Browsing by Author "Mwaniki, Frederick Mukundi"
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- ItemModelling and performance evaluation of a pseudo-random impulse sequence for in situ parameter estimation in energy applications(Stellenbosch : Stellenbosch University, 2020-03) Mwaniki, Frederick Mukundi; Vermeulen, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: System identification and parameter estimation procedures involve the use of experiments to find an accurate model for a target system. These experiments typically involve excitation of the target system with a perturbation signal and recording and analysing the system’s input and output waveforms. The time- and frequency-domain characteristics of the perturbation signal can have a significant influence on the system response and the accuracy of the parameter estimation experiment. An optimal perturbation signal should persistently excite all the relevant modes of the target system. Although a significant amount of research has been carried out on perturbation signals, the case of a suitable signal for high power, high voltage, in situ applications has not been thoroughly investigated. This study discusses the novel concept of a Pseudo-Random Impulse Sequence (PRIS) as a wideband perturbation signal for in situ parameter estimation in energy field applications. The time- and frequency-domain properties of the PRIS are analyzed and the effects of the various model parameters, including the time constants, sequence length and clock frequency are investigated through mathematical analysis and simulations to determine the suitability of the signal for system identification and parameter estimation applications. It is demonstrated that the time- and frequency-domain properties of the PRIS can be controlled by manipulating the associated clock frequency, time constants and sequence length. This controllability of the PRIS is highly desirable as it allows the user to focus the perturbation energy to suit a wide range of applications. Perturbation signals for use in the high power applications should be generated efficiently using circuit topologies that are compatible with the associated high voltage environment. A perturbation source circuit topology for generating the proposed PRIS signal is developed and analysed. It is shown that the PRIS can be generated using a compact and efficient design with highly reduced average losses compared to conventional sources such as the Pseudo-Random Binary Sequence (PRBS) topologies. The circuit topology is, furthermore, demonstrated to be optimal for in situ high power, high voltage applications. The circuit design considerations for the proposed PRIS source are discussed in detail. Accurate information on the grid impedance characteristics, especially from a particular Point of Connection (POC) is essential for harmonic penetration studies, compliance with harmonic limits for the grid integration of renewable energy sources, transient analysis, harmonic filter design and controller design. The performance of the PRIS signal is demonstrated successfully for an in situ case study application involving wideband characterization of the The venin equivalent grid impedance of a supply network. A novel experimental approach is proposed to improve the grid impedance estimation results by minimizing the effects of the non-stationary nature of the grid.