Distributed Generation and Its Impact on Power Quality in Low-Voltage Distribution Networks

This chapter is dedicated to review and investigate present approaches to power quality assessment in low-voltage (LV) networks with distributed generation (DG). Two complementary approaches are considered: firstly, origin of the emission limits requirement for the DG is searched in general electromagnetic compatibility (EMC) conditions used for the equipment and adopted to DG; secondly, rules and regulation of integration with a power system network is used in order to estimate the possible influence of DG on power quality in point of common coupling (PCC). An example of the regulation is control of reactive power consumption in function of active power generation known as cosφ (P) characteristic. This chapter constitutes the attitude that complementary approach brings improvement to the decision about the possible impact of DG in a power system network. It was shown that a combined approach allows to define a proposition of the limits of particular power quality parameters associated with the investigated node of LV network characterized by apparent short circuit power in the PCC (SkPCC). This combination brings desirable effect of criterion, making for integration of DG with LV networks. Mentioned attitude was investigated using a real case study of a photovoltaic (PV) system consisting of three independent one-phase subsystems. Estimated influence of the investigated PV on power quality parameters in the PCC was verified using real measurement. The measurement procedure allows to verify the real influence of the investigate DG on power quality in the PCC, however, the task in not easy due to problems of separation of the searched influence from the measurement background. One of the proposed approach is to affiliate changes of investigated power quality parameters with activities of the investigated DG, e.g., energy production. As it was presented in the case of influence of the investigated PV static voltage changes or total harmonic distortion in current in the PCC, a correlation index can be also implemented in order to classify the force of the common influence

Novel Power Quality Data Analysis and Reporting Framework for Wide-area system of registration and processing of power quality data

This paper presents a novel method for data analysis and visualization, including real-time visual monitoring and proposal for combined area PQ indices on the example of the developed and operational comprehensive system of registration, archiving and data processing for the wide-area monitoring of power quality in a separated part of  real power grid with distributed renewable generation. Real case studies related to power quality disturbances are presented.

Smart control of energy storage system in residential photovoltaic systems for economic and technical efficiency

In recent years, due to the increasing number of renewable energy sources, which are characterised by the stochastic nature of the generated power, interest in energy storage has increased. Commercial installations use simple deterministic methods with low economic efficiency. Hence, there is a need for intelligent algorithms that combine technical and economic aspects. Methods based on computational intelligence (CI) could be a solution. The paper presents an algorithm for optimising power flow in microgrids by using computational intelligence methods. This approach ensures technical and economic efficiency by combining multiple aspects in a single objective function with minimal numerical complexity. It is scalable to any industrial or residential microgrid system. The method uses load and generation forecasts at any time horizon and resolution and the actual specifications of the energy storage systems, ensuring that technological constraints are maintained. The paper presents selected calculation results for a typical residential microgrid supplied with a photovoltaic system. The results of the proposed algorithm are compared with the outcomes provided by a deterministic management system. The computational intelligence method allows the objective function to be adjusted to find the optimal balance of economic and technical effects. Initially, the authors tested the invented algorithm for technical effects, minimising the power exchanged with the distribution system. The application of the algorithm resulted in financial losses, €12.78 for the deterministic algorithm and €8.68 for the algorithm using computational intelligence. Thus, in the next step, a control favouring economic goals was checked using the CI algorithm. The case where charging the storage system from the grid was disabled resulted in a financial benefit of €10.02, whereas when the storage system was allowed to charge from the grid, €437.69. Despite the financial benefits, the application of the algorithm resulted in up to 1560 discharge cycles. Thus, a new unconventional case was considered in which technical and economic objectives were combined, leading to an optimum benefit of €255.17 with 560 discharge cycles per year. Further research of the algorithm will focus on the development of a fitness function coupled to the power system model

Analiza przebiegów odkształconych w układach z przekształtnikami

W artykule przedstawiono metodę wyznaczania częstotliwości, opracowaną na podstawie modelu Prony’ego. Metod została opracowana z założeniem, że analizowany proces zawiera dwie harmoniczne i szum. Dodatkowo, w celu poprawy dokładności metody, zastosowano filtrowanie medianowe. Zaprezentowana metoda może być wykorzystana w układach elektroenergetycznych, takich jak układy sterujące przekształtników

Power Distortion Issues in Wind Turbine Power Systems Under Transient States

In this paper time-frequency methods have been investigated for complex investigations of transient states in wind power plants. Application of parallel processing in time and frequency domain brought new findings in description of wind power plants working under transient conditions. Proposed algorithms represents standard Short-Time Fourier Transform (STFT) as well as alternative methods associated with Cohen’s class: Choi-Williams Distribution (CWD) and Zhao-Atlas-Marks Distribution (ZAMD). In order to explore advantages and disadvantages of the method several experiments were performed using model of squirrel-cage induction machine connected directly to the grid. Investigated phenomena concerned power distortion caused by switching-on capacitor banks and faults as well as influence of wind speed on instantaneous character of the transient states. Key Words: Power quality, power system harmonics, time-frequency analysis, wind power plants. 1

Integration Monitoring of On-grid Photovoltaic System: Case Study

The aim of the paper is to present possible using of monitoring systems associated with photovoltaic systems (PV) in point of its integration with electrical power system (EPS). Presented investigations is a case study of 15 kW Scientific Photovoltaic System. The paper contains a description of applied control and monitoring systems including monitoring of PV panels parameters, weather condition, PV DC/AC inverters as well as special monitoring systems dedicated to power quality (PQ) and shape of voltage and current. The aim of the paper is to exhibit a possibility to combine different monitoring systems of the PV in order to improve evaluation of integration of PV with EPS. Presented example contains selected elements of power quality assessment, power and energy production, weather conditions for selected period of PV system working time

Investigations of Influence on Power Quality of Superconducting Fault Current Limiter

Abstract. Waveforms obtained from a superconducting Fault Current Limiter are investigated using the Prony modelling technique. Comparable measurements with the use of standard tools of spectral analysis (like FFT) fail because of short data available and low levels of higher spectral components

Measurement of IEC groups and subgroups using advanced spectrum estimation methods

Abstract – IEC Standards characterize the waveform distortions in power systems with the amplitudes of harmonic and interharmonic groups and subgroups. These groups/subgroups utilise the waveform spectral components obtained by using a fixed frequency resolution DFT; while this choice represents a good compromise among different aims such as the need of good accuracy, simplification and unification. In some cases the power system waveforms are characterized by spectral components that the DFT with fixed frequency resolution can not capture with enough accuracy. This paper investigates the possibility of a group/subgroup evaluation using advanced spectrum estimation methods: the adaptive Prony, ESPRIT and root-MUSIC methods. The paper presents also the results of applications of these methods to test waveforms and to waveforms obtained from simulations of a real DC arc furnace plant