Rechargeable aqueous zinc-ion batteries (ZIBs) are promising candidates for advanced electrical energy storage systems owing to low cost, intrinsic safety, environmental benignity, and decent energy densities. Currently, significant research efforts are being made to develop high-performance positive electrodes for ZIBs. Nevertheless, there are still many obstacles to be overcome in pursuit of the comprehensive performance of cathode materials, including specific capacity, structural stability, rate performance, and so forth. Many manganese-based compounds have become the hotspots in the study of ZIB cathodes due to their advantages of natural abundance, less toxicity, and high operating voltage. Here, different energy storage mechanisms of various kinds of manganese-based compounds are summarized. Electrochemical results of manganese-based cathodes are compared and analyzed. Moreover, optimization strategies for addressing existing issues of these materials and improving ZIBs are discussed in detail.
This paper investigates a model-free tuning method of a fractional-order proportional–integral (FOPI) controller and its application for the speed regulation of a permanent magnet synchronous motor (PMSM). Firstly, the presented practical FOPI tuning method formulates the FOPI controller parameter identification problem via virtual reference feedback tuning (VRFT). Under the lack of accurate models, the proposed model-free method depends only on the measured input–output data of the closed-loop PMSM servo system. Secondly, Bode’s ideal transfer function is incorporated into the VRFT with consideration of the systematic fractional dynamics. Thus, the properties of the resulting system may be approximated to the desired fractional-order reference model. Thirdly, the proposed method fully considers optimal performance constraints on the stability requirements, sensitivity criteria, frequency-domain and time-domain characteristics. Then, the comprehensive optimization problem is derived and solved. Using suitably tuned parameters, the robustness and disturbance rejection ability of the VRFT-based FOPI control system are enhanced to achieve optimal performance. The convergence of the proposed method is proved by theoretical analysis. Finally, experimental results are presented to illustrate the effectiveness of the proposed model-free FOPI control method for the PMSM servo system.
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