Feed Forward and Integral Control of an EGR Valve 2011-01-0689
Automotive embedded control systems need to implement real-time
closed-loop control strategies for controlling valves, motors, etc.
The implementation needs to focus on use of low cost hardware and
efficient software with minimal foot-print so as to adequately meet
the application requirement. This paper highlights the low cost
hardware and software design concepts by way of a case study
related to control of progressive EGR valve. The control strategy
is based on "map-driven set-points" where percentage
opening of the valve is stored in the form of 16x16 matrices. The
set-points are accessed based on instantaneous throttle and engine
rpm values which form the row and column indices of the map.
The closed loop control algorithm eliminates the need for
multiplication by implementing "feed-forward with integral
control algorithm." A feed-forward map specifies the most
likely PWM duty cycle to be applied to the valve for a given
set-point. This allows the control strategy to function in an
open-loop manner for initial portion of the control cycle. When the
valve response to the feed-forward settles down a finite error
still exists between the actual output and the desired set-point.
However this error is small enough to be "integrated out"
by a simple integral algorithm based on summation. This approach
has been successfully tried out in real life application and proven
to be extremely useful in delivering required closed-loop accuracy
at lowest cost. Although the case-study is specifically based on
progressive EGR valve, the strategy can be gainfully employed for
different control applications with similar control