High-Frequency Harmonic Current Control of Power Converters

Resonant controllers are widely used in applications like active power filters and identification systems, where control of harmonics of high order (high frequency) is required. In such high-frequency range, to compensate the PWM/computational phase delay is necessary to avoid instability. Two approaches have been proposed in literature: a 2-sample delay compensation and a linear phase-leading compensation. In this work, a stability analysis has been performed to prove that linear phase compensation can leads to low frequency instability if the selectivity and sampling frequency of the resonant controllers are not properly chosen. A zone-phase compensation is proposed to solve the instability and to maximize the stability margins in all the frequency operating range. The analysis is validated by extensive simulation and by field experiments in a 1.6 MVA 6-parallel three-phase NPC grid impedance analyzer.