Fractional Order Load-Frequency Control of Interconnected Power Systems Using Chaotic Multi-objective Optimization

摘要

Fractional order proportional-integral-derivative (FOPID) controllers aredesigned for load frequency control (LFC) of two interconnected power systems.Conflicting time domain design objectives are considered in a multi objectiveoptimization (MOO) based design framework to design the gains and thefractional differ-integral orders of the FOPID controllers in the two areas.Here, we explore the effect of augmenting two different chaotic maps along withthe uniform random number generator (RNG) in the popular MOO algorithm - theNon-dominated Sorting Genetic Algorithm-II (NSGA-II). Different measures ofquality for MOO e.g. hypervolume indicator, moment of inertia based diversitymetric, total Pareto spread, spacing metric are adopted to select the best setof controller parameters from multiple runs of all the NSGA-II variants (i.e.nominal and chaotic versions). The chaotic versions of the NSGA-II algorithmare compared with the standard NSGA-II in terms of solution quality andcomputational time. In addition, the Pareto optimal fronts showing thetrade-off between the two conflicting time domain design objectives arecompared to show the advantage of using the FOPID controller over that withsimple PID controller. The nature of fast/slow and high/low noise amplificationeffects of the FOPID structure or the four quadrant operation in the twointer-connected areas of the power system is also explored. A fuzzy logic basedmethod has been adopted next to select the best compromise solution from thebest Pareto fronts corresponding to each MOO comparison criteria. The timedomain system responses are shown for the fuzzy best compromise solutions undernominal operating conditions. Comparative analysis on the merits and de-meritsof each controller structure is reported then. A robustness analysis is alsodone for the PID and the FOPID controllers.