Distributed voltage control optimization method and system for three-phase unbalanced distribution network

Abstract

This disclosure relates to the field of voltage control technology, and proposes a distributed voltage control optimization method and system for three-phase unbalanced distribution networks. It uses the active and reactive power output by single-phase distributed power sources connected to the distribution network and the three-phase distributed power sources as the control objects. By coordinating the power injected into each phase of the distribution network by the distributed power sources, it reduces the deviation of voltage at each node from the voltage reference value and the phase-to-phase voltage deviation, thereby achieving stable control of the voltage of each phase at each node of the distribution network. Two different control modes are designed according to the different degrees of voltage deviation in the three-phase distribution network, taking into account both voltage coordination and the maximum utilization of distributed generation (DG) energy. The distributed controller only communicates with adjacent units, reducing the requirements for the controller's computing power and communication performance.

Description

Technical Field

[0001] This disclosure relates to the technical field of voltage control, specifically to a distributed voltage control optimization method and system for a three-phase unbalanced distribution network. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] Modern society's demand for electricity is constantly increasing, while traditional fossil fuels are becoming increasingly scarce. Furthermore, the combustion of fossil fuels has generated a series of environmental problems. Therefore, there is an urgent need to utilize new energy forms for power generation and build clean and efficient new power systems. Distributed generation (DG) technology, with solar and wind power as its main energy sources, is developing rapidly. Especially with the continuous breakthroughs in power electronics technology, large-scale distributed power grid connection control has become possible. Currently, the proportion of photovoltaic power generation connected to the distribution network is gradually increasing, relieving the pressure on traditional thermal power units and greatly reducing the energy and environmental burden. However, the inherent uncertainty and intermittency of new energy sources also bring a series of new power quality problems. Distribution network voltage will rise to varying degrees due to the connection of distributed generation (DG), and voltage fluctuations will become more frequent. Especially with the connection of single-phase DG, such as rooftop photovoltaics, the distribution network system will operate in a three-phase unbalanced state, generating unbalanced voltage, increasing line losses, and affecting the normal operation of equipment. Therefore, research on optimized control methods for three-phase unbalanced distribution network voltage / power is particularly important.

[0004] According to the inventors, due to the relatively high impedance of the distribution network, the impact of both active and reactive power injection on node voltage cannot be ignored. However, with the development of power electronics technology, the output power of inverter-connected distributed generation (DG) systems can be rapidly and continuously regulated. This has made DG systems a key component in distribution network voltage regulation. Distribution network voltage control strategies that optimize DG output power can be categorized into three types based on their control structure:

[0005] 1) Distributed control. Local controllers use various distributed control algorithms, such as droop control and power factor control, to locally calculate the output power of the distributed generation (DG) to regulate the voltage. Distributed control does not require communication or a central controller, resulting in lower communication costs and less computational burden on the controller. However, it cannot achieve optimal control of the entire distribution network voltage.

[0006] 2) Centralized Control. A centralized controller collects and monitors the status information of the entire distribution network, and performs calculations using a specific optimization algorithm to obtain the DG power output that minimizes the deviation of the distribution network nodes. Centralized control can coordinate the power output of each DG unit, achieving optimal control of the entire distribution network voltage. However, it requires a centralized controller with strong computing power and needs to monitor global information; therefore, the controller has a large computational load and extremely high communication requirements.

[0007] 3) Distributed Control. Distributed control decomposes the global optimization problem into multiple sub-problems, which are then calculated in different distributed controllers to obtain the optimal power output of the distributed generation (DG) that can regulate the voltage of the entire distribution network. Distributed control can better coordinate the various DG units and distribute the total computational load of solving the control problem, reducing the computational burden on each controller. However, the design of the distributed control scheme has a significant impact on the control performance.

[0008] Furthermore, most existing research on distribution network voltage control strategies is based on the single-phase voltage power response principle. When the distribution network is operating in a balanced state, these control schemes can effectively regulate the voltage. However, when the distribution network is operating in a three-phase unbalanced state, control strategies based on the single-phase voltage power response principle may worsen the distribution network voltage. Research on three-phase unbalanced distribution network voltage control strategies is limited, and most studies focus only on the power control of single-phase distributed generation (DG), failing to leverage the independent power control capabilities of each phase of the three-phase DG. Summary of the Invention

[0009] To address the aforementioned issues, this disclosure proposes a distributed voltage control optimization method and system for three-phase unbalanced distribution networks. It uses the active and reactive power output by single-phase distributed generation sources connected to the distribution network and the three-phase distributed generation sources as the control objects. By coordinating the power injected into each phase of the distribution network by the distributed generation sources, it reduces the deviations between the voltage at each node and the voltage reference value, as well as the phase-to-phase voltage deviations, thereby achieving stable control of the voltage of each phase at each node of the distribution network. Two different control modes are designed based on the different degrees of voltage deviation in the three-phase distribution network, balancing voltage coordination and the maximum utilization of distributed generation (DG) energy. The distributed controller only communicates with adjacent units, reducing the requirements for the controller's computing power and communication performance.

