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Digital Controller Design for Fourth-Order Soft-Switching Boost Converter

Mummadi VeeracharyDept. of Electrical Engineering, IIT Delhi, New Delhi

INDIA

Abstract- In this paper a digital voltage-mode controller is

designed for a fourth-order soft-switching boost converter. Theproposed converter exhibits voltage gain same as that ofconventional boost converter but has lower source currentripple as compared to it. Additionally, it exhibits reduced switchtransition losses on account of zero voltage transition behavior.In soft-switching operation it exhibits seven different modes ofoperations in one switching cycle and also results in zero-voltagetransition to the switching devices. As there are severaloperating modes in one switching cycle the small-signal z-

domain transfer functions are formulated using MATALB basedsystem identification toolbox, which are then used in the direct

digital controller design. A sisotool of matlab is adopted toarrive at final digital voltage-mode controller. Closed-loopconverter performance is determined for a 12 to 28 V, 50 Wprototype in simulation and then compared with experimentalmeasurements. Experimental measurements are in closeagreement with simulations.

I. INTRODUCTION

witch-mode power supplies demands more accurate

and fast regulation of load voltage since they are being

extensively used as a source of power for critical medical

equipments/instruments, space crafts, computer processors,

communication systems, hybrid vehicles, electronic goodsand gadgets, etc. [1]-[2]. This widespread application may be

credited to implementation of digital control techniques and

availability of high performance, low cost FPGA/DSP.

Digital control techniques have following advantages over

their analog counterpart [3]-[4]: (i) possibility of more

advanced and functional control methods which can greatly

improve the dynamic performance of power converter

system, (ii) less susceptibility to parameter variation, (iii)

programmability, (iv) high flexibility, and (v) low power

consumption, etc,. Dc-Dc boosting converters are most

popular for delivering higher load voltages from given low

voltage source. Although, the conventional boost converter iscapable of stepping-up of voltages and meeting the load

demand at a predefined voltage levels, but (i) its full load

efficiency is low on account of higher switching losses, (ii)

higher source current ripple, and (iii) extreme duty ratio

operation unable to yield expected voltage gain, and

efficiency requirements etc,. To overcome some of these

limitations a fourth-order boost converter is proposed [4].

Although, this converter gives improved performance with

reference to the source current ripple, but its switching losses

are high on account of hard transition. This becomes even

more problematic in case switching frequency is increased to

further higher value.

Recently, soft-switching techniques are coming-up to

overcome the excessive switching losses occurring in the

conventional hard-switched dc-dc converters and to realize

higher efficiencies for the dc-dc converter at full-load

conditions [5]-[6]. A high gain soft-switching boost converter

topology is reported in the literature [7]. Here, the voltage

multiplier network not only serves as voltage amplification

but also results in soft-switching for the MOSFETs. It gives

higher boosting ratios at the expense of decreased efficiency.Analysis of zero-voltage transition based boost converter is

reported in ref[3]. Furthermore, ZVT structures for the

remaining six basic dc-dc converters also described.

However, there is not enough literature covering the

development of soft-switching schemes for higher order boost

converters such as fourth-order converters. Furthermore, very

few papers reported dealing the design aspects of digital

controllers for such kinds of converters. In order to bridge

this gap, this paper presents some investigations on (i)

realization of zero voltage transition feature for the fourth-

order boost converter, and (ii) digital controller design for thefourth-order soft-switching boost converter (FSOBC), which

ensures load voltage regulation while rejecting structured/

unstructured uncertainties in the converter including source

and load disturbances. Although analogue controllers are well

established for switch-mode dc-dc converters, digital

controllers offer many advantages over their analogue

counterparts. Due to latest developments in microcontrollers/

digital signal processors technology, there has been a growing

interest in the application of digital controllers for high

frequency conversion systems and low to medium power dc-

dc converters, due to the low price-to-performance ratio for

implementing complex control strategies.

Fig. 1. Circuit diagram of the soft-switching fourth-order boost converter.

S

978-1-4673-2605-6/12/$31.00 2012 IEEE

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Table I. Status on the devices in one switching cycle.

Mode Time

duration

Primary

switch

Auxiliary

switch

Primary

diode

Aux.

diode

I T0

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represents the small-signal dynamics of the FSOBC system ifthe residual of the model is within the allowable confidenceinterval. The control-to-output transfer function, Gvd(z), isobtained from the system identification tool for a 50 WattFSOBC is

3 2

4 3 2

( ) (0.5157 1.452 1.362 0.4233)( )

( 3.34 4.213 2.395 0.5227)( )

ovd

v z z z zG z

z z z zd z

+ = =

+ +

(1)

A two-pole two-zero digital controller is designed for thisconverter and it is:

1 2

3

( )( )( )

( 1)( )vc

k z a z aG z

z z a

=

(2)

where a1, a2, a3respectively are zero and pole locations in z-

plane.

