An intelligent pass-through algorithm for non-inverting buck-boost solar power optimizers

The non-inverting buck-boost is a converter topology commonly encountered in renewable energy applications, as it is able to provide a wide range of output voltages, while its input voltage can be regulated to extract the maximum power available from the source. When input and output voltage of this converter are in close proximity, special dead-zone avoidance controls must be activated, in order to achieve stable operation. Abundant literature documents detrimental effects of the dead-zone, deemed to cause uncontrollability, increased ripple and sub-harmonic oscillations in the regulated voltage. This paper proposes a new algorithm to avoid the operational dead-zone in the non-inverting buck-boost converter by introducing a pass-through operation. In this mode, the input port is directly linked to the output port of the converter, avoiding pulse width modulation (PWM) switching, whenever the voltage at these two ports is within a narrow range. Existing dead-zone avoidance techniques rely on using extra switches, or on using a buck-boost operation which inevitably increases the conversion losses. Conversely, the proposed technique does not rely on simultaneous buck and boost PWM operation and does not need additional hardware to activate the pass-through mode. The presented control algorithm is thoroughly discussed and implemented in a digital microcontroller. Finally, efficiency measurements and experimental results executed on a 200 W non-inverting buck-boost photovoltaic module integrated converter are used for performance evaluation.