Time-Division Multiplexing Control of Multi-Input Converters for Low-Power Solar Energy Harvesters

Many autonomous sensor nodes use small photovoltaic (PV) panels oriented toward the direction that provides the highest energy yield in the worst case scenario. Since all those panels operate at similar irradiance and temperature conditions, they can be properly biased at the same bias point by using a single maximum power point tracker (MPPT). But in applications that involve several PV panels with dissimilar orientations, using an MPPT tailored to each panel would increase system cost. A better design option is to implement the MPPT with a single multiple-input converter shared through time-division multiplexing (TDM) control. However, existing TDM controls are usually based on pulsewidth modulation converters wherein the high switching frequency of transistors results in excessive power losses for low-power systems. Consequently, low-power MPPTs are instead usually based on pulse frequency modulation (PFM) converters. This paper proposes a novel TDM control method for MPPTs based on PFM converters.