Research On Control Technology Of Single-phase Cascade H-bridge Active Power Filter

With the development of power electronic technology and the widespread use of power electronic devices,the harmonic problem of the grid is becoming more and more prominent.How to improve the environment and quality of the grid has become an urgent problem to be solved.Active Power Filter(APF)is the most prospect methods to suppress harmonic pollution of the grid,which has the advantages of good compensation effect,fast response speed and selective compensation for specific harmonics,etc.In this paper,the phase locked loop,harmonic detection,harmonic current control and capacitor voltage control of the active power filter based on cascaded H-bridge topology are carried out.Firstly,this paper introduces the working principle of the shunt APF and the single-phase cascade H-bridge converter,and introduces the techniques of carrier phase shift modulation,carrier cascade modulation and one-dimensional space vector modulation respectively.Then,aiming at the shortcomings of the traditional phase-locked loop method and the harmonic detection algorithm in steady-state accuracy and response speed,a new phase-locked loop method based on repetitive control and a new harmonic detection algorithm based on definite integral are proposed respectively.The detailed parameter design process and digital realization method are given.The new phase-locked loop method can accurately extract the fundamental positive sequence component,fundamental negative sequence component and the phase angle of the grid voltage in half cycle of the grid period under serious distortion of the grid voltage conditions.This paper proves that the single-phase grid voltage is a special case of unbalanced three-phase grid voltage,and the new phase locked loop can be applied to both three-phase and single-phase systems.The new harmonic detection algorithm can separate the active current component,reactive current component and harmonic component quickly and accurately under the serious distortion of grid current conditions.Then the harmonic current control and capacitor voltage control strategies of active power filter are studied.The inner loop is controlled by parallel PR regulator,which has the advantages of high flexibility and stability.The average value of the capacitor voltageon the dc side is controlled in outer loop firstly.Then the modulating wave of each basic H-bridge unit is constructed by means of vector reconstruction.The equalization of the capacitor voltage is realized.The algorithm is simple,easy to implement and has good effect.Finally,the above theoretical methods are simulated and analyzed based on MATLAB.A single-phase cascade H-bridge active power filter experimental platform is designed and built,which proved the correctness and effectiveness of the theoretical analysis.