Povzetek. V prispevku je prikazan pregled metod za določanje frekvence elektroenergetskega sistem... more Povzetek. V prispevku je prikazan pregled metod za določanje frekvence elektroenergetskega sistema. Podrobneje so prikazane najbolj perspektivne metode: iterativna metoda najmanjše vsote kvadratov odstopanj, izboljšana diskretna Fourierjeva transformacija in dekompozicija v ortogonalne komponente. Predstavljene so teoretične osnove posameznih metod ter njihove prednosti in slabosti. Lastnosti posameznih metod so numerično ovrednotene z vidika natančnosti določitve frekvence, dinamike odziva na spremembe parametrov vhodnega signala in vpliv nemodeliranih komponent vhodnega signala (višje harmonske komponente, subharmonske komponente, merilni šum) na določitev frekvence. Metode smo testirali s testnimi signali, ki ponazarjajo različna stanja elektroenergetskega sistema.
V publikaciji so predstavljene osnove elektromehanske pretvorbe in štirje osnovni električni stro... more V publikaciji so predstavljene osnove elektromehanske pretvorbe in štirje osnovni električni stroji: transformator, asinhronski stroj, sinhronski stroj in komutatorski stroj. Publikacija je razdeljena v pet poglavij. V nadaljevanju je predstavljena vsebina posameznih poglavij. Uvod: magnetno polje, vzbujanje navitij, induciranje napetosti, sile in vrtilni moment (navor), pretvarjanje električne moči v električno ali mehansko, izgube, izkoristek, segrevanje in hlajenje. Transformator: elementi gradnje, idealni in realni enofazni transformator, trifazni transformator, posebne izvedbe transformatorjev. Asinhronski stroj: opis gradnje z navitji in način delovanja, zagoni motorjev in spreminjanje hitrosti vrtenja ter vrtilnega momenta, asinhronski generator, enofazni asinhronski motorji. Sinhronski stroj: opis gradnje in način delovanja, obratovanje na togem omrežju, približna obravnava nasičenega stroja, vzbujalni sistemi in uporaba trajnih magnetov za vzbujanje, ter sinhronski motorji s trajnimi magneti. Komutatorski stroj: opis gradnje in način delovanja, reakcija kotve, problemi komutacije, elektronska komutacija, karakteristike različnih električnih vezav statorja in rotorja, spreminjanje hitrosti vrtenja, izmenični (univerzalni) komutatorski stroji.
Journal of the Science of Food and Agriculture, May 3, 2018
BACKGROUND: Milk fermentation takes place in the presence of various microorganisms , whereby a v... more BACKGROUND: Milk fermentation takes place in the presence of various microorganisms , whereby a variety of dairy products is produced. The oldest among them is kefir, which is usually produced by fermentation of milk with kefir grains. Carbon dioxide (CO 2), as one of the process products, also contributes to the characteristic flavor of kefir. The amount of CO 2 generated during fermentation depends on bioprocessing conditions and may change, which is not desirable at the industrial level. RESULTS: In this study we developed a simplified mathematical model of CO 2 release in the milk fermentation process. An intuitive approach based on superposition and experimental analysis was used for the modeling. The chemical system studied was considered as a twoinput (temperature, rotational frequency of the stirrer) one-output (CO 2 concentration) dynamic system. CONCLUSION: Based on an analysis of CO 2 release transients in the case of nonsimultaneous stepwise changed input quantities, two differential equations which describe the influence of the two input quantities on the output quantity were defined. The simulation results were verified by experiments. The proposed model can be used for a comprehensive analysis of the process studied and for the design and synthesis of advanced control systems, which will assure a controlled CO 2 release at the industrial level.
