1,721,007 research outputs found
Validation of a faulted rotor induction machine model with an insightful geometrical interpretation of physical quantities
No full textMany proposals about induction-machine broken-bar detection can be found in the literature. Disturbances that affect phase currents, current space vector, power, fluxes, torque, and speed have been utilized to diagnose mains-supplied machines. Nevertheless, there is still disagreement about how the fault signatures of the different variables correlate with the actual fault and how they depend on the operating conditions. This paper presents a simple but effective analytical representation of induction machines with rotor faults, based on a synchronous reference frame and on Steinmetz's phasors. The developed relationships can be visualized through equivalent circuits, feedback loop block diagrams, or geometrical loci, allowing a deep understanding of the underlying physical phenomena, particularly as functions of inertia and of the machine parameters. The insight thus gained helps to enhance the quantification of fault severity with respect to the usual diagnostic technique based on the sum of the sidebands, clearly defining for the first time the field of validity of such technique. The analytical results are verified through simulations and experiments. © 1982-2012 IEEE
Effect of passing clouds on the dynamic performance of a CSP tower receiver with molten salt heat storage
No full textThe present paper explores the off-design performance of a CSP tower receiver due to the passage of clouds over the solar field. A quasi steady-state performance model is considered in the first part of the paper, accounting for the optical performance of the solar field and receiver only, yielding the expected incoming heat flux distribution on the aperture plane of the receiver and without further considerations about the thermal performance of the receiver itself. The twofold aim of this analysis is to identify the type of cloud that brings about the worst operating conditions of the receiver and to define an aiming strategy that produces the most homogeneous distribution of the incoming heat flux, this being a indirect metric of reduced thermal stress on this component. It is observed that larger clouds have a more negative impact on the heat flux distribution whereas the effect of smaller clouds is easily compensated for by other uncovered areas of the field. Large differences in performance arise when considering different aiming strategies, what leads to the selection of one of these as the optimum one given that it manages to evenly distribute the heat flux over the receiver surface. This limits the number and intensity of hot spots without affecting the overall power production. The optimum strategy is based on pointing the heliostats towards different aiming spots strategically located on the receiver surface, depending on the distance between tower and heliostat. The second part of the paper presents an in-house code developed to study the transient thermal performance of the receiver. The outcome of this second analysis confirms the results of the previous optical study: the selected optimum strategy leads to a 1% higher efficiency of the receiver. Also, the temperature distribution of the larger shadows is more harmful than when several smaller clouds pass over the solar field, both for the larger temperature gradients in the receiver and for the production of molten salts. This is also confirmed in the last part of the paper where different patterns of combined cloud passages are explored in regards to the charge/discharge process of the thermal energy storage system
Severity Assessment of Rotor Faults in Closed Loop Induction Drives by Different Approaches
No full textIn this paper different procedures are validated to diagnose and assess the severity degree of rotor faults in closed loop controlled induction machines. The possible diagnostic indexes are investigated through spectral analysis of manipulated and controlled variables. Common control schemes have been considered to evaluate the diagnostic robustness towards operating condition and regulator parameters.
Voltage injection was considered as well as a possible tool for diagnostics by analyzing the amplitude of spectral lines arising in motor input current spectrum.
Experimental results guide the selection of suitable analytical models for the faulty machine. The experiments are obtained with a DSP based Current Controlled Voltage Source Inverter (CCVSI) supplying a 1.5 kW induction machine in which three different rotors differing in asymmetry degree were used
Current-Controlled Shape Memory Alloy Actuators for Automotive Tumble Flap
No full textMechatronics devices are becoming a mandatory option in the automotive framework, as high integration and low weight are common requirements for most applications. To this aim non-electric drives are being investigated. An attractive option is the use of Shape Memory Alloy (SMA) actuation technology that allows achieving a very high power/weight ratio for light and small actuators. Feasibility studies were made to show the potential of SMA as actuators.
