High power medium frequency power electronic traction transformer based on bidirectional Z-source-alike impedance network

摘要

Recently, the medium frequency power electronic traction transformer (PETT) has received increased attention in the rail transit applications due to its small size, light weight, more space availability for passengers, multiple interfaces and other additional functionalities. However, the switching frequency is limited by the thermal tolerance of semiconductors which deteriorate as the switching frequency and voltage increase. The 10 kV silicon carbide (SiC) based semiconductors have low switching loss, low conduction loss, no tail current and fast switching speed, but are still at the laboratory research levels. Considering the EMI, common mode current and cost issues in high voltage high frequency applications, the use of SiC based semiconductors is not a good candidate for PETT presently. This paper proposed a Silicon-based PETT topology which is embedded with a bidirectional z-source-alike impedance network at the primary dc-link. The input voltage of the LLC converters can be reduced through the combination control of the four-quadrant converter and the impedance network. Therefore, lower voltage rating devices such as 3.3 kV IGBTs instead of 6.5 kV IGBTs can be used in the LLC resonant converter and the switching frequency can be as high as 10 kHz without increasing the number of cascaded converters. Moreover, the double frequency power can also be blocked at the dc output side of four-quadrant converters to guarantee the zero voltage switching (ZVS) of LLC converters. Simulations and experiments are provided to verify the theoretical considerations and findings.