| الملخص: |
Abstract: Recently, riding through grid faults and supporting the grid voltage under faults have become major requirements in distributed energy resource (DER) units. There have been also extensive efforts in academia and industry to develop and implement control strategies to ride through voltage disturbances, and even to support the grid under such faulted conditions which can be named as low-voltage ride-through (LVRT) technology. Therefore, a comprehensive and comparative study seems to be very useful in order to analyze and discuss available LVRT reference-current-generation (LVRT-RCG) strategies in converter-interfaced DER units, compare their performances, and introduce their pros and cons. This thesis studies all existing (nine) LVRT-RCG strategies available in the literature. These strategies are categorized into two main groups. The analytical evaluations and mathematical assessments of all LVRT-RCG strategies are performed. For a comprehensive evaluation of these strategies, the following important parameters are used in this study: instantaneous active/reactive powers oscillation and maximum phase currents. Analytical expressions of these parameters are formulated, evaluated and used to conduct several evaluation and comparative studies on different strategies. Based on the obtained formulas for the maximum phase currents, the maximum allowable reactive power delivery (MARPD) equations are proposed specifically for each of the nine LVRT-RCG strategies. Proposed equations help each LVRT-RCG technique to provide their best voltage support under the specific maximum phase current restrictions imposed by DER owners. Using different test cases, the strategies are compared and the proposed equations are validated. This thesis can be helpful to evaluate the performance of existing LVRT-RCG strategies, solve their existing drawbacks, exploit the best performance out of each, combine their individual capabilities, and improve them. |