Study of Multi-level Active Power Filter Control without phase-locked-loop

In this paper, active power filter (APF) uses the novel virtual line-flux-linkage oriented control strategy, not only realizing the control for APF without phase-locked-loop (PLL), but also achieving a good inhibitory effect to interfere. However, there are some problems in the conventional method, such as the error of amplitude, the shift of phase angle and the nondeterminacy of initial oriented angle. In the thesis, two one-order low-pass filters are adopted instead of the pure integrator in the virtual line-flux-linkage observer, which can steady the phase and amplitude. Furthmore, an original scheme of harmonics detection under the rotating coordinate is advanced based on the simplified space vector pulse width modulation (SVPWM) strategy. Meanwhile, by use of the new SVPWM algorithm, the voltage space vector diagram of the three-level inverter can be simplified and applied into that of two-level inverter, and this makes the control for Neutral Point potential easier.