摘要 :
Airborne wind turbines (AWTs) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power ki...
展开
Airborne wind turbines (AWTs) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power kite flying at high speed perpendicular to the wind. On the kite are mounted a turbine, an electrical generator, and a power electronics converter. The electric power generated is transmitted via a medium voltage cable to the ground. Because of the high flight speed of the power kite, several times the actual wind speed, only a very small swept area of the turbine is required according to Betz's Law and/or a turbine of low weight for the generation of a given electric power. Moreover, because of the high turbine rotational speed, no gear transmission is necessary and the size of the generator is also reduced. For takeoff and landing of the power kite, the turbines act as propellers and the generators as motors, i.e., electric power is supplied so that the system can be maneuvered like a helicopter. In the present work, the configuration of power electronics converters for the implementation of a 100 kW AWT is considered. The major aspect here is the trade-off between power-to-weight ratio (W/kg) and efficiency. The dependence of cable weight and cable losses on the voltage level of power transmission is investigated, and a comparison is made between low voltage (LV) and medium voltage (MV) versions of generators. Furthermore, the interdependence of the weight and efficiency of a bidirectional dual active bridge dc–dc converter for coupling the rectified output voltage of a LV generator to the MV cable is discussed. On the basis of this discussion, the concept offering the best possible compromise of weight and efficiency in the power electronics system is selected and a model of the control behavior is derived for both the power flow directions. A control structure is then proposed and dimensioned. Furthermore, questions of electrom- gnetic compatibility and electrical safety are treated. In conclusion, the essential results of this paper are summarized, and an outlook on future research is given. To enable the reader to make simplified calculations and a comparison of a CWT with an AWT, the aerodynamic fundamentals of both the systems are summarized in highly simplified form in an Appendix, and numerical values are given for the 100 kW system discussed in this paper.
收起
摘要 :
The second part of the essence of three-phase PFC Rectifier Systems is dedicated to a comparative evaluation of four active three-phase PFC rectifiers that are of interest for industrial application: the active six-switch boost-ty...
展开
The second part of the essence of three-phase PFC Rectifier Systems is dedicated to a comparative evaluation of four active three-phase PFC rectifiers that are of interest for industrial application: the active six-switch boost-type PFC rectifier, the Vienna Rectifier (VR), the active six-switch buck-type PFC rectifier, and the Swiss Rectifier. Typical dynamic feed-back control structures of the considered topologies are shown, and analytical equations for calculating the current stresses of the power semiconductors are provided. In addition, EMI filtering is discussed. The rectifier systems are assessed and compared based on simple and demonstrative performance indices such as the semiconductor stresses, the required semiconductor chip area, the volume of the main passive components, the DM and CM conducted EMI noise levels, and the efficiency. Two implementation variants, a more advanced one using SiC JFETs and SiC Schottky diodes and one using Si IGBTs and SiC Schottky diodes, are considered. The comparison is extended with selected examples of hardware demonstrators of VR systems that are optimized for efficiency and/or power density. This allows to determine the tradeoff between efficiency and power density and to quantify a typical efficiency versus power density limit (Pareto-Front) for practical three-phase PFC rectifier systems using standard printed circuit board interconnection technology.
收起
摘要 :
The electromagnetic compatability (EMC) analysis of electromagnetic interference (EMI) filter circuits using 3-D numerical modeling by the partial element equivalent circuit (PEEC) method represents the central topic of this paper...
展开
The electromagnetic compatability (EMC) analysis of electromagnetic interference (EMI) filter circuits using 3-D numerical modeling by the partial element equivalent circuit (PEEC) method represents the central topic of this paper. The PEEC-based modeling method is introduced as a useful tool for the prediction of the high frequency performance of EMI input filters, which is affected by PCB component placement and self- and mutual-parasitic effects. Since the measuring of all these effects is rather difficult and time consuming, the modeling and simulation approach represents a valuable design aid before building the final hardware prototypes. The parasitic cancellation techniques proposed in the literature are modeled by the developed PEEC-boundary integral method (PEEC-BIM) and then verified by the transfer function and impedance measurements of the $Lhbox{--}C$ and $Chbox{--}Lhbox{--}C$ filter circuits. Good agreement between the PEEC-BIM simulation and the measurements is achieved in a wide frequency range. The PEEC-BIM method is implemented in an EMC simulation tool GeckoEMC. The main task of the presented research is the exploration of building an EMC modeling environment for virtual prototyping of EMI input filters and power converter systems.
