Alexis Polycarpou

Performance enhanced RES current controller with reduced computational complexity

The increased penetration of RES requires the development of advanced control techniques that can work accurately with improved performance and less computational resources under unbalanced and harmonically distorted grid conditions. The paper sets out with a benchmarking study of two existing current control techniques developed for compensating the harmonics and gird voltage unbalance. The techniques are analyzed in terms of their performance and computational complexity. Both techniques can work satisfactory under abnormal grid scenarios, but these techniques are computationally complex and the performance of one under unbalanced conditions is not accurate. The proposed controller (Type 1) presented, eliminates oscillations under unbalanced voltage conditions. Furthermore, it enhances the quality of the injected current and works efficiently with improved performance (low overshoot and less oscillation) at the time of fault. However, it slightly increases the computational complexity something that motivated the development of a further controller (Type 2) that can work with less computational resources and improved performance under such conditions.

The impact of load modeling on power flow studies for the cyprus power system

Models for the electrical equipment of the generation, transmission and distribution systems, which are required for power system analysis, may be available by the manufacturers and contractors or can be estimated by on-site tests or mathematical analysis. Due to the fact that the system load is characterized by randomness and time-varying physical properties, load representation in practical applications continues to be an area of uncertainty and the issue of load modeling remains an important and challenging research topic. The main task of this paper is the establishment of a method for estimating the parameter values for a nonlinear relationship between voltage and active and reactive load powers for medium voltage feeders in transmission substations. An application that employs the ZIP load model and determines parameter values based on real-time measurements is proposed. The impact of the established voltage-dependent load model on the power flow studies for practical systems is investigated. In order to verify its efficacy, the proposed load modeling methodology is applied on the isolated power system of Cyprus.

Development and Investigation of a Proposed Voltage Sag Index

A proposed voltage sag index based on power flow equations is developed and investigated in this paper. The index supervises the power quality of a system, through calculating the voltage sag profile caused by an increase in reactive demand due to induction motor starting. Mathematical equations representing the load angle of the system are also derived. The accuracy of the index is investigated for a range of load, transmission, and distribution line X/R ratio values as well as various motor loading levels. Results demonstrate the effectiveness and applicability of the proposed index.

Linear static parametric models for online parameter identification of power load models

Power load models are significant for power system transient analysis and voltage stability. However, as the load behavior is time varying in nature, the model parameters are also time varying and online parameter estimation algorithms are thus required. In this work we cast static and dynamic load models in linear parametric form and use them as a baseline to develop online parameter identification algorithms. The linear static parametric representation allows the consideration of a wide class of online parameter estimation algorithms. Here we indicatively consider quadratic and integral cost functions. The considered online estimation algorithms are assessed using real data obtained from the Electricity Authority of Cyprus. The simulation results indicate convergence to the expected parameter values.

Harmonic analysis of a 10.8 MW installed capacity wind farm in cyprus

This work presents current and voltage waveform data recorded from Ayia Anna wind farm in Cyprus and the subsequent analysis in Matlab using Fast Fourier Transform (FFT) algorithms. The analysis aims to investigate whether the harmonic content, is within acceptable IEEE standard limits. Recorded data were arranged in descending order with respect to output power generation. Total harmonic distortion (THD) for voltage and current were analyzed by classifying the measured data in three categories depending on the output power so that the harmonic distortion is correlated with the output power generated.

Automated recognition of irregularities in substation load profiles due to abnormal feeding arrangements

Detection of abnormal feeding through the concept of data mining is studied. The presented results are in the form of case studies for various abnormalities. The developed detection algorithm is based on feeding patterns that compare the load profile against a reference waveform in conjunction with a threshold to denote abnormality.