- Ph.D., Applied Sciences, Senior Lecturer, Department Electrical/Electronic Engineering, Ariel Universityedit
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The use of low-pass filters for smoothing energy flows in different applications is remarkable. However, in the case of a power (instead of a voltage) source, this circuit becomes non-linear and its transient process is difficult to... more
The use of low-pass filters for smoothing energy flows in different applications is remarkable. However, in the case of a power (instead of a voltage) source, this circuit becomes non-linear and its transient process is difficult to assess. Such cases are typical for renewable (PV and wind turbine) plants being equipped with DC-AC power converters.Submitted in the presented article is an approximation procedure, which gives a linearization and an efficiently approachable technique to compare real current (voltage) curves with estimated results. As a result, the development of low-pass filter fed by power source becomes relatively simple task.
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An approach allowing the creation of parameter uncertainties and external disturbances without any hardware parts supplementary to the nominal system is proposed in this manuscript. The emulating signal, reflecting the plant variations,... more
An approach allowing the creation of parameter uncertainties and external disturbances without any hardware parts supplementary to the nominal system is proposed in this manuscript. The emulating signal, reflecting the plant variations, essential for testing of controllers, is created in software and added to the plant input, forcing the nominal system output to resemble the output of a system with actual uncertainties and disturbances, thus allowing us to test the controller’s robustness prior to an actual field test. In addition, the full state vector of the emulated system may be reconstructed and fed back to the controller, if necessary. The proposed methods allow simultaneous emulation of any combination of time-varying parameter variations and external disturbances. The method can be related to a class of enhanced hardware-in-the-loop simulations, since the nominal hardware is present in the setup in addition to the controller under test. The proposed techniques can be used to test the performance of advanced control algorithms before their mass production. Extended simulation results are reported to confirm the feasibility of the proposed approaches.
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Electrification of Israel railroads is a successful project being realized during present time. Among the well-known advantages of electric train exploitation are high energetic efficiency, regenerative breaking, diminished pollution,... more
Electrification of Israel railroads is a successful project being realized during present time. Among the well-known advantages of electric train exploitation are high energetic efficiency, regenerative breaking, diminished pollution, flexibility of traffic control and improved transportation dynamics. However, the use of electric train is accompanied with some specific hurdles caused by significantly stochastic power flows. While in transit between stations an electric train has different phases of movement, during some consuming energy, but from time to time throughout braking processes they become generators transmitting energy back into the electric grid. This circumstance may produce voltage instability in distribution lines, which should be kept inside permissible limits to allow normal operation of electric equipment. Tap-changers on distribution transformers considered for a voltage regulation have sluggish response of ~7-8 sec. Therefore, fast changes of power stream can cause significant voltage deviations. If the voltage overcome explicit allowable level a trigger of a protection system is engendered disconnecting vehicles from a grid. The last causes extremely dangerous detriments and should be maximally prevented.Rapid and considerable changes in train power consumption, in addition may cause network frequency instability which in turn can violate electricity supply.Present article provides an original examination of the future stability of network frequency and distribution voltage which may be assumed when 420 km of Israel railroads will be electrified in the following 5–10 years. For such study special algorithm based on simulation approach was developed and applied. Predicting scenarios for frequency and distribution lines voltage control are represented below in the following text.
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Local and distributed PV solar plants become more and more widespread power generating facilities providing significant percentage of electricity supply. Together with numerous advantages massive rooftop PV installations (up to 5–10 kW)... more
Local and distributed PV solar plants become more and more widespread power generating facilities providing significant percentage of electricity supply. Together with numerous advantages massive rooftop PV installations (up to 5–10 kW) and utility-scale local plants of 5–20 MW in the low (LV) and middle (MV) voltage distribution networks produce a problem for voltage regulation. Rapid deviations in PV power inherent in this type of energy generate uncertainty in voltage control. Tap changers which are applicable to this purpose have sluggish reaction and occasionally couldn't be able to compensate fast changings of solar electricity. Together with the fluctuations of the consumer's power demands such disturbances can cause dangerous voltage instabilities. As a result, the protection system should disconnect PV stations from electricity supply what negatively affects electricity costs and reliability of the network. One of the possible solutions for mitigation voltage deviations is intermittent energy storage based on ultracapacitors (UC) usage. UC application can improve the voltage stability hence increasing complexity of energy equipment and energy costs. Therefore, the selection of UC bank should be done suitably considering technical and economic aspects of the problem. Current work represents a solution for improving the situation with local voltage regulation based on the appropriate selection of UC bank.