收起
摘要 :
An analytical model for the reliability of a dedicated short-range communication (DSRC) control channel (CCH) to handle safety applications in vehicular ad hoc networks (VANETs) is proposed. Specifically, the model enables the det...
展开
An analytical model for the reliability of a dedicated short-range communication (DSRC) control channel (CCH) to handle safety applications in vehicular ad hoc networks (VANETs) is proposed. Specifically, the model enables the determination of the probability of receiving status and safety messages from all vehicles within a transmitter's range and vehicles up to a certain distance, respectively. The proposed model is built based on a new mobility model that takes into account the vehicle's follow-on safety rule to derive accurately the relationship between the average vehicle speed and density. Moreover, the model takes into consideration 1) the impact of mobility on the density of vehicles around the transmitter, 2) the impact of the transmitter's and receiver's speeds on the system reliability, 3) the impact of channel fading by modeling the communication range as a random variable, and 4) the hidden terminal problem and transmission collisions from neighboring vehicles. It is shown that the current specifications of the DSRC may lead to severe performance degradation in dense and high-mobility conditions. Therefore, an adaptive algorithm is introduced to increase system reliability in terms of the probability of successful reception of the packet and the delay of emergency messages in a harsh vehicular environment. The proposed model and the enhancement algorithm are validated by simulation using realistic vehicular traces.
收起
摘要 :
In a pinched-beam ion diode, an intense electron beam focuses on-axis at the center of the anode and passes through the thin anode foil into a beam dump region behind the anode foil. The beam dump usually consists of an evacuated ...
展开
In a pinched-beam ion diode, an intense electron beam focuses on-axis at the center of the anode and passes through the thin anode foil into a beam dump region behind the anode foil. The beam dump usually consists of an evacuated cylindrical anode-can. Because of energy deposition from the intense electron beam, the interior surfaces of the anode-can are expected to be space-charge-limited emitters. Therefore, the electron space charge from the beam in the anode-can will draw ions off these surfaces. There is evidence from nuclear activation which suggests that ions exist in the anode-can with energies that significantly exceed those associated with the diode voltage. Analysis and particle-in-cell simulations show that a virtual cathode can form in the anode-can that accelerates ions up to the energy associated with the diode voltage. Additionally, a subset of these ions can form current bursts that are driven to the outer wall of the anode-can with ion energies as high as a few times the energy associated with the diode voltage.
收起
摘要 :
In this paper, a novel 3-D electromagnetic modeling approach which enables electromagnetic compatibility (EMC) analysis of power converter systems in an accurate and computationally efficient way is presented. The 3-D electromagne...
展开
In this paper, a novel 3-D electromagnetic modeling approach which enables electromagnetic compatibility (EMC) analysis of power converter systems in an accurate and computationally efficient way is presented. The 3-D electromagnetic modeling approach, implemented in the EMC simulation tool GeckoEMC, is based on two numerical techniques, the partial element equivalent circuit method and the boundary integral method (PEEC–BIM). The developed PEEC–BIM coupled method enables comprehensive EMC analysis taking into account different effects of the PCB layout, self-parasitics, mutual coupling, shielding, etc., which in turn provides a detailed insight into the electromagnetic behavior of power electronic systems in advance to the implementation of hardware prototypes. The modeling features of the GeckoEMC simulation tool for virtual design of electromagnetic interference (EMI) filters and power converters is demonstrated on the examples of a single-phase two-stage EMI filter and a practical EMI filter for a single-phase PFC input stage. Good agreement between the PEEC–BIM simulation and the small signal transfer function measurement results is achieved over a wide frequency range, from dc up to 30 MHz. The EMC simulation environment enables a step-by-step EMC analysis distinguishing the impact of various electromagnetic effects on the EMI filter performance and allowing an optimal EMI filter design.
收起
摘要 :
A solid-state transformer (SST) is a high-frequency power electronic converter that is used as a distribution power transformer. A common three-stage configuration of an SST consists of ac–dc rectifier, isolated dc–dc dual-activ...
