Transient Stability Enhancement of Electric Power Grid by Novel Braking Resistor Models

The dynamic braking resistor is one of the effective methods to enhance the transient stability of power grid system. In this work, two new braking resistor models, namely, rectifier controlled braking resistor and chopper rectifier controlled braking resistor mod-els, using a single unit of braking resistor are proposed, and their performance is compared with the existing thyristor controlled braking resistor model. Comparison is made in terms of the speed indices, number of components used, heat loss, harmonics, and cost. The effectiveness of the proposed methodology is tested through Matlab/ Simulink simu-lations considering both temporary and permanent faults in power system. Simulation results for all braking resistor models are compared and analyzed. The performance of the proposed models is comparable to the existing braking resistor model. Therefore, the proposed braking resistor models can be considered as an alternative to the existing BR model for improving the transient stability of power systems

Comparison of Stabilization Methods for Fixed-Speed Wind Generator Systems

Static Synchronous Compensator (STATCOM), Pitch control system, Braking Resistor (BR), and Superconducting Magnetic Energy Storage (SMES) have recently been reported as stabilization methods for fixed-speed wind generator systems. although the individual technologies are well documented, a comparative study of these systems has not been reported so far. This paper aims to fill in the gap, and provides a comprehensive analysis of these stabilization methods for fixed-speed wind generator systems. The analysis is performed in terms of transient stability enhancement, controller complexity, and cost. a novel feature of this work is that the transient stability analysis of wind generator system is carried out considering unsuccessful reclosing of circuit breakers. Simulation results demonstrate that the SMES is the most effective means of transient stability enhancement and minimization of both power and voltage fluctuations, but it is the most expensive device. The STATCOM is a cost-effective solution for transient stability enhancement and minimization of voltage fluctuations. The BR is the simplest in structure and a cost-effective solution for transient stability enhancement. The pitch controller is the cheapest one, but its response is much slower than that of other devices

Fault analysis and protection for wind power generation systems

Wind power is growing rapidly around the world as a means of dealing with the world energy shortage and associated environmental problems. Ambitious plans concerning renewable energy applications around European countries require a reliable yet economic system to generate, collect and transmit electrical power from renewable resources. In populous Europe, collective offshore large-scale wind farms are efficient and have the potential to reach this sustainable goal. This means that an even more reliable collection and transmission system is sought. However, this relatively new area of offshore wind power generation lacks systematic fault transient analysis and operational experience to enhance further development. At the same time, appropriate fault protection schemes are required. This thesis focuses on the analysis of fault conditions and investigates effective fault ride-through and protection schemes in the electrical systems of wind farms, for both small-scale land and large-scale offshore systems. Two variable-speed generation systems are considered: doubly-fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSGs) because of their popularity nowadays for wind turbines scaling to several-MW systems. The main content of the thesis is as follows. The protection issues of DFIGs are discussed, with a novel protection scheme proposed. Then the analysis of protection scheme options for the fully rated converter, direct-driven PMSGs are examined and performed with simulation comparisons. Further, the protection schemes for wind farm collection and transmission systems are studied in terms of voltage level, collection level wind farm collection grids and high-voltage transmission systems for multi-terminal DC connected transmission systems, the so-called “Supergrid”. Throughout the thesis, theoretical analyses of fault transient performances are detailed with PSCAD/EMTDC simulation results for verification. Finally, the economic aspect for possible redundant design of wind farm electrical systems is investigated based on operational and economic statistics from an example wind farm project

Fault Ride-Through Capacity Enhancement of Fixed Speed Wind Generator by A Modified Bridge-type Fault Current Limiter

Fault Ride-Through (FRT) is a common requirement to abide by grid code all over the world. In this work, to enhance the fault ride-through capability of a fixed speed wind generator system, a modified configuration of Bridge-Type Fault Current Limiter (BFCL) is proposed. To check the effectiveness of the proposed BFCL, its performance is compared with that of the Series Dynamic Braking Resistor (SDBR). A harmonic performance improvement by the proposed method is also analyzed. Three-line-to-ground (3LG), line-to-line (LL) and single-line-to-ground (1LG) faults were applied to one of the double circuit transmission lines connected to the wind generator system. Simulations were carried out using Matlab/Simulink software. Simulation results show that the proposed BFCL is very effective device to achieve the FRT and suppress fault current that eliminates the need for circuit breaker replacement. Also, the BFCL improves the harmonic performance and helps follow harmonic grid code. Moreover, it was found that the BFCL works better than the SDBR, and has some distinct advantages over the SDBR

