Electrical and Electronic Engineering - Research Publications
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ItemOn the use of switched linear controllers for stabilizability of implicit recursive equations(IEEE, 1998-01-01)Stabilizability of implicit recursive equations is investigated. These equations arise naturally in the context of output dead-beat control for systems described by NARMAX models. Due to non-uniqueness of the solutions of these equations a special kind of a constrained stabilizability problem is considered. We take a hybrid switching control approach in testing the existence of a locally stabilizing controller. A method for the design of a stabilizing switching controller is also presented.
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ItemAnalysis of minimum phase properties for non-affine nonlinear systems(IEEE, 1997)A system can be termed non-minimum phase according to some definitions available in the literature and yet the same system may exhibit stable zero output constrained dynamics. We show that for non-affine nonlinear systems there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are stable, whereas a discontinuous controller which achieves this exists. We give conditions for existence and present a method for design of discontinuous switching controllers which yield stable zero dynamics. In this sense, the results of this paper enlarge the class of non-affine nonlinear systems that can be termed minimum-phase.
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ItemMinimum phase properties for input nonaffine nonlinear systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1999-04)For input nonaffine nonlinear control systems, the minimum phase property of the system in general depends on the control law. Switching or discontinuous controllers may offer advantages in this context. In particular, there may not exist a continuous control law which would keep the output identically equal to zero and for which the zero output constrained dynamics are locally stable, whereas a discontinuous controller which achieves this exists. For single-input/single-output input nonaffine nonlinear systems we give sufficient conditions for existence and present a method for the design of discontinuous switching controllers which yield locally stable zero dynamics.
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ItemPV Controller Modification and its Impact on Assisting PV Penetration(ACM, 2020-06-12)Large-scale penetration of grid-following inverters into the electricity network presents various technical challenges to grid reliability. It is well-known that the ability of a grid to maintain a stable frequency is inhibited by adding traditional grid-tied photovoltaic (PV) generators. In this work, a detailed model of a simplified grid is presented, and it is shown that the proportion of PV generation and instability are positively correlated. The main instability phenomenon is captured by a Hopf Bifurcation in the field dynamics of the synchronous generator. Such a Hopf bifurcation severely constricts the feasible operating domain of the grid and may hinder normal operation. Modifying traditional grid-tied PV controllers and its impact on grid stability is assessed through small-signal, bifurcation and transient numerical analysis. Traditional PV controllers that are modified to virtual synchronous machine (VSM) type controllers show improvement in system damping. Unlike traditional grid-tied inverters, VSM inverters participate in critical modes of the synchronous generator (SG) and augment the operational domain of the SG+VSM system significantly, more importantly, almost eliminating the need for renewable energy curtailment. A case-study approach is used to present some key results on improvements in damping ratio, feasibility domain and transient stability. Finally, a feasibility domain curve is introduced and discussed in an aim to generalize the overall stability of any such system.
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ItemPolicy Options to Regulate PV in Low Voltage Grids-Australian Case with International Implications(Springer Nature, 2019-12)This article shows a socio-technical evaluation of the Australian case which has international implications for energy policy and regulation. Australia is one of few places globally that have faced domestic PV (photovoltaic system) adoption of above 50% of feeder connections. This leads to grid issues and is an emerging issue globally. Grid issues include over-voltage, thermal overload, frequency instability and voltage instability. This paper offers a policy process to regulate PV. This research extends earlier econometric modelling of Australian PVadoption data and extends it to focus on PVregulation in low voltage grids. This paper explores five policy options to help regulate PVin low voltage grids: the role of distribution businesses, inverter regulation, PVexport limits, cost reflective pricing, and storage. Policy complexity comes from the need to incorporate many stakeholder perspectives, and this research contributes to policy clarity by seeking a consensus.
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