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The correct selection of appropriate induction motor for a specific electric drive represents an important issue, especially when VFD is applied for the motor supply. A number of different approaches were suggested for this aim. Methods... more
The correct selection of appropriate induction motor for a specific electric drive represents an important issue, especially when VFD is applied for the motor supply. A number of different approaches were suggested for this aim. Methods of motors selection that founded on assessment and minimization of energy losses in the motor are preferable, since they provide optimal selection of a motor with a prolonged service time and maximum energy efficiency. There are three different kinds of losses in the motor: cooper resistive losses, mechanical and iron (core) losses. The present work describes the approach of iron losses estimation for a VFD FC51 of Danfoss Company. The method is based on the representation of supplied voltage (current) by the Fourier Transform and analytical description of iron losses by interpolation polynomials.
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In this paper, a two-stage power conversion system based on the electronic DC link is proposed for interfacing photovoltaic generators with AC mains. A bulk electrolytic capacitor, typically utilized as short-time energy storage device... more
In this paper, a two-stage power conversion system based on the electronic DC link is proposed for interfacing photovoltaic generators with AC mains. A bulk electrolytic capacitor, typically utilized as short-time energy storage device connected across the DC link is replaced by an electronic capacitor, consisting of a bidirectional DC-DC converter terminated by a much smaller capacitance. Since the electronic capacitor mimics the behavior of the bulk capacitance at the DC-link side, the original operation is retained in a plug-and-play manner. Simulations and experiments validate the proposed method feasibility.
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Today's PV solar power plants would be unimaginable without Maximum Power Point Tracking (MPPT) which automatically maximizes panels power output, thereby significantly increasing energy production. However, partial shading of PV... more
Today's PV solar power plants would be unimaginable without Maximum Power Point Tracking (MPPT) which automatically maximizes panels power output, thereby significantly increasing energy production. However, partial shading of PV panels in large solar plants is a serious obstacle for MPPT. Multiple local extremums will be observed while only one is the global maximum and has to be found. Some methods and algorithms for solving the problem of tracking the global maximum among locals are known. However, most require a prolonged search time with, therefore, diminished efficiency in situations characterized by sudden variation in solar irradiation. A uniquely efficient algorithm and electronic device was developed for improving total MPPT functionality. It is accomplished by tracking global maximum boundaries, the positions of which are translated into traditional MPPT with substantial localization accuracy. This localization algorithm is based on the assessment of each panel's current together with the usage of a simplified PV equivalent circuit. The proposed algorithm can determine the global maximum on an I-P curve at relatively high speeds, and is only restricted by digital control ability. Currently, this task would take no more than 50–100 us maximum. Therefore, the global maximum in any set of rapidly changing shading conditions can be found. Importantly, however, some unsolved questions remain regarding accuracy and sustainability of this approach. The present work analyzes these essential properties and concludes with the proposed MPPT algorithm.
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Article denotes a new approach for development equivalent electrical circuit of lead-acid batteries. It is based on a separated representation of chemical and electrical domains. Main advantage of the proposed simulation method is more... more
Article denotes a new approach for development equivalent electrical circuit of lead-acid batteries. It is based on a separated representation of chemical and electrical domains. Main advantage of the proposed simulation method is more accurate description of the battery behavior in different dynamic regimes without the need of additional fitting equivalent circuit parameters.
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Today's PV solar power plants would be unimaginable without Maximum Power Point Tracker (MPPT) electronic scheme increasing significantly energy production. Partial shading of PV panels in a big solar plant including hundreds and... more
Today's PV solar power plants would be unimaginable without Maximum Power Point Tracker (MPPT) electronic scheme increasing significantly energy production. Partial shading of PV panels in a big solar plant including hundreds and thousands those items becomes important problem for MPPT. The results of shading may not be only the proportional diminishing of the total electrical power but that is more seriously the generating multi-extreme power-current (P-I); power-voltage (P-V) curves, disturbing meaningfully the search algorithms of MPPT. Present work proposes the solution for determination of the global maximum position on the operating P-I or P-V curves providing for MPPT algorithm precision information which prevent missteps during optimization procedure. The developed method based on permanent monitoring of PV panels with the subsequent assessment of their solar irradiation and estimation of the global maximum location for the entire group of solar panels.
