The Feed Forward
Controller
By Doug Cooper and Allen Houtz
ABSTRACT: The most popular architectures for improved disturbance rejection performance are cascade control and the "feed forward with feedback trim" architecture introduced below. Like cascade, feed forward requires that additional instrumentation be purchased, installed and maintained. Both architectures also require additional engineering time for strategy design, implementation and tuning. Cascade control will have a small impact on set point tracking performance when compared to a traditional single-loop feedback design and this may or may not be considered beneficial depending on the process application. The feed forward element of a "feed forward with feedback trim" architecture does not impact set point tracking performance in any way.
Feed Forward Uses Models Within the Controller Architecture
By Doug Cooper and Allen Houtz
ABSTRACT: Both "feed forward with feedback trim" and cascade control can provide improved disturbance rejection performance. They have different architectures, however, and choosing between the two depends on our specific control objective and the ability to obtain certain process measurements.
Static Feed Forward and Disturbance Rejection in the Jacketed Reactor
By Doug Cooper and Allen Houtz
ABSTRACT: As discussed in previous articles, the purpose of the feed forward controller of the feed forward with feedback trim architecture is to reduce the impact of one specific disturbance, D, on our primary process variable, PV. An additional sensor must be located upstream in our process so we have a disturbance measurement that provides warning of impending disruption. The feed forward element uses this D measurement signal to compute and implement corrective control actions so the disturbance has minimal impact on stable operation. Here we build on the mathematical foundation of this previous material as we explore the popular and surprisingly powerful static feed forward computational element for this disturbance rejection architecture.