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Refrigeration systems occupy a large proportion of the home energy consumption in the United States. Precise temperature management is a key point to enhance the energy utilization efficiency. Since proportional-integral-derivative (PID) controllers absolutely dominate control engineering, a large number of different control structures and theories have been developed to enhance the efficiency of PID controllers. A benchmark refrigeration system was proposed in PID2018 as a simulation platform for researchers to implement different control strategies. In this paper, a novel control strategy is designed for the benchmark refrigeration system, where the fractional-order lead-lag compensator is in consort with the baseline controllers and contributes to accelerate the system response by increasing the system bandwidth, and the feedforward compensators are utilized to compensate the disturbances in the benchmark problem. The simulation results given in the benchmark problem show the straightforward effectiveness of the proposed control structure compared to the existing control methods.

Superheated steam temperature (SST) is a significant index for a coal-fired power plant. Its control is becoming more and more challenging for the reason that the control requirements are stricter and the load command changes extensively and frequently. To deal with the aforementioned challenges, previously the cascade control strategy was usually applied to the control of SST. However, its structure and tuning procedure are complex. To solve this problem, this paper proposes a single-loop control strategy for SST based on a hybrid active disturbance rejection control (ADRC). The stability and ability to reject the secondary disturbance are analyzed theoretically in order to perfect the theory of the hybrid ADRC. Then a tuning procedure is summarized for the hybrid ADRC by analyzing the influences of all parameters on control performance. Using the proposed tuning method, a simulation is carried out illustrating that the hybrid ADRC is able to improve the dynamic performance of SST with good robustness. Eventually, the hybrid ADRC is applied to the SST system of a power plant simulator. Experimental results indicate that the single-loop control strategy based on the hybrid ADRC has better control performance and simpler structure than cascade control strategies. The successful application of the proposed hybrid ADRC shows its promising prospect of field tests in future power industry with the increasing demand on integrating more renewables into the grid.