Siemens SINAMICS S120 - Page 176

Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
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Calculation example 3
A SINAMICS S150 converter in degree of protection IP20 is to be operated as a flywheel press drive on a 690 V
supply system at a maximum ambient temperature of 40 °C and at a maximum installation altitude of 1000 m. The
motor current I(t) (blue curve) and the motor frequency f(t) (red curve) over time are illustrated in diagram 1. The
flywheel is started up and accelerated to operating speed during phase T
1
. In steady-state press operation T
2
the
flywheel is braked and accelerated again periodically. At the end of the period of steady-state press operation, the
flywheel is decelerated and finally stopped during phase T
3
. The converter is to be operated at the factory-set pulse
frequency in vector control mode (vector-type drive object).
T
1
: Startup (acceleration) of the flywheel
T
2
: Steady-state, periodic press operation
T
3
: Stop (braking) of the flywheel
Diagram 1: Absolute value of motor current |I(t)| and motor frequency f(t)
1. Select the converter:
According to diagram 1, the converter must be capable of supplying a short-time current I
ShortTime
of 730 A. It therefore
requires a base load current I
H
of at least
I
ShortTime
/ 1.5 = 730 A / 1.5 = 487 A.
For this reason, a converter rated for V = 690 V and I
rated
= 575 A is selected which, according to catalog D 21.3, has
a base load current I
H
of 514 A and thus a short-time current I
ShortTime
of 1.5 * I
H
= 771 A. The factory-set pulse
frequency for vector control mode is 1.25 kHz.
We shall now use a calculation to determine whether the selected converter is suitable to operate as the press drive
on the factory-set pulse frequency under the conditions specified above.
2. Analyze the steady-state, periodic press operation during phase T
2
:
2.1. Determine the current derating factor k
D
during phase T
2
:
· k
Temp
: 1.0 (ambient temperature ≤ 40 °C, installation altitude < 1000 m, degree of protection IP20),
· k
Pulse
: 1.0 (factory-set pulse frequency)
· k
Parallel
: 1.0 (not a parallel connection of S120 Motor Modules)
· k
IGBT
: This factor must be taken into account owing to the periodic press operation during phase T
2
.
According to diagram 1, the following apply during phase T
2
:
- Current ratio ΔI = I
ShortTime
/ I
BaseLoad
= 400 A / 150 A = 2.67.
- Load duty cycle duration T = T
21
+ T
22
= 20 s.
With ΔI = 2.67 and T = 20 s, the derating factor is according to the derating characteristic 1 which is
applicable to the SINAMICS S150 converter with V = 690 V and I
rated
= 575 A: k
IGBT
= 0.96.
The current derating factor k
D
is therefore calculated as follows:
96.096.00.10.10.1 =×××=×××=
IGBTParallelPulseTempD
kkkkk .