Global adoption of renewable energy is increasing due to growing concern over climate change, increasing costs associated with conventional generation, and decreasing capital investment costs of renewable energy technologies. Specifically, wind power represents the most technologically mature renewable alternative and is recognized as a cost effective generation source in both large and small power systems. However, the variability due to the stochastic nature of the wind resource introduces technological limitations to the amount of wind power which can be integrated in a power system. Energy storage is seen as a solution to mitigate the variability in wind power output. Wind power and energy storage devices have the potential to contribute a substantial amount of renewable generation to meet the electricity demand in remote power systems. Remote power systems are characterized by their self reliance on electrical generation. The basic function of a remote power system is to provide the necessary power to satisfy the community’s electricity demand requirements as economically as possible with an adequate level of continuity and reliability. / Graduate

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This thesis presents and investigates Space Vector Modulation (SVM) switching strategies for (i) a multi-level Diode-Clamped Converter (DCC) and (ii) a multi-module Voltage-Sourced Converter (VSC) system in which each module is a conventional two-level VSC. Although the SVM strategies are general and applicable for n-level DCC and n-module VSC systems, this text only concentrates on five-level DCC and four-module VSC systems. For a five-level DCC, a computationally efficient SVM algorithm is proposed. The algorithm, that is based on a classifier Neural Network (NN), reduces the computational time for the SVM realization. Therefore, adequate saving of processor execution time, in each sampling period of SVM, is provided to carry out other functions, e.g. the calculations required for DC-capacitor voltage balancing task. The thesis also proposes a DC-capacitor voltage balancing strategy to counteract the voltage drift phenomenon of (i) a passive-front-end five-level DCC, and (ii) a back-to-back connected five-level DCC system. The proposed balancing strategy, that is based on augmenting the proposed SVM algorithm, takes advantage of the redundant switching states to minimize a quadratic cost function associated with voltage deviations of the DC-capacitors. The salient features of the proposed balancing strategy are (i) online calculation of SVM to select the best switching states, (ii) minimization of switching frequency, (iii) minimization of the THD content of the AC-side voltage, and (iv) no requirement for additional power circuitry. For a four-module VSC system a sequential sampling SVM strategy is proposed. The proposed strategy (i) provides harmonic cancellation/minimization at the net AC-side voltage of the multi-module VSC system, and (ii) offers a low switching frequency for each VSC module. Technical feasibility of the proposed SVM strategies for a five-level DCC and a four-module VSC system, as a STATCOM and a back-to-back HVDC system, are investigated and presented. The studies are conducted in the time-domain, in the PSCAD/EMTDC software environment.

Thesis (MEng) -- University of South Australia, 1992

Thesis (MEng) -- University of South Australia, 1992