Search

Conventional dual buck and boost inverter with a single input dc source (DBBI-SIDS) has the satisfactory performance of high efficiency, low total capacitance, and no leakage current. Nevertheless, the main current will flow through the two individual capacitors of the inverter, which may reduce their lifetimes. In this article, a new DBBI-SIDS will be proposed, where two extra mosfet switches at line frequency are adopted to be instead of the two individual capacitors of the conventional DBBI-SIDS. Different from the conventional DBBI-SIDS, the new inverter works in the pure full bridge mode. The detailed principle of operation is presented through equivalent circuits. The static characteristics and the control strategy of the proposed inverter will be also introduced in detail. A 110-V/50-Hz/550-W prototype has been developed in the laboratory, where experimental results have verified the desired performance of the proposed inverter.

Summarization: Nowadays, the Passivity-Based Control (PBC) has been successfully applied to digitally controlled Grid-Connected Inverter (GCI) with LCL filter. As a nonlinear method, the PBC controller has strong robustness against the parameter drift of the LCL filter and the grid impedance, where the parameters of the PBC controller still need to be designed carefully to achieve a good control performance. The existing design methods are based on separating the PBC controller into three control loops. Therefore, the design process is cumbersome, especially for inexperienced engineers, due to the complex structure of the PBC controller. In this article, an intelligent Particle Swarm Optimization (PSO) algorithm is utilized to simplify the parameters design of the PBC controller, where the difficulty of manual calculations is avoided and the parameters can be more easily and efficiently obtained using MATLAB in offline mode. Furthermore, a Kalman filter observer is adopted to estimate the state variables in the PBC controller, where only the grid-injected current needs to be sampled in the overall GCI system. Simulations and experiments are provided to verify the correctness and effectiveness of the proposed PBC controller design method. Παρουσιάστηκε στο: IEEE Access

Summarization: Nowadays, renewable energy sources (RES) in combination with power systems having the capability of storing electric energy are increasingly used in distributed generation applications. Multiport DC/AC inverters are required for the integration of RESs and energy storage systems with the electric grid and local loads. Recently, a variety of multiport DC/AC inverter topologies have been reported in the literature. In this paper, a comparative study of various alternative non-isolated DC/AC three-port converter (TPC) topologies is performed, when they are used as the power electronic interface between photovoltaic arrays, battery energy storage units and the electric grid/load. This study focuses on the performance of these topologies in terms of the leakage ground current and the battery ripple current during charging and discharging in distributed generation systems. A comparative performance evaluation of the alternative multiport DC/AC inverter topologies has been performed in Matlab/Simulink for the case of a 2 kW distributed energy system and the simulation results are presented. Παρουσιάστηκε στο: 2021 10th International Conference on Modern Circuits and Systems Technologies

Summarization: This paper focuses on the design of a low-voltage power converter for an on-chip PV cell-level inverter. Various topologies are discussed for the DC/DC stage, whereas the ZVS quasi-resonant boost and the synchronous boost are considered the most appropriate for this application. Both the aforementioned topologies are modeled and evaluated in terms of efficiency, by the aid of PSpice simulations. Due to requirements and limitations of the available 0.18 μm CMOS process technology, the synchronous boost is finally chosen as the most appropriate solution. As for the DC/AC stage, the H-bridge inverter configuration is selected, as a simple, compact and cost-effective solution. A prototype converter is designed and constructed with discrete components, so as to validate the functionality and performance of the proposed system. Finally, experimental results are presented, indicating the high efficiency that can be achieved. Παρουσιάστηκε στο: 2021 10th International Conference on Modern Circuits and Systems Technologies

Summarization: An extensive utilization of wireless sensor networks has evolved during the last years for monitoring various environmental and artificial processes. When operating in remote locations, the nodes of wireless sensor networks are typically power supplied by an energy production and management system, comprising low-power renewable energy sources, a power electronic converter, and a battery-based energy storage unit. In this paper, a methodology is proposed for optimally designing the energy production and processing system of a wireless sensor network node simultaneously at both the renewable power-supply system level and the power converter circuit level, through a unified design process. The impact of the objective function type on the power-supply design is also investigated in this paper. Design optimization and experimental results are presented, which demonstrate that the optimized power-supply structures derived by applying the proposed optimization technique exhibit lower cost of generated energy compared to partially optimized or totally nonoptimized structures and by that reduce the cost of the overall wireless sensor network node. Presented on: IEEE Transactions on Industrial Informatics

