Maximum Attainable Output Voltage With Space Vector Modulation Svm; Maximum Attainable Output Voltage With Pulse-Edge Modulation Pem - Siemens SINAMICS G130 Engineering Manual

Maximum attainable output voltage with space vector modulation SVM

Space vector modulation SVM generates pulse patterns which approximate an ideal sinusoidal motor voltage through
voltage pulses with constant amplitude and corresponding pulse-duty factor. The peak value of the maximum
(fundamental) voltage that can be attained in this way corresponds to the amplitude of the DC link voltage V
Thus the theoretical maximum motor voltage with space vector modulation which results is:
1
=
V
SVM max
2
The true amplitude of the DC link voltage V
of rectifiers of the type used with SINAMICS G130 and G150 and also with S120 Basic Line Modules, it averages
1,41 V with no load, 1.35
*
Line
≈ 1.32
amplitude of V
DCLink
is:
V = 0.935
SVM max *
As a result of voltage drops in the converter and minimum pulse times and interlock times in the gating unit
responsible for generating the IGBT gating pulse pattern, the values in practice are lower. In practice, the values are:
≈ 0.92
V V
SVM max
*
For SINAMICS G130 chassis and G150 cabinets that were supplied with firmware versions < V2.3 until the autumn of
2005, this value is the maximum attainable output voltage as devices with this firmware are not capable of utilizing
pulse-edge modulation.

Maximum attainable output voltage with pulse-edge modulation PEM

It is possible to increase the inverter output voltage above the values attained with space vector modulation by not
pulsing over the entire fundamental-wave period, but only at its edges. This process is referred to as pulse-edge
modulation (PEM). The basic waveform of the motor voltage is then as shown below.
Motor voltage with pulse-edge modulation PEM
The maximum possible output voltage is attained when clocking is performed with the fundamental frequency only,
i.e. when "pulsing" ceases altogether. The output voltage then consists of 120° rectangular blocks with the amplitude
of the DC link voltage. The fundamental frequency RMS value of the output voltage can then be calculated as:
6
= ⋅
V V
π
rect
So it is possible with pure rectangular modulation to achieve a motor voltage which is slightly higher than the line
voltage. However, the motor voltage then has an unsuitable harmonic spectrum which causes major stray losses in
the motor and utilizes the motor inefficiently. It is for this reason that pure square-wave modulation is not utilized on
SINAMICS converters.
The pulse-edge modulation method used on SINAMICS converters permits a maximum output voltage which is only
slightly lower than the line voltage, even when allowance is made for voltage drops in the converter:
V = 0.97 V
PEM max
*
The pulse-edge modulation process uses optimized pulse patterns which cause only minor harmonic currents and
therefore utilize the connected motor efficiently. Commercially available standard motors for 50 Hz or 60 Hz and
utilized according to temperature class B in mains operation can be partially utilized according to temperature class F
at the nominal working point up to rated torque when operated with pulse-edge modulation.
Fundamental Principles and System Description
⋅
V
DCLink
is determined by the method of line voltage rectification. In the case
DCLink
V with partial load and 1.32
*
Line
at full load
V , the motor voltage theoretically attainable with space vector modulation
* Line
V
Line
(with pulse frequency of 2.0 kHz or 1.25 kHz according to the factory setting)
Line
6
= ⋅ ⋅
. 1 32 V
DCLink Line
π
Line
V .with full load. Thus with the true DC link voltage
*
Line
= ⋅
. 1 03 V
Line
SINAMICS Engineering Manual - May 2008
Engineering Information
15/396
© Siemens AG
.
DCLink