Search

This paper presents a new centralized adaptive underfrequency load shedding controller that is integrated with a distribution state estimator to improve the frequency stability of islanded microgrids. While underfrequency load shedding is a well-established corrective emergency frequency-control action, it is not entirely suitable for use in microgrids with low inertia and a limited number of measurement devices. The novel centralized controller presented in this paper overcomes these challenges by incorporating a distribution state estimator to estimate the power consumption of the demand. In parallel to this, the actual active power imbalance in the microgrid is estimated by simultaneously monitoring the system frequency and its rate of change. The centralized controller uses these two variables to determine the correct amount of load to be shed. The performance of the proposed controller has been validated using computer simulations of the actual distribution network in Malaysia. These simulation results show the effectiveness of the proposed centralized controller for preventing power system instabilities, which might lead to cascading outages and even a complete blackout in microgrids that have been disconnected/islanded, from the main grid. [ABSTRACT FROM AUTHOR]

The solar energy generation has grown significantly in the past years. The importance of PV penetration in power system as a major element of renewable energy source has seen it being widely used on a global scale. Despite its promising success, PV penetration presents various issues and its impact on the distribution system has to address for seamless integration in the power system. In this paper, a comprehensive overview on important issues affecting the distribution system as a result of PV penetration is presented. Pertinent issues such as voltage fluctuation, voltage rise, voltage balance, and harmonics and their effect on the system are discussed in details. The islanding issues, which are of critical importance to the stability and integrity of the system, are also thoroughly reviewed. Details on different islanding techniques – remote and local techniques and their advantage and disadvantages are shown. Therefore, this paper can provide useful information and serve as a reference for researchers and utility engineers on issues to be considered with regards to PV penetration. [ABSTRACT FROM AUTHOR]

Highlights: [•] The requirement of DG interconnection with existing power system is discussed. [•] Various islanding detection techniques are discussed with their merits and demerits. [•] New islanding detection strategy is proposed for multiple mini hydro type DGs. [•] The proposed strategy is based on dq/dt and load connecting strategy. [•] The effectiveness of strategy is verified on various other cases. [ABSTRACT FROM AUTHOR]

Abstract: Under-Frequency Load Shedding (UFLS) is a common technique to maintain power system stability by removing the overload in some part of the system. The existing UFLS schemes operate successfully in the interconnected grid system. A particular approach of UFLS scheme is required for an islanded system which is known to be not as strong as the grid. This paper presents a new approach of UFLS scheme for the implementation in an islanded distribution system. The scheme is based on a combination of adaptive and intelligent techniques. The disturbance magnitude for response based and event based is treated differently: (1) event based is based on the power imbalance and (2) response based is based on the swing equation which relies on the frequency and rate of change of frequency measurement. Dynamic simulation on an intentional islanding operation is performed on an existing Malaysian network interconnected with a mini hydro generation. The objective is to investigate the effectiveness of the proposed scheme. The simulation results demonstrate that the proposed scheme is capable of improving the frequency response of the islanded system. A significant finding is that the scheme can successfully reduce the effect of power deficiency following the grid connected to islanding operation transition. [Copyright &y& Elsevier]

Highlights: [•] A new approach to detect and locate high impedance fault is proposed. [•] Wavelet transforms and predetermined faulty database is used to locate the fault. [•] A simulation using PSCAD/EMTP was done to detect and locate high impedance fault. [•] A typical 11kV underground system in Malaysia was used in the simulation. [Copyright &y& Elsevier]