Active filtering of electric power has now become a mature technology for harmonic and reactive power compensation in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) AC power networks with nonlinear loads. This paper presents a comprehensive review of active filter (AF) configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than 200 research publications on the subject is also appended for a quick reference.

A review of active filters for power quality improvement

1. Introduction. 2. The Nature of Power System Oscillations. 3. Modal Analysis of Power Systems. 4. Modal Analysis for Control. 5. Power System Structure and Oscillations. 6. Generator Controls. 7. Power System Stabilizers. 8. Power System Stabilizers - Problems and Solutions. 9. Robust Control. 10. Damping by Electronic Power System Devices. A1. Model Data Formats and Block Diagrams. A2. Equal Eigenvalues. Index.

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Power System Oscillations

(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

Energy systems models are important methods used to generate a range of insight and analysis on the supply and demand of energy. Developed over the second half of the twentieth century, they are now seeing increased relevance in the face of stringent climate policy, energy security and economic development concerns, and increasing challenges due to the changing nature of the twenty-first century energy system. In this paper, we look particularly at models relevant to national and international energy policy, grouping them into four categories: energy systems optimization models, energy systems simulation models, power systems and electricity market models, and qualitative and mixed-methods scenarios. We examine four challenges they face and the efforts being taken to address them: (1) resolving time and space, (2) balancing uncertainty and transparency, (3) addressing the growing complexity of the energy system, and (4) integrating human behavior and social risks and opportunities. In discussing these challenges, we present possible avenues for future research and make recommendations to ensure the continued relevance for energy systems models as important sources of information for policy-making.

https://www.pfenninger.org/publications-pdf/Pfenninger%20et%20al_2014_Energy%20systems%20modeling%20for%20twenty-first%20century%20energy%20challenges.pdf

Energy systems modeling for twenty-first century energy challenges

In recent researches on inverter-based distributed generators, disadvantages of traditional grid-connected current control, such as no grid-forming ability and lack of inertia, have been pointed out. As a result, novel control methods like droop control and virtual synchronous generator (VSG) have been proposed. In both methods, droop characteristics are used to control active and reactive power, and the only difference between them is that VSG has virtual inertia with the emulation of swing equation, whereas droop control has no inertia. In this paper, dynamic characteristics of both control methods are studied, in both stand-alone mode and synchronous-generator-connected mode, to understand the differences caused by swing equation. Small-signal models are built to compare transient responses of frequency during a small loading transition, and state-space models are built to analyze oscillation of output active power. Effects of delays in both controls are also studied, and an inertial droop control method is proposed based on the comparison. The results are verified by simulations and experiments. It is suggested that VSG control and proposed inertial droop control inherits the advantages of droop control, and in addition, provides inertia support for the system.

Comparison of Dynamic Characteristics Between Virtual Synchronous Generator and Droop Control in Inverter-Based Distributed Generators

