Reduction of Electromagnetic Interference in DC-DC Converter using Chaos

L.Premalatha EEE Department, Anand Institute of higher Technology

Affliated to Anna University Chennai,Tamilnadu,India

C.Ravichandran EEE Department,Anand Institute of higher Technology

Affliated to Anna University Chennai,Tamilnadu,India

Abstract—This paper analyses the reduction of electromagnetic interference and improvement of electromagnetic compatibility in a DC-DC Buck converter using chaos. Spectrum analysis was carried out on the converter using Matlab-Simulink and the results confirm the reduction of spectral peaks during the chaotic operation of the converter. It is found that there is good agreement between the simulation and experiment results.

Keywords—converter; chaos; electromagnetic interference; frequency spectrum

I. INTRODUCTION Since their introduction at the end of 1960s, switched mode

power supplies (SMPS) have become more and more popular, being used in the majority of today’s electronic and electric equipment.

It is reported in literature [1]-[4] that SMPS are highly nonlinear in nature because of the switching characteristics and have chaotic operation in certain parameter range.

One of the undesirable features of switch-mode pulse width modulated (PWM) DC-DC power converters is their generation of conducted and radiated electromagnetic interference (EMI) at the switching frequency and its harmonics [5]. EMI currents, if not filtered, can corrupt the power source to the converter and interfere with the operation of other equipments running from the same source. Radiated EMI noise will be picked up by, and interfere with the operation of adjacent equipment. The EMI noises will frequently be large enough to cause the converter to violate the limits for interference mandated by various regulatory bodies such as the FCC and CISPRR [6].

The conducted EMI performance of the system can be improved by using a filter with larger component values or more complexity, but these measures usually increase the filter’s cost [7]. Various methods of amelioration have been proposed based on spread spectrum techniques [8]-[10]. These include periodic or pseudorandom modulation of pulse width or switching frequency. Implementing any of the above requires extra circuitry, adding to size and cost. This paper work is based on the concept of improvement of Electromagnetic compatibility using chaos [11]. It is given in these papers that operating a

system in chaos, where the ripple waveform becomes aperiodic, have the effect of spectral spreading without any additional circuitry which can be effectively used in countering the EM1 problem. For achieving this, the dc-dc converter in the SMPS has to be operated in chaos mode by suitably adjusting the parameters so that EMC compliance is obtained.

II. ELECTROMAGNETIC INTERFERENCE Electromagnetic Interference (EMI) is an unwanted effect

in the electrical system due to electromagnetic radiation and electromagnetic conduction. Electromagnetic radiation and electromagnetic conduction are differentiated by the way an EM field propagates. Conducted EMI is caused by the physical contact of the conductors as opposed to radiated EMI which is caused by induction. EMI behavior is dependent on the frequency of operation and cannot be controlled at higher frequencies. For lower frequencies, EMI is caused by conduction and, for higher frequencies, by radiation. As electronic products become smaller and more complex, the system design has to be efficient and effective to reduce the corresponding increase in EMI.

III. SPREAD SPECTRUM TECHNIQUE Spreading the spectrum of a frequency means distributing

the energy that was originally concentrated at one frequency (or more accurately over a narrow band of frequencies) over a wider band, thereby reducing peak emissions. The energy is distributed by modulating the signal slowly between two frequency boundaries. The method of modulation dramatically influences the amount of EMI reduction. Fundamentally spread spectrum switching involves varying the switching frequency from cycle to cycle. This changes the frequency spectrum from a train of large spikes located at the switching frequency and its harmonics to a smoother, more continuous spectrum with reduced but more densely packed peaks at a greater number of frequencies.

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IV. BUCK CONVERTER Fig. 1 shows the block diagram of the buck converter that

uses a PWM (Pulse width modulation) voltage loop that can display a variety of behavior as its parameters are disturbed.

Figure 1. Buck converter schematic

Fig. 2 shows PWM switching, in which the average power to a load is controlled by opening and closing the switch in rapid fashion. The average output voltage as seen by the load resistor R is equal to: Vo (avg) = (Ton /T) x Vin (1) Reducing Ton reduces Vo(avg). This method of control is referred to as pulse width modulation (PWM).

