High-order filters, such as LCL, are more commonly employed in grid-connected inverters (GcIs) as an interference element for the better attenuation of switching harmonics. However, LCL filters may have resonance poles and antiresonance zeros in the frequency response with inverter side current. This may affect the stability of the system and limit the control bandwidth with the simple single-loop PI control. This becomes severe with the introduction of grid impedance due to the large distance between renewable energy sources and the power grid. To mitigate this effect, active damping and sensorless damping is preferred with pre-information about grid impedance. In this paper, linear active disturbance rejection control (ADRC) is introduced, first to L filter type GcI and later extended to LCL filter type GcIs with minimum modification. From the frequency analysis, it is shown that the characteristics of the proposed control scheme remain the same even with a change in filter order and grid impedance. The resonance poles and antiresonance zeros in the LCL filter are compensated via the pole–zero cancelation technique. In addition to this, the preserve bandwidth, simple control design, and decoupled current control are also achieved with the proposed method. The robustness of the proposed method is compared with the single-loop PI control under different filter types and grid impedance uncertainty through MATLAB simulation and experimental outcomes.

This paper presents a control algorithm to reduce the computational burden of model predictive control in a grid-connected single-phase $N$ -cell cascaded flying capacitor H-bridge (CFCHB) multilevel converter of a solid-state transformer. The proposed control algorithm is a finite-control-set model predictive control (FCS-MPC) that is based on a hierarchical structure controlling the grid current, DC-link voltage, and flying capacitor voltage, using each cost function through three layers. Unlike the conventional multi objective cost function that evaluates and compares all candidates to determine the optimal state, the proposed method uses a single-objective cost function by separating the control variables to determine the optimal state through calculation without comparison. Therefore, the amount of computation is significantly reduced compared with that of the conventional method, and the execution time is shortened. Thus, the sampling period can be shortened and the switching frequency can be increased. Further, it can lead to using a smaller inductor to produce a high-quality grid current, which can help reduce the system size and cost. The execution time is not large, even if the voltage level increases and the effect of time reduction is large compared to the existing method, because the computational burden of the proposed method is linearly proportional to the number of cells. The voltage level expansion is easy and suitable for digital system implementation, and the control performance is not affected. The effectiveness of the proposed method is verified through the simulation of a single-phase 250 kW 9-cell CFCHB multilevel converter using PSIM and an experiment with a single-phase 2 kW 3-cell CFCHB multilevel converter at the laboratory scale.

This paper is an attempt to present a simple yet innovative planning method for determining the type of common bus in a hub station (HS), devised on efficiency and reliability grounds. The efficiency is evaluated by modeling the efficiency curves of the converters under part-load and full-load conditions, hence enabling a realistic estimate of the efficiency. Reliability evaluation is executed by modeling the failure and repair rate distributions of the HS components. The optimal common bus type selection is based on both the efficiency and reliability metrics of the HS. The deterministic factor in the type of common bus selection is proved to be the number of components in the HS. The results indicate that DC and AC systems have comparable efficiencies with a meagre difference of 1.26%. The failure rate of AC common bus architecture is 22% greater than DC common bus architecture resulting in a 1.788 times reliability advantage of the DC system. Moreover, the greater number of components in the case of a AC common bus adds to the economic advantage of DC with a lower number of components leading DC to be an optimal design.

The new millennium witnessed an unanticipated escalation in the installation of rooftop solar panels, particularly due to the development of highly efficient power electronic converters (PECs). The ‘battle of currents’ between AC and DC, which settled in the favor of AC in the nineteenth century, reignited as DC is striking back due to this technological augmentation. The shifting trend towards DC is more pronounced in the residential sector, which necessitates a comparative analysis of AC and DC at distribution scale on realistic grounds. Modern home data extracted from the energy information administration (EIA) has been utilized to devise a mathematical model based on bottom-up approach. The comparative analysis has been performed encompassing scenarios of varying PEC efficiencies as a result of daily load variation. Moreover, the scenarios of multiple PEC efficiencies and rooftop solar capacities are also considered. The comparative analysis revealed efficiency advantage of 1.966%, 1.41% and 1.17% in favor of DC as compared to AC for the scenarios considered. In the end future recommendations are presented to further enhance the efficiency of DC, thereby providing a concrete standing for power industry decision of adopting DC at distribution scale.