Dongyuan Shi

Power flow study and voltage stability analysis for distribution systems with distributed generation

The voltage instability phenomena may occur in distribution networks. The decline of voltage stability level will restrict the increase of load served by distribution companies. Distributed generation (DG) is increasingly drawing great attention of people. The development of DGs will bring new chances to traditional power systems. DGs connected to distribution networks are potential to improve the system voltage stability. In this paper, the familiar interfaces between DGs and distribution networks are introduced. The operation modes and control characteristics of typical DGs, including asynchronous generators, synchronous generators with constant values of excitation voltage, and fuel cells, are analyzed. Based on the models of DGs proposed in power flow calculations, a new method for constructing a sensitivity matrix is presented, which is available to calculate the power flow of distribution networks with multiple types of DGs. Using this method presented here, the impacts of DGs on the system voltage stability are studied. These impacts are quantified by a voltage stability index introduced in this paper. Some important conclusions are obtained. A 90-bus system is analyzed to give an illustration of the feasibility of the proposed method

A New Approach to Fault Diagnosis of Power Systems Using Fuzzy Reasoning Spiking Neural P Systems

Fault diagnosis of power systems is an important task in power system operation. In this paper, fuzzy reasoning spiking neural P systems (FRSN P systems) are implemented for fault diagnosis of power systems for the first time. As a graphical modeling tool, FRSN P systems are able to represent fuzzy knowledge and perform fuzzy reasoning well. When the cause-effect relationship between candidate faulted section and protective devices is represented by the FRSN P systems, the diagnostic conclusion can be drawn by means of a simple parallel matrix based reasoning algorithm. Three different power systems are used to demonstrate the feasibility and effectiveness of the proposed fault diagnosis approach. The simulations show that the developed FRSN P systems based diagnostic model has notable characteristics of easiness in implementation, rapidity in parallel reasoning, and capability in handling uncertainties. In addition, it is independent of the scale of power system and can be used as a reliable tool for fault diagnosis of power systems.

Enhancements to the Cumulant Method for probabilistic load flow studies

This paper introduces two enhancements to the Cumulant Method (CM) for probabilistic load flow studies. The first one is to handle the correlation between input random variables. This enhancement models the correlated input random variables as a function of several independent ones by Cholesky decomposition and modifies CM equations. The second one is to adopt Monte Carlo sampling techniques to calculate the cumulants of input random variable with complex distribution function. The accuracy and efficiency of the proposed approaches are verified against Monte Carlo simulation method on modified IEEE 14-bus system. The impacts of wind speed correlation on power system operation are investigated by the proposed approaches.

Research on Digital Simulation Platform for Networked Substation

Communication network plays an important role in substation automation system. Industrial Ethernet will replace the parallel wires and extend to process level. Therefore, the substation network should be carefully designed according to the system function constrains, network performance, cost, maintainability and expansibility. Since the design of substation network could not be accomplished only by experience or theoretic calculation, digital simulation platform will become an appropriate method. This paper discusses the necessity of digital simulation platform, which consists of simulation kernel, network analyzer, time server, various simulation models and common graphics platform. It also discusses the simulation process of the digital simulation platform. And simulation models, simulation kernel, network analyzer and other issues to be solved are presented.

A matrix-based fault section estimation algorithm for complex distribution systems

This paper proposes an application of matrix algorithm to fault section estimation in complex distribution systems based on directed over-current information recorded by FTU (feeder terminal unit). First, a concise unified criterion for fault location in multi-source distribution networks is put forward, which can locate both the multiple faults and the end faults. Considering the communication problems which result in incomplete or distorted FTU over-current information, solutions are given for both situations. When the FTU information is incomplete, the fault section estimation process can be carried on as normal with ignorance of the node whose information is unknown. When the fault information suffers from aberrance, fault section candidates are located first based on the unified criterion under no information aberrance. Then the final fault area is selected in terms of the fault information sequence revision cost defined in the paper. The case studies show that the approaches proposed are both correct and feasible, which can effectively resolve the fault location issues in the case of being lack of information or suffering from information aberrance, thus with great potential for application in real-time distribution network fault section estimation programs.

