Digital current control of a voltage source converter with active damping of LCL resonance

LCL filters installed at converter outputs offer higher harmonic attenuation than L-filters but careful design is required to damp LCL resonance, which can cause poorly damped oscillations and even instability. A new topology is presented for a discrete-time current controller which damps this resonance, combining deadbeat current control with optimal state-feedback pole assignment. By separating the state feedback gains into deadbeat and damping feedback loops, transient overcurrent protection is realizable while preserving the desired pole locations. Moreover, the controller is shown to be robust to parameter uncertainty in the grid conductance. Experimental tests verify that fast well-damped transient response and overcurrent protection is possible at low switching frequencies relative to the resonant frequency.