Francisco Gonzalez-Longatt

The number of fully-rated converter wind turbine generators equipped with a Permanent Magnet Synchronous Generator (PMSG) has sensibly increased in the late years. The optimal utilization and controllability of a PMSG is achieved using a Pulse Width Modulation – Voltage Source Converter (PWM-VSC) that allows interfacing the electric machine with the distribution network by means of a DC link. The generator/Machine-Side Converter (MSC) controls the operation of the PMSG. This paper proposes a… Show more

The number of fully-rated converter wind turbine generators equipped with a Permanent Magnet Synchronous Generator (PMSG) has sensibly increased in the late years. The optimal utilization and controllability of a PMSG is achieved using a Pulse Width Modulation – Voltage Source Converter (PWM-VSC) that allows interfacing the electric machine with the distribution network by means of a DC link. The generator/Machine-Side Converter (MSC) controls the operation of the PMSG. This paper proposes a methodology to assess the feasibility of the steady-state working points of PMSG based wind turbines without running a set of time-consuming time-domain simulations. Three control objectives for MSC are usually considered: stator voltage control, unitary power factor control and torque control. The aim of the present paper is that of providing an analytical methodology to check the feasibility of the steady-state working points dictated by different control strategies of the MSC starting from the specific operational constraints provided by the wind power plants characteristics. The effectiveness of the proposed methodology is demonstrated comparing numerical results of a MATLAB® implementation against dedicated time-domain simulations. Simulations results demonstrated the appropriate performance of the proposed methodology characterized by the almost negligible computational time required. Show less

This paper discusses the impact of wind penetration on frequency control of a thermal dominated system considering Generation Rate Constraints (GRC) and dead band non-linearities. The hidden inertia emulation and coordinated operation of conventional power generation systems with wind energy can effectively alleviate the frequency excursions during sudden load disturbances. Conventional energy storage device like Flywheel Energy Storage (FES) system can be used in conjunction with wind… Show more

This paper discusses the impact of wind penetration on frequency control of a thermal dominated system considering Generation Rate Constraints (GRC) and dead band non-linearities. The hidden inertia emulation and coordinated operation of conventional power generation systems with wind energy can effectively alleviate the frequency excursions during sudden load disturbances. Conventional energy storage device like Flywheel Energy Storage (FES) system can be used in conjunction with wind integrated power system to overcome the intermittent nature of power generation. Thyristor Controlled Series Compensator (TCSC) is found to be effective in damping low frequency oscillations in weak tie-lines and supplement the frequency regulation. A stochastic population based evolutionary computation technique - Particle Swarm Optimization (PSO) is used to tune the controller gains. A strategy comprising inertia control, coordinated operation of conventional generation units with wind energy and TCSC-FES has been proposed to enhance the frequency regulation which is effective in controlling low frequency oscillations as established by the simulation results. Show less

This paper introduces an approach based on the Swarm Variant of the Mean-Variance Mapping Optimization (MVMO-S) to solve the multi-scenario formulation of the optimal placement and coordinated tuning of power system supplementary damping controllers (POCDCs). The effectiveness of the approach is evaluated based on the classical IEEE 39-bus (New England) test
system. Numerical results include performance comparisons with other metaheuristic optimization techniques, namely,
comprehensive… Show more

This paper introduces an approach based on the Swarm Variant of the Mean-Variance Mapping Optimization (MVMO-S) to solve the multi-scenario formulation of the optimal placement and coordinated tuning of power system supplementary damping controllers (POCDCs). The effectiveness of the approach is evaluated based on the classical IEEE 39-bus (New England) test
system. Numerical results include performance comparisons with other metaheuristic optimization techniques, namely,
comprehensive learning particle swarm optimization (CLPSO), genetic algorithm with multi-parent crossover (GA-MPC), differential evolution DE algorithm with adaptive crossover operator, linearized biogeography-based optimization with reinitialization (LBBO), and covariance matrix adaptation evolution strategy (CMA-ES). Show less

Future power systems face several challenges. One of them is the use of high power converters that decouple new energy sources from the AC power grid. This situation decreases the total system inertia affecting its ability to overcome system frequency disturbances. The wind power industry has created several controllers to enable inertial response on wind turbines generators: artificial, emulated, simulated, or synthetic inertial. This paper deals with the issues related to the emulated inertia… Show more

