Digital Realization of Capacitor-Voltage Feedback Active Damping for LCL-Filtered Grid Converters

The capacitor voltage of an LCL-filter can also be used for active damping, if it is fed back for synchronization. By this way, an extra current sensor can be avoided. Compared with the existing active damping techniques designed with capacitor current feedback, the capacitor voltage feedback active damping would however demand a noise-sensitive derivative term. A digital realization of this derivative term is generally a challenge with many methods developed for resolving it. However, these methods are still facing drawbacks, which have been comprehensively explained in this paper. To overcome their drawbacks, a new derivative method is then proposed, based on the non-ideal generalized integrator. The performance of the proposed derivative has been found to match the ideal "s" function closely. Active damping based on capacitor voltage feedback can therefore be realized accurately, as demonstrated by the presented experimental results.