Winco DGC-2020 - Manual (Page 331)

9400200990 Rev K DGC-2020 Tuning PID Settings C-1
APPENDIX C
 TUNING PID SETTINGS
INTRODUCTION
The LSM-2020 (Load Share Module) and DGC-2020 utilize three controllers to accomplish
synchronization, load sharing, and speed trim functions. The controllers are a speed controller, a voltage
controller, and a kW load controller. The voltage and speed controller are in effect when the DGC-2020 is
synchronizing the generator to a bus. When synchronizing, these controllers adjust the speed and voltage
output of the generator to match that of the bus. After the generator is paralleled to a bus, the load share
controller controls the kW output of the machine to share equally on a percentage basis with the other
generators on the bus. All generators participating in load sharing are connected together with load share
lines which are used to communicate analog load share information between the machines.
When the generator is paralleled to the bus and load sharing is enabled, the speed trim function, if
enabled in all machines on the bus, will ensure that the bus frequency is maintained at the frequency set
by the speed trim setting. Speed trim is in effect only in the situation where the generator breaker is
closed and load control and speed trim are enabled. Speed trim is not in effect when the breaker is open,
since the default mode when the breaker is open is droop, and speed trim would counteract droop. Speed
trim is not in effect when the breaker is closed unless load control is enabled. When load control is
enabled, it is possible that load control could cause the system frequency to drift, and speed trim can be
employed to counteract the drift. The drift can occur due to inaccuracies in measured KW vs. desired KW,
since KW measurement accuracy is around 3%.
The load share module utilizes PID (Proportional, Integral, Derivative) Control to accomplish load sharing,
speed control, and voltage control. A brief description of the three 3 main tuning parameters, and their
effects on system behavior, is presented below.
 K
p
- Proportional Gain - The proportional term makes a change to the output that is proportional to
the current error value. The proportional response can be adjusted by multiplying the error by a
constant K
p
, called the proportional gain. Larger K
p
typically means faster response since the larger
the error, the larger the feedback to compensate. An excessively large proportional gain will lead to
process instability.
 K
i
- Integral Gain - The contribution from the integral term is proportional to both the magnitude of the
error and the duration of the error. Some integral gain is required in order for the system to achieve
zero steady state error. The integral term (when added to the proportional term) accelerates the
movement of the process towards setpoint and eliminates the residual steady-state error that occurs
with a proportional only controller. Larger K
i
implies steady state errors are eliminated quicker. The
trade-off is larger overshoot: any negative error integrated during transient response must be
integrated away by positive error before reaching steady state.
 K
d
- Derivative Gain - The derivative term slows the rate of change of the controller output and is
used to reduce the magnitude of the overshoot produced by the integral component and improve the
combined controller-process stability. However, differentiation of a signal amplifies noise in the signal
and thus this term in the controller may be sensitive to noise in the error term, and can cause a
process to become unstable if the noise and the derivative gain are sufficiently large. Larger K
d
decreases overshoot, but slows down transient response and may lead to instability.
Table C-1 shows the effects of increasing parameters.
Table C-1. Effects of Increasing Parameters
Parameter Rise Time Overshoot Setting Time Steady State Error
Kp Decrease Increase Small Change Decrease
Ki Decrease Increase Increase Eliminate
Kd Small Change Decrease Decrease None