A nonlinear discrete-time observer for inverter control

A discrete-time high-gain observer is designed in order to estimate the DC voltage of an inverter used as a dynamic electric load emulator. Since the use of LMI techniques makes it possible to obtain a stable observer for a range of bounded duty ratio, the nonlinear-in-the-input average model, which can be expressed as a linear parameter-varying system, is formulated in polytopic form. A robustified version is proposed when exogenous disturbances such as current injection on DC side are present. The nonlinear observers are then discretized, with the hold-equivalent technique, in order to achieve both numerical stability and accuracy as the sampling rate is increased. Nonlinear observer designs proposed in this paper are validated by means of numerical simulations that demonstrate the stability property and performance recovery of a typical state feedback scheme by a high-gain observer-based output feedback.