Small-signal analysis of naturally-sampled single-edge PWM control loops

Mouton, Toit and Cox, Stephen and McGrath, Brendan and Risbo, Lars and Putzeys, Bruno (2017) Small-signal analysis of naturally-sampled single-edge PWM control loops. IEEE Transactions on Power Electronics . p. 1. ISSN 0885-8993

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This paper presents a simple method to analyse the behaviour of feedback loops that contain a naturally-sampled single-edge pulse-width modulator. A small-signal model is derived by means of simple geometric arguments. It is shown how this small-signal model can be used to analyse the stability of the continuous-time pulse-width modulated feedback loop by using standard z-domain techniques. The strategy relies on familiar concepts like transfer functions and small-signal gains and does not require any in-depth knowledge of non-linear systems. A simple design process, where the continuous-time compensator is designed directly in the z-domain, is developed and detailed design equations are derived for a PI current regulator. It is shown how the proposed strategy can accurately predict instability that cannot be explained by means of the well-known average model of the pulse-width modulator. The theoretical analysis is confirmed by means of detailed timedomain simulations. The mechanisms that lead to instability are discussed and an equation for the critical loop gain is derived.

Item Type: Article
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Keywords: Small-signal model, pulse-width modulation, stability, bifurcation
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Mathematical Sciences
Identification Number: 10.1109/TPEL.2017.2666720
Depositing User: Eprints, Support
Date Deposited: 09 May 2017 10:25
Last Modified: 10 May 2017 01:09

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