About The Authors. Preface. Acknowledgements. List of Symbols. PART I: INTRODUCTION TO POWER SYSTEMS. 1 Introduction . 1.1 Stability and Control of a Dynamic System. 1.2 Classification of Power System Dynamics. 1.3 Two Pairs of Important Quantities: Reactive Power/Voltage and Real Power/Frequency. 1.4 Stability of Power System. 1.5 Security of Power System. 1.6 Brief Historical Overview. 2. Power System Components. 2.1 Structure of the Electrical Power System. 2.2 Generating Units. 2.3 Substations. 2.4 Transmission and Distribution Network. 2.5 Protection. 2.6 Wide Area Measurement Systems. 3. The Power System in the Steady-State. 3.1. Transmission Lines. 3.2. Transformers. 3.3. Synchronous Generators. 3.4. Power System Loads. 3.5. Network Equations. 3.6. Power Flows in Transmission Networks. PART II: INTRODUCTION TO POWER SYSTEM DYNAMICS. 4. Electromagnetic Phenomena. 4.1. Fundamentals. 4.2. Three-Phase Short-Circuit on a Synchronous Generator. 4.3. Phase-to-Phase Short-Circuit. 4.4. Synchronization. 4.5. Short Circuit in a Network and its Clearing. 5. Electromechanical Dynamics - Small Disturbances. 5.1. Swing Equation. 5.2. Damping Power. 5.3. Equilibrium Points. 5.4. Steady-State Stability of Unregulated System. 5.5. Steady-State Stability of the Regulated System. 6. Electromechanical Dynamics - Large Disturbances. 6.1. Transient Stability. 6.2. Swings in Multi-Machine Systems. 6.3. Direct Method for Stability Assessment. 6.4. Synchronization. 6.5. Asynchronous Operation and Resynchronization. 6.6 Out-Of-Step Protection Systems. 6.7. Torsional Oscillations in the Drive Shaft. 7. Wind Power. 7.1 Wind Turbines. 7.2 Induction Machine Equivalent Circuit. 7.3 Induction Generator Coupled to the Grid. 7.4 Induction Generators with Slightly Increased Speed Range Via External Rotor Resistance. 7.5 Induction Generators with Significantly Increased Speed Range: DFIGs. 7.6 Fully Rated Converter Systems: Wide Speed Control. 7.7 Peak Power Tracking Of Variable Speed Wind Turbines. 7.8 Connections of Wind Farms. 7.9 Fault Behaviour of Induction Generators. 7.10 Influence of Wind Generators on Power System Stability. 8. Voltage Stability. 8.1. Network Feasibility. 8.2. Stability Criteria. 8.3. Critical Load Demand and Voltage Collapse. 8.4. Static Analysis. 8.5. Dynamic Analysis. 8.6. Prevention of Voltage Collapse. 8.7. Self-Excitation of a Generator Operating on a Capacitive Load. 9. Frequency Stability and Control. 9.1. Automatic Generation Control. 9.2. Stage I - Rotor Swings in the Generators. 9.3. Stage II - Frequency Drop. 9.4. Stage III - Primary Control. 9.5. STAGE IV - Secondary Control. 9.6. FACTS Devices in Tie-Lines. 10. Stability Enhancement. 10.1. Power System Stabilizers. 10.2. Fast Valving. 10.3. Braking Resistors. 10.4. Generator Tripping. 10.5. Shunt FACTS Devices. 10.6. Series Compensators. 10.7. Unified Power Flow Controller . PART III: ADVANCED TOPICS IN POWER SYSTEM DYNAMICS. 11. Advanced Power System Modelling. 11.1 Synchronous Generator. 11.2. Excitation Systems. 11.3. Turbines and Turbine Governors. 11.4. FACTS Devices. 12. Steady-State Stability of Multi-Machine System. 12.1. Mathematical Background. 12.2. Steady-State Stability of Unregulated System. 12.3. Steady-State Stability of The Regulated System. 13. Power System Dynamic Simulation. 13.1. Numerical Integration Methods. 13.2. The Partitioned-Solution. 13.3. The Simultaneous Solution Methods. 13.4. Comparison Between the Methods. 14. Power System Model Reduction - Equivalents. 14.1. Types of Equivalents. 14.2. Network Transformation. 14.3. Aggregation of Generating Units. 14.4. Equivalent Model of External Subsystem. 14.5. Coherency Recognition. 14.6. Properties of Coherency-Based Equivalents. Appendix. References. Index.

Power system dynamics : stability and control

Power System Components. The Power System in the Steady-State. Electromagnetic Phenomena. Electromechanical Dynamics - Small Disturbances. Electromechanical Dynamics - Large Disturbances. Voltage Stability. Frequency Variations. Stability Enhancement. Advanced Power System Modelling. Power System Model Reduction - Equivalents. Steady-State Stability of Multi-Machine System. Power System Dynamic Simulation. Appendix. References. Index.

Power system dynamics and stability

An optimal excitation control strategy for a synchronous generator is derived using Lyapunov's direct method and the nonlinear system equations. The control strategy requires neither phase compensation nor wash-out circuits characteristic of standard power system stabilisers (PSS). By using a nonlinear system model, the control strategy is optimal over a wide range of rotor angle and swing frequency changes. The excitation control system required to implement the control strategy is hierarchical and has a different structure to the traditional excitation control system with PSS. In the proposed structure a primary controller damps quickly any power swings using the synchronous EMF as the feedback signal. A secondary controller maintains constant generator voltage by adjusting the reference value of the synchronous EMF fed to the primary controller to that required by the actual operating conditions. The proposed excitation control system has been tested on a single generator-infinite busbar system with the simulation results showing excellent damping of power swings over a wide range of operating conditions whilst retaining good voltage control.

Excitation control system for use with synchronous generators

Large interconnected power systems often suffer from weakly damped swings between synchronous generators and subsystems. This paper presents an approach, based on the use of the nonlinear system model and application of the direct Lyapunov method, to improve damping of power swings using the unified power flow controller (UPFC). A state-variable control strategy has been derived as well as its implementation using locally available signals of real and reactive power. The results of simulation tests, undertaken using a small multi-machine system model, have been presented.

Application of the direct Lyapunov method to improve damping of power swings by control of UPFC

This paper describes new structures for stability-enhancing excitation controllers designed using a nonlinear multi-machine system model and Lyapunov's direct method. Two control structures are presented: a hierarchical structure In which the AVR is the master controller and the PSS the slave controller and a traditional structure in which the PSS constitutes a supplementary loop to the main AVR. Both controllers are shown to be robust, as the damping they introduce into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralized approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system are presented that confirm the above and show that the two control structures are very effective in damping both local and inter-area power swings.

Jan Machowski

Papers

Power system dynamics : stability and control

Power system dynamics and stability

Excitation control system for use with synchronous generators

Application of the direct Lyapunov method to improve damping of power swings by control of UPFC

Decentralized stability-enhancing control of synchronous generator