Backpressure protection control method for 300MW high back pressure unit system

The invention provides a backpressure protection control method for a 300MW high back pressure unit system. The method comprises the steps of first reducing the operating load of a unit when safety margin of backpressure protection is smaller than 0; continuously reducing the operating load of the unit when the change rate of the safety margin with time is greater than 0 until the safety margin of backpressure protection is not smaller than 0; increasing the operating load of the unit when the change rate of the safety margin with time is smaller than 0 until the safety margin of backpressure protection is not smaller than 0. The load of the unit is adjusted according to the value of the safety margin, so that automatic control over the backpressure of the 300MW high back pressure unit system is realized, and the safety coefficient of the 300MW high back pressure unit system is improved.