This paper presents the exact transient solution to the unbalanced and balanced faults in the doubly-fed induction machine (DFIM). Stator currents, rotor currents, and stator fluxes have been validated using simulation and experiment. The work is meant to strengthen and fasten the predictability of large DFIMs in the design stage to comply with mechanical constraints or grid fault issues. Moreover, the analytical approach reduces the computational costs of large-scale stability studies and is especially suited to the initial phase, where a of plethora design computations must be carried out for the DFIM before it is checked for its transient interaction with the power system. The possibility to dynamically estimate the DFIM performance is simplified by original equations derived from first principles. First, case studies of two large 265 MVA DFIMs are used to verify the analytical approach, and to justify the proposed "large machine approximation" using simulation with an exact match. Finally, laboratory measurements were conducted on a 10.96 kVA and a 1.94 kVA DFIM to validate the transient current peaks predicted in the proposed analytic expressions for two-phase and three-phase faults, respectively.

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One of the attractive benefits of slotless machines is low losses at high speeds, which could be emphasized by a careful stator core loss assessment, potentially available already at the pre-design stage. Unfortunately, mainstream iron loss estimation methods are typically implemented in the finite element analysis (FEA) environment with a constant-coefficients dummy model, leading to weak extrapolations with huge errors. In this paper, an analytical method for iron loss prediction in the stator core of slotless PM machines is derived. It is based on the extension of the 2-D field solution over the entire machine geometry. Then, the analytical solution is combined with variable-or constantcoefficient loss models (i.e., VARCO or CCM), which can be efficiently computed by vectorized post-processing. VARCO loss models are shown to be preferred at a general level. Moreover, the paper proposes a lookup-table-based (LUT) solution as an alternative approach. The main contribution lies in the numerical link between the analytical field solution and the iron loss estimate, with the aid of a code implementation of the proposed methodology. First, the models are compared against a sufficiently dense dataset available from laminations manufacturer for validation purposes. Then, all the methods are compared for the slotless machine case. Finally, the models are applied to a real case study and validated experimentally.