4.19.2 22-4* Sleep Mode
Sleep mode allows the frequency converter to stop itself in
situations where the system is in balance. This function
saves energy and prevents excessive pressure, water
excessively cooled in cooling towers, and building pressuri-
zation problems in the system. This is also important as
some applications prevent the frequency converter from
adjusting the motor down to low speed. This might
damage pumps, cause insufficient lubrication in gearboxes,
and make fans unstable.
If the load on the system allows for stop of the motor and
the load is monitored, the motor can be stopped by
activating the sleep mode function. This is not a normal
stop command but ramps the motor down to 0 RPM and
stops energizing the motor. When in sleep mode, certain
conditions are monitored to find out when load has been
applied to the system again.
To facilitate use of the sleep mode function, the action
takes place at raising edge of the external digital input
signal applied, and the sleep mode enable is level-based
(programmed via the parameters for configuration of the
digital inputs,
parameter group 5-1* Digital Inputs
). Then,
the frequency converter judges the conditions for going
into sleep mode or wake up automatically.
If digital input for sleep mode enable was removed during
the sleep status, the frequency converter could still come
out of wake up according to the real wake-up conditions
for this time.
There are 2 different ways of using the sleep mode
function after sleep mode function is enabled:
1) In systems where the pressure or temperature is
controlled by an external PI controller, the wake-up
conditions cannot be based on feedback from the
pressure/temperature transducer as the setpoint is not
known. Set
parameter 1-00 Configuration Mode
to
[0] Speed
open loop
.
FC
e30bg835.10
P
P
S ys te m
P
S et
f
O ut
f
R ef
External PID
controller
Illustration 4.49 Sleep Mode Function
e30bg834.10
p
(P r essur e)
T ime
T ime
P
S et
Sleep mode
ac tiv a t ed
f
R ef
= f
W ake-up
(F r equenc y)
f
R ef
f
R ef /
f
O ut
f
R ef
f
O ut
f
W ake-up
f
O ut
Digital input
enabled
p
System
Illustration 4.50 Sequence Diagram
In the example above, the speed reference is set by an
external reference signal from external PI controller.
Desired pressure P
set
is not known for the frequency
converter. When low speed is detected, the motor is going
into sleep mode and stopped, but the reference signal (f
ref
)
from the external controller is still monitored. Because of
the low pressure created, the controller increases the
reference signal to gain pressure. When the reference
signal has reached a set value, f
wake
, which is set in
parameter 22-42 Wake-up Speed [RPM]
or
parameter 22-43 Wake-up Speed [Hz]
, the motor restarts.
Parameter Descriptions
VLT® AutomationDrive FC 361
154
Danfoss A/S © 03/2019 All rights reserved.
MG06J202
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