Hortensia Amaris

Integration of renewable energy sources in smart grids by means of evolutionary optimization algorithms

Nowadays, modern power networks have to face a number of challenges such as growing electricity demand, aging utility infrastructure and not to forget the environmental impact of the greenhouse gases produced by conventional electric generation. In order to increase renewable energy penetration but without disregarding security and reliability matters during the process, distribution power networks need to evolve to a flexible power network, better known as smart grid, in which distributed intelligence, communication technologies and automated control systems work as the driving factors. Taking into consideration this new frame, intelligent optimization techniques emerge as the only suitable way to optimally design this smart grid. In this paper, a generalized optimization formulation is introduced to determine the optimal location of distributed generators to offer reactive power capability. In order to find a suitable solution to such Reactive Power Management problem, genetic algorithms are applied in those cases where different multiobjective functions are to be considered. A more detailed description of the genetic algorithm evolution process is shown in a microgrid example.

Voltage stability in distribution networks with DG

This paper presents a methodology for optimal placement of DG units in power networks to guarantee the voltage profile, maximize loadability conditions in normal and in contingencies situations. The methodology aims in finding the configuration, among a set of system components, which meets the desired system reliability requirements taking into account stability limits. Results shown in the paper indicate that the proposed formulations can be used to determine which the best buses are where the addition of small distributed generator units can greatly enhance the voltage stability of the whole network and power transfer capability under contingencies.

Current Reference Control for Shunt Active Power Filters Under Nonsinusoidal Voltage Conditions

This paper shows a new algorithm in the natural abc coordinates to calculate the current reference in a shunt active power filter. It modifies the Fryzes algorithm based on classical power theories for obtaining an optimal estimation in the current reference when the voltage in the utility is distorted. The aim of the method is twofold; first, to mitigate the harmonic components and second, to improve the power factor in the system blocking the reactive components. The feasibility of the algorithm in real-time applications has been tested with different waveforms and the results are compared by means of the total harmonic distortion in the grid current and the system power factor before and after the compensation. In addition, the results obtained in the experimental setup show the correct performance of the algorithm and demonstrate its easy implementation in industrial systems.

Future work on harmonics - some expert opinions Part II - supraharmonics, standards and measurements

A workshop on power system harmonics was organized in Stockholm in January 2014. On the agenda was among others a discussion on what are the main issues on harmonics at the moment and in the near future. Some of the issues discussed at that workshop are presented in this paper and its companion paper. In this paper the following issues will be addressed: the appearance of emission at higher frequencies (supraharmonics); the need for new and improved standards; measurement issues and data analysis.

A frequency domain approach to wind turbines for flicker analysis

Wind turbines may have an important impact on power quality. Flicker is a more serious issue for fixed-speed wind turbines because these turbines produce electric power following the variations of the incident wind. During continuous operation, wind variations will result in power fluctuations and consequently in voltage fluctuations. It is necessary to evaluate wind turbines flicker emission level, and traditionally time domain simulations have been used to perform the analysis. This paper presents a complete frequency domain model to study flicker produced during wind turbines continuous operation. The model includes a realistic wind speed model as observed by the wind turbine and also a frequency domain induction generator model is presented. The frequency domain model has been compared with a time domain model. The frequency domain approach, as shown in the paper, may be very useful for flicker analysis in electric networks.

Future work on harmonics - some expert opinions Part I - wind and solar power

A workshop on power system harmonics was organized in Stockholm in January 2014. On the agenda was among others a discussion on what are the main issues on harmonics at the moment and in the near future. The results of this discussion are summarized in this paper and some of the issues are discussed in more detail in this paper and in its companion paper. This paper discusses emission from wind and solar power as well as advantages and disadvantages of active and passive filters.

Transmission Network Cost Allocation Based on Circuit Theory and the Aumann-Shapley Method

This paper presents a new method to allocate the costs of the transmission system among generators and loads. The allocation is calculated for each branch of the transmission system to identify and quantify the individual responsibility of generators and loads. A two-step method based on the perfect coupling of the circuit theory with the Aumann-Shapley method is proposed here. First: to determine the participation of the generators in the costs of the transmission network, the generators are modeled as current injections and the loads as impedances. Second: to determine the participation of the loads in the cost of the transmission network, the loads are modeled as current sources and the generators as impedances. The Aumann-Shapley method and the circuit theory are used to calculate the participation of each real and imaginary current component in the “Allocation of the costs of the transmission system” game by considering them as independent agents. The properties of the Aumann-Shapley method ensure equitable allocation and recovery of the total costs. Numerical results are presented and discussed to demonstrate the applicability of the proposed method.

Propagation of Flicker in Electric Power Networks Due to Wind Energy Conversions Systems

Wind Energy Conversion Systems (WECS) produce fluctuating output power, which may cause voltage fluctuations and flicker. Flicker assessment in networks may be difficult, since its evaluation requires long computing time and special procedures to calculate the flicker severity index, Pst. A frequency domain method to study flicker propagation is presented. This method is based on propagation of frequency components from WECS output currents throughout the grid. In this way, a fast flicker analysis in a network of any size can be performed. An algorithm for flicker measurement in the frequency domain, which allows Pst calculation, is proposed. Several study cases were performed, and results are compared with time domain simulations, showing good agreement between them.

Computation of voltage sag initiation with Fourier based algorithm, Kalman filter and Wavelets

Dynamic Voltage Restorers (DVR) have been successfully applied for voltage dip mitigation in the last years. Especially in systems with nonlinear loads and wind turbine generation DVR units support the Power Quality enhancement. The reliability and quality of DVR operation depends mostly on fast and accurate voltage dip detection. Detection methodologies must be able to detect a voltage dip as fast as possible and be immune to other types of perturbations. In this paper we address the problem of voltage dip estimation using carefully selected advanced signal processing methods such as Fourier based algorithm, Kalman filtering and Wavelets. Additionally, the traditional and common technique of RMS value tracking has been mentioned. The algorithms have been tested under different conditions: voltage dip with phase jump, noise, frequency variations.

Application of advanced signal processing methods for accurate detection of voltage dips

Custom Power Devices like the dynamic voltage restorer have been applied for voltage dip mitigation in the last years. These electronic equipments need fast and reliable voltage dip detection algorithms. Such detection methodologies must be able to detect a voltage dip as fast as possible and be immune to other types of perturbations. In this paper we address the problem of voltage dip estimation by using different advanced signal processing methods such as Kalman filtering, Fourier based algorithms and Wavelet processing. The three algorithms have been tested under different conditions: voltage dip with phase jump, noise, frequency variations. The final implementation on a Texas Instrument DSP TMS320F2812DSP has been done.