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ABSTRACT: This paper proposes a saturation compensation strategy for single phase grid-connected power converters based on line frequency transformer. High power quality operations requires the direct control of injected grid current providing zero steady-state error at grid frequency. A zero steady-state error at grid frequency can be obtained by a control in a synchronous reference frame that ensures an infinite open loop gain at fundamental frequency and a superior disturbance rejection. However, the direct control of grid current is archived providing that transformer core saturation is avoided. Since the transformer blocks out the DC components the feedback loop closed on the transformer output current can lead to core saturation. This paper presents a compensation strategy based only on the monitoring of the output current distortion around voltage zero crossings. The proposed solution is free from offset problems, since no DC measurement is required. Experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation.
Electrical Machines (ICEM), 2010 XIX International Conference on; 10/2010
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ABSTRACT: Mechanical imbalances and bearing faults account for a large majority of the faults in a machine, particularly for small-medium size machines. Therefore, their diagnosis is an intensively investigated field of research. Recently, many research activities were focused on the diagnosis of bearing faults by current signals. This paper compares the bearing fault detection capability obtained with the vibration and current signals. The paper contribution is the use of a simple and effective signal processing technique for both current and vibration signals, and a theoretical analysis of the physical link between faults, modeled as a torque disturbance, and current components. The focus of the paper is on the theoretical development of the correlation between torque disturbances and the amplitude of the current components, together with a review of fault models used in the literature. Another contribution is the re-creation of realistic incipient faults and their experimental validation. Radial effects are visible only in case of large failures that result in air-gap variations. Experiments are reported that confirm the proposed approach.
IEEE Transactions on Industry Applications 09/2010; · 1.66 Impact Factor
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ABSTRACT: This article proposes a new control scheme for a distributed cogeneration (microcogeneration) plant using three-phase induction machine as an electric generator. This control scheme assures a better energy-conversion quality. The plant can be operated as a grid-connected generator with load tracking or as an isolated generator. In isolated operation, the induction generator is excited with a current-controlled voltage source inverter (CCVSI) having a suitable capacitive bank the DC side. During grid-connected operations, the same converter can be used for power factor correction.
IEEE Industry Applications Magazine 01/2010; · 0.64 Impact Factor
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ABSTRACT: This paper compares the available technologies for linear electromagnetic alternators and categorizes them in order to find the best solutions for the thermoacoustic based CHCP. Tubular oscillating permanent magnet actuator featuring SMC stator with a quasi-Halbach PM slider is analyzed and modeled theoretically. Here, a similar configuration is compared to other moving magnet structure but employing open modular construction with laminated magnetic steel winding cores and a critical comparison is made relying on electromagnetic and mechanical simulations to retrieve the best solution for the thermoacoustic application.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: In grid connected power converters both from renewable or traditional energy sources a line frequency transformer is usually employed in order to suppress the DC component. Recently, solutions based on a high frequency transformer or without transformer, usually referred as transformerless, are being investigated in order to reduce size, weight and costs. As a consequence, unless a suitable remedy is adopted, a DC component, that might overcome limits forced by international standards, may appear. This paper proposes a simple and cheap solution to reduce the DC current component injected into the grid in case of a full-bridge, single phase, transformerless converter. The proposed strategy is intrinsically insensitive to offset measurement errors and can be utilized as a robust and dynamic offset compensator for the Hall effect sensor mostly used as current transducer. Experimental results, performed for different current values and for different current control architectures, show the effectiveness of the proposed solution.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: This paper investigates diagnostic techniques for electrical machines with special reference to induction machines and to papers published in the last ten years. A comprehensive list of references is reported and examined, and research activities classified into four main topics: 1) electrical faults; 2) mechanical faults; 3) signal processing for analysis and monitoring; and 4) artificial intelligence and decision-making techniques.
IEEE Transactions on Industrial Electronics 01/2009; · 5.16 Impact Factor
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ABSTRACT: Early diagnosis of faults in induction machines is an extensively investigated field, for cost and maintenance savings. Mechanical imbalances and bearing faults account for a large majority of faults in a machine, especially for small-medium size machines. Therefore their diagnosis is an intensively investigated field or research. Recently many research activities were focused on the diagnosis of bearing faults by current signal. Stator current components are generated at predictable frequencies related to the electrical supply and mechanical frequencies of bearing faults. However their detection is not always reliable, since the amplitude of fault signatures in the current signal is very low. This paper compares the bearing fault detection capability obtained with vibration and current signals. To this aim a testbed is realized that allows to test vibration and current signal on a machine with healthy or faulty bearings. Signal processing techniques for both cases are reviewed and compared in order to show which procedure is best suited to the different type of bearing faults. The paper contribution is the use of a simple and effective signal processing technique for both current and vibration signals, and a theoretical analysis of the physical link between faults and current components including torque ripple effects. As expected because of the different nature of vibration and current, bearing fault diagnosis is effective only for those fault whose mechanical frequency rate is quite low. Experiments are reported that confirm the proposed approach.
