252 research outputs found
Incipient Fault Diagnosis in Ultrareliable Electrical Machines
No full textEarly detection of incipient faults in ac drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. In low power motors, the insulation degradation is principally due to the steep voltage variations caused by the voltage source converters that drive the machines. In the last years, with the coming to market of new no-Si based power devices, which achieve great values of dv/dt, fast tracking of electrical fault has became a topic of primary importance. In this paper, a new method to detect the presence of incipient faults in ultrareliable electric machines is presented and compared with a previous solution. The different methods were extensively evaluated by means of experimental results. It is shown that potential winding faults can be detected at an early stage of fault inception and thus measures can be taken to limit propagation
Self-commissioning of interior permanent magnet synchronous motor drives with high-frequency current injection
No full textThe knowledge of electrical and mechanical parameters of high-performance electromechanical drive systems is of paramount importance for designing high-performance controllers and/or developing accurate simulation models. By high-performance control is meant least torque (position) ripple for torque (position) control. Machine parameters are typically load and temperature dependent. This makes their estimation a challenging task. In this paper, a simple and robust method for parameter estimation at rotor standstill is presented. The estimated parameters are stator resistance through dc test, dq inductances using high-frequency injection and permanent magnet flux by means of a closed-loop speed control maintaining rotor stationary. The proposed method does not require either locking the rotor or additional/special power supplies. The validity of the suggested method has been verified by implementation on Interior Permanent Magnet Synchronous Motors (IPMSMs). Finally, the estimated parameters have been compared against results obtained through finite element simulations and with machine magnetic characterization, separately performed, to validate the method's effectiveness. Saturation and cross-saturation effects are taken care of through amplitude modulation and cross-axis current application, respectivel
On Torque Improvement by Current Harmonic Injection in Isotropic and Anisotropic Multi-Phase Machines
No full textMulti-phase machines give the possibility to increase the torque injecting and controlling current harmonics of different orders. This work investigates the current harmonic injection techniques for both isotropic and anisotropic machines. The proposed analysis shows that for anisotropic machines, both amplitudes and angles of the optimal current injection should not be predicted based on the BEMFs only. An analytical model is used to assess the differences in terms of no load and load voltage spectra. Considering these differences, a current injection technique based on the harmonic content of the voltage waveforms is proposed. In addition, the analysis to determine the optimum amplitudes and angles to maximise the torque capability is carried out by means FEA and compared with the techniques based on the analytical model. The FEA are carried out for both Surface Permanent Magnet (SPM) and V-shape Interior Permanent Magnet (IPM) machines with dual three-phase winding layouts, and injecting the fifth harmonic of current. Finally, the proposed concept is validated via experimental test on a dual three-phase V-Shape IPM machine. The results show that current harmonic injection based on the voltage vectors is applicable for both isotropic and anisotropic machines with good accuracy
Squirrel Cage Induction Motor: A Design-Based Comparison between Aluminium and Copper Cages
No full textIn many industrial applications the self-starting capability of electric motors is still an important requirement enabling to simplify the drive architecture and increase the system's reliability. The efficiency improvement of this motor topology has been targeted by various national and international regulatory authorities with ad-hoc policies. Indeed, a lower energy consumption leads to the twofold benefits of reducing the operational costs and the emissions. The adoption of a copper cage has been successfully proven to reduce the motor losses. However, this could affect other performance indexes, such as the starting torque. In this paper, the advantages and drawbacks of adopting a copper cage are analysed in depth by comparing the motors performance at different operating conditions, with respect to the more common aluminium cage. Starting from a set of induction machines optimized with an aluminium cage, the effect of the direct material cage substitution is analysed both in terms of electromagnetic and thermal aspects. The overall performance are also compared against machines specifically optimized with a copper cage. With the presented performance comparison exercise, general design guidelines are outlined aimed at improving the efficiency without deteriorating other performance metrics
Multistress Characterization of Fault Mechanisms in Aerospace Electric Actuators
No full textThe concept behind the more electric aircraft is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical, and bleed air/pneumatic systems, and pursue efficiency, reliability, and maintainability. This paper presents a specialized test rig whose main objective is to assess insulation lifespan modeling under various stress conditions, especially investigating the interaction between ageing factors. The test setup is able to reproduce a multitude of environmental and operational conditions at which electric drives and motors, used in aerospace applications, are subjected. It is thus possible to tailor the test cycle in order to mimic the working cycle of an electrical motor during real operation in aircraft application. The developed test-rig is aimed at projecting the technology readiness to higher levels of maturity in the context of electrical motors and drives for aerospace applications. Its other objective is to validate and support the development of a comprehensive insulation degradation model
Magnetic Equivalent Circuit Modelling of Synchronous Machines
