Combinatorial test design is a plan of test that aims to reduce the amount of test cases systematically by choosing a subset of the test cases based on the combination of input variables. The subset covers all possible combinations of a given strength and hence tries to match the effectiveness of the exhaustive set. This mechanism of reduction has been used successfully in software testing research with t-way testing (where t indicates the interaction strength of combinations). Potentially, other systems may exhibit many similarities with this approach. Hence, it could form an emerging application in different areas of research due to its usefulness. To this end, more recently it has been applied in a few research areasudsuccessfully. In this paper, we explore the applicability of combinatorial test design technique for Fractional Order (FO), Proportional-Integral-Derivative (PID) parameter design controller, named as FOPID, for an automatic voltage regulator (AVR) system. Throughout the paper, we justify this new application theoretically and practically through simulations. In addition, we report on first experiments indicating its practical use in this field. We design different algorithms and adapted other strategies to cover all the combinations with an optimumudand effective test set. Our findings indicate that combinatorial test design can find theudcombinations that lead to optimum design. Besides this, we also found that by increasingudthe strength of combination, we can approach to the optimum design in a way that with onlyud4-way combinatorial set, we can get the effectiveness of an exhaustive test set. This significantlyudreduced the number of tests needed and thus leads to an approach that optimizesuddesign of parameters quickly.
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