Fault ride-through of wind farms using series dynamic braking resistors

Wind power is one of the world's fastest growing industries. The resulting penetration of wind power has led to substantial changes in requirements for large wind farms. Fault Ride-Through (FRT) was an important new requirement for wind farms to remain connected and actively contribute to system stability during a wide range of network faults. The wind industry responded with several approaches to FRT compliance including dynamic Reactive Power Compensation (dRPC) and pitch control. New requirements, combined with the reduced cost and increased efficiency of power electronic converters has led to the increasing dominance of Variable Speed Wind Turbines (VSWTs). Recent research has therefore focused on VSWTs. This Thesis presents a new technology, invented and developed during my PhD project, which provides a rearguard opportunity for Fixed Speed Wind Turbines (FSWTs) to comply with FRT requirementsu sing a series Dynamic Braking Resistor (sDBR). sDBR contributes directly to the balance of active power during a fault by inserting a series resistor into the generation circuit, increasing generator terminal voltage. The aim of the analysis, simulation and experimental work in this Thesis is to demonstrate the potential and scope of sDBR to contribute to FRT compliance of FSWTs. sDBR is shown to be a simple and effective means of displacing expensive dRPC to achieve full compliance with Great Britain's FRT requirements. It is also shown to be capable of contributing to compliance with the more onerous FRT requirements in conjunction with other technologies. Detailed transient simulations of sDBR were confirmed by experimental results using a 7.5kW test-rig. Although the FSWT market is severely weakened, opportunities remain in niche markets for new and existing wind farms. Continued research into high-speed switching, variable resistance and integrated control could further improve basic sDBR performance. Further research into new applications with distribution networks,s mall wind turbines and doubly-fed induction generators could also extend its application in new markets with longer horizons.EThOS - Electronic Theses Online ServiceEPSRC : NaRECGBUnited Kingdo

Development of Robust and Dynamic Control Solutions for Energy Storage Enabled Hybrid AC/DC Microgrids

Development of Robust and Dynamic Control Solutions for Energy Storage Enabled Hybrid AC/DC Microgrid

Modeling and dynamic stability of distributed generations

The objective of this dissertation is to develop dynamic models for distributed generations (DG), to investigate their impacts on dynamic stability of power distribution systems, and to design controllers for DGs to improve the dynamic stability of the integrated power distribution system.;A two-year distributed generation (DG) project at West Virginia University (WVU) evaluated the impact of various DG sources on actual distribution systems by performing computer simulations. The data is supplied by two regional electric utilities of two actual distribution systems each. In this project several important issues were investigated, including the availability of simulation tools and impacts of DGs connected to a distribution line under a variety of line operating conditions. Based on this preliminary research the further most interesting topics for continued research were raised.;The continued research has focused on deeper investigation, such as, modeling DG sources, evaluating their interaction and impacts, and improving the dynamic stability of the integrated power distribution system. Four specific DGs are studied in this dissertation: fuel cell power plant, wind turbine induction generator, gas turbine synchronous generator and diesel engine synchronous generator.;A full-order synchronous generator model represents the generator models of gas turbine generator and diesel engine generator. A simplified gas turbine model has been chosen to be implemented. A practical diesel engine for emergency use is modeled. The generator model of wind turbine induction generator is represented by a full-order induction generator. The rated power operating regime is considered for impacts evaluations and controller design. Two types of fuel cell models are developed. The first one is a model of already operational phosphoric acid fuel cell (PAFC) obtained through data fitting and the second one is dynamic model of solid oxide fuel cell (SOFC). Since fuel cells are connected to the electric power network via inverters, an inverter model has been developed.;Multi-DG controls are investigated in this dissertation. One DG control is fuel cell control, the other one is wind-turbine control. The control of fuel cell (SOFC) plant is through the inverter to adjust active power injection to the network during the transient time. The control of wind turbine generator is through the parallel connected SVC by adjusting reactive power injection to the system. Both control schemes are centralized.;Linear analysis methodologies are utilized in designing the controller. In the fuel cell control design, two pairs of critical modes are screened out using eigenvalue analysis. The participation factors of DGs with respect to the modes are calculated. Two specific lead-lag compensation units are designed to damp each mode separately. The gains of the two compensation units were then obtained via optimal control methodology. In wind turbine DG control design procedure, three rotor speed deviations are used as input signals while the controller outputs are the firing angle for the SVC and the pitch angle for the wind-turbine DG. An output feedback controller is designed. The dynamic load characteristic is also considered by modeling it as a structured uncertainty. mu-analysis is used to evaluate the robust stability of the controllers with respect to the uncertain parameters in the dynamic loads. The IEEE-13 node radial feeder with existing gas turbine and diesel engine DGs is used as a test system to evaluate the multi-DG control. The simulation results demonstrate the effectiveness of the control strategies.;Coordinated operation of all the DGs is investigated. Simulation results show that good configurations within DGs along the system can improve the system stability. Furthermore, the fast acting SVC is very effective in improving damping. Among the DGs investigated in this research, the fuel cell plant control is the best choice for the coordinated operation.;Finally, the approach to model a complete three-phase power distribution system is implemented. The impact of the developed DGs models is evaluated on a three-phase unbalanced distribution system. The three-phase 13-node IEEE system with gas turbine and diesel engine DGs is simulated using MATLAB/Simulink\u27s Power System Blockset (PSB). In the simulation, a three-phase thyristor controlled braking resistor (TCBR) is connected to absorb the surplus energy when the system is subjected to a disturbance. The three-phase dynamic simulation demonstrates the effectiveness of the proposed strategy