This paper proposes the application of a SMA actuator for automotive tumble flaps. A critical comparison between traditional and SMA actuators is presented, and the attention is focused on the power converter used to “drive” the SMA. Experiments were made on a prototype realized for angular control of tumble flaps of an air intake manifold for internal combustion engines that allows achieving better gas combustion and higher performances. The proposed control scheme includes a current feedback that allows a sensorless control position for the tumble shaft
Design and Control of a High-density High-voltage Smart Converter for Food Ohmic Heating
No full textThe design of an innovative converter for ohmic heating of fluid foods is presented. Application-specific requirements are addressed with new solutions and verified on a commercial-size 60 kW prototype. A multi-output high-voltage (0.8 to 4 kV) transformer with automatic tap change enriches a basic H-bridge topology, enabling processing of a wide set of foods and allowing grounding one of the outputs. High power density is achieved by power switches Pareto optimization in the reliability-efficiency objectives and by pushing the switching frequency up to 30 kHz, solving the electrode corrosion problem, too. Reproducible and reliable operation is assured by three different control strategies: load variability is dealt with a high-dynamics power control, repeatable output is guaranteed by input voltage compensation, optimal working point is ensured by control of the transformer primary current DC component. This last control allows also removing the output capacitors, improving density metrics with respect to the state-of-the-art. Analytical models for all control strategies are given to support dynamic performance tuning while guaranteeing stability
Monitoring of Induction Motors Rotor Faults by non Invasive Sensors
No full textThe features of stator currents and core vibration signals are investigated in order to improve the MCSA diagnostic procedure to detect rotor faults in induction machines. In fact the usual procedure based on the sideband components near the fundamental one may fail for the presence of inter-bar currents that reduce the amplitudes of these components. On the other hand the inter-bar currents modify the core vibration; therefore the analysis of both line currents and core vibration signals may increase the effectiveness of the diagnostic procedure
Estimation of Diagonal Volterra Kernels of an Audio System During Normal Operation with Multiple Least Mean Squares Adaptive Filters
No full textThe usage of Complete Volterra Kernels for emulating the nonlinear behavior of sound systems has been investigated for decades. Due to the computational load, the real-time implementation is typically limited to second order distortion and not feasible for higher orders. This is usually unsatisfactory for audio systems in which the disturbing distortions occur mostly at orders three and five. The same authors of this work already solved the problem with the Diagonal Volterra Kernels technique, which allowed to model arbitrarily high distortion orders. The estimation of the coefficients was obtained by exciting the system with an Exponential Sine Sweep signal. However, the result was often suboptimal since the signal reproduced by the sound system is usually different from a sinusoid. In this paper, a new method for estimating the Diagonal Volterra Kernels coefficients is proposed, by employing any music, noise or speech signal being played by a sound system in real-time. Multiple Least Mean Square algorithms are used to estimate the coefficients up to the 5 th distortion order, thus allowing to emulate the nonlinearities of a typical audio system
A New Method to Discern Mechanical Unbalances from Rotor Faults in Induction Machines
No full textIntensive researches have been spent with the aim of separating load torque unbalance and rotor faults effects in induction machines by devoted diagnostic procedures. Recently, current space vector active and reactive components due to these troubles are considered for their different relevance in correspondence of the two events: the torque unbalance seems to affect more the active component than the reactive one, vice versa the rotor faults.
In this paper it is shown that the space vector components amplitude and their phase displacement must be considered, being the latter the main parameter: if the active component leads or lags the reactive one by less than π/2 a rotor fault is present, otherwise a torque unbalance is present. Regarding the components amplitude, it depends, overall, besides on trouble severity, on the operating conditions and on the combined rotor-load inertia
Low-cost Sensorless BLDC for Organic Fluids Treatment in Sterile Environments
No full textThis paper presents the design and realization of a brushless DC motor-based gear pump for the treatment of organic fluids in sterile environments. Details of the FEM simulations used throughout the mechanical and electromagnetic design of the electrical machine and of the sensorless control algorithm, implemented on a motion control-oriented fixed point DSP, are reported.
Construction and experimental testing of a prototype are reported as well. The realized pump features a very compact design and a fairly efficient operation
- …
