Active-Damping Virtual Circuit Control for Grid-Tied Converters With Differential-Mode and Common-Mode Output Filters

This article presents a virtual circuit control method of designing a resonant-damping discrete-time controller for grid-tied voltage source converters with differential-mode (DM) and common-mode (CM) output filters. The method provides an intuitive way to specify the desired closed-loop behavior by means of a virtual reference circuit rather than abstract mathematical criteria such as closed-loop poles and weighting matrices. Therefore, the existing passive filter designs, which cannot be practically implemented due to excessive losses, and the well-established theory of filters can be exploited. The DM grid current and the CM capacitor voltage, which are the primary control objectives, inherit the main properties of their underlying virtual reference circuits, e.g., resonance damping and low-frequency behavior. On this account, to fortify the controller against grid impedance variations, a virtual circuit with a series resistor at the grid side is considered. Accordingly, the CM voltage and DM current controllers can be easily designed based on the low-frequency behavior of virtual circuits. The method can also be straightforwardly equipped with conventional controllers to enhance system performance, such as harmonic compensation. The simulation and experimental results verify the effectiveness of the DM and CM resonant damping and dynamic performance.