The coordinated control system of 780 MW "Two-Pull-One" type gas-steam combined cycle unit in Taiyanggong Plant was presented.Different load distribution schemes were put forward for two different operation modes:"Two-Pull-One" mode and "One-Pull-One" mode

respectively.On the basis of basic proportion

the PID algorithm was employed to perform the load distribution scheme revision and complete the total power coordination control of combined cycle unit.Moreover

for gas turbine trip and steam turbine trip

protection function in MARK-VIDCS instruction for steam turbine trip interlocking gas turbine trip was canceled

and quick open control function for bypass relief valve

desuperheating water regulating valve and stop valve was added.Load disturbance test was performed with load rising/falling rate of 30 MW/min

under automatic generation control(AGC) condition.The results showed that

the unit ran stably and had good ability of peak load regulation.During the load regulating process

the maximum dynamic load deviation was lower than 6 MW

and the average static load deviation was lower than 4 MW.