Volume 5, Issue 2

Optimal power flow (OPF) is one of the nonlinear problems of power system. The various algorithms for solving optimal power flow problem are found in the literature. The genetic algorithm (GA) based solution techniques are found to be most suitable because of their ability of simultaneous multidimensional search for optimal solution. This paper presents a novel GA-Fuzzy based approach for solving OPF. The GA parameters e.g. crossover and mutation probabilities are governed by fuzzy rule base. Algorithms for GA-OPF and GA-Fuzzy (GAF) OPF are developed and compared. The results obtained for these systems demonstrate that the GAF-OPF has faster convergence and lesser generation costs as compared to various methods tested for above systems.

Mitigation of voltage-sag effects on loads due to the starting of an induction motor is considered. If a series compensator is connected upstream of the motor, the large transient current caused by the switching event could damage the compensator or deplete the energy stored in it. Maximum motor-starting current and the required energy during the starting process are derived from which the ratings of the compensator can be determined. Simulation verifies the analysis is effective and the compensator is shown to be able to maintain good supply quality during the motor- start event.

This paper introduces a new power flow tracing and subsequently loss allocation method based on loop analysis. The knowledge of the loop paths aids in the visualisation of presumed transfer of power throughout the transmission network. A formalised process of loop identification, based on graph theory, is introduced to ensure that each loop contains at least one active source. This way, the system losses can be readily and justifiably allocated to the active sources in the network without involving any approximations. The proposed method is applied to both a small test system and the IEEE 14-bus test system, demonstrating the features and limitations of the proposed methodology.

A transmission system based on voltage-source three-level flying capacitor (FC) multilevel converters with selective harmonic elimination pulse-width modulation (SHE-PWM) control is presented in this paper. The generation of the switching patterns for each power device is described taking into account the natural balancing of the FC voltages. A new and simple control method for balancing the FC voltages of the FC converter when using SHE-PWM is proposed which is based on the small change of the firing angle according to the load current polarity. Implementation of the SHE-PWM with capacitor voltage balancing is provided. Simulation studies for a 300MW/+-150kV transmission system are presented to confirm the satisfactory performance of the proposed system.

A dc-ripple reinjection concept, described in the literature with reference to the line-commutated current source converter, is applied in this paper to the self-commutated current source converter. This is achieved by means of a reinjection converter fed, via a single-phase transformer, from the triple frequency ripple signal. It is shown that the three-phase bridge can be made to operate effectively at any multiple of the six-pulse number and, thus, presents an effective alternative to the use of ac and dc side filters.

In an Inductively Coupled Power Transfer (ICPT) system, a multiplicity of (moving) loads take power from an elongated conductive loop (track) excited by a current in the range of 15-125A by magnetic induction at a VLF frequency of between 5-50kHz. In this application, the track performs the same function as a distribution line in a power system. However, frequency deviations cannot be tolerated in ICPT systems and therefore there are difficulties with inrush power surges as loads switch on. In severe cases, the inrush surge may compromise the security of the whole system.This paper proposes a solution to this problem using an ICPT pickup controller with input shaping where the poles that can cause an inrush are not excited. The paper is supported by theoretical analysis and experimental measurements and is applicable across a wide range of ICPT sizes and applications. The solution reduces the inrush effects to 10% of an uncontrolled system.

The flexible AC transmission system (FACTS) in a power system improves the stability, reduces the losses, reduces the cost of generation and also improves the loadability of the system. In the proposed work, a non-traditional optimization technique, a Genetic Algorithm (GA) is conjunction with Fuzzy logic (FL) is used to optimize the various process parameters involved in introduction of FACTS devices in a power system. The various parameters taken into consideration were the location of the device, their type, and their rated value of the devices. The simulation was performed on a 30-bus power system with various types of FACTS controllers, modeled for steady state studies. The optimization results are compared to the solution given by another search method. This comparison confirms the efficiency of the proposed method which makes it promising to solve combinorial problem of FACTS device location in a power system network.