Control Of Distribution Networks Research Articles

A Customized Voltage Control Strategy for Electric Vehicles in Distribution Networks With Reinforcement Learning Method

The increasing electric vehicles (EVs) at charging stations will impose great challenges on the conventional voltage control in distribution networks. In this article, a two-stage voltage control strategy based on deep reinforcement learning is proposed to mitigate voltage violations caused by the uncertainty of EVs and load. In the first stage, the charging demand of EVs is predicted based on trip chain theory and simulated by Monte Carlo simulation. The optimal power flow is then performed to determine the day-ahead dispatch of on-load tap changer and capacitor banks. In the second stage, the real-time voltage control problem is formulated as a Markov Game considering both reactive power control and vehicle to grid modes of EVs. The problem is solved by the deep deterministic policy gradient algorithm to develop a well-trained control strategy that can be implemented online. Moreover, a novel customized charging criterion is proposed to conduct the charging behavior of EVs and guarantee full charging at the departure time. The proposed approach is tested on the IEEE 33-bus and 123-bus distribution systems and comparative simulation results show the effectiveness in addressing voltage problems.

An Extended Control Strategy for Weakly Meshed Distribution Networks With Soft Open Points and Distributed Generation

As part of the smart grid concept, different strategies specialized for power flow control in distribution networks have been developed. One of the possible solutions to optimize the utilization of existing capacities and increase distributed generation penetration is the implementation of Soft Open Points. Soft Open Points are modular devices based on power electronic converters that enable closing loops in the network without negative consequences regarding fault current propagation. Introducing the concept of soft open points in the distribution network enables power flow control in a particular part of the network and voltage control in the soft open point connecting nodes. The control strategy proposed in this paper addresses the main obstacle for appropriate exploitation of soft open points, defining reference values for control variables in the case of large-scale distribution systems. Furthermore, the proposed strategy also deals with data unavailability problems, that is, soft open point control under communication interruption. The proposed control algorithm incorporates centralized optimal power flow calculations and an estimation algorithm based on a multivariate polynomial regression. The optimal power flow is used to calculate the control variables in normal operation modes. The procedure based on multivariate polynomial regression was used to estimate the reference values of the control variables when the optimal power flow results were unavailable. This feature makes the proposed algorithm applicable to communication interruptions when only limited data capture is available. The algorithm proposed in this study was implemented and tested on a test network considering different scenarios. Conclusions and simulation results make this algorithm applicable to an actual soft open point controller.

Research on the Bi-Level Optimization Model of Distribution Network Based on Distributed Cooperative Control

The uncertainty of high-permeability renewable energy output brings about great challenges to the operation control in distribution network. The traditional control mode has lower reliability, higher calculation and greater communication pressure. It is more difficult to realize the technical requirements of “plug and play” of power components. Therefore, a bi-level coordinated control model is proposed for the operation and energy management optimization of active distribution network with multi-microgrid in this paper. The consensus algorithm which exists in the multi-agent system is applied in the upper-level model and the capacity utilization ratio of the different microgrids is set as the consistent variable because the ratio of resistance and reactance is usually larger in distribution network and the interests in the different microgrid entities should be distributed fairly. Moreover, in the lower-level model, the lowest operating cost is the final goal and the model predictive control rolling optimization is utilized to reasonably allocate the output of the equipments in the microgrid according to the changing trend of renewable energy. Thereby the tracking of the upper-level control commands is realized. Finally, the simulations are conducted in the IEEE-33 nodes distribution system connected to a multi-microgrid to verify the feasibility and effectiveness of the proposed method, in which a reference for the optimal operation of higher penetration renewable energy to distribution network is provided.

Technology and application of operation control of DC distribution network

DC distribution network consists of distributed generation, energy storage, load and AC distribution network, With the rapid development of DC distribution network and the increasing proportion of DC load, the operation mode of DC distribution network is more flexible. Different from the traditional AC distribution network, the traditional AC distribution network has a single operation mode, while the DC distribution network can operate in both parallel mode and island mode. Therefore, a control method suitable for different operation modes of DC distribution network is urgently needed. In this paper, a control method about loop closing and loop opening of DC distribution network is proposed. When receiving the command of loop closing or loop opening from the master station or local monitoring system, the loop closing control is judged by the switch state, fault state and operation state of converter. It solves the problem that the traditional AC distribution network control strategy is not applicable in DC distribution network, it realizes the smooth switching of DC distribution network closed loop operation and opened loop operation. This method has been used in the DC coordinated control device and successfully applied in the national key research and development plan of Suzhou active distribution network.

