直接空冷与湿冷机组在排汽末端有很大区别，导致直接空冷机组不能沿用普通湿冷机组的背压保护控制方法。为此提出背压保护安全裕度的概念，并给出了应用于直接空冷机组的基于背压保护安全裕度的模糊控制方法。考虑到直接空冷机组背压很容易受到环境温度和风机风速的影响，建立了基于传统变工况特性的空冷机组数学模型。仿真算例表明，该方法能够较大程度地保证机组在最经济和安全的状态下运行。

Air-cooling systems and water-cooling systems of steam turbine differ much in their ends of exhaust, as a result that the method of back pressure control for ordinary water-cooling systems is not applicable to air-cooling systems. Therefore, the safety margin of back-pressure control is provided, based on which the fuzzy control approach is proposed for applying in direct air-cooled units. The back pressure of air cooled steam condenser is easy to be influenced by the local environmental temperature and the fans speed, so that a mathematical model is developed based on the traditional air-cooled units with off-design characteristics. It is verified by the simulation that the approach to a large extent can ensure the air-cooling system operating under most cost-efficient and safest conditions.