Direct Frequency Control Based MPPT Algorithm of LLC Resonant Converter for Photovoltaic System

LLC resonant converter has advantages in efficiency when applied to photovoltaic(PV) system. However, renowned maximum power point tracking(MPPT) algorithms are mostly based on pulse width modulation(PWM) while LLC resonant converter is a pulse frequency modulation(PFM) converter. Using a PWM MPPT method in LLC converter might cause the loss of soft switching characteristic. Therefore, an MPPT algorithm based on PFM is needed. In this paper, a direct frequency control based MPPT algorithm is proposed by analyzing the relationship between switching frequency and voltage of PV array. The parameter design constraints of LLC resonant converter to achieve MPPT is also provided. Experimental results are given to verify the validity of the analysis.