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ABSTRACT Nowadays, the need of compact moveable powerful electrical sources is going up. The most well-known applications of these arrangements are needed in automotive and transportation industry, in devices of emergency starting of... more
ABSTRACT Nowadays, the need of compact moveable powerful electrical sources is going up. The most well-known applications of these arrangements are needed in automotive and transportation industry, in devices of emergency starting of internal combustion engines, for supplying pulses of high current in special equipment and so on. Most of these implementations may be developed on the base of conventional electrochemical storage batteries (ESB). ESB are representing the suitable kind of rechargeable electrical sources and may be applicable in moveable equipment. But the power parameters of batteries compare to their dimensions leave much to be desired. If the high power (current) is required (together with the small dimensions of the energy system) the employ of ESB only is not really capable. The synergetic combination of ESB together with UC seems to be very promising solution in this case. A conjunction between these two different energy sources links together the outstanding power characteristics of UC with relatively high specific energy of ESB. However, the combination of these devices requires decisions of some technical problems. For example, when the voltages of UC and ESB a priori are different, and this difference is used for special goal, for example to provide high load current when the battery is weak and unable to deliver the needed power. The special inverter has to be included between UC and ESB in this case. Its major function is providing UC charging from ESB. The problem of UC charging is stemming from its very small (sometimes negligible) internal resistance and usual connection between terminals of UC and ESB may cause to the serious difficulties such as a very high equalizing current, small charging efficiency and diminished battery's service life. These problems become expremely smart when UC before charging is fully or partially empty. Additional serious difficulties are associated with electric security needs. This kind of devices are equipped, as a- rule, with flexible cables are being ended by special clamps for load connecting. An occasionally shortening of these clamps during a device leading to a load may cause serious troubles. Thus, the preventing of such cases depicts an important technical challenge. The supplementary problem is represented by the need to switch the power supply on at the right moment of time and only after this device will be connected by cables to the load. This problem is issuing in principle from the previous one. If it will be solved this would solve automatically the first problem too because the switching power supply at the needed moment of time means that shortening of clamps before their connection to the load will not cause any damage. Thus, this device has to be equipped with special power circuit and it's control system which algorithm will i) avoid occasionally clamp shortening ii) will define the moment of time when the load has to be connected to the power supply. The presented work is dealing with the research and development of this kind of compact electric source where conventional ESB is used with UC, a special electronic circuit provides the optimal connection between these two electrical devices and makes available the protected functionality of the entire energy system.
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Currently, the Israeli energy industry faces the challenge of a considerable increase in solar electricity production. Being a relatively isolated system, the significant expansion of solar electricity may cause problems with electricity... more
Currently, the Israeli energy industry faces the challenge of a considerable increase in solar electricity production. Being a relatively isolated system, the significant expansion of solar electricity may cause problems with electricity quality. The electrical storage installation can resolve this problem. In Israel's situation, the optimal solution can be the creation of a channel between the Mediterranean and the Dead Sea. The channel can solve three closely related problems: the increased production of desalinated water for domestic, industrial, and agricultural needs; the prevention of a permanent Dead Sea level decline and its imminent disappearance; the development of hydro-pumping electrical storage stations; and the creation of numerous PV facilities in the Negev area for national electricity generation. However, a detailed analysis should be done for the estimation of the possible increase of solar electric generation with the consideration of a stochastic PV outcome a...
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Currently, the Israeli energy industry faces the challenge of a considerable increase in solar electricity production. As a relatively isolated system, the significant expansion of solar electricity may cause problems with electricity... more
Currently, the Israeli energy industry faces the challenge of a considerable increase in solar electricity production. As a relatively isolated system, the significant expansion of solar electricity may cause problems with electricity quality. Electrical storage installation can resolve this problem. In Israel’s situation, the optimal solution could be the creation of a channel between the Mediterranean and the Dead Sea. The channel can solve three closely related problems: the increased production of desalinated water for domestic, industrial, and agricultural needs; the prevention of a permanent Dead Sea level decline and its imminent disappearance; the development of hydro-pumping electrical storage stations; and the creation of numerous PV facilities in the Negev area for national electricity generation. However, detailed analysis should be conducted for the estimation of the possible increase in solar electric generation with consideration of a stochastic PV outcome and the pot...
