Modelling and control of united power flow controller for reinforcement of transmission systems

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The work involved in the thesis is concentrated on modelling and control of UPFC. The overall objective is to provide effective methods and tools for assessing the impact of UPFC in the reinforcement of transmission systems. The thesis clarifies modelling and control of UPFC into several subproblems, in which the associated models, algorithms and control strategies of UPFC have been systematically reviewed. An electromagnetic transient prototype model of the UPFC has been set up by using its detailed power electronic device as well as its internal closed-loop controller. The problems encountered in the process of building such a model and the way of handling them by EMTP have been discussed. This EMTP-based simulator of SPWM UPFC implemented has provided a useful tool to assist the development and validation of more detailed and practical model of the UPFC for further studies. The steady-state modelling and control for the UPFC has been developed, including: (i) The power injection model of the UPFC suitable for its implementation in an optimal multiplier power flow computation method has been derived in rectangular form. The effectiveness of the proposed algorithm has been compared with the user defined model method. (ii) A systematic method for deriving the control capabilities of the UPFC has been proposed based on predicting the feasibility limit of the system. Using an index derived from optimal multiplier, three dimensional diagrams describing the ranges have been obtained. The results are also verified through the singular value decomposition algorithm. (iii) A power injection model based control method (PIM) has been proposed and implemented to directly derive the UPFC parameters as so to achieve the control objectives. The assumptions, algorithmic process and validation of the PIM have been investigated in detail. Its pros and cons are also discussed. (iv) Five internal limits of the UPFC device have been derived as the constraints to its performance. A complete set of control rules considering these limits as well as their implementation in the PlM have been constructed to form the basis of optimal UPFC control strategies for its steady-state local control. All the above proposed methods are tested and validated on the IEEE 30-bus system, a practical 306-bus system and a meshed network. The thesis concludes by suggesting the future research areas in further UPFC studies

Analysis and robust decentralized control of power systems using FACTS devices

Today\u27s changing electric power systems create a growing need for flexible, reliable, fast responding, and accurate answers to questions of analysis, simulation, and design in the fields of electric power generation, transmission, distribution, and consumption. The Flexible Alternating Current Transmission Systems (FACTS) technology program utilizes power electronics components to replace conventional mechanical elements yielding increased flexibility in controlling the electric power system. Benefits include decreased response times and improved overall dynamic system behavior. FACTS devices allow the design of new control strategies, e.g., independent control of active and reactive power flows, which were not realizable a decade ago. However, FACTS components also create uncertainties. Besides the choice of the FACTS devices available, decisions concerning the location, rating, and operating scheme must be made. All of them require reliable numerical tools with appropriate stability, accuracy, and validity of results. This dissertation develops methods to model and control electric power systems including FACTS devices on the transmission level as well as the application of the software tools created to simulate, analyze, and improve the transient stability of electric power systems.;The Power Analysis Toolbox (PAT) developed is embedded in the MATLAB/Simulink environment. The toolbox provides numerous models for the different components of a power system and utilizes an advanced data structure that not only increases data organization and transparency but also simplifies the efforts necessary to incorporate new elements. The functions provided facilitate the computation of steady-state solutions and perform steady-state voltage stability analysis, nonlinear dynamic studies, as well as linearization around a chosen operating point.;Applying intelligent control design in the form of a fuzzy power system damping scheme applied to the Unified Power Flow Controller (UPFC) is proposed. Supplementary damping signals are generated based on local active power flow measurements guaranteeing feasibility. The effectiveness of this controller for longitudinal power systems under dynamic conditions is shown using a Two Area - Four Machine system. When large disturbances are applied, simulation results show that this design can enhance power system operation and damping characteristics. Investigations of meshed power systems such as the New England - New York power system are performed to gain further insight into adverse controller effects

