In gas turbine engine operation, it is known for the engine fuel control to provide for control during hard transients such as accelerations. Typically, the engine manufacturer specifies a desired acceleration ("N-Dot") schedule which is not flat, but of a complex shape. Part of the complexity is due to the need to avoid engine operation in the compressor stall region. The schedule input is typically the measured gas generator speed, NG.
A problem with this scheme is that the control is unable to command the engine to accurately follow the desired acceleration schedule. This is due to control design tradeoffs between bandwidth limitations which result from a overriding desire to improve the control's transient performance. The bandwidth is limited by the stability of the control along with the rise characteristics of the acceleration schedule. As a result, the engine may be undesirably operated in the stall region, which in itself may cause catastrophic engine problems.
To compensate for the poor tracking by the control of the acceleration schedule, it is known to manually shift the schedule before implementation in the control so as to avoid any undesired operating regions. However, besides consuming more time and cost during the control design phase, the manual shifting does not provide a true solution to the problem.
USPTO Backgrounds
USPTO Backgrounds