A Matrix-Type Back-to-Back Three-Phase Isolated AC–AC Converter

This article proposes a matrix-type back-to-back three-phase isolated AC–AC converter consisting of a three-phase rectifier, a dual active bridge (DAB) converter, and a three-phase inverter. Both the rectifier and inverter employ a two-phase-clamped discontinuous pulse-width modulation strategy, which is characterized by two phase modulation signals being clamped and the other one phase arm with high-frequency modulation. Moreover, for the rectifier and inverter, a control method indqsynchronous reference frame with a wide range of reactive power control capability is developed. Due to the time-varying primary-side and secondary-side six-pulse DC-link voltages, a single-phase-shift modulation strategy with variable phase shift angle is developed for the DAB to maintain constant transferred power and balanced instantaneous input and output power. In this way, symmetric and sinusoidal inputs/outputs are achieved with the cancellation of the bulky DC-link capacitors required in conventional topologies. The proposed topology integrates the advantages of traditional voltage-source type back-to-back converter and DAB converter, including sinusoidal inputs and outputs, extended reactive power control range, high power density, and high conversion efficiency. The effectiveness of the presented methods is verified by a 5-kW experimental prototype.