M. S. Rahman

A decentralised multi-agent approach to enhance the stability of smart microgrids with renewable energy

This paper presents the impact of large penetration of wind power on the transient stability through a dynamic evaluation of the critical clearing times (CCTs) by using intelligent agent-based approach. A decentralised multi-agent-based framework is developed, where agents represent a number of physical device models to form a complex infrastructure for computation and communication. They enable the dynamic flow of information and energy for the interaction between the physical processes and their activities. These agents dynamically adapt online measurements and use the CCT information for relay coordination to improve the transient stability of power systems. Simulations are carried out on a smart microgrid system for faults at increasing wind power penetration levels and the improvement in transient stability using the proposed agent-based framework is demonstrated.

Distributed agent-based control scheme for single-phase parallel inverters in microgrids with photovoltaic systems

In this paper, an agent-based distributed control scheme is presented to control single-phase parallel inverters in solar photovoltaic (PV) systems connected to microgrids. A communication assisted multi-agent framework is developed within microgrids where agents perform their tasks in a distributed manner with an aim of stabilizing load voltage and current under normal and faulted conditions through the asymptotic tracking of the reference current signal. The distributed agent-based control scheme requires information from the neighboring agents through communication network to decide control actions. The proposed control scheme utilizes Ziegler-Nichols (Z-N) tuning approach to design proportional integral (PI) controllers for controlling inverters within the multi-agent system (MAS). A microgrid with parallel inverter-connected solar PV systems is considered for simulations under normal and faulted conditions where results show the excellency of the proposed agent-based scheme in comparison to the conventional scheme without MAS.

Impact of distributed generation and series compensation on distribution network

In this paper, the voltage profile and power quality issues of a distribution network with distributed generator (DG) and series compensation are investigated. A doubly-fed induction generator (DFIG)-based DG unit and a series capacitor (SC) and a thyristor-controlled series capacitor (TCSC) are considered for the analysis. Series compensation is implemented to reduce voltage drops in the line and feeder, and to minimize the reactive power mismatch caused by integrating DFIG units. The converter of the DFIG is modeled as an unbalanced harmonic-generating source and the load is modeled according in IEC standard 61000. The impacts of DG and series compensation on voltage profile, stability margin, dynamic stability and harmonic distortion of a distribution network are investigated in detail. Case studies are conducted on a widely used 15-bus distribution network in the DIgSILENT PowerFactory environment. The simulation results demonstrate that series compensation can enhance the collapse margin, reduce bus voltage sensitivity to reactive power and also improve both dynamic and transient voltage stabilities.

A multi-agent approach for security of future power grid protection systems

In this paper, an innovative agent-based security scheme is proposed for identifying potential impacts of cyber attacks in smart grid protection systems. Smart grids are critical cyber-physical energy systems (CPESs), where potential attacks can manipulate the normal operation of digital relays by injecting malicious control signals. This event could cause the relays to trip at undesired time which in turn results unintentional trippings, even if there are no faults. The proposed scheme identifies the malicious cyber attacks by utilizing cyber and physical properties of power systems. Moreover, the agents further distinguishes attacks from physical faults and their potential is validated through computer simulation using a benchmark power system.

Distributed multi-agent scheme to improve dynamic voltage stability of distribution networks

In this paper, a distributed multi-agent scheme is presented for reactive power management with renewable energy sources (RESs). The multi-agent system (MAS) framework is developed for distribution systems to improve the stability which is mostly dominated by voltage and the agents in this framework coordinate among themselves using online information and energy flow. In this paper, the agents basically perform two tasks- reactive power estimation and necessary control actions. The topology of distribution network is used to estimate the required reactive power for maintaining voltage stability where distributed static synchronous compensators(DSTATCOMs) are used to supply this reactive power. The DSTATCOM is controlled by using a linear quadratic regulator (LQR) controller within the agent framework. The proposed scheme is further compared with the conventional approach to validate the simulation results.

