Electric power systems foresee challenges in stability due to the high penetration of power electronics interfaced renewable energy sources. The value of energy storage systems (ESS) to provide fast frequency response has been more and more recognized. Although the development of energy storage technologies has made ESSs technically feasible to be integrated in larger scale with required performance, the policies, grid codes and economic issues are still presenting barriers for wider application and investment. Recent years, a few regions and countries have designed new services to meet the upcoming grid challenges. A number of grid-scale ESS projects are also implemented aiming to trial performance, demonstrate values, and gain experience. This paper makes a review on the above mentioned aspects, including the emerging frequency regulation services, updated grid codes and grid-scale ESS projects. Some key technical issues are also discussed and prospects are outlined.

Low voltage direct current (LVDC) distribution systems have recently been considered as an alternative approach to provide flexible infrastructure with enhanced controllability to facilitate the integration of low-carbon technologies (LCTs). To date, there is no business-as-usual example of LVDC for utility applications and only few trials have been developed so far. The deployment of LVDC in general will present revolutionary changes in LV distribution networks. This will require a rethinking of network design principles and the enablement of integrated solutions. This discussion paper reviews the current practice in utility-scale LVDC distribution networks worldwide. The paper also presents a new multizone architecture approach which can be used to better understand future of LVDC systems, and exploit their inherent flexibility to allow synergistic integration of multiple energy technologies.

This  paper  investigates  the  detection  of  short-circuit   faults   in   the   stator   winding   of   a   Wind   Energy Conversion  System  (WECS)  based  on  a Doubly-Fed  Induction Generator  (DFIG).  The  Cumulative  Sum  (CUSUM)  algorithm is  used  to  detect  the  change  in  the  stator  negative-sequence current  magnitude  which  is used  as  the  fault residual.  The  grid voltage  unbalance  is  considered  along  with  the  fault  position and  its  severity  to  evaluate  the  effect  on  the  residual.  The generator  is  modeled  using  the  winding-function  approach. Simulation  results  are  presented  for  a  15  kW  system  operated, under  a  power control strategy, at  rated conditions.  It  is shown that the fault-detection method is able to detect the fault rapidly and  is  not  influenced  by  the  grid  voltage  unbalance  within normal limits.

This paper evaluates the modern trends of energy storage in the UK and reviews its application in the context of wind energy systems. This research takes into account the advantages/disadvantages and trends of different technical options of energy storage technology based on modern and future industry and government projects. Additionally, this research identifies and quantifies, in terms of profitability, the revenue streams available in the UK for energy storage projects, using the most up-to-date information. This research also identifies the revenue streams suitable for wind power and energy storage, and discusses the current UK regulatory framework for its implementation. The results of this research are of high value for those looking into the techno-economic aspects of wind energy integration with energy storage and provide a framework where industry and universities can position development or research efforts with a fresh view of the opportunities ahead.

LV direct current (LVDC) distribution systems have recently been considered as an alternative approach to electrical distribution system infrastructure as they possess the flexibility and controllability that is required to facilitate the integration of low carbon technologies (LCT). For example, energising existing LV AC cables by DC with higher voltages (>0.4kV) can potentially release additional power capacity on LV cables and reduce the associated thermal losses. However, converting existing AC cables for DC operation may change the cable performance under faulted conditions, resulting in a change to its lifetime. The nature of future LVDC systems can be capacitive due to the characteristic of particular customers such as battery energy storage systems (BESS) and electric vehicles (EVs). A short-circuit fault on the DC side may lead to a discharge/release of significant transient energy in LV cables which was never anticipated under traditional LVAC networks. This paper quantifies the transient DC fault let-through energy which can be imposed on existing AC cables used for DC operation, and draws conclusions on the potential impact of such phenomena on the cable performance. A detailed model of an LVDC test network with three-core LV cables is developed using PSCAD/EMTDC for simulation studies.