In the chapter, milk fermentation for kefir production is studied. The traditional kefir producti... more In the chapter, milk fermentation for kefir production is studied. The traditional kefir production process based on inoculating kefir grains into milk is considered. The quality and quantity of the produced kefir also depend on the dynamics of the fermentation process. The chapter presents the design and synthesis of the closed-loop control system in which changing the bioreactor’s temperature is used to control the time course of the concentration of dissolved CO2. In the chapter: (1) a nonlinear dynamic mathematical model of the fermentation process, which allows evaluating the influence of the bioreactor’s temperature on the dynamics of the fermentation process, is presented; (2) the design and synthesis of a conventional linear control system with constant parameters are carried out; (3) an adaptive control system that enables the tracking of the courses of the quantities of the fermentation process to the desired reference trajectories without the time-consuming preliminary identification of the parameters of the fermentation process model is developed. The numerical, experimental, and analytic outcomes of the study are presented.
Available commercial applications of power system stabilizers assure optimal damping of synchrono... more Available commercial applications of power system stabilizers assure optimal damping of synchronous generator's oscillations only in a small part of operating range. Parameters of the power system stabilizer are usually tuned for the selected operating point. Extensive variations of the synchronous generator's operation result in changed dynamic characteristics. This is the reason that the power system stabilizer tuned for the nominal operating point does not satisfy preferred damping in the overall operation area. The small-signal stability and the transient stability of the synchronous generators have represented an attractive problem for testing different concepts of the modern control theory. Of all the methods, the adaptive control has proved to be the most suitable for the design of the power system stabilizers. The adaptive control has been used in order to assure the optimal damping through the entire synchronous generator's operating range. The use of the adapti...
Rapeseed is one of the important oil seed crops throughout the world, on third place among the oi... more Rapeseed is one of the important oil seed crops throughout the world, on third place among the oil seed crops after soybean and palm in production of vegetable oils. Recent studies on rapeseed response to different levels of nitrogen fertilizer and stated that oil yield increased with low to moderate nitrogen rates. The experiment was conducted in field, in two representative locations for Banat Plain, in three replications. At Sanandrei, the experience was located on molic reddish preluvosoil, and at Jimbolia, the experiences were placed on a typically chernozem. Experimental factors were four levels of chemical N fertilizer (0, 100, 150 and 200 kg N ha −1), compared with the control. The genetic material was the hybrids DK IMIDO CL and DK IMIRON CL. The highest rate of fertilizer (200 kg N ha −1) showed the greatest grain yield, 3026 kg/ha at Sanandrei and 3633 kg/ha at Jimbolia, an increased grain yield per unit of area by 176% respectively 135%, compared with the least application of nitrogen fertilizer (control). About the oil content, the best results were recorded at level of 150 kg N ha −1 , in both locations, with a difference of 120% respectively 129% compared with the control.
The growing population and lack of change in resources of cultivated land have led to the search ... more The growing population and lack of change in resources of cultivated land have led to the search for more efficient farming solutions. The recovery of soil is facilitated by using chemicals designed for the enrichment of cultivated soil. Fertilisers are made of a combination of various substances that determine not only the chemical but also the shape characteristics of the fertiliser pellets. The effect of the quality of fertilisation on yield size is related to even distribution. Shape and size are closely related to the quality of the fertilisation process. The intense control of the production process would not be possible without automatised and quick measurements within the production line. Constant control is necessary to ensure that the products meet quality standards. The contactless assessment of pellet sizes allows a quick reaction to changes in production quality and reduces the costs arising from the reprocessing of defective pellets. The results of the assessment of pe...
The biochemical industry is one of the most important modern industries. Biochemical reactors are... more The biochemical industry is one of the most important modern industries. Biochemical reactors are crucial devices of the biochemical industry. The essential bioprocess carried out in bioreactors is the fermentation process. A thorough insight into the fermentation process and the knowledge how to control it are essential for effective use of bioreactors to produce high quality and quantitatively enough products. The development of the control system starts with the determination of a mathematical model that describes the steady state and dynamic properties of the controlled plant satisfactorily, and is suitable for the development of the control system. The paper analyses the fermentation process in bioreactors thoroughly, using existing mathematical models. Most existing mathematical models do not allow the design of a control system for controlling the fermentation process in batch bioreactors. Due to this, a mathematical model was developed and presented that allows the developme...
