Peak current mode control is a popular method of SMPS control due the inherent cycle-by- cycle current limiting, feed-forward control and current sharing ability it provides. However, the subharmonic oscillations which plague peak current mode control must be removed using slope compensation. Until the work presented in this thesis, there have been no true digital implementations of peak current mode control due to the difficulties associated with implementing a digital form of slope compensation. This thesis introduces a complete digital peak current mode converter which uses a novel method of digital slope compensation to remove the subharmonic oscillations observed when using peak current mode control. The digital implementation of peak current mode control is applied to a Buck converter design example which directly compares the proposed digital scheme with an equivalent analog scheme. Exact analytical design equations are derived which allow a specified crossover frequency and phase margin to be achieved concurrently. The l6W Buck converter design example compares the digital peak current mode controlled converter with an analog converter designed to the same specification and tested on the same power stage PCB. The detailed steady state, transient and frequency response results from the hardware experimentations show excellent correlation with the MATLAB simulated converter and are in good agreement with the equivalent analog converter. The crossover frequency is specified as 15kHz and is measured as 14.71kHz on the proposed digital converter with a measured phase margin only 5' less than the specification. The results confirm that the operation of the proposed digital peak current mode control scheme is functionally similar to analog peak current mode control.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:602418 |
| Date | January 2013 |
| Creators | Hallworth, Michael |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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