Exponentially convergent estimator to improve performance of voltage source converters

In this study, the authors introduce an exponentially convergent estimator of load power to improve the performance of voltage source converter (VSC) applications. This estimator, based on a non-linear reduced-order observer, is used to estimate the load power and its time derivative. The estimated signals are feedforwarded to build a non-linear controller in order to improve the whole system performance. The main advantage of the proposed estimator is that it presents linear error dynamics which allows to design the observer by using linear techniques. In this way, the observer transient performance (i.e. convergence rate) is clearly established in the whole VSC operation range. The feedback controller is based on input-output feedback linearisation considering the energy as output so that the DC-voltage internal dynamics is avoided and linear control strategies can be also used in the controller design. Several tests - including performance in presence of switching frequency, parameter uncertainties and disturbances in the AC input voltage - validate the proposed technique.