Tham khảo tài liệu 'gas turbine engineering handbook 2 episode 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Control Systems and Instrumentation 635 Gas turbine instrumentation has expanded in the past few years from simple control systems to more complex diagnostic and monitoring systems that are designed to avert major catastrophes and operate a unit at its peak performance. Control Systems All gas turbines are provided with a control system by the manufacturer. The control system has three fundamental functions startup and shutdown sequencing steady-state control when the unit is in operation and protection of the gas turbine. Control systems can be an open loop or closed loop system. The openloop system positions the manipulated variable either manually or on a programmed basis without using any process measurements. A closed loop control system is one which receives one or more measured process variables and then uses it to move the manipulated variable to control a device. Most combined cycle power plants have a closed loop control system. Closed loop systems include either a feedback or feedforward control loop or both to control the plant. In a feedback control loop the controlled variable is compared to a set point. The difference between the controlled variable to the set point is the deviation for the controller to act on to minimize the deviation. A feedforward control system uses the measured load or set point to position the manipulated variable in such a manner to minimize any resulting deviation. In many cases the feedforward control is usually combined with a feedback system to eliminate any offset resulting from inaccurate measurements and calculations. The feedback controller can either bias or multiply the feedforward calculation. A controller has tuning parameters related to proportional integrated derivative lag deadtime and sampling functions. A negative control loop will oscillate if the controller gain is too high but if it is too low it will be ineffective. The controller must be properly related to the process parameters to ensure close-loop .
