to the previous rule a so that , and follow Adjust all the items that meet the requirements from largest to smallest. harmonics of order h, then if the harmonic voltage is less than Then adjust according to the integral control ; c. If all harmonics that need to be compensated are less than the minimum value allowed by virtual conductance control, use integral control to adjust the harmonic adjustment coefficient , by adjusting the integral control If the effective value of each harmonic superposition is greater than the maximum allowable current of the converter, for the maximum value The corresponding jth harmonic, Equal to the maximum allowable current of the converter and adjusted by integral control The difference between the effective values ​​of all harmonics of the current order is divided by the effective value of the superposition of the initial reference values ​​of the compensation current of each harmonic, and then the rules in b are used to adjust the harmonics of other orders.

8. The method for comprehensive harmonic control of distribution network based on photovoltaic local control according to claim 3 is characterized in that: In step S3.2, the control principle for the current limit correction of the photovoltaic converter using harmonic current compensation control is: Calculate the effective value of the initial reference value of each harmonic compensation current after superposition, compare it with the maximum allowable current of the converter, and proportionally reduce or expand the compensation coefficient of each harmonic current , so that the reference value of the corrected harmonic compensation current is equal to the maximum allowable current of the converter. , then let , and then recalculate Up to all harmonics Or the reference value of the corrected harmonic compensation current is equal to the maximum allowable current of the converter.

9. A device for comprehensive harmonic control of distribution network based on photovoltaic local control, comprising a memory and one or more processors, wherein the memory stores executable code, characterized in that: When the processor executes the executable code, a comprehensive method for controlling harmonics in a distribution network based on photovoltaic local control according to any one of claims 1 to 8 is implemented.

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