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ABSTRACT: The main aim of active-filter-based power-quality improvement schemes is to reduce the total harmonic distortion (THD) and improve power factor (PF). According to standards, selective harmonic distortion (SHD) should be controlled too. Non-sinusoidal current owing to non-linear loads causes a non-sinusoidal voltage. Under such conditions, any attempt to make the power factor unity by usual methods will cause a non-sinusoidal current, which increases the THD. Also, attempt for harmonic-free current may not conclude unity power factor because of harmonics present in the voltage. Thus, there is a tradeoff between reduction of THD and improvement in power factor. One of the solutions to this tradeoff is to optimise PF while keeping THD and SHD into their specified limits. Differential evolution (DE) is introduced in this study and used for this optimisation problem, and the results are compared with four types of particle swarm optimisation (PSO), including conventional PSO, linearly decreasing inertia PSO, Type 1 PSO, constant inertia PSO and with the traditional optimisation method. It is seen that DE algorithm converges to a better result much faster than the other algorithms. Furthermore, using fuzzy strategy a multi-objective optimisation is proposed to optimise PF and THD simultaneously while keeping SHD in its limit. It is observed that using these optimisation methods, PF and THD are more improved.
IET Generation Transmission & Distribution 10/2011; · 1.20 Impact Factor
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ABSTRACT: Harmonic pollution minimisation in voltage-source programmed pulse-width modulation (PPWM) inverters is defined as a time-limited optimisation problem in real-time applications with variable DC sources. In order to obtain minimum total harmonic distortion (THD) as the objective function, shuffled-frog-leaping algorithm (SFLA) is modified and employed to calculate the switching angles and compared with non-linear programming as a traditional optimisation method. In addition, particle swarm optimisation and three of its modified versions as popular evolutionary optimisation algorithms are employed to ensure the capability of the proposed optimisation method. Moreover, modified sinusoidal PWM (MSPWM) THD is compared with PPWM THD. Furthermore, as the DC bus voltage in some applications might have high variations (in amplitude or frequency of fluctuations) in a short time, to acquire adequate response speed to this variation of DC source of inverters in real-time control applications, a neural network (NN) is trained by the off-line calculated results of MSFLA for various desired modulation indexes (various DC voltages). Simulation results demonstrate the accurate and high-speed response of the designed NN. The main contribution of this study is to provide a fast accurate method which can track the variation of DC source of inverters with high-quality solutions in real-time control applications.
IET Power Electronics 10/2011; · 1.62 Impact Factor
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ABSTRACT: The unstoppable increase in the capacity of power generation and also the stability problems due to the capacity of transmission lines cause new and different congestion management methods to be appeared in power systems. This paper proposes a congestion management method based on Optimal Power Flow (OPF) in order to analyze the effect of reserve generation in total generation and total cost of a power system. The optimization method which is used in OPF is Differential Evolution algorithm. The proposed method is applied on IEEE 24-bus RTS system and the result including power generation and the cost of the energy and reserve power production are presented and compared before and after congestion management and also with and without the existence of reserve generation.
Electrical Engineering (ICEE), 2011 19th Iranian Conference on; 06/2011
