IMPROVING ENERGY EFFICIENCY IN BUILDINGS USING MICROGRIDS

Modern society has a growing need for the electricity. To protect the environment, future energy demand must be met with more environmentally friendly technologies, such as renewable energy sources. Because of its vast availability, solar radiation has been used for decades to generate electricity through photovoltaic systems (PV) for residential, educational, and commercial buildings. However, the growth of distributed generation (and renewable energy sources) across power systems in industrialized countries has created new challenges. Random renewable generation causes an imbalance between electricity production and consumption, so smart grids and microgrids may be solutions. In this article, we investigate improving the energy efficiency in the Faculty of Electrical Engineering building in Osijek by using a microgrid. To do so, we compared the total electricity consumption of the building and the production of a 10 kWp photovoltaic power plant on that building. The improvement in energy efficiency of the building produced a maximum savings of up to 10% of the building’s total electricity consumption

Demand Side Management inside a Smart House

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

Demand side management in the distribution system with photovoltaic generation

Posljednjih godina učinjen je znatan napor na uključivanju obnovljivih izvora električne energije u elektroenergetski sustav. Nepredvidiva prozvodnja obnovljivih izvora električne energije stvara neravnotežu između proizvodnje i potrošnje, što onda zahtijeva elektrane s brzim odzivom, ili sustave skladištenja električne energije. Opće prihvaćeno rješenje za uravnoteženje potrošnje je koncept naprednih mreža, a jedan od elemenata učinkovitosti naprednih mreža je sposobnost za uravnoteženje potražnje i opskrbe u stvarnom vremenu. U ovom radu razvijen je model dijela distribucijske mreže grada Osijeka i to na temelju rezultata mjerenja ukupne potrošnje obiteljske kuće u Osijeku, potrošnje klimatizacijskog uređaja te proizvodnje fotonaponske elektrane. Također, predložen je algoritam za upravljanje potražnjom u stvarnom vremenu. Algoritam sadrži usklađeno upravljanje klimatizacijskim uređajima ovisno o proizvodnji fotonaponskih elektrana te o potrošnji u distribucijskoj mreži, a u cilju snižavanja vršne potražnje u distribucijskoj mreži.Recently, there has been made a great effort to include electricity generation from the renewable energy sources into the power system. Random renewable generation creates the imbalance between electricity production and consumption, which requires power plants with fast response or energy storage systems. Generally accepted solution for load balancing is the concept of smart grids and one of the elements of smart grid efficiency is the ability of real-time demand-supply balancing. In this paper, the model of the part of power distribution network of the city of Osijek has been created based on results of the power measurements of total electricity consumption in a family house in Osijek, air conditioning system consumption and PV power plant production. Also, algorithm for real-time load management is proposed. It assumes coordinated control of air conditioning system units depending on the production of PV power plants and electricity consumption of distribution network, in order to reduce peak demand in the distribution network

Voltage variation performance indices in distribution network

U ovom radu analizira se razdioba naponskih propada na distribucijskom izvodu u istočnom dijelu Hrvatske. Prikazan je rezultat nadzora (monitoringa) pokazatelja kvalitete električne energije na transformatorskoj stanici 110/35 kV. Mjerenje je izvedeno pomoću mrežnih analizatora kvalitete električne energije i to na sekundarnim stranama dvaju transformatora. Rezultati su objedinjeni i statistički obrađeni: naponski događaji klasificirani su u skladu s normama EN 50160 i IEEE 1159:1995, a izračunati su i pokazatelji učestalosti promjena efektivne vrijednosti napona. Istraživanje je izvedeno u sklopu projekta Leonardo Power Quality Initiative, u kojem je Elektrotehnički fakultet Osijek bio pridruženi partner.This paper analyzes voltage sags distribution for distribution feeder in eastern Croatia. It presents the result of online power quality indices monitoring at 110/35 kV transformer station. Measurements were performed at the secondary sides of two transformers, by the power quality network analyzers. Results are aggregated and statistically arranged: voltage events were classified according to the EN 50160 and IEEE 1159:1995, and RMS variation performance indices were calculated. The research was performed during the Leonardo Power Quality Initiative project, since the Faculty of Electrical Engineering in Osijek was the LPQI\u27s affiliate partner

Review of Non-Traditional Optimization Methods for Allocation of Distributed Generation and Energy Storage in Distribution 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

Identification of Even-Order Harmonics Injected by Semiconverter into the AC Grid

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

Optimal Re-Dispatching of Cascaded Hydropower Plants Using Quadratic Programming and Chance-Constrained Programming

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

Harmonic Distortion Prediction Model of a Grid-Tie Photovoltaic Inverter Using an Artificial Neural Network

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

Identification of Even-Order Harmonics Injected by Semiconverter into the AC Grid

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

Determining the Optimal Location and Number of Voltage Dip Monitoring Devices Using the Binary Bat Algorithm

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)