Many modern synchronous generators in power systems are extremely weakly damped. The reasons are ... more Many modern synchronous generators in power systems are extremely weakly damped. The reasons are cost optimization of the machine building and introduction of the additional control equipment into power systems. Oscillations of the synchronous generators and related stability problems of the power systems are harmful and can lead to failures in operation and to damages. The only useful solution to increase damping of the unwanted oscillations represents the implementation of the power system stabilizers. Power system stabilizers generate the additional control signal which changes synchronous generator field excitation voltage. Modern power system stabilizers are integrated into static excitation systems of the synchronous generators. Available commercial power system stabilizers are based on linear control theory. Due to the nonlinear dynamics of the synchronous generator, current stabilizers do not assure optimal damping of the synchronous generator's oscillations in the entir...
The biochemical technology has been developing extremely fast since the middle of the last centur... more The biochemical technology has been developing extremely fast since the middle of the last century. The main reason for such development represents a requirement for large production of high-quality biologically manufactured products such as pharmaceuticals, foods, and beverages. The impact of the biochemical industry on the world economy is enormous. The great importance of this industry also results in intensive development in scientific disciplines relevant to the development of biochemical technology. In addition to developments in the fields of biology and chemistry, which enable to understand complex biochemical processes, development in the field of control theory and applications is also very important. In the paper, the control for the biochemical reactor for the milk fermentation was studied. During the fermentation process, the biophysical quantities must be precisely controlled to obtain the high-quality product. To control these quantities, the bioreactor's stirring...
This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) respons... more This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) response during transmission network faults. The simplest and safest solution is to switch IIDGs off during network faults without impacting the network voltages. A more elaborate and efficient concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving positive- and negative-sequence voltage measured at the connection point. In this way the magnitude and phase of the injected currents can be adjusted, although the generated power will depend on the actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust IIDGs’ fault current injection through the required active and reactive power, employing the same voltage characteristics. The proposed, i.e., power-based concept, is more definite than the current-based one, since the required power will always be generated. The discussed concepts for the fault current injection by...
Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Recenzija Review ... more Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Recenzija Review Boštjan Polajžer (Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Maja Atanasijević-Kunc (Univerza v Ljubljani, Fakulteta za elektrotehniko) Lektoriranje Language editing Vlasta Praprotnik Tehnična urednika Technical editors Jožef Ritonja (Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko)
The basic characteristic of batch bioreactors is their inability to inflow or outflow the substan... more The basic characteristic of batch bioreactors is their inability to inflow or outflow the substances during the fermentation process. This follows in the simple construction and maintenance, which is the significant advantage of batch bioreactors. Unfortunately, this characteristic also results in the inability of the current industrial and laboratory batch bioreactors to control fermentation production during the process duration. In some recent studies, it was shown that changing the temperature could influence the execution of the fermentation process. The presented paper shows that this phenomenon could be used to develop the closed-loop control system for the fermentation production control in batch bioreactors. First, based on theoretical work, experiments, and numerical methods, the appropriate structure of the mathematical model was determined and parameters were identified. Next, the closed-loop control system structure for batch bioreactor was proposed, and the linear and ...
In this paper, a non-linear 7 th order dynamic model and a linearized 3 rd order dynamic model of... more In this paper, a non-linear 7 th order dynamic model and a linearized 3 rd order dynamic model of a synchronous generator connected to an infinite bus are presented and compared in details. Parameters and equations of the both models are explained and summarized. They represent a useful starting point for work in areas of synchronous generators' construction, analysis, control systems design and synthesis. Novelty of this work represents a detailed research of applicability of the linearized model in an entire operating range. Established theoretical conclusions were confirmed with numerical results. Restrictions of utilizing the linearized model are presented. On a basis of the analysis for the synchronous generators of different power, their applicability with feasibility and accuracy was evaluated by certain objective criteria.
