This paper is concerned with the stability analysis of fixed-point state-space digital filters with generalized overflow arithmetic and a time-varying delay. This paper aims to derive a delay and nonlinear function bound dependent asymptotical stability criterion with less conservatism. Firstly, a new Lyapunov functional with several augmented terms, including extra free matrices and overflow nonlinear function, is constructed such that it has a relaxed positive condition. Then, for bounding the summation term arising in the forward difference of Lyapunov functional, a new lemma is developed to introduce the terms for linking the delayed states and the overflow nonlinear function, the Wirtinger-based summation inequality and several zero-value terms are applied to add more cross terms. As a result, a stability criterion with less conservatism is established and its conservatism. Finally, several numerical examples are given to illustrate the advantages of the proposed method.
A nonlinear control without using anemometer is proposed to achieve the maximum power of the wind turbine (WT) based on two-mass model in this paper. To track the maximum power points, the optimal tip speed ratio control strategy requiring to know the optimal rotor speed of the WT (ORS) is employed. To achieve the ORS, a torque observer is designed to estimate the aerodynamic torque, then the ORS can be obtained by the corresponding calculations based on the estimated torque. Due to the high nonlinearities of the WT and time-varying wind speed, a nonlinear control based on feedback linearization control (FLC) is adopted to track the ORS. In the FLC, the WT is linearized firstly, then the rotor speed controller is designed via linear control technique. The effectiveness of the proposed control strategy is verified by simulation studies. The simulation results show that, compared with the traditional PI control based on torque estimation and FLC based on wind speed estimation, the proposed control strategy provides better dynamic performances and higher power conversion efficiency.
The advancement in power electronic makes the cage-type induction machine(IM) be suitable to be used as a starter/generator(S/G). Because the IM must start the engine to a high ignition speed with a low voltage battery ,a method which employs delta-connection stator winding is proposed. Similarities and differences of basic direct torque control(DTC) in IM with delta-connection and starconnection stator winding are investigated. In order to convert the IM from starting mode to generating mode smoothly, a method by changing the direction of electromagnetic torque is presented. The disadvantage of basic DTC is that it has a big torque ripple . In generating mode ,the torque ripple can cause voltage ripple. In order to decrease voltage ripple, DTC based on space vector modulation(SVM-DTC) is researched. Creation method of reference voltage vector which includes change trend and magnitude information of flux and torque is presented. Experimental results verify that the induction starter/generator system can successfully start the engine with the low voltage battery and can convert from starting mode to generating mode smoothly under basic-DTC. The system has a preferable stable and dynamic generation performance under SVM-DTC.
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