[0010] To achieve the above objectives, the present disclosure adopts the following technical solution:

[0011] One or more embodiments provide a distributed voltage control optimization method for a three-phase unbalanced distribution network, comprising the following steps:

[0012] Based on the obtained phase voltages of each node in the distribution network, determine the degree of voltage deviation in the three-phase distribution network;

[0013] Select the control mode based on the degree of voltage deviation in the three-phase distribution network;

[0014] When the distribution network voltage deviation is less than the set voltage deviation threshold, the control operates in the preventive control mode, and the DG operates in the maximum power point tracking state, adjusting the distribution network voltage by optimizing the reactive power output of each phase of the DG.

[0015] When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage.

[0016] One or more embodiments provide a distributed voltage control optimization system for a three-phase unbalanced distribution network, comprising: a distributed DG controller installed at each DG power source access point, each distributed DG controller being communicatively connected to a corresponding DG power source and controlling the output power of the corresponding DG power source, and each distributed DG controller being communicatively connected to adjacent distributed DG controllers; the distributed DG controllers executing the aforementioned distributed voltage control optimization method for a three-phase unbalanced distribution network.

[0017] One or more embodiments provide a distributed voltage control optimization system for a three-phase unbalanced distribution network, comprising:

[0018] Judgment module: configured to determine the degree of three-phase distribution network voltage deviation based on the acquired phase voltages of each node in the distribution network;

[0019] Mode selection module: configured to select the control mode based on the degree of three-phase distribution network voltage deviation;

[0020] DG calculation and control module: It is configured to operate in preventive control mode when the distribution network voltage deviation is less than the set voltage deviation threshold, and the DG operates in maximum power point tracking state to adjust the distribution network voltage by optimizing the reactive power output of each phase of the DG.

[0021] When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage.

[0022] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0023] In this disclosure, the voltage control mode of the controller is determined based on the phase voltage of each measuring node and the phase power output of each distributed generation (DG). When the phase voltage deviation is small, the preventive control mode is selected, while when the phase voltage deviation is large, the emergency control mode is used. Then, combined with the power information transmitted by adjacent controllers, the distributed DG controller uses a distributed model predictive control algorithm to optimize and calculate the optimal DG power output value that minimizes the objective function in the corresponding control mode, thereby minimizing the deviation between the phase voltage and the reference value of the three-phase unbalanced distribution network.

[0024] The advantages of this disclosure, as well as its additional advantages, will be described in detail in the following specific embodiments. Attached Figure Description

[0025] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute a limitation thereof.

[0026] Figure 1 A typical three-phase unbalanced distribution network structure diagram provided in Embodiment 1 of this disclosure;

[0027] Figure 2 This disclosure presents a schematic flowchart of a distributed voltage control method according to Embodiment 2.

[0028] Figure 3 Simulation example of Embodiment 2 of this disclosure: Three-phase voltage diagram of a typical node in a three-phase distribution network under normal operating conditions using the method of this disclosure;

[0029] Figure 4 The simulation example of Embodiment 2 of this disclosure shows the three-phase voltage diagram of a typical node in a three-phase distribution network after applying the control method of this disclosure under normal operating conditions.

[0030] Figure 5 The simulation example of Embodiment 2 of this disclosure shows the average voltage deviation of the entire three-phase distribution network in phase A before and after applying the control method of this disclosure under normal operating conditions.

[0031] Figure 6 Simulation example of Embodiment 2 of this disclosure: Three-phase voltage diagram of a typical node in a three-phase distribution network under a large disturbance, applying the control method of this disclosure;

[0032] Figure 7 The simulation example of Embodiment 2 of this disclosure shows the three-phase voltage diagram of a typical node in a three-phase distribution network after applying the control method of this disclosure under a large disturbance (large disturbance situation - emergency control mode);

[0033] Figure 8 The simulation example of Embodiment 2 of this disclosure shows the average voltage deviation of the entire three-phase distribution network in phase A before and after applying the control method of this disclosure under a large disturbance (under a large disturbance). Detailed Implementation

[0034] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0036] It should be noted that the terminology used herein is for descriptive purposes only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. It should be noted that, without conflict, the various embodiments and features within those embodiments can be combined with each other. The embodiments will now be described in detail with reference to the accompanying drawings.

[0037] To achieve stable voltage control in a three-phase unbalanced distribution network while coordinating the active and reactive power outputs of both single-phase and three-phase distributed generation (DG) units, fully leveraging their respective regulatory roles, and minimizing demands on communication and computing performance, this disclosure proposes a distributed voltage optimization control method. This method optimizes and coordinates the active and reactive power outputs of each phase of the DG unit, bringing the three-phase voltages of each bus in the distribution network close to the voltage reference value, thereby achieving stable voltage control in the three-phase unbalanced distribution network and mitigating voltage fluctuations. Specific embodiments are described below.

[0038] Example 1

[0039] In one or more of the technical solutions disclosed in the embodiments, such as Figures 1-2 As shown, this embodiment provides a distributed voltage control optimization system for a three-phase unbalanced distribution network, including a distributed DG controller set at each DG power source access point. Each distributed DG controller is communicatively connected to the corresponding DG power source and controls the output power of the corresponding DG power source. Each distributed DG controller is communicatively connected to adjacent distributed DG controllers, and each distributed DG controller controls the power output of the distributed power source (DG) connected to it.

