This scheme can attenuate the double line frequency voltage ripple during low voltage ride through, thereby maintaining the DC bus voltage within a safe operating range. In addition, reference [33] used a sliding mode variable structure control scheme to enhance the robustness of DC bus voltage. However, it does not have universality due to additional load resistance parameters during the implementation of this scheme. Recently, observer-based control strategies have also been developed and applied in the regulation of DC bus voltage, such as the Luenberger observer [34], disturbance observer ESO (extended state observer) [35], etc. An ESO idea originated from the Luenberger observer without relying on the precise model of the object, so it is widely used to estimate unknown disturbances [36]. ADRC structure first used the Original ESO [37]. ADRC summarizes internal uncertainty and external disturbances of objects as generalized disturbances and constructs ESO and feedback control laws to deal with real-time estimation and compensation [38]. In addition, the inverter is also a system sensitive to nonlinear and time-varying because it involves aging issues and thermal effects [39]. In fact, the primary function of a photovoltaic inverter is to convert the direct current generated by the photovoltaic cell array into alternating current. This alternating current is then synchronized with the grid at the same frequency and phase, allowing for the seamless integration of photovoltaic power into the grid. Additionally, by employing appropriate control strategies, a smooth waveform of grid-connected current can be achieved, thereby enhancing power quality. The common control strategies for photovoltaic inverters in three-phase grid-connected photovoltaic power generation systems include photovoltaic plus, boost converters, phase-locked loop (PLL), maximum power point tracking (MPPT), _dq_ decoupling control, current inner loop control, and voltage outer loop control, among others [6]. These control methods are essential for achieving efficient operation of photovoltaic power generation systems and enhancing power quality. Among these solutions, the PLL regulates the DC bus in photovoltaic systems. Its primary function is to ensure synchronization between the photovoltaic power generation system and the power grid, thereby preventing power loss or equipment damage caused by voltage mismatches. Furthermore, the PLL helps the system maintain stable operation under varying conditions, such as fluctuations in light intensity. For instance, [PERSON] et al. [40] proposed an analytical method to evaluate the small-signal stability of three pathways related to voltage dynamics in the current control of a Voltage Source Converter (VSC) connected to a weak AC grid via a series-compensatedAC line. They validated each stability limit imposed by the Small-Signal Criterion (SCL), the Gvir/kAD ratio, and the PLL bandwidth through simulation. All the above factors have led to difficulties in the robustness control of DC bus voltage. The strong robustness of control systems based on ADRC generation mainly depends on the estimation accuracy of ESO for generalized disturbances. Therefore, this article proposes a cascaded ESO to improve disturbance estimation performance. The second level ESO is responsible for supplementing the remaining turbulence not estimated by the first level ESO, thus providing sufficient disturbance information for the feedback control circuit to perform compensation. Finally, this paper conducted simulation comparisons between the improved ADRC and the traditional ADRC under various operating conditions. The results show that the proposed control strategy can effectively suppress transient fluctuations of DC bus voltage under multi-source disturbances and improve dynamic response performance. Besides Section 1 of the introduction, the remainder of this paper is structured as follows. Section 2 shows an LCL-Filtered Grid-Connected Inverter based on Pade Approximation and Stability Description.