Siemens SINAMICS G130 Engineering Manual page 58

Fundamental Principles and System Description
Engineering Information
Longer dips of more than 50 ms can only be handled reliably if the energy flow from the supply to the DC link is
maintained or if favorable boundary conditions are given in the case of multi-motor drives.
With the line-commutated, unregulated Infeeds, Basic Infeed and Smart Infeed, this is only the case if the supply
voltage dips not lower than on values of approx. 75 % of the nominal supply voltage V
external auxiliary supply, 50 % of all typical supply voltage dips can be dealt with (range A), with an external auxiliary
supply, this increases to 70 % (ranges A and B).
With the self-commutated, regulated Infeed, SINAMICS Active Infeed, the energy flow from the supply to the DC link
is maintained even if the supply voltage dips to around 50 % of the nominal supply voltage (ranges A and B). Without
an external auxiliary supply, 50 % of all typical supply voltage dips can be dealt with as in the case with unregulated
Infeeds (range A). With an external auxiliary supply, however, this increases to almost 100 % (ranges A and B). Thus
the regulated SINAMICS Active Infeed offers clear advantages in comparison with the unregulated Basic and Smart
Infeed for supplies which often experience relatively large voltage dips.
Measures for the reduction of the effects of large and long supply voltage dips
Kinetic Buffering
Longer supply voltage dips of more than 50 ms and larger than 50 % of the nominal supply voltage V
to range F can, due to the more or less interrupted energy flow from the supply to the DC link, be bridged without a
fault trip only if the motor can provide energy to buffer the DC link. This is the case at drives with sufficiently large
rotating masses. In such cases, the kinetic buffering function can be used. This function is included as a standard in
the firmware of SINAMICS converters and inverters and can be activated by parametrization when required. During a
supply voltage dip, the kinetic buffering function takes energy from the rotating masses for the buffering of the DC link
and thus prevents a fault trip. After the supply voltage dip the rotating masses are accelerated again. This procedure
can be used if sufficiently large rotating masses are available in order to buffer the supply voltage dip for a long
enough time period and if the driven process can tolerate a reversal in the direction of energy flow during the supply
voltage dip. With sufficiently large rotating masses, very large supply voltage dips and even supply voltage failures
which last for several seconds can be bridged without a fault trip of the drive.
Automatic Re-Start in combination with Flying-Restart
With deep and prolonged supply voltage dips within range F or with prolonged power outages, a fault trip is
unavoidable. This trip can be accepted in many applications, as long as the drive is able to re-start again by its own
after the voltage dip or voltage failure and as long as the drive is able to accelerate again to the original operating
condition. For this, the automatic re-start function can be used. If a re-start after a supply voltage dip is expected with
a rotating motor, the automatic re-start function must be combined with the flying re-start function.
The flying restart function detects the direction of rotation and the speed of the motor and accelerates the motor from
its current speed. The acceleration process can be started on condition that
- the motor is almost fully de-magnetized,
- the current speed has been detected (in encoderless operation), and
- the motor has been magnetized again.
The following diagram shows the typical flying restart sequence for an asynchronous (induction) motor operating
without an encoder.
Flying restart of an encoderless asynchronous motor
Since the de-magnetizing time for small motors (< 100 kW) is a few seconds, and for large motors (> 1 MW) up to 20
seconds, very fast flying restart of large motors cannot be achieved unless additional measures are taken.
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(ranges A and B). Without an
N
corresponding
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