[0040] In this embodiment, each distributed DG controller in the DG control section determines its voltage control mode by measuring the phase voltage of each node and the phase power output of the DG. When the phase voltage deviation is small, a preventive control mode is selected, while when the phase voltage deviation is large, an emergency control mode is operated. Then, combining the power information transmitted by adjacent controllers, the distributed DG controller uses a distributed model predictive control algorithm to optimize and calculate the optimal DG power output value that minimizes the objective function in the corresponding control mode, thereby minimizing the deviation between the phase voltage and the reference value of the three-phase unbalanced distribution network.

[0041] Furthermore, it also includes an adjacent controller communication channel, which is used to establish a two-way connection between geographically adjacent DG controllers, share the power information calculated by the DG control system, and achieve the purpose of coordinated control between the outputs of each DG in a distributed manner, so as to realize the optimal control of the three-phase distribution network as a whole.

[0042] In this embodiment, the distributed generation controller communicates only with adjacent controllers, reducing the requirements for communication performance and controller computing power. At the same time, it ensures the energy utilization of distributed power sources, reduces energy waste, and achieves stable control of the three-phase voltage of the distribution network.

[0043] Because the operating conditions of a three-phase distribution network vary, the deviation of each phase voltage from the reference value differs, and the demand for voltage regulation also varies. Therefore, while ensuring the effectiveness of three-phase voltage regulation, this embodiment designs two different control modes: a preventive control mode and an emergency control mode. When the distribution network voltage deviation is less than a preset voltage deviation threshold, the distributed controller operates in preventive control mode, and the DG operates in maximum power point tracking (MPPT) state, adjusting the distribution network voltage only by optimizing the reactive power output of each phase of the DG. When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the distributed controller operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to adjust the distribution network voltage.

[0044] The two control modes differ in their specific implementation methods due to the different control variables they consider, as detailed below:

[0045] In the preventive control mode, the distributed generation (DG) control is designed to address the voltage control problem in the three-phase distribution network. A distributed model predictive control is established, using measured network information and power information transmitted from adjacent controllers to optimize the reactive power output of each phase of the DG, thereby reducing voltage deviations in each phase of the distribution network. Under this control mode, the DG operates in maximum power point tracking (MPPT) mode. The reactive power output of the DG is constrained based on its rated power. Considering actual operating conditions and states, network power flow is constrained, further reducing the variation in reactive power output of each phase of the DG and meeting the requirements of actual operation.

[0046] The distributed generation (DG) is in emergency control mode. To ensure that the three-phase distribution network voltage can be effectively controlled as soon as possible, the active and reactive power outputs of each phase of the DG are coordinated and optimized. Similarly, the distributed model predictive control algorithm is used to solve the objective function of reducing the voltage deviation of each phase of the distribution network, so as to achieve rapid and stable control of the three-phase distribution network. In this process, the active power output of each phase of the DG is controlled. The active power output constraint of the DG is calculated based on the measured active power of the DG, and then the reactive power output constraint of the DG is obtained by combining the rated power. At the same time, the attenuation of the active power output of each phase of the DG is minimized, so as to reduce energy waste while ensuring stable control of the voltage of each phase.

[0047] In other words, the control process of the distributed voltage control system in this embodiment is as follows:

[0048] Three-phase power distribution network operation;

[0049] The distributed generation (DG) controller measures the voltage information of each phase of the distribution network node, determines the network operating status, and selects the operating mode of the controller. Then, based on the measured power output information of each phase of the DG, it obtains the DG output limit constraint. Then, combined with the power information transmitted by the adjacent controller, it calculates the power output of each phase of the DG that satisfies the objective of minimizing the deviation between the voltage of each phase of the distribution network and the reference value. The control command is then sent to the distributed power generation device to realize voltage control, and at the same time, the calculated optimal power information is transmitted to the adjacent controller.

[0050] Example 2

[0051] In one or more of the technical solutions disclosed in the embodiments, such as Figures 1-8 As shown, a distributed voltage control optimization method for a three-phase unbalanced distribution network can be implemented in each distributed generation (DG) controller, including the following steps:

[0052] Step 1: Determine the degree of voltage deviation in the three-phase distribution network based on the obtained phase voltages of each node in the distribution network;

[0053] Step 2: Select the control mode based on the degree of three-phase distribution network voltage deviation;

[0054] When the distribution network voltage deviation is less than the set voltage deviation threshold, the control operates in the preventive control mode, and the DG operates in the maximum power point tracking state, adjusting the distribution network voltage by optimizing the reactive power output of each phase of the DG.

[0055] When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage.

[0056] A specific implementation scheme, prevention and control mode: taking the reactive power output of DG as the control object, taking the minimum voltage deviation of each phase of the distribution network and the minimum change of DG reactive power output as the objective function, and solving to obtain the optimal DG reactive power output command.

[0057] Emergency control mode: The active and reactive power outputs of each phase of the DG are taken as the control objects. The objective functions are to minimize the voltage deviation of each phase of the distribution network and the active power attenuation of the DG. The optimal active and reactive power output commands of the DG are obtained by solving the problem and feeding them back to the DG to realize the voltage control of each phase.

