A Fault Diagnosis And Tolerance Strategy For Modular DC-DC Converter System

Recently,modular DC-DC converter system has been widely applied in various high power DC-DC conversion situations,such as communication,aerospace,HVDC and so on.It has excellent advantages in flexibility,standardization and low voltage/current stress.To guarantee a safe and high-performance operation,the reliability of the system should be taken into account.According to the industrial survey,switch failures tend to be the most common fault in power converters,including open circuit fault(OCF)and short circuit fault(SCF).Therefore,real-time diagnosis and proper tolerance strategy for switch faults are necessary to ensure the continuous and reliable operation of the system.Aiming for coping with the power switch failures,a fault diagnosis and tolerance strategy of the modular DCDC converter system is proposed in this paper.Firstly,a general control strategy for series-parallel DC-DC systems is introduced.It can achieve a desired output voltage and the equilibrium of the constituted modules.The fault diagnosis and tolerance method in next chapters is based on this control strategy.By analyzing the feature of the DC-DC converter under fault condition,magnetic components voltages are chosen as diagnostic criteria in this paper.It can be easily measured by adding an auxiliary winding into each magnetic core,and additional sensors are needless.For a single DC-DC converter,diagnostic circuits are designed based on the time-sequence feature of magnetic components voltages and gate-driver signals.Fault could be detected within one switching period.Besides,this fault diagnosis strategy can be extended to most topologies of PWM DC-DC converters.For modular system,faults can be detected and located accurately based on the circuit for individual module.The performance will not affected by the connection of the system,so it is suitable to various series-parallel system.To further improve the reliability of the diagnostic circuit,a circuit for preventing misdiagnosis is added to the original one.The optimized circuit shows excellent performance under dynamic situations without sacrificing any merits.After fault detection,fault-tolerant control will guarantee the normal operation by immediately isolating faulty module and selectively inserting redundant module.The proper time-sequence arrangement in faulttolerant process makes the transition fast and seamless.To verify the effectiveness of the proposed diagnosis and tolerance strategy,a threemodule forward converter prototype is built.The experimental results show that fault can be identified and located promptly,while the system can be reconfigured quickly by the tolerant circuit to make the system keep steady running.Moreover,the strategy is available to various DC-DC series-parallel systems.