Distributed Multi-Agent-Based Protection Scheme for Transient Stability Enhancement in Power Systems

Abstract This paper presents a new distributed agent-based scheme to enhance the transient stability of power systems by maintaining phase angle cohesiveness of interconnected generators through proper relay coordination with critical clearing time (CCT) information. In this distributed multi-agent infrastructure, intelligent agents represent various physical device models to provide dynamic information and energy flow among different physical processes of power systems. The agents can communicate with each other in a distributed manner with a final aim to control circuit breakers (CBs) with CCT information as this is the key issue for maintaining and enhancing the transient stability of power systems. The performance of the proposed scheme is evaluated on a standard IEEE 39-bus New England benchmark system under different large disturbances such as three-phase short-circuit faults and changes in loads within the systems. From the simulation results, it is found that the proposed scheme significantly enhances the transient stability of power systems as compared to a conventional scheme of static CB operation.

Distributed multi-agent scheme to enhance cyber security of smart power grids

This paper presents a distributed multi-agent scheme for enhancing the cyber security of smart grids which integrates computational resources, physical processes, and communication capabilities. Smart grid infrastructures are vulnerable to various cyber attacks and noises whose influences are significant for reliable and secure operations. A distributed agent-based framework is developed to investigate the interactions between physical processes and cyber activities where the attacks are considered as additive sensor fault signals and noises as randomly generated disturbance signals. A model of innovative physical process-oriented counter-measure and abnormal angle-state observer is designed for detection and mitigation against integrity attacks. Furthermore, this model helps to identify if the observation errors are caused either by attacks or noises.

Agent based coordinated control of protection devices for transient stability enhancement

This paper presents the use of the multi-agent technology in order to enhance the transient stability of power systems by the dynamic evaluation of the critical clearing time (CCT) including the effect of the distance of fault locations and the impact of the renewable energy source (RES) integration. A multi-agent framework is developed in this research, where the intelligent agents use an algorithm for coordinating the protection devices to isolate the faulted part from the rest of the system before the corresponding CCT, so as to increase the stability margin of the system for the transient stability assessment. Simulations are carried out on a multimachine test system for different fault locations and the stability of the system is observed from the simulation of the machines relative rotor angles.

A multi-agent approach for enhancing transient stability of smart grids with renewable energy

This paper presents the use of an intelligent multi-agent system (MAS) approach to investigate the effect of a sudden change in generator load and the impact of integrating renewable energy sources (RESs) on the enhancement of the transient stability of smart power grids. In this proposed approach, an algorithm is developed through which intelligent agents properly coordinate a systems protective relays using the critical clearing time (CCT) information to avoid loss of synchronism. An IEEE 14-bus test system is used to dynamically evaluate the on-line performance and effectiveness of the proposed approach. The simulation results show that the individual agents provide a powerful framework to successfully enhance the transient stability of the system for different fault locations under various generator load conditions and increasing penetration of wind power.

Voltage stability analysis of power distribution networks using multi-agent approach

In this paper, a communication assisted multi-agent system (MAS) is proposed for improving the voltage profile of distribution systems through proper estimation and control of reactive power. Since renewable energy sources (RESs) connected to distribution networks are highly unpredictable in nature, it is more important to maintain the voltage profile within the permissible limits during this atmospheric changes. The agents in the designed MAS improve the voltage stability which is mostly dominated by reactive power and coordinate their tasks through online information and power flow. The agents effectively estimates the adequate amount of reactive power from the topology of distribution network and maintain voltage stability where distributed static synchronous compensators (DSTATCOMs) are used to supply this reactive power. The main control approach is based on designing a linear quadratic regulator (LQR) with an integrator within the agent framework to control the DSTATCOM. The proposed scheme is validated by comparing it with the conventional PI controller and the simulation results show that the proposed scheme performs in a much better and smarter way even with communication delay.