摘要 :
In this paper, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firin...
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In this paper, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firing delay angles and, consequently, on the specific power locus followed by the ac/dc converter. This power locus ensures minimum fifth and seventh harmonics (total rms) in the input current which provides minimum input current total harmonic distortion when the reactive power is less than 0.5 p.u. The series APF is connected between the load and the converter output via a magnetic amplifier to eliminate the dc current from the APF inverter, thus reducing inverter losses. Voltage harmonic compensation using a series APF, with and without a magnetic amplifier, is examined with both resistive and inductive loads. The simulation results for compensating a 3.3-kV MV 12-pulse converter system are experimentally verified using a scaled prototype 12-pulse converter with a series APF.
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Previously, we proposed using an interpolated average CT (IACT) method for attenuation correction (AC) in positron emission tomography (PET), which is a good, low-dose approximation of cine average CT (CACT) to reduce misalignment...
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Previously, we proposed using an interpolated average CT (IACT) method for attenuation correction (AC) in positron emission tomography (PET), which is a good, low-dose approximation of cine average CT (CACT) to reduce misalignments and improve quantification in PET/CT. This study aims to evaluate the performance of IACT for different motion amplitudes. We used the digital four-dimensional (4-D) extended cardiac-torso phantom (XCAT) to simulate maximum of 2, 3, and 4 cm respiratory motions. The respiratory cycle was divided into 13 phases, with average activity and attenuation maps to represent $^{18}$ F-fluorodeoxyglucose ($^{18}$F-FDG) distributions with average respiratory motions and CACT, respectively. The end-inspiration, end-expiration, and midrespiratory phases of the XCAT attenuation maps represented three different helical CTs (i.e., HCT-1, HCT-5, and HCT-8). The IACTs were generated using: 1) 2 extreme + 11 interpolated phases (IACT$_{rm 2o}$ ); 2) 2 phases right after the extreme phases + 11 interpolated phases (IACT $_{rm 2s}$); 3) 4 original + 9 interpolated phases (IACT$_{rm 4o}$). A spherical lesion with a target-to-background ratio (TBR) of 4:1 and a diameter of 25 mm was placed in the base of right lung. The noise-free and noisy sinograms with attenuation modeling were generated and reconstructed with different noise-free and noisy AC maps (CACT, HCTs, and IACTs) by Software for Tomographic Image Reconstruction, respectively, using ordered subset expectation maximization(OS-EM) with up to 300 updates. Normalized mean-square error, mutual information (MI), TBR, image profile, and noi- e-contrast tradeoff were analyzed. The PET reconstructed images with AC using CACT showed least difference as compared to the original phantom, followed by IACT $_{rm 4o}$, IACT$_{rm 2o}$, IACT$_{rm 2s}$, HCT-5, HCT-8, and HCT-1. Significant artifacts were observed in the reconstructed images using HCTs for AC. The MI differences between IACT $_{rm 2o}$ and IACT$_{rm 4o}$ /CACT were <0.41% and <2.17%, respectively. With a slight misplacement of the two extreme phases, IACT$_{rm 2s}$ was still comparable to IACT $_{rm 2o}$ with MI difference of <2.23%. The IACT is a robust and accurate low-dose alternate to CACT.
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This paper presents the theory and implementation of an integrated sensing technique for the real-time measurement of applied actuation conditions in a micro-turbo-generator. The device is composed of a microturbine rotor with mag...
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This paper presents the theory and implementation of an integrated sensing technique for the real-time measurement of applied actuation conditions in a micro-turbo-generator. The device is composed of a microturbine rotor with magnetic components and a stator with planar coils for electromagnetic induction. While the rotor is actuated with pressurized nitrogen, the induced voltages are extracted to generate and deliver electrical power as well as to monitor the pneumatic actuation parameters. It is demonstrated that the rotor speed, applied gas flow rate, and pressure show repeatable high linearity with respect to voltage frequency and amplitude in different devices. Sensitivity values of 83 Hz/krpm, 140 Hz/slm, and 1428 Hz/psi together with $R^{2}$ values larger than 0.97 are achieved. The integrated sensing technique presented in this paper will eliminate the need for external sensing components in continuous device screening, and lead to closed-loop control for autonomous tuning of desired operating conditions in rotary microgenerators.
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This study presents a second-order sliding-mode control (2-SMC) scheme for a wind turbine-driven doubly fed induction generator (DFIG). The tasks of grid synchronisation and power control are undertaken by two different algorithms...
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This study presents a second-order sliding-mode control (2-SMC) scheme for a wind turbine-driven doubly fed induction generator (DFIG). The tasks of grid synchronisation and power control are undertaken by two different algorithms, designed to command the rotor-side converter at a fixed switching frequency. Effective tuning equations for the parameters of both controllers are derived. A procedure is also provided that guarantees bumpless transfer between the two controllers at the instant of connecting the DFIG to the grid. The resulting 2-SMC scheme is experimentally validated on a laboratory-scale 7 kW DFIG test bench. Experimental results evidence both the high dynamic performance and the superior robustness achieved with the proposed control scheme.
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This study presents statistical properties of the vehicle-to-vehicle Nakagami??Hoyt channel model with diffused line of sight (LOS) under isotropic condition. The envelope and phase probability density functions, spatial-time auto...
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This study presents statistical properties of the vehicle-to-vehicle Nakagami??Hoyt channel model with diffused line of sight (LOS) under isotropic condition. The envelope and phase probability density functions, spatial-time autocorrelation function, the power spectral density, level crossing rate, the average duration of fade, squared time autocorrelation function and mean-square error of time autocorrelation function of the Nakagami??Hoyt channel have been derived under the assumption that both the transmitter and receiver are mobile having omnidirectional antennas and a diffused LOS component is present. The model has been validated using the inverse fast Fourier transform-based simulator. The simulator and analytical results corroborate.
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