Industry Applications Society Annual Meeting, 2008. IAS '08. IEEE; 11/2008
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ABSTRACT: Trigeneration stands for the combined production of electricity, heat, and cooling (CHCP). This paper reviews and compares CHCP system based on solar energy with respect to traditional CHCP ones. A further comparison is made among the possible technologies for solar CHCP to assess the technical solutions more suited to residential applications. Beyond photovoltaic based systems, two other solutions are proposed: a concentrated sunlight all-thermoacoustic system and an hybrid thermo-photovoltaic system. In a grid-connected energy market, the adoption of CHCP plants may become profitable with respect to traditional systems, where the single energies are produced or purchased separately. Specifically, the onset of solar trigeneration can lead to a substantial improvement, overcoming many of the traditional drawback associated with micro-cogeneration and trigeneration. The result is a trigeneration system based totally on renewable energy. This is especially attractive for the residential demand, provided that a cost-effective technical solution is available.
Industry Applications Society Annual Meeting, 2008. IAS '08. IEEE; 11/2008
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ABSTRACT: This paper proposes a high performance control in a d-q reference frame for a single-phase grid connected converter. The proposed control allows to obtain easily an infinite control loop gain at fundamental frequency and a superior disturbance rejection: this assures only active current injection thus maximum conversion efficiency and decreases current distortion. The control has been implemented in a single-stage converter for single-phase PV systems. The converter is a standard full-bridge three-level voltage source inverter that delivers a sinusoidal current to the grid through an inductive filter and a line frequency isolation transformer. The transformer blocks out the DC components injected in the grid but the current feedback, closed around the output of the transformer, can lead to core saturation. To avoid saturation a compensation strategy has been developed relying on output current distortion in correspondence of voltage zero crossings. Simulation and experimental results confirm the effectiveness of the proposed control architecture and of the strategy adopted to avoid transformer core saturation.
Industry Applications Society Annual Meeting, 2008. IAS '08. IEEE; 11/2008
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ABSTRACT: This paper describes a simple dc-dc step-up converter topology for switch-mode dc power supplies. The proposed configuration is well suited for high-power applications with battery supply. In the automotive framework, the push-pull architecture is the most widespread. However, as power increases, the use of a full-bridge architecture is mandatory. This paper presents a full-bridge architecture where the traditional single-phase transformer is replaced by a three-phase transformer. A prototype was realized and tested for the power supply of automotive devices. In this environment, one of the most important requirements is the ability to provide a burst of power during short-duration events, together with high-efficiency and high-quality output voltage. The latter constraints can be achieved by only using closed-loop switch-mode dc-dc converters at high switching frequency, thus reducing converter efficiency and creating electromagnetic-compatibility (EMC) problems. In this paper, the aforementioned issues were tackled relying on an open-loop topology. Open-loop converters are feasible if the output resistance of the converter is as low as possible, and a possible solution is the minimization of power losses. The solution is the use of a three-phase transformer with a delta-wye connection within a full-bridge converter topology. The configuration will be referred to as 3boost power supply. The three-phase transformer replaces the common single-phase transformer, and it is driven by a three-phase full-bridge inverter operating in six-step modulation. At secondary, a three-phase full wave diode rectifier is used to obtain the output dc voltage level. Therefore, a unitary transformer utilization factor is achieved. A simple theoretical comparison between the three types of converters-push-pull, conventional full bridge, and 3boost is shown. A low-power version of the converter was realized. Experiments confirm that this topology allows to achieve a high efficiency, a low-
er ripple factor, and a good EMC behavior.
IEEE Transactions on Industrial Electronics 02/2008; · 5.16 Impact Factor
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ABSTRACT: This paper describes the realization of a high-performance drive based on stepping motors, with a specific reference to the optimal choice of pulsewidth modulation. An original modulation technique is proposed that allows, in conjunction with current feedback, to achieve high performances together with a reduced current ripple. A prototype digital signal processor-based drive was realized for a small-size stepping motor.
IEEE Transactions on Industrial Electronics 01/2008; · 5.16 Impact Factor
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ABSTRACT: Motor current signature analysis (MCSA) is a method usually adopted to detect troubles in induction machines. However misunderstandings can be found about the mechanisms linking the anomalies to the current spectrum components. To improve the comprehension of these mechanisms a rotor flux observer to compute field current and torque current is proposed. Input currents and voltages and mechanical speed are the signals taken into account for the computation. The effects of mechanical unbalance and of mixed eccentricity and then the effect of a rotor asymmetry are considered. For the experiments a machine presenting an intrinsic rotor asymmetry and an intrinsic mixed eccentricity is utilized. A mechanical unbalance and an artificial increment of mixed eccentricity are introduced. The peculiarities of the considered variables due to the different troubles and their dependence on machine load are evidenced.