Future power systems face several challenges. One of them is the use of high power converters that decouple new energy sources from the AC power grid. This situation decreases the total system inertia affecting its ability to overcome system frequency disturbances. The wind power industry has created several controllers to enable inertial response on wind turbines generators: artificial, emulated, simulated, or synthetic inertial. This paper deals with the issues related to the emulated inertia of wind turbines based on full-converters and their effect on the under-frequency protection schemes during the recovery period after system frequency disturbances happen. The main contribution of this paper is to demonstrate the recovery period of under-frequency transients in future power systems which integrate wind turbines with emulated inertia capability does not completely avoid the worse scenarios in terms of under-frequency load shedding. The extra power delivered from a wind turbine during frequency disturbances can substantially reduce the rate of frequency change. Thus it provides time for the active governors to respond. Show less

he renewable energy sources (RES) such as photovoltaic (PV) are basically DC power sources. In the present scenario, the integration of RES to power distribution infrastructure necessitates the DC-AC converter. Moreover the DC loads in the buildings is ever increasing with the use of CFL, LED, refrigerator, TV, fan, air conditioner, laptop, and other electronics in workplaces and homes. This forced to introduce the internal or external AC-DC converter to tie the DC load to AC distribution… Show more

he renewable energy sources (RES) such as photovoltaic (PV) are basically DC power sources. In the present scenario, the integration of RES to power distribution infrastructure necessitates the DC-AC converter. Moreover the DC loads in the buildings is ever increasing with the use of CFL, LED, refrigerator, TV, fan, air conditioner, laptop, and other electronics in workplaces and homes. This forced to introduce the internal or external AC-DC converter to tie the DC load to AC distribution infrastructure of existing power system. This is further adding losses and complexity. This AC-DC converter stage can be reduces up to a certain level by DC distribution system (DCDS). Secondly the multi voltage rating of RES and DC load insists to introduce DC-DC converter in DCDS infrastructure. This will further add losses and complexity. In this paper a standard voltage level DCDS is proposed to minimize the system losses, complexity. To verify the simulated results in terms of building load and converter losses, a DCDS equipped with different energy sources like solar panel (PV), public utility (PU) and battery bank (BB) is compared with ACDS. Show less

The Venezuelan government has established more aggressive policies and incentives for renewable energy resources in recent time, especially in terms of wind power. Although several
academic efforts to make publicly available wind energy resource data in Venezuela, there is a lack of information in terms of local wind resource putting in risk development in areas where potential is good enough for commercial exploitation. The objective of this paper is to presents a very comprehensive wind… Show more

The Venezuelan government has established more aggressive policies and incentives for renewable energy resources in recent time, especially in terms of wind power. Although several
academic efforts to make publicly available wind energy resource data in Venezuela, there is a lack of information in terms of local wind resource putting in risk development in areas where potential is good enough for commercial exploitation. The objective of this paper is to presents a very comprehensive wind resource assessment at Los Taques, Venezuela based on on-site observation anemometry. This is unique paper because it is the first ever wind energy assessment in Los Taques using hourly data recorded during three years in an on-site ground weather station contrary to studies based on daily values based on radar or satellite data. The applied methodology has been developed based on the characteristic of the data obtained from the on-site anemometry.
Results of wind energy assessment and evaluations on a 100 MW wind farm shows the wind energy resource available in Los Taques is enough for commercial use and the results Show less

Due to its variable nature, the increasing penetration of wind power plants into power systems poses new challenges for reliable and secure operation. Considering that model-based time-domain simulation constitutes a widely used approach for assessing the power system dynamic performance as well as for making proper decisions concerning operational and planning security strategies, there has been a great research effort, especially in the last decade, to cover different issues on modelling of… Show more

Due to its variable nature, the increasing penetration of wind power plants into power systems poses new challenges for reliable and secure operation. Considering that model-based time-domain simulation constitutes a widely used approach for assessing the power system dynamic performance as well as for making proper decisions concerning operational and planning security strategies, there has been a great research effort, especially in the last decade, to cover different issues on modelling of wind generation systems (WGS). Remarkably, the development of models that entail a compromise between accuracy and simplicity is one of the main concerns for enabling the simulation of large-scale systems. This chapter addresses the implementation of two simplified models of WGs by using the functionalities of DIgSILENT simulation language (DSL). The first one is the reduced third-order model of the doubly fed induction generator (DFIG), for which suitable models for multiple point tracking, the rotor-side controller (RSC), current controller, and speed and pitch controller are adopted. The second model constitutes a generic equivalent model, which can be used for representation of the stationary and dynamic response of wind power plants comprising several DFIGs. RMS-type simulation results are presented to illustrate the suitability of the adopted modelling approaches. Show less