Setting Calculation of the Directional Relays Considering Dynamic Changes in the Network Topology

Identifying some typical and critical system conditions is an important and key step in conducting setting calculation of the directional relays. Under these normal operation or contingency conditions, fault calculation is performed to determine the suitable settings or check relay performance such that their fundamental protective objectives are met for a variety of system configurations and conditions. This paper analyzes the impact of dynamic change of network topology on the relay setting, which includes line outages, breaking of loops and operation mode switching of power substations or plants. Electrical coupling indices of loops are introduced to determine the break-loop lines, whose outage will result in great impact on the distribution of fault current. In addition, sensitivity factors are derived for determining the substations or plants and their corresponding operation modes which have the greatest potential impact on the fault current magnitude. Examples are presented to verify the validity and simplicity of the proposed methods.

Multiobjective optimal network reconfiguration considering the charging load of PHEV

Energy crisis and environmental pollution make the electric vehicle (EV) become a hot topic. The connection of EVs to the power grid brings great challenges to the electric utilities. This paper proposes a multiobjective network reconfiguration methodology based on quantum-inspired binary particle swarm algorithm that aims at alleviating the adverse impact of plug-in hybrid electric vehicle (PHEV) on distribution system. The fuzzy sets are used to handle the multiobjective. The methodology involves two steps: load level division and network reconfiguration on each load level. Two different charging patterns of PHEV are considered in this analysis: uncoordinated charging and coordinated charging. The simulation results of a 33-bus distribution system show that the proposed methodology has a good effect on achieving the energy loss reduction and improving the voltage quality considering the charging load of PHEV.

A method for coherency identification based on singular value decomposition

A novel method to identify coherent generator groups based on singular value decomposition (SVD) in power system is presented in this paper. Via the SVD algorithm, the high-dimensional real-time rotor-angle data of generators is projected into low-dimensional subspace, and the key characteristic coefficients indicating the information of coherency is obtained. Then, the coherency identification is realized by running k-means clustering algorithm on the coefficients. The dimensionality reduction for clustering algorithm by SVD speeds up the coherency identification. Using the real-time rotor-angle data, the proposed method has the potential to be applied to measured data to implement coherency identification. The effectiveness of this method is demonstrated by the simulation results on IEEE 39-bus system.

Provision of Two-area Automatic Generation Control by Demand-side Electric Vehicle Battery Swapping Stations

Application of demand-side resources to automatic generation control (AGC) has a great significance for improving the dynamic control performance of power system frequency regulation. This paper investigates the possibility of providing regulation services by demand-side energy storage in electric vehicle battery swapping stations (BSS). An interaction framework, namely station-to-grid (S2G), is presented to integrate BSS energy storage into power grid for giving benefits to frequency regulation. The BSS can be regarded as a lumped battery energy storage station through S2G framework. A supplementary AGC method using demand-side BSS energy storage is developed considering the vehicle user demand of battery swapping. The effects to the AGC performance are evaluated through simulations by using a two-area interconnected power grid model with step and random load disturbance. The results show that the demand-side BSS can significantly suppress the frequency deviation and tie-line power fluctuations.

Implementing fuzzy reasoning spiking neural P system for fault diagnosis of power systems

Fault diagnosis of power systems is of great significance in restoring the outage area as soon as possible. In this paper, fuzzy reasoning spiking neural P system (FRSN P system) is implemented for fault diagnosis of power systems for the first time. As a graphical modeling tool, FRSN P system is able to represent fuzzy knowledge and perform fuzzy reasoning well. When the cause-effect relationships between candidate faulted section and protective devices are represented by the FRSN P system, the faulty conclusion can be drawn by means of a simple parallel matrix-based operation. A 14-bus power system is used to demonstrate the effectiveness of the proposed diagnosis method. The simulations show that FRSN P system has notable characteristics of being easy to implement, rapid parallel reasoning, and handling uncertainty.