User Manual

Page 37
EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
[e-mail]
PSB 9000 2.5 kW Series
3.3.4 Internal resistance regulation (source mode)
Internal resistance control (short: CR) of power supplies is the simulation of a virtual internal resistor which is in
seriestotheload.AccordingtoOhm’slaw,thisresistancecausesavoltagedrop,whichwillresultinadi󰀨erence
between the adjusted output voltage and the actual output voltage. This will also work in CC or CP mode whereas
theactualoutputvoltagewilldi󰀨erevenmorefromtheadjustedvoltage,becausebothmodeslimittheoutput
voltage additionally.
Theadjustableresistancerangeofaparticularmodelisgiveninthetechnicalspecications.Thevoltageregulation
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 simulated power dissipation of Ri.
3.3.5 Resistance regulation / constant resistance (sink mode)
In sink mode, when the device is working as electronic load, the operating principle is based on a variable internal
resistance. Constant resistance mode (CR) is sort of a natural attribute of a load. It attempts to set the internal
resistancetotheuserdenedvaluebyadjustingtheinputcurrentdependingonthemeasuredinputvoltageac-
cording to formula I
IN
= U
IN
/ R
SET
, which is derived from Ohm’s law.
WithseriesPSB9000,thedi󰀨erencebetweenanexternalvoltagesuppliedtothedeviceandthesetvalueof
voltage determines the true current. There are two situations:
a) The voltage on the DC input is higher than the voltage set value
In this situation, the above formula extends to
I
IN
= (U
IN
- U
SET
) / R
SET
.
An example: the supplied voltage on the DC input is 200 V, the resistance
R
SET
isadjustedto10Ωandthevoltage
set value
U
SET
is set to 0 V. When switching the DC input on the current should go to 20 A and the actual resistance
R
MON
shouldshowapprox.as10Ω.Whenadjustingthevoltagesetvalue
U
SET
to 100 V now, the current would
lower to 10 A while the actual resistance
R
MON
shouldremainat10Ω.
b) The voltage on the DC input is equal to or lower than the voltage set value
The PSB 9000 would not draw any current and enter CV mode. In a situation where the supplied input voltage is
approx. equal to or oscillating around the voltage set value, the sink mode would permanently toggle between CV
and CR. It’s thus not advised to adjust the voltage set value to the same level as the external source.
The internal resistance is naturally limited between almost zero and maximum, where the resolution of current
regulation becomes very inaccurate. Because the internal resistance can’t have a value of zero, the lower limit is
denedtoanachievableminimum.Thisensuresthattheinternalelectronicload,atverylowinputvoltages,can
consume a high input current from the source, up to the adjusted current set value.
While the DC input is switched on and constant resistance mode is active, the condition “CR mode active” will be
indicated on the graphics display by the abbreviation CR, as well it will be stored as internal status that can be
read via digital interface.