The development and application of heuristic optimization algorithms have gained a renewed interest due to the limitations of classical optimization tools for tackling several hard-to-solve problems in different engineering fields. Due to the complex nature of power system dynamics, electrical engineering optimization problems usually present a discontinuous multimodal and non-convex landscape that necessarily has to be handled by heuristic optimization algorithms. While most of the pioneer… Show more

The development and application of heuristic optimization algorithms have gained a renewed interest due to the limitations of classical optimization tools for tackling several hard-to-solve problems in different engineering fields. Due to the complex nature of power system dynamics, electrical engineering optimization problems usually present a discontinuous multimodal and non-convex landscape that necessarily has to be handled by heuristic optimization algorithms. While most of the pioneer heuristic optimization approaches, such as genetic algorithms, particle swarm optimization, and differential evolution, are undergoing different types of modifications and extensions in order to improve their performance, great focus is also being put into the development of new approaches aiming at conceptual simplicity, easy adaptability for a variety of optimization-based applications, and outstanding performance. The mean–variance mapping optimization (MVMO) is a recent contribution to the family of evolutionary optimization algorithms. Its novel search mechanism performs within a normalized range of the search space for all optimization variables and follows a single parent–offspring pair approach. Besides, MVMO is characterized by a continuously updated knowledge archive storing the n-best solutions achieved so far, from which a special mapping function, which accounts for the mean and variance of the optimization variables, is applied for mutation operation. In this way, the algorithm proceeds by projecting randomly selected variables onto the corresponding mapping function that guides the solution toward the best set achieved so far. Despite the orientation on the best solution, the algorithm keeps on searching globally. This chapter addresses key aspects concerning the implementation of MVMO by using DIgSILENT programming language (DPL). Show less

The use of probabilistic framework is of great importance for the development of comprehensive approaches, which are suitable for coping with increasing uncertainties in power system operation and planning. While huge effort has been put in the past into the conception of probabilistic methods to deal with stochastic load flow calculation, there is an increasing interest on the development of new approaches to ascertain the implications of changing operating conditions in terms of power system… Show more

The use of probabilistic framework is of great importance for the development of comprehensive approaches, which are suitable for coping with increasing uncertainties in power system operation and planning. While huge effort has been put in the past into the conception of probabilistic methods to deal with stochastic load flow calculation, there is an increasing interest on the development of new approaches to ascertain the implications of changing operating conditions in terms of power system dynamic performance. Among the main concerns on this regard is the determination of the degree of exposure to poorly damped low-frequency oscillations (LFOs), which occur typically in the range of 0.1–1.0 Hz. This chapter concerns the implementation of a Monte Carlo (MC)-based approach for evaluation of oscillatory instability risk by using the functionalities for modelling and programming of DIgSILENT PowerFactory. Particularly, the DIgSILENT programming language (DPL) is used to structure the steps of the MC repetitive procedure, namely sampling of uncertain input variables, automated scenario generation, and storage of eigenanalysis outcomes. The chapter also illustrates the implementation of the PST 16 benchmark system, which has a relative large size, and is appropriated to study different kinds of stability problems, especially LFOs. Based on characteristic parameters of the European power systems, different built-in models available in DIgSILENT are used to model the system components. Numerical experiments performed on this system support the relevance of the MC-based approach. Show less

The continuous increase on the penetration levels of Renewable Energy Sources (RESs) in power systems has led to radical changes on the design, operation, and control of the electrical network. This paper investigates the influence of these changes on the operation of a transmission network by developing a set of indices, spanning from power losses to GHG emissions reduction. These indices are attempting to quantify any impacts therefore providing a tool for assessing the RES penetration in… Show more

The continuous increase on the penetration levels of Renewable Energy Sources (RESs) in power systems has led to radical changes on the design, operation, and control of the electrical network. This paper investigates the influence of these changes on the operation of a transmission network by developing a set of indices, spanning from power losses to GHG emissions reduction. These indices are attempting to quantify any impacts therefore providing a tool for assessing the RES penetration in transmission networks, mainly for isolated systems. These individual indices are assigned an analogous weight and are mingled to provide a single multiobjective index that performs a final evaluation. These indices are used to evaluate the impact of the integration of RES into the classic WSCC 3-machine, 9-bus transmission network. Show less

