How to calculate the back emf (electromotive force)?


During the electrical machine design in MANATEE software, one may want to calculate the back emf (electromotive force). This calculation is also necessary when feeding the electrical machine in terms of voltage, as MANATEE electrical equivalent circuit are then used to calculate currents. Calculation of the bemf is not required when carrying current-driven vibroacoustic simulation.

The back emf can be calculated using three methods in MANATEE:

  1. user-defined value (fundamental)
  2. fast calculation using subdomain model
  3. calculation using FEMM

Once the waveform is calculated it can be visualized with the post processing plot_bemf.

GUI implementation

To be completed.

Scripting implementation

To enforce a fundamental value manually one must use

Input.Simu.type_comp_PhiPM = 0;  

The back electromative force calculation is then based on the Permanent Magnet fundamental RMS flux linkage input in Input.Electrical.PhiPM0s.

To calculate and store the flux linkage and resulting back emf using FEMM one must use

Input.Simu.type_comp_PhiPM = 1;  

If the flux linkage file of the machine has already been stored and is found by MANATEE it will be used automatically to avoid new calculations. The flux linkage waveform is stored in the Results folder of MANATEE, it contains the following data:

  • FreqPhiPMn,PhiPMn,PhasePhiPMn: cells containing the frequency, magnitude and phase of the flux linkage waveform for each phase of stator winding
  • Freq0PhiPM, PhiPM0,PhasePhiPM0: values of the fundamental frequency, magnitude and phase of phase A flux linkage
  • PhiPM: cells containing the flux linkage waveform in each phase
  • EPM: cell containg the back emf waveform in each phase
  • timePM, alphaPhiPM: time and angle vectors corresponding to PhiPM and EPM

If one wants to enforce the calculation in FEMM without loading existing flux linkage data this can be done with

Input.Simu.type_comp_PhiPM = 2;  

To load a specific flux linkage data file one stored in Input.Simu.filename_PhiPM one must set

Input.Simu.type_comp_PhiPM = 3;  

Finally, to use the subdomain model for back electromotive force calculation (recommended method for its speed and accuracy) one can set

Input.Simu.type_comp_PhiPM = 4;  

A specific discretization is defined for the calculation of flux linkage and back emf. The number of angular steps for the rotor rotation of 360/p (two pole pitches) is defined in Input.Simu.Na_PhiPM.