Povzetek. V prispevku je prikazan pregled metod za določanje frekvence elektroenergetskega sistem... more Povzetek. V prispevku je prikazan pregled metod za določanje frekvence elektroenergetskega sistema. Podrobneje so prikazane najbolj perspektivne metode: iterativna metoda najmanjše vsote kvadratov odstopanj, izboljšana diskretna Fourierjeva transformacija in dekompozicija v ortogonalne komponente. Predstavljene so teoretične osnove posameznih metod ter njihove prednosti in slabosti. Lastnosti posameznih metod so numerično ovrednotene z vidika natančnosti določitve frekvence, dinamike odziva na spremembe parametrov vhodnega signala in vpliv nemodeliranih komponent vhodnega signala (višje harmonske komponente, subharmonske komponente, merilni šum) na določitev frekvence. Metode smo testirali s testnimi signali, ki ponazarjajo različna stanja elektroenergetskega sistema.
V publikaciji so predstavljene osnove elektromehanske pretvorbe in štirje osnovni električni stro... more V publikaciji so predstavljene osnove elektromehanske pretvorbe in štirje osnovni električni stroji: transformator, asinhronski stroj, sinhronski stroj in komutatorski stroj. Publikacija je razdeljena v pet poglavij. V nadaljevanju je predstavljena vsebina posameznih poglavij. Uvod: magnetno polje, vzbujanje navitij, induciranje napetosti, sile in vrtilni moment (navor), pretvarjanje električne moči v električno ali mehansko, izgube, izkoristek, segrevanje in hlajenje. Transformator: elementi gradnje, idealni in realni enofazni transformator, trifazni transformator, posebne izvedbe transformatorjev. Asinhronski stroj: opis gradnje z navitji in način delovanja, zagoni motorjev in spreminjanje hitrosti vrtenja ter vrtilnega momenta, asinhronski generator, enofazni asinhronski motorji. Sinhronski stroj: opis gradnje in način delovanja, obratovanje na togem omrežju, približna obravnava nasičenega stroja, vzbujalni sistemi in uporaba trajnih magnetov za vzbujanje, ter sinhronski motorji s trajnimi magneti. Komutatorski stroj: opis gradnje in način delovanja, reakcija kotve, problemi komutacije, elektronska komutacija, karakteristike različnih električnih vezav statorja in rotorja, spreminjanje hitrosti vrtenja, izmenični (univerzalni) komutatorski stroji.
Journal of the Science of Food and Agriculture, May 3, 2018
BACKGROUND: Milk fermentation takes place in the presence of various microorganisms , whereby a v... more BACKGROUND: Milk fermentation takes place in the presence of various microorganisms , whereby a variety of dairy products is produced. The oldest among them is kefir, which is usually produced by fermentation of milk with kefir grains. Carbon dioxide (CO 2), as one of the process products, also contributes to the characteristic flavor of kefir. The amount of CO 2 generated during fermentation depends on bioprocessing conditions and may change, which is not desirable at the industrial level. RESULTS: In this study we developed a simplified mathematical model of CO 2 release in the milk fermentation process. An intuitive approach based on superposition and experimental analysis was used for the modeling. The chemical system studied was considered as a twoinput (temperature, rotational frequency of the stirrer) one-output (CO 2 concentration) dynamic system. CONCLUSION: Based on an analysis of CO 2 release transients in the case of nonsimultaneous stepwise changed input quantities, two differential equations which describe the influence of the two input quantities on the output quantity were defined. The simulation results were verified by experiments. The proposed model can be used for a comprehensive analysis of the process studied and for the design and synthesis of advanced control systems, which will assure a controlled CO 2 release at the industrial level.
