Modelling and digital control of two-phase interleaved coupled-inductor non-isolated DC-DC converters
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Date
2016
Authors
Barry, Brendan C.
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Publisher
University College Cork
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Abstract
This thesis focuses on the complete mathematical modelling and digital closed-loop control of two-phase interleaved coupled-inductor non-isolated dc-dc converters. Coupled-inductors have been shown to reduce the cost, size, and weight of high-power magnetic components while increasing efficiency. The complete large-signal model of the coupled-inductor boost converter is presented and compared to the traditional single-phase and two-phase discrete inductor dc-dc converters. The CCM-DCM mode maps are presented and discussed for the coupled-inductor boost converter. Sample analyses of several different CCM and DCM modes of operation are also presented. The different CCM and DCM waveforms are experimentally produced by a 1 kW laboratory prototype. Following on from the large-signal model, the complete small-signal model of the coupledinductor boost converter is presented. The method of solving for the small signal models is discussed, and sample analyses of several different CCM and DCM modes of operation are presented. Calculated and experimental frequency sweeps for several of the CCM and DCM modes of operation are produced and compared to verify the accuracy of the small-signal models. Controllers for the 1 kW prototype are designed from the transfer functions derived from the small-signal models. The control strategy of average-current-mode control is digitally implemented, which uses an outer voltage loop and an inner current loop to eliminate any error between the output and the desired output. The FPGA used in testing is the Altera Cyclone III FPGA. Initially, PI controllers are developed and compared to simulated results. In order to improve the closed-loop performance of the converter, the inner current loop PI controllers are replaced with Type II compensators. Several compensators are designed as examples for a number of CCM and DCM modes of operation. Finally, to increase the stability of the converter, bumpless PI control and forced-output control utilizing the Type II compensators are introduced and implemented.
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Keywords
Coupled-inductor , Continuous-conduction mode , Discontinuous-conduction mode , Control , DC-DC converter
Citation
Barry, B. C. 2016. Modelling and digital control of two-phase interleaved coupled-inductor non-isolated DC-DC converters. PhD Thesis, University College Cork.