A supercritical coal-fired power generating unit equipped with single-line auxiliaries ran at 50%load for a long time after being put into service

the poor control accuracy at low load makes the unit be unable to satisfy the requirements of coordination control

and brings out several problems

such as the superheat temperature

large fluctuation of feedwater and main steam pressures

great disturbance of the induced draft fan

slow load response to the primary frequency regulation

unable to effectively guarantee the unit thermal efficiency and safety risk.To solve these problems

this paper puts forward a series of countermeasures

like modifying the mill inlet air flow measurement device

improving the furnace pressure control

reducing the primary air ratio during low load operation

dynamically adapting the feedwater and superheating temperature control strategy using variable parameter

adding the primary frequency regulation valve position response demand

and optimizing the boiler main control circuit and low load feed-forward loop.The low load 170~200MW(48%~57%)varying load test results indicate that

the optimized coordination control can meet the unit's operation requirement during load increasing/descending process.This optimized control strategy has a certain reference for low load safe operation of units equipped with single line auxiliaries.