Application of repetitive control strategy with variable frequency adaptability in SAPF

Abstract:

To improve the accuracy of compensating current tracking control for shunt active power filters (SAPF) under the condition of grid frequency fluctuation and suppress the harmonic pollution of power grid effectively, a frequency-adaptive repetitive control strategy is proposed in this paper. A multi-rate repetitive control system is built based on a selective repetitive controller with an adjustable sampling rate. The multi-rate repetitive control system is transformed into a frequency-adaptive uniform-rate selective repetitive control system (FUSRCS) by a finite impulse response (FIR) filter based on Lagrange linear interpolation. To enable the FUSRCS to adapt to grid frequency fluctuations, the coefficients of the approximate expression of the delay link in the repetitive controller are adjusted according to the grid frequency. The compensator is designed and the stability, convergence and steady-state error of FUSRCS are analyzed. The mathematical model of three-phase SAPF is established, and a compensation current compound repetitive control system based on FUSRCS is designed according to the actual data. Simulation and experimental results indicate the SAPF based on FUSRCS can maintain high compensation current tracking accuracy and good compensation effect under steady-state grid frequency deviations, dynamic grid frequency variations, and load switching. Compared with conventional repetitive control, FUSRCS not only offers frequency adaptability, but also reduces the computational burden of the control system, enhances the dynamic response speed, and solves the problems caused by multi-rate repetitive control systems.