Control of Active Power Decoupling Circuit Based on Parametric Oscillator

In this article, we tested the buck-plus-unfolder bidirectional converter as the active power decoupling circuit to suppress the unknown low-frequency ripples on the dc bus. Due to its bipolar operation, the buffering capacitor voltage needs to be half of the frequency of the disturbance. We exploit the parametric resonance phenomenon to build a virtual oscillator controller for the converter. Unlike direct resonance, the parametric one occurs when the parameter of the reactive element of the oscillator varies around twice of the resonance frequency. The dc bus voltage ripple is chosen as the modulation signal for the oscillator. A frequency adaptive mechanism is further embedded in the controller to update the resonance frequency. With the references constructed from the states of the oscillator, a proportional-feedforward controller is designed to track the reference for the buffering capacitor voltage. The proposed control algorithm has been verified by both simulation and experiments.