Selma Hanjalic

Modeling a group of consumers in order to analyze power quality

Application of new technology, the power electronics in the first place, has significantly improved the performance of individual consumers and increased their efficiency. The consequence of this is a presence of non-linear consumers in a network which are responsible for injection of higher harmonics and flickers into the network. A classification of consumers in the 0.4 kV network is presented in this paper. This classification is based on the measurements of the current waveform and the power of consumers. The measurements were realized using a measuring device for monitoring power quality. The measurements were made for a household that has appliances of new generation. It has been analyzed total and individual current of household appliances. In the first part of this work is presented relation between the new generation of household appliances and power quality (PQ). The second part of this paper is considering the problems of modeling a group of consumers with the purpose of analyzing the power quality. The measurements of a group of consumers, that were performed in laboratory conditions, provided us enough data for proposing a mathematical model.

Voltage conditions estimation in frequency domain of power systems based on measuring power quality

Power quality (PQ) is becoming important factor in proper functioning and operating of power systems (PS). Continuous PQ monitoring represents basics for efficient exploitation of power systems. Systems for continuous PQ monitoring and their networking with central system are major investments. This paper lists conditions for modeling of certain PS elements and describes concept of power network modeling in PQ analysis. First part of the paper gives mathematical formulation of the problem; second part describes high voltage transmission line in frequent domain using system of phase values, while the third part of the paper is an example in time domain modeled in EMTP-RV software package using system of phase values. Performance of power network in quasi-stationary state is analyzed and during the simulation five changes of voltage conditions occur as consequence of overloading. The PS is loaded with nonlinear loads generating high current and voltage harmonics. Voltage and current harmonic in the places of energy exchange are observed; furthermore estimation of voltage harmonics in the places with no PQ monitors is conducted. Conclusions of the paper indicate possible usage of presented algorithm for real time PQ analysis and for post PQ analysis.

Optimal control of small hydropower plants and power transformer tap changer in distribution network in order to minimize active power losses

In the concept of distribution generators (DG) integration, distribution network becomes active and philosophy of network guidance and control changes. The presence of DG in the network often results in the active losses increase and thus the maintenance costs raise. This problem is offen noted in radial networks, as DG in this type of networks make network doubly fed. This paper gives an answer how to run one or more small hydropower plants (SHPP) in a radial network with minimal losses. In this paper, the analysis of power flows, combined with optimization methods and technical constraints (voltage constraints according to EN50160) are carried out. One example with detailed calculations, conclusions and diagrams comments is conducted. The conclusions in this paper directly indicate the possible measures to be implemented in order to achieve a higher SHPP and distribution network performance.

Modeling and the impact on power quality of hybrid solar - wind power plants

Many renewable energy sources are not able to provide the demanded electrical energy during the day. This problem is getting more important with the increase of power plants which are based on renewable energy. The proposed method for overcoming the aforementioned problem is the building of hybrid power plants with two or three different energy sources. The most common hybrid power plants are solar-wind power plants, who produce electricity by using the complementary characteristics of solar irradiation and wind speed. The hybrid solar-wind power plants contain a lot of power electronic devices that affect the power quality disturbances. Therefore, an analysis of the dynamic of such power plants is necessary. First part of this paper presents the modeling of hybrid solar-wind power plants. The second part analyzes the impact on power quality of hybrid solar-wind power plant during its daily working cycle.

Hybrid solar — wind power plants — simulation of a daily cycle and the criteria for the connection to the power grid

Renewable energy sources in addition to all the advantages over the non-renewable energy sources have a lot of limitations, where the biggest of them are the price and the inability of constant electricity generation. One way of overcoming the problem of inability of constant electricity generation is to build hybrid power plants with renewable energy sources. This primarily highlights hybrid solar - wind power plants, which produce electricity by using solar radiation and wind energy. Since the hybrid solar - wind power plants consist of a photovoltaic power plant and a wind power plant and are usually constructed as a distributed source, it is necessary that the regulatory frameworks define criteria and actions for the connection of a hybrid solar - wind power plant in the power system. This paper gives a short overview of criteria and actions for the connection of a hybrid solar - wind power plant in the power system according to official documents in Bosnia and Herzegovina.

A frequency-based method for complete identification of some types of wiener-type plants based on relay feedback

This paper proposes a new closed loop frequency based method for a parametric identification of some types of Wiener-type nonlinear plants. It provides a parametric model of the linear part of the plant, and a point by point relationship between input and output of the nonlinear part of the plant. Two approaches are proposed for the identification of the nonlinear part. The first approach is slower, but it does not require any additional equipment expect the relay. The second approach is much faster, but it requires some additional equipment.