In a supercritical 600 MW unit

the coal quality changes and the primary air flow measurement of the coal mill is inaccurate

so the boiler load can not be automatically controlled.Against this problem

two boiler load control strategies were analyzed

the feed coal following the feed water mode and the feed water following the feed coal mode.On this basis

a boiler load control strategy with coal quality automatic calibration function was applied to optimize the feed water and feed fuel system.The results show that

in automatic generation control(AGC)mode with large load variations

the boiler load control system can respond the AGC load demand with speed of 1.0~1.5%/min

and can constrain the main steam pressure and temperature controlling error within ±0.4 MPa and ±4 ℃ respectively

which meets the corresponding target aim in the DL/T 774—2004.