Pole position identification (PPI) in case the motor shaft is blocked: Application hints for 'PPI at standstill'
Question:
i950, i700: What should be considered when using the 'PPI at standstill'?
Answer: The pole position identification mode 'PPI at standstill' allows the identification of the pole position of permanently excited synchronous motors (SM, PSM) whose motor shaft is locked. Unlike the other PPI modes, 'PPI at standstill' requires a locked motor shaft - the motor shaft should not move if possible. However, there are also motor types and motor versions for which the identification method cannot be used.
Lenze therefore recommends the following procedure to find out whether the 'PPI at standstill' is applicable to the existing synchronous motor type:
First carry out a reference measurement with the 'PPI-360°' mode on the load-free motor and freely rotating motor shaft. Identification of the polarity by PPI-360° is possible for all motor versions, if necessary with adjustments of the PLI parameters.
Then perform the 'PPI at standstill' several times on the motor with locked (blocked) motor shaft and compare the identified polling values with the reference value. If relatively large deviations (>> 15°) from the reference value occur, further measuring steps are required.
Then perform the 'PPI at standstill' several times at different electrical angular positions in the range 0...180°. To do this, turn the motor shaft mechanically and lock it again. See tip. The spread of the deviations from the reference value should be similarly large at different electrical angular positions. The PPI at standstill can then be used.
If there are clearly different scattering of the values, the reason could be that the measuring method does not hit the magnetic "operating point" of the synchronous motor. In this case, the i700 and i950 servo inverters offer the option of increasing the current amplitude of the measurement pulses in order to optimally hit the magnetic operating point of the motor. If the increased current amplitude results in equally large deviations from the reference value at different electrical angular positions, then the 'PPI at standstill' is applicable. However, if the scattering continues to vary significantly, it can be assumed that the 'PLI at standstill' cannot be used for the synchronous motor at hand.
Hint:
Relationship between the electrical and mechanical angle of rotation:
(mechanical angle of rotation) = (electrical angle of rotation) / number of pole pairs
Example: Synchronous motor (6-pole / number of pole pairs = 3):
0° to 180° electrically correspond to a mechanical rotation of the motor shaft by 60° = (180°/ 3)
