The power electronic traction transformer (PETT) consists of a single-phase cascaded H-bridge (CHB) converter and several output-parallel DC/DC converters. In order to make the PETT work steadily, it is needed to maintain its intermediate-dc-voltage balance and output-current sharing between different cells. In this paper, an overview of PETT balance control strategies is presented at first. Their basic control principle, main control structure and interrelation are investigated. Based on the control tasks of CHB and DC/DC converters, the balance control strategies can be classified into two categories. With the comparison of them, the second balance-control category has several advantages in the aspect of ac-input-current quality, balance control effectiveness, computation resource occupation and soft-starting performance, while it also brings several disadvantages with regard to auxiliary-power-supply design and balance-control regulation range. Finally, further research towards the simulation and experiment based on a five-cell PETT laboratory prototype with rated power of 30 kW is carried out.
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