DCDC Converters  Dynamic Model Design and Experimental Verification
(2005) Abstract
 To obtain high performance control of a dcdc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. 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 for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for... (More)  To obtain high performance control of a dcdc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. 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 for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for control. The controltooutput transfer function, the output impedance, and the audio susceptibility were derived for the buck, boost, and buckboost converters operated in continuous conduction mode in the case of resistive load. The use of load current can be seen as gain scheduling in the case where the load is a resistor. Gain scheduling can be considered a special case of adaptive control. The majority of the results in the licentiate thesis were validated by comparing the frequency responses predicted by the analytic models and switched largesignal simulation models.
In this thesis, additional results are presented for the buck converter. Experimental results obtained by means of a network analyzer verify the derived controltooutput transfer function and the audio susceptibility but not the output impedance at low frequencies. In the experimental buck converter there are stray resistances in the inductor, transistor, and diode but these stray resistances were not considered in the licentiate thesis. A new transfer function for the output impedance is derived where these stray resistances are considered and it is in good agreement with the experimental result also at low frequencies.
If the current to the output capacitor is measured in addition to the output voltage and the inductor current, the load current can be calculated as the difference between the inductor and capacitor currents in the case of the buck converter. Hence, the measurement of the load current can be replaced by measurement of the capacitor current. If this possibility is utilized and the capacitor current is measured by means of a current transformer, a lowfrequency resonance is introduced in the frequency responses according to experimental results. The reason for this resonance is due to the highpassfilter characteristics of the current transformer. A new analytic model is derived which predicts the resonance. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/24326
 author
 Johansson, Bengt ^{LU}
 supervisor

 Gustaf Olsson ^{LU}
 Matz Lenells
 opponent

 Professor Kyyrä, Jorma, Helsinki University of Technology, Finland
 organization
 publishing date
 2005
 type
 Thesis
 publication status
 published
 subject
 keywords
 robotics, buck, dcdc converter, modeling, audio susceptibility, currentmode control, load current, gain scheduling, current transformer, experimental verification, Electronics and Electrical technology, Automation, Elektronik och elektroteknik, Elektroteknik, Electrical engineering, reglerteknik, robotteknik, Automatiska system, control engineering
 pages
 194 pages
 publisher
 Department of Industrial Electrical Engineering and Automation, Lund Institute of Technology
 defense location
 room M:B in Mbuilding, Ole Römers Väg 1, Lund Institute of Technology
 defense date
 20050112 13:15:00
 ISBN
 9188934349
 language
 English
 LU publication?
 yes
 id
 78fb59bb34cc4b05b23aadfc863e3d4a (old id 24326)
 date added to LUP
 20160404 11:18:27
 date last changed
 20181121 21:03:59
@phdthesis{78fb59bb34cc4b05b23aadfc863e3d4a, abstract = {To obtain high performance control of a dcdc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. 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.<br/><br> <br/><br> In peak currentmode control, the output voltage and the inductor current are measured and utilized for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for control. The controltooutput transfer function, the output impedance, and the audio susceptibility were derived for the buck, boost, and buckboost converters operated in continuous conduction mode in the case of resistive load. The use of load current can be seen as gain scheduling in the case where the load is a resistor. Gain scheduling can be considered a special case of adaptive control. The majority of the results in the licentiate thesis were validated by comparing the frequency responses predicted by the analytic models and switched largesignal simulation models.<br/><br> <br/><br> In this thesis, additional results are presented for the buck converter. Experimental results obtained by means of a network analyzer verify the derived controltooutput transfer function and the audio susceptibility but not the output impedance at low frequencies. In the experimental buck converter there are stray resistances in the inductor, transistor, and diode but these stray resistances were not considered in the licentiate thesis. A new transfer function for the output impedance is derived where these stray resistances are considered and it is in good agreement with the experimental result also at low frequencies.<br/><br> <br/><br> If the current to the output capacitor is measured in addition to the output voltage and the inductor current, the load current can be calculated as the difference between the inductor and capacitor currents in the case of the buck converter. Hence, the measurement of the load current can be replaced by measurement of the capacitor current. If this possibility is utilized and the capacitor current is measured by means of a current transformer, a lowfrequency resonance is introduced in the frequency responses according to experimental results. The reason for this resonance is due to the highpassfilter characteristics of the current transformer. A new analytic model is derived which predicts the resonance.}, author = {Johansson, Bengt}, isbn = {9188934349}, language = {eng}, publisher = {Department of Industrial Electrical Engineering and Automation, Lund Institute of Technology}, school = {Lund University}, title = {DCDC Converters  Dynamic Model Design and Experimental Verification}, url = {https://lup.lub.lu.se/search/ws/files/5743115/26469.pdf}, year = {2005}, }