This work described the operational capabilities of a platform developed to assist decision makers to determine the optimal location and configuration of desalination plants to be powered by renewable energy sources. The platform, called DESiRES, operates under an open source geographical information system interface. Interoperability with geostatictical and optimization design algorithm modules was achieved via the location based information provided by the geographical module. The current stage of DESiRES platform development (i.e., study areas, data used, etc.) was presented along with the basic platform functionalities, showing a great potential for design and assessment of desalination in the Mediterranean region.

Nowadays, the management of water is of paramount importance for modern societies due to the high water-availability requirements. The application of water management schemes requires the installation of water level data-acquisition systems in multiple, geographically isolated large-scale storage tanks of water distribution networks. Existing techniques for liquid level sensing have either been applied over a relatively small measurement range, or require special scientific equipment of high cost, or they are not convenient for transportation, installation and long-term maintenance in multiple large-scale water storage tanks of water distribution networks in cities, communities, etc. In this paper, a review of prior art on liquid level sensing is initially presented. Then, the operational characteristics and performance of a novel capacitive-type water level measurement system are investigated through simulations and experimental tests conducted in two water storage tanks of a city-scale water distribution network. It is demonstrated that the proposed capacitive water level measurement system achieves equivalent performance with that of a commercially-available ultrasound water-level sensing device and simultaneously exhibits a much lower manufacturing cost.

ThermoElectric Generators (TEGs) are capable to harvest the ambient thermal energy for power-supplying sensors, actuators, biomedical devices etc. in the μW up to several hundreds of Watts range. In this paper, a Maximum Power Point Tracking (MPPT) method for TEG elements is proposed, which is based on controlling a power converter such that it operates on a pre-programmed locus of operating points close to the MPPs of the power–voltage curves of the TEG power source. Compared to the past-proposed MPPT methods for TEGs, the technique presented in this paper has the advantage of operational and design simplicity. Thus, its implementation using off-the-shelf microelectronic components with low-power consumption characteristics is enabled, without being required to employ specialized integrated circuits or signal processing units of high development cost. Experimental results are presented, which demonstrate that for MPP power levels of the TEG source in the range of 1–17 mW, the average deviation of the power produced by the proposed system from the MPP power of the TEG source is 1.87%.

Nowadays, wind energy conversion systems (WECSs) are widely employed in stand-alone systems for providing power to isolated loads, as well as in distributed generation systems, microgrids, and smart grids. In all of these applications, appropriate energy management processes must be performed for maximizing the energy produced by the wind turbines and transfer the generated energy to the consumer with high efficiency and required power quality. In this chapter, an overview of modern energy management techniques for WECS is presented, in terms of both the hardware architecture employed and the control methods that are applied.

—A substantial growth of the installed photovoltaic systems capacity has occurred around the world during the last decade, thus enhancing the availability of electric energy in an environmentally friendly way. The maximum power point tracking technique enables maximization of the energy production of photovoltaic sources during stochastically varying solar irradiation and ambient temperature conditions. Thus, the overall efficiency of the photovoltaic energy production system is increased. Numerous techniques have been presented during the last decade for implementing the maximum power point tracking process in a photovoltaic system. This article provides an overview of the operating principles of these techniques, which are suited for either uniform or non-uniform solar irradiation conditions. The operational characteristics and implementation requirements of these maximum power point tracking methods are also analyzed to demonstrate their performance features.

Transformerless PV inverters are known to generate undesirable ground leakage currents due to the lack of galvanic isolation between the PV array and the electric grid. This paper initially discusses the different types of transformerless PV inverter topologies that have been proposed to overcome this problem. It then proposes a new topology, which extends the commercially successful HERIC inverter with the addition of a mid-DC-link clamping configuration. Such configurations are known to cause a highly desirable reduction of the ground leakage currents, which is demonstrated through simulation results from MATLAB-Simulink and PLECS. The proposed topology is finally compared to other transformerless topologies with respect to other aspects, such as efficiency and component count.

