Behzad Jandaghi’s research while affiliated with University of Alberta and other places

In electric machine drive systems, hardware-in-theloop (HIL) emulation provides accurate testing of actual control system prototypes and protection devices interfaced with the electric machine model on a real-time simulator in a nondestructive environment particularly when faults are studied. A compromise between the model accuracy and computational burden makes the magnetic equivalent circuit (MEC) model ideal for real-time simulation of electric machines. However, satisfying the timing constraints of real-time simulation to accommodate internal machine faults is still challenging due to the nonlinearity and movement of electric machines. In this paper, the transmission line modeling (TLM) method is utilized to keep the MEC coefficient matrix unchanged during nonlinear iterations. Afterwards, for the first time, the entire potential of the TLM method for pre-calculation is exploited by proposing an efficient matrix re-ordering combined with the left-looking Gilbert-Peierls algorithm to minimize the computational burden of the sparse MEC matrix LU decomposition required in each time-step due to movement. Furthermore, the massive hardware architecture of the field programmable gate array (FPGA) is used as the platform for implementation to fully exploit parallelism. With the proposed MEC-based real-time TLM (RT-TLM) method, the minimum time-step as low as 500 μs can be achieved and the results validation with 2-D finite element model (FEM) of the commercial Jmag-Designer® software shows the accuracy and efficiency of the proposed methodology.

Finite element method (FEM) based hardware-in- the-loop (HIL) emulation provides the most accurate and fast prototype platform for real-time design and testing of electric machines in a non-destructive 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 solution of numerous decoupled nonlinear equations for fairly large number of TLM iterations in comparison with the conventional Newton-Raphson (N-R) method remains a challenge. This paper proposes a novel real-time TLM (RT-TLM) method based on finite pre-calculated lower and upper (LU) triangular decompositions, and field programmable gate array (FPGA) hardware implementation to exploit TLM parallelism for real-time simulation of magnetodynamics in electric machines. A 2-D FEM simulation of a single-sided linear induction machine (SLIM) is emulated in hardware and the results are validated experimentally and with Jmag- Designer’ software to show the effectiveness of the proposed method.

A brushless doubly fed machine is equipped with two decoupled windings on its stator, known as the power winding and the control winding. The power winding reactive power can be controlled by voltage amplitude fed by the machine-side converter to the control winding, affecting both the converter size and machine efficiency. This paper investigates different proposed scenarios for optimal reactive power flow targeted to minimize the converter cost and maximize the machine efficiency. Previously, the grid-side converter has not been used for reactive power compensation. However, in the present paper it is shown how the grid-side converter can be effectively used to reduce the converter cost by controlling the flow of reactive power. The optimal power winding reactive powers for minimizing the converter cost and for maximizing the output power are not the same. Then the priority of minimizing converter cost over maximizing machine output power has been justified.

Finite element method (FEM) is widely used for accurate design and analysis of electric machines; however, it suffers from long execution time. In this paper, for the first time hardware acceleration of 2D FEM for a single-sided linear induction motor (SLIM) on the field programmable gate array (FPGA) is proposed. The nonlinearity of the iron core as well as the movement are taken into consideration. A new sparse solver is proposed based on left looking Gilbert-Peierls algorithm for the system of linear equations of FEM that need to be solved in different iterations and time steps. Implementation of the model is performed in a massively paralleled and deeply pipelined hardware architecture using VHDL coding with single precision floating-point number representation. The proposed emulation was performed at various time steps resulting in significant average speed-up of 9.73 times in comparison with JMAG-Designer® as a commercial finite element software, and the overall hardware latency of each time step for the emulation was 49.2ms in average with minimum achievable FPGA clock of 5.59ns.

Linear induction machines are widely used in transportation systems due to their many advantages. Design and prototyping of electric machines are an expensive and time-consuming 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 step-size 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 real-time simulation are verified by the experimental results as well as a 2-D finite-element simulation in JMAG software.

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.

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.

Brushless Doubly fed machines have two stator windings and an especial cage rotor. The main advantage of the machine is higher reliability in compare with DFIGs. Cross coupling is the mechanism, which provides indirect coupling of the two stator windings. In this paper, time and space harmonics in a BDFM are studied to find a criterion for evaluating different rotor designs and better cross coupling, based on the space harmonics. Then the equivalent space and time harmonic circuits are established, using basic equivalent circuit. Finally, the effects of these harmonics on the torque-speed characteristic are studied.

In this paper, an analytical method for increasing the steady state torque per ampere capability for BDFMs, using equivalent circuit is presented. In this approach, uni-current proposition proposed to define a unique current value for optimization, and find the current angel corresponding to maximum torque. The accuracy of the proposition is verified by simulation. The effect of pole pair number selection of power and control windings on maximum torque is explained by dividing torque expression into synchronous and asynchronous terms. Finally, the optimal current values and optimal torque are achieved. Based on the optimal value of torque, or MTPA index, analytical optimization of machine design is suggested, which can be performed by manipulation of components of the MTPA index