Research On Fault-tolerant Control Strategy Of Three-phase Three-level PWM Rectifier Under Typical Faults

In recent years,there is an urgent need for high-power,high-efficiency and compact converters in electric vehicles,smart grid systems,aerospace and other fields.Among them,three-level PWM rectifier has become a research hotspot due to its low switching loss and low harmonic content.However,due to the extensive use of switching devices,the rectifier system is prone to switch device failures,which will lead to the system to reduce operating performance,and may even damage other equipment,leading to disastrous subsequent failures.Therefore,it is of great significance to study the fault-tolerant control strategy of three-level rectifier switching devices.Firstly,the mathematical model of diode clamped three-level PWM rectifier is deduced,and the double closed-loop control strategy and space vector pulse width modulation method are expounded.Then,the change of current flow path in the rectifier circuit after open circuit fault or short circuit fault of different switching devices is analyzed.By monitoring the clamping diode current,the switching state of the bridge arm and the change of the voltage and current of the bridge arm,the switch device with fault can be quickly and accurately located,and the fault type of the fault device can be diagnosed.Secondly,according to the change of voltage space vector after switching device fault,the fault is divided into three types : I type,Ⅱ type and Ⅲ type.The fault-tolerant control strategy based on space vector redundancy is used for type Ⅰ and Ⅱ faults,and the fault-tolerant control strategy based on PWM switching mode correction is used for type Ⅲ faults.Through Matlab simulation,it is verified that after the single-tube short-circuit fault or open-circuit fault occurs in the power tube of the diode-clamped three-level PWM rectifier,the above two fault-tolerant control methods can effectively reduce the distortion of the grid-side current and the pulsation of the DC-side voltage,so that the rectifier can operate continuously and stably,with high reliability and no additional cost.Finally,the fault-tolerant diode clamped three-level PWM rectifier controller in the loop experimental platform is built,and the fault-tolerant control experiment of the rectifier is carried out on the experimental platform,which verifies the effectiveness of the fault-tolerant controller designed in this thesis.