7,595 research outputs found
Mid-term outcome of reductive Kay annuloplasty of the tricuspid valve in association with mitral valve surgery.
No full textMid-term outcome of reductive Kay annuloplasty of the tricuspid valve in association with mitral valve surgery.. In INTERACTIVE CARDIOVASCULAR AND THORACIC SURGERY
Nardi, P; Pellegrino, A; Nicolò, F; Zeitani, J; Grego, S; Polisca, P; Scafuri, A; Chiariello, L
Design Tradeoffs Between Constant Power Speed Range,Uncontrolled Generator Operation and Rated Current of IPM MotorDrives
No full textA closed-form approximate formulation is proposed to establish a relationship between the uncontrolled generator operation of IPM motors at high speed and the constant power speed range and drive current capabilities. High saliency IPM motors of the PM-assisted synchronous reluctance type are mainly considered in the analysis, since they are proved to have the most favorable ratio between flux weakening capability and uncontrolled generator voltage. The results of the analysis show the tight relationship between the uncontrolled overvoltage and the constant power speed range of the drive. Moreover, where the uncontrolled voltage is higher, the relationship between the constant power speed range and the motor current amplitude becomes stiffer: for small current variations a large reduction of the speed range can occur. The analysis is validated experimentally on two motors of very different size (500 W and 1 MW
Performance comparison between Surface Mounted and Interior PM motor drives for Electric Vehicle application
No full textElectric Vehicles make use of permanent magnet synchronous traction motors for their high torque density and efficiency. A comparison between interior permanent magnet (IPM) and surface mounted permanent magnet (SPM) motors is carried out, in terms of performance at given inverter ratings. The results of the analysis, based on a simplified analytical model and confirmed by FE analysis, show that the two motors have similar rated power but that the SPM motor has barely no overload capability, independently of the available inverter current. Moreover the loss behavior of the two motors is rather different in the various operating ranges with the SPM one better at low speed due to short end connections but penalized at high speed by the need of a significant de-excitation current. The analysis is validated through finite-element simulation of two actual motor design
Position estimation delays in signal injection-based sensorless PMSM drives
No full textThe causes of position estimation delays and their effects on the sensorless control of permanent magnet synchronous motor drives are investigated. The position of a permanent magnet synchronous machine is estimated via the injection of high frequency voltage signals. The delays under investigation are due to the digital implementation of the control algorithm and to the digital filters adopted for decoupling the inspection signals from the fundamental components of the stator current measures. If not correctly modeled and compensated, such delays can reduce the performance of the control scheme. Experimental results are provided, proving the accuracy of the modeling approach and the effectiveness of the related compensation strateg
Position-sensorless control of permanent-magnet-assisted synchronous reluctance motor
No full textThe sensorless control of permanent-magnet-assisted synchronous reluctance (PMASR) motors is investigated, in order to conjugate the advantages of the sensorless control with full exploitation of the allowed operating area, for a given inverter. An additional pulsating flux is injected in the d-axis direction at low and zero speed, while it is dropped out, at large speed, to save voltage and additional loss. A flux-observer-based control scheme is used, which includes an accurate knowledge of the motor magnetic behavior. This leads, in general, to good robustness against load variations, by counteracting the magnetic cross saturation effect. Moreover, it allows an easy and effective correspondence between the wanted torque and flux and the set values of the chosen control variables, that is d-axis flux and q-axis current. Experimental verification of the proposed method is given, both steady-state and dynamic performance are outlined. A prototype PMASR motor will be used to this aim, as part of a purposely assembled prototype drive, for light traction application (electric scooter
Accurate Inverter Error Compensation and Related Self-Commissioning Scheme in Sensorless Induction Motor Drives
No full textThis paper presents a technique for accurately identifying and compensating the inverter nonlinear voltage errors that deteriorate the performance of sensorless field-oriented controlled drives at low speed. The inverter model is more accurate than the standard signum-based models that are common in the literature, and the self-identification method is based on the feedback signal of the closed-loop flux observer in dc current steady-state conditions. The inverter model can be identified directly by the digital controller at the drive startup with no extra measures other than the motor phase currents and dc-link voltage. After the commissioning session, the compensation does not require to be tuned furthermore and is robust against temperature detuning. The experimental results, presented here for a rotor-flux-oriented SFOC IM drive for home appliances, demonstrate the feasibility of the proposed solution
Asymmetric synthesis and absolute configuration of 3-aminosubstituted isothiazole S-oxides
No full textTaking into account the importance in medicinal- and agro-chemistry of optically active isothiazole
derivatives, we became interested in the asymmetric preparation of 3-aminosubstituted isothiazole 1-oxides [1]. A solution of 1 in CH2Cl2 with an equimolecular amount of (-)-2b was irradiated at 400W, 80°C.
Sulfoxide 3 was produced in 80% overall yield and 50% ee together with little amount of sulfone (8%) after 1h. (-)-2a gave much slower reactions.
In order to determine the absolute configuration (AC) of the new 3-aminosubstituted isothiazole Soxides,
we simulated [2,3] the ECD spectrum of (+)-3-aminomethyl isothiazole S-oxide, (+)-3b in the range 380-200 nm, both in the gas phase and ethanol at the TDDFT/B3LYP/aug-cc-pVDZ level of calculation. To this end we used (S)-3b which exists almost as a single conformer at the DFT/B3LYP/6-31G* level of calculation.
In Figure are reported the experimental (black line) ECD spectrum of (+)-3b and predicted ECD spectra of (S)-3b, taking into account the first 30 excited states both in the gas phase and ethanol. In the gas phase (green line), even if the positions and intensities of predicted ECD bands do not perfectly match the experimental data, the experimental spectrum shows a sequence of negative, positive, negative Cotton effects which is reproduced in the theoretical spectrum, indicating the (+)/(S) correlation. Including the ethanol effect (red line), significantly improves the agreement between calculated and experimental data, strongly supporting the (+)/(S) configurational correlation. We can conclude that (+)-3b possesses (S) AC and therefore the chiral auxiliaries (-)- 2b induces the preferential formation of the (S) antipode in the above asymmetric oxidation reaction.
1. Clerici, F.; Gelmi, M. L.; Pellegrino, S.; Pocar, D. “Chemistry of biologically active isothiazoles”, in Topics in Heterocyclic Chemistry, 9 (Bioactive Heterocycles III), 2007, 179-264. Publisher: Springer GmbH, 2. Frisch, M.J. et al., Gaussian 03; Gaussian, Inc.: Pittsburgh, PA, USA, 2003, http://www.gaussian.com/.
3. see, for instance: Tartaglia, S.; Padula, D.; Scafato, P.; Chiummiento, L.; Rosini, C.
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