Volume 7, Issue 4

This paper investigates the problem of contemporaneously choosing optimal locations and sizes for both shunt capacitors and series voltage regulators in three-phase unbalanced distribution systems. The sizing and placement procedure not only minimizes the power losses along distribution feeders but also makes sure that both capacitors and series regulators will have the minimum possible impact on the harmonic distortion of bus voltages in the system. The fact that distribution systems can operate under unbalanced loading conditions means that the optimization will have to account for any unbalances in the system. A genetic algorithm, which successfully solves the above-described problem, is developed and tested. This paper presents the results of simulations for a 34-bus IEEE distribution test system.

This paper presents the design, analysis and development of a novel tapped star connected autotransformer based twenty-four-pulse ac-dc converter for improving power quality at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMD’s). A star connected autotransformer with four windings per phase at different phase angles is used to realize the proposed twenty-four-pulse ac-dc converter. The basic design equations are derived to calculate the number of turns in different windings for achieving the harmonic reduction in the proposed autotransformer. The design of autotransformer is further modified for making it suitable for retrofit applications to replace presently used 6-pulse diode bridge rectifier. The proposed 24-pulse ac-dc converter is able to eliminate up to 21st harmonics in the supply current along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. Different power quality indices on input ac mains and on dc bus for a VCIMD fed from a 12-pulse and a 24-pulse ac-dc converters are also given to compare their performance. Various tests are conducted on the developed prototype of proposed autotransformer based 24-pulse ac-dc converter. Different power quality indices are measured on developed 24-pulse ac-dc converter to validate the design and simulation model.

There is no unique definition of non-active power for nonsinusoidal systems. A new definition of non-active power is proposed in this paper. This definition is based on energy transfer and provides a unique solution for non-active power of single-phase systems under both sinusoidal and non-sinusoidal conditions. An example is used to illustrate the use of this new definition. Energy transfer calculated using the new definition provides the same energy transfer determined from the non-sinusoidal non-active instantaneous power. This is consistent with the existing definition of active power that is also based on energy transfer.

This paper presents an approach for short-term electricity price and load forecasting using the artificial neural network (ANN) computing technique. The described approach uses the three-layered ANN paradigm with back-propagation. The publicly available data, acquired from the deregulated Victorian power system, was used for training and testing the ANN. The ANN approach based on similarity technique has been proposed according to which the load and price curves are forecasted by using the information of the days being similar to that of the forecast day. A Euclidean norm with weighted factors is used for the selection of similar days. Two different ANN models, one for load forecasting and another for price forecasting, have been proposed. Test results show that average price and load MAPEs for the year 2003 by using the ANN approach are obtained as 14.29% and 0.95%, respectively. MAPE values obtained from the price and load forecasting results confirm considerable value of the ANN based approach in forecasting short-term electricity prices and loads.

In this paper, a proportional plus integral (PI) type sliding surface has been proposed for designing a fuzzy variable structure controller to solve load-frequency control problem in presence of load disturbances. It is shown that the proposed controller is effective and robust enough when the system suffers from mismatched condition but the model uncertainty and disturbance are assumed to be bounded. Furthermore, the proposed control strategy drives the states to the sliding surface and also maintains the sliding motion. To illustrate the approach presented has been tested on load-frequency control of power systems and the analytical claims have been justified under the uncertainty involved in the load demand of inter-connected power systems.

HVDC and FACTS devices have been widely applied in power system for their excellent and flexible control ability. Their contributions to the damping of system oscillations are of great importance for achieving satisfactory system performance. However, previous experience has shown that there may be negative interactions among FACTS devices whose supplementary controllers are designed separately. This may deteriorate system performance and even make system unstable. The interactions of HVDC and SVC during system oscillation were analyzed in this paper. The coordinate supplementary damping controller for HVDC and SVC were then designed based on projective control principle. The criterion of synthetic residue is adopted in choosing the proper input wide area signals. Eigenvalue analysis and time domain simulations were performed on a two-area system and the results demonstrated the effectiveness of the proposed controller.

One of the most important tasks of System Operator (SO) is to manage congestion as it threatens system security and may cause rise in electricity price resulting in market inefficiency. In corrective action congestion management schemes, it is crucial for SO to select the most sensitive generators to re-schedule their real and reactive powers and the loads to curtail in extreme congestion management. This paper proposed the selection of most sensitive generators and loads to re-schedule their generation and load curtailment based on the improved line flow sensitivity indices to manage congestion. The impact of slack bus on power flow sensitivity factors has been determined to encourage fair competition in the electricity markets. Effect of bilateral and multilateral transactions, and impact of multi-line congestion on congestion cost has also been studied. The generators’ reactive power bid has been modeled by a continuous differentiable tangent hyperbolic function. The proposed concept of congestion management has been tested on a practical 75-bus Indian system and IEEE-118-bus test system.