Obtaining the maximum power output in real time is indispensable to the operation of grid connected photovoltaic (PV) power systems under given atmospheric conditions. Focusing on the resistance effect of the solar cells, we propose a new and simple method to directly determine the dynamic resistance of the PV modules from an irradiated current voltage characteristic curve. In our method, we develop the ability to determine the dynamic resistance with a combination of finite series-and shunt-connected resistance. A series of experiments, including numerical simulations and field data tests, are conducted to examine the dynamic behavior of the PV modules during power tracking. Experimental results show that the proposed direct resistance-estimation method allows the PV modules to achieve their maximum power and impedance matching under various operation conditions. (C) 2011 Elsevier Ltd. All rights reserved.