Göran Andersson

Fast calculation of a voltage stability index

The minimum singular value of the power flow Jacobian matrix has been used as a static voltage stability index, indicating the distance between the studied operating point and the steady-state voltage stability limit. A fast method to calculate the minimum singular value and the corresponding (left and right) singular vectors is presented. The main advantages of the algorithm are the small amount of computation time needed, and that it only requires information available from an ordinary program for power flow calculations. The proposed method fully utilizes the sparsity of the power flow Jacobian matrix and the memory requirements for the computation are low. These advantages are preserved when applied to various submatrices of the Jacobian matrix. The algorithm was applied to small test systems and to a large system with over 1000 nodes, with satisfactory results. >

Voltage stability indices for stressed power systems

The use of static voltage stability indices based on a singular value decomposition of the power flow Jacobian matrix and matrices derived from the Jacobian matrix is discussed. It is shown that such indices, together with the singular vectors, contain substantial and important information about the proximity to voltage instability and also about critical buses and disturbances from a voltage instability point of view. This is done by a theoretical analysis of the linear power flow equations and an analysis from model power systems as well as realistic power systems (1033 nodes). It is argued that indices based on these matrices are useful for the system analyst in planning and operations planning. >

A Robust Control Strategy for Shunt and Series Reactive Compensators to Dame Electromechanical Oscillations

This paper examines the enhancement of power system stability properties by use of thyristor controlled series capacitors (TCSCs) and static var systems (SVCs). Models suitable for incorporation in dynamic simulation programs used to study angle stability are analyzed. A control strategy for damping of electromechanical power oscillations using an energy function method is derived. Using this control strategy each device (TCSC and SVC) will contribute to the damping of power swings without deteriorating the effect of the other power oscillation damping (POD) devices. The damping effect is robust with respect to loading condition, fault location, and network structure. Furthermore, the control inputs are based on local signals. The effectiveness of the controls is demonstrated for model power systems.

Electricity market regulations and their impact on distributed generation

Distributed generation (DG) has attracted a lot of attention recently and might become more important in future power generation systems. As different definitions are used worldwide, the paper briefly discusses the definition of DG. The future development of DG, however, will, to a not insignificant part, depend on the legal framework. As the legal framework can vary significantly for different competitive electricity markets, this paper briefly identifies and analyses some variations in the regulatory approaches, e.g. for power exchanges, balance services and ancillary services, in different countries. It also illustrates the influence of market regulations on the development of distributed power generation. Based on this analysis, it can be concluded that regulatory aspects might decisively influence the development of distributed power generation.

Voltage dependent reactive power limits for voltage stability studies

This paper presents and studies a static model for synchronous generators with voltage dependent reactive power limits due to maximum stator current, maximum and minimum rotor (field) current as well as maximum rotor angle (underexcitation) limiters. The proposed generator model for static voltage stability studies can be included in an ordinary power flow program, and results from studies on a test system with twenty generators are presented. The influence of voltage dependent reactive power limits is compared with fixed (conventional) limits, by use of the minimum singular value of the power flow Jacobian matrix and related submatrices as indicators of the static voltage stability limit. >

Overview of government and market driven programs for the promotion of renewable power generation

This paper presents and briefly evaluates some existing government instruments and market schemes which support the development of renewable energy generation. The brief evaluation focuses on the incentives provided by the various instruments to reduce production costs. The instruments and schemes are: feed-in tariffs, net metering, bidding process, fixed quotas, green certificate trading, green power exchange, green pricing.

On undervoltage load shedding in power systems

This paper presents an analytical basis and criterion for undervoltage load shedding in power systems. If the voltage is unstable, the proposed undervoltage load shedding criterion can be used to calculate the amount of load which must be shed to stabilise the voltage magnitude. By using a dynamic load model it has been possible to form the criterion which gives the amount of load which has to be shed to stabilise the system in each point in time. The criterion is general and can be applied to any power system.

On the analysis of long-term voltage stability

Abstract This paper presents definitions, models and numerical methods suitable for the study of long-term voltage phenomena, and is an effort to combine ideas presented in other papers by the authors as well as to present some recent numerical results. A main objective for the performed work has been to improve and develop methods for analysis and simulation of power systems in the vicinity of the voltage stability limit. The role of voltage support devices hitting limits is discussed.

A versatile approach for the control of FACTS equipment in multimachine power systems

Abstract In this paper a systematic design method is presented for the control of FACTS (flexible AC transmission systems) components in multimachine power systems. A set of linear state equations with the FACTS components as control variables and an output equation, which links the locally available signals with the system state variables, are derived. Based on the model, a decentralized control approach is proposed. Thyristor controlled series capacitors (TCSC) and thyristor controlled braking resistors (TCBR) are taken as examples to demonstrate the effectiveness of the approach.

Application of modal analysis of zeros to power systems control and stability

This paper describes how to perform modal analysis of system zeros. Based on this, an approach to design and analyze controllers for large scale systems, e.g. power systems, which supplements conventional methods is proposed. The main idea is to adjust the existing structure of the system by retuning internal control loops to relocate critical zeros, thus removing the constraints that arise when zeros are at unsuitable locations; the small-signal dynamics of the power system will be more controllable with a particular device, and even its observability in certain signals will increase. This will improve robustness of the controlled system. Transfer function zeros, how to compute them and the limitations they pose are discussed. A test power system is used for illustrations.