Original methodology for the calculation of island operation event occurrence possibility is proposed for the photovoltaic power plants connected to medium voltage grid. Within the methodology ...description, event fault tree with number of pairs of basic initial events is discussed, where probability for the basic events are defined and flow chart for the proposed calculation is given. The novelty in the approach for probability calculation includes also proposal for development of frequency distribution functions for concerned power generation and consumption variables which have to be modelled for the probability calculations, for which the triangular distributions curves have been chosen. Being boundary conditions for definition of non-detected island event, borders of non-detection zones are defined for the common island detection protection functions: over frequency and under frequency, over voltage and under voltage and rate of change of frequency functions. Comparison of the island event probability is presented on case study example, with conclusion that standard voltage and frequency protection alone are not satisfying, but ROCOF protection could be suitable, subject to particular local grid characteristic and calculative verification of probability.
The late Spanish grid code established that, to avoid island operation, renewable power sources have to be disconnected from the grid in the case of a voltage sag. This would threaten the system ...stability in case of massive penetration of renewable sources and motivated a recent revision of the code. The new code establishes strict ratios between active and reactive currents during the sag and requests that the plant must quickly resume its normal operation, when the voltage sag ends. Existing installations are also affected if they want to enjoy the premiums associated with renewable generation. When full upgrading of existing installations is not practical, this study proposes a plug-in shunt-connected power electronics device to help solar plants comply with the new grid code, without modifying the solar inverters. The device and its control algorithm are explained in this study and experimental results using photo-voltaic inverters without low-voltage ride-through capability are presented. Solar inverters remain unaware of the voltage sag and they can be led quickly and smoothly back into the grid when the sag is over.
► We propose an Islanding Security Region (ISR) concept. ► ISR provides security assessment of island operation. ► By comparing the system state with ISR, system operator knows when to island. ► The ...computation efficiency can be increased by Artificial Neural Network (ANN). ► By ANN, the online application of ISR can be feasible.
There has been a high penetration level of Distributed Generations (DGs) in distribution systems in Denmark. Even more DGs are expected to be installed in the coming years. With that, to utilize them in maintaining the security of power supply is of great concern for Danish utilities. During the emergency in the power system, some distribution networks may be intentionally separated from the main grid to avoid complete system collapse. If DGs in those networks could continuously run instead of immediately being shut down, the blackout could be avoided and the reliability of supply could be increased. However, when to island or how to ensure the islanded systems can survive the islanding transition is uncertain. This article proposes an Islanding Security Region (ISR) concept to provide security assessment of island operation. By comparing the system operating state with the ISR, the system operator can clearly know if it is suitable to conduct island operation at one specific moment. Besides, in order to improve the computation efficiency, the Artificial Neural Network (ANN) is applied for fast ISR formation. Thus, online application of ISR based islanding security assessment could be realized.
The paper adopts the method of modularized modeling, creating an electro-mechanic simulation model for a Microturbine Generation System (MTGS), including the micro-turbine engine, permanent magnetic ...synchronous generator, rectifier and inverter. In this paper, control strategy for grid-connected and islanding operations of a micro-turbine generation system is researched, the former adopts output voltage control strategy to maintain the output voltage of the load, and the latter adopts a dual closed-loop control algorithm based on PQ decoupling. A new control strategy to regulate the output power of MTGS based on the combination of decoupled control of output voltage and hysteresis current control is also introduced. Simulations have been done, and result proves the feasibility of the strategy.
This paper presents control of a multiple stages steam turbine which is switched into the island operation. The frequency in an electrical grid is stated on nominal value which is in UCTE grid 50 Hz. ...When deviation of frequency is higher then 0.2 Hz, the switching of particular steam units into the island operation is only the chance how to maintain the supply of, at least, some small grids. The other possibility how to keep power units in operation, to be prepared for the next synchronization to the grid, is to switch them to operation status in which they supply only their self-consumption. This change of the operating state is the most dynamic load change for the control system of the unit. The multiple stages turbines are equipped with high pressure hydraulic valves for steam turbine governing. Influence of the intercept valve on steam turbine control during the switching process into the island operation is examined in Matlab Simuling software.
This paper presents a coordinated control strategy of a battery energy storage system (BESS) and distributed generation (DG) units for the island operation of the Danish island of Bornholm. The ...Bornholm power system is able to transit from the grid connected operation with the Nordic power system to the isolated island operation. In order to ensure the secure island operation, the coordinated control of the BESS and the DG has been proposed to stabilize the frequency of the system after the transition to the island operation. In the proposed coordinate control scheme, the BESS is used to provide the primary frequency control and the DG units are used to provide the secondary frequency control. As such, the proposed control scheme can strike a balance of the frequency control speed and the energy used from the BESS for the frequency control support. The real-time model of the Bornholm power system was used to carry out case studies using real time digital simulator (RTDS) to illustrate the performance of the coordinated control strategy. Case study results show that the proposed control strategy can efficiently help stabilize the frequency under different conditions.
The topology of energy storage inverter is adopted with T-type three-level structure. The characteristics are analysed when the T-type three-level energy storage inverter is working on the ...grid-connected and isolated-island operation. In order to satisfy the stable switching operation from grid-connected to isolated-island, a seamless switching control strategy based on the virtual synchronous generator is proposed. A simulation model of seamless switching control for T-type three-level energy storage converter is built in MATLAB to verify the correctness of the proposed strategy.
Regarding the AC UPS fault accident happened in one compressor station which caused severe consequence with gas transmission pipeline, this paper lists the possible reasons based on the recorded ...fault code and equipment configuration, and solutions are proposed for modification. In the end, recommendations are given for the future project design of AC UPS.
This paper presents a general framework for Microgrids control based on Multi Agent System Technology. The proposed architecture is capable to integrate several functionalities, adaptable to the ...complexity and the size of the Microgrid. To achieve this, the idea of layered learning is used, where the various controls and actions of the agents are grouped depending on their effect on the environment. Moreover this paper, focus on how the agent will cooperate in order to achieve their goals. The core of the cooperation is a Multi Agent Reinforcement Learning Algorithm that allows the system to operate autonomously in island mode.
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