Control of Multi-cell AC/DC and Cascaded H-bridge DC/AC-basedAC/DC/AC Converter

摘要

A single-phase two-stage AC/DC/AC converter topology is investigated in this paper, which involves multi-winding transformer-fed multi-cell AC/DC and cascaded H-bridge multi-level (CHBMLI) DC/AC converter stages. Both the converter stages utilize current control using the fixed and uniform switching methods, which simultaneously achieve the regulation of the DC link voltages of all the cells. The proposed control loop for the AC/DC converter stage uses a single-voltage sensor to control the DC link voltages of all the cells using self-voltage regulating property of the multi-winding transformer. This single-control loop uses the feedback of the instantaneous AC current at the primary of the transformer and any one of the DC link voltage to achieve the input AC current control and multiple DC link voltage control. The fixed frequency ramp comparison current control in AC/DC stage of the converter provides a uniform switching cycle among all the units. A phase-shifted multi-carrier PWM (PS-MCPWM)-based fixed frequency current control of the DC/AC converter comprising CHBMLI provides equal loading across all DC links of the AC/DC converter. The results are verified through PSCAD simulations and experimental results are obtained through the LabVIEW FPGA controller implemented for two-cell, five-level converter topology.