Nicolae Golovanov

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.

Storage selection for DG applications containing virtual synchronous generators

The paper is presenting an algorithm for establishing the best types of electrical storages for the virtual synchronous generator (VSG), depending on the application case and desired nominal power of the VSG. The resulting application provides a description of available technologies in terms of characteristics matching the desired properties of the storage in accordance with the scenarios described by the user.

Impact of embedded generation on the voltage quality of distribution networks

The increasing concerns related to the global warming process determined the shifting towards the use of distributed generation (DG) designed to meet the environmental restrictions. The increasing penetration rate for the DG in the energy systems is raising technical and non technical problems that must be quickly solved in order to deeply exploit the opportunities and benefits offered by the DG technologies. In this paper, the analysis of the impact of distributed generation units on the voltage quality in a 6 kV medium voltage network is conducted. The distributed generation units may require an inverter before their interconnection to the mains. Thus, these converters can produce harmonics that propagate in the distribution network. The case studies are conducted using the software package ATP- EMTP on an existing 6 kV network.

The connection to the grid of wind turbines

With a view to the integration in national power system of new power plants based on renewable energy sources, such as wind energy, this paper presents the technical requirements related to the connection of the wind power plants to the main grid. Grid connected wind turbines may cause power quality problems, such as voltage variation and flicker, and therefore, the connection of wind farms requires new connecting rules to avoid negative effects on the existing electrical system. System operators usually issue these rules in the form of grid codes. The paper should be helpful to facilitate the orientation in finding of adequate type of wind turbines that can be installed in the intended sites, dependent on specific conditions.

Wind generation assessment proposal by experimental harmonic and distortion factor analysis

The ever-increasing presence of the wind generation in Romania power system triggers a vast array of challenges ranging from reliability, fault-ride-through capabilities, green certificates incentives, etc. The impact on power quality of a wind farm located in south-east of Romania composed of 45 wind turbines is investigated. The paper deals with power quality case studies conducted on existing renewable sources based systems. Harmonics determined by a wind farm up to 200 MW are analyzed. The measurements are carried out in different points of the power system supplying the wind farm. The correlation between the generated power and the main harmonic indices is highlighted.

Power quality impact of high capacity end-users

The random load variation, as in case of the arc furnaces, determines random voltage variations at the supply bus-bars., the can affect the power quality delivered to other customers, supplied by the same bus-bars. The value of the instantaneous flicker sensation S(t) is measured by means of an instrument, the so-called flickermeter. The setting-up of the flickermeter model is done in Simulink, the simulation tool, in the MATLAB environment. The present paper deals with the case study of an existing ac arc furnace facility. The 110 kV monitoring campaign was conducted using the ION 7600 equipment. The main power quality indices regarding harmonics and flicker levels are reported in the paper with reference to IEEE standards.

Steady state disturbance analysis in PV systems

This work presents the influence of the photovoltaic (PV) systems on steady state power quality events. Voltage variations and possible resonance conditions may appear between PV and the customer plant. Both stand alone and grid connected systems configurations are investigated on theoretical and experimental point of view. An existing PV system is used for the application of the studies performed in the paper confirming the theory considerations.

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.

The management of Power quality, Energy efficiency and the performance of the companies

The paper presents a relationship among three important concepts: Power quality, Energy efficiency and Performance of the company operating in energy field. In most of cases, the improvement of Power quality determines an increase of the Energy efficiency and, of course, the increasing of the performance of the company. The balancing between two of them, could give us the optimum solution to act in the strategic plan, which will be implemented. Some ideas for meeting of the scope of each company operating in the energy sector, increasing the performance of the company, are presented in this paper.

Wind farms access to the Romanian transport system

Nowadays, wind generation is developing in the whole world. In conformity with the Romanian present regulations, the wind energy producers must obtain the technical interconnection approval, which consists in the documents presented to the Transmission Grid Operator: an interconnection study for the wind turbines, urbanism certificate, and the property certificate. As the wind turbines are increasingly penetrating the power systems, their impact on power quality is becoming important. Electrical flicker is produced due to the wind turbine switching operations (start or stop), and due to the continuous operation. The paper deals with the access of the wind farms to the Romanian transport system, both from the legislative (policies, regulations, certificates, and incentives) and from the power quality point of view. The flicker study becomes necessary as the wind power penetration level increases quickly.