Damping interarea and torsional oscillations using FACTS devices

A problem of interest in the power industry is the mitigation of interarea and torsional oscillations. Interarea oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transfer over a corridor is high relative to the transmission strength. These oscillations can severely restrict system operations and, in some cases, can lead to widespread system disturbances. Torsional oscillations are induced due to the interaction between transmission system disturbances and turbine-generator shaft systems. The high torsional stresses induced due to some of these disturbances reduce the life expectancy of the turbine-generators and, in severe cases, may cause shaft damage. This thesis reports the development of novel control techniques for Flexible AC Transmission System (FACTS) devices for the purpose of damping power system interarea and torsional oscillations. In this context, investigations are conducted on a typical three-area power system incorporating FACTS devices. The Genetic Algorithm (GA) and fuzzy logic techniques are used for designing the FACTS controllers. Although attention is focused in the investigations of this thesis on the Unified Power Flow Controller (UPFC), studies are also conducted on two other FACTS devices, a three voltage-source converter Generalized Unified Power Flow Controller (GUPFC) and a voltage-source converter back-to-back HVdc link. The results of the investigations conducted in this thesis show that the achieved control designs are effective in damping interarea oscillations as well as the high torsional torques induced in turbine-generator shafts due to clearing and high-speed reclosing of transmission system faults. The controller design procedures adopted in this thesis are general and can be applied to other FACTS devices incorporated in a power system. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating FACTS devices

Robust Coordinated Control of FACTS Devices in Large Power Systems

With the rapid development of power electronics, Flexible AC Transmission Systems (FACTS) devices have been proposed and implemented in power systems. This research mainly investigates the robust coordinated control of FACTS devices and traditional power system controllers in large power systems. The following objectives have been achieved: 1. FACTS modeling and controller design: FACTS devices are modeled using the current injection method. Linear and non-linear methods for the FACTS damping controller design are developed. 2. Optimal choice and allocation of FACTS devices: Using the genetic algorithms, the locations of the FACTS devices, their types and rated values are optimized simultaneously. The objective function, which consists of the investment costs for FACTS devices and the generation costs, is minimized. 3. Adaptive FACTS transient controller design using ANFIS technology: This objective deals with the development of fuzzy adaptive FACTS transient stability controller. Furthermore, by means of Adaptive Network based Fuzzy Inference System (ANFIS) technology, the fuzzy controller parameters are optimized. 4. Simultaneous coordinated tuning of FACTS damping controller and conventional Power System Stabilizers (PSSs): Using the linearized power system model and the parameter-constrained non-linear optimization algorithm, interactions among PSS and FACTS damping controllers are considered. The controller parameters are optimized simultaneously to achieve a global optimal damping behavior. 5. Robust FACTS loop-shaping Power Oscillation Damping (POD) controller design in multi-machine power systems: By applying the model reduction and modern robust loop-shaping control technique, the FACTS robust loop-shaping POD controller is realized. This controller exploits the advantages of both conventional loop-shaping and modern H infinite robust control technique. Moreover, it is a decentralized approach and suitable for FACTS controller design in real large power systems. Die Dissertation erscheint parallel im Logos-Verlag, Berlin mit der ISBN 3-8325-0570-

A New Converter Station Topology to Improve the Overall Performance of a Doubly Fed Induction Generator-Based Wind Energy Conversion System

This thesis presents a reliable and cost effective technique that calls for reconfiguration of the existing converters of a typical Doubly Fed Induction Generator to include a coil of low internal resistance. A coil within the DC link is the only hardware component required to implement this technique. With a proper control scheme, activated during fault conditions, this coil can provide the same degree of performance as a superconducting magnetic energy storage unit during fault conditions

Transmission congestion management by optimal placement of FACTS devices

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University, 13/09/2010.This thesis describes the implementation of the Flexible AC Transmission Systems (FACTS) devices to develop a market-based approach to the problem of transmission congestion management in a Balancing Market. The causes, remedies and pricing methods of transmission congestion are briefly reviewed. Balancing Market exists in markets in which most of the trading is done via decentralized bilateral contracts. In these markets only final adjustments necessary to ensure secure system operation is carried out at a centralized Balancing Market. Each market player can participate in the Balancing Market by submitting offers and bids to increase and decrease its initially submitted active generation output. In this research a method is proposed to reduce costs associated with congestion re-dispatch in a Balancing Market by optimal placement of FACTS devices, and in particular Thyristor Controlled Phase Shifter Transformers (TCPST). The proposed technique is applicable to both Mixed Integer Linear Programming (MILP) and Mixed Integer Non-Linear Programming (MINLP). In the MILP a power system network is represented by a simplified DC power flow under a MILP structure and the Market participants' offers and bids are also represented by linear models. Results show that applications of FACTS devices can significantly reduce costs of congestion re-dispatch. The application of the method based on the MINLP creates a nonlinear and non-convex AC OPF problem that might be trapped in local sub-optima solutions. The reliability of the solution that determines the optimal placement of FACTS devices is an important issue and is carried out by investigation of alternative solvers. The behavior of the MINLP solvers is presented and finally the best solvers for this particular optimization problem are introduced. The application of DC OPF is very common in industry. The accuracy of the DC OPF results is investigated and a comparison between the DC and AC OPF is presented