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Sustainable development systems are based on three pillars: economic development, environmental stewardship, and social equity [...]
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One of the traditional difficulties in the courses "Power Electronics" and "Electrical Drives" is parameters estimation in the non-linear electronic schemes including inductances, capacitances, resistances as well as... more
One of the traditional difficulties in the courses "Power Electronics" and "Electrical Drives" is parameters estimation in the non-linear electronic schemes including inductances, capacitances, resistances as well as diodes and switches. These schemes could be found in equivalent circuits of electric motors and multiple electronic devices that are applicable in power electronics. Taking into account complications to solve non-linear ordinary differential equations (ODE) describing occurring processes and their parameters typical student has a problem to achieve analytical results. Numerous linearization methods were used in the past that was aiming to make things easier and this way to get roughly approximate however analytical solution. Today coarsely estimated results are inacceptable as a rule. Therefore, typical approach in this case is an application of simulation software programs such as PSIM, MATLAB Simulink, WOLFRAM Matematica and others giving excellent...
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In the field of renewable energy, the extraction of parameters for solar photovoltaic (PV) cells is a widely studied area of research. Parameter extraction of solar PV cell is a highly non-linear complex optimization problem. In this... more
In the field of renewable energy, the extraction of parameters for solar photovoltaic (PV) cells is a widely studied area of research. Parameter extraction of solar PV cell is a highly non-linear complex optimization problem. In this research work, the authors have explored grey wolf optimization (GWO) algorithm to estimate the optimized value of the unknown parameters of a PV cell. The simulation results have been compared with five different pre-existing optimization algorithms: gravitational search algorithm (GSA), a hybrid of particle swarm optimization and gravitational search algorithm (PSOGSA), sine cosine (SCA), chicken swarm optimization (CSO) and cultural algorithm (CA). Furthermore, a comparison with the algorithms existing in the literature is also carried out. The comparative results comprehensively demonstrate that GWO outperforms the existing optimization algorithms in terms of root mean square error (RMSE) and the rate of convergence. Furthermore, the statistical res...
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Parameter estimation of the nonlinear electronic schemes, including inductances, capacitances, resistances, and switches represents a nontrivial problem in the “power electronics” and “electrical drives” courses. Difficulties could be... more
Parameter estimation of the nonlinear electronic schemes, including inductances, capacitances, resistances, and switches represents a nontrivial problem in the “power electronics” and “electrical drives” courses. Difficulties could be observed during solutions of electrical circuits, which describe the behavior of electric motors in drives, and various electronic appliances are being used in power electronics. This situation is a result of complicated analytical approaches aiming to solve nonlinear ordinary differential equations describing the occurring processes. A typical student has a significant problem in attaining the analytical results. Various methods of linearization nonlinear elements permitting to obtain roughly analytical solutions and simplified solution were applied over the past. Nowadays, coarsely obtained results are not acceptable as a rule. As a result, smart simulation based on PSIM, MATLAB Simulink, and WOLFRAM Mathematica giving excellent opportunity for accur...
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The partial shading conditions significantly affect the functionality of solar power plants despite the presence of multiple maximum power point tracking systems. The primary cause of this problem is the presence of local maxima in the... more
The partial shading conditions significantly affect the functionality of solar power plants despite the presence of multiple maximum power point tracking systems. The primary cause of this problem is the presence of local maxima in the power–current and/or power–voltage characteristic curves that restrict the functionality of the conventional maximum power point tracking systems. The present article proposes a modified algorithm based on the simplified equivalent circuit of solar cells to improve the functionality of traditional maximum power point tracking systems. This algorithm provides a method for regularly monitoring the photo-current of each solar module. The upper and lower boundaries of the regulating parameter such as current or voltage are decided very precisely, which is helpful to find the location of the global maximum. During a sequential search, the control system accurately determines the lower and upper boundaries of the global maximum. Simultaneously, the maximum ...
