Local Demagnetization Detection in Six-Phase Permanent Magnet Synchronous Machines

The partial demagnetization process in surface-mounted permanent-magnet synchronous motors (SMPMSMs) negatively affects the performance of an electric drive, reducing the rated torque and the efficiency of the machine. This article presents a comprehensive analysis of the rotor demagnetization caused by an overcurrent event for a six-phase SMPMSM. Multiphase drives may become a key solution for safety-critical applications because they allow one to increase the intrinsic reliability of electric systems and monitor the health state of electric motors and power converters. This article proposes a diagnostic algorithm for the online detection of rotor demagnetization faults that also considers the magnetization direction of the magnets. The effects of the parallel or radial magnetization of the rotor magnets are analyzed for multiphase machines. The technique quantifies the demagnetization degree to estimate the fault severity and corrects the angular position of the encoder to ensure maximum motor performance under postfault conditions. Experimental tests have been carried out on two identical six-phase PMSMs differing only in the size of the rotor magnets to emulate the effect of trailing-edge demagnetization. The experimental results confirm the effectiveness and robustness of the proposed solution

Fault-Tolerant Torque Control Based on Common and Differential Mode Modeling for Multi-Three-Phase Induction Machines

Among the multiphase solutions, multi-three-phase drives are experiencing significant industrial development since they can be configured as multiple three-phase units operating in parallel. The literature reports several control approaches to perform the torque regulation of multi-three-phase machines. Most of such solutions use the vector space decomposition (VSD) approach since it allows the control of a multi-three-phase machine using the conventional control schemes of three-phase drives, reducing the complexity of the control algorithm. However, this advantage is practically lost in the case of open-three-phase faults. Indeed, the post-fault operation of the VSD-based drive schemes requires the implementation of additional control modules, often specifically designed for the machine under consideration. Therefore, this paper aims at proposing a novel control approach that allows using any control scheme developed for three-phase motors to perform the torque regulation of a multi-three-phase machine both in healthy and faulty operation. In this way, the previously mentioned drawbacks of the VSD-based control schemes in dealing with the machine's faulty operation are avoided. Moreover, the simplicity of the control algorithm is always preserved regardless of the machine operating condition. The proposed solution has been experimentally validated through a 12-phase induction motor, rated 10 kW at 6000 r/min, which uses a quadruple-three-phase configuration of the stator winding

Fault-Tolerant Torque Controller Based on Adaptive Decoupled Multi-Stator Modeling for Multi-Three-Phase Induction Motor Drives

Among the multiphase solutions, multi-three-phase drives are becoming more and more widespread in practice as they can be modularly supplied by conventional three-phase inverters. The literature reports several control approaches to perform the torque regulation of multi-three-phase machines. Most of such solutions use the vector space decomposition (VSD) approach since it allows the control of a multi-three-phase machine using the conventional control schemes of three-phase drives, thus reducing the complexity of the control algorithm. However, this advantage is practically lost in the case of open-three-phase faults. Indeed, the postfault operation of the VSD-based drive schemes requires the implementation of additional control modules, often specifically designed for the machine under consideration. Therefore, this article aims to propose a novel control approach that allows using any control scheme developed for three-phase motors to perform the torque regulation of a multi-three-phase machine both in healthy and faulty operation. In this way, the previously mentioned drawbacks of the VSD-based control schemes in dealing with the faulty operation of the machine are avoided. Moreover, the simplicity of the control algorithm is always preserved, regardless of the machine's operating condition. The proposed solution has been experimentally validated through a 12-phase induction motor, rated 10 kW at 6000 r/min, using a quadruple-three-phase configuration of the stator winding

A Simple Braking Method for Six-phase Induction Motor Drives with Unidirectional Power Flow in the Base-speed Region

Induction motor drives supplied from diode front-end rectifiers are commonly used in industrial applications due to their low cost and reliability. However, the two-quadrant operation of such a topology makes the regenerative braking impossible. Braking resistors can be used to dissipate the braking power and provide enhanced braking capability, but additional hardware is then necessary. Alternatively, the braking power can be dissipated within the inverter/motor by control software reconfiguration. In this scenario, the additional degrees of freedom of multiphase drives can be used to increase the system losses without disturbing the flux and torque production. Experimental results confirm the possibility to enhance the braking capability of six-phase drives with only few changes in the control scheme

