Collaborative Disturbance Rejection Voltage Control Technology for Distribution Stations under Distributed Resource Coordination

In order to improve the stability of the voltage in the distribution system, a distributed resource coordination-based coordinated anti-interference voltage control technology for distribution stations is proposed. The study analyzes the anti-interference capabilities of different types of renewable energy, energy storage, electric vehicles, and control distributed photovoltaic grid-connected inverters based on the analysis results. The objective function and constraints of voltage control are set. Voltage control is performed by adjusting the photovoltaic inverter and reactive power compensation device. The experimental results show that the proposed method can achieve stable control of system voltage under both photovoltaic output fluctuations and load fluctuations, indicating that its control effect is good.


Introduction
With the continuous rapid growth of the national economy, the demand for electricity load has increased rapidly, leading to higher requirements for power quality and supply reliability [1].For power companies, a low power factor directly impacts the power and energy losses in the grid, as well as the voltage loss and stability of power transmission lines.In severe cases, it may lead to "voltage collapse" [2].Comprehensive monitoring and voltage control in distribution substations are essential to achieve a reasonable balance of reactive power flow in the grid, thereby effectively controlling the grid voltage.This is of great significance for improving the voltage quality of the grid and ensuring the safety and reliability of the power system.
In the above context, relevant scholars have proposed some effective methods to control the voltage in the distribution station area.The voltage control method proposed in [3] is based on the sensitivity of capacitors to voltage.This method takes into account the actual reactive power variation of capacitors with voltage changes and provides a way to obtain the sensitivity matrix of voltage to capacitors.Based on this, a novel remote control method for low-voltage capacitors is proposed.The effectiveness and rationality of this control method were verified through simulation using an IEEE 33-node distribution network model.However, it was observed that under this control method, there were significant voltage fluctuations in the equipment within the distribution substation area.The optimization method for reactive power and voltage in distribution substations based on goal programming was proposed in [4].This method begins by designing target values for the maximum and minimum voltage limits, as well as the network loss rate for the users.Subsequently, an optimization model for reactive power and voltage is established, with the primary objective of minimizing the sum of deviations between the highest and lowest voltages and their target values.The secondary objective is to minimize the deviation between the network loss rate and its target value.Finally, the particle swarm optimization algorithm is employed to solve the model.Simulation results demonstrate that this method can effectively control the voltage within the target range according to the established priority structure.However, due to fluctuations in photovoltaic output, there may still be issues with system voltage instability.Ning et al. [5] proposed a real-time voltage control method for a distribution network based on the coordination of transformer and demand response.This method uses real-time measurement data collected by data terminals to determine the status of the transformer tap changer and load-shedding requirements to maintain voltage stability.In addition, the load voltage sensitivity matrix is established, which can be used for voltage sensitivity analysis in demand response.Finally, the effectiveness and robustness of this method were verified through simulation.It can improve voltage distribution and effectively maintain the distribution network voltage within the allowable range in emergency situations.However, this method also has the problem of voltage instability.
In order to solve the problems existing in the existing methods mentioned above, a distributed resource coordination-based distributed radio station interval collaborative anti-interference voltage control technology is proposed.

