CST – Computer Simulation Technology

Permanent Magnet DC Machine Simulation

The construction and simulation of a permanent magnet DC motor using CST EM STUDIO® (CST EMS) is demonstrated. CST EMS offers an extremely user-friendly interface with powerful CAD and parameterization features. Non-linear materials are taken into account in the magnetostatic simulations. Figure 1 shows the components of the motor which were all constructed in CST EMS. A Visual Basic for Applications (VBA) macro was developed to allow any rotor configuration to be automatically generated based on standard design parameters.

Figure 1: Constituent components of the PM DC motor

The stator iron was a hollow cylinder, a primitive shape in CST EMS with the non-linear iron material characteristics. The permanent magnets are segments of radially magnetized ferrites. The rotor is also based on a cylinder primitive which has the shaft and slots cut away. The double-layer winding was created as a 3D polygon for which the coordinates were provided as a text file. The commutator does not have to be modeled. Different current distributions are correctly taken into account by rotating the rotor. The complete geometry is shown in Figure 2....

Figure 2: Rotor geometry showing the complex winding arrangement

Two typical modes of operation can be modeled:

  1. Simulation of zero-load operation: non-linear, magnetostatic simulation, no current through the windings, magnetic field generated by the permanent magnet. Simulation results, magnetic flux density (magnitude in the air gap; check of the saturation of the stator yoke and the rotor teeth).
  2. Simulation of load operation: non-linear magnetostatic simulation, nominal current through the windings, load angle applied by rotating the rotor iron and the coils. Simulation results: check of demagnetization of the ferrites due to the armature reaction.

Figure 3 shows the tetrahedral mesh used for the simulation.

Figure 3: Tetrahedral mesh view

Figure 4 shows the flux density in both contour and vector forms on a user-defined cut-plane for the load operation case. Other quantities may be derived from the magnetic field quantities via post-processing templates in conjunction with parameterization.

Figure 4: Contour and vector plots of the magnetic flux density on a cut-plane through the motor for load operation

Features which are an extremely powerful aid for the setup and simulation of permanent magnet motors include:

  • • tetrahedral meshing
  • • a non-linear, magnetostatic solver
  • • parameterization of the geometry (the CST EMS model is embedded in a design procedure)
  • • parameterization of the rotor angle and the armature current to allow the computation of different operating points
  • • loading of 3D polygons from file to create complicated winding models

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