Classical dq0 Algorithm

This represents the fourth subcircuit diagram in the simulation circuit schematic for an active power filter. The core algorithm implemented in this circuit is the classical dq0 algorithm, a widely adopted control strategy for active power filters in power systems. The dq0 algorithm operates in the dq reference frame, where three-phase voltages and currents are transformed into orthogonal d-axis and q-axis components using Park transformation. This transformation enables independent control of active and reactive power components through proportional-integral (PI) regulators. Key implementation steps include: 1) Clarke transformation converting abc phases to αβ coordinates, 2) Park transformation rotating αβ to dq reference frame synchronized with grid voltage via phase-locked loop (PLL), 3) PI controllers processing dq components to generate compensation signals, and 4) inverse transformations restoring the signals to three-phase coordinates. The algorithm effectively suppresses harmonics and disturbances in power systems by generating compensating currents that cancel out distortions, thereby delivering stable and purified power output with typical total harmonic distortion (THD) reduction capabilities exceeding 85%.