Battery Energy Storage Systems (BESS) based on Li-Ion technology are considered to be one of the providers of services in the future power system. Although prices for Li-Ion batteries are falling ...continuously, it is still difficult to achieve profitability from a single service today. Multi-use operation of BESS in order to reach a so-called “value-stacking” of services therefore is a hotly debated topic in literature, since such an operation holds the potential to increase profitability dramatically. The multi-use operation of a BESS can be divided into two parts: the operational planning phase and the real-time operation. While the operational planning phase has been examined in many studies, there seems to be a lack of discussion for the real-time operation. This paper therefore tries to address the topic of the real-time operation in more detail. For this reason, this paper discusses concepts for implementing a real-time multi-use operation and introduces the novel concept of dynamic prioritization, which allows resolving conflicts of services. Besides the ability to cope with abnormal grid conditions, this concept also holds potential for a better utilization of resources during normal grid conditions. A mathematical framework is used to describe several services and their interaction, taking into account the concept of dynamic prioritization. Several applications are presented in order to demonstrate the behavior of the concept during normal and abnormal grid conditions. These applications are simulated in Matlab/Simulink for specific events and in the form of long-time simulations.
In this paper, a small hydropower microgrid solution with high applicability is proposed to solve the problem of high line failure rate and long maintenance time, which can improve the reliability of ...distribution network in mountainous areas. In this scheme, small hydropower and local load constitute a low-cost but efficient microgrid operation to improve the reliability of rural electricity. In this scheme, small-sized hydropower and local load constitute microgrid operation. In case of failure, the scheme makes full use of the independent operation of microgrid to provide qualified power quality to local load. This scheme is easy to realize and does not need additional energy storage, so it has good economy. Firstly, the frequency disturbance characteristics of small hydropower microgrid is analyzed, which lays a theoretical foundation for small hydropower microgrid operation. Then it introduces the island operation mode to grid-connected operation mode transition of small hydropower, including the key technologies such as frequency adjustment strategy in island operation stage. Finally, the simulation studies show the effectiveness of the method.
A review of the ongoing research on black start (BS) service integrated with offshore wind farms (OWFs) is presented in this paper. The overall goal is to firstly gain a better understanding of the ...BS capabilities required by modern power systems. Subsequently, the challenges faced by OWFs as novel BS service providers as well as an outlook on the ongoing research which may provide solutions to these are presented. OWFs have the potential to be a fast and environmentally friendly technology to provide BS services for power system restoration and, therefore, to ensure resiliency after blackouts. As a power electronic-based system, OWFs can be equipped with a self-starter in the system in order to perform BS. The self-start unit could be a synchronous generator (SG) or a power electronic unit such as a grid-forming (GFM) converter. Preliminary BS studies performed in PSCAD/EMTDC are presented in a simplified OWF system via an SG as the self-start unit. Consequently, technical challenges during the BS procedure in an OWF benchmark system are outlined via theoretical discussions and simulations results. This is useful to understand the threats to power electronics during BS. Finally, the most relevant GFM strategies in the state-of-the-art literature are presented and their application to OWF BS is discussed.
This paper presents a method for supplying stable electricity using renewable energy sources and energy storage systems (ESSs) in a small-scale microgrid (MG) such as an island. Traditional control ...methods, such as master–slave control and droop control, have focused on equalizing power sharing among a small number of generators and do not deal well with emergencies such as unplanned generator failures. This paper proposes a control method that can stably maintain the frequency of the MG in various situations by combining the advantages of master–slave control and droop control and complementing the disadvantages. Simulations were performed under various conditions to verify the proposed control method.
