Due to its simplicity, low voltage stress, high reliability, low switch and inductor losses, and small inductor size, the Buck-Boost chopper has attracted a lot of attention in applications where it is necessary to step-up or step-down the DC voltage. In this paper a hybrid model of the Buck-Boost DC-DC converter using the PWA (piecewise affine) modeling framework is proposed, and then a PID controller is designed based on the PWA model. Finally, the particle swarm optimization (PSO) method is used to determine near optimum PID controller parameters. Designing the controller and analyzing the performance of the system based on the non-linear model are very difficult, so we used the PWA as an alternative solution. The proposed piecewise affine hybrid model lets decide about the control strategy and analyze the stability and performance of the closed loop control system using the classical control theory. Extensive simulations show the superiority of the PWA over the small signal linear model in prediction of the system behavior.

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