Power factor control on the synchronous generator of a CHP unit

About the project

INDOP's CHP unit generates electricity with a MAN gas engine and a Meccalte synchronous generator. The power factor was controlled in a Siemens controller (CPU 1512C) via an automatic voltage regulator (AVR), which always maintained a value of 1. To certify the units for the Polish market, the control must set and hold the power factor anywhere between 0.9 capacitive and 0.9 inductive, as precisely as possible, since grid disturbances and engine misfires often occur in the field.

Based on measurements on the unit, we prepared a simulation model (the system behaves as a first-order lag with dead time) and two PID controllers: the first controls the power factor directly, the second indirectly via reactive power. The measurements from the Janitza power analyser and the setpoint are filtered with a first-order filter so that a setpoint change or measurement noise does not cause a step at the AVR input.

We tuned the controllers using the CHR method on a unit with a rated power of 250 kW and tested them on a 50 kW unit at 60 and 100 % power. Both control schemes work stably over the whole required range, and control via reactive power gave smaller power factor deviations.

How it went

1. On-site measurements: responses of the unit to small manual changes of the control variable, recorded in TIA Portal.
2. Model and simulation: identification of the dynamics and initial PID controller parameters.
3. Implementation in the controller: filters, conversion of the inductive and capacitive regions, discrete PID in SCL (with Sistemi INES).
4. Tests on the 250 kW and 50 kW units: setpoint changes between 0.9 capacitive and 0.9 inductive, and the response to disturbances.