Simulation of electrical machines, circuits and control systems using finite element method and system simulator

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Doctoral thesis (monograph)
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TKK dissertations, 2
The aim of this study is to provide a combined simulation environment capable of modelling and analyzing the interaction between electrical machines and controlled converters. For that purpose, two indirect methods are presented for coupling the magnetic field computation of electrical machines with the simulation of circuits and control systems. The methods are implemented for the system simulator SIMULINK as functional blocks, which solve the field and circuit equations relating to the electrical machine and allow coupling with arbitrary models of circuits and control systems. The presented methods are referred to as the current output approach and circuit parameter approach, respectively. In the current output approach, the coupling is carried out by the phase currents, which are solved together with the magnetic field by the finite element method (FEM) using the supply voltages as input. In the circuit parameter approach, the electrical machine is characterized by the electromotive force, dynamic inductance and resistance, which are solved by FEM at each time step. Both the approaches allow the use of different time steps for the finite element analysis and the simulation of circuits and control systems. The methods are evaluated by several examples relating to wound-rotor induction machines, cage induction machines, passive circuit elements, frequency converters and closed-loop control systems. In the simulation of electrical machines and passive circuits, both methods provide results that are relatively accurate but not as reliable as those that can be obtained by direct coupling. In the simulation of controlled frequency converters, the performance of the current output approach is excellent, but the circuit parameter approach is not suitable for such simulation. As a conclusion of the results, an optimal simulation environment is proposed for simulating electrical machines, circuits and control systems. In such an environment, the magnetic field and circuit equations are coupled directly in a FEM-circuit simulator, and the control systems are modelled in a system simulator with an indirect coupling to the FEM-circuit simulator.
electrical machines, finite element method, coupled problems, system simulators, control systems
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