In the chapter, milk fermentation for kefir production is studied. The traditional kefir producti... more In the chapter, milk fermentation for kefir production is studied. The traditional kefir production process based on inoculating kefir grains into milk is considered. The quality and quantity of the produced kefir also depend on the dynamics of the fermentation process. The chapter presents the design and synthesis of the closed-loop control system in which changing the bioreactor’s temperature is used to control the time course of the concentration of dissolved CO2. In the chapter: (1) a nonlinear dynamic mathematical model of the fermentation process, which allows evaluating the influence of the bioreactor’s temperature on the dynamics of the fermentation process, is presented; (2) the design and synthesis of a conventional linear control system with constant parameters are carried out; (3) an adaptive control system that enables the tracking of the courses of the quantities of the fermentation process to the desired reference trajectories without the time-consuming preliminary identification of the parameters of the fermentation process model is developed. The numerical, experimental, and analytic outcomes of the study are presented.
Available commercial applications of power system stabilizers assure optimal damping of synchrono... more Available commercial applications of power system stabilizers assure optimal damping of synchronous generator's oscillations only in a small part of operating range. Parameters of the power system stabilizer are usually tuned for the selected operating point. Extensive variations of the synchronous generator's operation result in changed dynamic characteristics. This is the reason that the power system stabilizer tuned for the nominal operating point does not satisfy preferred damping in the overall operation area. The small-signal stability and the transient stability of the synchronous generators have represented an attractive problem for testing different concepts of the modern control theory. Of all the methods, the adaptive control has proved to be the most suitable for the design of the power system stabilizers. The adaptive control has been used in order to assure the optimal damping through the entire synchronous generator's operating range. The use of the adapti...
Rapeseed is one of the important oil seed crops throughout the world, on third place among the oi... more Rapeseed is one of the important oil seed crops throughout the world, on third place among the oil seed crops after soybean and palm in production of vegetable oils. Recent studies on rapeseed response to different levels of nitrogen fertilizer and stated that oil yield increased with low to moderate nitrogen rates. The experiment was conducted in field, in two representative locations for Banat Plain, in three replications. At Sanandrei, the experience was located on molic reddish preluvosoil, and at Jimbolia, the experiences were placed on a typically chernozem. Experimental factors were four levels of chemical N fertilizer (0, 100, 150 and 200 kg N ha −1), compared with the control. The genetic material was the hybrids DK IMIDO CL and DK IMIRON CL. The highest rate of fertilizer (200 kg N ha −1) showed the greatest grain yield, 3026 kg/ha at Sanandrei and 3633 kg/ha at Jimbolia, an increased grain yield per unit of area by 176% respectively 135%, compared with the least application of nitrogen fertilizer (control). About the oil content, the best results were recorded at level of 150 kg N ha −1 , in both locations, with a difference of 120% respectively 129% compared with the control.
The growing population and lack of change in resources of cultivated land have led to the search ... more The growing population and lack of change in resources of cultivated land have led to the search for more efficient farming solutions. The recovery of soil is facilitated by using chemicals designed for the enrichment of cultivated soil. Fertilisers are made of a combination of various substances that determine not only the chemical but also the shape characteristics of the fertiliser pellets. The effect of the quality of fertilisation on yield size is related to even distribution. Shape and size are closely related to the quality of the fertilisation process. The intense control of the production process would not be possible without automatised and quick measurements within the production line. Constant control is necessary to ensure that the products meet quality standards. The contactless assessment of pellet sizes allows a quick reaction to changes in production quality and reduces the costs arising from the reprocessing of defective pellets. The results of the assessment of pe...
The biochemical industry is one of the most important modern industries. Biochemical reactors are... more The biochemical industry is one of the most important modern industries. Biochemical reactors are crucial devices of the biochemical industry. The essential bioprocess carried out in bioreactors is the fermentation process. A thorough insight into the fermentation process and the knowledge how to control it are essential for effective use of bioreactors to produce high quality and quantitatively enough products. The development of the control system starts with the determination of a mathematical model that describes the steady state and dynamic properties of the controlled plant satisfactorily, and is suitable for the development of the control system. The paper analyses the fermentation process in bioreactors thoroughly, using existing mathematical models. Most existing mathematical models do not allow the design of a control system for controlling the fermentation process in batch bioreactors. Due to this, a mathematical model was developed and presented that allows the developme...
