6 Adjusting the PID settings
The elgris HYBRID controller has a real time PID controller to adjust the amount of PV power within
the system. By setting one value to zero, P, PI or PID controllers can be set. For standard applications,
the PI controller is a good starting point.
The PID controller takes the current power value (single or three phase) as current value and the
setpoint (grid or generator setpoint) as desired value.
The settings for P, I and D can be changed according to the application. Please note the following:
The P value is the proportional gain of the error between setpoint and current value. The
higher the P value, the more the controller will react to a change of load.
When the solar system over reacts on load changes, the P factor is too high. The other way
around, when the response is not high enough, the P factor is too small.
The I value is the integrated value of the past error over time. The longer and error exist, the
more the I part will affect the output.
When the reaction time on a load change is too slow, the I factor is too low. Opposite, when
the system is unstable (oscillating around a value) the I factor is too high.
The D value is for future trends. When there are big load changes in a very small time interval
this can be compensated by adding some D factor. The D factor only has influence on load
changes and not in a steady system.
The values entered on the settings page are divided by 1000.
6.1 Manual tuning
If the system must remain online, one tuning method is to first set I and D values to zero. Increase
the P until the output of the loop oscillates, then the P should be set to approximately half of that
value for a "quarter amplitude decay" type response. Then increase I until any offset is corrected in
enough time for the process. However, too much I will cause instability.
Finally, increase D, if required, until the loop is acceptably quick to reach its reference after a load
disturbance. However, too much D will cause excessive response and overshoot. A fast PID loop
tuning usually overshoots slightly to reach the setpoint more quickly; however, some systems cannot
accept overshoot, in which case an overdamped closed-loop system is required, which will require a
P setting significantly less than half that of the P setting that was causing oscillation.
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