Lenze i700 - Manual (Page 71)

Lenze · i700 servo inverter · Reference manual · DMS 1.5 EN · 03/2014 · TD05
71
5 Motor control & motor settings
5.7 Compensating for inverter influence on output voltage
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5.7 Compensating for inverter influence on output voltage
Functional description
An inverter generates a three-phase voltage system with pulse width modulation. Inherent to its
functional principle, the inverter also generates current-dependent and switching frequency-
dependent losses which influence the output voltage. The motor voltage actually provided at the
output terminals is not measured in order to compensate for deviations if need be. Instead, an
adjustment is made by means of the inverter characteristic to compensate for deviations.
Among other things, the inverter characteristic depends on the length of the motor cable and at
least has to be individually determined once for the connected motor by means of the device
command "Calculate inv. characteristic". For an automatic determination of the motor parameters,
this ensures that the current has a sinusoidal form.
Identification of the inverter characteristic - procedure
If no error is pending, the motor is energised during the procedure with a maximum DC current
corresponding to the lower of the two following values:
• Ideally, the first value should be reached, the second value is to ensure that the load on the
motor is not too high during this test.
• During the procedure, the motor current increases to the maximum value specified and falls
back to "0" to repeat the cycle with a negative current sign. Altogether, the maximum value is
reached four times.
• The switching frequency of the inverter is set to rated switching frequency and after the
procedure, it is reset to the original value.
• If the switching frequency should be changed later during operation, the characteristic will
automatically be adapted to the current switching frequency.

Note!
In the V/f characteristic control mode the procedure described below is recommended
because a well-adapted inverter characteristic leads to a significantly improved drive
behaviour during V/f operation.

Danger!
This procedure may only be carried out during commissioning, not during operation!
During the procedure the motor is energised so that:
• it cannot be excluded that the connected mechanical components may move!
• the windings heat up.
If you repeat the procedure, ensure that the motor is not thermally overloaded
(particularly if no temperature feedback is used).
or
2 Rated device current ⋅
2 1.8 Rated motor current ⋅ ⋅