The integration of photovoltaic (PV) systems with the grid connected four-leg voltage source inverters (4LVSI) offers more efficient power conversion and distribution. However, the complexity of these higher-order systems presents significant control challenges due to the sensitive nature of both DC bus voltage and 4LVSI output currents, which introduce complex dynamic interactions within the 4LVSI control system and limit its overall control performance, particularly under system uncertainties and disturbances such as variations in irradiance, PV cell temperature, and grid voltage. To address these challenges, an enhanced active disturbance rejection control (EADRC) scheme based on a super-twisting sliding mode observer (STSMO) is designed for the outer DC bus voltage control loop. The STSMO is incorporated in the ADRC method for its fast uncertainties and external disturbances estimations, high resilience against uncertainties, and good immunity to measurement noise. The proposed STSMO-based ADRC approach effectively estimates and compensates for system uncertainties and external disturbances, thereby enhancing DC bus voltage dynamics and stability, improving resilience against uncertainties, increasing immunity to measurement noise, ensuring better steady-state accuracy of the DC bus voltage, and increasing system reliability while reducing cost and size. The effectiveness and superiority of the proposed control method for the PV grid-connected 4LVSI system are validated through both simulation and real-time studies using the OPAL-RT simulator. The results demonstrate robust performance under parameter uncertainties and disturbances, including variations in irradiance, PV cell temperature, DC bus capacitor value, and grid voltage sags.

In practical three‐phase PWM rectifiers, external disturbances, such as changes in load and grid voltage, and internal disturbances, such as DC capacitor uncertainty, have caused major problems, including DC‐link voltage fluctuations, harmonic distortion, and power factor degradation. They can also cause problems with power balance, stability, system dynamics, reduced efficiency, and increased stress. This paper proposes an enhanced linear state observer (ELSO) with a PLL‐less voltage‐oriented control (PLL‐less VOC) method for a three‐phase PWM rectifier in the synchronous coordinate frame (dq coordinate), aiming to simultaneously improve the DC‐link voltage dynamics, disturbance rejection ability, and the grid current control loop’s transient response. The ELSO is suggested instead of the load current sensor not only to estimate the disturbance but also to estimate the overall switching losses of the PWM rectifier, resulting in good DC‐link voltage disturbance rejection and transient fluctuation suppression, high robustness against DC capacitance change, low size and cost, and high reliability. Furthermore, contrary to the traditional VOC method, where the PLL and Park transforms are important parts for controlling the rectifier in the dq coordinate, the PLL‐less VOC method can control the grid currents directly in the dq coordinate without needing PLL and Park transforms, which can offer a fast transient response and low computational burden. The frequency domain analysis of the ELSO is used to identify its gains and enhance its stability and disturbance rejection capability. Finally, hardware‐in‐the‐loop (HIL) simulation using the OPAL‐RT 4510 real‐time simulator is also given to confirm the superiority and efficacy of the suggested control method.