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Recent research on wind-farm control methods has focused until now on maximising the efficiency and durability of farm operations, as verified for a normalised electrical layout. However, with the increase of turbine size and capacity, it is necessary to develop modifications of the farm management plan that can support the increasing demands of the wind-turbine industry. Here the authors propose a modification that focuses on a proportional reactive power-dispatch method that is applied to radial offshore farm networks. They improve a previously developed method of proportionally distributing reactive power commands by considering the actual configuration of an offshore platform. To confirm the applicability of this method in transient state, they examine case studies using a time-varying signal for a reactive power reference under fluctuating wind. Electromagnetic transients using DC software tools are used to estimate the electrical loss and verify the efficiency of this strategy.

In recent years, the expansion of renewable energy in electric power systems has been increasing at such a rapid pace that it has started affecting frequency stability. Renewable generators connected to the grid produce variable amounts of power, and in most cases have no inherent inertia response (IR) to the system frequency. Therefore, the high penetration of renewable generators in the system results in low inertia and frequency distortion. If renewable generators account for a high proportion of the supply in a power system, the use of energy storage systems (ESSs) with frequency-support algorithms (in the place of synchronous generators) can stabilize the network. The participation of ESSs in frequency support must be organized precisely, so that they are fully devoted to their own purpose. In this paper, the frequency-support parameters of ESSs are calculated for achieving stable frequency response from a network. An estimation and calibration process is conducted during the active power-order change of the ESSs in the substation, and is verified through electromagnetic-transients-including-DC (EMTDC)-based simulations.

Recent development and cost down of PV(Photovoltaic) technology drive change of power system structure. The participation of PV generation is increasing, and the size of each PV farm is getting larger. In order to integrate large PV farms into the main grid, substation for interconnection needs to be sized properly. Unlike substations for load and conventional generators, PV farm substation has an uneven utilization ratio due to characteristics of solar radiation. With proper sizing method for the capacity of the substation can reduce the building cost of facilities. A combination of an energy storage system can further reduce the capacity of the substation. Battery energy storage system (BESS) can shift the peak production of PV during the daytime to midnight. According to market circumstances, BESS can reduce further construction costs by producing profit based on time difference of electric cost. For proper sizing of substation capacity, several factors must be considered including environmental factors, market structure and BESS in the system. In this article, a series of assessment methodology is introduced to calculate the optimized capacity of substation and BESS for PV farm interconnection. The long-term solar radiation data is analyzed for a given site of the PV farm. Based on market structure, the operation of BESS is optimized to make maximum profit during operation. The iterative calculation of each step results in the calculation of the optimized capacity of BESS and substation for given PV farm size.

The recent development of a number of advanced wind farm (WF) operation strategies, using designed verification studies, has resulted in various operational and economic improvements. These applications focused on stabilised conditions to confirm the improved effect derived from a maximum power extraction condition. In the case of large-scale WFs, however, a physical area with realistic environmental variations should be considered in order to conduct applicable case studies. In this study, the authors propose a modified reactive power allocation strategy, based on proportional techniques, with the system components of a WF structure for utilisation under a variety of practical situations. The proposed method introduces a modified loss prediction model, which takes the resistive components of the wind turbine into consideration. Each analysis is conducted to confirm the feasibility of active reference assignment in terms of loss reduction and flexibility. The simulations are based on electromagnetic transients using DC software tools to perform electrical loss estimation, in order to verify the effectiveness of this strategy.

In the future, Distribution network will face many challenges due to increased acceptance of renewable resources such as photovoltaic (PV)and wind power. Typical problems that arise from increased penetration of renewable resources include overvoltage issues, load imbalances on each feeder, and fluctuations in power output. In this paper, we consider installing Soft-Open Points (SOPs) to solve these problems. SOP is a power electronic device installed at the normally-open point (NOP) of the distribution network. Typically, SOPs are comprised of voltage source converters (VSCs), which can control the power flow between the feeders. In this paper, we discuss the method of calculating the optimal operating point of a SOP using the Particle-Swarm Optimization (PSO) algorithm using the characteristics of the SOP that can independently control the active and reactive power flows. The IEEE-33 bus test system was modified to verify the proposed method and the objective function for the bus voltage deviation and the index for the total line losses can be minimized simultaneously by using the PSO algorithm to optimize the multiple objective function Algorithm.

