Stability of power systems with large amounts of distributed generation

This four-part dissertation is essentially concerned with some theoretical aspects of the stability studies of power systems with large penetration levels of distributed generation. In particular, in Parts I and II the main emphasis is placed upon the transient rotor angle and voltage stability. The remaining two parts are devoted to some system-theoretic and practical aspects of identification and modeling of aggregate power system loads, design of auxiliary robust control, and a general qualitative discussion on the impact that distributed generation has on the power systems. One of the central themes of this dissertation is the development of analytical tools for studying the dynamic properties of power systems with asynchronous generators. It appears that the use of traditional tools for nonlinear system analysis is problematic, which diverted the focus of this thesis to new analytical tools such as, for example, the Extended Invariance Principle. In the framework of the Extended Invariance Principle, new extended Lyapunov functions are developed for the investigation of transient stability of power systems with both synchronous and asynchronous generators. In most voltage stability studies, one of the most common hypotheses is the deterministic nature of the power systems, which might be inadequate in power systems with large fractions of intrinsically intermittent generation, such as, for instance, wind farms. To explicitly account for the presence of intermittent (uncertain) generation and/or stochastic consumption, this thesis presents a new method for voltage stability analysis which makes an extensive use of interval arithmetics. It is a commonly recognized fact that power system load modeling has a major impact on the dynamic behavior of the power system. To properly represent the loads in system analysis and simulations, adequate load models are needed. In many cases, one of the most reliable ways to obtain such models is to apply a system identification method. This dissertation presents new load identification methodologies which are based on the minimization of a certain prediction error. In some cases, DG can provide ancillary services by operating in a load following mode. In such a case, it is important to ensure that the distributed generator is able to accurately follow the load variations in the presence of disturbances. To enhance the load following capabilities of a solid oxide fuel plant, this thesis suggests the use of robust control. This dissertation is concluded by a general discussion on the possible impacts that large amounts of DG might have on the operation, control, and stability of electric power systems

Modeling Adequacy for Cascading Failure Analysis

This paper describes the mechanisms of cascading failure as the cause of severe blackouts. The severe blackouts that occurred in 2003 affecting large metropolitan areas around the globe are first reviewed. Then the probable root cause of each blackout events is identified in order to seek effective corrective preventive solutions. Several of the well-known techniques for cascading failure analysis and correction are discussed and characterized based on their fundamental features. Thereupon a new model power system component is proposed for simulating cascading failure in actual networks.QC 20111213</p

Comparing Variance Reduction Techniques for Monte Carlo Simulation of Trading and Security in a Three-Area Power System

Abstract-A variance reduction technique is a method used to reduce the variance of a Monte Carlo Simulation. In this paper four of the most commonly used variance reduction techniques are tested to estimate the trade of between trading and security in a three-area electric power system. The comparison is made by regarding both the variance reduction and the bias induced by the method

Monte Carlo Analysis of the Trade-Off between Trading and Security in a Two-Area System

QC 2011120

Comparing Variance Reduction Techniques for Monte Carlo Simulation of Trading and Security in a Three-Area Power System

A variance reduction technique is a method used to reduce the variance of a Monte Carlo Simulation. In this paper four of the most commonly used variance reduction techniques are tested to estimate the trade of between trading and security in a three-area electric power system. The comparison is made by regarding both the variance reduction and the bias induced by the method.© 2008 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 2011032

Improved rotor angular speed measurement : a key for proper power grid stabilization

This paper is presents a new Extended Kalman filter-based method for the estimation of the rotor angular speed of a synchronous machine. The main utility of the estimated speed is in the power system stabilizer. The paper briefly reviews the problems associated with the existing methods for reliable and accurate rotor speed measurement or estimation. It is shown, that the existing methods of rotor speed estimation have some severe drawbacks and may cause the power system stabilizer to produce negative damping over a specific frequency range, when an inaccurate rotor speed signal is used as the input to the power system stabilizer. The new rotor speed estimation method was implemented on an industrial control platform and integrated in a modern digital excitation system. A series of hardware-in-the-loop simulations were run to examine the properties of the new speed estimator. The simulations confirm that the new speed offers superior performance in terms of speed estimation accuracy which allows the proper damping of oscillations over a frequency range of interest.

Limiting transformer overload on distribution systems with high penetration of PV using energy storage systems

In this work, different strategies to limit the over- loading of the transformer in a distribution system are investigated and the solutions based on installing different number of energy storage systems (ESS) of different size and at different locations are devised. In addition, this paper also proposes a simple and effective sizing and siting algorithm for ESS. The sizes for the proposed number of ESS are calculated and then compared for two different conditions: A) when the photovoltaic (PV) is used at 100% of its daily production and B) when the PV peaks are curtailed. The problem solved in this paper originates from a study of a real distribution network located at the southwest of Zurich in Switzerland where the load and photovoltaic (PV) profiles for one year were used to produce the simulation results

Model predictive control of energy systems with hybrid storage

In this work an algorithm to control the power flow of an electric power system with two integrated energy storage systems is investigated. The power system under consideration consists of a conventional distribution feeder that supplies the power to satisfy the customers’ demand, a set of photovoltaic (PV) panels that also contribute to the power generation, one unit of Lithium-Ion battery storage for the intra-day use and a combined power-to-gas (PtG) and gas-to-power installation that converts the power excess in the summertime into hydrogen and injects power back to the system in the wintertime. The proposed control algorithm is based on model predictive control tailored for the energy system under investigation. To demonstrate the performance of the proposed control, a set of synthetic PV and demand profiles representing future conditions in Switzerland were created and used as input data to the system model. The synthesized generation and consumption data span a whole year of operation. A number of detailed simulations performed in the framework of the study reported in this paper demonstrate the effectiveness of the proposed control algorithm and provided invaluable insights into the optimum operation of the complex integrated power system

Feasibility analysis of the Power-to-Gas concept in the future Swiss power system

This paper presents a qualitative and quantitative feasibility analysis of the Power-to-Gas (PtG) technology in the future Swiss power grid which will be characterized by a significant share of intermittent renewable energy sources. The focus is placed on establishing the resolution to effectively integrate renewable energy sources (RES) into Swiss power grid through energy storage systems including pumped hydro storage (PHS) and PtG, which is commonly known to offer the advantage of a long-term storage over other storage options

Advanced control of energy storage systems for PV installation maximizing self-consumption

In this work, a new framework for control of power flow of an energy storage is proposed. As part of the framework, an advanced controller for manipulating the power flow of an energy storage system, a photovoltaic (PV) source, and the utility grid is developed. The new controller relies on the Model-based Predictive Control (MPC) concept. The proposed controller realizes an optimal control scheme that maximizes the local self-consumption of renewable energy source. At the same time, the energy consumption supplied by the electric grid is minimized subject to its price posted in the grid. The presented approach is evaluated through computer-aided simulations using data available from a real installation in Switzerland. The data consists of photovoltaic panels, industrial building as a load as well as a battery energy storage system (BESS)