[0058] In this embodiment, the active and reactive power outputs of each phase of a single-phase distributed power source and a three-phase distributed power source in a three-phase distribution network are taken as the control objects. Two control modes are designed according to different operating states of the distribution network. By coordinating the power output of each phase of the distributed power source, stable control of the voltage of each phase of each node in the distribution network is achieved.

[0059] In a specific embodiment, the control mode is selected based on the degree of three-phase distribution network voltage deviation, which is the mode selection part:

[0060] Based on the relationship between the measured voltage deviation of each phase of the node and the preset voltage deviation threshold, the operating status of the three-phase distribution network and the demand for voltage regulation are determined, thereby deciding the control mode of the distributed controller.

[0061] If the voltage deviation of all nodes is within the threshold, that is... The distributed controller operates in preventative control mode. Where V... j (0) represents the measured voltage amplitude of a phase at a node in a three-phase distribution network. Here, each phase of all nodes is treated as a separate point and renumbered; V ref This represents the reference voltage, which is set to 1.0 pu in this embodiment; V pre The voltage deviation threshold can be set to 0.2 pu in this embodiment. If the voltage deviation of any node exceeds the threshold, the distributed controller will operate in emergency control mode.

[0062] Furthermore, it also includes a mode switching method. Before the mode selection in step 2, the predicted voltage after the predicted mode switching is first calculated. Then, based on the relationship between the predicted voltage and the voltage deviation of each phase of the node and the preset voltage deviation threshold, it is determined whether to switch the control mode so that all bus voltages after the mode switching are within the set deviation range to achieve mode switching.

[0063] A mode switching scheme that uses mode changes to predict voltage can assist in mode selection and switching, and can avoid rapid voltage fluctuations caused by frequent changes in control mode.

[0064] After confirming that the distributed DG controller is running in prevention mode:

[0065] Distributed generation (DG) operates in maximum power point tracking (MPPT) mode. The reactive power limit constraints of each phase of the distributed generation are determined based on the reactive power output of a single-phase DG and the active power output of each phase of the DG. The network power flow constraints are determined based on the voltage flow relationship of the three-phase distribution network.

[0066] Based on the objective function and constraints, determine the measured values ​​required for control and the DG output power data transmitted by adjacent controllers;

[0067] The optimal reactive power output of each phase of the DG is calculated based on the measured values ​​of the three-phase distribution network and the power data transmitted by adjacent controllers according to the distributed model predictive control (DMPC) algorithm.

[0068] After optimization calculation, the calculation result command is sent to the distributed generation unit to control its reactive power output, and the calculation result is transmitted to the adjacent controller to coordinate the reactive power output of each distributed power source and achieve voltage stability of the distribution network.

[0069] In a specific implementation example, the prevention and control model section includes:

[0070] 1) Construct an optimization objective function that includes voltage stability requirements and reactive power margin requirements of distributed generation (DG): The objective function is to minimize the voltage deviation of each phase in the distribution network and the change in reactive power output of the DG. Specifically, the objective function of the preventive control mode can be expressed as: minimizing the sum of the squares of the deviations between the voltage of each phase at each node in the three-phase distribution network and its voltage reference value, and the Euclidean norm of the change in reactive power generated by the DG;

[0071] The method in this embodiment is applied to the voltage control of a three-phase distribution network. The main problem it solves is the stability of the voltage of each phase at each node. The DG controller in this part operates in a preventive control mode, and the control variable is the reactive power output of each phase of the DG. Therefore, while regulating the voltage, the reduction of reactive power changes in each phase of the DG is considered. The optimized objective function is as follows:

[0072]

[0073] Where, ΔQ DGi The reactive power output change vector of each phase of DGi is represented by Q. DGi,φ Composition: If DGi is a single-phase distributed power source, then ΔQ DGi The change in reactive power injection in this phase can be denoted as ΔQ. SDGi If DGi is a three-phase distributed power source, then ΔQ DGi N represents the vector composed of changes in three-phase reactive power; PThis represents the prediction step size of the distributed model predictive control algorithm; N is the number of nodes in the three-phase distribution network, and 3*N indicates that the voltage of each phase at each node is processed separately; w vj and W Qi These are the weighting coefficients for voltage deviation and reactive power output variation, and their specific values ​​can be adjusted according to different application scenarios. The first term on the right side of the objective function is to minimize the voltage deviation of each phase of each node from the set voltage reference value, and the second term is to minimize the reactive power output variation of each phase of the DG.

[0074] 2) Determine the reactive power output constraints of each phase of the DG and the distribution network voltage constraints expressed in terms of voltage sensitivity:

[0075] The constraints of the objective function in Formula 1 can include two parts: equality constraints considering the relationship between the voltage of each node and the power injection of each phase in the three-phase distribution network, and inequality constraints considering the reactive power output limit of each phase of the DG.

[0076] Optionally, considering the inequality constraints on the reactive power output of each phase of the DG unit, i.e., the reactive power output of the DG determined by the inverter should be between the upper and lower limits of its capacity, can be determined based on the active power output of the DG maximum power point tracking and the rated power of the DG.

