Active Damping Method Equivalent to Series Resistor Effect for LCL Filters in a Grid-connected PWM Converters

This paper proposes an active damping method for LCL filters of grid-connected converters. LCL filters are mainly utilized for the interface of distributed generation systems to the grid due to their small size and effectiveness of current harmonics attenuation. However, owing to the resonance of LCL filters, bandwidth of the current controller of the converters is usually limited far to the resonant frequency of the LCL filter. Otherwise, the system stability would be threatened, especially in high power systems where switching frequency and internal loss are relatively low. In this paper, an active damping method equivalent to the implementation of resistors in series to the filter capacitors is suggested and it is shown that the bandwidth of the LCL filter with the proposed damping method can be extended further than that with a conventional capacitor current feedback type damping method. The effectiveness of the proposed method is experimentally confirmed with a 5kW battery energy storage system connected to the grid.