A variable step-size MPPT method applied for a partial-shadow PV system

Under partial shading conditions, the power-voltage curves of the solar arrays will produce many power operating points. The global maximum power point (GMPP) needs to be tracked to output the real maximum power to avoid to fall into local maximum power points. Although the full-range search method can trace the global maximum power point, the tracking time and accuracy of the system will be affected by the step size of the duty cycle. Therefore, the auto-scaling step-size (ASSS) method is combined with the full-range search method to track the global MPP in this paper. The tracking program starts from zero duty cycle to track, and if there is a point with power greater than the last maximum power, then uses the ASSS method to track a new MPP. Otherwise, the program continues to scan until the duty cycle comes to one. Then the duty cycle of the global maximum power point is output to complete the track. From the results of the experiment and simulation, the tracking speed of the proposed method is faster than that only with the full-range search method.