Renewable generation in power systems has proved to be challenging for system operators owing to the increasing levels of penetration. The operation of power systems currently requires additional flexibility and reserves due to the intermittency and unpredictability of renewable generators. However, it is difficult to precisely predict and control the stochastic nature of renewable sources, nevertheless, its capacity continues to increase. To monitor and control renewable generators efficiently, the entire system needs to be established in a hierarchical order. This study proposed the concept of a substation that is uniquely designed for renewable interconnection. The purpose of this substation is simple: to make the renewable generators dispatchable to operators such that each group of renewable generators is sufficiently stable to be considered as conventional generators. For this purpose, methods for sizing and controlling energy storage system are proposed based on forecasts and error distributions.

Power System with high penetration of inverter based renewable generators have several problems such as voltage instability and frequency deviation. The most severe problems for such network is lack of inertia due to fewer number of synchronous generators connected to the grid. As portion of synchronous generators in network decrease, low inertia of system can be a major problem which hinder the additional renewable generator deployment. Energy Storage System (ESS) is adequate solution for this problems by providing inertia response and governor response to low inertia network. In this paper, actual network system study was conducted to integrate large wind farms in small network with low inertia. ESS and is installed at each point of interconnection of windfarms. Inertia response operation strategy of ESS is suggested to protect system from low frequency load shedding and also provide emergency reactive power compensation to prevent cascading failure of network due to voltage under fault ride through standard of wind turbines.

Climate change and global warming are becoming important problems around the globe. To prevent these environmental problems, many countries try to reduce their emissions of greenhouse gases (GHGs) and manage the consumption of energy. The Korea Electric Power Corporation (KEPCO) introduced smart grid (SG) technologies to its branch office in 2014. This was the first demonstration of a smart grid on a building, called the Smart Grid Station (SGS). However, the smart grid industry is stagnant despite of the efforts of KEPCO. The authors analyzed the achievements to date, and proved the effects of the SGS by comparing its early targets to its performance. To evaluate the performance, we analyzed the data of 2015 with the data of 2014 in three aspects: peak reduction, power consumption reduction, and electricity fee savings. Furthermore, we studied the economic analysis including photovoltaic (PV) and energy storage system (ESS) electricity fee savings, as well as running cost savings by electric vehicles. Through the evaluation, the authors proved that the performance surpassed the early targets and that the system is economical. With the advantages of the SGS, we suggested directions to expand the system.

Various control methods and applications have been introduced to power systems in order to alleviate the uncertainties of relying on renewable sources. This paper, focusing on a reactive power allocation process, discusses the development of a self-modification algorithm and its introduction to an online reference management system. The algorithm is designed to predict unexpected situations occurring in real-time operations, when, due to technical issues, the control system becomes unavailable. A test system has been formed to check the feasibility of the composed method. As the main purpose of the feasibility study is checking availability with a complex solution, case studies are designed to adapt a reactive power allocation method based on loss minimization. When unexpected systemic errors were induced, the proposed modification plan changed order automatically with maintaining previous objective function. The improved effects, caused by realistic responses, are classified according to EMTDC (Electro-Magnetic Transient Design and Control) analysis.

In order to solve the problems brought upon by off-shore wind-power plants, it is important to improve fault ride-through capability when an on-shore fault occurs in order to prevent DC overvoltage. In this paper, a coordinated control strategy is implemented for a doubly-fed induction generator (DFIG)-based off-shore wind farm, which connects to on-shore land by a modular multilevel converter (MMC)-based high voltage direct current (HVDC) transmission system during an on-shore fault. The proposed control strategy adjusts the DC voltage of the off-shore converter to ride through fault condition, simultaneously varying off-shore AC frequency. The grid-side converter detects the frequency difference, and the rotor-side converter curtails the output power of the DFIG. The surplus energy will be accumulated at the rotor by accelerating the rotor speed and DC link by rising DC voltage. By the time the fault ends, energy stored in the rotor and energy stored in the DC capacitor will be released to the on-shore side to restore the normal transmission state. Based on the control strategy, the off-shore wind farm will ride through an on-shore fault with minimum rotor stress. To verify the validity of the proposed control strategy, a DFIG-based wind farm connecting to the on-shore side by an MMC HVDC system is simulated by PSCAD with an on-shore Point of Common Coupling side fault scenario.