Fixed-frequency implementation of sliding-mode controllers for photovoltaic systems

Traditional implementation of sliding-mode controllers, based on hysteresis comparators, exhibits variable switching frequency. Such a condition makes it difficult to select the semiconductor devices, design the passive elements of dc/dc converters, and design the sensing filters usually adopted for removing the switching noise from currents and voltages. Those problems are always present in photovoltaic systems based on variable-frequency sliding-mode controllers. Therefore, this paper proposes an implementation methodology for sliding-mode controllers providing constant switching frequency, which is aimed for grid-connected photovoltaic applications. The proposed solution does not compromise the power production of the PV system, hence it provides the same PV power in comparison with the classical variable-frequency implementation. Finally, the performance and correct operation of the fixed-frequency implementation are demonstrated using both simulation and experimental results.