Francisco M. Gonzalez-Longatt

Two-Step Spectral Clustering Controlled Islanding Algorithm

Controlled islanding is an active and effective way of avoiding catastrophic wide area blackouts. It is usually considered as a constrained combinatorial optimization problem. However, the combinatorial explosion of the solution space that occurs for large power systems increases the complexity of solving it. This paper proposes a two-step controlled islanding algorithm that uses spectral clustering to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations. The objective function used in this controlled islanding algorithm is the minimal power-flow disruption. The sole constraint applied to this solution is related to generator coherency. In the first step of the algorithm, the generator nodes are grouped using normalized spectral clustering, based on their dynamic models, to produce groups of coherent generators. In the second step of the algorithm, the islanding solution that provides the minimum power-flow disruption whilst satisfying the constraint of coherent generator groups is determined by grouping all nodes using constrained spectral clustering. Simulation results, obtained using the IEEE 9, 39 and 118-bus test systems, show that the proposed algorithm is computationally efficient when solving the controlled islanding problem, particularly in the case of a large power system.

Optimal Electric Network Design for a Large Offshore Wind Farm Based on a Modified Genetic Algorithm Approach

The increasing development of large-scale offshore wind farms around the world has caused many new technical and economic challenges to emerge. The capital cost of the electrical network that supports a large offshore wind farm constitutes a significant proportion of the total cost of the wind farm. Thus, finding the optimal design of this electrical network is an important task, a task that is addressed in this paper. A cost model has been developed that includes a more realistic treatment of the cost of transformers, transformer substations, and cables. These improvements make this cost model more detailed than others that are currently in use. A novel solution algorithm is used. This algorithm is based on an improved genetic algorithm and includes a specific algorithm that considers different cable cross sections when designing the radial arrays. The proposed approach is tested with a large offshore wind farm; this testing has shown that the proposed algorithm produces valid optimal electrical network designs.

Effects of the synthetic inertia from wind power on the total system inertia: simulation study

The future power systems face several challenges; one of them is the use of high power converters that virtually decouple primary energy source from the AC power grid. An important consequence of this modified the total system inertia and affecting its ability to overcome system frequencys disturbances. The wind power industry has created a controller to enable inertial response on wind turbines generators: Synthetic Inertial. This paper evaluates the effects of the synthetic inertia provided by wind turbines on the total system inertia after a system frequency disturbance. The main contribution of this paper is to demonstrate that during an under-frequency transients on future power systems, the synthetic inertia not completely avoid worse scenarios in terms of under-frequency load shedding. The extra power delivered from a wind turbine during frequency disturbances can increase “momentary” the total system inertia and substantially reduce the rate of change of frequency providing time for the active governors to respond. However, synthetic inertia might not completely avoid under-frequency load shedding.

Frequency Control and Inertial Response Schemes for the Future Power Networks

Future power systems face several challenges: (i) the high penetration level of renewable energy from highly variable generators connected over power converters, (ii) several technologies for energy storage with very different time constants, some of them using power converters as an interface to the grid, and (iii) a pan-European transmission network facilitating the integration of large-scale renewable energy sources and the balancing and transportation of electricity based on underwater multi-terminal high voltage direct current (MTDC) transmission. All of them have an element in common, high power converters that decouple the new energy sources from the pre-existent AC power systems. During a system frequency disturbance, the generation/demand power balance is lost, the system frequency will change at a rate initially determined by the total system inertia. However, future power systems will increase the installed power capacity (MVA) but the effective system inertial response will stay the same nowadays, because the new generation units based on power converters creates a decoupling effect of the real inertia and the AC grid. The result is deeper frequency excursions of system disturbances. A considerable reduction in the ability to overcome system frequency disturbances is expected, the inertia response may be decreased. The aim of this chapter is to present the fundamental aspects of system frequency control and inertial response schemes for the future power networks.

A simplified model for dynamic behavior of permanent magnet synchronous generator for direct drive wind turbines

In this paper, a simplified model to represent variable speed wind turbines in power system dynamics simulations is presented. This model is based in the use of controls-oriented model for permanent magnet synchronous generator supplying voltage-stiff bus system, including intrinsic torque/load properties. First, the modeling approach is commented upon and models of the subsystems of which a variable speed wind turbine consists are discussed. Then, time-domain simulations have been performed for one study case in order to demonstrate the suitable use of the model proposed in this paper. Results have shown that the model developed performs satisfactorily for slow dynamic when compared with the results obtained from simulation considering the detailed model.

