An isolated modular multi‐level AC/AC converter with high‐frequency link and pulse flip circuit for fractional frequency transmission system application

Abstract

Based on the modular topology and the traditional voltage-sourced converter (VSC) model, this paper presents an isolated modular multi-level AC/AC converter with highfrequency (HF) link and pulse flip circuit for fractional frequency transmission system (FFTS) application. The proposed converter uses the HF transformer to realize electrical isolation, omitting the industrial frequency (IF) transformer with large volume and heavy weight. In the primary side of the HF transformer, the power transmission is realized by the rectifier and the inverter. In the secondary side of the HF transformer, the double Hbridges are used to realize the natural freewheeling of the leakage current, which solves the problem of voltage overshoot. On the basis of carrier phase-shifted pulse width modulation (CPS-PWM), an improved modulation strategy is proposed to realize the HF output voltage of the inverter. It has the advantages of easy expansion, no circulation current, good output voltage quality, low cost and no need of offshore converter station, so it has great potential in the field of offshore wind power grid connection. The working principle, natural freewheeling modes, modulation method and overall system control scheme of the proposed topology are introduced in detail, and the feasibility of the proposed topology is verified by simulation in MATLAB/Simulink environment and test through APPSIM platform.

Third harmonic injection control for co‐phase traction power supply system using direct AC/AC full‐bridge modular multilevel converter

“…The full-bridge sub-module (FB-SM) can achieve positive, negative, and zero-level output. Based on this feature, fullbridge modular multilevel converter (FB-MMC) can convert the three-phase AC voltage directly into single-phase AC voltage [18,19] and act as a co-phase power supply system converter for railway supplies without the complicated AC/DC/AC process, which has a simpler construction and higher efficiency. FB-MMC is used in [20] to convert the three-phase voltage directly into single-phase voltage and proposes a corresponding control strategy, but the closed-loop control of the single-phase AC voltage is not achieved.…”

Simulation Model of Single-Phase AC-AC Converter by Using MATLAB

“…The simulation included a review of alternating current circuits of both types, single and three phases, with different loads, including fixed and variable ones [47][48][49][50]. It also highlighted the fact that it has a 1-phase H.W.C or 1-phase F.W.C transformer, as will be mentioned later [51][52][53][54][55].…”