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The increasingly widespread occurrences of fast-changing loads, as in, for example, the charging of electrical vehicles and the stochastic output of PV generating facilities, are causing imbalances between generated and consumed power... more
The increasingly widespread occurrences of fast-changing loads, as in, for example, the charging of electrical vehicles and the stochastic output of PV generating facilities, are causing imbalances between generated and consumed power flows. The deviations in voltage cause noteworthy technical problems. The tap-changers in today’s transformers are slow-reacting and thus cannot effectively correct the imbalance. Tap-changers should be replaced by special appliances, installed in distribution lines, that can effectively estimate voltage RMS and refine imbalances during a fraction of the AC period, preferably less than half. This article suggests specially developed methods for RMS assessment based on approximating instantaneous voltage magnitudes using harmonics and correcting coefficients.
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In this paper, average modeling of a dual-supercapacitor bank, actively balanced by a bidirectional buck-boost converter is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50%... more
In this paper, average modeling of a dual-supercapacitor bank, actively balanced by a bidirectional buck-boost converter is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Dynamical equations of the system are developed in order to derive the switching-cycle-averaged model. Simulations support the presented findings.
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Diesel generator based auxiliary power units (DG-APU) are widely used in different civil and military applications. Fuel economy and service life are probably the most important issues concerning their operation. Controlling engine... more
Diesel generator based auxiliary power units (DG-APU) are widely used in different civil and military applications. Fuel economy and service life are probably the most important issues concerning their operation. Controlling engine throttle position in accordance with the load power allows regulating fuel supply to the engine to optimize fuel consumption. Despite the advantage of the method, control stability is sacrificed in case of light load operation as follows. When the DG-APU is running with a light load, engine throttle position should be nearly closed in order to minimize fuel consumption. If a load step is applied in such situation, engine velocity may drop sharply until complete stop because of insufficient control system bandwidth. This is why velocity and throttle position of a DG-APU should not be decreased below some level even if load power is low to maintain reliability at the expense of increased specific fuel consumption. Moreover, for small diesel-generators the t...
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The rapid advancement of electronic devices induces urgent demand for portable energy sources for uninterrupted operation. This paper presents the method for the generation of electrical energy using the variable-capacitance of a special... more
The rapid advancement of electronic devices induces urgent demand for portable energy sources for uninterrupted operation. This paper presents the method for the generation of electrical energy using the variable-capacitance of a special capacitor. Analytical calculations show that the electrostatic energy of an isolated capacitor increases significantly if the permittivity of the dielectric layer decreases. Importantly, the charge on capacitor plates should be constant. At the first stage, a thin and porous oxide layer is grown on one surface of both electrodes using the standard anodization process. After that, an electrolyte-soaked membrane is inserted between both electrodes. The variable-capacitance is achieved by the axial movement of one electrode against the other one. This proposed method is useful to reduce the negative effect of the air gap; as a result, the efficiency of the electrostatic generator enhances significantly. This electrostatic generator is useful for portable electronic devices, such as mobile phones, global positioning systems, and medical devices.
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In this paper, a two-stage power conversion system based on the electronic DC link is proposed for interfacing photovoltaic generators with AC mains. A bulk electrolytic capacitor, typically utilized as short-time energy storage device... more
In this paper, a two-stage power conversion system based on the electronic DC link is proposed for interfacing photovoltaic generators with AC mains. A bulk electrolytic capacitor, typically utilized as short-time energy storage device connected across the DC link is replaced by an electronic capacitor, consisting of a bidirectional DC-DC converter terminated by a much smaller capacitance. Since the electronic capacitor mimics the behavior of the bulk capacitance at the DC-link side, the original operation is retained in a plug-and-play manner. Simulations and experiments validate the proposed method feasibility.
