209Section 12 Paralleling System InformationTP-6953 7/19
12.4.5 System Synchronization
Enabling System Synchronization mode in any
controller on a paralleling bus will make all the
generators on that paralleling bus respond to the speed
and voltage bias that is provided to that generator.
Note: External bias must be enabled.
The Speed and Voltage Bias both respond with identical
range to their action o n a single generator.
This mode allows external controls to synchronize a
generator bus to another source (such as an older
generator or a utility) while retaining individual generator
control within each generator controller.
Generator Management, kW and kVAR Sharing, and
Load Management are still active in system
synchronization mode. System Control Mode can be
used while the generators on the paralleling bus are in a
variety of operating states, including synchronizing to
the paralleling bus or soft-unloading.
12.4.6 Real Power Control
The real power output of a generator is related to how
much mechanical power the engine is making. When a
generator is operating as a single unit, there is no good
way to control the power output of the generator without
controlling the power requirements of the load. In a
parallel system, there is more than one source that can
supply the load—hence the power can be shared
between the sources, allowing it to be controlled.
Because the output of the generators is tied together,
the speed of the generators will remain essentially
identical, regardless o f the mechanical torque that a
single engine provides (providing that the load requires
enough mechanical power that the single engine isn’t
overpowering the other engines on the bus and forcing
them to accelerate and that it d oesn’t require more than
the other generators can handle).
If the speed bias is increased, the engine governor will
try to increase the air/fuel flow to the engine to cause it to
accelerate. If the engine speed is unable to change, the
engine torque will steadily increase as long as the target
speed remains higher than the actual speed. This allows
the Power Control logic to increase the load on a
paralleled generator.
If the speed bias is decreased, the engine governor will
try to decrease the air/fuel flow to the engine to cause it
to decelerate. If the engine speed is unable to change,
the engine torque will steadily decrease as long as the
target speed remains lower than the actual speed. This
allows the Power Control logic to decrease the load on a
paralleled generator.
kW Sharing
While the controller is operating as part of a standby
power system or a prime power system that is not in
parallel with another source, the primary (and default)
real power control mode is kW sharing. In this mode,
each generator tries to control output power to the
percentage of the bus capacity (the ratio between the
total load on the bus and the total capacity of all online
generators).
Generators that are m aking too much power will adjust
their speed bias down, while generators that are not
making enough power will adjust their speed bias up.
The result is that there is no net change in the bus
frequency.
If the bus frequency does drift away from nominal (due to
soft loading, soft unloading, or possible fuel supply
issues) there is a frequency trim feature in the controller
that constantly drives the frequency toward the nominal
frequency to correct for such errors. Trims must be
enabled to allow the frequency trim to adjust the speed
bias to maintain constant frequency. Trim should only be
disabled on an islanded (not connected to the utility grid)
system if the system is having trouble sharing load, and
then only as a troubleshooting step.
Frequency Trim is unnecessary in synchronism with the
utility grid.
Note: Frequency and Voltage Trim are enabled and
disabled with a common parameter (Enable
Trims). To disable one individually, the P, I, and D
gains must be set to 0.
The Real Power Controller uses the Real Power
Sharing gains for operation in kW Sharing mode.
To Next Page
Loading...
