An analytical approach is developed to predict the inverter high frequency pulse width modulation (PWM) switching caused eddy-current losses in a permanent magnet brushless dc motor. The model uses polar coordinates to take curvature effects into account, and is also capable of including the space harmonic effect of the stator magnetic field and the stator lamination effect on the losses. The model was applied to an existing motor design and was verified with the finite element method. Good agreement was achieved between the two approaches. Hence, the model is expected to be very helpful in predicting PWM switching losses in permanent magnet machine design.Index Terms-Eddy-current loss, permanent magnet brushless dc motors, pulse width modulation switching, space harmonics.
With the aim of considering the problem of excess fuel cold energy and excessive power consumption of refrigerated containers on large LNG-powered container ships, a new utilisation method using LNG-fuelled cold energy to cool refrigerated containers in cargo holds is proposed in this study, and the main structure of the cold storage in the method is modelled in three dimensions. Then, combined with the different conditions, 15 different combination schemes of high temperature cold storage and low temperature cold storage are designed to utilise the cold energy of LNG fuel, the exergy efficiency and cold energy utilisation rate calculation model of the system is established. The simulation tool ‘Aspen HYSYS’ is used to simulate and calculate the exergy efficiency and cold energy utilisation rate of the system under 15 combinations, verifying the feasibility of the scheme. According to the characteristics of such a ship’s cross-seasonal navigation routes and the number of refrigerated containers loaded in different ports, the combination schemes of the number of low-temperature cold storage and high-temperature cold storage are selected. Thus, the average exergy efficiency and cold energy utilisation rate of the whole line is obtained, which proves that LNG-powered container ships could effectively utilise the cold energy of LNG. By calculating the total electric energy consumed by refrigerated containers on the whole sailing route, before and after the adoption of the LNG cold energy method, it is found that the adoption of this new method can promote the realisation of energy saving and emission reduction of ships.
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