[0077]

[0078] Among them, Q DGi,φ S DGi,φ and P DGiM,φ These represent the reactive power output of DGi in phase φ, the rated power of DGi, and the active power output of DGi under maximum power point tracking, respectively.

[0079] Considering the equality constraints on the relationship between the voltage at each node and the power injection of each phase in a three-phase distribution network—that is, the power flow constraints in a three-phase distribution network where the three-phase voltage sensitivity characterizes the relationship between three-phase power and the voltage of each phase—and based on the characteristics of the three-phase distribution network itself, by processing the power-voltage relationship of the three-phase distribution network, a three-phase voltage sensitivity that reflects the sensitivity of the distribution network voltage to changes in the output of each phase of the distributed generation (DG) is obtained. Then, the three-phase voltage power function is Taylor-expanded, and combined with the power information transmitted from adjacent controllers, the predicted value of the voltage at the k-th step in the distributed model predictive control is obtained. The equality constraints on the relationship between the voltage at each node and the power injection of each phase in a three-phase distribution network are as follows:

[0080]

[0081] Among them, V j (0) represents the phase voltage value sampled and measured in the current power distribution network; N represents the sensitivity of the phase voltage to changes in the reactive power output of each phase of the DG; iThis represents the set of DG controllers adjacent to DGi; This represents the optimized reactive power information that DGl transmits to the adjacent DGi.

[0082] When the adjacent controller is a single-phase DG, and the power information it transmits has not reached its reactive power output limit (i.e., there is still reactive power margin for voltage regulation), the three-phase reactive power output of the three-phase DG should remain balanced. This satisfies the three-phase DG reactive power output balance constraint when the reactive power of the single-phase DG has not reached its output limit, as follows:

[0083]

[0084] in, Q represents the maximum change in reactive power output of a single-phase distributed generator (DG). DGi,a (k), Q DGi,b (k), Q DGi,c (k) represents the reactive power output of the three-phase DG, specifically phases a, b, and c.

[0085] 3) Based on the objective function and constraints, solve the objective function to determine the required distribution network measurements to achieve the objective function. Specifically, based on the measured three-phase distribution network data, calculate the key variable in the established distributed model predictive control problem (objective function formula 1), namely the DG output constraint, namely the three-phase voltage sensitivity. Then, solve the optimization problem based on the obtained three-phase voltage sensitivity, that is, solve the objective function shown in formula 1 to obtain the optimal reactive power output of each phase of the DG unit.

[0086] Specifically, the solution method is as follows:

[0087] According to circuit principles, the relationship between voltage and power is as follows:

[0088]

[0089] in, and Let i be the injected power and voltage phasor at node i. S i and V i Indicate their conjugate complex number; Let represent the nodal admittance matrix for the three phases, where each phase of a node is considered a separate node. Taking the partial derivatives of both sides of the above equation with respect to active and reactive power, we can obtain the sensitivity of the voltage at node i to the power injection at node j, as follows:

[0090]

[0091]

[0092] Here, Re() represents taking the real part of the complex number within the parentheses. Thus, after obtaining the sensitivity of each phase voltage of the three-phase distribution network to power injection, the objective function can be solved to obtain the optimal DG injection power for each phase.

[0093] In some embodiments, after determining that the distributed DG controller is operating in emergency control mode:

[0094] Based on the current active power output of the distributed generation, determine the adjustable active power constraints of each phase of the distributed generation, and then determine the reactive power limit constraints and network power flow constraints of each phase of the distributed generation.

[0095] Based on the objective function and constraints, determine the network measurement values ​​and DG output power data transmitted by adjacent controllers that need to be obtained for the solution;

[0096] The optimal active and reactive power outputs of each phase of the DG are calculated based on the measured values ​​of the three-phase distribution network and the power data transmitted by adjacent controllers using the distributed model predictive control algorithm.

[0097] The calculation results are sent to the distributed generation unit to attenuate its active power output and coordinate its reactive power output. At the same time, the calculation results are transmitted to the adjacent controllers to coordinate the power output of each distributed power source and ensure the voltage stability of the distribution network.

[0098] In a specific implementation example, the emergency control mode section is as follows:

[0099] 1) Construct an optimization objective function that includes voltage stability requirements and DG active power attenuation requirements: The objective function is to minimize the voltage deviation of each phase of the distribution network and the active power attenuation of DG.

[0100] In emergency mode, the active power change requirement of the distributed generation controller is to minimize the active power attenuation of each phase of the distributed energy source in the three-phase distribution network.

[0101] When the measured phase voltage deviation at a node exceeds a preset threshold, the distributed generation (DG) controller operates in emergency control mode. The control variables are the active and reactive power output of each phase of the DG, working together to reduce the voltage deviation at each node of the three-phase distribution network while minimizing energy loss, i.e., minimizing the attenuation of active power. The objective function of the DG controller in emergency mode can be expressed as minimizing the sum of the squares of the deviations between the phase voltage at each node and its reference voltage value in the three-phase distribution network, and the Euclidean norm of the change in active power generated by the DG. Therefore, the optimized objective function is as follows:

[0102]

[0103] Wherein, ΔP DGi W represents the reactive power output change vector of each phase of DGi; PiThis is a weighting coefficient for changes in active power output, i.e., active power attenuation, and its specific value can be adjusted according to different application scenarios. The first term on the right side of the objective function is to minimize the phase voltage V at each node. j (k) and reference value V ref The voltage deviation is the first term, and the second term is to minimize the change in active power output of each phase of the distributed generation (DG), that is, to reduce the energy waste captured by the distributed generation (DG).