The flexible photovoltaic (PV) modules have the advantage of easily fitting on curved surfaces, but in that case their power-voltage characteristic exhibits local maximum power points (MPPs) where the PV module power production is suboptimal. In this paper, the effect of geometrical installation parameters of flexible PV modules, such as the bending angle, tilt angle, and orientation, on the shape of the power-voltage characteristic is experimentally investigated. Then, a new method of tracking the global MPP of flexible PV modules is proposed. An experimental, comparative study is also presented, which demonstrates that compared to the past-proposed MPP tracking (MPPT) techniques, the system proposed in this paper is capable to detect the global MPP of a flexible PV module with less search steps. Thus, the power loss during the global MPPT process is minimized and the energy production of the flexible PV module is maximized.

The digital implementations of Sinusoidal Pulse Width Modulation (SPWM) generators have dominated over their counterparts based on analog circuits. In this paper, an FPGA-based SPWM generator is presented, which is capable to operate at switching frequencies up to 1 MHz (requiring FPGA operation at 100-160 MHz), thus it is capable to support the high switching frequency requirements of modern single-phase dc/ac power converters. The proposed design occupies a small fraction of a medium-sized FPGA and, thus, can be incorporated in larger designs. Additionally, it has a flexible architecture that can be tuned to a variety of single-phase dc/ac inverter applications. The post-layout simulation and experimental results confirm that compared to the past-proposed SPWM generation designs, the SPWM generator presented in this paper exhibits much faster switching frequency, lower power consumption, and higher accuracy of generating the desired SPWM waveform.

The design optimization of H5, H6, neutral point clamped, active-neutral point clamped, and conergy-NPC transformerless photovoltaic (PV) inverters is presented in this paper. The components reliability in terms of the corresponding malfunctions, affecting the PV inverter maintenance cost during the operational lifetime period of the PV installation, is also considered in the optimization process. According to the results of the proposed design method, different optimal values of the PV inverter design variables are derived for each PV inverter topology and installation site. The H5, H6, neutral point clamped, active-neutral point clamped and conergy-NPC PV inverters designed using the proposed optimization process feature lower levelized cost of generated electricity and lifetime cost, longer mean time between failures and inject more PV-generated energy into the electric grid than their nonoptimized counterparts, thus maximizing the total economic benefit obtained during the operational time of the PV system.

Large-scale photovoltaic (PV) plants enable the reduction of the PV plant cost per watt of nominal power that is installed. In this paper, a new method is presented for the calculation of the optimal configuration of large PV plants, such that the levelized cost of the generated electricity (LCOE) is minimized. The proposed design optimization process is performed by considering the impact of the number of components, as well as their type and arrangement within the installation field, on the tradeoff between the lifetime cost and the corresponding energy production of the PV plant. The high-accuracy feature of the energy production calculations that are performed by the proposed design tool has been validated using experimental operational data of an existing PV plant. The design results demonstrate that using the proposed optimization method allows a reduction of the cost of the energy that is generated by the large-scale PV plant, thus enabling the maximization of the economic benefit that is obtained during the operational lifetime period of the PV system.

Summarization: This paper presents a new methodology for optimal design of transformerless photovoltaic (PV) inverters targeting a cost-effective deployment of grid-connected PV systems. The optimal switching frequency as well as the optimal values and types of the PV inverter components is calculated such that the PV inverter LCOE generated during the PV system lifetime period is minimized. The LCOE is also calculated considering the failure rates of the components, which affect the reliability performance and lifetime maintenance cost of the PV inverter. A design example is presented, demonstrating that compared to the nonoptimized PV inverter structures, the PV inverters designed using the proposed optimization methodology exhibit lower total manufacturing and lifetime maintenance cost and inject more energy into the electric-grid and by that minimizing LCOE. Παρουσιάστηκε στο: 27th Annual IEEE Applied Power Electronics Conference and Exposition

Summarization: The power-voltage characteristic of photovoltaic (PV) arrays operating under partial-shading conditions exhibits multiple local maximum power points (MPPs). In this paper, a new method to track the global MPP is presented, which is based on controlling a dc/dc converter connected at the PV array output, such that it behaves as a constant input-power load. The proposed method has the advantage that it can be applied in either stand-alone or grid-connected PV systems comprising PV arrays with unknown electrical characteristics and does not require knowledge about the PV modules configuration within the PV array. The experimental results verify that the proposed global MPP method guarantees convergence to the global MPP under any partial-shading conditions. Compared with past-proposed methods, the global MPP tracking process is accomplished after far fewer PV array power perturbation steps. Presented on: IEEE Journal of Photovoltaics