展开
A solid-state transformer (SST) is a high-frequency power electronic converter that is used as a distribution power transformer. A common three-stage configuration of an SST consists of ac–dc rectifier, isolated dc–dc dual-active-bridge (DAB) converter, and dc–ac inverter. This study addresses the controller design issue for a dc–dc DAB converter when driving a regulated single-phase dc–ac inverter. Since the switching frequency of the inverter stage is much higher than that of the DAB stage, the single-phase inverter is modeled as a double-line-frequency (e.g., 120 Hz) current sink. The effect of 120-Hz current by the single-phase inverter is studied. The limitation of a PI-controller, low gain at 120 Hz, is investigated. Two methods are proposed to improve the regulation of the output voltage of DAB converters. The first one uses a bandstop filter and feedforward, while the second method uses an additional proportional-resonant controller in the feedback loop. Theoretical analysis, simulation, and experiment results are provided.
收起
摘要 :
Although pneumatic actuators have been widely used in industry and other application areas, its weakness in low-energy efficiency is well known. Aiming for energy efficiency improvement, this paper presents a new hybrid pneumatic ...
展开
Although pneumatic actuators have been widely used in industry and other application areas, its weakness in low-energy efficiency is well known. Aiming for energy efficiency improvement, this paper presents a new hybrid pneumatic system that will recover energy from the exhaust compressed air through a scroll expander. The scroll expander drives a generator to convert the exhaust compressed air energy to electrical energy; thus, the proposed system is entitled “pneumatic-electrical” system. A closed-loop coordinate control strategy is engaged and proven to be essential in maintaining proper actuator operation status, while the scroll expander is connected in. The overall system mathematical model is derived and simulation results are presented in this paper. A test rig is set up to verify the feasibility of the proposed system structure. Both simulation and test results indicate that the proposed scheme is realistic and work well.
收起
摘要 :
A handset antenna modeling and design technique using space mapping (SM) is presented. Thin-wire models are exploited as coarse models in the SM algorithms, while the fine models are high-accuracy electromagnetic simulations. The ...
展开
A handset antenna modeling and design technique using space mapping (SM) is presented. Thin-wire models are exploited as coarse models in the SM algorithms, while the fine models are high-accuracy electromagnetic simulations. The thin-wire models capture the basic physics of handset antennas but are not as accurate as the fine model. On the other hand, they are computationally cheap when analyzed by the method of moments solvers. Detailed guidelines for building thin-wire models are provided. Two SM algorithms are employed: 1) implicit, input and output space mapping and 2) implicit and output space mapping. An internal dual-band patch antenna and an arm-folded planar inverted F antenna are designed through our approach. For comparison, direct optimizations have been performed in each example.
收起
摘要 :
This paper presents the analysis and realization of a topology suitable to realize a power factor correction (PFC) rectifier with a thickness of only a few millimeters. The low height of the converter requires all components to be...
展开
This paper presents the analysis and realization of a topology suitable to realize a power factor correction (PFC) rectifier with a thickness of only a few millimeters. The low height of the converter requires all components to be integrated into the printed circuit board (PCB). Still reasonable dimensions of the converter PCB are feasible (221 mm $times$ 157 mm for a 200 W PFC rectifier), since PCB-integrated inductors and capacitors allow for high energy densities due to their large surface area which facilitates a low thermal resistance to ambient. A multicell totem-pole PFC rectifier employing a soft-switching modulation scheme over the complete mains period is identified as an adequate topology. The mode of operation is entitled triangular current mode (TCM) due to the triangular-shaped inductor currents. The modulation technique requires a reliable description of the switching transition of a half-bridge in order to provide accurate timing parameters. For this purpose, a simplified model of the nonlinear MOSFETs’ output capacitances facilitates closed-form analytical expressions for duty cycle and switching frequency. Furthermore, this paper details the control of three interleaved converter cells which yields a reduction of the input current ripple. A 200 W TCM PFC rectifier with a low height of 5 mm has been realized and measurement results are provided in order to validate the theoretical considerations. The presented TCM PFC rectifier achieves an efficiency of 94.6% and a power factor of 99.3% at nominal power.
收起