When planning power system operation it is important to have reliable models of the elements of the power system. Fixed speed wind turbines are a widely installed generation technology that use a single squirrel cage induction generator. The local wind profile and the properties of the induction machine constitute the main considerations when modeling these wind turbines. Existing methods for estimating the parameter values of induction machine models use a wide variety of parameter estimation… Show more

When planning power system operation it is important to have reliable models of the elements of the power system. Fixed speed wind turbines are a widely installed generation technology that use a single squirrel cage induction generator. The local wind profile and the properties of the induction machine constitute the main considerations when modeling these wind turbines. Existing methods for estimating the parameter values of induction machine models use a wide variety of parameter estimation algorithms but primarily use active and reactive power measurements made during start-up or direct mechanical testing to fit the model to. Proposed here is a parameter estimation method that applies improved particle swarm optimization to active and reactive power measurements made during a deviation in system frequency to estimate the parameter values of an induction machine model. This method has shown good accuracy and the use of on-line data may prove beneficial in future applications. Show less

The aim of this paper is to evaluate the impact of the wake effect on both the steady-state operation and dynamic performance of a wind farm and provide conclusions that can be used as thumb rules in generic assessments where the full details of the wind farms are unknown. A simplified explicit model of the wake effect is presented, which includes: the cumulative impact of multiple shadowing, the effects of wind direction and the wind speed time delay. The model is implemented in MATLAB® and… Show more

The aim of this paper is to evaluate the impact of the wake effect on both the steady-state operation and dynamic performance of a wind farm and provide conclusions that can be used as thumb rules in generic assessments where the full details of the wind farms are unknown. A simplified explicit model of the wake effect is presented, which includes: the cumulative impact of multiple shadowing, the effects of wind direction and the wind speed time delay. The model is implemented in MATLAB® and then integrated into a power system simulation package to describe the wake effect and its impact on a wind farm, particularly in terms of the wake coefficient and overall active power losses. Results for two wind farm layouts are presented to illustrate the importance of wind turbine spacing and the directionality of wind speeds when assessing the wake effect during steady-state operation and dynamic behavior. Show less

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… Show more

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. Show less

An induction generator (IG) is preferred to a synchronous generator in many renewable energy applications. In order to achieve proper control of an induction generator it is important to have accurate knowledge of its model parameters. In this paper, an Improved Particle Swarm Optimization (IPSO) approach is used to estimate the model parameters of an IG. The IPSO is executed based on the response of the active and reactive power flows associated with the IG to a change in the frequency of the… Show more

An induction generator (IG) is preferred to a synchronous generator in many renewable energy applications. In order to achieve proper control of an induction generator it is important to have accurate knowledge of its model parameters. In this paper, an Improved Particle Swarm Optimization (IPSO) approach is used to estimate the model parameters of an IG. The IPSO is executed based on the response of the active and reactive power flows associated with the IG to a change in the frequency of the external system, which the IG is connected to. This change in frequency is applied when the IG is operating in steady state, to represent the scenario where the IG parameters must be estimated on-line, and during a large disturbance to the system equilibrium. This approach is in contrast to others in the literature that estimate the parameters of an induction machine based on its start-up behavior, or the results of mechanical tests. Therefore, this approach should offer benefits when the parameters of the IG being modeled may vary over time and need to be estimated on-line. Show less

An induction generator (IG) is preferred to a synchronous generator in many renewable energy applications. In order to achieve proper control of an induction generator it is important to have accurate knowledge of its model parameters. In this paper, an Improved Particle Swarm Optimization (IPSO) approach is used to estimate the model parameters of an IG. The IPSO is executed based on the response of the active and reactive power flows associated with the IG to a change in the frequency of the… Show more

An induction generator (IG) is preferred to a synchronous generator in many renewable energy applications. In order to achieve proper control of an induction generator it is important to have accurate knowledge of its model parameters. In this paper, an Improved Particle Swarm Optimization (IPSO) approach is used to estimate the model parameters of an IG. The IPSO is executed based on the response of the active and reactive power flows associated with the IG to a change in the frequency of the external system, which the IG is connected to. This change in frequency is applied when the IG is operating in steady state, to represent the scenario where the IG parameters must be estimated on-line, and during a large disturbance to the system equilibrium. This approach is in contrast to others in the literature that estimate the parameters of an induction machine based on its start-up behavior, or the results of mechanical tests. Therefore, this approach should offer benefits when the parameters of the IG being modeled may vary over time and need to be estimated on-line. Show less