Several countries with considerable PhotoVoltaic (PV) installations are facing a challenge of overloading the power infrastructure during peak-power production hours. Regulations have been imposed on the PV systems, where more active power control should be flexibly performed. As an advanced control strategy, the Absolute Active Power Control (AAPC) can effectively solve the overloading issues by limiting the maximum possible PV power to a certain level (i.e., the power limitation), and also benefit the inverter reliability. However, its feasibility is challenged by the energy loss. An increase of the inverter lifetime and a reduction of the energy yield can alter the cost of energy, demanding an optimization of the power limitation. Therefore, aiming at minimizing the Levelized Cost of Energy (LCOE), the power limit is optimized for the AAPC strategy in this paper. The optimization method is demonstrated on a 3-kW single-phase PV system considering a real-field mission profile (i.e., solar irradiance and ambient temperature). The optimization results have revealed that superior performance in terms of LCOE and energy production can be obtained by enabling the AAPC strategy, compared to the conventional PV inverter operating only in the maximum power point tracking mode. In the presented case study, the minimum of LCOE is achieved for the system when the power limit is optimized to a certain level of the designed maximum feed-in power (i.e., 3 kW). In addition, the proposed LCOE-based analysis method can be used in the design of PV inverters considering mission profiles.

The market of PV systems is rapidly expanding during the last years and the transformerless DC/AC inverters are key components in this evolution. Despite its design and control simplicity, a transformerless full-bridge DC/AC inverter may exhibit a high leakage ground current, due to capacitive coupling between the solar panels and ground, which prohibits its employment in single-phase PV systems. Thus, multiple alternative transformerless PV inverter topologies have been developed in the past, which, however, comprise additional power devices and/or passive components. In this paper, a new modulation method is proposed for optimally controlling the power switches of transformerless single-phase full-bridge PV inverters, such that their leakage ground current is minimized. The design results demonstrate that by using the proposed technique, the leakage ground current of transformerless full-bridge inverters is reduced below the maximum limit imposed by the VDE 0126-1-1 standard, thus enabling their application in single-phase PV installations, instead of more complex PV inverter structures.

Wireless Sensor Networks (WSNs) are widely used during the last years in various environmental and industrial applications and they are frequently installed in geographically isolated areas, where access to electricity is not available. In such cases, the WSN nodes are power-supplied by Renewable Energy Sources (RES), accompanied by energy-storage units. In this paper, a design optimization method is presented for deriving the optimal configuration of the RES-based energy production system of a WSN node, such that its total lifetime cost is minimized, while simultaneously it is guaranteed that the data-acquisition equipment of the WSN node is uninterruptedly power-supplied during the entire year. The design results verify that by applying the proposed optimization technique, RES-based power-supply structures with a lower lifetime cost are derived, compared to the non-optimally designed configurations. Experimental results are also presented, demonstrating the successful operation of a RES-based power-supply system, which has been optimally designed using the proposed method.

Summarization: In this paper, a detailed study and implementation of a reliable and efficient regenerative braking system is presented. It is applied on a prototype electric vehicle, that uses a hydrogen fuel cell as its only power source. Supercapacitors are used to store the energy that is generated during braking, transistors for switching the alternative circuits and an embedded computer controller program undertakes the synchronization of the system tasks. A finite state machine was designed to create a simple but robust technique to control the transistor switches according to the system's sensory inputs. The system is powered by its own supercapacitors, and thus it may be used in a plug-and-play manner. On-road test drives proved the system's reliability and efficiency. Presented on

The implementation of water management techniques in various environmental applications requires the measurement of the level of water stored in artificial storage tanks (e.g. in cities, communities etc.) or natural reservoirs. In this paper, the design of a water-level sensor is presented, which is based on the Time-Domain Reflectometry (TDR) technique. The proposed TDR sensor comprises a sensing probe constructed using low-cost and widely-available multilayer and stainless steel tubes. A simple signal-conditioning circuit has been designed for interfacing the acquired measurements to a digital data-acquisition device through an I2C communication bus. Thus, the manufacturing cost and power consumption of the proposed sensor are relatively low, enabling its incorporation in Wireless Sensor Networks which are power-supplied by Renewable Energy Sources. The operation of the proposed sensor has been tested in a city-scale storage tank of drinking water. The experimental results verify that the proposed sensor achieves equivalent accuracy performance with a commercially available ultrasound water-level sensor, which, however, is of higher cost.

