Gabriela Nicoleta Sava

Comparison of active crowbar protection schemes for DFIGs wind turbines

The doubly fed induction generators (DFIGs) are used in almost 50% of the offshore and onshore wind power plants. The DFIGs offer advantages compared to fix speed induction generators. The DFIGs are sensitive to grid voltage disturbances and require additional protection for the rotor side power electronic converter, like crowbar protection. In the present paper two active crowbar topologies are compared, IGBT with bypass resistor and rectifier with IGBT, which were the most studied in the scientific literature. A DFIG model with analyzed crowbar protections was implemented in Matlab/Simulink. The simulation results reveal that both solutions can limit the rotor current and the dc link voltage values. However, the solution with rectifier offers better results.

Performance analysis of a 310Wp photovoltaic module based on single and double diode model

This paper presents a complete simulator developed in Matlab™ for a photovoltaic (PV) module. The most important contributions of the paper is the use of single and double diode model to simulate a PV module. In the paper are also implemented numerical methods to provide more characteristic parameters that are not provided by the manufacturers such as Rs, Rp, Ipv, I01 and I02. The numerical methods are suitably implemented to face the nonlinear nature of I-V and P-V curves that are characteristics to PV output. The accuracy of the simulator using single and double diode models is verified by applying the data-sheet from manufacturers. Furthermore, the double-diode model simulation results performed in Matlab™ are analyzed in comparison with the experimental data of a real 310 Wp photovoltaic module unit. The paper also highlights the effects of different shunt and series resistances and how it operates in different temperature conditions and irradiation levels.

Improved LVRT based on coordination control of active crowbar and reactive power for doubly fed induction generators

This paper proposes a control system, for crowbar protection and voltage support, for wind turbines equipped with doubly fed induction generator. The control system based on PI controller enables the low voltage ride through capability of the wind turbines. The reactive power control of doubly fed induction generators is mostly achieved by controlling its rotor side converter. The proposed control system allows regulating the reactive power using the rotor side converter as well as the grid side converter. During crowbar activation, the rotor side converter can no more control the reactive power. The proposed system controls the voltage at the point of common coupling to be above the imposed low voltage ride through curve, until the grid side converter returns to normal operation. The proposed models were implemented in Matlab/Simulink. The case studies refer to a control system with hysteresis band for the crowbar protection of a 3MW doubly fed induction generator based wind turbine. The simulation results highlights that the proposed control improves the coordination between grid side converter, rotor side converter, and crowbar protection.

Achieving energy savings and thermal comfort through intermittent heating in very low energy buildings

Energy efficiency and human comfort are key aspects for future owners. Climate conditions plays and important role on choosing the right policy for energy consumption in order to achieve desired interior comfort. Based on these assumptions, current paper is focused on use of various simulated scenarios and measured data in order to evaluate how intermittent heating can reduce energy consumption while mentioning user comfort at desired parameters. The passive house, which is the subject of current article, is a real house and is equipped with an in-house developed automated control solution and serves as a didactic and research platform.

Quality cost of power supply and pay-back capital of this

This paper reviews the importance of improving the power supply quality. It presents the main stages for a study of amelioration or improvement of the power quality. A basic description of accounting of the damages caused by poor quality of the electric power is given together with different examples. Then, solutions for pay-back possibility of the quality costs for electric power suppliers and power consumers are identified.

Multi-criteria approach for maintenance management in HV substations

Safety, reliability, affordability, sustainability for power supply depends on equipment and implementation of new technologies. The main contribution of this paper is the development of a multi-criteria evaluation questionnaire for assessing equipment breakdown consequences. The development and implementation of such questionnaire for electrical equipment and priority setting for the maintenance plan will have a significant contribution in choosing the optimal asset and risk management solutions. The approach of considering safety and environmental impact in the maintenance management process is an important step in the evolution of maintenance departments into the new perspective, following world concerns and complying with ISO 14001 and OHSAS 18001 standards. The case - study selected for the testing phase analyzed the questionnaires provided by the operators of substations located in the central region of Romania. It is a collaborative and very environmentally sensitive approach to long-term management HV substations.

A new mathematical model for assessing optimization decisions of the loading factor flowing through substation transformers

The paper proposes a new mathematical model used to determine the optimum loading for power system substations equipped with only one transformer. Because of the cyclic way of the planning process, the capacity and density of electrical substations are influenced by the technological progress and previous adopted measures. Operations knowledge comes in handy in day by day activities but only strategic knowledge confers electric companies an edge. In comparison with the methods used until now, the proposed model takes into consideration aspects related to operation, monitoring and maintenance costs throughout the lifetime of transformers. The proposed model is applied to a 110 kV/MV transformer with different rated powers of 2.5, 16, 80, and 400 MVA considered for an electrical distribution grid. The goal is following tendencies instead of on-point.

Effect of component design on the DC/DC power converters dynamics

This paper analyzes the impact of converter design elements on the operating performance of DC/DC converters, used worldwide for renewable energy sources. The design of inductor and capacitor elements is made considering the acceptable output ripple of voltage and current. This paper presents the methodology for determining the inductances and capacitances required for DC/DC converter operation within the acceptable power system limits. Simulations are carried on for investigating the dynamic stability of DC/DC converter.

Optimal bypass diode configuration for PV arrays under shading influence

Under partial shading conditions caused by the unevenly radiation and other ambient environmental conditions the operation of solar cells is influenced. Depending on the degree of shading, the phenomenon causes the decrease of solar cells output power. In the present paper two bypass diode configurations are compared, PV module with a bypass diode across each cell and with a bypass diode across each group cell, which are the most studied in the scientific literature. A PV module with analyzed bypass configurations was implemented in PSpice. This paper analyses the effects of bypass diode configurations on photovoltaic systems operation under various shaded degrees. The simulation results reveal that both solutions can limit the effects of this shading phenomenon and thus enhance the operational performance of photovoltaic (PV) systems. Further, the analysis of simulation results for I-V and P-V characteristic curves highlight the advantages and disadvantages of each type of bypass diode configuration, and also their use in practice.

Power quality measurements and analysis for a Romanian WPP

World wide the wind power plants are located far away from the existing interconnection substations to the power system. Therefore, compensation methods are considered for the reactance of long distance cable connection. High voltage DC transmission cables for wind power plants interconnection to the grid can also be considered and used. In the present paper, the problems raised by AC cables, from power quality point of view, are analyzed. A real wind power plant system of 80 MW connected to the public grid, located in the south-east area of Romania, is analyzed. Power quality measurements were conducted in different points of the analyzed real case study.