In response to the growing need for efficient and sustainable energy systems, phase shifters are pivotal in enhancing the flexibility and reliability of power grids while facilitating the integration of renewable energy sources. This paper conducts a comprehensive economic evaluation of various phase shifter technologies, including symmetrical dual-core mechanical phase shifters, electronic phase shifters, and controllable phase shifters, using a lifecycle cost (LCC) analysis framework tailored for the energy sector. The assessment employs probability distributions and Monte Carlo simulation methods to analyze their economic performance, considering key energy-related cost factors such as initial investment, operational efficiency, maintenance, and decommissioning. An uncertainty analysis is introduced to refine the accuracy of LCC calculations, while sensitivity analysis highlights the influence of cost fluctuations—especially in initial investment and operating costs—on overall performance. The results reveal that while large-capacity phase shifters involve higher upfront costs, their superior operational efficiency and lower long-term unit costs can provide substantial economic advantages for sustainable energy applications. These findings offer valuable insights for optimizing energy equipment selection and guiding investment decisions in the transition toward greener and more resilient energy systems.

The series-connected chain MMC with DC-blocking capacitor (C-SCMMC) is an emerging topology for HVDC tapping applications with high voltage and relatively low power capacity. However, the DC-blocking capacitor can be bulky and costly, which deteriorates its economy and flexibility. This paper investigates the feasibility of DC-blocking capacitor reduction, with special emphasis on the characteristics, control, and parameter design. The principle of C-SCMMC considering the DC-blocking capacitor dynamics is firstly modeled and analyzed, and the ripples and harmonics, as well as their influences on the external performance of the converter, are analyzed; then, improved control strategies, namely, the grid-tied harmonics suppression and current control, are proposed considering the enlarged DC-blocking capacitor voltage ripple; after that, the influence of reduced DC-blocking capacitor on the operation range and parameter design are analyzed, and the economic advantage is demonstrated via parameter design and comparison based on a typical bench mark. Analysis shows that the DC-blocking capacitor voltage ripple is coupled with other parameters, such as the arm output voltage and SM capacitance, and the advised range is from 0.1 to 0.3 p.u. at unity power factor to reduce the overall cost. In a typical design, the C-SCMMC can reduce the number of SMs by 2/3 and the capacitor energy storage capacity by 15% compared to the conventional MMC. Finally, simulation results obtained in MATLAB/Simulink 2024b are provided to verify the feasibility of the proposed converter and the correctness of the parameter design.

With the rapid development of DC grids, resonant DC circuit breakers (RDCBs) have become critical for fault isolation. However, existing RDCBs often suffer from severe energy mismatches, and components, including mechanical switches, resonant capacitors, and power electronic devices, suffer from excessive internal overvoltage during the current interruption process. To address these issues, a novel RDCB with a capacitor self-charging current excitation source (CES) is proposed in this paper. First, by controlling the charging process of CES by the fault current, the injected energy is matched with the commutation requirements, significantly reducing the transient recovery voltage (TRV) applied to the mechanical switch. Second, to suppress the voltage applied to the resonant capacitor, a metal oxide arrestor (MOA) should be connected directly in parallel with the resonant capacitor, avoiding overvoltage caused by the internal oscillation between the resonant inductance and the resonant capacitor. Furthermore, an anti-parallel magnetic core is designed for CES, ensuring dynamic current sharing among parallel IGBTs while maintaining a zero-inductance characteristic externally. Simulation results verify that the proposed RDCB reduces the peak TRV by at least 64% compared with existing RDCBs. Furthermore, the effectiveness of the proposed overvoltage suppression methods is validated, significantly improving the interrupting reliability.