Novel topologies for three-level back-to-back converters based on matrix converter theory

Abstract

To reduce the increase in switching losses caused by PWM operations at both the input and output stages of three-level back-to-back (3L-BTB) converters, two novel topologies of 3L-BTB converters, which are three-level indirect matrix converter (3L-IMC) and the symmetrical three-level back-to-back (S3L-BTB) converter, together with a new modulation strategy are developed. The proposed 3L-BTB converters are based on the double-carrier-based dipolar PWM theory of the matrix converters, and are comprised of a fundamental-frequency switching rectifier and a PWM inverter. The slow-switching rectifier is employed to generate the required max-mid-min dc links for the PWM inverter stage. The switching losses and EMI at the input are significantly reduced as compared to those of the conventional PWM rectifier. Moreover, the topology of the S3L-BTB converter allows the rectifier to be operated in the usual PWM mode and becomes the conventional PWM 3L-BTB converter if required. Simulations are conducted, and the results confirm the performances of the proposed converters as AC/AC converters and their benefit in loss reduction. The laboratory prototype of the S3L-BTB converter is also constructed and tested. The experimental results are in good agreement with the theoretical results.