This paper presents a robust control technique for DC-DC boost converters used in photovoltaic (solar) systems, particularly under conditions of time-varying disturbances. The proposed solution employs high-order super-twisting sliding mode control (HOSM), which is designed to improve system performance by reducing steady-state fluctuations and dynamically adjusting controller gains in response to changing solar irradiance. This significantly improves the converter’s ability to handle variations in solar input, ensuring more stable and efficient operation. Compared to traditional proportional-integral (PI) control, the HOSM technique shows superior robustness to uncertainties and disturbances, making it well suited to the variable nature of solar power generation. Extensive simulation results confirm the effectiveness of this control approach and highlight its potential for optimising the stability and efficiency of isolated flyback converters in photovoltaic systems. This technique offers a promising way to improve the reliability and performance of renewable energy systems, ensuring more consistent energy harvesting.