[0104] 2) Determine the active and reactive power output constraints of each phase of the distribution grid (DG) and the distribution network voltage constraints expressed in terms of voltage sensitivity:

[0105] The operational constraints of the emergency control mode, namely the constraints of the objective function mentioned in equation (8), mainly consist of three parts: the inequality constraints of the active power output of each phase of the DG unit considering the current active power output of the DG, the inequality constraints considering the reactive power output limit of each phase of the DG unit, and the equality constraints characterizing the relationship between the voltage of each node of the three-phase distribution and the power injection of each phase.

[0106] Specifically, the constraints in emergency mode include the active power output of each phase of the distributed generation (DG) being between zero and maximum output, the reactive power output being between the upper and lower limits of reactive power compensation capability, and the power flow constraints on the relationship between three-phase power and three-phase voltage expressed by voltage sensitivity in a three-phase distribution network.

[0107] Considering the inequality constraints on the active power output of each phase of the DG unit and the inequality constraints on the reactive power output of each phase of the DG unit, the following can be obtained based on the current active power output of the DG and the rated power of the DG:

[0108] 0≤P DGi,φ ≤P DGiM,φ (9)

[0109]

[0110] Where P DGi,φ This represents the active power output of DGi in phase φ.

[0111] Specifically, considering the characteristics of the three-phase distribution network and the three-phase voltage sensitivity mentioned earlier, the active power output of each phase of the distributed generation (DG) is added to the control variables to obtain the prediction of the voltage value at step k in the distributed model predictive control.

[0112]

[0113] in, The sensitivity of the phase voltage to changes in the active power output of each phase of the DG; ΔP DGi This represents the change vector of active power output for each phase of DG i; This represents the optimized active power information that DGl transmits to the adjacent DGi.

[0114] In this embodiment, after selecting the emergency control mode and the preventive control mode, the distributed model predictive control algorithm is used. The concept of distributed model predictive control includes the problem establishment, solution and prediction solution process, as well as the power information exchange process between controllers.

[0115] 3) Solve the problem based on the objective function and constraints to determine the required power distribution network measurements to achieve the objective function;

[0116] The solution method for this part is basically the same as that for the prevention and control mode, except that the required power information of adjacent DGs includes the optimized active power output of each phase of the DG.

[0117] In this embodiment, the solution method used in the distributed generation (DG) controller is a distributed model predictive control method. Compared with the commonly used centralized model predictive control, the voltage optimization problem of the entire three-phase distribution network is decomposed into each DG controller through bidirectional communication between adjacent controllers, reducing the computational burden on each controller. Furthermore, due to the continuous rolling optimization and feedback correction of model predictive control, the overall voltage control effect is guaranteed, and the optimal power output of each phase of the DG is obtained.

[0118] In this embodiment, the control of the DG is distributed, requiring only communication with adjacent DG units to exchange power information;

[0119] The specific process of implementing distributed control under the prevention mode includes:

[0120] The distributed controller uses network measurement information and power information transmitted by adjacent controllers to solve the problem based on a distributed model predictive control algorithm, with the goal of optimizing the overall voltage of the three-phase distribution network.

[0121] After solving, the calculated three-phase power information of the DG is transmitted to the adjacent controller to realize distributed coordinated control.

[0122] In a specific implementation example, the mode switching method is as follows:

[0123] If a distributed generation (DG) controller selects its operating mode solely based on the deviation between the measured voltage and the reference value, the voltage may fluctuate around a threshold value during significant disturbances. To eliminate unexpected fluctuations, when the controller switches from emergency mode to preventative mode, all bus voltages after the mode switch should also be within a predefined deviation range, i.e.:

[0124]

[0125] in The mode change predicted voltage is calculated based on the optimal reactive power output of each phase of the distributed generation (DG) obtained when switching to preventive mode, and the change in active power recovery to maximum power point tracking. This is combined with the linear expression for predicted voltage established from the three-phase voltage sensitivity. It can be obtained using the following formula:

[0126]

[0127] in, This represents the optimal reactive power output obtained assuming a switch to prevention mode.

[0128] The mode switching scheme adopted in this embodiment ensures that after switching to the prevention mode, when the active power no longer participates in voltage regulation and returns to the maximum tracking state, the three-phase voltage of the distribution network can still be maintained within the allowable range, thus meeting the requirements for stable voltage regulation.

[0129] To illustrate the effectiveness of the control method in this embodiment, the technical solution of this application will be described in detail below with reference to specific simulation embodiments and comparative examples.

