Luis Rouco

An eigenvalue sensitivity approach to location and controller design of controllable series capacitors for damping power system oscillations

This paper presents tools and methods to study the application of controllable series capacitors for damping power system electromechanical oscillations. Two problems are discussed-location and controller design. The location of a controllable series capacitor consists of determining the series capacitor of the power system where the modulation of its series reactance will be more effective to damp out the modes of interest. It also involves the selection of the input variable to the controller. The basic design of the controller requires the design of the phase compensation network and the calculation of the controller gain. Small signal models of the power system and the corresponding eigenvalue sensitivities are used to address both problems.

Maximum Frequency Deviation Calculation in Small Isolated Power Systems

Large frequency deviations due to a number of disturbances are frequent in small isolated power systems. The maximum frequency deviation in the system is limited to prevent other generator tripping. It is important to have an accurate model to calculate it, both for system planning and operation. A new simplified model to calculate the maximum frequency deviation when either a generator or load-related disturbance occurs in these systems is presented. This model takes into account the response of governor-prime mover even when different technologies are present in the power system. Model parameters can be easily obtained from either more complex models or from test records. Simulation results for an actual power system aimed at checking the model accuracy are presented. High accuracy is obtained while computation time is reduced due to the simplicity of the model.

Synchrony, aggregation, and multi-area eigenanalysis

This paper explores synchrony, a generalization of the concept of slow-coherency, and outlines how it can form the basis for efficient construction of dynamic equivalents by aggregation. The paper describes a novel approach for selecting the inter-area modes that are to be represented by the aggregate model. A clustering algorithm for recognizing approximate synchrony is presented, and improvements over the standard slow-coherency recognition algorithm are noted. Using for illustration a 23-generator power system model with 325 state variables, the paper demonstrates the effectiveness of a synchrony-based approach to decomposing the eigenanalysis of the electromechanical modes, separating the computation of inter-area and intra-area modes in the style of multi-area selective modal analysis.

An LP-based optimal power flow for transmission losses and generator reactive margins minimization

This paper describes a mixed-integer linear programming optimal power flow. The objective function consists of minimizing transmission losses and generator reactive outputs. The problem constraints are the power flow equations and the bounds of the power system variables (generator reactive outputs, bus voltages, transformer taps and branch power flows). The proposed method is an iterative process that linearizes in each iteration both the objective function and the constraints. In addition, the objective function is represented by a set of tangent cuts. The discrete nature of shunt reactors and capacitors is modeled by integer variables. The performance of the method is illustrated in an actual scenario of the Spanish power system.

Dynamic patterns and model order reduction in small-signal models of doubly fed induction generators for wind power applications

This paper investigates the dynamic patterns that arise in the small-signal models of doubly fed induction generators for wind power applications. Dynamic patterns are associations between eigenvalues and state variables of linear dynamic systems that can be identified using participation factors. Based on the identified dynamic patterns, reduced order models are proposed and compared with detailed models

A Method for the Design of UFLS Schemes of Small Isolated Power Systems

This paper presents a systematic method for the design of robust and efficient underfrequency load-shedding (UFLS) schemes. UFLS schemes play an important role in protecting the system integrity. The systematic method consists first in selecting representative operating and contingency (OC) scenarios by means of a clustering algorithm and subsequently, in tuning UFLS scheme parameters by dint of a simulated annealing optimization algorithm. The approach is applied to a small isolated Spanish power system. The systematic method leads to a robust and efficient UFLS scheme. The resulting design is also compared to a design based on OC scenarios determined by the common practice of OC scenario selection. The possibility of rearranging UFLS stages and the influence of minimum allowable frequency constraints is analyzed as well. Finally, an analysis of the impact of increasing converter-connected generation (CCG) is presented.

Large-Scale Power System Dynamic Equivalents Based on Standard and Border Synchrony

This paper fills the gap between the well-known in control theory model reduction techniques based on the balanced realization and the structure preserving dynamic model equivalencing approaches used in power systems. The relations between the synchrony and the loss of controllability and observability are investigated and, from that, new aggregation methodologies are proposed for two distinct situations. The first one corresponds to the case, already treated in the literature, where a full model is available for the power system which must be reduced. For the second one, which is new, it is considered that part of the data of the power system is not available when the reduction is performed. Both small theoretic and large-scale realistic examples are considered.

Coordinated design of multiple controllers for damping power system oscillations

This paper details an approach for designing multiple controllers for damping power system electromechanical oscillations. The approach is based on the first-order sensitivities of the eigenvalues of the power system linear model. It is divided into two steps: the independent design of the phase compensation networks of the controllers and the coordinated design of the gains of the controllers. Power system stabilizers of generators and damping controllers of FACTS devices can be designed using the proposed approach. The approach is illustrated in a small-scale power system that exhibits both local and inter-area oscillations.

Modeling of thermal generating units for automatic generation control purposes

A simple discrete time model of a thermal unit has been formally developed for designing automatic generation control (AGC) controllers. This model has been developed using data obtained from specific tests and historical records. This model consists of a nonlinear block followed by a linear one. The nonlinear block consists of a dead band and a load change rate limiter, while the linear block consists of a second-order linear model and an offset. Although most of these elements have already been included in unit models for AGC presented in the literature, a certain mix up exists about which of them are necessary. This is clarified in this paper. It has been found that the unit response is mainly determined by the rate limiter, while the other model components are used for a better fitting to the real response. An identification procedure is proposed to estimate the values of the models parameters.

Multi-area analysis of small signal stability in large electric power systems by SMA

The authors present an efficient methodology for the analysis of small signal stability in large electric power systems. It is based on the selective modal analysis approach and assumes a multi-area structure of the small signal behavior in large power systems. In the proposed procedure, the system modes are separated into two categories (the inter-area and the intra-area modes) and are independently determined. Results of the application to a realistic large power system with 266 generators and 1472 buses are discussed. >