UBC Theses and Dissertations

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UBC Theses and Dissertations

Average-value modeling of high power ac-ac and ac-dc converters for power systems transient studies Ebrahimi, Seyyedmilad


The ac–ac and ac–dc line-commutated converters are widely used in various high-power applications due to their high reliability and efficiency and low cost. Efficient and accurate computer simulations are necessary to analyze various aspects of power systems in both normal and unbalanced/faulty conditions where using detailed switching models of converters is computationally expensive due to switching. As an alternative, for system-level studies, the so-called parametric average-value modeling (PAVM) technique has been developed to achieve computationally efficient models of power-electronic converters that neglect the switching and capture the averaged dynamics of converters only. In this thesis, the PAVM methodology is extended to three-phase ac–ac class of converter systems. Furthermore, a generalized PAVM (GPAVM) is proposed for ac–dc converters that includes the ac harmonics in thyristor-controlled rectifier models considering their dependency on the line frequency. It is shown that any existing PAVM can be realized as a subset of the proposed GPAVM. Then, the PAVM methodology is extended to rectifiers with internal faults. The new formulation considers the asymmetrical operation of rectifiers by including the ac-side harmonics in both positive and negative sequences as well as dc components that may be present on ac variables. Finally, a new parametric methodology is presented that can provide continuous–detailed models of rectifiers which can also reconstruct the switching details similar to discrete–switching–detailed models. However, the proposed parametric–detailed model is continuous and can be simulated with much larger time-steps. Moreover, the new model can be easily converted to a PAVM by disabling the reconstruction of dc details/switching. All the models in this dissertation are verified by extensive experimental measurements and computer studies using detailed models of the subject converters. It is demonstrated that all the proposed new models have excellent accuracy over a wide range of operating conditions while being computationally much faster than the corresponding detailed switching models. It is envisioned that the models and methodologies proposed in this dissertation will receive wide acceptance in the research community and simulation software industry, and will enable the next generation of power systems simulation tools.

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