Modeling Electrical Drives

Electrical drives contain various components and techniques. The electrical machine is actually only one part of the model of the electrical drive. It is connected to a power converter on one side, the mechanical drive train on the other side. For some electrical machines, such as the PMSM, the output from its position sensor is connected to a control system. The overall control system mostly contains an inner and outer loop. The inner loop is for the control of the current in the machine or the commutation. The outer loop is for speed or position control. The control loop be analog, such as a PI control, or a digital control, modeled by a program written in a programming language like C.

The model of the electrical machine can be a basic equivalent circuit model or based on characteristics obtained by a FEM program. The equivalent models can be parameterised and are are described in this guide. The models that are based on characteristics from a FEM program are dependent on the type of characteristics calculated in the FEM analysis. Also a combination of both methods is possible, for example, the the inductance of an PMSM can be a constant parameter, while the emf is tabulated in a file calculated by a FEM program.

The power electronics can be modeled in detail using MOSFETs and a modulation principle, or by a simple controlled voltage source. In the following paragraphs we will use the various modeling methods and show how to combine the models into one multilevel model. For the modeled drives we will, where applicapable, model the power electronics, the mains, the electrical machine, filters, mechanical model and the control. Use will be made of the existing models that reside in the library.

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