Maximum Attainable Output Voltage With Pulse-Edge Modulation Pem - Siemens SINAMICS G130 Engineering Manual

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 reality are lower. In practice, therefore, the
value for space vector modulation without overmodulation must be assumed to be as follows:
This value applies precisely to pulse frequencies of 2.0 kHz or 1.25 kHz according to the factory setting. At higher
pulse frequencies, it decreases by approximately 0.5 % per kHz.
1.1.2.3

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 (SVM) by
pulsing only at the edges of the fundamental-wave period rather than over the entire fundamental-wave period. 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:
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:
The pulse-edge modulation method uses optimized pulse patterns which cause only minor harmonic currents and
therefore utilize the connected motor very efficiently. Commercially available standard asynchronous motors for
50 Hz or 60 Hz operation utilized according to temperature class 130 (previously temperature class B) in operation
directly on line can be utilized according to temperature class 155 (previously temperature class F) when operated
with pulse-edge modulation at the nominal operating point up to rated torque.
Pulse-edge modulation is available as standard in vector control mode (drive object of vector type) on all SINAMICS
units described in this engineering manual:
·
SINAMICS G130 *
·
SINAMICS G150 *
·
SINAMICS S150 *
·
SINAMICS S120 *
·
SINAMICS S120 *
For SINAMICS G130 and G150 converters, the modulator mode (parameter p1802) is automatically preset to value 9
(pulse-edge modulation) since "Pumps and fans" is the default technological application (parameter p0500 = 1). This
is because SINAMICS G converters are predominantly deployed in conjunction with asynchronous motors without
Fundamental Principles and System Description
V
SVM max
6
= × =
V V
DCLink
rect
p
V
PEM max
)
Chassis
)
Cabinets
)
Cabinets
)
Motor Modules / Chassis format
)
Motor Modules / Cabinet Modules format
≈ 0.92 V
* Line
6
× × =
. 1 32 V . 1 03
Line
p
≈ 0.97 V
* Line
SINAMICS Engineering Manual – November 2015
Engineering Information
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Line
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