This paper makes an assessment of the typical main steam temperature system in thermal power plant. Due to main steam temperature system is a cascade control system. So, it should be assessed with the performance assessment method of cascade control systems. So firstly, this paper deduces the theoretical process of performance assessment of cascade control system based on minimum variance. Then with this method assesses the performance of four typical loads in thermal power plants when using

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... ive disturbance rejection-proportion (ADRC-P) cascade control and smith active disturbance rejection-proportion (SADRC-P) cascade control respectively. Finally, makes comparison of the results. Results show that, when using the same control strategy, different loads has different performance. Load with lager inertia has better performance; When using different control strategies, performance under SADRC-P control is better than that under ADRC-P control. 306 Copyright ⓒ 2015 SERSC and Smith ADRC control strategy to main steam temperature control system. And it turns out that using these control strategies can effectively improve the dynamic response of control system. This paper taking a 600MW supercritical once-through boiler for study assesses the performance (rejection of random disturbance) of four typical loads under ADRC control and Smith ADRC control respectively. Copyright ⓒ 2015 SERSC 307 predictor pre-estimate the possible effect on the controlled object of the applied control action, without waiting for the controlled object reacting. This process will obviously improve the dynamic performance of the control system. In order to make full use of the advantage of smith structure, some scholars presented Smith ADRC control strategy [6], combining ADRC control with Smith control shown as Figure 3 . This strategy has achieved good results too when applied to main steam temperature control system.