A Three-Phase Adaptive Active Damper for Improving the Stability of Grid-Connected Inverters Under Weak Grid

Abstract

When a grid-connected inverter is connected to a weak grid, the system may be instable. An adaptive active damper can be connected to the point of common coupling (PCC), which can automatically regulate a virtual resistor to the critical value to stabilize the system. Furthermore, a harmonic-current-reference compensation method is adopted to make the active damper more accurately simulate the virtual resistor in a wide frequency range. This paper investigates the harmonic-current-reference compensation for the stationary α-β frame, synchronous d-q frame, and decoupled synchronous d-q frame-controlled three-phase adaptive active damper. With the proposed method, the active damper controls the active and reactive power directly and improves the stability of the grid-connected inverters under weak grid at the same time. Simulation tests on the system of a 10-kVA three-phase grid-connected inverter and a 3-kVA active damper is carried out to verify the effectiveness of the proposed control scheme of the active damper.