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… Show more

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. Show less

This paper introduces a new digital signal processing algorithm for frequency and amplitude estimation based on Unscented Kalman Filter (UKF). The results of computer simulated and realistic synthetic data tests are presented. The initial parameters used during the tests were chosen carefully using an established parameter estimation method, the Self Tuning Least Square (STLS). It is concluded that the proposed algorithm is simple, efficient and has low computational demands compare to STLS… Show more

This paper introduces a new digital signal processing algorithm for frequency and amplitude estimation based on Unscented Kalman Filter (UKF). The results of computer simulated and realistic synthetic data tests are presented. The initial parameters used during the tests were chosen carefully using an established parameter estimation method, the Self Tuning Least Square (STLS). It is concluded that the proposed algorithm is simple, efficient and has low computational demands compare to STLS which makes the UKF a very promising method in next generation of power quality monitoring devices. Show less

Load modeling is a very important aspect of voltage stability analysis as load characteristics governs voltage behavior. In this paper a compact solution to extract parameters of a load model is presented, which includes estimation of power components based on Improved Recursive Newton Type Algorithm and estimation of parameters of a dynamic Load Model using Genetic Algorithms. The paper demonstrates the influence of the preprocessing of the instantaneous values on the final estimation of load… Show more

Load modeling is a very important aspect of voltage stability analysis as load characteristics governs voltage behavior. In this paper a compact solution to extract parameters of a load model is presented, which includes estimation of power components based on Improved Recursive Newton Type Algorithm and estimation of parameters of a dynamic Load Model using Genetic Algorithms. The paper demonstrates the influence of the preprocessing of the instantaneous values on the final estimation of load parameters. All tests were carried out using 9-buses P.M. Anderson system built in DIgSILENT. Show less

The inertia constant of a system describes the initial, transient, frequency behaviour of that system when subjected to a real power disturbance. Therefore, the inertia constant of a system can be a useful tool when investigating the frequency stability of a system. The use of the swing equation is a viable method for estimating the inertia constant, if a measurement system that can provide time stamped measurements of the frequency and power dynamics during a disturbance is available. An… Show more

The inertia constant of a system describes the initial, transient, frequency behaviour of that system when subjected to a real power disturbance. Therefore, the inertia constant of a system can be a useful tool when investigating the frequency stability of a system. The use of the swing equation is a viable method for estimating the inertia constant, if a measurement system that can provide time stamped measurements of the frequency and power dynamics during a disturbance is available. An example of such a system is a Wide Area Monitoring system that is capable of monitoring the frequency at all, or a select set, of generation sites. A method for estimating the inertia constant based on this data is developed and demonstrated for two simple networks. This demonstration is performed using computer simulations in the DigSILENT PowerFactory software package. The inertia constant estimation method is implemented in the MATLAB environment. Show less

La integración de grandes bloques de generación eólica en los sistemas eléctricos de
potencia ha sido tema de investigación en las últimas décadas debido a la particularidad de este
tipo de generación y a su impacto sobre la operación de la red. Basados en la experiencia europea
sobre este ámbito, esta investigación plantea las bases a seguir para la interconexión de parques
eólicos a los sistemas eléctricos evaluando principalmente la estabilidad del mismo en régimen
permanente… Show more

La integración de grandes bloques de generación eólica en los sistemas eléctricos de
potencia ha sido tema de investigación en las últimas décadas debido a la particularidad de este
tipo de generación y a su impacto sobre la operación de la red. Basados en la experiencia europea
sobre este ámbito, esta investigación plantea las bases a seguir para la interconexión de parques
eólicos a los sistemas eléctricos evaluando principalmente la estabilidad del mismo en régimen
permanente y ante perturbaciones. Como caso de estudio se propone la incorporación de un
parque de 24 MW en el sistema eléctrico SENECA de la Isla de Margarita (Venezuela) donde
predominan plantas de generación termoeléctricas. Se emplearon modelos dinámicos tanto de los
aerogeneradores de velocidad fija propuestos como del sistema de transmisión y de las unidades
de generación convencionales. Para el sistema mecánico de la turbina se utilizó un modelo de dos
masas mientras que para el generador de inducción jaula de ardilla se utilizó un modelo de 5to
orden. El mecanismo de control elegido fue el de variación del ángulo de paso (Pitch Control).
Se establecieron criterios de aceptabilidad para las pruebas y se realizaron simulaciones ante
distintos tipos de contingencias usando DIgSILENT Power Factory®. Se observó que el sistema
cumple con los criterios considerados al combinar la implantación del parque eólico con
compensación reactiva. Show less