In this study, the feedback effects of a three-phase half-controlled rectifier (also known as a semiconverter) to three-phase AC power grid was analyzed. Special attention was paid to the ...identification of harmonic order of the phase current. As a reference point for analysis, the mathematical model of an uncontrolled rectifier was used. The harmonic order of the phase current was identified by displaying the measurement results as well as using a mathematical model that is easily applicable, although this is unusual for harmonic analysis because it is based on time domain data. For this purpose, laboratory models of uncontrolled and half-controlled rectifiers were assembled. For both converters, the results obtained by practical laboratory measurements were compared to the mathematically obtained results, with the commutation in the mathematical model being ignored. The effects of commutation were analyzed in more detail for the laboratory model. For the semiconverter, the characteristic waveforms were studied for few different firing angles of the thyristor. Additionally, total power factor and total harmonic distortion of phase current were determined for all chosen firing angles. Finally, a comprehensive conclusion was drawn based on theoretically and practically obtained results on the appearance of even-order current harmonics, which should be taken into consideration when designing input filters and which contributes to power quality of the AC power grid.
Voltage dips represent a significant power quality problem. The main cause of voltage dips and short-term interruptions is an electrical short circuit that occurs in transmission or distribution ...networks. Faults in the power system are stochastic by nature and the main cause of voltage dips. As faults in the transmission system can affect more customers than faults in the distribution system, to reduce the number of dips, it is not enough to invest in a small part of the transmission or distribution system. Only targeted investment in the whole (or a large part of the) power system will reduce voltage dips. Therefore, monitoring parts of the power system is very important. The ideal solution would be to cover the entire system so that a power quality (PQ) monitor is installed on each bus, but this method is not economically justified. This paper presents an advanced method for determining the optimal location and the optimal number of voltage dip measuring devices. The proposed algorithm uses a monitor reach area matrix created by short-circuit simulations, and the coefficient of the exposed area. Single-phase and three-phase short circuits are simulated in DIgSILENT software on the IEEE 39 bus test system, using international standard IEC 60909. After determining the monitor reach area matrix of all potential monitor positions, the binary bat algorithm with a coefficient of the exposed area of the system bus is used to minimize the proposed objective function, i.e., to determine the optimal location and number of measuring devices. Performance of the binary bat algorithm is compared to the mixed-integer linear programming algorithm solved by using the GNU Linear Programming Kit (GLPK).
Active distribution grids that contain energy sources (so-called distributed generation or DG) are nowadays a reality. Besides the many benefits DGs bring to the distribution grid, some challenges ...are associated with their integration. Since there are DGs now in the distribution grid, the occurrence of islanding operation is possible. Since an islanding operation can be dangerous, it is necessary to have an effective method to detect it. In the last decade, scientists have made a great effort to develop and test various islanding detection methods (IDMs). Many approaches have been tested, and the methods based on computational intelligence (CI) have shown great potential. Among them, artificial neural networks (ANNs) gained most of the research attention. This paper focuses on ANN application for islanding detection. It gives an exhaustive review of the ANN types used for islanding detection, the types of input data, and their transformation to fit the ANNs. Furthermore, various applications based on specific input data, preprocessing types, different learning algorithms, real-time implementation, and various distribution models used for ANN are reviewed. This paper investigates the potential of ANNs to enhance islanding detection accuracy, reduce non-detection zone (NDZ), and contribute to an overall efficient detection method.
Expanding the number of photovoltaic (PV) systems integrated into a grid raises many concerns regarding protection, system safety, and power quality. In order to monitor the effects of the current ...harmonics generated by PV systems, this paper presents long-term current harmonic distortion prediction models. The proposed models use a multilayer perceptron neural network, a type of artificial neural network (ANN), with input parameters that are easy to measure in order to predict current harmonics. The models were trained with one-year worth of measurements of power quality at the point of common coupling of the PV system with the distribution network and the meteorological parameters measured at the test site. A total of six different models were developed, tested, and validated regarding a number of hidden layers and input parameters. The results show that the model with three input parameters and two hidden layers generates the best prediction performance.
Here, the impacts of biogas power plants and photovoltaic (PV) power plants on the power quality in the distribution network are presented and analysed. The biogas power plant's influence on the ...current harmonics is explored, as a synchronous generator powers the biogas power plant, and the PV plants are connected to the distribution network via the inverter. All the analyses are based on actual measurements that are performed in the last 10 years. Results of the analysis of these numerous measurements were a challenge for investigation how large share of PV systems in distribution network with non-linear loads influence on THD from one side and how biogas power plant with a synchronous generator can improve THD from the other side. In order to investigate interaction of the biomass power plant and PV power plants on the power quality in distribution network, computer model was developed in DIgSILENT Power Factory where PV power plant and household were modelled as a source of current harmonic injections and biomass power plant was modelled as synchronous machine, as a source of voltage harmonics. Analysis of harmonic behaviour in different scenarios is examined through the performed simulations.
