Active damping of LCL-filter resonance based on virtual resistor for PWM rectifiers — stability analysis with different filter parameters

This publication presents the investigation of active damping of resonance oscillations with virtual resistor for grid-connected PWM rectifiers with LCL-filter for different filter parameters. Using the voltage-oriented PI current control with converter current feedback, additional active damping of the filter resonance is necessary for stable operation. In the literature different methods are proposed that differ in number of sensors and complexity of control algorithms. If higher damping of the switching ripple current is required LCL-filters with lower resonance frequencies can be used. Resulting low ratios between resonance frequency and control frequency challenge the control with respect to damping of resonance. Moreover, some active damping methods are not suitable for these filter settings. Here the active damping concept based on virtual resistor is analyzed concerning stability for two significant filter configurations. It turns out that it is applicable for configurations with higher resonance frequency, whereas systems lower resonance frequencies can poorly be damped. Additionally the method exhibits the advantage of simple implementation but the disadvantage of additional current sensors. Theoretical analyses and of the selected method with time-discrete implementation are shown in this paper. Theory is verified by experimental results.