A Flying Capacitior Multi-Level DC-DC Converter With Fault-Tolerant Operation Capability

In recent years,power electronics technology has been widely used in industrial equipment,communication system,transportation,aerospace and other aspects and is developing rapidly,making the flyover capacitor multi-level converter used in various fields.According to the investigation,the switching device is the most vulnerable component in the system,and there are a lot of switching devices in the flyover capacitive multi-level converter,so it is of great significance to carry out the reliability research.The flyover capacitive multilevel converter with fault-tolerant operation ability is one of the best solutions to improve system reliability.In this paper,a flyover capacitive multi-level DC-DC converter with fault-tolerant operation capability is proposed.The topology can realize fault tolerance of the system by adding redundant components.At the same time,the fault diagnosis method of switching device is designed to find and locate the fault in time.Then the fault tolerant strategy is adopted to make the converter enter the fault tolerant operation mode so as to improve the reliability of the system.The research results of this paper are mainly reflected in the following aspects:Firstly,the flyover capacitive multi-level DC-DC converter is studied,and the redundancy structure is analyzed,and the fault-tolerant strategy is designed.Then a switch fault diagnosis method considering magnetic elements is proposed.According to the level number of inductance voltage,the inductance voltage is collected by mutual inductor and comparator,and the inductance voltage is converted into digital signal by AD analog-to-digital converter.The results of analog to digital conversion of multilevel inductor voltage are discussed in detail,and the relationship between different faults and inductor voltage digital signal and switching control signal is found out.According to the analysis results,a switch fault diagnosis method is designed to identify the fault type and locate the fault.A four-level converter simulation platform is built for open-circuit and short-circuit faults.The simulation results verify that the diagnosis method can identify the short-circuit and open-circuit faults effectively and quickly,and locate the faults.Secondly,the fault-tolerant operation of the fly-capacitor multi-level converter is studied.The short-circuit fault of unit 2 was simulated by changing the carrier phase sequence and adding adjustment balance network respectively to observe the process of voltage rebalancing across the flying capacitor after fault-tolerant operation.The two cases were compared and analyzed.The simulation results show that the balance network is beneficial to speed up the convergence time of the flying capacitor voltage,and is of great significance to improving the reliability of the system.Finally,the experimental platform of flying cross-capacitor four-level DC-DC converter is built,and its hardware circuit design and software design are introduced in detail.Experimental results show that the proposed fault diagnosis method is fast(within 15us)and accurate.At the same time,the results of fault-tolerant experiment also verify the validity of the fault-tolerant strategy.