Input Reactive Power Controller With a Novel Active Damping Strategy for a Matrix Converter Fed Direct Torque Controlled DFIG for Wind Power Generation

Abstract

The LC filter at the matrix converter (MC) input, excited by the PWM MC input current, introduces unwanted resonance oscillations in the input line current. The problem is more severe with a direct torque controlled (DTC) MC due to variable switching frequency operation. Active damping of this oscillation is preferred as it eliminates the power loss in the damping resistance. However, no such active damping strategy for a DTC-controlled MC-fed system has been reported in the literature so far. This article presents an input reactive power controller and a novel active damping strategy to improve the input filter current quality of an MC-fed doubly fed induction generator (DFIG) for variable speed constant frequency wind power generation. For the MC input reactive power control, superior performance of a multi-loop control structure over single-loop is established by experimental results. Stability analysis of the closed-loop input filter system using a small-signal model reveals that the system damping is the lowest in the sub-synchronous generating mode with unity DFIG stator power factor and can be improved by proper selection of the active damping controller parameters. Effects of these parameters on the system damping are predicted from the small-signal model and verified experimentally.