Claudio Bianchini

Bearing Fault Model for Induction Motor With Externally Induced Vibration

This paper investigates the relationship between vibration and current in induction motors operated under external vibrations. Two approaches are usually available to define this relationship. The former is based on airgap variations, while the latter is based on torque perturbation. This paper is focused on the airgap variation model. The ball bearing fault is modeled by contact mechanics. External vibrations often occur in many industrial applications where externally induced vibrations of suitable amplitude cause cyclic radial loading on the machine shaft. The model is validated by experiments, owing to a dedicated test setup, where an external vibration source (shaker) was employed, together with ball bearing alterations in order to decrease the stiffness of the support along the radial direction. To maximize the effects of externally induced vibrations, the frequency chosen was near the flexural resonance of the rotor (determined by finite-element method analysis). The direction of the external vibration is radial with respect to the axis of the electric machine under test. During tests, both stator phase currents and vibration of the machine were sampled. The test setup allowed one to vary the machine speed and load, vibration amplitude, and bearing stiffness (damage level). Radial effects are usually visible only in the case of large failures that result in significant airgap variations, as confirmed by experiments.

Fault Detection of Linear Bearings in Brushless AC Linear Motors by Vibration Analysis

Electric linear motors are spreading in industrial automation because they allow for direct drive applications with very high dynamic performances, high reliability, and high flexibility in trajectory generation. The moving part of the motor is linked to the fixed part by means of linear bearings. As in many other electric machines, bearings represent one of the most vulnerable parts because they are prone to wear and contamination. In the case of linear roller bearings, this issue is even more critical as the rail cannot be easily fully enclosed and protected from environmental contamination, unlike the radial rotating bearing counterpart. This paper presents a diagnostic method based on vibration analysis to identify which signature is related to a specific fault.

Review of Design Solutions for Internal Permanent-Magnet Machines Cogging Torque Reduction

Internal permanent-magnet synchronous machines are spreading in industrial production. They feature high torque density and extended speed range that are key issues in many fields of applications, however their cogging torque is typically quite high. Many methods and design guidelines for cogging torque reduction exist in literature and this paper compares them. For this purpose, the different design guidelines are applied to a common reference machine in order to assess their effectiveness. Computer finite element analysis (FEA) are carried out for each case in order to compare the cogging torque reduction capability of the different techniques. The side effects of these techniques, such as back-EMF and rated torque profile distortions, will be taken into account. The paper contribution is to compare the various cogging torque reduction techniques and magnetic geometries on a common reference machine to identify the most effective ones.

Fault detection of a five-phase Permanent-Magnet machine

The paper focuses on the fault detection of a five-phase permanent-magnet (PM) machine. This machine has been designed for fault tolerant applications, and it is characterised by a mutual inductance equal to zero and a high self inductance, with the purpose to limit the short circuit current. The effects of a limited number of short-circuited turns were investigated by theoretical and finite element (FE) analysis, and then a procedure for fault detection has been proposed, focusing on the severity of the fault (i.e. the number of short-circuited turns and the related current).

Evaluation of Combined Reference Frame Transformation for Interturn Fault Detection in Permanent-Magnet Multiphase Machines

This paper focuses on modeling and experimental validation of a diagnostic fault classification procedure for interturn fault detection in permanent-magnet (PM) multiphase machines designed for fault-tolerant electric drives. The diagnostic procedure is based on the symmetrical component theory and relies upon the combined space vector vector D that gathers information from the two original space vectors obtained with different reference frames. The diagnostic index effectiveness and robustness were also investigated against other fault types such as rotor eccentricities and magnet damage to assess its discrimination capability. The proposed procedure was experimentally evaluated for the interturn fault case on a five-phase PM machine. Experiments were carried out at different speed and load levels, with increasing numbers of short-circuited turns. Both simulation and experimental results demonstrated the feasibility of the proposed diagnostic method.

Solar Trigeneration for Residential Applications, a Feasible Alternative to Traditional Micro-Cogeneration and Trigeneration Plants

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.

Active Rectifier With Integrated System Control for Microwind Power Systems

This paper presents simple and effective control strategies for the active rectifier stage (ac/dc stage) of a grid-connected low-power system for microwind applications employing permanent magnet synchronous generator (PMSG). In particular, a novel algorithm for the estimation of the rotor angle of the PMSG, based on flux estimators, was implemented using an adaptive low-pass filter coupled with a feed-forward compensator. This enabled a very smooth start-up operation of the PMSG, obtained by preloading the values of the flux estimator and using a single-voltage transformer (VT) transducer. The solution for the power flow control between the active rectifier and the other(s) power converters connected to the common dc link was implemented without any digital communication between them, in order to obtain a solution suitable for modular architectures (e.g., to be used in conjunction with a grid-connected converter and/or an energy storage system). Simulation and experimental results confirmed the effectiveness of the proposed solutions. The experimental validation was conducted using a grid-connected converter as load for the proposed active rectifier.

Arc Linear Motors for Direct Drive Robots: Galileo Sphere

This paper presents the design of an arc linear motor for a new type of robot, named Galileo Sphere, based on direct drive technology for pick and place operations. Pick and place robots require high dynamics and position accuracy and repeatability. A classical implementation is based on rotating electric machines with reduction gearboxes and kinematic mechanisms that convert the rotating motion to linear where necessary. The direct drive technology reduce mechanical losses, backlash, MTBF and a number of components. This technology also achieves higher dynamic and accuracy. The robot has a polar-like configuration with 5 degree of freedom. A dynamical simulator was used to assess motors, that satisfies a typical pick and place trajectory with the different payload. The proposed solution resulted feasible, even at high working frequencies and with payloads up to 4 kg. The precision and repeatability remained high, within 100 mum. The working is a spherical sector with 1870 mm maximum diameter, and 450 mm vertical reach.

Performance analysis of a modified Current Source Inverter for photovoltaic microinverter applications

This paper analyzes the performance of a grid-tied photovoltaic module integrated, transformerless, three-phase Current Source Inverter (CSI). The design exploits CSI inherent step-up capability to obtain a single stage power interfacing between the low voltage PV input and the high AC voltage output, to be fed into the distribution grid. A modified CSI converter topology is proposed along with a suitable PWM strategy and a simple closed loop control. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed in single-stage PV microinverter supplied by a single low voltage PV panel. The principle of operation and control is described, and the traditional CSI topology has been simulated numerically in Matlab/Simulink environment. Results obtained with the proposed topology are presented and evaluated in order to validate the theoretical assumptions.

CSI7: A Modified Three-Phase Current-Source Inverter for Modular Photovoltaic Applications

This paper analyzes the performance of a grid-tied, wide power range, transformerless, modified three-phase current-source inverter (CSI), named CSI7. The CSI7 topology is here analyzed along with a suitable space vector modulation strategy able to attenuate the excitation of the output CL filter. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed as a single-stage photovoltaic (PV) inverter, with a particular emphasis on injected grid current distortion and ground leakage current values. The inverter wide input range allows interfacing PV strings of different module count with a simple closed-loop control. The principle of operation and control is described; the viability of the CSI7 topology was assessed with simulations and extensive experiments on a full-size laboratory prototype.