Distributed Cooperative Secondary Voltage Control in an Unbalanced Microgrid

The negative-sequence reactive power-conductance(Q^(−)-G) droop control strategy is a conventional method to compensate for the output unbalanced voltages in an islanded MG.Nevertheless, the conflict between unbalanced voltage compensation and negative-sequence reactive power sharing, caused bythe impedance mismatching of distribution lines and distributedgenerators, has not been solved only by Q^(−)-G droop control.In this paper, a distributed cooperative secondary unbalancedvoltage control strategy is proposed to decrease the outputvoltage unbalance factor (VUF) of each droop-controlled DG,as well as to further enhance the negative-sequence reactivepower sharing effectiveness among DGs by properly shiftingup and down the Q^(−)-G droop characteristics of each DG.An algorithm for adaptive VUF weight coefficient is proposedto better suppress VUF under severe imbalance conditions.Furthermore, a negative-sequence small-signal model of an MGunder an unbalanced condition, considering the communicationdelay time of the proposed SUVC, is established to analyze thesystem’s stability and transient performance under the influenceof some critical parameters. Finally, the effectiveness of theproposed strategy is validated by the simulation results froma real-time emulator of StarSim HIL.

Distributed Stretching Control of Web Production System

The stretching process,as a key phase of web production system,pursues the target velocities of rollers and the web tensions of spans between the successive rollers to guarantee proper stretching ratios. This requires the stable velocities and velocity ratios of large number rollers separated throughout the workshop. To this goal,a distributed cooperative controller is designed to coordinate the velocities of the rollers to the desired values as well as the target ratios between the upper and lower rollers. During the whole evolution,only the neighbor rollers can exchange the working information,and neither global information nor central controller is required. It is proven that all the rollers asymptotically achieve the desired velocity ratios via the proposed control law,which is also demonstrated by numerical simulation.

Distributed Step-by-step Finite-time Consensus Design for Battery Energy Storage Devices with Droop Control

As all generators are distributed in different areas among large scale power systems,the cooperative manipulation of the multi-generator system cannot operate well without consideration of the distance information of the generators.A distributed step-by-step finite-time consensus scheme for the heterogeneous battery energy storage system(BESS)is proposed in this paper,where the coordinated consensus can come into reality within a limited time,which is appealing for the electrical engineering community.To be concrete,at first,all BESSs are classified into several clusters according to their locations,and in each cluster,there is an active leader in charge of information receiving from outside.Then,in order to coordinate the multi BESSs,five inputs,which are function oriented,were used to achieve energy level balancing,active/reactive power sharing,and the consensus of voltage and frequency of the multi BESSs.Furthermore,the frequency and voltage restoration to the nominal values of the main grid were made possible by the introduction of a virtual leader,which is actually an external leader.Compared with the centralized methods,this control scheme is entirely distributed,and each BESS only utilizes the information of its own and its neighbors.In addition,this control is robust to the load perturbation and the plug-and-play of the communication topology.Finally,some simulation experiments are executed on the modified IEEE 57-bus system to verify the suggested scheme.

Distributed cooperative voltage control based on curve-fitting in active distribution networks

This study investigates a hybrid hierarchical multi-agent system for distributed cooperative voltage control in active distribution networks. The hybrid hierarchical multi-agent system adopts on-load tap-changing(OLTC) agents for the distribution transformers and feeder control section(FCS) agents for the distributed generators(DGs). The objective is to minimize the voltage deviations over the network. The FCS agents also have the objective of minimizing reductions in DG power output. A least squares method is used for curve fitting to achieve the two objectives. The OLTC agent receives voltage information from the FCS agents to evaluate the state of the voltage in each feeder and the distribution network and cooperates with the FCS agents to control the voltage of the network.The FCS agents exchange the fitted curve parameters and basic information on the DGs with other agents to achieve the objectives. The effectiveness of the proposed distributed cooperative voltage control scheme is verified through simulations. Depending on the network voltages obtained by the OLTC agent, different operations are executed to prevent voltage limit violations and to minimize the voltage deviations and reductions in the DG power outputs.

Distributed Cooperative Coverage of Mobile Robots with Consensus-Based Connectivity Estimation

This paper deals with the discrete-time connected coverage problem with the constraint that only local information can be utilized for each robot. In such distributed framework, global connectivity characterized by the second smallest eigenvalue of topology Laplacian is estimated through introducing distributed minimal-time consensus algorithm and power iteration algorithm. A self-deployment algorithm is developed to disperse the robots with the precondition that the estimated second smallest eigenvalue is positive at each time-step. Since thus connectivity constraint does not impose to preserve some certain edges, the self-deployment strategy developed in this paper reserves a sufficient degree of freedom for the motion of robots. Theoretical analysis demonstrates that each pair of neighbor robots can finally reach the largest objective distance from each other while the group keeps connected all the time, which is also shown by simulations.

Distributed cooperative formation of multiple mobile agents with preserved connectivity

This paper investigates distributed cooperative formation control of a group of multiple mobile agents with a virtual leader,where information exchange among agents is modeled by the group topology,and the states of the virtual leader are known only by parts of the agents.We develop a class of distributed formation control laws with similar form.The steered group is proved to achieve the desired formation objectives as long as the intersection of the initial communication topology and the formation goal topology is connected.This requirement of connectivity can be easily achieved by many practical applications;consequently,our developed distributed control laws are effective and feasible.Furthermore,for the developed control laws,we show the influence of different information flow graph of agents on the convergence rate and robustness to node and connection failures.

A Privacy-preserving Algorithm for AC Microgrid Cyber-physical System Against False Data Injection Attacks

A new privacy-preserving algorithm based on the Paillier cryptosystem including a new cooperative control strategy is proposed in this paper, which can resist the false data injection(FDI) attack based on the finite-time control theory and the data encryption strategy. Compared with the existing algorithms, the proposed privacy-preserving algorithm avoids the direct transmission of the ciphertext of frequency data in communication links while avoiding complex iterations and communications. It builds a secure data transmission environment that can ensure data security in the AC microgrid cyber-physical system(CPS). This algorithm provides effective protection for AC microgrid CPS in different cases of FDI attacks. At the same time, it can completely eliminate the adverse effects caused by the FDI attack. Finally, the effectiveness, security, and advantages of this algorithm are verified in the improved IEEE 34-node test microgrid system with six distributed generators(DGs) in different cases of FDI attacks.