Frost maintains forests and grasslands as alternate states in a montane tropical forest–grassland mosaic; but alien tree invasion and warming can disrupt this balance

1. Forest–grassland mosaics, with abrupt boundaries between the two vegetation types, occur across the globe. Fire and herbivory are widely considered primary drivers that maintain these mosaics by limiting tree establishment in grasslands, while edaphic factors and frosts are generally considered to be secondary factors that reinforce these effects. However, the relative importance of these drivers likely varies across systems. In particular, although frost is known to occur in many montane tropical mosaics, experimental evidence for its role as a driving factor is limited. 2. We used replicated in situ transplant and warming experiments to examine the role of microclimate (frost and freezing temperatures) and soil in influencing germination and seedling survival of both native forest trees and alien invasive Acacia trees in grasslands of a tropical montane forest–grassland mosaic in the Western Ghats of southern India. 3. Seed germination of both native and alien tree species was higher in grasslands regardless of soil type, indicating that germination was not the limiting stage to tree establishment. However, irrespective of soil type, native seedlings in grasslands incurred high mortality following winter frosts and freezing temperatures relative to native seedlings in adjoining forests where freezing temperatures did not occur. Seedling survival through the tropical winter was thus a primary limitation to native tree establishment in grasslands. In contrast, alien Acacia seedlings in grasslands incurred much lower levels of winter mortality. Experimental night‐time warming in grasslands significantly enhanced over‐winter survival of all tree seedlings, but increases were much greater for alien Acacia than for native tree seedlings. 4. Synthesis. Our results provide evidence for a primary role for frost and freezing temperatures in limiting tree establishment in grasslands of this tropical montane forest–grassland mosaic. Future increases in temperature are likely to release trees from this limitation and favour tree expansion into grasslands, with rates of expansion of non‐native Acacia likely to be much greater than that of native trees. We suggest that studies of frost limitation to plant establishment are needed across a range of tropical ecosystems to re‐evaluate the general importance of frost as a driver of vegetation transitions in the tropics

Detection and classification of turn fault and high-resistance connection fault in inverter-fed permanent magnet machines based on high-frequency signals

Winding turn fault and high-resistance connection (HRC) fault will lead to different consequences and require different mitigation actions. In this study, the differentiating features between a turn fault and HRC fault are analysed and compared in a three-phase surface-mounted permanent magnet machine fed by the inverter with pulse-width-modulation voltages. The resultant high-frequency components in both voltages and currents are utilised for the fault detection and classification based on the high-frequency impedance and ripple current, without requiring modifications to the machine or interface design. Extensive simulations show that this method is capable of fault detection and classification in both transient and steady-state operations

On Social Utility Payoffs in Games: A Methodological Comparison betwen Behavioural and Rational Game Theory

Are the recent findings of Behavioural Game Theory (BGT) on unselfish behaviours relevant for the progress of game theory? Is the methodology of BGT, centred around the attempt to study theoretically players\u2019 utility functions in the light of the feedback that experimental evidence can produce on the theory, a satisfactory one? Or is the creation of various types of \u2018social preferences\u2019 just wasteful tinkering? This article compares BGT with the methodology of Rational Game Theory (RGT). BGT is viewed as a more promising and constructive approach, with regard to the relationship between experimental data and theoretical modelling. However, I also argue that today RGT and BGT are closer to one another than often thought

Behavioral Economics Has Two 'Souls': Do They Both Depart from Economic Rationality?

In this paper, I argue that behavioral economics, far from being a monolithic theory, consists of two different \u2018souls\u2019 and that a fundamental asymmetry exists between them, with regard to the nature of the departures from the economics\u2019 \u2018canonical model\u2019 they focus on. While a first class of departures deals with the major cognitive limitations and systematic biases in decision-making affecting economic behavior, a second research area investigates deviations from the classic assumption that economic agents are systematically driven by the pursuit of material self-interest. Even though on methodological grounds the two research areas share a broadly inductive approach \u2013 as they both aim at incorporating the major results obtained through several empirical methods (in particular, via experimental work) into formal economic analysis \u2013, I claim that rather different methodological conclusions and regulatory and policy implications can be drawn, depending on the cognitive or social nature of the departures from the standard economic model under study