Diagnostics for Electric Machines, Power Electronics and Drives, 2007. SDEMPED 2007. IEEE International Symposium on; 10/2007
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ABSTRACT: Textile applications require peculiar specifications in terms of accuracy and speed from drives. In this paper a high dynamic control for a linear drive was realized. A vector control for a magnetic disc stepper motor was realized that allows huge linear acceleration and accurate speed control.
Electric Machines & Drives Conference, 2007. IEMDC '07. IEEE International; 06/2007
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ABSTRACT: This paper deals with different procedures that can be applied to diagnose the severity degree of rotor faults in closed loop controlled induction machines. A solution based on field oriented control (FOC) was investigated in order to validate the robustness of the diagnostic procedures towards the regulator parameters. Different diagnostic procedures were investigated, that rely on different diagnostic indexes. Specifically a few electric quantities are considered as possible fault alert signals: the spectral analysis of manipulated and controlled variables, the voltage homopolar components (voltage zero sequence), and the spectral analysis of motor input current due to a high frequency voltage injection. It turns out that the last quantity is a simple and effective index able to detect and quantify the fault severity degree. The procedures based on the above mentioned quantities are validated by experiments made with a DSP based current controlled voltage source inverter (CCVSI) supplying an induction machine with three rotors in different health conditions.
Electric Machines & Drives Conference, 2007. IEMDC '07. IEEE International; 06/2007
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ABSTRACT: The MCSA diagnostic procedures for the rotor diagnosis of induction machines are mostly based on the sideband lines near the supply frequency line that appear in the input current spectrum. The left component (1-2s)f is the effect of rotor backward rotating field caused by the cage rotor asymmetry and it varies with the asymmetry degree and with the rotor current, i.e. with the machine load. The right component (1+2s)f is caused by the speed ripple created by the left component, being the combined machine-load inertia the main parameter that spreads the asymmetry effect into the two sideband components. Theoretically it can be shown that the sum of the two components is not affected by the speed ripple effect and therefore this sum may be used as an effective diagnostic index to state rotor conditions. The above results can be experimentally validated only once a suitable test set-up is realized that allows changing the inertia value. To this aim a test bed was designed so that the virtual inertia of the mechanical system can be chosen by the user. This allows to prove the theoretical claims and to obtain a thorough understanding about the effect of inertia on sideband components, improving the performance of rotor condition monitoring techniques
IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference on; 12/2006
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ABSTRACT: Mechatronics 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
IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference on; 12/2006
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ABSTRACT: Multi-variable monitoring systems for on-line monitoring of induction motors allow larger versatility and robustness. In case of rotor faults, the diagnostic procedure based on sideband current components 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. In this paper the features of stator currents and core vibration signals are investigated in order to achieve an accurate and reliable diagnostic system. Moreover stray flux signals are considered to explore the possibility of obtaining further information
IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference on; 12/2006
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ABSTRACT: This paper deals with the control of a distributed cogeneration (micro-cogeneration) plant using a three-phase induction machine as electric generator. The plant can be operated as a grid connected generator with load tracking or as isolated generator. In isolated operation the induction generator is excited with a current controlled voltage source inverter (CCVSI) with a suitable capacitive bank in the DC side. During grid connected operation the same converter can be used for power factor correction. The control scheme relies on air-gap flux field oriented control based on ADMC401 DSP. A better energy conversion quality is achieved thanks to the control of the exciting current component. This allows to obtain higher efficiency, higher control dynamic and a very robust behaviour in case of transient variation of the prime mover speed
Industry Applications Conference, 2006. 41st IAS Annual Meeting. Conference Record of the 2006 IEEE; 11/2006
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ABSTRACT: The knowledge of induction motor rotor quantities is essential to precisely define the machine energy efficiency and it is useful for the implementation of diagnostic techniques. This paper aims at investigating rotor quantities measured on an actual device and computed by a model reproducing the machine. Results were compared and discussed
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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ABSTRACT: Several techniques were presented in the literature in order to perform accurate tracking of frequencies for different purposes. Most of them are modified versions of the traditional discrete Fourier transform (DFT) or other spectrum-estimation techniques. This paper presents a procedure based on the statistical analysis of the current signal in the time domain, referred to as maximum covariance method for frequency tracking (MCMFT), which allows to obtain high-frequency resolution independent of the sampling frequency and of the time acquisition period. Owing to the proposed procedure, the spectrum lines related to supply frequency or to rotor-slotting frequency for an induction machine can be detected with extreme accuracy within a wide range of sampled data conditions. Then, an accurate slip computation, or speed estimation, for sensorless control or distribution network diagnosis can be performed. Comparisons between previously existing methods and the proposed one are reported, in order to critically analyze its performances. Two different-sized induction machines were used for the experiments.
IEEE Transactions on Industry Applications 02/2006; · 1.66 Impact Factor
