A full-bridge diode-clamped multilevel LLC resonant converter suitable for power conversion systems that use high input voltage, such as railway vehicles, is proposed in this paper. In order to eliminate the voltage deviations of the capacitors connected in series to the high voltage input DC link, a novel modulation strategy referred to as multi-neighboring reference vector discontinuous pulse-width modulation (MNRV DPWM) is proposed. Unlike the existing two-level resonant converter that varies the operating frequency to hold the output voltage constant, the proposed multilevel resonant converter modulates the amplitude of the fundamental wave input to a resonance tank while fixing the operating frequency at the resonance point. Therefore, the design of passive elements becomes easier, and stable operation is possible over a wide operating range with only one power conversion stage. In this paper, the control algorithm and operation characteristics of the newly proposed full-bridge diode-clamped four-level LLC resonant converter are analyzed in detail and design guidelines are presented. The feasibility of the proposed converter is verified through a simulation and an experiment with a prototype converter.

In this paper, we propose a novel full-bridge (FB) diode-clamped four-level symmetric switching converter. Multi-neighboring reference vector discontinuous PWM (MNRV DPWM) for FB topology was implemented through symmetric half-bridge (HB)-based control using an offset voltage addition method. A diode-clamped four-level symmetrical switching circuit with pulse-amplitude modulation (PAM) was proposed and its working principle was explained in detail. Voltage gain, duty loss factor, and zero-voltage-switching (ZVS) condition were derived by analyzing the steady-state operating characteristics of the proposed converter. The required input and output capacitance values were also calculated explicitly. The voltages across the series-connected input DC-link capacitors were well balanced and the output voltage was controlled in a simple linear manner by PAM. The proposed method has the advantage of reducing circulating current compared to the existing phase-shift method because there is an additional powering period. The effectiveness of the proposed converter was verified through simulation and prototype experiments. The power conversion efficiency exceeded 91.44% at an output power ( P_O ) of 250W or higher, with a peak efficiency of 95.23% achieved at P_O =750W.

In this paper, a three-phase diode-clamped four-level PWM inverter with offset voltage injection is proposed. The proposed inverter is based on multi-neighboring reference vector (discontinuous) pulse-width modulation (MNRV (D)PWM), where multiple adjacent reference vectors with different charging/discharging characteristics of the capacitors are selected depending on the location of the command voltage. These reference vectors are evenly utilized, and the duty ratio of the remaining reference vector as a degree of freedom is adjusted to satisfy the volt·time product. Additionally, the proposed MNRV (D)PWM can generate various (D)PWM forms by applying the offset voltage injection method. By extending the methodology applied to the four-level inverter, a general MNRV (D)PWM method applicable to general high-dimensional multilevel multiphase PWM inverters is also proposed. It is demonstrated that MNRV (D)PWM can be applied not only to dc/ac but also to dc/dc topologies. The ripple component of the dc-link voltage has been confirmed to be related to the three-phase summation of the product of the duty of the E voltage level vector and the phase current. Through various simulations and prototype experiments, the steady-state operating characteristics have been confirmed, demonstrating reduced average switching frequency and superior THD performance compared to conventional methods. Furthermore, proficient management of fluctuations in the dc-link voltage reference and sustained voltage equilibrium are exemplified.

This paper presents a Fuzzy logic-based train control algorithm designed to enhance energy efficiency across a complete railway route. The proposed framework dynamically integrates practical information such as curvature data, gradient profiles, and station schedules to optimize acceleration, coasting, and braking phases. By using Fuzzy logic, the algorithm adaptively balances energy consumption, travel time, and stopping precision. Key features include predictive speed scanning and adaptive PI control, enabling comprehensive energy optimization. Simulation results confirm significant energy savings while maintaining operational reliability and precision. This study highlights the potential of Fuzzy-based control systems in advancing sustainable railway operations.

This paper introduces the multi-neighboring reference vector discontinuous pulse-width modulation (MNRV DPWM) with offset voltage injection methodology tailored for single-phase diode-clamped four-level PWM inverters. By evenly utilizing multiple adjacent reference vectors with diverse charging/discharging characteristics of dc-link capacitors and employing duty compensators to adjust minor voltage discrepancies under practical conditions, precise tracking of commanded voltages is ensured even under transient conditions, while maintaining balanced voltages across the dc-link capacitors. This approach proposes various continuous/discontinuous modulation types using intentionally designed offset voltages to minimize dc-link voltage variation. Notably, setting the offset voltage to zero interestingly implements conventional virtual-vector PWM. By analyzing the sum of the product of the duty ratio of the basis vector and the phase current, the relationship with the dc-link voltage fluctuation was analyzed mathematically rigorously. Through various simulations and prototype experiments, the steady-state operational characteristics of the proposed method have been validated, demonstrating lower average switching frequencies and superior total harmonic distortion performance compared to conventional method. Specifically, with a power factor of pf =0.9 and a modulation index m =0.3, the proposed method achieves an output voltage THD ranging from 86% to 126% and an output current THD between 4.65% and 5.45%, marking an improvement compared to the conventional carrier-overlapped PWM, which recorded a voltage THD of 121% and a current THD of 7.35%. Additionally, proposed method reduces the average switching frequency by approximately 30% and the control operation time by about 22% compared to existing methods. The stability of the dc-link voltage equilibrium under transient conditions was also successfully verified.