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Research Interests: CRC()
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The maximum power point tracking (MPPT) systems relate to photovoltaic (PV) power plants for maximum energy production. An efficient MPPT systems is needed for large solar plants including several serially and parallel-connected PV panels... more
The maximum power point tracking (MPPT) systems relate to photovoltaic (PV) power plants for maximum energy production. An efficient MPPT systems is needed for large solar plants including several serially and parallel-connected PV panels especially functioning in partial shading conditions. A proportional decrease in electrical power will be a result of inhomogeneous irradiation (partial shading), as well as multiple local maximums may appear. The presence of multiple local maximums is the most difficult obstacle for traditional MPPT which is based on a sequential search of an optimum working point. The present article submits a new algorithm that can be corresponded to the mathematical modeling with elements of Artificial Intelligence (AI). It combines the advantages of AI with those are typical to conventional methods applicable for homogeneous irradiation. A proposed method is to use permanent monitoring of a voltage, a current and temperature of each PV panel placed in the string. An MPPT algorithm determines the position of a global maximum (GM) based on this information and in accordance with the previously obtained math model of individual PV panels. Owing principles of AI, math models should be periodically précised during the service life of the PV plant. Since none of the presented math algorithms can provide localization of GM with the accuracy, required for the modern MPPT, the proposed method desire to be complemented by a conventional approach, let say perturbation and observation or incremental conductance techniques. For example, an algorithm finding zero roots of a power derivative versus current change was used in our work. Proposed algorithm can achieve GM with relatively high speed that is only restricted by digital control ability. Currently, this task would take no more than 50–100 ms maximum. Therefore, the global maximum can be found for any rapidly changing solar irradiation.
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Electrical storage components such as ultracapacitors (UC) attract enlarged regard in different industry sectors from electric vehicles up to renewable power plants. Among existing storage technologies stand out asymmetric Li-ion hybrid... more
Electrical storage components such as ultracapacitors (UC) attract enlarged regard in different industry sectors from electric vehicles up to renewable power plants. Among existing storage technologies stand out asymmetric Li-ion hybrid and symmetric double-layer UC. Both devices able to provide prominent charge/discharge current together with extremely prolonged service life. However, Li-ion UC have twofold higher energy density and service life compared to that of conventional double-layer UC. Whereas a double-layer capacitor (DLUC) ensure four-six times lower internal resistance and more stable capacitance which isn’t dependent on UC voltage. This guarantee more stable functionality and higher charge-discharge current.The developer of storage facilities to provide an optimal design should know mentioned above electrical properties of UC.Considering relative novelty of these storage technologies (Li-ion UC is manufactured 6-7 years only, DLUC $\sim15$ years) two major parameters (internal resistance and capacitance) and their comparison aren’t yet determined for a full range of their applicability.Considering this fact, the current article represents preliminary results of UC dynamic properties. In fact, they are internal resistance and capacitance testing of UC CPQ2300S (2300F, 2.2-3.8V, JSR Co.) and of BCAP3400 (3400F, 2.85V, Maxwell Technologies Co.). As these parameters are significantly changing with current, voltage and capacitor temperature following ranges were chosen: current 20-100A, and a voltage-due to the permissible range.
Research Interests: IEEE()
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Today, despite the presence of well-developed and high efficient Maximum Power Point Trackers (MPPT) in all PV stations, remains the problem of their proper functionality during partial shading. Existing MPPT algorithms use sequential... more
Today, despite the presence of well-developed and high efficient Maximum Power Point Trackers (MPPT) in all PV stations, remains the problem of their proper functionality during partial shading. Existing MPPT algorithms use sequential search procedures, therefore, they may falsely operate during partial shading. The reason of this obstacle is numerous local maximums appearing in the P-I or P-V characteristic curves. This impedes conventional MPPT systems to find the global maximum (GM) and significantly restricts the ultimate electric output of PV plants.The present article proposes the improved algorithm for MPPT functionality. The method based on a photo-current estimation of each PV panel. Owing this information, submitted algorithm provides permanent assessment of the upper and the low limits of regulating parameter (a current or a voltage) between which its optimal value that ensures GM is located. Further, conventional MPPT entering the work can easily find the nearest maximum that obviously is GM.Present work describes this new method to find more accurate and fast estimations of the GM boundaries and to keep GM even during fast changings partial shading conditions, which will cause the higher overall efficiency of MPPT.