Reliability is one of the most important parameters in aircrafts. In this paper, a method for the calculation of reliability (i.e. number of failures / 106 hours) of a three-phase full-bridge inverter, which is employed in the dynamic waste heat recovery system of an aircraft, is presented. The main factors for the reliability analysis that have to be considered is the topology of the inverter, the ambient temperature conditions, the power switches (type and modulation technique), and the harmonic filter. The power inverter reliability has been calculated using a software program developed under the Matlab platform, which was used to calculate the failure rate of each device of the inverter, such as the power switches, the DC-bus capacitor and the filter inductor, given the operating switching frequency value. The results indicate that at higher switching frequency levels the inverter of the DWHR system exhibits a high failure rate, thus resulting in a lower Mean Time Between Failures (MTBF).

Wireless Sensor Networks (WSNs) are widely installed during the last years for monitoring multiple parameters of interest over distributed areas in the environment, buildings and industries. The WSN nodes are frequently installed in geographically remote areas. Thus, they are power-supplied by renewable energy sources and a DC-DC power converter is employed for interfacing the generated energy to a battery bank and the electric load of the WSN node. In this paper, an optimization method is presented for performing circuit-level optimization of a Photovoltaic (PV) power-supplied Boost-type DC-DC power converter, which is employed in a WSN node. Using the proposed technique enables to calculate the optimal switching frequency and values of the components comprising the circuit of the DC-DC converter, such that either the power loss at nominal output power, or the total power loss during the year, or the Levelized Cost Of the Electricity generated (LCOE), are alternatively minimized. The design optimization and experimental results demonstrate the features of the proposed technique and confirm the performance superiority of the DC-DC converters, which are designed using the proposed method, compared to the non-optimized DC-DC converter structures.

Water-level sensors are indispensable for monitoring the level of water in storage tanks, which are used in drinking water distribution networks. In this paper, a long-range capacitive-type water-level sensor is presented. The proposed sensor is constructed using widely-available multilayer tubes, which are used for building drinking water systems. Thus, both the manufacturing cost of the sensor and the cost of the associated electronic circuits, which are used for interfacing the sensor to a digital data-acquisition unit, are low. The performance of the proposed sensor has been evaluated in a water storage tank of a city-scale water distribution network. The experimental results indicate that the accuracy of the proposed experimental prototype sensor is equivalent to that of a commercially available ultrasound water level sensor, while, additionally, its manufacturing cost is significantly lower.

Summarization: A methodology for optimal sizing of stand-alone PV/WG systems is presented. The purpose of the proposed methodology is to suggest, among a list of commercially available system devices, the optimal number and type of units ensuring that the 20-year round total system cost is minimized subject to the constraint that the load energy requirements are completely covered, resulting in zero load rejection. The 20-year round total system cost is equal to the sum of the respective components capital and maintenance costs. The cost (objective) function minimization is implemented using genetic algorithms, which, compared to conventional optimization methods such as dynamic programming and gradient techniques, have the ability to attain the global optimum with relative computational simplicity. The proposed method has been applied for the design of a power generation system which supplies a residential household. The simulation results verify that hybrid PV/WG systems feature lower system cost compared to the cases where either exclusively WG or exclusively PV sources are used. Παρουσιάστηκε στο: Solar Energy

Pulse width modulation (PWM) has been widely used in power converter control. Most high power level converters operate at switching frequencies up to 500 kHz, while operating frequencies in excess of 1 MHz at high power levels can be achieved using the planar transformer technology. The contribution of this paper is the development of a high-frequency PWM generator architecture for power converter control using FPGA and CPLD ICs. The resulting PWM frequency depends on the target FPGA or CPLD device speed grade and the duty cycle resolution requirements. The post-layout timing simulation results are presented, showing that PWM frequencies up to 3.985 MHz can be produced with a duty cycle resolution of 1.56%. Additionally, experimental results are also presented for low cost functional verification of the proposed architecture.

