Brushless Doubly-Fed Induction Generator has attractive features to be the first choice in next generation of wind generators. However, its efficiency and power-to-weight ratio are slightly lower in comparison to induction machine with the same rating. Considerable part of these imperfections arises from the rotor design, which produces magnetic field with considerable undesirable spatial harmonics. This paper proposes a novel rotor configuration to reduce spatial harmonic distortion of air-gap magnetic field as well as improving some drawbacks of the conventional structure, including unequal magnitudes of rotor bar currents, teeth saturation at low average air gap magnetic fields, high core loss and inefficient magnetic material utilization. The rotor loops are connected in series in the new scheme rather than nested arrangement of the conventional design. Furthermore, the Imperialist Competitive Algorithm is used for optimising the conductor distributions in order to improve spatial distribution of the rotor magneto-motive force. The rotor current is evaluated in each iterative step using electric equivalent circuit. The analytical procedure of determining the circuit parameters is modified for the case of series loops. Effectiveness of the novel configuration is verified by comparing the results of optimised and conventional designs in several experimental and simulation studies.

The brushless doubly-fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. The aim of this work is to present a nodal-based magnetic equivalent circuit (MEC) model of the BDFIG which provides performance characteristics and flux density distributions. The model takes into account stator winding distributions, special configuration of rotor bars, slotting effects, teeth saturation, flux fringing and current displacement effects. The real flux tubes are considered for creating an MEC network and calculating its non-linear elements. A method for simplifying the rotor magnetic network has been applied and Gauss elimination with partial pivoting approach is used to solve the equation system with sparse coefficient matrix. The model parameters are based solely on geometrical data and thus it is an appropriate tool for population-based design studies instead of computationally intense analysis of the finite element method. The steady-state results of the proposed model are verified experimentally. The comparisons demonstrate the effectiveness of the proposed model especially when the core is magnetically saturated.

Linear induction machines are widely used in transportation systems due to their many advantages. Design and prototyping of electric machines are an expensive and timeconsuming process; hardware-in-the-loop simulation provides an efficient alternative. In this paper, a field-programmable gate array-based real-time digital emulation of single-sided linear induction motor with the drive system is proposed. Implementation of the model is performed in both fixed-point using Xilinx system generator and floating-point number representations using a handwritten VHSIC Hardware Description Language code. Then, an evaluation in terms of real-time stepsize and accuracy as well as hardware resource utilization is provided. The whole design was fully paralleled, which resulted in a considerable reduction of model execution time. The minimum time step of 2.3 and 0.8 µs was achieved for floating-point and fixed-point implementations, respectively. The results of the realtime simulation are verified by the experimental results as well as a 2-D finite-element simulation in JMAG software.

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Finite-element method (FEM) based hardwarein-the-loop emulation provides the most accurate and fast prototype platform for real-time design and testing of electric machines in a nondestructive environment. The application of transmission line modeling (TLM) can expeditiously reduce the FEM execution time by decoupling the nonlinear elements of the FEM equivalent network using transmission lines to keep the stiffness matrix unchanged through the simulation for static cases. However, in electric machines the TLM method suffers from the change of stiffness matrix in the time-stepped procedure due to movement. Furthermore, time consumption for the solution of numerous decoupled nonlinear equations for a fairly large number of TLM iterations in comparison with the conventional Newton-Raphson method remains a challenge. This paper proposes a novel real-time TLM method based on finite precalculated lower and upper triangular decompositions and field programmable gate array hardware implementation to exploit TLM parallelism for real-time simulation of magnetodynamics in electric machines. A two-dimensional FEM simulation of a single-sided linear induction machine is emulated in hardware and the results are validated experimentally and with Jmag-Designer software to show the effectiveness of the proposed method.