The invention relates to a method and a
system for controlling negative pressure of furnace hearths of a thermal power
plant. The controlling
system comprises a control panel, a PID (proportion, integration and differentiation) adjustor, a summator, a proportion coefficient changing unit, an integration time changing unit, a primary fan RB (runback) feedforward unit, an induced draft fan stationary blade M / A
station and an induced draft fan stationary blade control output end, the proportion coefficient changing unit and the integration time changing unit are respectively connected with the PID adjustor, and the primary fan RB feedforward unit is connected with a
single loop circuit through the summator. By adding a parameter changing function to the controlling
system and primary fan RB feedforward, when primary fan RB occurs, a proportion coefficient is increased, so that response speed of the adjustor to deviation amplitude is increased, integration time is increased,
integral action is reduced, and adverse
impact brought by
lag of integral adjusting is eliminated. When the primary fan RB occurs, an induced draft fan
stator blade is quickly closed through feedforward, so that the problem that
overpressure of the furnace hearths during the primary fan RB is effectively prevented, and
pressure control level of the furnace hearths and operating safety of thermal
power unit are improved.