A Center Point Iteration MPPT Method With Application on the Frequency-Modulated LLC Microinverter

Maximum power point tracking (MPPT) is an essential technique to harvest PV power under varying environments. Perturb and observe (P& O) algorithms are the most broadly used MPPT due to their effectiveness and simplicity. However, it is difficult to balance the tracking speed and oscillation requirements in the conventional P& O with fixed perturb. Adaptive P& O techniques have been proposed as a solution to these problems. However, they are based on duty cycle modulation for conventional pulse width modulation converters. None of them deal with the variable frequency modulation for resonant converters. In this paper, a center point iteration MPPT is proposed, with its variable perturb in frequency. The proposed scheme overcomes the drawbacks of conventional P& O with a simple calculation. Moreover, it is suitable for various power curves, especially the LLC microinverter power curves, which may confuse conventional MPPT algorithms. The effectiveness of the proposed MPPT method was verified in theory. A 300 W prototype was constructed, and the experimental results verified the effectiveness of the proposed center point iteration MPPT. An advanced version was also introduced in order to accelerate the tracking speed.