Photovoltaic generation systems (PGSs) frequently experience partially shaded conditions (PSCs). Because PSC creates several peak values on the power-to-voltage characteristic curve, developing an algorithm that facilitates tracking global maximum power point (GMPP) is crucial. Therefore, this study introduced a two-stage GMPP tracking algorithm. In the first stage, this study developed the segmentation rules after performing extensive simulations on existing products. During the second stage, this study proposed a novel variable step-size perturb and observe method to increase the speed of searching for GMPP. The presented method feature advantages, such as simple structures, high tracking speeds, enhanced tracking accuracy, improved success rate, and easy integration with original PGS firmware. To verify the correctness of the proposed method, this study developed a 2 kW PUS prototype, which was used in subsequent simulations and experiments to assess method performance. (C) 2014 Elsevier Ltd. All rights reserved.