Control strategy for DC soft open point in large scale distribution networks with distributed generators

Development of power electronic devices and their implementation in power distribution networks significantly improve not only the easier integration of distributed generation into distribution networks but also the further refinement of control algorithms specialized in the application of power management procedures in distribution systems. Implementation of DC Soft Open Points (DCSOP) for closing loops in distribution networks could serve as one of the most representative examples of the use of power electronics devices as a management resources in modern distribution networks. The paper describes the possibilities of application of DCSOP used for loops closure and power flow control in medium voltage distribution networks with integrated distributed generators. Considering all benefits of loops closure and the controllability of the DCSOP, DCSOP has been considered as a management resource capable of achieving the desired/optimal state in the distribution network. The management strategy proposed in this paper covers two cases: the first case where adequate communication infrastructure is available when all DCSOP operation is based on Optimal Power Flow (OPF) calculations, and the second case when OPF results are unavailable for some reason (most often due to communication interruptions) and DCSOP operation is based on processing available data using neural network based algorithm. The proposed management strategy has been implemented and tested on the IEEE 33 distribution test network with integrated distributed generators. The simulation results, described in this paper, can serve not only as a basis for further scientific research but also as a basis for the practical implementation of real controllers based on the proposed algorithm and its application in practice, in real distribution networks.

Real-Time Demand Response Strategy of Temperature-Controlled Load for High Elastic Distribution Network

With the development of distribution network, high elastic distribution system with multiple integration needs more response resources from the user-side to participate in the more flexible distribution network interaction. In the face of emergency or accident, the traditional power grid operating control system often takes part in the response in the form of cutting off the whole line load, which will greatly affect the power consumption of users. In this context, this paper proposes a temperature-controlled load shedding method for high elastic distribution network with real-time response. Taking the temperature-controlled load aggregate as the response resource, the temperature-controlled load control method suitable for system frequency and voltage recovery is analyzed, and the temperature-controlled load dispatching strategy participating in the emergency control of high elastic distribution network is formed. Specifically, according to the energy storage characteristics and service time flexibility of temperature-controlled load, the aggregate response model of temperature-controlled load is established to determine the control mode of temperature-controlled load. Then, a temperature-controlled load disaster reduction method based on the real-time response of high elastic load is proposed to realize the participation of temperature-controlled load in system disaster reduction. Finally, the voltage and frequency recovery characteristics of the system are analyzed in a 10 machine 39 bus system.

A Multi-Agent-Based Self-Healing Framework Considering Fault Tolerance and Automatic Restoration for Distribution Networks

Increasing penetration of distributed generators (DGs) brings new challenges to the control and protection of distribution networks. This article proposes a control and protection framework based on Multi-agent System (MAS), in which situation awareness of zone agents plays an important role. The main protection is designed to locate and isolate faults based on the peer-to-peer communication among the zone agents. Fault-tolerant mechanisms, including self-inspection and backup protection, are developed to cope with the malfunction of individual MAS and local communication failure. An automatic parallel restoration scheme that doesn’t require complete grid information is proposed to restore the power supply. Comprehensive simulation studies are carried out on a 71-bus distribution network with DGs using DIgSILENT, and the results have shown the effectiveness of the proposed self-healing framework.

Modelling and Simulation Analysis of Power Flow Router in Energy Internet

With a large number of distributed generation (DG) and controllable load connected to the power grid under the background of energy Internet development, the security and stability of the grid are challenged. Power flow control has become a problem of the operation of the power grid. Power flow router (PFR) has become an important element of energy Internet. It is an effective way to realize the power flow control of active distribution network when abundant distributed resources are connected to the grid. In this paper, the steady-state and dynamic operation characteristics of PFR are studied, and the corresponding mathematical model is established. The effect of PFR on optimizing the power flow and improving the dynamic characteristics of distribution network is analysed by the 14-node distribution network case simulating.

Оценка технико-экономического эффекта применения устройств автоматического регулирования напряжения на трансформаторах 10/0,4 кВ в распределительных электрических сетях

