OBSERVER BASED ACTIVE DAMPING OF LCL RESONANCE IN GRID CONNECTED VOLTAGE SOURCE CONVERTERS
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Voltage source converters (VSC) with LCL filters are attractive in grid connected power electronics because they greatly reduce pollution of the utility voltage due to switching harmonics. However, the presence of the LCL network can cause stability issues due to its inherent resonance behavior, therefore damping is necessary. This work proposes novel current controller that uses Luenberger observer as a sensor replacement and state predictor to predict filter capacitor current. The use of the observer alleviates the impact of control delay and also eliminates the need for additional sensors. The predicted filter capacitor current passed through virtual resistor creates damping effect, while outer loop with feedforward terms ensures instantaneous current command tracking with zero steady state error. This project with simulation results demonstrates true active damping and the effectiveness of the virtual resistance in high power active front end (AFE) drives.