**6. Discussion**

 In Section 3.1, it can be seen that all the uncertain terms in Equation (12) can be divided into three categories, which are the ones related to the load current, the ones related to the uncertain parameters, and the ones related to both the load current and the uncertain parameters. In Sections 5.1 and 5.2, there are no parameter uncertainties or mismatches, then the designed observer only estimates the uncertain term related to the load current. In this way, the observer operates as a load current observer, and the two subsections of 5.1 and 5.2 focus on the steady-state and dynamic performance of the designed observer and the proposed two-layer MPC. In Section 5.3, parameter uncertainties exist, and the designed observer estimates the sum of all the uncertain terms. Thus Section 5.3 focuses on the robustness performance against the parameter mismatches of the LC filter.

Compared with the dual observers used method in [31] and the additional current sensors based method in [32], only one observer is used to observer all the uncertain terms caused by the parameter uncertainties and the load current in a centralized way. This not only improves the system robustness against both the parameter uncertainties of the filter inductor and the filter capacitor, but also avoids the use of additional load current sensors and observers. And this also leads to a reduction in both the amount of calculation and the economic cost for the hardware configuration. In addition, the layered

structure of the proposed MPC further reduces the computation. It can be inferred that the proposed robust MPC can also be extended to general inverters with LC filters, which are widely used in distributed generation systems, energy storage systems, and uninterruptible power supplies.