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An application of magnetic amplifiers that were frequently used in the past, still appears in power systems. Despite distinguished benefits of semiconductor electronics, some important advantages of the magnetic amplifier (MA) such as... more
An application of magnetic amplifiers that were frequently used in the past, still appears in power systems. Despite distinguished benefits of semiconductor electronics, some important advantages of the magnetic amplifier (MA) such as noticeable reliability and sustainability, provide its applications in power control till now. The basic principle of MA is based on a nonlinearity of magnetization curve leading to the effect of saturation in the magnetic circuit. AC coils which are wound on such a core depending on the operating point location may have significantly different impedance one that can provide regulating of power flow. The regulating process is ensured by an additional DC coil which can change working point by controlling DC current flowing through.The common problem of MA operation is inducing in a DC coil of electromotive force (EMF) led by an AC current flowing in the AC winding. This impact creates substantial obstacles in DC current control and should be diminished as much as possible.Several solutions are applicable to resolve this complication among which stands out the use of magnetic coils with perpendicular magnetic fields.In this article presented specially developed perpendicular coils design one inside and another outside novel toroidal magnetic core made thin ferromagnetic ribbon with high ferromagnetic permeability. These windings owing original core design and good ferromagnetic properties can provide substantial amplification coefficient of MA.Two frameworks of magnetic core are investigated in this article. One is made like a serpentine continuously winded ribbon. The other is represented by separated sections of ribbons that wound and then fixed by means of micro-welding. Ribbon segments touching each other with their edges and wound in several layers, the upper layers above the lower ones thus, to close air gaps between the lower lying sections.The investigation results of both these designs are presented in this article.
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Widespread applications of AC motors fed by variable frequency drives in electrified vehicles have become a conventional technical solution. The flexibility of control, low cost, and high energy efficiency attract developers and engineers... more
Widespread applications of AC motors fed by variable frequency drives in electrified vehicles have become a conventional technical solution. The flexibility of control, low cost, and high energy efficiency attract developers and engineers to apply these appliances in cars, railway trains, trams, etc. The distinctive characteristic of vehicles is a wide range of required rotation speed and torque. This circumstance means that the problems of the AC motor (nominal power, synchronous speed) and gearbox (transmission ratio) become non-trivial and necessitate optimal selection to ensure the best functionality of the entire driving system. This study proposes an approach for the optimal choice of a specific AC motor (nominal rating, synchronous speed) and the transmission ratio of the gearbox by analyzing the entire system’s losses. The optimal selection of an AC motor ensures maximum energy efficiency for a specific transportation driving cycle.
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Electrification of Israel railroads is a successful project being realized during present time. Among the well-known advantages of electric train exploitation are high energetic efficiency, regenerative breaking, diminished pollution,... more
Electrification of Israel railroads is a successful project being realized during present time. Among the well-known advantages of electric train exploitation are high energetic efficiency, regenerative breaking, diminished pollution, flexibility of traffic control and improved transportation dynamics. However, the use of electric train is accompanied with some specific hurdles caused by significantly stochastic power flows. While in transit between stations an electric train has different phases of movement, during some consuming energy, but from time to time throughout braking processes they become generators transmitting energy back into the electric grid. This circumstance may produce voltage instability in distribution lines, which should be kept inside permissible limits to allow normal operation of electric equipment. Tap-changers on distribution transformers considered for a voltage regulation have sluggish response of ~7-8 sec. Therefore, fast changes of power stream can cause significant voltage deviations. If the voltage overcome explicit allowable level a trigger of a protection system is engendered disconnecting vehicles from a grid. The last causes extremely dangerous detriments and should be maximally prevented.Rapid and considerable changes in train power consumption, in addition may cause network frequency instability which in turn can violate electricity supply.Present article provides an original examination of the future stability of network frequency and distribution voltage which may be assumed when 420 km of Israel railroads will be electrified in the following 5–10 years. For such study special algorithm based on simulation approach was developed and applied. Predicting scenarios for frequency and distribution lines voltage control are represented below in the following text.
Research Interests: IEEE()
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The use of low-pass filters for smoothing energy flows in different applications is remarkable. However, in the case of a power (instead of a voltage) source, this circuit becomes non-linear and its transient process is difficult to... more
The use of low-pass filters for smoothing energy flows in different applications is remarkable. However, in the case of a power (instead of a voltage) source, this circuit becomes non-linear and its transient process is difficult to assess. Such cases are typical for renewable (PV and wind turbine) plants being equipped with DC-AC power converters.Submitted in the presented article is an approximation procedure, which gives a linearization and an efficiently approachable technique to compare real current (voltage) curves with estimated results. As a result, the development of low-pass filter fed by power source becomes relatively simple task.
