M. Shafiul Alam

Continuous wavelet transform based analysis of low frequency oscillation in power system

Low frequency oscillation is a threat to the stability of interconnected power system. Proper identification of the low frequency oscillation is crucial. In this work continuous wavelet transform (CWT) with complex morlet wavelet is used to extract modal information of the power system oscillations. The modal information of the measured signal such as frequency and damping is determined from the magnitude and phase plot of the complex valued wavelet coefficients. The proposed technique is applied to the measured signal of a two area power system to detect inter area mode of oscillation and results are compared with Eigenvalue analysis method.

VSC-HVDC system stability augmentation with bridge type fault current limiter

Voltage source converter high voltage DC (VSC-HVDC) system has number of advantages over traditional line commutated converter HVDC (LCC-HVDC). However, VSC-HVDC system is exposed to high current due to faults having great negative effect on converters. In order to limit fault current to relatively low level, bridge type fault current limiter (BFCL) for VSC-HVDC system has been proposed in this study. Fault current limiters are placed with the AC gird sides of VSC-HVDC system. Real and reactive power controller for the VSC-HVDC has been developed based on current control mode. Symmetrical as well as unsymmetrical faults are applied to evaluate the effectiveness of proposed BFCL controller in order to limit the fault current and improve system stability. Simulations are carried out with real time digital simulator (RTDS) to validate the efficacy of the proposed BFCL solution. The results show the potential of the proposed scheme to limit the fault current and improve greatly the system performance.

Direct control of three-phase smart load for neutral current mitigation

Electric Spring (ES), a power electronic based device, has been recently developed to improve various attributes of future power systems with high penetration of intermittent renewable energy sources. ES is connected in series with non-critical load to form an adaptive load, known as smart load. This configuration has been successfully used to mitigate voltage and frequency fluctuations, ensure demand side management, and improve power quality. It has also been used to reduce three-phase power imbalance and so the adverse effect of neutral current is eliminated. In this work a novel control scheme, based on run time impedance measurement, is proposed to mitigate neutral current from unbalanced three-phase system. Mathematical analysis is also given and corresponding simulations are carried out to substantiate the theoretical framework. Simulation results show the efficacy of presented technique under various unbalanced loading conditions.

Impact study of a generation rich island and development of auto load shedding scheme to improve service reliability

Abnormal conditions in a power system create fluctuations to electrical quantities such as voltage, frequency and current. Some of them may lead to fall of system frequency and sometimes extreme abnormality leads to system blackout. Planned and proper islanding may protect the system from complete blackout even in case of extreme abnormalities. Islanding operation not only helps stabilizing a faulted system but also supports power supplies to critical and important loads, in extreme emergency. But the islanding systems are weaker than integrated system so the stability of islands is the prime concern when an integrated system is disintegrated. In this paper different impacts on a generation rich island have been studied and a frequency based auto load shedding scheme has been developed for sudden load addition, generation outage and combined effect of both to the island. The developed scheme has been applied to Dhaka Island (the largest and generation rich island of Bangladesh Power System) to validate the effectiveness of the developed technique. Various types of abnormalities to the test system have been simulated and for the simulation purpose CYME PSAF (Power System Analysis Framework) has been used.

Switching signal reduction of load aggregator with optimal dispatch of electric vehicle performing V2G regulation service

Environmental concerns over the production of greenhouse gas have led to the development of environmental friendly transportation such as electric vehicle (EV). As the number of EVs is increasing day by day, it will have a great impact on grid operation and electricity market. Significant amount of EV charging during peak hour will cause branch congestions and low voltage. Moreover, high penetration of EVs plays an important role in altering electricity price. Thus, optimal scheduling of EVs charging is inevitable from the perspective of both system reliability and market. Load aggregators can combine the capacities of many EVs to participate in wholesale energy market. In this paper, optimal dispatch algorithm of EVs is developed and tested on a system consisting 1000 EVs. The advantage of the algorithm is that it requires less number of communication signals and less expensive infrastructure. EVs are turned on and turned off in binary fashion based on priority to follow the regulation signal.

Comparison of series and combined series-shunt compensation on East-West Interconnectors of Bangladesh Power System

Utilization of the existing transmission line capacity to its fullest is most important due to the continuous growth of the demand and rising cost of new transmission infrastructures. Due to the problems associated with voltage drop and stability limits, a transmission line can not be loaded up to its thermal limit. The potential benefits of installing Flexible AC Transmission System (FACTS) devices on the system for enhancing power transmission capacity and stability are well known. Two main members of FACTS family like thyristor controlled series capacitor (TCSC) and static var compensator (SVC) have been widely studied and reported in technical literature and have been shown as effective as well as time saving alternative to building new transmission lines for enhancing power transmission capacity and stability. This paper compares the application of series and series-shunt compensation by means of TCSC and SVC to show enhancement of power transmission capacity and stability of East-West Interconnected System (EWIS) of Bangladesh Power System (BPS). Two SVCs are connected in parallel with two buses in the western region of the interconnectors and two TCSCs are connected in series with the interconnectors. Bifurcation, steady state, and transient analyses are performed to compare positive effect of series and series-shunt compensation on transmission capacity and stability in BPS network.