This paper proposes a new n-port hybrid dc circuit breaker for offshore multiterminal HVDC grid application. The n-port dc circuit breaker can substitute n - 1 hybrid dc circuit breakers at a dc bus with n - 1 adjacent dc transmission lines. The system-level behavior of the proposed multiport hybrid dc circuit breaker is similar to other hybrid dc circuit breakers. The operation principles of the proposed multiport dc circuit breaker are introduced, analyzed, and compared to the existing solution in this work. The components ratings are compared to the existing solution, and the functionality of the proposed device is verified by simulation.

A fully operational multiterminal dc (MTDC) grid will play a strategic role for mainland ac systems interconnection and to integrate offshore wind farms. The importance of such infrastructure requires its compliance with fault ride through (FRT) capability in case of mainland ac faults. In order to provide FRT capability in MTDC grids, communication-free advanced control functionalities exploiting a set of local control rules at the converter stations and wind turbines are identified. The proposed control functionalities are responsible for mitigating the dc voltage rise effect resulting from the reduction of active power injection into onshore ac systems during grid faults. The proposed strategies envision a fast control of the wind turbine active power output as a function of the dc grid voltage rise and constitute alternative options in order to avoid the use of classical solutions based on the installation of chopper resistors in the MTDC grid. The feasibility and robustness of the proposed strategies are demonstrated and discussed in the paper under different circumstances.

Present distribution network voltage design practice limits the distributed generation capacity that can be connected to 11 kV networks. It has been shown previously that adoption of a more active approach to network voltage control can significantly increase distributed generation capacity. One way to do this is to control the target voltage of automatic voltage control relays at primary substations. A basic design for a controller to do this has been created, comprising three algorithms. A statistical state estimation algorithm estimates the voltage magnitude at each network node supplied by the primary substation, using real-time measurements, network data and load data. The estimate accuracy depends on the number and placement of real-time measurements. Studies using an 11 kV feeder model showed that an acceptable accuracy could be obtained with one or two measurements. The state estimator uses pseudo measurements for unmeasured loads. A load model was constructed using load profiles to calculate the pseudo measurements. The calculated pseudo measurements were inaccurate, but it was found that acceptable state estimate accuracy could be obtained with inaccurate pseudo measurements. A control algorithm alters the AVC relay target voltage, based on the maximum and minimum node voltage magnitude estimates. A simulation on a four-feeder network showed that the algorithm enabled the generator power export to be more than doubled.

This paper details an optimization tool for the planning and operation of battery energy storage systems (BESS) in island power systems with high wind penetration. The selection of the most suitable battery technology, its sizing and location is achieved through a comparative analysis of the operational and capital expenditure of the islanded system during the planning horizon with and without the deployment of the BESS solution. An operational algorithm is developed consisting on sequentially closer to time of delivery optimization stages in order to provide a robust quantification of the technical, environmental, and economic impacts of the battery system. The developed methodology is assessed and validated in a real-world case study of a Portuguese island with a high share of wind generation. Results show that BESS enhances the flexibility of the islanded power system thus ensuring a higher accommodation of wind energy with significant economic benefits.