Improved Quality of Compensation in Three-Level Shunt Active Power Filter Using Fractal Approach Based Current Hysteresis Controller

Current error space phase based hysteresis controlled shunt active power filter (SAPF) requires two (inner and outer) hysteresis bands for vector selection and for sector detection, respectively. Current error space phasor moves many times out of the inner hexagonal boundary (and touches the outer band) in one fundamental cycle to detect appropriate sector. This adversely affects the compensation provided by SAPF, resulting in less reduction of THD level in the source current. In this paper, fractal approach is proposed and analyzed to eliminate outer hysteresis band and look-up table for sector change detection. This technique is integrated with current error space phasor based hysteresis controller for a three-level SAPF. Performance of current error space phasor based hysteresis controller for three-level Flying Capacitor converters used in SAPF is presented for outer hysteresis band approach as well as fractal approach of sector detection. The proposed fractal approach for SAPF allows precise and comparatively improved compensation of harmonic currents produced by nonlinear loads.