Volts/Hz Slope And Cut-In Frequency; Voltage Regulator Gain - Kohler 38RCL Manual

6.5.3 Volts/Hz Slope and Cut-In
Frequency
The Volts/Hz setting for the voltage regulator performs
the following functions on the generator:
Serves as a method for unloading the engine to allow
D
recovery during a sharp increase in load
Serves as a means of protection for the alternator to
D
avoid saturating the field (rotor heating) at low
frequencies
The slope and cut-in frequency of the volts/Hz curve are
set at the factory to allow the generator to meet factory
performance standards. They should not be adjusted
except under unique circumstances and under direction
from a Kohler factory representative.
If the slope of the Volts/Hz curve is set too low, the
engine will not be unloaded quickly enough to recover
from a quick load increase. If the slope is set too high,
the voltage will dip dramatically with a quick load
increase, which will cause temporary brownouts.
The cut-in frequency is typically set to 1 Hz below
system frequency so that normally small frequency
variations do not cause the voltage to vary. Setting the
cut-in frequency further from rated frequency may
adversely affect the generator's ability to recover
frequency after a sharp load increase.
See Figure 6-10 for an illustration of the volts/Hz curves
for 50 and 60 Hz.
Figure 6-10 Volts/Hz Curves
82 Section 6 Component Testing and Adjustment
6.5.4

Voltage Regulator Gain

The gain of the inner loop of the hybrid regulator is set at
the factory and is not adjustable in the field. The Voltage
Regulator Gain listed in SiteTech is for the outer loop.
The outer loop is responsible for correcting the setpoint
to the inner loop to ensure that the generator output is
regulated to the RMS regulator setpoint. The outer loop
thus corrects for wave-shape distortion, temperature
variations in the inner loop circuitry, inter-board
metering variations, etc. Typically the outer loop only
adjusts the setpoint to the inner loop on initial startup
(battery is first plugged in) and after calibration has
changed.
At a gain setting of 1, it will take 128 seconds to adjust
the voltage output 1%. At a gain setting of 255, the
voltage adjustment rate is related to the difference
between the target voltage and the measured voltage,
but could vary up to 3.1% per second.
At lower gains, the voltage may reach the target value
very slowly, but the chance of overshoot from the two
controller loops fighting is minimal. At higher gains,
there is a chance that the outer loop will change the
setpoint faster than the inner loop can accommodate,
resulting in unstable output voltage. This may show up
as slight flicker on a light bulb.
Note: The RMS correction outer loop is not active when
the controller is in Volts/Hz mode; the last known
correction factor, or inner loop setpoint, is used.
TP-6811 7/16