Combined optimal pulse width modulation and pulse frequency modulation strategy for controlling switched mode DC–DC converters over a wide range of loads

• Published in: IET control theory & applications Vol. 6; no. 13; pp. 1973 - 1983
• Main Authors: Ling, B.W.-K., Bingham, C., Iu, H.H.-C., Teo, K.-L.
• Format: Journal Article
• Language: English
• Published: Stevenage Institution of Engineering and Technology 01.09.2012; John Wiley & Sons, Inc
• Subjects: Applied sciences; Computer science; control theory; systems; Control system synthesis; Control theory. Systems; Converters; Convertors; Electrical engineering. Electrical power engineering; Electrical machines; Exact sciences and technology; Optimal control; Frequency modulation; Voltage current curve; Computer simulation; Direct current convertor; Multiobjective programming; Satisfaction; Operating mode; Control synthesis; Specification; Pulse modulation; Steady state; Constrained optimization; Control constraint; Output voltage; Optimal control; Ripple; Pulse duration modulation
• ISSN: 1751-8644; 1751-8652
• DOI: 10.1049/iet-cta.2011.0396

This paper develops a combined optimal pulse width modulation (PWM) and pulse frequency modulation (PFM) strategy for controlling switched mode DC-DC converters. The peak ripple magnitudes of both the output-voltages and -currents during all operating modes over a wide range of loads are minimised subject to specifications on the minimum efficiency bounds of the converters. This problem is posed as a multi-objective functional inequality constrained optimal control problem. By expressing the initial state of each operating mode at the steady state as a function of the switched time instants, as well as applying the time scaling transform method and the constraint transcription method, the multi-objective functional inequality constrained optimal control problem is converted to a conventional optimal control problem. Finally, a control parameterisation technique is applied to solve the problem. Computer numerical simulations show that the combined control strategy could achieve low peak ripple magnitudes of both the output-voltages and -currents for all operating modes over a wide range of loads and guarantees the satisfaction of the specifications on the minimum efficiency bounds of the converter over a wide range of loads. [PUBLICATION ABSTRACT]