PowerFactory Applications for Power System Analysis

This book presents a comprehensive set of guidelines and applications of DIgSILENT PowerFactory, an advanced power system simulation software package, for different types of power systems studies. Written by specialists in the field, it combines expertise and years of experience in the use of DIgSILENT PowerFactory with a deep understanding of power systems analysis. These complementary approaches therefore provide a fresh perspective on how to model, simulate and analyse power systems. It presents methodological approaches for modelling of system components, including both classical and non-conventional devices used in generation, transmission and distribution systems, discussing relevant assumptions and implications on performance assessment. This background is complemented with several guidelines for advanced use of DSL and DPL languages as well as for interfacing with other software packages, which is of great value for creating and performing different types of steady-state and dynamic performance simulation analysis. All employed test case studies are provided as supporting material to the reader to ease recreation of all examples presented in the book as well as to facilitate their use in other cases related to planning and operation studies. Providing an invaluable resource for the formal instruction of power system undergraduate/postgraduate students, this book is also a useful reference for engineers working in power system operation and planning.

Solution of ac/dc power flow on a multiterminal HVDC system: Illustrative case supergrid phase I

This paper presents an algorithm for the sequential solution of the ac/dc power flow, which is proposed for the analysis of multi-terminal HVDC systems (MTDC). This sequential power flow algorithm can be implemented easily in an existing ac power flow package and is very flexible when it compared with unified methods. Gauss-Siedel algorithm is used to solve dc power balance equations, it offers two keys advantages: very fast and simple computational implementation, and errors do not accumulate during the calculation. The algorithm is tested using the WSCC 3-machine, 9-bus system with a 3-terminal MTDC network and results compared with those obtained from DIgSILENT® PowerFactoryTM demonstrating the validity of the proposed algorithm. As aggregate value, a representative test case of the projected scheme for the phase I of the Supergrid project on the North Sea is presented, the proposed approach presented in this paper is used to calculate DC power flows for some scenarios.

Estimation of generator inertia available during a disturbance

The inertia of a power system is a key factor in determining the initial frequency decline after a disturbance. Low system inertia can allow large frequency declines to occur that could lead to violation of frequency security limits, particularly in smaller power systems, or play a key role in allowing cascading outages to occur. Future developments in power systems will mean that the system inertia will become highly variable and take values that would traditionally have been considered very low. Presented is a method for the robust estimation of the generator inertia available in the system during a disturbance. This method has been validated using simulations of the IEEE 39-bus system in DIgSILENTTM PowerFactory®. Inertia estimates for a variety of disturbance types and noise conditions have been made, and found to have a median error of 1.53% with inter-quartile range of 6.6%.

Effects of the Synthetic Inertia from wind power on the total system inertia after a frequency disturbance

The future power systems face several challenges; one of them is the use of high power converters that virtually decouple primary energy source from the AC power grid. An important consequence of this situation is their effect on total system inertia and the ability to overcome the systems frequency disturbances. The wind power industry has created a controller to enable inertial response on wind turbines generators: Synthetic Inertial. This paper evaluates the effects of the inertia emulation of wind turbines based on full-converters and their effect on total system inertia after frequency disturbances happen. The main contribution of this paper is to demonstrate (based on simulations) that during an under-frequency transients on future power systems, synthetic inertia does not completely avoid worse scenarios in terms of under-frequency load shedding. The extra power delivered from a wind turbine during frequency disturbances can increase “momentary” the total system inertia and substantially reduce the rate of change of frequency providing time for the active governors to respond. However, synthetic inertia might not completely avoid under-frequency load shedding.

Modeling and simulation of PEM fuel cell with bond graph and 20sim

Due to the increasing and highly promising use of fuel cells as an important electrical energy source, its modeling has been a major research issue for some years, trying to find mathematical models precise enough to accurately predict how a cell will behave in a real world system, without becoming too complex. Many attempts have been made using different techniques. In this paper, the authors describe a static model for the PEM (proton exchange membrane) fuel cell, developed by means of bond graphs and simulated in 20 sim. The model proves to be simple and accurate, reproducing the characteristic curve of a commercial PEM fuel cell.