© EA Elektro-Automatik in 2022, this information is subject to change without notice
38
06230920_manual_ps_10000_3u_15kw_en_01
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 to CC. The current flowing 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 adjusted 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.
While the DC output is switched on and constant current mode is active, the condition “CC mode active” will be indicated on
the graphic display with 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.
3.2.2.1
Voltage overshootings
In certain situations it’s possible that the device generates a voltage overshooting. Such situations are when the device is
in CC, with the actual voltage being unregulated, and either a jump in the current set value is initiated which would bring the
device out of CC or when the load is suddenly cut from the power supply by an external means. Peak and duration of the
overshooting aren’t exactly defined, but as rule of thumb it shouldn’t exceed a peak of 1-2% of the rated voltage (on top of
the voltage setting) while the duration mainly depends on the charging state of the capacities on the DC output and also the
capacity value.
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 flowing 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 true resistance.
Power limiting operates according to the auto-range principle such that at lower output
voltages higher current flows 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 abbreviation
CP
, as well stored
as status which can also be read as a status message via digital interface.
3.2.3.1
Power derating
Primarily, the models in this series are designed for 400 V AC supply, but can also operate on a three-phase supply of 208 V (USA,
Japan). In order to limit the AC current when running on this low input voltage, they switch to a derating mode which reduces
the available DC power. In particular, a 5 kW model would reduce to 3 kW, a 10 kW model to 6 kw and a 15 kW model to 9 kW.
The switchover is determined once when the device is powered and depends on the currently present AC supply voltage. It
means that it cannot switch back and forth between derated and underated mode during operation. The full power is thus
only available with AC voltages from 380 V or higher.
Once derated, the device would show a permanent information in the display and all values related to the power are reduced
in their adjustment range. This also applies to master-slave operation of derated units.
3.2.4
Internal resistance regulation
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 difference 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
differ even more from the adjusted voltage, because both modes limit the output voltage additionally. CR mode is actually
running in CV, but will be indicated as CR on display once the adjusted resistance value is reached.
The adjustable resistance range of a particular model is given in the technical specifications. The voltage regulation in de
-
pendency 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. Clarification:
U
Act
= U
Set
- I
Act
* R
Set
P
Set
, I
Set
P
Ri
= (U
Set
- U
Act
) * I
Act
