User manual

Page 41
EA Elektro-Automatik GmbH
Helmholtzstr. 31-33 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
[e-mail]
PSI 9000 DT Series
3.2.2 Current regulation / constant current / current limiting
Current regulation is also known as current limiting or constant current mode (CC).
The DC output current is held constant by the power supply, once the output current to the load reaches the adjusted
limit.ThenthepowersupplyautomaticallyswitchesThecurrentowingfromthepowersupplyisdeterminedbythe
output voltage and the load’s true resistance. As long as the output current is lower than the adjusted current limit,
the device will be either in constant voltage or constant power mode. If, however, the power consumption reaches
the set maximum power value, the device will switch automatically to power limiting and sets the output current
according to I
MAX
= P
SET
/ U
IN
, even if the maximum current value is higher. The current set value, as determined
by the user, is always an upper limit only.
While the DC output is switched on and constant current mode is active, then the condition “CC mode active” will
be indicated on the graphic display by the abbreviation CC and this message will be passed as a signal to the
analog interface, as well stored as status which can also be read as a status message via digital interface.
3.2.3 Power regulation / constant power / power limiting
Power regulation, also known as power limiting or constant power (CP), keeps the
DCoutputpowerofapowersupplyconstantifthecurrentowingtotheloadin
relation to the output voltage and the resistance of load reaches the adjusted value
according to P = U * I resp. P = U² / R. The power limiting then regulates the output
current according to I = sqr(P / R), where R is the load’s resistance.
Power limiting operates according to the auto-range principle such that at lower
outputvoltageshighercurrentowsandviceversainordertomaintainconstant
power within the range P
N
(see diagram to the right).
While the DC output is switched on and constant power mode is active, then the
condition “CP mode active” will be shown on the graphic display by the abbrevia-
tion CP, as well stored as status which can also be read as a status message via
digital interface.
3.2.3.1 Power derating
Due to fusing and cross sections of conductors and the extended input voltage range, power supply models with
1500Wratedoutputpowerhaveaxedderating,whichbecomesactivebelowacertaininputvoltagelevel(for
value see „1.8.3. Specic technical data“). It then derates the maximum available output power down to approx.
1000 W. The derating only affects the power stage, so the full range for power set value adjustment remains,
though the device will not provide full output power anymore. In this situation, constant power operation can not
be indicated by status “CP”. Active derating can then only be detected by reading the actual values of voltage and
current and by calculating the power.
No status “CP” available if the adjusted power set value (Psel) is bigger than the derated actual
output power of the device. It means, derating is not signalled anywhere.
3.2.4 Internal resistance regulation
Internal resistance control (abbr. CR) of power supplies is the simulation of a virtual internal resistor which is in
series to the voltage source and thus also in series to the load. According to Ohm’s law, this causes a voltage
drop, which will result in a difference between adjusted output voltage and actual output voltage. This will work in
constant current mode as well as in constant power mode, but here the output voltage will differ even more from
the adjusted voltage, because then constant voltage is not active.
Theadjustableresistancerangeofaparticularmodelisgiveninthetechnicalspecications.Thevoltagesetting
in dependency of the resistance set value and the output current is done by calculation in a fast ARM controller,
beingonlyalittleslowerthanothercontrollersinsidethecontrolcircuit.Clarication:
U
Act
= U
Set
- I
Act
* R
Set
P
Set
, I
Set
P
Ri
= (U
Set
- U
Act
) * I
Act
With resistance mode being activated the function generator will be unavailable and the actual
power value provided by the device does not include the power dissipation of Ri.