The increasing penetration of renewable energies in the power system is demanding new services from wind farms. In particular, system operators are concerned about system restoration after a black-out and new grid codes are under consideration that demand the participation of wind farms in the restoration process. Black start requires the wind farms to be capable of controlling voltage and frequency in an isolated grid. This paper proposes the use of a novel grid forming control for doubly fed induction generators (DFIG) for restoring the system after a black-out. The proposed grid forming control uses the rotor flux orientation principle, that allows to generate an internal electromotive force for controlling in this way the terminal voltage and frequency. Then, it is demonstrated that the rotor flux magnitude and frequency can be controlled by means of the rotor voltage applied the rotor side converter of the DFIG. The paper also proposes a wind turbine control system for balancing the power demanded by the load at the wind turbine mechanical system. Black start capability of the proposed control system has been validated through a comprehensive simulation. The simulated system consists of a wind farm with two DFIG-based wind turbines connected in parallel to a point of common coupling that supplies an induction motor through a feeder. Also, the synchronization of the isolated system to a main grid has been simulated, demonstrating the ability of the proposed control system for successfully completing the restoration process.

A naive battery operation optimization attempts to maximize short-term profits. However, it has been shown that this approach does not optimize long-term profitability, as it neglects battery degradation. Since a battery can perform a limited number of cycles during its lifetime, it may be better to operate the battery only when profits are on the high side. Researchers have dealt with this issue using various strategies to restrain battery usage, reducing short-term benefits in exchange for an increase in long-term profits. Determining this operation restraint is a topic scarcely developed in the literature. It is common to arbitrarily quantify degradation impact into short-term operation, which has proven to have an extensive impact on long-term results. This paper carries out a critical review of different methods of degradation control for short-time operation. A classification of different practices found in the literature is presented. Strengths and weaknesses of each approach are pointed out, and future possible contributions to this topic are remarked upon. The most common methodology is implemented in a simulation for demonstration purposes.

The massive penetration of renewable energy sources in electrical systems has been displacing synchronous generators (SGs) from conventional power plants in the last few years. Renewable generation plants are usually connected to power grids through electronic power converters, which cannot provide the same power generation services as SGs due to their mode of operation. Recently, different concepts have been proposed for electronic converter control in an attempt to emulate the performance of SGs, resulting in the so-called grid-forming converters (GFCs). This paper proposes a new GFC control strategy based on the reactive power synchronization (RPS) method, which decouples the synchronizing power and the active power control of renewable generation source to which a converter is connected. For this purpose, this study assesses three power sources: batteries, photovoltaic (PV) plants, and full-converter wind turbines. Moreover, the study proposes models and controls for each of these sources, whose dynamics exert a decisive influence on the grid services provided by renewable energy plants. Thereafter, the study proposes a GFC-RPS control scheme and verifies its effectiveness in different applications; for example, inertial response, which provides power immediately through a fast frequency response after a grid has experienced a load variation. Unlike storage systems and wind turbines, PV plants can only render these services if they are not operating at maximum power. Further, the study validates the GFC-RPS control strategy for regulating AC voltage at the output terminals of a converter. Finally, the paper assesses GFC hot swapping during the transition from a grid-connected to an isolated-operation mode while feeding a dynamic load. Results revealed that both the voltage and frequency remain stable, thereby demonstrating that the proposed GFC-RPS control indeed acts as a true voltage source and emulates the behavior of a conventional SG.

This paper addresses the design and analysis of a voltage and frequency control (VFC) strategy for full converter (FC)-based wind energy conversion systems (WECSs) and its applicability for the supply of an isolated load. When supplying an isolated load, the role of the back-to-back converters in the FC must change with respect to a grid-connected application. Voltage and frequency are established by the FC line side converter (LSC), while the generator side converter (GSC) is responsible for maintaining constant voltage in the DC link. Thus, the roles of the converters in the WECS are inverted. Under such control strategies, the LSC will automatically supply the load power and hence, in order to maintain a stable operation of the WECS, the wind turbine (WT) power must also be controlled in a load-following strategy. The proposed VFC is fully modelled and a stability analysis is performed. Then, the operation of the WECS under the proposed VFC is simulated and tested on a real-time test bench, demonstrating the performance of the VFC for the isolated operation of the WECS.

The propagation of hybrid power systems (solar–diesel–battery) has led to the development of new energy management system (EMS) strategies for the effective management of all power generation technologies related to hybrid microgrids. This paper proposes two novel EMS strategies for isolated hybrid microgrids, highlighting their strengths and weaknesses using simulations. The proposed strategies are different from the EMS strategies reported thus far in the literature because the former enable the real-time operation of the hybrid microgrid, which always guarantees the correct operation of a microgrid. The priority EMS strategy works by assigning a priority order, while the optimal EMS strategy is based on an optimization criterion, which is set as the minimum marginal cost in this case. The results have been obtained using MATLAB/Simulink to verify and compare the effectiveness of the proposed strategies, through a dynamic microgrid model to simulate the conditions of a real-time operation. The differences in the EMS strategies as well as their individual strengths and weaknesses, are presented and discussed. The results show that the proposed EMS strategies can manage the system operation under different scenarios and help power system operator obtain the optimal operation schemes of the microgrid.