A critical analysis of Z-source converters considering the effects of internal resistances

Nowadays Z-source networks are the most promising power converter networks that cover almost all electric power conversion (dc–dc, dc–ac, ac–dc and ac–ac) applications. However, the controller design is critical for Z-source converter (ZSC) due to the presence right-half-plane zero (RHPZ) in the control-to-capacitor-voltage transfer function. This RHPZ exhibits non-minimum phase undershoot in the capacitor voltage and also in the dc-link voltage waveforms. A perfect small-signal model is required to predict locations of the RHP zero and its dynamics. This paper contributes towards the small-signal analysis of ZSC under continuous conduction mode considering the parasitic resistance of the inductor, equivalent series resistance of the capacitor, internal resistances of active switch and forward voltage drop of the diode. The maximum allowable value of shoot-through duty ratio (STDR) and voltage gain for different values of the internal resistance and load resistance are discussed in this paper. The accuracy of the developed small-signal average model is compared with detailed circuit model in MATLAB/SIMULINK. Finally, the steady-state simulation results of ZSC are validated with hardware results.     

Visual requirements analytics: a framework and case study

For many software projects, keeping requirements on track needs an effective and efficient path from data to decision. Visual analytics creates such a path that enables the human to extract insights by interacting with the relevant information. While various requirements visualization techniques exist, few have produced end-to-end value to practitioners. In this paper, we advance the literature on visual requirements analytics by characterizing its key components and relationships in a framework. We follow the goal–question–metric paradigm to define the framework by teasing out five conceptual goals (user, data, model, visualization, and knowledge), their specific operationalizations, and their interconnections. The framework allows us to not only assess existing approaches, but also create tool enhancements in a principled manner. We evaluate our enhanced tool support through a case study where massive, heterogeneous, and dynamic requirements are processed, visualized, and analyzed. Working together with practitioners on a contemporary software project within its real-life context leads to the main finding that visual analytics can help tackle both open-ended visual exploration tasks and well-structured visual exploitation tasks in requirements engineering. In addition, the study helps the practitioners to reach actionable decisions in a wide range of areas relating to their project, ranging from theme and outlier identification, over requirements tracing, to risk assessment. Overall, our work illuminates how the data-to-decision analytical capabilities could be improved by the increased interactivity of requirements visualization.     

Transient electron transport in the III–V compound semiconductors gallium arsenide and gallium nitride

A three-valley Monte Carlo simulation approach is used for a detailed comparative analysis of the transient electron transport that occurs within bulk zinc blende gallium arsenide and bulk wurtzite gallium nitride. We find that in both cases that the electron drift velocity and the average electron energy field-dependent “settling times” are strongly correlated, and that the electric field resulting in the shortest electron transit-time is a function of the channel length. The calculated dependence of the peak transient electron drift velocity on the applied electric field can be used for the design optimization of short-channel high-frequency devices.     

Analysis of RCD snubber based non-ideal Z-source inverter using average modelling approaches

ABSTRACT

Z-Source inverters (ZSIs) are one of the most promising single-stage power converters in modern industrial applications. However, these ZSIs exhibit non-minimum phase behaviour as a result of right half-plane (RHP) zero in the converter transfer functions and impose a constraint on the controller design. A detailed mathematical model of the converter plays a crucial role in the design of an efficient control strategy. This paper presents a detailed mathematical model of non-ideal ZSI using averaged modelling approaches and its comparisons are summarised. The pole-zero and step response plots reveals the impact of parasitic elements and parameter variations on system steady-state and dynamic performance. Finally, the effects are outlined, which gives a basic guideline to the designers in the converter performance optimisation such as the feedback control bandwidth, damping factor, resonant frequency, and overshoot/undershoot in the desired output. The sensitivity function is defined for a voltage gain of ZSI with respect to system parasitic elements and snubber parameters. In order to validate the theoretical analysis of converter dynamics, a laboratory prototype model of 50 watts ZSI is developed. Further, a hardware implimentation of PID-based capacitor voltage control is shown to check the effectiveness of the derived transfer functions on closed-loop performance.     

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