Three phase four wire Active power filter

Hello, I am currently working on a three phase four wire shunt active power filter using PQ theory, with a hysteresis controller for harmonic and reactive power compensation. however, even if the method gives good results, harmonic 3 is the only one left, the rest of the harmonics are less than 1 and because of this harmonic I cannot have a Total THD of less than 6. anyone have a solution please