Zbigniew Leonowicz

Power Quality Evaluation using Advanced Spectrum Estimation Methods

The authors show that the use of high-resolution spectrum estimation methods instead of Fourier-based techniques can improve the accuracy of measurement of spectral parameters of distorted waveforms encountered in power systems, in particular the estimation of the power quality indices (such as inter/harmonic groups and subgroups). The comparison of the frequency and amplitude estimation error, based on numerical simulations is presented. Presentation of selected power quality indices is then followed by comparison of estimation error in the case of application of FFT-based algorithms and parametric methods. Investigated waveforms are typical for dc arc furnace plant. MUSIC and ESPRIT high-resolution methods are used to analyze waveforms in a supply system of a DC arc furnace. Reduction of variance of results is achieved by using robust averaging procedure (winsorized mean).

TIME-FREQUENCY ANALYSIS OF NON-STATIONARY THREE PHASE SIGNALS

New method of observation and diagnosis of inverter-fed induction motor drives is developed and tested. Unsymmetrical conditions concerning the machine impedances or valves operation are reflected in the spectrum of the current space- phasor. We estimate the spectrum of the space-phasor with the help of the Wigner-Ville distribution (WVD) and we obtain its time-frequency representation with excellent time and frequency resolution. The proposed method is tested with nonstationary multiple- component signals occurring during the fault operation of inverter-fed drives and transmission lines. Copyright

Optimal sizing of renewable energy plant-storage system for network support

The quest to meet the ever increasing demand for energy coupled with the need to curtail the emission of CO2 has led to the deployment of renewable energy sources into the electrical network over the past decades. This development, although very desirable, comes with the known downside of fluctuating production, especially when dealing with wind and solar power sources. This introduces variations in voltage and frequency along with harmonic pollution that need to be constantly controlled. System operators are required to balance demand and supply and are sometimes forced to cut out supply from renewable energy sources in order to maintain network stability, resulting in losses. This paper shows an approach to sizing of renewable energy plant and storage system using particle-swarm optimization. The background aim is to support the hosting capacity of the network where the unit is connected.

Mitigating the impact of distributed generation on directional overcurrent relay coordination by adaptive protection scheme

Distributed Generation (DG) brought new challenges for protection engineers since standard relay settings of traditional system may no longer function correctly under the new conditions of DG. The extreme case is coordination loss between primary and backup relays. The directional overcurrent relay (DOCR) which is the most implemented protection device in the electrical network also suffers performance degradation in presence of DG. Therefore, the paper proposes the mitigation of DG impact on DOCR coordination employing adaptive protection scheme (APS) using differential evolution algorithm (DE). The impacts of DG prior and after the application of APS are presented and a new mitigation scheme is proposed.

Advanced Control of the Dynamic Voltage Restorer for Mitigating Voltage Sags in Power Systems

The paper presents a vector control with two cascaded loops to improve the properties of Dynamic Voltage Restorer (DVR) to minimize Voltage Sags on the grid. Thereby, a vector controlled structure was built on the rotating dq-coordinate system with the combination of voltage control and the current control. The proposed DVR control method is modelled using MATLAB-Simulink. It is tested using balanced/unbalanced voltage sags as well as fluctuant and distorted voltages. As a result, by using this controlling method, the dynamic characteristics of the system have been improved significantly. The system performed with higher accuracy, faster response and lower distortion in the voltage sags compensation. The paper presents real time experimental results to verify the performance of the proposed method in real environments.

Analysis and modeling of STATCOM for regulate the voltage in power systems

In this paper, modeling of STATCOM for regulate the voltage in power flow calculation is proposed. Based on power flow, the proposed technique has been presented and tested on 26-bus power system. The results proved the correctness of the proposed technique. The influence of the STATCOM on regulating voltage and decreasing power losses has also been discussed in detail.

A microgrid with PV production and energy storage for an university building

The paper describes a measurement campaign conducted at the Engineering Department of Astronautics, Electrical and Energetic, Sapienza University of Rome. Starting from measurement campaign, in the context of building an urban microgrid, a PV plant and a energy storage system has been proposed. The measurements were conducted in two relevant period of the year in order to know the power consumption of the facility. The knowledge of total energy demand by electrical loads allows the identification of most efficient strategies for energy utilization by using the PV production and energy storage.

Assessment of e-vehicles availability in charging pool for support services in smart grids: Case study based on real data

This paper proposes a contribution to the employment of electric vehicles (EVs) understood as a storage technology for tackling the challenge of grid compatible integration of renewables and electro mobility. For this purpose, a concept for the integration of mobile energy storage is presented (electric vehicles with V2G capability). This concept was evaluated in real live conditions. In particular, the availability of EVs at charging stations and the prerequisites for information and communication technology development between an electric vehicle, a charging point and an intelligent control system is considered in detail because it is the foundation for the practical utilization of EVs serving as mobile storages in electrical grids.

Analysis and simulation of causes of voltage sags using EMTP

This paper presents an inclusive set of EMTP models used to simulate the cause of voltage sags such as short circuits, transformer energizing, induction motor starting. Voltage sag is usually described as characteristics of both magnitude and duration, but it is also necessary to detect phase angle jump in order to identify sags phenomena and finding the solutions, especially for sags due to short circuits. In case of the simulation of voltage sags due to short circuit, their effect on the magnitude, duration and phase-jump are studied.

Long term performance of a PV system with monocrystalline PV cells — a case study

The paper presents long term performance analysis of a photovoltaic system with monocrystalline silicon PV cells, operated at the Faculty of Electrical Engineering at the Wroclaw University of Science and Technology. As part of the analysis a simulation of photovoltaic system with similar technical parameters was done and compared to the real installation. The results of this research include characteristics of average value of generated power and energy, insolation, module temperature and outside temperature.