Power Quality Enhancement in Solar/Wind/Battery Integrated Renewable Energy Systems Using UPQC with a Modified Robust PID Controller

The increasing integration of renewable energy sources into modern electrical networks has created significant challenges related to power quality, voltage regulation, harmonic distortion, reactive-power management, and dynamic stability. Solar photovoltaic (PV) and wind energy systems are inherently intermittent because their power generation depends on environmental conditions, while nonlinear loads and power electronic converters can further deteriorate voltage and current quality. This study proposes a Solar/Wind/Battery integrated renewable-energy system incorporating a Unified Power Quality Conditioner (UPQC) controlled by a Modified Robust Proportional–Integral–Derivative (MRPID) controller. The UPQC employs coordinated series and shunt voltage-source converters to compensate voltage- and current-related disturbances, while battery energy storage provides an energy-buffering mechanism between renewable generation and load demand. The proposed MRPID controller is developed to improve disturbance rejection, transient response, steady-state accuracy, and robustness compared with conventional PI and PID controllers. The complete system is modeled and simulated in MATLAB/Simulink under normal and disturbed operating conditions, including voltage sag, voltage swell, harmonic distortion, nonlinear loading, sudden load variations, and renewable-generation variations. Performance is evaluated using current total harmonic distortion (THD), RMS voltage, RMS current, active power, reactive power, power factor, and DC-link voltage. The simulation results demonstrate that the MRPID-controlled UPQC achieves a current THD of 2.50%, compared with 6.42% for PI and 3.87% for PID, corresponding to an 80.54% THD improvement. The proposed configuration also achieves 230 V RMS voltage, 104.80 A RMS current, 80 kW active power, 6 kVAR reactive power, 0.998 power factor, and 800 V DC-link voltage. The results demonstrate the potential of the proposed approach for improving power quality and dynamic performance in renewable-energy-based distribution systems and microgrids.