Many modern synchronous generators in power systems are extremely weakly damped. The reasons are ... more Many modern synchronous generators in power systems are extremely weakly damped. The reasons are cost optimization of the machine building and introduction of the additional control equipment into power systems. Oscillations of the synchronous generators and related stability problems of the power systems are harmful and can lead to failures in operation and to damages. The only useful solution to increase damping of the unwanted oscillations represents the implementation of the power system stabilizers. Power system stabilizers generate the additional control signal which changes synchronous generator field excitation voltage. Modern power system stabilizers are integrated into static excitation systems of the synchronous generators. Available commercial power system stabilizers are based on linear control theory. Due to the nonlinear dynamics of the synchronous generator, current stabilizers do not assure optimal damping of the synchronous generator's oscillations in the entir...
The biochemical technology has been developing extremely fast since the middle of the last centur... more The biochemical technology has been developing extremely fast since the middle of the last century. The main reason for such development represents a requirement for large production of high-quality biologically manufactured products such as pharmaceuticals, foods, and beverages. The impact of the biochemical industry on the world economy is enormous. The great importance of this industry also results in intensive development in scientific disciplines relevant to the development of biochemical technology. In addition to developments in the fields of biology and chemistry, which enable to understand complex biochemical processes, development in the field of control theory and applications is also very important. In the paper, the control for the biochemical reactor for the milk fermentation was studied. During the fermentation process, the biophysical quantities must be precisely controlled to obtain the high-quality product. To control these quantities, the bioreactor's stirring...
This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) respons... more This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) response during transmission network faults. The simplest and safest solution is to switch IIDGs off during network faults without impacting the network voltages. A more elaborate and efficient concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving positive- and negative-sequence voltage measured at the connection point. In this way the magnitude and phase of the injected currents can be adjusted, although the generated power will depend on the actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust IIDGs’ fault current injection through the required active and reactive power, employing the same voltage characteristics. The proposed, i.e., power-based concept, is more definite than the current-based one, since the required power will always be generated. The discussed concepts for the fault current injection by...
Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Recenzija Review ... more Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Recenzija Review Boštjan Polajžer (Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko) Maja Atanasijević-Kunc (Univerza v Ljubljani, Fakulteta za elektrotehniko) Lektoriranje Language editing Vlasta Praprotnik Tehnična urednika Technical editors Jožef Ritonja (Univerza v Mariboru, Fakulteta za elektrotehniko, računalništvo in informatiko)
The basic characteristic of batch bioreactors is their inability to inflow or outflow the substan... more The basic characteristic of batch bioreactors is their inability to inflow or outflow the substances during the fermentation process. This follows in the simple construction and maintenance, which is the significant advantage of batch bioreactors. Unfortunately, this characteristic also results in the inability of the current industrial and laboratory batch bioreactors to control fermentation production during the process duration. In some recent studies, it was shown that changing the temperature could influence the execution of the fermentation process. The presented paper shows that this phenomenon could be used to develop the closed-loop control system for the fermentation production control in batch bioreactors. First, based on theoretical work, experiments, and numerical methods, the appropriate structure of the mathematical model was determined and parameters were identified. Next, the closed-loop control system structure for batch bioreactor was proposed, and the linear and ...
In this paper, a non-linear 7 th order dynamic model and a linearized 3 rd order dynamic model of... more In this paper, a non-linear 7 th order dynamic model and a linearized 3 rd order dynamic model of a synchronous generator connected to an infinite bus are presented and compared in details. Parameters and equations of the both models are explained and summarized. They represent a useful starting point for work in areas of synchronous generators' construction, analysis, control systems design and synthesis. Novelty of this work represents a detailed research of applicability of the linearized model in an entire operating range. Established theoretical conclusions were confirmed with numerical results. Restrictions of utilizing the linearized model are presented. On a basis of the analysis for the synchronous generators of different power, their applicability with feasibility and accuracy was evaluated by certain objective criteria.
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