An Optimal Frequency-Modulated Hybrid MPPT Algorithm for the LLC Resonant Converter in PV Power Applications

The maximum power point tracking (MPPT) is an essential function of the PV power system to achieve the maximum PV power utilization. Traditionally, the MPPT can be realized by a duty cycle modulated dc–dc converter. However, if the
LLC
resonant converter is considered for the PV power system, the frequency-modulated MPPT algorithm should be adopted. Several strategies such as the frequency-based perturbation and observation (P&O) method and the center point iteration (CPI) method were proposed for the
LLC
resonant converter. However, with the conventional P&O method, there will be a tradeoff between the tracking speed and the oscillation phenomenon. Besides, the CPI method is unable to maintain the maximum power output under varying environmental conditions. In view of this, an optimal frequency-modulated hybrid MPPT algorithm is proposed in this article. First, the proposed frequency-modulated impedance-matching (FMIM) method is developed to track an optimal operation point under present environmental conditions. Then, the P&O concept will be utilized to ensure maximum power harvesting from the PV array. On the other hand, the operation point calculated via the FMIM is very close to the real MPP. Therefore, the perturbation amount of the P&O method can be minimized to avoid the oscillation around the maximum power point. Operational principles and thorough mathematical derivations are also developed. Finally, both simulation results and hardware verifications obtained from a 500-W prototype circuit demonstrate the performance and feasibility of the proposed MPPT.