Ripple Voltage Suppression and Control Strategy for CHB-Based Solid-State Transformer

For cascade H-bridge-based solid state transformer (CHB-based SST), the ripple voltage in its dc bus will restrict the optimization of volume and energy density. To suppress and control the ripple voltage, a new control strategy is proposed in this article. First, the topology and control strategy of CHB-based SST are described briefly. In this article, all the topologies of CHB-based SST are divided into two categories when considering the differences in their energy transfer paths. Then, this article analyzes the dc ripple voltage generation mechanism of CHB-based SST, and pointing out that taking full use of the dc/dc stage is the key point for ripple suppression. Meanwhile, the ripple voltage suppression strategies for topologies I and II are proposed. Considering the dc/dc stage is a nonlinear link, a linear fitting method has been shown to analysis the performance of the dc control loop and ripple control loop. Finally, simulation and experiment results are shown to verify the proposed control strategy.

Automated summary

This article proposes a new control strategy for cascade H-bridge-based solid state transformer (CHB-based SST) to suppress and control the ripple voltage in its dc bus. The analysis on the generation mechanism of dc ripple voltage and different ripple voltage suppression strategies for topologies I and II are presented. The performance of the control loops is evaluated using a linear fitting method in consideration of the nonlinear characteristics of the dc/dc stage.