In the optimization process of control logic before run back test of unit no.4 in Shanghai Baogang Power Plant

it is discovered that the design defects existing in calculating logic for outlet air pressure of the forced draft fan.The calculation of air pressure is a typical problem in two-dimensional curved surface fitting

owing to there isn't two-dimensional curved surface fitting functions in Ovation DCS made from Emerson Control System Corp in USA can be used to calculate the air pressure of forced draft fan

therefore

a method of one-dimensional interpolation function multiplied by the correction coefficient has been adopted

however

a large deviation exists between the calculated result and the designed value.For this two improvement methods for logic cofiguration have been put forward

i.e.the one method is as follows:after carrying out sectionally fitting for the upper limiting curve and the lower limiting curve of the designed curves for the air pressure of forced draft fan

the linear interpolation calculation has to be conducted again according to other one-dimension;the another method is as in the following:the upper limiting curve and lower limiting curve based on the designed curves of air pressure in the forced draft fan have to carry out linear interpolation calculation according to two dimensions.Adopting Ovation DCS virtual controller

emulation has been carried out for the original algorithm and two improved algorithms

all have substantially enhanced the accuracy of calculation.