[0130] The operation flow of the distributed voltage control optimization method for three-phase unbalanced distribution networks mentioned in this embodiment is as follows: Figure 2 As shown, the data communication between the distributed generation (DG) controller and adjacent controllers is illustrated. The key aspect lies in the control method within the DG controller, which includes two control modes. Figure 1 The typical three-phase unbalanced power distribution network mentioned in the text is simulated using programming. Figure 3 , Figure 4 What is displayed is the three-phase voltage information before and after control of a typical node in the network (here, we take node 20 of single-phase distributed generation 3 connection) under normal operating conditions, that is, when the active power of each phase injected into the distribution network by DG changes. Figure 5 This demonstrates the improvement of the overall A-phase voltage of the three-phase distribution network before and after the application of the voltage control method of this embodiment. After applying the voltage control method of this embodiment, the voltage deviation is minimal and can be stabilized within 0.01 pu. Figure 6 , Figure 7 The demonstration shows the critical node voltage before and after the application of the method when an unexpected disturbance occurred in the distribution network, specifically a sudden load increase in phase A of node 31 from t=20s to t=40s. Figure 6 and Figure 7 It can be seen that the voltage control method of this embodiment can stabilize the voltage in a relatively short time. Figure 8 The method is presented to show the average voltage deviation of the three-phase distribution network in phase A before and after its application. This embodiment shows better control performance under different operating conditions, and the addition of a mode switching scheme reduces voltage fluctuations.

[0131] This embodiment comprehensively considers the control functions of single-phase DG and three-phase DG in a three-phase distribution network. It optimizes the output power of each phase of the DG in a distributed manner and controls the voltage of each phase at each node of the distribution network. The objective function is set to minimize the deviation between the voltage of each phase at the distribution network node and the reference value. It is not only suitable for three-phase unbalanced power grids, but also can achieve voltage regulation for distribution networks operating in a three-phase balanced state.

[0132] This embodiment designs two control modes based on the deviation between the measured phase voltage and the reference value, taking into account the coordination between the control of the distribution network node voltage and the energy utilization of distributed power sources; then, a mode switching scheme that uses mode changes to predict voltage is designed to assist in mode selection and switching, avoiding rapid voltage fluctuations caused by frequent changes in control modes.

[0133] This embodiment adopts a distributed voltage control method, which does not require a high-performance central controller, has low communication requirements, and has low construction and maintenance costs; the DG controller only exchanges information with adjacent controllers to achieve coordination between different DG outputs and avoid voltage regulation effect conflicts.

[0134] Example 3

[0135] Based on Example 1, this example provides a distributed voltage control optimization system for a three-phase unbalanced distribution network, including:

[0136] Judgment module: configured to determine the degree of three-phase distribution network voltage deviation based on the acquired phase voltages of each node in the distribution network;

[0137] Mode selection module: configured to select the control mode based on the degree of three-phase distribution network voltage deviation;

[0138] DG calculation and control module: It is configured to operate in preventive control mode when the distribution network voltage deviation is less than the set voltage deviation threshold, and the DG operates in maximum power point tracking state to adjust the distribution network voltage by optimizing the reactive power output of each phase of the DG.

[0139] When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage.

[0140] Furthermore, it also includes a parameter value preset module, which is configured to preset the control time, the deviation reference voltage for mode selection, and the weight value of the objective function.

[0141] Furthermore, it also includes a mode switching module: configured to select the DG controller's operating mode as either a preventative mode or an emergency control mode based on the predicted voltage of the mode change.

[0142] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0143] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A distributed voltage control optimization method for a three-phase unbalanced distribution network, characterized in that, Includes the following steps: Based on the obtained phase voltages of each node in the distribution network, determine the degree of voltage deviation in the three-phase distribution network; Select the control mode based on the degree of voltage deviation in the three-phase distribution network; When the distribution network voltage deviation is less than the set voltage deviation threshold, the control operates in the preventive control mode, and the DG operates in the maximum power point tracking state, adjusting the distribution network voltage by optimizing the reactive power output of each phase of the DG. Prevention and control mode: Taking the reactive power output of DG as the control object, and taking the minimum voltage deviation of each phase of the distribution network and the minimum change of DG reactive power output as the objective function, the optimal DG reactive power output command is obtained by solving the problem. The objective function of the prevention and control mode is to minimize the sum of the square of the deviation between the voltage of each phase at each node and its voltage reference value and the Euclidean norm of the change in reactive power generated by the DG. When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage. Emergency control mode: The active and reactive power outputs of each phase of the DG are taken as the control objects, and the objective functions are to minimize the voltage deviation of each phase of the distribution network and minimize the active power attenuation of the DG. The optimal active and reactive power output commands of the DG are obtained by solving the problem and feeding them back to the DG to realize the voltage control of each phase of the distribution network. The objective function under emergency control mode can be expressed as minimizing the sum of the squares of the deviations between the voltage of each phase at each node and its voltage reference value in the three-phase distribution network and the Euclidean norm of the change in active power generated by the DG.

