Improved Models for DCDC Converters
(2003) Abstract
 To obtain high performance control of a dcdc converter, a good model
of the converter is needed. It is suitable to consider the load to be included in
the converter model since it usually affects the dynamics. The load is often
the most variable part of this system. If the load current and the output
voltage are measured there are good possibilities to obtain a good model of
the load online. Adaptive control can then be applied to improve the control.
In peak currentmode control, the output voltage and the inductor
current are measured and utilized by the controller. This thesis analyses some
properties that can be obtained if the load current is also measured... (More)  To obtain high performance control of a dcdc converter, a good model
of the converter is needed. It is suitable to consider the load to be included in
the converter model since it usually affects the dynamics. The load is often
the most variable part of this system. If the load current and the output
voltage are measured there are good possibilities to obtain a good model of
the load online. Adaptive control can then be applied to improve the control.
In peak currentmode control, the output voltage and the inductor
current are measured and utilized by the controller. This thesis analyses some
properties that can be obtained if the load current is also measured and
utilized for control. Accurate expressions for the controltooutput transfer
function, the output impedance, and the audio susceptibility are derived for
the buck, boost, and buckboost converters operated in continuous
conduction mode in the case where the load is a linear resistor. If the
measured load current is utilized properly by the controller, the output
impedance becomes low and the controltooutput transfer function becomes
almost invariant for different loads. The use of load current acts as a
feedforward term if the load is a current source. However, if the load is a
resistor the load current is influenced by changes in the output voltage and
the stability is affected. Therefore, the use of load current is not a feedforward
action in this case. Instead it can be seen as gain scheduling, which can be
considered a special case of adaptive control.
In the thesis it is also shown that the two published models for currentmode
control, Ridley (1991) and Tan and Middlebrook (1995), give accurate
expressions for the controltooutput transfer function and the output
impedance but not for the audio susceptibility. A novel model for the audio
susceptibility is presented and it is used to improve the two published models.
Most of the results in the thesis are validated by comparing the frequency
responses predicted by the expressions and switched largesignal simulation
models. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/587910
 author
 Johansson, Bengt ^{LU}
 supervisor

 Gustaf Olsson ^{LU}
 organization
 publishing date
 2003
 type
 Thesis
 publication status
 published
 subject
 pages
 353 pages
 publisher
 Department of Industrial Electrical Engineering and Automation, Lund Institute of Technology
 ISBN
 9188934292
 language
 English
 LU publication?
 yes
 id
 68a19aa22b22499f8d21910c3bcaf81a (old id 587910)
 alternative location
 http://www.iea.lth.se/publications/Theses/LTHIEA1037.pdf
 date added to LUP
 20071030 09:31:00
 date last changed
 20160919 08:45:08
@misc{68a19aa22b22499f8d21910c3bcaf81a, abstract = {To obtain high performance control of a dcdc converter, a good model<br/><br> of the converter is needed. It is suitable to consider the load to be included in<br/><br> the converter model since it usually affects the dynamics. The load is often<br/><br> the most variable part of this system. If the load current and the output<br/><br> voltage are measured there are good possibilities to obtain a good model of<br/><br> the load online. Adaptive control can then be applied to improve the control.<br/><br> In peak currentmode control, the output voltage and the inductor<br/><br> current are measured and utilized by the controller. This thesis analyses some<br/><br> properties that can be obtained if the load current is also measured and<br/><br> utilized for control. Accurate expressions for the controltooutput transfer<br/><br> function, the output impedance, and the audio susceptibility are derived for<br/><br> the buck, boost, and buckboost converters operated in continuous<br/><br> conduction mode in the case where the load is a linear resistor. If the<br/><br> measured load current is utilized properly by the controller, the output<br/><br> impedance becomes low and the controltooutput transfer function becomes<br/><br> almost invariant for different loads. The use of load current acts as a<br/><br> feedforward term if the load is a current source. However, if the load is a<br/><br> resistor the load current is influenced by changes in the output voltage and<br/><br> the stability is affected. Therefore, the use of load current is not a feedforward<br/><br> action in this case. Instead it can be seen as gain scheduling, which can be<br/><br> considered a special case of adaptive control.<br/><br> In the thesis it is also shown that the two published models for currentmode<br/><br> control, Ridley (1991) and Tan and Middlebrook (1995), give accurate<br/><br> expressions for the controltooutput transfer function and the output<br/><br> impedance but not for the audio susceptibility. A novel model for the audio<br/><br> susceptibility is presented and it is used to improve the two published models.<br/><br> Most of the results in the thesis are validated by comparing the frequency<br/><br> responses predicted by the expressions and switched largesignal simulation<br/><br> models.}, author = {Johansson, Bengt}, isbn = {9188934292}, language = {eng}, note = {Licentiate Thesis}, pages = {353}, publisher = {Department of Industrial Electrical Engineering and Automation, Lund Institute of Technology}, title = {Improved Models for DCDC Converters}, year = {2003}, }