In this paper, a two-level model for probabilistic microgrid scheduling, considering the uncertainties of electricity price and predicted load, is present for microgrid performance in both island ...mode and connection to the main grid. The two-level model of ideal microgrid scheduling using the Banders decomposition method is decomposing into the main problem for operation in the main grid connection mode and subproblems for performance in island mode. The primary problem's objective function is to reduce the cost of microgrid performance, while the subproblem's objective function looks at the adequacy of microgrid production and the microgrid's ability to serve loads without interruption in the case of islands. In this method, if there is not enough power to supply loads in the mode of existing islands, a cut is added to the main issue to revise the microgrid performance program. Finally, the simulation results for both the microgrid connection mode to the main grid and the islands mode are present. In both modes, the modeling results demonstrate excellent microgrid performance.
Cooperating with distributed energy storage, distributed generation is with the potential of supply load stably under both normal and failure periods of distribution network. Therefore, distributed ...generation has not only electricity value, but also capacity value. The capacity value can be characterized by credible capacity index. However, the uncertainty of the distributed generation output and the sequential characteristics of energy-storage operation must be considered during a united credible capacity evaluation. A united credible capacity evaluation method of distributed generation and energy storage based on active island operation is proposed. The proposed method carries out day-ahead economic dispatching under a normal state and island partition under a fault state, alternately, to realize accurate reliability calculation, which is the key link of credible capacity searching. The main work is as follows. First, a day-ahead economic dispatching model under normal state is established to obtain the sequential remaining electricity information of energy storage. Second, the models of maximum island partition and optimal island rectification are established based on electricity sufficiency and power balance information. By solving the maximum island partition and optimal island rectification models alternately, optimal island partition schemes under the fault state could be achieved. Then, the convergence criterion based on variance coefficients instead of artificial selection is designed in reliability calculation. Finally, the united credible capacity of distributed generation and energy storage is evaluated in the PG&E 69-bus system. It is found that credible capacity value increases by 23%, 53%, and 61%, respectively, under the energy storage allocation ratios of 20%, 30%, and 40%. It can be seen that the integration of energy storage makes a significant impact on distributed generation credible capacity value.
The high penetration of distributed generation power plants, based on renewable energy sources (RESs), is boosting the connection of power converters to the electrical network. This generation ...concept would permit to form local networks, microgrids, when the main grid falls due to any kind of contingency in the network. However, the connection and disconnection of these local networks may give rise to undesired transient overcurrents that should be avoided. In order to solve this drawback, this paper presents a method oriented to carry out a stable intentional disconnection/reconnection of local grids from the main electrical network under grid-fault conditions. This control method has been implemented in a grid-connected power converter that acts as an intelligent connection agent (ICA) and adapts its operation mode according to its connection state. The proposed control also manages the operation of a controlled switch, which is responsible of disconnecting/reconnecting the microgrid from the mains. In this paper, the behavior of the ICA under transient conditions will be discussed, and finally, its simulated and experimental performance will be shown.
This study presents a mixed integer linear programming-based approach for determining the optimal strategy for reliability improvement in radial distribution networks where island operation of ...distributed generators (DGs) is allowed. The proposed approach simultaneously defines the optimal number, type, and location of new automation devices (ADs) to be installed in a network, the optimal relocation of the existing ADs and the optimal creation of DG islands. The load curtailment possibility in creating islands is considered along with the multi-level load model. The presented numerical results indicate the effectiveness of the proposed approach and the importance of simultaneous consideration of the aforementioned individual strategies in determining the best reliability improvement strategy in radial distribution networks with DGs.
Armature-reaction-compensated permanent-magnet synchronous generators are a particular type of hybrid excitation synchronous generators, where the main flux is created by the permanent magnets and ...the field winding is needed only to compensate the armature reaction. This paper studies the feasibility of an armature-reaction-compensated permanent magnet synchronous generator in island operation by comparison with a conventional electrically excited synchronous generator and permanent magnet synchronous generator. The aim of this paper is to demonstrate the performance of an armature-reaction-compensated permanent magnet synchronous generator and its operation principle in island operation. As part of the study, a 55 kW prototype was built and tested. The experimental results of the prototype are presented.
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