A comprehensive circuit and modulation design of mixed frequency conversion cascaded power electronic transformer

Abstract

The power electronic transformer (PET) is one of the promising equipment of the energy Internet. In a distributed network, cascaded (cascaded full-bridge, CFB)-type PETs can withstand high-voltage stress and contain a low-voltage DC (LVDC) port, which provides access for distributed generation (DG). However, the hardware cost of the traditional CFB-type topologies remains high, and structure compactness can still be improved. The recently presented mixed-frequency conversion cascade PET (MFCC-PET) is one of the promising solutions. In this study, a comprehensive circuit design of MFCC-PET, a low-voltage distortion nearest-level pulse width modulation (NL-PWM), and a sub-module (SM) voltage balancing strategy for the proposed modulation method under mixed-frequency conversion are presented. A 100 V/2,000 W MFCC-PET prototype is built based on the above analysis and successfully placed into operation.