A wind-generator (WG) maximum-power-point-tracking (MPPT) system is presented, consisting of a high-efficiency buck-type dc/dc converter and a microcontroller-based control unit running the MPPT function. The advantages of the proposed MPPT method are that no knowledge of the WG optimal power characteristic or measurement of the wind speed is required and the WG operates at a variable speed. Thus, the system features higher reliability, lower complexity and cost, and less mechanical stress of the WG. Experimental results of the proposed system indicate near-optimal WG output power, increased by 11%-50% compared to a WG directly connected via a rectifier to the battery bank. Thus, better exploitation of the available wind energy is achieved, especially under low wind speeds.

Δημοσίευση σε επιστημονικό περιοδικό Summarization: A real-time system for protecting and monitoring a DC/AC converter has been designed and constructed. The proposed system consists of (a) a hardware protection unit for fast reaction, load protection and inverter fail-safe operation and (b) a microcontroller unit for calculating critical parameters of the inverter operation. The control unit malfunctions have not been investigated in this study. The proposed hardware architecture and sensors form a low-cost and reliable control unit. The experimental results show that the proposed system ensures the inverter protection and fail-safe features. The proposed unit can be used to increase the reliability of any power inverter in AC motor drives, renewable energy systems, etc. or can be incorporated in any UPS system. Presented on: Microelectronics Journal

The transformerless DC/AC inverter topologies are employed in Photovoltaic systems in order to improve the power conversion efficiency, power density and cost. The Active-Neutral Point Clamped (Active-NPC) transformerless inverters have the advantage of achieving better thermal balance among their power semiconductors. In this paper, a new modulation technique is proposed for optimally controlling the power switches employed in transformerless Active-NPC inverters. The design results demonstrate that compared to the existing PWM strategies, using the proposed method results in lower total power losses and significantly better distribution of the power losses among the semiconductors of the Active-NPC inverter.

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.

Dense monitoring of environmental parameters (e.g. air/soil humidity, ambient temperature) is critical in precision agriculture, urban area monitoring and environmental modeling applications. In this paper, the design of a novel wireless sensor network (WSN) is proposed, consisting of low-power and low-cost sensor nodes, deployed in a bistatic architecture (i.e. carrier emitter in a different location than the receiver) and achieving long-range backscatter communication. The tags modulate sensor information using analog frequency modulation (FM) and frequency division multiple access (FDMA) at the subcarrier frequency, even though a single carrier is assumed. In sharp contrast to prior art, the developed backscatter sensor network performs environmental monitoring over a relatively wide area. A proof-of-concept prototype WSN application has been developed for capacitive relative humidity (RH) sensing, with 1.5 mW per tag, 0.9 RMSE and range on the order of 50 m.

The electrical signals generated by plants provide information about their physiology. A low-cost and low-power-consumption (≈ 240 μW) wireless sensor node is proposed, which measures the electrical signal generated across selected points on a plant and wirelessly transmits it to a data-collection device (reader) through a backscattering-based communication link. The proposed sensor node is appropriate for large-scale Wireless Sensor Networks (WSNs) agricultural applications, which are capable of collecting information about the health status of multiple plants over a broad area, with low cost and low power-consumption. Experimental results are presented for avocado and orange trees, demonstrating the successful operation of the proposed sensor node.

Summarization: System latency (time delay) and its visible consequences are fundamental Virtual Environment (VE) deficiencies that can hamper user perception and performance. This paper presents an immersive simulation system which improves upon current latency measurement and minimization techniques. Hardware used for latency measurements and minimization is assembled based on low-cost and portable equipment, most of them commonly found in an academic facility without reduction in accuracy of measurements. A custom-made mechanism of measuring and minimizing end-to-end head tracking latency in an immersive VE is assembled. The mechanism is based on an oscilloscope comparing two signals. One is generated due to the head-tracker movement by a shaft encoder attached on a servo motor moving the tracker. The other signal is generated by the visual consequences of this movement in the VE using a photodiode attached to the computer monitor. Visualization and application-level control of latency in the VE was implemented using the XVR platform. Minimization processes resulted in almost 50% reduction of initial measured latency. The description of the mechanism by which VE latency is measured and minimized will be essential to guide system countermeasures such as predictive compensation. Παρουσιάστηκε στο: 10th International Conference on Virtual Reality Continuum and Its Applications in Industry

