LOAD SHARING MODULE (LSM A4) INTERNAL OPERATION - Continued
Speed Trim Summer
The speed trim potentiometer is the FREQUENCY potentiometer on the EMCP and permits manual adjustment of
the load or frequency of the generator. This signal is summed with the output of the sync dynamics summer and
input to the PWM circuit. The potentiometer can trim the frequency of the generator output approximately 10%
above and below nominal in unit mode. In parallel mode, the potentiometer can change the load demand if in
droop mode also.
Pulse Width Modulation (PWM) Output
The PWM circuit takes the sum of all the inputs and converts the analog voltage level to a PWM signal for driving
Engine Control Module (ECM), setting the engine speed. The frequency is approximately 500 Hz. The duty cycle
ranges from 10% for lowest decrease in speed or load, to 90% for maximum increase in speed or load percentage.
The duty cycle varies according to the magnitude of difference between the desired load and the actual power
Relay A4K1 is energized when the ISOCHRONOUS/DROOP switch is in ISOCHRONOUS and the load contactor
is energized. The contacts of A4K1 connect the load sharing input/output to the load comparator circuit. The 24
Vdc input from the batteries is converted to a plus and minus power source (+V and -V) and a plus and minus
reference supply (+VR and -VR) for the amplifiers in the module. In a non-paralleled condition, or when the
ISOCHRONOUS/DROOP switch is in DROOP, the load comparator circuit is not connected to the load sharing
lines. A4K1 is open in Droop mode and the external PAR relay disconnects this output from any other generators
in Unit mode. In this configuration, the power measured by the load power monitoring circuits are summed with the
Sync input from the GSC and the speed trim potentiometer and the PWM output generated from that signal. In a
paralleled condition, you must be in isochronous mode in order to connect the load sharing lines to at least one
other (possibly more) LSM A4. In this mode, this average load signal of all generator sets in parallel is then
summed with the sync input and the speed trim potentiometer input to generate the PWM signal to the ECM. By
doing this, the speed loop is biased to divide the load equally between paralleled generator sets.
In a paralleled condition with Droop enabled, the frequency will vary with load. To minimize this, one generator
must be in isochronous mode. This generator set maintains the frequency of the system. On the paralleled
generator sets in droop mode, the droop percentage set into the LSM by the droop potentiometer and the speed
setting determine the load that is carried by the individual generator.