Enhanced QRLS adaptive control strategy for power quality improvement in single-phase grid tied photovoltaic and hybrid energy storage

The increasing reliance on renewable energy sources introduces challenges such as power quality issues, voltage flickers, and grid synchronization. The issues are further intensified by the intermittent nature of solar irradiance, which causes significant voltage and frequency fluctuations in the grid. The paper presents a single-phase dual-stage grid-integrated photovoltaic system with a hybrid energy storage system (HESS) controlled by a quaternion kernel recursive least-squares (QRLS) algorithm. The QRLS-based voltage source converter control offers multifunctional capability of a nonlinear system, including total harmonic distortion (THD) mitigation, DC-bus voltage stabilization, and voltage sag/swell compensation. The HESS with battery and ultracapacitor provides a suitable blend of power and energy density to deal with system irregularities at the grid, load, and PV side. The HESS, combining a battery and ultracapacitor, ensures fast transient response and energy balance. Experiments show a DC bus voltage deviation of only ±1% and THD is reduced to 0.43%. The system remains stable with constant power and THD below 1%. It also works well during irradiance changes, load variations, and voltage sags or surges, meeting IEEE 1547 standards.