An Optimized Fault-Tolerant Control Strategy Based on Dynamic Modulation Voltage Adjustment for Solid-State Transformers

Solid-state transformers (SSTs) have broad application prospects in medium-voltage dc distribution systems. However, the large number of switching devices in SSTs makes it prone to failure. The cascaded structure of SSTs facilitates redundant fault-tolerant control in the event of a failure. Nevertheless, traditional redundancy-based fault-tolerant control methods will lead to current surges when bypassing or inserting a module. In this article, an optimized fault-tolerant control strategy based on modulation voltage correction is proposed. To reduce the voltage and current fluctuations caused by the removal of the faulty module, the new modulation voltage signal is calculated by the bus voltage of the normal operating modules, the bus voltage of the redundant module and the original modulation voltage signal. The principle of dynamic adjustment of modulation voltage is analyzed. Furthermore, during the fault-tolerant shifting process, the control mode is changed to achieve smooth fault-tolerant shifting while ensuring control continuity. The effectiveness of the proposed fault-tolerant control strategy is verified through simulation and experiments.