Open-Loop And Closed-Loop Control Modes; General Information About Speed Adjustment; V/F Control Modes - Siemens SINAMICS G130 Engineering Manual

1.1.4

Open-loop and closed-loop control modes

The standard firmware of the SINAMICS converters of type G130, G150, S120 and S150 described in this manual
offers a range of different open-loop and closed-loop control modes for three-phase motors:
·
V/f open-loop control modes for applications with simple control requirements
·
Field-oriented closed-loop control modes for applications which require highly precise and highly dynamic
control functionality
1.1.4.1

General information about speed adjustment

The steady-state speed/torque characteristic of an asynchronous motor can be shifted in converter-fed operation
through adjustment of the frequency and voltage, as illustrated in the diagram below. The speed/torque characteristic
in "bold" print represents the motor's characteristic when it is operating directly on the mains supply at rated
frequency f and rated voltage V
rated
Shifting the speed/torque characteristic of an asynchronous motor by adjusting frequency and voltage
As long as the voltage is adjusted in proportion to the frequency, the ratio between voltage and frequency remains
constant and thus also the magnetic flux, the available torque and the stalling torque of the motor. This is known as
the constant flux range or the base speed range.
If the frequency is increased further after the maximum possible output voltage of the converter has been reached,
the ratio between voltage and frequency decreases again and thus also the magnetic flux in the motor. This is known
as the field-weakening range. With asynchronous motors operating in the field weakening range, the available torque
M decreases in relation to the rated torque M
remains constant. The stalling torque in the field-weakening range M
torque M in the constant flux range in proportion to the ratio (f
k
1.1.4.2

V/f control modes

V/f control is a simple method of adjusting the speed of three-phase motors. V/f control is based on the principle of
varying the frequency in order to adjust the motor speed, while at the same time applying a voltage setpoint
according to the characteristic of the V/f curve selected in the firmware. The gating unit generates pulse patterns to
control the IGBTs in the three phases of the converter's power unit.
Fundamental Principles and System Description
.
rated
approximately in proportion to the ratio f
rated
SINAMICS Engineering Manual – November 2015
Engineering Information
decreases in relation to the stalling
k-reduced
2
/f) .
rated
/f. The output power
rated
27/528
Ó Siemens AG