Summarization: The DC/AC inverters are the key elements in grid-connected PV energy production systems. In this paper, new design optimization techniques focused on transformerless (very high efficiency) PV inverters are proposed. They have been developed based on an analysis of the deficiencies of the current, state-of-the-art PV inverters design technology, which limits the amount of PV energy supplied into the electric grid. The influences of the electric grid regulations and standards and the PV array operational characteristics on the design of grid-connected PV inverters have also been considered. The simulation results verify that the proposed optimization techniques enable the maximization of the PV energy injected into the electric grid by the optimized PV installation. Παρουσιάστηκε στο: 26th Annual IEEE Applied Power Electronics Conference and Exposition

An absolute sea-level monitoring and altimeter calibration permanent facility has been established on the isle of Gavdos, 50 km south of the island of Crete, Greece. This calibration/validation facility has been chosen because Gavdos is under a crossing point of the ground-tracks of Jason-1 satellite, and adjacent to an Envisat pass. Satellite altimeter missions are evaluated at that site using external measurements from tide gauges, GPS, a DORIS beacon, meteorological sensors, wave-height sensors, airborne campaigns for gravity and sea-surface topography, water-vapour radiometry, solar atmospheric spectrometry, GPS buoys, altimeter transponder, Satellite Laser Ranging, etc. The mean sea level and the earth's tectonic deformation field in the region have also been determined accurately. Comparison over the cycles 70 to 77 of the Jason-1 satellite indicate that its absolute mean bias for the sea-surface heights is 13 mm ± 20 mm. The GAVDOS project has started in December 2001 and has been in the context of an international calibration/validation effort of the Jason-1 Science Working Team.

In this study, a methodology for the design optimisation and the economic analysis of photovoltaic grid-connected systems (PVGCSs) is presented. The purpose of the proposed methodology is to suggest, among a list of commercially available system devices, the optimal number and type of system devices and the optimal values of the photovoltaic (PV) module installation details, such that the total net economic benefit achieved during the system operational lifetime period is maximised. The decision variables included in the optimisation process are the optimal number and type of the PV modules and the DC/AC converters, the PV modules optimal tilt angle, the optimal arrangement of the PV modules within the available installation area and the optimal distribution of the PV modules among the DC/AC converters. The economic viability of the resulting PVGCS configuration is explored according to the net present value, the discounted payback period and the internal rate of return methods. The proposed method has been applied for the optimal design of a PVGCS interconnected to the electric network of an island with significant solar irradiation potential and the corresponding optimal sizing and economic analysis results are presented.

Summarization: A new method for the design of a bidirectional inverter based on the sinusoidal pulse-width modulation principle and the use of a low-cost and lightweight ferrite-core transformer is presented. The inverter is designed for either ohmic or inductive loads. In the case of inductive loads, the reactive power is transferred back to the DC input power source using a new active rectifier design. The inverter is controlled by two minimum-time feedback loops, providing relatively low output voltage distortion (less than 2% for DC input higher than 24 V) and good load regulation (better than 2%), while the inverter efficiency remains relatively constant (from 80 to 85%) over a wide output power range (75 to 200 W) and DC input voltage range (23 to 28 V). Theoretical results are experimentally verified using a laboratory prototype Presented on: IEE Proceedings Electric Power Applications

In this paper, a methodology for the optimal sizing of a Battery Energy Storage System (BESS) targeting to supply a predefined and constant (guaranteed) amount of power to an isolated electric grid during the peak load-demand hours is presented. The BESS battery bank is charged using that part of the energy produced by wind parks interconnected with the power system, which is rejected by the electric network due to grid stability limitations. Thus, using the proposed BESS configuration results in increment of the wind energy penetration in the isolated power system and reduction of the air pollution caused by the thermal power stations. The economic viability of the optimally sized BESS configuration is investigated by calculating the investment discounted payback period and internal rate of return. The proposed method has been applied for the optimal design of a BESS supporting the isolated electric network of a remote island with significant wind potential. According to the economic analysis results, the installation of the proposed BESS is economically beneficial for both the BESS investor and the local electric network operator.