Kazan engineers proposed a system for UAVs with two loops: the first changes the PID controller parameters depending on the operating mode, and the second additionally corrects fuel delivery using fuzzy logic.
The main idea of the design is not to force the engine to operate according to the same algorithm under all conditions. The controller calculates the reduced rotor speed and takes into account atmospheric pressure, after which it changes the coefficients of the main PID controller.
If the speed begins to deviate from the required value, a fuzzy corrector additionally comes into play: it evaluates the magnitude of the error and the speed of its change and adds its correction to the fuel pump control signal.
It is this combination that distinguishes the proposed system from a controller with constant coefficients. According to the authors, it should allow for faster response to transient modes of a small turbojet engine when it is necessary to change fuel delivery and bring the rotor to new speeds.
For this, the system receives data from several sensors: rotor speed, pressure behind the compressor, gas temperature behind the turbine, and atmospheric pressure are monitored. The control element is an electrically driven fuel pump, and both algorithms operate in a programmable controller.
An interesting engineering paradox emerges: instead of trying to simplify the control of a small turbojet engine, the authors added another level of correction.
The meaning of such a complication is to make the automation take into account not only the current deviation of the speed but also how quickly it occurs, in order to more accurately influence the fuel system.