Research Of Fault Tolerant Operation Of T-Type Three-Level Active Power Filter

The development of power electronic technology makes the power electronic equipment possess the advantages of high efficiency and fast response,so it is widely used in the power system.However,when power electronics are applied,a large amount of harmonics will be generated,which will become the main harmonic source in the power system and seriously influence the power quality and the power stability of the grid.Active power filter(APF)has been widely used in power system because it can compensate harmonics dynamically.With the increase of the nonlinear load capacity in the power grid,the traditional two-level active power filter can not meet the requirements of harmonic compensation,so more number of voltage in the inverter is needed to improve the capacity of active power filter.The active power filter not only can not compensate the harmonic,but also the inverter itself will become a harmonic source,increase the harmonic power,for a inverter is contained.So the fault of active power filter must be detected rapidly and on this basis,fault-tolerant control strategies must be employed to achieve the function of compensating harmonics.In this paper,the harmonic compensation control of T-type three-level active power filter is studied,and the fault diagnosis and fault-tolerant operation control of T-type three-level inverter with open circuit fault at different locations are further studied.The main work of this article is as follows:(1)The working principle of T-type three-level active power filter is introduced in detail.The topology and control methods of T-type three-level inverter,harmonic detection and harmonic tracking strategy of active power filter are studied deeply.(2)According to the T-type three-level active power filter,three-level SVPWM control strategy for T-type three-level inverter is introduced,harmonic detection algorithm improved by adaptive algorithm,and the synthesized tracking strategy schemed between PID controller and repetitive controller in serial topology structure.Moreover,according to the characteristics of the inverter circuit,the parameters of repetitive controller are designed to realize the harmonic compensation function.The corresponding simulation model is established in Matlab to verify the feasibility of the above control strategies.(3)Operation characteristics of T-type three-level inverter with open circuit fault in power devices occurred at different positions are studied.On this basis,the fault characteristics of power devices of horizontal bridge and vertical bridge are introduced respectively,and two kinds of fault diagnosis for different locations faulty power devices are realized.A simulation model is established to prove the practicability of the two fault diagnosis algorithms.(4)Two-level and three-level fault-tolerance strategy are proposed respectively for the open circuit fault of power device in horizontal bridge arm.For the open circuit fault of powerdevice in vertical bridge arm,the fault-tolerant control is realized by changing the topology of T-type three-level inverter,and a simulation model is built to verify the feasibility of fault-tolerant control.(5)In order to further validate the control algorithm,the fault diagnosis and fault-tolerant operation algorithm proposed in this paper,a T-type three-level active power filter experimental platform is built.This paper introduces the composition of the experimental platform detailedly,and the feasibility of the algorithm is verified by experimental results.