OSG-PLL-based method of a solar PV grid-interfaced transformer-less cascaded H-bridge multilevel inverter for power quality enhancement

The ever-growing demand for renewable energy sources has prompted significant interest in the integration of solar photovoltaic (SPV) system into the power grid. Transformer-based inverters in PV system not only elevate the weight, size, and cost of the inverter but also diminish its efficiency. To address this issue, this research presents a single-phase transformer-less five-level cascaded H-bridge multilevel inverter (CHB-MLI) using a single SPV source. The primary objective of this study is to enhance power quality and mitigate harmonics while integrating renewable energy sources into the grid. To control the inverter output voltage, a phase disposition-pulse width modulation (PD-PWM) technique is applied. An orthogonal signal generator-based phase-locked loop (OSG-PLL) is implemented to synchronize the inverter output with the grid voltage and frequency. To regulate the DC link voltage, grid voltage and current a cascaded proportional-integral (PI) and proportional resonant (PR) control strategy is implemented. The self-voltage balancing capability and simplified control scheme of this CHB-MLI make it highly suitable for PV applications. A comparative analysis is conducted to assess the strengths and weaknesses of the suggested multilevel inverter topology. The proposed control strategy improves power quality, reducing multilevel inverter voltage distortion to 4.20% and grid current distortion to 1.91%. The performance of both standalone and grid-connected system is evaluated using MATLAB/Simulink and validated in real time using OPAL-RT (OP5600) test setup.