No full textDesign of electric machines constitutes a complex and nonlinear problem where the primary design tool is mainly the finite element method (FEM) in the absence of an accurate and easy to implement analytical technique. Although the accuracy of the FEM is high, its adoption within multi-objective optimization is hindered by the high computational burden. The latter is further exacerbated when more than one operating point needs to be optimized as in traction applications. This paper presents a highly accurate and computationally efficient magnetic equivalent circuit (MEC) model which can be used to design electric machines. MEC model is derived in a general fashion so that any machine can be freely defined with minor geometrical discrepancy. The flux paths are identified based on bi-directional reluctance cells considering material non-linearity. Once solved, it is then possible to obtain all electromagnetic performance indexes such as flux linkages, torque and torque ripple. Accuracy of the MEC model is verified using FEM, showing good agreement between results but obtained in a fraction of time (circa 12 to 20 times faster). The presented modeling approach is then used to perform a sensitivity study focusing on the effects of the discretization and so the trade-off with the computational time
Response to Discussion of “A modular speed-drooped system for high reliability integrated modular motor drives”
No full textThe authors appreciate the interest shown in our paper. In the paper under discussion [1], a distributed speed control strategy suitable for multi-three-phase machines with enhanced power sharing capability is presented. The focus of the manuscript is on the power sharing transient controllability achieved by using a sharing regulator based on the droop controller, which was introduced for the first time by Fingas and Lehn [2]. In [1], the authors added the outermost loop in charge of restoring the drooped output speed. The overall control strategy and the design procedure of each loop - current, sharing, and speed - is presented and validated by means of experimental results. Two off-the-shelf three-phase induction machines coupled on the same shaft and controlled by a custom inverter were loaded by a third off-the-shelf three- phase induction machine
Rotor Slot Design of Squirrel Cage Induction Motors with Improved Rated Efficiency and Starting Capability
No full textAmong the electro-mechanical devices transforming energy from electrical to mechanical, the squirrel cage induction motor can be surely considered a workhorse of the industry due to its robustness, low cost and good performance when directly fed by the a.c. grid. Being the most influencing motor topology in terms of energy consumption, optimizing the efficiency of squirrel cage induction motors could lead to a great impact towards the reduction of the human environmental footprint. The induction motor design aided by finite element analysis presents significant challenges because an accurate performance prediction requires a considerable computational burden. This paper makes use of an innovative fast and accurate performance evaluation method embedded into an automatic design procedure to optimize different rotor slot geometries. After introducing the performance estimation approach, its advantages and limits are discussed comparing its prediction with the experimental tests carried out on an off-the-shelf induction motor. Different rotor cage structures with increasing geometrical complexity are then optimized in terms of starting and rated performance adopting the same design optimization process, the same stator geometry and constituent materials. The analysis of the optimal solutions shows how it is possible to improve the rated efficiency without compromising other performance indexes. The presented results can be used as general design guidelines of squirrel cage induction motors for industrial applications
Performance improvement of bearingless multi-sector PMSM with optimal robust position control
No full textBearingless machines are relatively new devices that consent to suspend and spin the rotor at the same time. They commonly rely on two independent sets of three-phase windings to achieve a decoupled torque and suspension force control. Instead, the winding structure of the proposed multi-sector permanent magnet (MSPM) bearingless machine permits to combine the force and torque generation in the same three-phase winding. In this paper the theoretical principles for the torque and suspension force generation are described and a reference current calculation strategy is provided. Then, a robust optimal position controller is synthesized. A Multiple Resonant Controller (MRC) is then integrated in the control scheme in order to suppress the position oscillations due to different periodic force disturbances and enhance the levitation performance. The Linear-Quadratic Regulator (LQR) combined with the Linear Matrix Inequalities (LMI) theory have been used to obtain the optimal controller gains that guarantee a good system robustness. Simulation and experimental results will be presented to validate the proposed position controller with a prototype bearingless MSPM machine
Modeling, analysis and design optimization of a permanent magnet assisted synchronous reluctance machine
No full textABSTRACT
This Master Thesis deals with the electromagnetic and thermal performance of a permanent magnet assisted synchronous reluctance machine for traction application, carrying out a comparison between two windings configuration and between two technics for torque ripple reduction.
In the first chapter, an excursus about the kinds of electrical machines and their application areas is presented.
In the second chapter, the mathematical model and the main features of an IPM motor are presented. The capability curves and the circle diagram are introduced to better describe the IPM performances; at the end the concept of the interaction between the model parameters and the saturation effects and cross saturation in a real machine are shown. In addition a brief introduction to FEM analysis is presented.
In the third chapter, the electro-magnetic performance of the reference machine are presented.
In the fourth chapter a preliminary comparison between toroidal windings configuration and distributed windings configuration in terms of electromagnetic performance is presented. At the chapter end an efficiency comparison for different motor dimensions is presented.
In the fifth chapter, the thermal problem for electrical machine is introduced and the main heat removal equations are presented. The equivalent lumped parameters thermal circuits for each windings topology are modeled with the purpose to continue the comparison in terms of thermal performance defining the toroidal winding advantages and drawbacks for different motor dimensions.
In the sixth chapter, two reduction technics of ripple torque are introduced. The purpose is find a way that permit to reduce the torque ripple without worsen the performance. Fractional slot windings and a new rotor design are introduced and FEM analysis provide and validate the torque ripple results
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