Research On Fault Diagnosis And Fault Tolerant Operation Control Of Cascaded H-Bridge Photovoltaic Inverters

Cascaded H-bridge topology has been widely concerned and applied in photovoltaic grid-connected inverters.However,in the normal operation of photovoltaic grid-connected system,faults occur frequently.The subsequent effects of faults not only reflect the influence on the output characteristics of AC and DC side of the system,but also leave hidden risks for the safe and stable operation of the whole system.Therefore,the rapid diagnosis of fault sources and the corresponding fault tolerant operation have become the research focus in recent years.For the cascaded H-bridge photovoltaic grid-connected inverter,the open-circuit fault diagnosis of the module has always been very important.Although the influence of open-circuit fault has a delay effect,it is still necessary to quickly complete the accurate positioning of the fault switch.Cascaded H bridge is presented in this paper,the normal operation of the photovoltaic(pv)grid inverter model under the single polarity carrier phase-shifting modulation strategy,this paper proposes a rapid diagnosis scheme based on carrier sampling,in the aspect of hardware through the exchange of in each module H bridge output increase the voltage sensor,through the fault in flow strength analysis to each switch tube after the changes of the output voltage of the fault as fault feature,At the top of the each at the bottom of the carrier and the output voltage sampling module and compared with the dc side capacitor voltage complete fault location diagnosis,diagnosis is completed and adopt corresponding measures to reduce the degree of fault,the proposed diagnostic solution compared with the existing schemes,the diagnosis speed got bigger,the fault diagnosis of all modules are independent of each other,And the diagnosis time can be completed in one carrier cycle.For single pipe fault occurring within the H bridge module after the fault-tolerant control problem in the research,design a kind of based on the maximum output power of single pipe failure fault-tolerant control method,the control scheme is adopted by the theory of fault module according to the interval of the bypass is given its power instruction value,and through the injection of the fundamental frequency of the zero sequence component approach to implement the interphase power balance.The proposed scheme can ensure that other normal modules still work stably near the maximum power point,and at the same time,in order to maximize the output power of the fault module,the given value of the maximum power of the fault module in the non-fault region can be deduced,so as to realize the optimization of the output power of the system.Finally,the experimental prototype of the cascaded H-bridge grid-connected photovoltaic inverter in the laboratory is used to complete the verification work of relevant schemes,which proves the effectiveness and engineering application of the proposed scheme.