The article addresses the problem of ensuring permissible voltage levels in distribution electrical networks of various types: distribution networks of large cities, regional distribution electrical networks, and distribution electrical networks containing renewable energy sources. The most typical factors causing the voltage to go beyond the permissible limits specified by the relevant regulatory documents are pointed out. The negative factors conducive to the voltage at the consumer end deviating from the permissible limits, including a long length of network lines, high network load, low controllability of the network, load schedule nonuniformity, and poor observability of the network, are analyzed. The existing principles of voltage control in electrical distribution networks, namely, automatic and seasonal regulation, are studied. A distribution electrical network test model representing a real network fragment is developed. The model operation modes have been verified based on the data of measurements carried out in the original distribution electrical network. The voltage distributions in a medium voltage network during its operation under the conditions of the highest and lowest loads are demonstrated. It is shown, on the test model example, how the network voltage can be controlled by automatically regulating the voltage at the power supply center and selecting a fixed position of the NLTC at 10/0.4 kV transformer substations. It is shown that the use of power transformer OLTCs does not ensure sufficient means for adequately controlling the voltage in networks containing long power lines and featuring highly nonuniform seasonal and daily load schedules. The technical efficiency and economic feasibility of using automatic voltage regulation devices on 10/0.4 kV transformers for local voltage control are analyzed. The economic efficiency of applying automatic voltage regulation devices at 6--10/0.4 kV substations was evaluated in comparison with other means for improving the power distribution network voltage quality by upgrading the 10 kV feeder lines or installing a voltage booster at the inlet to the problematic 10 kV network section. The application field of automatic voltage regulators in the form of semiconductor devices for regulating the transformer output voltage at distribution transformer substations is shown.

Аппаратные решения для энергосберегающих технологий управления объектами распределительных сетей на базе силовых полупроводниковых устройств

The article considers topical issues in development of energysaving technologies to optimize the control of distribution networks according to the criterion of minimum power losses. The technology consists in introducing new hardware to control the modes based on static devices. Based on the analysis of the existing hardware created to control the modes of distributio networks, the developed circuitry solutions of the power part and the control system of the multifunctional thyristor voltage transformer and hybrid thyristor capacitor are proposed. Their main technical characteristics and ways to reduce voltage asymmetry, limiting short circuit currents and regulating reactive power are det ermined. The use of software and hardware solutions was recommended for a wide range of energy conservation tasks, both in the electric power sector and at the level of industrial facilities

Adaptive Voltage Control of Distribution Network with High Proportion PV

With the increase of grid-connected PV capacity, voltage regulation at point of common coupling by controlling the reactive power injected into the grid is available. This paper presents an adaptive voltage control strategy for distribution network with high proportion PV system. The PI gain of the voltage controller is automatically adjusted by the extremum seeking algorithm to dynamically respond to the changes of the network. The PI gains are updated online through the minimization of a cost function, which represents the voltage controller performance. Finally, a distribution network model of 5 MW photovoltaic power generation system is built in MATLAB / Simulink to verify the effectiveness of the proposed control strategy.

Ddpg-Based Adaptive Voltage Control of Distribution Networks with Multi-Terminal Sop

Ddpg-Based Adaptive Voltage Control of Distribution Networks with Multi-Terminal Sop

An Experimental Set-up and Performance Evaluation of EPON-Based 5G RAN Architecture Enabled by Distributed Network Control Management

An Experimental Set-up and Performance Evaluation of EPON-Based 5G RAN Architecture Enabled by Distributed Network Control Management

Two-Stage Deep Reinforcement Learning for Inverter-Based Volt-VAR Control in Active Distribution Networks

Model-based Vol/VAR optimization method is widely used to eliminate voltage violations and reduce network losses. However, the parameters of active distribution networks(ADNs) are not onsite identified, so significant errors may be involved in the model and make the model-based method infeasible. To cope with this critical issue, we propose a novel two-stage deep reinforcement learning (DRL) method to improve the voltage profile by regulating inverter-based energy resources, which consists of offline stage and online stage. In the offline stage, a highly efficient adversarial reinforcement learning algorithm is developed to train an offline agent robust to the model mismatch. In the sequential online stage, we transfer the offline agent safely as the online agent to perform continuous learning and controlling online with significantly improved safety and efficiency. Numerical simulations on IEEE test networks not only demonstrate that the proposed adversarial reinforcement learning algorithm outperforms the state-of-art algorithm, but also show that our proposed two-stage method achieves much better performance than the existing DRL based methods in the online application.

Research and improvement of current control strategy of active power filter

With the continuous development of science and technology, there are many power quality problems which are different from those in the past. A large number of innovative electrical equipment will bring a lot of harmonics in the process of work, which will not only cause potential safety problems in the power system, but also cause serious harm and impact on the normal operation of all power dependent working equipment. In this paper, active power filter (APF) is studied for harmonic control of distribution network. A new APF current compound control method is proposed, which is based on Deadbeat and repeat plus LADRC in series. It improves the accuracy of harmonic compensation, enhances the anti-interference ability and dynamic performance, and achieves the purpose of precise control of current loop.

