Methods for Improvement of the Quality of the Power Turbine Speed Control of a Gas Turbine Engine

Abstract

The article is dedicated to the task of improvement of the quality of the electronic system of automatic control of the gas turbine engines. An analysis was done of the control loop speed power turbines with various electronic controllers. The authors studied the linear PD controller, PD controller with reduced proportional coefficient, quadratic regulator, variable gain controller, fuzzy P controller and fuzzy P controller with a corrective differentiator. A study of the dynamic stability of the quality and quantity parameters of operation of each of the regulators is presented. When a control loop speed power turbine is operated with an original PD controller the required quality of the transients is not ensured. Achievement of the desired speed of the power turbine is accompanied by an overshoot of about 4 % and 0,2 % of the amplitude fluctuations. The transient time can be up to 20 seconds. Reduction of the proportional gain ensures an aperiodic transient increase of the stability margin (no overshoot) and enhances the static accuracy. But the performance is not efficient enough. The transient time is 15 seconds. A quadratic regulator improves the system performance, but does not ensure the required stability margin. The transient factor is accompanied by an overshoot of about 4 % of the amplitude fluctuations. A variable gain controller provides an aperiodic transient increase of the static accuracy and stability margin (no overshoot and amplitude fluctuations). However, the performance is not efficient enough. The transient time is 16.5 seconds. Fuzzy P controller ensures high static accuracy and speed, but the transition process is accompanied by a deregulation. In order to reduce the overshoot and ensure an aperiodic transition process in the fuzzy logic controller a differentiator is added with a negative gain. Because of the negative sign of the gain the differentiator compensates for the overshoot. For correct functioning of the controller the differentiator operates in a strictly defined range, and the error on the speed of the power turbine is within the range of ±[0,25 %, 2,9] %. The resulting controller improves the system's performance up to 6 seconds, but it also ensures an aperiodic transient and high static accuracy of the system. Thereby the required quality control is achieved, when the speed of the power turbine is the best with a non-linear or piecewise-linear controller. For example, it can be PD-controller including a fuzzy P-gain and a differentiator with a limited interval of operation. Within this operating range it depends on the mismatch errors of the power turbine speed.