Stochastic production from wind power plants imposes additional uncertainty in power system operation. It can cause problems in load and generation balancing in the power system and can also cause ...congestion in the transmission network. This paper deals with the problems of congestion in the transmission network, which are caused by the production of wind power plants. An optimization model for corrective congestion management is developed. Congestions are relieved by re-dispatching several cascaded hydropower plants. Optimization methodology covers the optimization period of one day divided into the 24 segments for each hour. The developed optimization methodology consists of two optimization stages. The objective of the first optimization stage is to obtain an optimal day-ahead dispatch plan of the hydropower plants that maximizes profit from selling energy to the day-ahead electricity market. If such a dispatch plan, together with the wind power plant production, causes congestion in the transmission network, the second optimization stage is started. The objective of the second optimization stage is the minimization of the re-dispatching of cascaded hydropower plants in order to avoid possible congestion. The concept of chance-constrained programming is used in order to consider uncertain wind power production. The first optimization stage is defined as a mixed-integer linear programming problem and the second optimization stage is defined as a quadratic programming (QP) problem, in combination with chance-constrained programming. The developed optimization model is tested and verified using the model of a real-life power system.
The integration of distributed energy sources transforms passive distributed grid, in which the energy flows only in one direction (from the source to the consumer), in an active one, in which energy ...flows in both directions. To maximize positive impacts, which distributed generation (DG) can provide to the distribution network, it is necessary to determine the optimal allocation of distributed generation. The optimal allocation can be determined by using the optimization method. There are two main categories: exact methods (traditional) and heuristic (non-traditional) methods. Exact methods search for global optimum while heuristic methods achieve satisfactory solutions with greater computation speed. This paper gives a brief review of non-traditional methods used for determining optimal location and optimal power of DG with the aim to reduce real power losses and to improve voltage characteristics. Also, there is a review of the application of those methods in determining the optimal power, optimal location and optimal cycle of charging/discharging of electrical energy storage systems.
In this paper, a fuzzy expert off-line system has been developed for fault diagnosis in the distribution network based on the structural and functional operation of the relay and circuit breakers. ...Functional operations (correct operation, false operation and
failure to operate) of the relays and circuit breakers are described by fuzzy logic. Input data for the proposed fuzzy expert fault diagnosis system (FDS) are status and time stamps of the alarms, associated with relays and circuit breakers. The diagnostic system
from a huge number of alarms sets, logically organizes and quantifies the diagnosis. FDS can diagnose correct operation, false
operation and failure to operate of the relays and circuit breakers. Also, it can identify and quantify fault location based on the
Hamacher’s operator of a fuzzy union. The additional contribution of this paper is in modeling unknown information using linear
fuzzy membership function. Statuses of certain components may be unknown due to telemetry failures or are simply unavailable to
the operator and proposed FDS can make diagnosis in such a situation. Developed fuzzy expert FDS is tested on the two examples
of faults in real life distribution network
Demand Side Management inside a Smart House Šipoš, Mario; Primorac, Mario; Klaić, Zvonimir
International journal of electrical and computer engineering systems,
12/2015, Letnik:
6., Številka:
2.
Journal Article
Recenzirano
Odprti dostop
The upgraded traditional grid, also known as the smart grid, that incorporates information and communications technologies will change not only electricity production but also consumption. In ...combination with Photovoltaics (PV) and electrical storage, demand side management (DSM) is a promising solution for net-zero energy building (NZEB). NZEB will be able to produce energy for its own needs and also feed a surplus back to the grid. In scientific papers, it has already been proven that the use of electrical energy storage can improve the power quality and store variable production of renewable energy. Smart meters are a step forward because they enable a two-way communication between a customer and a utility. In this way, it will be possible to monitor consumption and electricity prices on the market in real time. Furthermore, this will enable the consumer to turn off devices that are large loads, or let the DSM system known as load management do its job such to reduce energy consumption in a given period. DSM will automatically switch off a big load in a manner that does not disturb user comfort. Smart appliances at the end-user level such as the Internet protocol (IP) addressable appliance controlled by external signals from the utility or end-user will enable load shifting to off-peak periods. Solar radiation is prevalent everywhere and can be used to generate electricity at the point of consumption, thereby reducing the losses in transmission. Only one hour of solar radiation is sufficient to cover the annual consumption; this shows that the future of low-carbon energy production lies in the use of solar radiation.
Probability Density Functions of Voltage Sags Measured Indices Voltage sags can cause interruptions of industrial processes, which could result as a malfunction of equipment and considerable economic ...losses. Thus, it is very useful to see certain rules of voltage sags occurrence due to duration and depth. This paper presents statistical analyses of voltage sags in several domestic and industrial transformer stations. Voltage sag probability functions are calculated from actual measurement data, by means of a hill climbing algorithm. Lognormal and Weibull frequency distribution functions are used to describe distribution of measured voltage dips.
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