2. The distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 1, characterized in that, After confirming that the distributed DG controller is running in prevention mode: The distributed generation operates in maximum power point tracking (MPPT) mode. The reactive power limit constraints of each phase of the distributed generation are determined based on the reactive power output of a single-phase DG and the active power output of each phase of the DG. The network power flow constraints are determined based on the voltage flow relationship of the three-phase distribution network. Based on the objective function and constraints, determine the measured values ​​required for control and the DG output power data transmitted by adjacent controllers; The optimal reactive power output of each phase of the DG is calculated based on the measured values ​​of the three-phase distribution network and the power data transmitted by the adjacent controllers according to the distributed model predictive control algorithm. After optimization calculation, the calculation result command is sent to the distributed generation unit to control its reactive power output, and the calculation result is transmitted to the adjacent controller to coordinate the reactive power output of each distributed power source and achieve voltage stability of the distribution network.

3. The distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 2, characterized in that, The constraints of the prevention and control mode include: the reactive power output of the DG determined by the inverter should be between the upper and lower limits of its capacity; the power flow constraint in the three-phase distribution network is characterized by the three-phase voltage sensitivity to represent the relationship between the three-phase power and the voltage of each phase; and the three-phase DG reactive power output balance constraint when the reactive power of a single-phase DG does not reach the upper limit of its output. The objective function of the prevention and control mode is solved by calculating the three-phase voltage sensitivity of the DG output limit constraint based on the measured three-phase distribution network data. Then, the objective function is solved based on the obtained three-phase voltage sensitivity to obtain the optimal reactive power output of each phase of the DG unit.

4. The distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 1, characterized in that, After confirming that the distributed DG controller is operating in emergency control mode: Based on the current active power output of the distributed generation, determine the adjustable active power constraints of each phase of the distributed generation, and determine the reactive power limit constraints and network power flow constraints of each phase of the distributed generation. Based on the objective function and constraints, determine the network measurement values ​​and adjacent controller transmission data required for the solution; The optimal active and reactive power outputs of each phase of the DG are calculated based on the measured values ​​of the three-phase distribution network and the power data transmitted by adjacent controllers using the distributed model predictive control algorithm. The calculation results are sent to the distributed generation unit to attenuate its active power output and coordinate its reactive power output. At the same time, the calculation results are transmitted to the adjacent controllers to coordinate the power output of each distributed power source and ensure the voltage stability of the distribution network.

5. The distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 4, characterized in that, The constraints of the emergency control mode include: the active power output of each phase of the DG should be between zero and the maximum output, the reactive power output should be between the upper and lower limits of the reactive power compensation capability, and the power flow constraints of the relationship between the three-phase power and the three-phase voltage expressed by voltage sensitivity in the three-phase distribution network.

6. The distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 1, characterized in that: It also includes a mode switching method. Before mode selection, the predicted voltage after mode switching is first calculated. Then, based on the relationship between the predicted voltage and the voltage deviation of each phase of the node and the preset voltage deviation threshold, it is determined whether to switch the control mode so that all bus voltages after mode switching are within the set deviation range.

7. A distributed voltage control optimization system for a three-phase unbalanced distribution network, characterized in that, include: A distributed DG controller is installed at each DG power supply access point. Each distributed DG controller is communicatively connected to the corresponding DG power supply and controls the output power of the corresponding DG power supply. Each distributed DG controller is communicatively connected to adjacent distributed DG controllers. The distributed DG controller executes the distributed voltage control optimization method for a three-phase unbalanced distribution network as described in any one of claims 1-6.

8. The distributed voltage control optimization system for a three-phase unbalanced distribution network as described in claim 7, characterized in that: When a three-phase distribution network is in operation, the distributed generation (DG) controller measures the voltage information of each phase of the distribution network nodes, determines the network operating status, selects the operating mode of the controller, and then obtains the DG output limit constraint based on the measured power output information of each phase of the DG. Then, combined with the power information transmitted by the adjacent controllers, it calculates the power output of each phase of the DG that satisfies the objective of minimizing the deviation between the voltage of each phase of the distribution network and the reference value. The control command is then sent to the distributed generation to realize voltage control, and the calculated optimal power information is transmitted to the adjacent controllers.

9. A distributed voltage control optimization system for a three-phase unbalanced distribution network based on the distributed voltage control optimization method for a three-phase unbalanced distribution network as described in claim 1, characterized in that, include: Judgment module: configured to determine the degree of three-phase distribution network voltage deviation based on the acquired phase voltages of each node in the distribution network; Mode selection module: configured to select the control mode based on the degree of three-phase distribution network voltage deviation; DG calculation and control module: It is configured to operate in preventive control mode when the distribution network voltage deviation is less than the set voltage deviation threshold, and the DG operates in maximum power point tracking state to adjust the distribution network voltage by optimizing the reactive power output of each phase of the DG. When the distribution network voltage deviation exceeds the preset voltage deviation threshold, the control operates in emergency control mode, coordinating and optimizing the active and reactive power output of each phase of the DG to regulate the distribution network voltage.

10. A distributed voltage control optimization system for a three-phase unbalanced distribution network as described in claim 9, characterized in that: It also includes a parameter value preset module, which is configured to preset the control time, the deviation reference voltage for mode selection, and the weight value of the objective function. Alternatively, it may include a mode switching module configured to select the DG controller's operating mode as either a preventative mode or an emergency control mode based on the predicted voltage of the mode change.

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