Manual 02879 723PLUS/Analog Load Sharing
Woodward 91
Fuel Control
The basic operation of the 723PLUS control is to provide a dynamically stable
closed loop path between the engine fuel delivery system and feedback paths of
engine speed and generator load. If generator load is not directly available, a
second feedback path from the Fuel Demand is used to control load. The speed
will be controlled at a reference set point which is the sum of the Speed
Reference and the bias signals. The bias signals come from the Load Control or
the Droop Function (depending on the position of the CB AUX Switch) and the
Synchronizer Input. The closed loop path is interrupted by an LSS (Low Signal
Selector) which will limit the Fuel Demand to the lowest value of all inputs. Inputs
(other than the PID control signal) which can limit the Fuel Demand include a Min
Fuel Function, a Max Fuel Function, a Start Limit Function, an External Fuel Limit
Function, and a Torsional Limit Function. A very short duration Bump Actuator
Function will also limit the Fuel Demand when it is applied. The Fuel Demand is
a dimensionless value based on percentage of required fuel where 0 percent
generally represents no fuel and 100 percent represents maximum fuel. The Fuel
Demand is supplied to the Actuator Function to produce an Actuator Current.
The Actuator Current is supplied to an Actuator which will control the fuel delivery
system.
Control Dynamics
The control algorithms used in the 723PLUS Speed Control are designed
specifically for reciprocating engine applications. The control offers a powerful
set of dynamics to closely match a wide variety of fuel delivery systems and
processes.
Constant dynamics remain fixed as entered and do not vary with engine speed.
Dynamics may still vary with fuel demand by using the 5-Gain mapped dynamics
or the gain slope. Constant dynamics are useful for fuel systems and processes
that tend to be equally stable at reduced speed and rated speed.
Variable dynamics vary gain by the ratio of actual engine speed to rated speed,
and inversely vary reset by the ratio of rated speed to actual engine speed. The
variable dynamics value is multiplied by the gain or the 5-Gain mapped dynamics
setting (whichever is elected). Variable dynamics are useful for fuel systems and
processes that tend to be less stable at reduced speed operation.
The 5-Gain mapped dynamics is a two-dimensional curve with five breakpoints
that vary gain as a function of fuel demand. The 5-Gain mapped dynamics
compensate for non-linear fuel systems and are useful for engines or processes
whose dynamics change in a non-linear manner with load.
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