Increasing the operating area of shunt active filters by advanced nonlinear control

This work is aimed to rigorously manage voltage saturation and maximum current constraints in Shunt Active Filters. In this respect, assuming “unconstrained” control algorithms have already been defined to achieve standard objectives for such devices (i.e. current tracking for harmonic compensation and DC-bus voltage boundness), a plug-in unit, oriented to extend the system operating region and at the same time preserving good performance under large transients and overload conditions, is presented. This solution allows to improve availability, robustness and composability of Shunt Active Filters, which are expected to be key features in present and next generation complex and possibly “smart” power grids. The proposed unit is composed by two parts. First, a suitable anti-windup strategy is defined in order to deal with control input saturation. Its main purpose is to preserve the original “unconstrained error dynamics”, in face of input saturation, while guaranteeing low computational burden and reduced performance impairment (the latter goal, in harmonic compensation context, leads to rather non-standard problem formulation). To this aim, the anti-windup acts on the current references through a suitably-designed additional dynamics. Then, in order to cope with current limitations, an additional strategy has been designed; again the current references is suitably shaped to comply with the features and bounds of the system, augmented with the above-mentioned anti-windup solution. The proposed scheme can be simply joined to any kind of unconstrained controller adopted to steer Shunt Active Filters. In this work, an Internal-Model-based current controller is adopted as a benchmark case. The proposed approach is validate through extensive simulation tests.