An enhancement of 22 dB in directivity, and 15 dB in return loss was achieved in an improved wiggly-line coupler. The improvement was obtained by introducing two new degrees of freedom to the wiggly-line. Heat maps of coupling,... more
An enhancement of 22 dB in directivity, and 15 dB in return loss was achieved in an improved wiggly-line coupler. The improvement was obtained by introducing two new degrees of freedom to the wiggly-line. Heat maps of coupling, directivity and return loss, as a function of the new degrees of freedom, show previously unavailable fine-tuning capabilities, from which optimal parameters were derived. The use of the improved wiggly-line allows a better even- and odd-mode phase velocity compensation, and an improvement of 42% of even- and odd-mode velocity difference is shown. The improved wiggly-line concept is used to design a tight, tandem, 1.6dB coupler as a center stage of 3-stage symmetrical wideband, 6-18 GHz, 90- degree hybrid coupler implemented in microstrip coupled line topology using bond wires for the tandem section. The loose stage is designed using periodic, quasi-lumped, capacitively-loaded coupled lines. A CST simulation of each design step is shown.
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The Vanadium Redox Flow Battery (VRB) represents a significant opportunity for future Energy Storage Systems (ESS), which will be the crucial element in Renewable Power Plants. Main expectations of VRB relate to its prolonged service... more
The Vanadium Redox Flow Battery (VRB) represents a significant opportunity for future Energy Storage Systems (ESS), which will be the crucial element in Renewable Power Plants. Main expectations of VRB relate to its prolonged service life, high-energy efficiency, outstanding dynamic response and flexible controllability during charge/discharge processes. The typical cell of VRB consists of two compartments (positive and negative) divided by a proton exchange membrane (PEM). The carbon electrodes in each compartment provide the electrochemical reduction-oxidation reactions in electrolyte. Carbon felt material as a rule is chosen for electrodes development due to its ability to provide intensive electrochemical reaction owing enlarged external surface and thus a sufficient current (power). The electrolyte on the base of sulfuric acid includes two pairs of vanadium ions with valences: (2+, 3+) in the negative compartment and (4+, 5+) in the positive one. The main volume of electrolyte is stored in two separate tanks and is pumped through both cell’s compartments. There are two main reasons for electrolyte pumping. The first one is the restricted solubility of active vanadium species in sulfuric acid that leads to have an enlarged amount of electrolyte volume, which may be located outside of the cells only. The second reason is the need to decrease concentration polarization effects on the electrode surface. Electric current creates the layer of inactive ions on the electrode surface that increases internal electrical resistance, reduces electromotive force and the battery power. Electrolyte circulation eliminates the effect of polarization but causes hydrodynamic losses. They may be diminished by the optimization of electrolyte flow rate based on correct description of hydrodynamic properties of a carbon felt and on accurate depiction of battery electrical losses.The present research proposes a novel approach to optimization of electrolyte pumping with the purpose to obtain maximum VRB efficiency.Copyright © 2014 by ASME
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Abstract: On-line estimation of the battery potential and ability of successfully starting a given engine under specific environmental conditions is a major problem in predicting maintenance strategy of any cars fleet. Battery aging and... more
Abstract: On-line estimation of the battery potential and ability of successfully starting a given engine under specific environmental conditions is a major problem in predicting maintenance strategy of any cars fleet. Battery aging and low operation temperatures are important ...
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ABSTRACT Abstract The paper offers a novel approach to parameter estimation of a single-diode solar cell/panel equivalent circuit, based on analysis of either technical characteristics supplied by the manufacturer or user-obtained... more
ABSTRACT Abstract The paper offers a novel approach to parameter estimation of a single-diode solar cell/panel equivalent circuit, based on analysis of either technical characteristics supplied by the manufacturer or user-obtained experimental I–V curve. The derived model allows predicting the solar cell/panel output for arbitrary environmental conditions. The method combines a solution of an algebraic equations system with an optimization algorithm. The main advantage of the proposed method is that in order to obtain the required parameters ...