Analysis of the anti-interference ability of different types of renewable energy, energy storage, and electric vehicles
During the operation of distribution networks, various voltage disturbances and transient overvoltages can occur, which may lead to system faults or failures, greatly impacting the reliability and stability of the power supply.To ensure stable operation between distribution substations, it is necessary to implement coordinated interference rejection voltage control.This involves coordinating the actions of multiple substations to counteract voltage fluctuations, implement interference rejection control measures, and regulate the voltage to ensure system voltage stability.Therefore, in order to guarantee the stable operation of distribution substations, it is important to analyze the interference rejection capabilities of different types of renewable energy sources, energy storage systems, and electric vehicles before implementing voltage control measures.
(1) For renewable energy sources such as solar photovoltaic (PV) and wind power, the output power undergoes significant variations due to seasonal and weather changes.It poses a great challenge when the grid load increases [6].One key approach to enhance the interference rejection capability of PV and wind power systems is to adjust the system's output through control loops to meet the requirements of the distribution network.This can include controlling the variations in output voltage and frequency.
(2) Energy storage devices (such as lithium-ion batteries) are an important component of antiinterference measures, as they can buffer voltage and frequency changes in the distribution network.By controlling the smart grid system built on energy storage devices, the improvement of antiinterference ability can also be achieved.If there are fluctuations in the power grid, the system can activate energy storage facilities to reduce battery utilization and extend battery life, including allocating and managing distributed energy storage facilities to maximize their utilization efficiency.
(3) Electric vehicles generate large load peaks every time they are charged.If the load can be reasonably distributed within a time and space range, it can reduce the load peak of the power grid and improve its anti-interference ability.
Overall, improving the anti-interference ability of these devices requires different technical means, such as controlling loops, establishing smart grid systems, and allocating energy, to enable these devices to adapt to different load peaks and fluctuations and to some extent, ensure the stability of the distribution network.

Control of distributed photovoltaic grid connected inverters
By analyzing the anti-interference ability of different types of renewable energy, energy storage, and electric vehicles, evaluating their response ability in the event of disturbances, and strengthening the stability and reliability of the power grid system, research is conducted on the control of distributed photovoltaic grid-connected inverters.
In a distributed photovoltaic (PV) power generation system, when the PV inverter is connected to the grid, the grid-connected inverter typically operates at the unity power factor.The set value for the output reactive power of the grid-connected inverter is usually set to zero [7][8].However, when the grid voltage exceeds its limit, and it is necessary to restrict the output of the distributed PV system, the working mode of the inverter can be adjusted by modifying the set value of the reactive power.This effectively regulates the grid voltage at point k U .If the output active power of the grid-connected inverter is P and the capacity is V , then the maximum value w Q of the reactive power it can output is: in the formula, P is the maximum active power output of the distributed photovoltaic power generation system based on maximum power tracking.Therefore, the reference value of reactive power absorbed by grid-connected inverters varies with voltage as follows: in the formula, P U represents the voltage of the generator, and Q U represents the voltage at the load end.The reference value of absorbed reactive power is calculated based on the real-time k U limit value and voltage power droop characteristics.At the same time, the k U limit value is multiplied by the adjustment coefficient and added to the real-time power output of the photovoltaic system to obtain the set value of output power during the control process of the grid-connected inverter: in the formula, ref U represents the reference voltage for the inverter controller.' P denotes the desired setpoint for the output active power, while ' Q represents the specified value for the output reactive power.Additionally, P f and c f are the control coefficients used for adjusting the active power and reactive power, respectively.The power factor is determined based on the power factor range: in the formula,  represents the power factor of a circuit component, which is the phase difference between the voltage and current of the component.n represents the minimum allowable power factor value for the circuit component.After equal power coordinate transformation, the voltage is synchronously rotated into the coordinate system: represents the reference value for the d-axis component of the current vector in the same coordinate system.Consequently, the current reference value on the d-q coordinate axis can be obtained, allowing for the adjustment of k U .

