For the 2×660 MW air cooling units of Shenhua Guohua Dingzhou Power Generation Plant

the variations of turbine back pressure and fuel calorific value usually affect much on the unit efficiency

in variable loads and different environmental conditions.Using the conventional calorific value correction method will accumulate and increase the deviation of the coordinated control parameters gradually

resulting in decrease in unit load response speed and operation stability.Thus

on the basis of direct command balance principle

a new calorific value calibration method was put forward.Comprehensively considering such factors as the effects of fuel calorific value and turbine back pressure on the unit efficiency

and efficiency difference of unit with differentloads under the same external environmental condition

this new method performed relative reasonable correction on the relationship of the boiler fuel quantity instructions

to ensure the control quality of the coordinated control system under different working conditions.After the new calorific value calibration method was employed

the unit load dropped from 600MW to 300MW

the turbine back pressure dropped from 8.9kPa to 7.8kPa

and the integral output of the boiler master control pressure regulator dropped from +0.2to-1.2(affected by the mill shutdown). After the load variation

the maximum deviation of main steam pressure was +0.2 MPa and-0.4MPa

which was reasonable;the unit load increased from 445 MW to 495 MW

with the load variation rate of 2%/min

the load response time of 40s

load dynamic deviation less than 0.5%

the maximum dynamic deviation of main steam pressure of-0.2MPa

and the steady state deviation close to 0.