Real-Time Coordinated Control of Low-Voltage DC Distribution Network With Soft Opening Point

In low-voltage dc distribution networks (DDNs), the load terminals typically employ voltage-source inverters to provide ac supply to the consumers. These load terminals can potentially experience poor voltage regulation especially in the presence of intermittent photovoltaic sources and uncoordinated charging patterns of plugged-in electric vehicles. Variations in power absorption and generation at different points can potentially create significant voltage drop/rise at the load terminals and may reduce the power quality at the ac side of the loads. In order to mitigate this issue, this article suggests a real-time coordinated supervisory control strategy that estimates the present state of the network and generates a set of references for the controllable sources such that the load voltage deviations are minimized. This article also proposes a power-electronic-converter-based soft open point (SOP) that provides a seamless connection of the remote end and gives an additional degree of freedom to control the circulating current among the feeders. Detailed description and control strategy of the SOP is presented. Steady-state analysis carried out on a three-feeder DDN is presented with and without the proposed SOP. Real-time simulation with an Ethernet-based transmission control protocol/Internet protocol communication system along with experimental results is presented to validate the implementation and effectiveness of the control strategy.

Dynamic Optimization of SVR Control Parameters for Improving Tap Operation Efficiency of Voltage Control in Distribution Networks

In this study, we propose a new optimization method to determine the control parameters of a step voltage regulator (SVR) to maximize its voltage control characteristic in distribution networks (DNs) with photovoltaic systems. Considering the service life of an SVR, the proposed method evaluates the expected number of tap operations and the voltage control performance based on the past voltage measurements obtained with sensors in the DN. Subsequently, the time series of two control parameters, that is, the reference voltage and the dead bandwidth, are determined for the most improved voltage control characteristic of the SVR, maintaining the number of tap operations within the upper limit. Voltage control simulation using a realistic 6.6‐kV DN model is conducted to show that the proposed method significantly reduces the voltage violation compared with the conventional SVR control using fixed parameters, as well as the alternative SVR operation developed in our previous study, in which the reference voltage was temporally updated. In addition, the simulation results demonstrate that the proposed method realizes efficient tap operations to mitigate the voltage violation, whereas the conventional method requires a much larger number of tap operations to mitigate the voltage violation to the same degree. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Fog-Based Distributed Networked Control for Connected Autonomous Vehicles

With the rapid developments of wireless communication and increasing number of connected vehicles, Vehicular Ad Hoc Networks (VANETs) enable cyberinteractions in the physical transportation system. Future networks require real-time control capability to support delay-sensitive application such as connected autonomous vehicles. In recent years, fog computing becomes an emerging technology to deal with the insufficiency in traditional cloud computing. In this paper, a fog-based distributed network control design is proposed toward connected and automated vehicle application. The proposed architecture combines VANETs with the new fog paradigm to enhance the connectivity and collaboration among distributed vehicles. A case study of connected cruise control (CCC) is introduced to demonstrate the efficiency of the proposed architecture and control design. Finally, we discuss some future research directions and open issues to be addressed.

MEDIUM VOLTAGE DIRECT CURRENT (MVDC), A NEW SYSTEM FOR THE MANAGEMENT AND OPERABILITY OF ELECTRICITY DISTRIBUTION GRIDS

The challenges in the operation of the electricity grids of the future, especially due to an increase in demand and connected distributed generation, are forcing utilities to propose solutions that improve the controllability and capacity of the grids. The connection of direct current links in medium voltage (MVDC) may be one of these solutions whose features could improve the efficiency and flexibility of these networks. The aim of this article is to describe this technology, its basic operation and different control strategies, and to indicate the applications that these links currently have, with special emphasis on those that will improve operation and control in medium-voltage distribution networks, some of which are already in operation. KEYWORDS: MVDC, VSC, distribution grids, direct current links, independent power control

A Mean-Field Voltage Control Approach for Active Distribution Networks With Uncertainties

A model-free distributed control scheme that implements active voltage control in low voltage distribution network (LVDN) is proposed. By solving an individual Hamilton-Jacobi-Bellman-Flemming function with public information, users can compute a good approximation to their optimal control trajectory and take uncertainties into account in a distributed manner. A detailed mathematical framework is given, accompanied by a discussion on the different entries of uncertainties. The proposed control scheme uses a broadcast signal to indicate the probability distribution in mean field theory, and to streamline the demand on Fokker-Planck-Kolmogorov PDE or Mc-Kean Vlasov SDE, which relieves the computational burden. A realistic semiurban distribution network is modified as the study case, with a benchmark of centralized ACOPF to study the performance of the proposed approach. Moreover, two special cases including communication latency and packet loss are given as well, in order to test the robustness of the proposed approach. The results prove that the proposed approach is able to deliver good approximation to the optimal control with uncertainty in a model-free and distributed manner.