Robust control of DC-DC boost converter / by Hisham Mahmood.

Abstract

In this thesis, a robust controller comprising of a PI with phase-lead compensator for a DC-DC boost converter designed using classical frequency response method is presented. The superior performance of this controller in comparison with H[symbol] and passivity based integral controllers from the literature is shown. The robustness of the controller to boost converter parameter deviations, disturbance magnitudes and polarity which lead to worst case stability is investigated. This approach offers an alternative to the traditional unstructured uncertainty envelop approach used in the literature. Investigation into the nonlinearity arising from parasitic parameters in a boost converter is also presented in this thesis. It is shown that this nonlinearity can cause instability in boost converter control. This nonlinearity makes robust controller design difficult due to the sensitivity to disturbances. Static and dynamic voltage collapses are then studied. New non-iterative formulae are derived using the bilinear averaged model to calculate the voltage collapse point due to the parasitic parameters. Using these simple formulae boost converter stable operating region and disturbance limits can be calculated in the design phase. The use of these formulae for the design of the boost converter control system is studied. Static characteristics formula and the proposed controller performance are verified experimentally.