Haishun Sun

A Fully Decentralized Multi-Agent System for Intelligent Restoration of Power Distribution Network Incorporating Distributed Generations [Application Notes]

In the distribution network fault management, service restoration is a very important component. When a fault occurs, it is necessary to restore power to these deenergized loads as soon as possible. The restoration problem could be formulated as a multilevel, multi-objective optimization problem with constraints [1].

Feasibility Study of Segmenting Large Power System Interconnections With AC Link Using Energy Storage Technology

This paper studies the feasibility of segmenting large power system interconnections with AC link using energy storage technology, similar to the DC link, for improving the system dynamic stability. Firstly, the segmentation validity of the AC interconnected power system using energy storage technology is proved in terms of theoretical analysis, and then a simple and effective control strategy is proposed. Moreover, the influences of the energy storage device location and capacity on the proposed method are discussed in detail. The effectiveness of the proposed method for large AC interconnected power system segmentation is verified by simulations in two AC interconnected power systems.

Multi agent system based wide area protection against cascading events

In this paper, a multi-agent system based wide area protection scheme is proposed in order to prevent long term voltage instability induced cascading events. The distributed relays and controllers work as a device agent which not only executes the normal function automatically but also can be modified to fulfill the extra function according to external requirements. The control center is designed as a highest level agent in MAS to coordinate all the lower agents to prevent the system wide voltage disturbance. A hybrid simulation platform with MATLAB and RTDS is set up to demonstrate the effectiveness of proposed protection strategy. The simulation results indicate that the proposed multi agent control system can effectively coordinate the distributed relays and controllers to prevent the long term voltage instability induced cascading events.

Multiagent System-Based Wide-Area Protection and Control Scheme Against Cascading Events

In this paper, a multiagent system-based wide-area protection and control scheme is proposed to deal with the long-term voltage instability-induced cascading trips. Based on sensitivity analysis between the relay operation margin and power system state variables, an optimal emergency control strategy is defined to adjust the emergency states timely and prevent the unexpected relay trips. In order to supervise the control process and further minimize the load loss, an agent-based process control is adopted to monitor the states of distributed controllers and adjust the emergency control strategy. A hybrid simulation platform based on LabVIEW and real-time digital simulator is set up to simulate a blackout case in the power system of Eastern Denmark and to demonstrate the effectiveness of the proposed MAS-based protection strategy.

Control and protection cooperation strategy for voltage instability

Most cascaded blackouts are caused by unexpected backup relay operations due to low voltage or overload state caused by post fault load restoration dynamics. If such state can be sensed and adjusted appropriately before those relay actions, system stability might be sustained. This paper proposed a control and protection cooperation strategy to prevent post fault voltage instability. The multi-agent technology is applied for the strategy implementation; the criteria based on wide area measured impedances are defined to choose the control strategy, such as tap changer adjusting or load shedding; and the sensitivity based load shedding has been adopted to save the system from severe states. A test system is built in real time digital simulator (RTDS) and has demonstrated the effectiveness of the proposed method.

Power System Structural Vulnerability Assessment Based on an Improved Maximum Flow Approach

With the increasing complexity of the power grid and the concerns on major blackouts, there is an urgent need for an efficient and effective tool to assess the power system structural vulnerability. To tackle this challenge, this paper proposes a maximum flow-based complex network approach to identify the critical lines in a system. The proposed method consists of two major steps. First, the power network is modeled as a graph with edges (transmission lines, transformers, etc.) and nodes (buses, substations, etc.). The critical scenarios are identified by using the principal component analysis and convex hull. Then the second step is to use an improved maximum flow-based complex network approach for topology analysis. Weighted vertices in the network are considered, enabling taking the selected operating conditions into consideration when identifying the vulnerable lines. The proposed method is validated using the western Danish power system. The vulnerable lines in the network are ranked. Simulation results demonstrate the effectiveness of the method by intentional attacks and comparison with the planning strategy from the system operator.

A new energy storage system based on flywheel

This paper proposes a new Energy Storage System based on flywheel called the multi-functional Flexible Power Conditioner (FPC). It consists of the doubly-fed induction machine (DFIM) with very large rotating inertia and a voltage-source pulse width modulation (PWM) rectifier-inverter used as an AC exciter. A simulation model for FPC is built up and is simulated in three operating states, including phase modulation, subsynchronous and super-synchronous. The FPC 10kW model machine is developed and is tested in these proposed operating states and Direct-start. These results show that the proposed equipment provides an effective measure to enhance power system stability.

Wide area protection scheme preventing cascading events caused by load flow transferring

Load flow transferring after an initial contingency is regarded as one of the main reasons of causing unexpected cascading trips. A multi agent system (MAS) based wide area protection strategy is proposed in this paper to predict the load flow transferring from the point of view of impedance relays, and prevent the unexpected relay operations accordingly. The variations of node injections during the post fault transient period will be also considered in the prediction algorithm. The power system of Eastern Denmark modeled in real time digital simulator (RTDS) will be used to demonstrate the proposed strategy. The simulation results indicate this strategy can successfully predict and prevent the unexpected relay operation caused by load flow transferring.

A Novel Energy Storage System based on Flywheel for Improving Power System Stability

In this paper, a novel flywheel energy storage device, called the flexible power conditioner, which integrates both the characteristics of the flywheel energy storage and the doubly-fed induction machine, is proposed to improve power system stability. A prototype is developed and its principle, composition, and design are described in detail. The control system is investigated and the operating characteristics are analyzed. The test results based on the prototype are presented and evaluated. The test results illustrate that the prototype meets the design requirement on power regulation and starting, and provides a cost-effective and effective means to improve power system stability.

Multi agent system based process control in wide area protection against cascading events

In order to prevent long term voltage instability induced cascading events; a multi agent system (MAS) based wide area protection strategy is proposed in this paper. Due to some unexpected failures of control strategy execution or the consequent unexpected disturbance, the power system will face more complex emergent situation than planned. The process control strategy will be applied to improve the effectiveness and reliability of MAS based control strategy. The supervisory agent will help control center in the high level to manage not only the regular control process against the estimated emergent states, but also those unusual control process variations when unexpected situation is experienced. A hybrid simulation platform based on MATLAB/LabVIEW and real time digital simulator (RTDS) is set up to simulate a voltage collapse case in the power system of Eastern Denmark and demonstrate the effectiveness of the improved MAS based protection strategy.