MODELING AND CONTROL OF INTERLINE POWER FLOW CONTROLLER FOR POWER SYSTEM STABILITY ENHANCEMENT

Mitigation of power system oscillations is the problem of concern in the power industry as these oscillations, when exhibiting poor damping; affect the transmission line power transfer capability and power system stability. These oscillations greatly restrict power system operations and, in some cases, can also lead to widespread system disturbances. In this context, the Flexible AC Transmission System (FACTS) device, Interline Power Flow Controller (IPFC) employed to improve the transmission capability can be additionally utilized for damping control of power system oscillations. IPFC based damping controller design for power system stability requires proper and adequate mathematical representation of power system incorporating the FACTS device. This thesis reports the investigation on the development of steady state model, the dynamic nonlinear mathematical model of the power system installed with the IPFC for stability studies and the linearized extended Phillips Heffron model for the design of control techniques to enhance the damping of the lightly damped oscillations modes. In this context, the mathematical models of the single machine infinite bus (SMIB) power system and multi-machine power system incorporated with IPFC are established. The controllers for the IPFC are designed for enhancing the power system stability. The eigenvalue analysis and nonlinear simulation studies of the investigations conducted on the SMIB and Multi-machine power systems installed with IPFC demonstrate that the control designs are effective in damping the power system oscillations. The results presented in this thesis would provide useful information to electric power utilities engaged in scheduling and operating with the FACTS device, IPFC

Power System Simulation, Control and Optimization

This Special Issue “Power System Simulation, Control and Optimization” offers valuable insights into the most recent research developments in these topics. The analysis, operation, and control of power systems are increasingly complex tasks that require advanced simulation models to analyze and control the effects of transformations concerning electricity grids today: Massive integration of renewable energies, progressive implementation of electric vehicles, development of intelligent networks, and progressive evolution of the applications of artificial intelligence

Decentralized operation and control of integrated transactive and physical grids

The objective of this research is to develop a decentralized grid architecture to manage the physical and transactive aspects of power systems. With exponentially decreasing prices of PV the adoption of volatile and non-dispatchable sources into the grid has increased. This has two key impacts. Physical phenomenon like congestion of power flow corridors and voltage volatility become more prevalent. Similarly, with increasing prosumers, a multi-agent system is created, with each asset owner wanting to transact power. Existing transactive and physical control solutions are centralized, rely on low-latency communications, often require detailed knowledge of network topologies and are often highly coupled. The proposed research showcases fast localized grid control solutions in the form of hybrid transformers to manage physical phenomenon like congestion and voltage volatility. Furthermore, a decentralized, communication-free and topology-agnostic real-time pricing mechanism is proposed to enable collective stabilization even under wide variations in available generation. Thus, an architecture is presented where the transactive and physical grid constraints are handled in a decoupled fashion while being integrated through the physics of the network.Ph.D

Control of transmission system power flows

Power flow (PF) control can increase the utilization of the transmission system and connect lower cost generation with load. While PF controllers have demonstrated the ability to realize dynamic PF control for more than 25 years, PF control has been sparsely implemented. This research re-examines PF control in light of the recent development of fractionally-rated PF controllers and the incremental power flow (IPF) control concept. IPF control is the transfer of an incremental quantity of power from a specified source bus to specified destination bus along a specified path without influencing power flows on circuits outside of the path. The objectives of the research are to develop power system operation and planning methods compatible with IPF control, test the technical viability of IPF control, develop transmission planning frameworks leveraging PF and IPF control, develop power system operation and planning tools compatible with PF control, and quantify the impacts of PF and IPF control on multi-decade transmission planning. The results suggest that planning and operation of the power system are feasible with PF controllers and may lead to cost savings. The proposed planning frameworks may incent transmission investment and be compatible with the existing transmission planning process. If the results of the planning tool demonstration scale to the national level, the annual savings in electricity expenditures would be $13 billion per year (2010$). The proposed incremental packetized energy concept may facilitate a reduction in the environmental impact of energy consumption and lead to additional cost savings.Ph.D