Browsing by Author "Tomlinson, Daniels Males"
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- ItemA Fixed Switching Frequency technique for finite-set model predictive control of power electronic converters(Stellenbosch : Stellenbosch University, 2016-03) Tomlinson, Daniels Males; Mouton, H. du T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: A fixed switching frequency scheme for finite-control-set model predictive control is resented. The purpose of the control scheme is to achieve an output waveform quality that compares well to that of a pulse-width-modulator-based linear controller, while retaining the benefits of model predictive control such as the ability to easily control multiple variables without complex control loops. By enforcing a fixed switching frequency it becomes easier to ensure that resonant poles are not excited and assists with EMI compliance. The controller is divided into two parts: The off-line calculation and storage of the coefficients of the prediction equations and the on-line evaluation of the controller. For every valid actuation choice at each sampling step in the switching period, an equation for the average value over one or more switching periods is calculated and stored in a lookup table. The on-line controller uses the lookup table to load the appropriate equations, based on the current position within the switching period. This reduces the on-line calculation effort and allows higher sampling rates to be achieved while predicting over a long prediction horizon. The controller is implemented and experimentally verified for the voltage control and input-bus stabilisation of a 12.75 kV medium voltage electronic voltage regulator for the regulation of medium voltage distribution feeders. The voltage regulator design is discussed in detail and consists of a multi-level AC-to-AC converter topology that is connected in a shunt-series configuration to an appropriate transformer. The leakage inductance of the transformer together with the large input-bus capacitor forms an input LC-filter that may become resonant. It is shown through simulation and experimental results that the controller is able to maintain a fixed switching frequency with good reference tracking and waveform quality while suppressing the input-bus resonance. It is further shown that the control scheme can be generalised. This is experimentally demonstrated for the voltage control and capacitor balancing of a five-level flying capacitor converter with an output LC filter. The results show that the controller is able to maintain a fixed switching frequency with a fast transient response, a good waveform quality with a low THD while also actively keeping the flying capacitor voltages balanced. Lastly, the controller is compared to a pulse-width-modulator-based linear resonant regulator for the current control of a single-leg inverter. The two controllers are extensively evaluated through simulation and the results show that the model predictive controller compares well to the linear controller in terms of waveform quality and transient response.