Implementation of voltage control
According to research on the actual distribution area, when the load rate is below 35%, the voltage can be appropriately reduced.When the load rate is above 65%, the voltage can be appropriately reduced.In the case of high light load voltage on the line, it is necessary to adjust the distribution transformer tap to slightly decrease the voltage in the entire distribution station area and perform reactive power compensation at appropriate nodes [9][10].Based on the aforementioned analysis, the objective function for voltage control is set as follows: in the formula, i U represents the voltage per unit value of each node; is U represents the lower voltage limit per unit value of each node, which can be set based on the weight of each node's line loss characteristics and load static voltage characteristics; i represents the node number; n represents the total number of nodes in the entire distribution area; P   represents the change in the iron loss of the distribution transformer; P   represents the copper loss variation value of the distribution transformer; P   represents the variation value of line loss in the distribution station area.
The corresponding constraint conditions are: in the formula, i I represents the current phasor of node i ; i G represents the admittance matrix of node i .
Based on the aforementioned objective function and constraints, voltage control is achieved by adjusting both the photovoltaic inverter and the reactive power compensation device.
The specific steps are as follows: 1. Adjustment of the photovoltaic inverter output voltage: The inverter's output voltage is directly linked to the photovoltaic array's output voltage.By fine-tuning parameters such as the inverter's DC voltage, output current, and power factor, the output voltage can be effectively controlled.When the grid voltage is below the desired level, the inverter's output voltage can be increased to compensate.Conversely, if the grid voltage is too high, the inverter's output voltage can be lowered.
2. Fine-tuning of the reactive power compensation device: The reactive power compensation device plays a vital role in regulating reactive power output, hence controlling the grid voltage.By adjusting its capacity and response speed, the device can effectively manage reactive power flow.In scenarios where the grid voltage exceeds the desired range, increasing the reactive power compensation capacity allows excess reactive power absorption.Conversely, if the grid voltage is too low, appropriate adjustments can be made to address the issue.

Experimental study
To validate the feasibility and application effectiveness of the coordinated interference rejection voltage control technique in distribution substations under distributed resource coordination, experimental research has been conducted.In this study, the improved IEEE 33-node system using distributed photovoltaic technology was employed to simulate and verify the effectiveness of the voltage control method in the distribution substation area.Multiple photovoltaic power sources are connected to the system, denoted as PV, the active output of the PV is 0.5 MW, the capacity of the photovoltaic inverter is 0.8 MVA, and the interconnection line is not connected.For this distribution system, the voltage stability of the system under photovoltaic output fluctuations was tested, and the test results are shown in Table 1.  1, it can be observed that, under fluctuating photovoltaic output conditions, the proposed control method maintains the system voltage around 220 V with fluctuations not exceeding 5 V.This effectively enhances the voltage stability of the distribution network.On the other hand, without utilizing the proposed control method, the system voltage may become excessively high or low, potentially leading to damage to electrical equipment or unstable system voltage.Therefore, it is evident that this method ensures the stability and reliability of the system voltage.This is achieved by setting a voltage control objective function and constraints and adjusting the photovoltaic inverter and reactive power compensation device to achieve voltage control, thereby improving the system's voltage stability.
In order to further validate the application effectiveness of this method, tests were conducted on the voltage stability of the system under load fluctuations.The test results are shown in Table 2.It is evident from Table 2 that without the proposed control method, the system voltage fluctuates significantly under load fluctuations.This can potentially lead to damage to electrical equipment or unstable system voltage.However, by implementing this control method, the voltage stability of the distribution network can be effectively improved.Under load fluctuations, the system voltage becomes more stable.This is because this method analyzes the anti-interference ability of different types of renewable energy, energy storage, and electric vehicles before voltage control.It improves the collaborative anti-interference voltage control effect between distribution stations.It realizes collaborative anti-interference voltage control between distribution stations and improves the stability and reliability of distribution network voltage.

Conclusions
To enhance the effectiveness of voltage control in distribution substation areas, a voltage control technique based on coordinated interference rejection and utilizing distributed resources has been proposed.Through experiments, the following conclusions have been drawn: (1) By analyzing the interference rejection capabilities of different types of renewable energy, energy storage, and electric vehicles, coordinated interference rejection voltage control between distribution substations has been achieved.This has resulted in improved voltage stability and reliability of the distribution network.
(2) Under fluctuating photovoltaic output and load conditions, the implementation of this control method has effectively maintained the system voltage near the target value with minimal fluctuations.This demonstrates excellent voltage stability and reliability.
Therefore, the voltage control technique based on coordinated interference rejection in distribution substations, utilizing distributed resources, is an effective approach for voltage control.
in the formula, ref P and ref Q denote the reference values for the equivalent DC voltage and equivalent DC current, respectively.d U represents the d-axis component of the voltage vector in the d-q coordinate system.In contrast, _ref d i