© EPS Stromversorgung in 2022, this information is subject to change without notice
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30000800_manual_psb_10000_4u_30kw_en_04
3.3.5
Resistance regulation / constant resistance (sink mode)
In sink mode when the device is working as electronic load, which operating principle is based on a variable internal resis-
tance. Constant resistance mode (CR) is almost a natural characteristic. The load attempts to set the internal resistance to
the user defined value by determining the input current depending on the input voltage according to formula I
IN
= U
IN
/ R
SET
,
which is derived from Ohm’s law.
With series PSB 10000, the difference between an external voltage supplied to the device and the set value of voltage deter-
mines 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 10000 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 be-
comes very inaccurate. Because the internal resistance can’t have a value of zero, the lower limit is defined 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.
3.3.6
Sink-source mode switching
The switchover between sink and source mode happens automatically and only depends on the device’s voltage setting and
actual value on the DC terminal or the remote sense connector, if in use.
It means, that when connecting an external voltage source to the DC terminal, only the voltage set value determines the op-
eration mode. When connecting an external load which can’t generate a voltage, only source mode can be run.
Rules for applications with external voltage source connected:
•
If the voltage set value is higher than the actual voltage of the external source, the device will run in source mode
•
If the voltage set value is lower, it will run in sink mode
To run one of both modes explicitly, i.e. without automatic switchover, it would require following:
•
for “source only mode” adjust the current set value for the sink mode to 0
•
for “sink only mode” adjust the voltage set value to 0
3.3.7
Dynamic characteristics and stability criteria
When working in sink mode, the device becomes an electronic load which is characterized by short rise and fall times of the
current, which are achieved by a high bandwidth of the internal regulation circuit.
In case of testing sources with own regulation circuits at the load, like for example power supplies, a regulation instability
may occur. This instability is caused if the complete system (feeding source and electronic load) has too little phase and
gain margin at certain frequencies. 180 ° phase shift at > 0dB amplification fulfills the condition for an oscillation and results
in instability. The same can occur when using sources without own regulation circuit like batteries and when the connection
cables are highly inductive or inductive-capacitive.
The instability is not caused by a malfunction of the load, but by the behavior of the complete system. An improvement of
the phase and gain margin can solve this. In practice, this is primarily done by switching the internal voltage regulator be-
tween dynamics modes called
Slow
,
Fast
and
Normal
. The switch is either found in the device settings (see
3.5.3.1) or the
quick menu (see
3.5.9). The user can only try the different settings to see if the desired effect is achieved. Should there be
an improvement due to one of these settings, but the oscillation remains, an additional measure can be to install a capacity
directly to the DC input, perhaps alternatively to the remote sense input, if connected to the source. The value to achieve the
expected result is not defined and has to be found out. We recommend:
10/60/80 V models: 1000uF....4700uF
200/360 V models: 100uF...470uF
500 V models: 47uF...150uF
750/920/1000 V models: 22uF...100uF
1500/2000 V models: 4.7uF...22uF