III. DIGITAL VOLTAGE-MODE CONTROLLER DESIGN

Several single-loop controlling techniques are reported in

literature for power supplies. Each of these controlling

techniques has their own advantages and limitations. In

applications needing load voltage regulation single-loopvoltage-mode control strategy is simple and widely used

scheme to achieve reasonably good dynamic response. In

view of this a single-loop voltage-mode digital controller is

discussed in this section. Taking the above transfer functions

and using the control block diagram, Fig. 2, digital controller

is designed. The control-loop stability is assessed by the

loopgain, defined by eqn. 3, where the digital delay in the

loop is also included.

vmc de vdT(z)=G (z)G (z)G (z) (3)

The digital controller has been designed using the sisotoolof matlab and the pole-zero locations have been decided

based on the gain margin (GM), phase margin (PM)

requirements. The final design trade-off pole-zero locations

is: a1=0.78, a2=0.98, a3=0.36, k=0.8466 and this design is

resulted in the stability margins: GM=9 dB, PM=620 and

crossover frequency of 460 Hz. The final resulting loopgain

bode plot is shown in Fig. 3.

IV. SIMULATION AND EXPERIMENTAL RESULTS

A 30 Wattprototype FSOBC system has been designed to

verify the ZVT performance of the proposed converter and its

controller regulation capability. The converter is suppliedfrom a 12 Vbattery and the desired load voltage is 28 V. The

parameters of the designed converter to meet the

specifications (IL1

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After studying the converter soft-switching performance

the feasibility of the designed digital controller is verified.

For demonstration the closed-loop converter system

regulation capability is tested for: (i) load perturbation from

26 to 13 , (ii) supply voltage change from 10 to 15 V and

the corresponding experimental results are shown in Fig. 7,

where the observations clearly indicate the load voltage

regulation feature against load and source perturbations.

(a)

Simulation

(b) Experimentally measured

Fig. 4. Waveform showing ZVS operation of the main switch SM.

V. CONCLUSION

In this paper a soft-switching fourth order boost converter

performance has been analyzed. Small-signal z-domain

transfer functions were formulated using system identification

toolbox of the MATLAB, and then used in the direct digital

controller design. Digital voltage-mode controller has been

designed for the proposed converter and its validity is verified

both in simulation and experiment. Theoretical analysisresults were in close agreement experimental measurements.

(a) Simulation

(b) Experimentally measured

Fig. 5. Waveforms showing ZCS operation of the main diode DM.

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(a)Simulation

(b) Experimental measurements

Fig. 6. Waveforms of auxiliary switch SA.

(a) Load resistance perturbation (R: 26 13 )

(b) Source voltage perturbation (Vg: 10 15 V)

Fig. 7. Experimentally measured dynamic response of load voltage.

Table II. Converter parameters.Power stage

parameter

Value

L1 50 H

L2 150 H

Lr 10 H

Cr 10 nF

C1 100 F

C2 110 F

fs 50 kHz

R 26

REFERENCES

[1] Guichao Hua, Ching-Shan Leu, Yimin Jiang, Fred C. Y. Lee, NovelZero- Voltage-Transition PWM Converters, IEEE Trans. On PowerElectronics, 1994, Vol. 9, No. 2, pp. 213-219.

[2] Ying-Chun Chuang, Yu-Lung Ke High-Efficiency and Low-StressZVTPWM DC-to-DC Converter for Battery Charger IEEE Trans. OnIndustrial Electronics, 2008, Vol. 55, No. 8, pp. 3030-3037.

[3] G. Hua and F. C. Lee, Novel zero-voltage-transition PWMconverters, in Proc. IEEE PESC92, 1992, pp.5561.

[4] B. Krishna Mohan, Robust Digital Voltage-mode Controller for fifthorder Boost Converter, IEEE Trans. Ind. Electron., Jan. 2011, vol.58,no.1, pp. 263-277.

[5] JacekJ. Jozwik, Marian K. Kazimierczuk, Dual Sepic PWMSwitching - Mode DC/DC Power Converter IEEE Trans on IndustrialElectronics, 1989, Vol. 36, No. 1, pp.64-70.

[6] Haci Bodur, A. Faruk Bakan, An improved ZCT-PWM DC-DCconverter for high power and high frequency applications, IEEETrans. on Industrial Electronics, 2004, Vol. 51(1), pp. 89-95.

[7] R. Sekhar, Digital Voltage-mode Controller Design for High gainSoft-Switching Boost Converter, IEEE Proc. on PEDES2010, Dec.2010, pp. 1-5.

[8] MATLAB, user manual, 2005.[9] PSIM, user manual, 2005.[10] dSPIC30F60100, Microchip, user manual, 2009.