Siemens SINAMICS G150 Operating Instructions Manual page 439

To ensure that the drive does not stall during acceleration, p1611 can be increased or
acceleration pre-control for the speed controller can be used. This is also advisable to
ensure that the motor is not subject to thermal overload at low speeds.
If the moment of inertia of the drive is almost constant, acceleration precontrol using p1496
offers more advantages than the supplementary accelerating torque with p1611. For the
rotating measurement, the moment of inertia of the drive is determined using p1900 = 3 and
p1960 = 1.
Vector control without a speed sensor has the following characteristics at low frequencies:
● Closed-loop controlled operation for passive loads up to approx. 0 Hz output frequency
(p0500 = 2), for p1750.2 = 1 and p1750.3 = 1).
● Start an induction motor in the closed-loop controlled mode (after the motor has been
completely excited), if the speed setpoint before the ramp-function generator is greater
than p1755.
● Reversing without the need to change into the open-loop controlled mode is possible, if
the range of the changeover speed (p1755) is passed through in a shorter time than the
selected changeover delay time (p1758), and the speed setpoint in front of the ramp-
function generator lies outside the open-loop controlled speed range (p1755).
● In the closed-loop torque controlled mode, at low speeds, the system always switches
over into the open-loop controlled mode.
Note
Precondition
In this case, the speed setpoint upstream of the ramp-function generator must be greater
than the changeover speed in p1755.
Closed-loop operation up to approx. 0 Hz (settable via parameter p1755) and the ability to
start or reverse at 0 Hz directly in closed-loop operation (settable via parameter p1750)
result in the following benefits:
● No switchover operation required within closed-loop control (bumpless behavior, no
frequency dips, no discontinuities in the torque).
● Closed-loop speed control without encoder down to and including 0 Hz
● Passive loads down to a frequency of 0 Hz
● Steady-state closed-loop speed control down to approx. 0 Hz possible
● Higher dynamic performance when compared to open-loop controlled operation
Note
Automatic changeover
If, in the closed-loop controlled mode, start from 0 Hz or reversing takes longer than 2 s, or
the time set in p1758 - then the system automatically changes over from closed-loop
controlled into open-loop controlled operation.
Converter cabinet units
Operating Instructions, 07/2016, A5E03347396A
Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without encoder
439