The output tracking problem of gear transmission servo (GTS) systems with backlash nonlinearity is studied in this paper. A new concept-"soft degree"-is proposed to overcome the nondifferentiable "hard" characteristic of the backlash nonlinearity. Furthermore, a detailed softening process-static softening is presented, where a backstepping control algorithm is developed to guarantee that the output of the controlled systems can track any given desired sufficiently smooth trajectory by arbitrary precision and the limit cycles that appear due to backlash nonlinearity can be avoided. Simulation results validate the effectiveness of the proposed controller.Note to Practitioners-Backlash universally exists in gear transmissions where the moving parts temporarily lose direct contact, which is a major factor affecting the systems dynamic performance and steady precision. Existing approaches for eliminating backlash nonlinearity are mainly divided to two categories due to the nondifferentiable property of the traditional deadzone model: one is the inverse model compensation method, which is not preferable in practical applications for the existence of physical inertia; the other is a multimodel switching method that divides the controlled system into several subsystems and then designs controllers for each subsystem, which makes the control design problem very complex and difficult. Motivated by these, this paper proposes a "soft degree" concept based on a recently developed differentiable deadzone model, and then presents a practical backstepping algorithm to achieve not only high-precision output tracing but also limit cycles elimination.
Tapped-inductor provides the property of wider voltage conversion range similar to an auto-transformer and can be integrated to a switched-mode power converter to enhance the power conversion efficiency. Its low component count has attracted applications with extreme voltage conversion ratios. Circuit family is presented and a general tapping concept for diode, transistor or both has been described. Its boost converter version is used as an example for the study. Detailed comparisons between tapped-inductor boost and conventional boost are carried out, which include the comparison of voltage gain, component stress and efficiency with the presence of the parasitic components. Experimental results present solid verification of the analysis of performance of tapped-inductor boost converter under extreme conversion ratios. The proposed study has introduced formulations for both transistor and diode tapping and can be extended to other tapped-inductor DC-DC converters as a family of circuits, and thus provides an understanding of the effect of the parasitic components that affect the efficiency under extreme conversion ratio.
Loss-Of-Excitation (LOE) condition of a generator may cause severe damages on both generator and the interconnected systems. This paper analyses the behaviours of different LOE protection schemes, such as R-X, G-B, P-Q and U-I schemes, for a hydro generator, which is connected to an infinite bus. Based on the simulation results, the reliability and stability of existing LOE protection schemes are compared and a preferred scheme is selected. An improvement to the scheme is also proposed to prevent the LOE relay incorrect operation during external faults, such as short-circuit faults on busbar or transmission lines.
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