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

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, three novel topologies of 3L-BTB converters together with a new modulation strategy are developed based on the matrix converter theory. The proposed BTB converters 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 buses for the PWM inverter stage. The switching losses and EMI at the input are thus significantly reduced as compared to those of the conventional PWM rectifier. Among the new topologies, one structure with modified Vienna rectifier is also proposed for unidirectional power flow applications. The proposed BTB topologies allow the rectifiers to be operated in the usual PWM mode if required, by which the proposed converters become the conventional PWM BTB converters.