Constantin Bulac

Optimal SVC placement in electric power systems using a genetic algorithms based method

The problem of improving the voltage profile and reducing power losses in electrical networks is a task that must be solved in an optimal manner. At present time, this optimality can be achieved by efficient usage of existing facilities alongside with installing FACTS devices. The Static VAr Compensator (SVC) was chosen for study as its maturity and acceptable costs make it more usable in practical applications than other FACTS devices This paper proposes a genetic algorithm that tries to identify the optimal location and size of an SVC. A multi-criteria function is developed, comprising of both operational objectives and investment costs. The computer program is run on a 13 nodes test system, assessing improvements in voltage profile and reducing power losses. The purpose of this study is to validate the solution method in order for it to be adapted for systems of higher dimensionality.

Multi-criteria Reconfiguration of Distribution Electrical Networks for Minimization of Power Losses and Damage Cost due to Power Supply Interruption

The paper presents a reconfiguration method for electrical distribution networks under normal operating conditions. The method uses a multi-criteria objective function that considers economic related aspects: the cost of power losses and the cost of damages due to power supply interruption following some faults occurring into the distribution network. The restrictions of the optimization problem are related to arborescence, connectivity and the security of the electrical network subject to the thermal limit of the network branches and voltage level at the consumers. A heuristic method is applied to solve the mathematical model, which consists in searching into the solutions space based on a branch exchange strategy.

An approach to modal analysis of power system angle stability

An approach to modal analysis and modal identification is proposed, capable of complementing the panoply of existing methods. It is based on a hybrid time-domain-direct transient stability method called SIME (for single machine equivalent). In short, SIME uses a conventional transient stability program to transform the time varying parameters of the system into those of a one-machine infinite bus (OMIB) equivalent system. The representations of this OMIB allow substantial reduction of the original problems dimensionality. Many important advantages may result. For example, the multimachine system unstable equilibrium point (UEP) can readily be derived from the OMIB UEP, which is calculated analytically and unambiguously in a two-dimensional space. Further, the interplay between multimachine and OMIB characteristics and their complementary properties provides a better understanding and handling of damping, inter-area oscillations and their control. More generally, modal analysis and modal identification tasks get closer to each other and easier to handle. The paper essentially focuses on the approach as such, rather than on potential applications. Simulations carried out on a 3-machine system illustrate the main features.

Coordination of distributed generators through the virtual power plant concept

In this paper the authors propose a market strategy of a microgrid incorporating a virtual power plant. For exemplification, a configuration consisting of different types of distributed generators and a lumped load are considered. The aim of the virtual power plant is to maximize the profit by minimization of the total cost involved for electrical energy generation by the distributed generators that are part of the virtual power plant.

Power transfer capacity enhancement using SVC

This paper presents the results of a feasibility study for installing FACTS devices in the South-Eastern part of Romanian power grid (Dobrogea - a peninsular area), to increase the transfer capacity to the rest of the grid. This study assumed, on one hand, the scheduled increase in generated power in the area, mainly due to two new units in the Cernavod ă nuclear power plant (1400 MW installed power) and wind generation with an estimated installed power of over 1600 MW. On the other hand, the scenarios considered the present topology and future developments of the transmission network. The increase in generated power in the S-E part of the power grid may lead to changes in the power market schedules, causing generation decrease or even shut down of other generators, leading to power flow changes and power system stability problems.

Implementation studies of secondary voltage control on the Romanian power grid

Improvement of the voltage control of transmission networks is nowadays becoming a challenging problem. This paper presents some preliminary results related to the perspective applications of the secondary voltage control on the Romanian power grid. System robustness with respect to the tripping of lines and generators is checked through simulations with and without secondary voltage control.

Load flow management in the interconnected power systems using UPFC devices

The deregulation of electricity supply industry has introduced new opportunity for competition to reduce the cost and cut the price. It is a tremendous challenge for utilities to maintain an economical and reliable supply in such an environment. The PFAC program developed by authors to analyze the power flow in power systems with FACTS devices, has been tested on the 220 kV-400 kV network of the Romanian Power Grid. We have taken into consideration several possible scenarios, leading to two types of congestions: the first type is related to nodal power release, and the second to the supply of a deficit area. Simulations prove the fact that in both cases we can regulate power flow so that to reduce and eliminate congestions if we use the UPFC device.

On-line power systems voltage stability monitoring using artificial neural networks

A method for on-line voltage stability monitoring of a power system based on Multilayer Perceptron (MLP) neural network is proposed in this paper. Considering that the power system is operating under quasistatic conditions, by using power flow model and singular value decomposition of the reduced Jacobian matrix, a suitable index to quantify the proximity of power system voltage instability is defined. Then, a neuronal network is trained to learn the correlation between the key factors of the voltage stability phenomena and this index. Once trained, the neural network provides the above mentioned voltage stability index as output for a predefined set of input variables that are known as directly influencing the stability conditions of the power system. Since the input variables for the neural network may be obtained from the steady state estimator, the proposed method can be implemented as a function of the Energy Management System (EMS) for on-line voltage stability monitoring. Tests are carried out using the IEEE 30-bus system, where different operating scenarios are considered.

Optimal generation scheduling strategy in a microgrid

This paper presents a strategy for optimal generation scheduling in a microgrid. Several small generation units of different type are considered, that is a wind system, a photovoltaic system and a gas engine unit. In order to maximize the use of renewable energy sources (RES) a storage battery is also integrated. Two generation scheduling algorithms are elaborated, either aiming at minimizing the use of fuel based unit or at maximizing the lifetime of the battery. The simulations have been performed in Matlab.

Optimizing the costs of reactive power for the coordinated voltage control service

This paper presents a procedure for minimizing the costs involved with the reactive power - voltage control using the synchronous generators/compensators as ancillary service. The procedure combines an optimal power flow algorithm and the secondary voltage control algorithm, the first aiming to minimize the reactive power costs injected/absorbed by the synchronous generators/ compensators, while the second one assuming proportional loading of the generators with respect to their maximum capability limit. The reactive power of a generator can be controlled by the system operator by specifying a certain voltage at the generator terminals.