Frequency Domain Delay Performance Analysis of Heavy-Duty Gas Turbine Control System: Theory and Experiment

Time delay phenomena commonly exist in practical control systems, usually bringing negative impacts on system performance, such as instability. In this article, the delay performance of a heavy-duty gas turbine control system is studied from the perspective of frequency domain. First, discrete mathematical models of the load/speed control loop and temperature control loop of an MS109FA 275MW single-shaft heavy-duty gas turbine are introduced. Then, each delayed control loop is transformed into a feedback interconnection system of a linear time-invariant plant and a delay-induced operator. Using the small-gain theorem, sufficient criterion for delay stability is derived. And a lower bound on delay margin, which guarantees the system stability, can be inspected with the help of a closed-loop Bode plot. The proposed delay margin results are further extended to the case considering loops switching. The tradeoff between achieving delay margin and tracking performance is also analyzed, which indicates that integral control can reduce the delay margin. Finally, the proposed theoretical results are applied to a hardware in-the-loop simulation system, and the experimental results are provided to demonstrate the effectiveness of our methods.