A simple mixed-signal MPPT circuit for photovoltaic applications

The paper proposes a mixed-signal circuit approach for the Maximum Power Point Tracking (MPPT) for interfacing photovoltaic (PV) panels with batteries or inverters connected to the utility grid. The proposed circuit is aimed to a low cost single-chip IC implementation and it is based on the incremental conductance method, widely used in the literature when more complex microcontrollers or DSPs are used. Analog-to-Digital Converters (ADC) or Digital to Analog Converters (DAC) are avoided and the digital logic is reduced to a few elementary operations (a XOR port, a flip-flop and a counter). The analog part of the circuit implements most of the MPPT algorithm by exploiting the linear region of a field-effect transistor to measure and to store the absolute conductance of the operating point, and by using few analog switches, operational amplifiers and a comparator, to elaborate, after the duty-cycle perturbation, the value of the incremental conductance and to compare it with the absolute one. The digital logic imposes the timing of the different phases and the direction of the search algorithm. Simulation and experimental results on a 35 W PV panel, when a high-frequency dc-dc boost converter is employed as a MPP tracker, verify the validity and effectiveness of the proposed solution.