This paper presents a scheme for supervisory control of wind farms. We concentrate on reduction of power output variation, but the proposed scheme can also be used for system-wide controls that are related to power variation, such as frequency control or damping of power swings. The scheme may utilize either a separate (external) energy storage device or a power reserve achieved through part-loading of one or more turbines in a wind farm. The proposed supervisory control scheme has been validated on a model of a wind farm with four turbines. Simulations have confirmed the usefulness of the scheme. The proposed control system is general and could also be used for other types of intermittent generators such as wave or solar.

Expected bulk connection of renewable energy sources to existing distribution networks may change dynamic properties of power systems and increase the size of power system models used for the analysis of power system operation and stability problems. To reduce the size and complexity of modelling, distribution networks could be replaced by their dynamic equivalents. This paper focuses on identification of dynamic equivalents of distribution network from measured disturbance data. The validity of derived state-space models has been confirmed by simulation.

Bulk connection of renewable energy sources to the existing distribution networks in the recent years has resulted in high increase of the power systems complexity. This also has changed (and will be changing) dynamic properties of the power systems. Both of these factors lead to the increasing size of the power system models, which are essential to analysis of the power system operation and stability problems. Due to the difficulties related to obtaining data for these models, dynamic equivalencing becomes an interesting solution to the future power systems modelling. Proper equivalencing method is supposed to maintain the main dynamic characteristics of a power system whilst optimally (reasonably) reducing its size. This paper focuses on deriving dynamic equivalents of distribution network taking distributed generators into consideration. The dynamic equivalents are established by system identification method

For protection against electric shock in low voltage systems residual current devices are commonly used. However, their proper operation can be interfered when high frequency earth fault current occurs. Serious hazard of electrocution exists then. In order to detect such a current, it is necessary to modify parameters of residual current devices, especially the operating point of their current transformer. The authors proposed the modification in the structure of residual current devices. This modification improves sensitivity of residual current devices when high frequency earth fault current occurs. The test of the modified residual current device proved that the authors’ proposition is appropriate.

This paper refers to the issue that mainly appears in distribution grids, where renewable energy sources (RES) are widely installed. In such grids, one of the main problems is the coordination of energy production time with demand time, especially if photovoltaic energy sources are present. To face this problem, battery energy storage units (ESU) can be installed. In recent years, more and more attention has been paid to optimizing the use of ESU. This paper contains a simple description of available solutions for the application of ESU as well as an original proposal for selecting the optimal location and control of ESU. The ESU selection method is based on the use of a genetic algorithm and the ESU control method utilizes the fuzzy logic. The combination of the aforementioned methods/algorithms of ESU application is named an integrated algorithm. The performance of the proposed algorithm was validated by multivariate computer simulations with the use of the real low-voltage grid model. The DIgSILENT PowerFactory environment was employed to develop the simulation model of the integrated algorithm. The proposal was utilized to improve the voltage level in the distribution grid and to install the optimal number of ESU. Based on daily load variations for selected load profiles, it was shown that after the ESU application the voltage deviations in the analyzed network were significantly limited. Moreover, the analysis proves that both the location of ESU in the grid and the control of their active and reactive power are important from the point of view of reducing overall costs.