Figure 2. .PWM switching

In fig.1,the voltage v(t) across the load resistance R is applied to the non-inverting input of an amplifier with gain a; A constant voltage Vref is applied to the inverting input; the output of the amplifier is the control voltage

This is applied to the inverting input of the comparator; the non-inverting input is fed by an independently generated ramp voltage Vr(t), which periodically and linearly rises from a lower voltage VL to an upper voltage VU in a time T and then instantaneously returns to VL .

The voltage across the capacitor ‘V’ and the inductor current ‘i’ are taken as two state variables.

VI. SIMULATION RESULTS

A.Periodic and Chaotic state simulation results

The buck converter with design specifications as R = 25 Ù, L = 22 mH, C = 10µF, Vref = l0V, and switching frequency = 2.5kHz. The output voltage is set at 11 V and the system is operated in periodic state. The periodic operation of the converter is obtained when the input voltage is 16V and the waveforms are given in Fig. 3.

3.a.capacitor voltage waveform

3.b.inductor current waveform

Out

put v

olta

ge (v

olts

)

Time (sec)

Time (sec)

Indu

ctor

cur

rent

(am

ps)

VU

VL

Vc Vr

t

t

Ton Toff

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3.c.state space portrait

Figure.3 Periodic operation of buck converter

With the output voltage again fixed at 11V ,the input voltage is varied and at Vin= 29 V, the system operates chaotically. The chaotic waveforms are as shown in Fig. 4.

4.a.capacitor voltage waveform

4.b.inductor current waveform

4.c.state space portrait

Figure.4 Chaotic operation of buck converter b.Spectrum analysis results

The spectrum is related to the Fourier transform of the signal, which transforms the signal into its frequency domain. The Fourier transform displays the signals in the frequency domain, and shows the frequency content of that signal. The power density spectrums of the output voltage during periodic and chaotic state are simulated using Matlab.The comparison of both the spectrums is shown in Fig. 5.

Figure.5 Simulation result of comparison of periodic and chaotic spectrum

It is found that the power is densely concentrated at the fundamental frequency of 2.5 KHz and its harmonics (specific frequencies) during periodic operation whereas the spectrum is continuous and the amplitudes of the spectral peaks are reduced during chaotic operation. This is because the total emitted energy did not change; rather the energy gets spread over a wider frequency range thereby reducing peak emissions. The plot shows that operating the system in chaotic mode is effective at lowering the peak level of both fundamental and harmonic peaks. The simulation results of spectral analysis are verified with the experimental results as shown in Fig.6.

Out

put v

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ge (v

olts

)

Inductor current (amps)

Time (sec)

Time (sec)

Inductor current (amps)

Indu

ctor

cur

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(am

ps)

Out

put v

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ge (v

olts

)

Pow

er sp

ectru

m (

dB)

Frequency (Hz)

Out

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)

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6.a. Periodic spectrum

6.b. Chaotic spectrum

6.c. Comparison of periodic and chaotic spectrum

Figure 6. Experimental results

VII. CONCLUSION Reduction of electromagnetic interference with spread spectrum technique application to a DC-DC buck converter using chaos is presented in this paper. It is found that implementation of spread spectrum technique by operating the system in chaotic mode reduces the EMI and improves the system performance. Also the technique reduces the packaging and shielding costs.

ACKNOWLEDGMENT This work is supported by Defence Research and Development Organization DRDO(ER&IPR) under project No.ERIP/ER/0905107/M/01/1199. The authors are thankful to DRDO as well as Management of Anand Institute of Higher Technology for their continuous support of this work.

REFERENCES [1] J.H.B.Deane and D.C.Hamill, “Instability,subharmonics and chaos in

power electronic systems,” IEEE Trans. on Power electronics,vol.5,no.3,1990,pp.260-268.

[2] K.Chakrabarty, G.Poddar and Soumitro Banerjee, “Bifurcation behaviour of buck converter,” IEEE Trans.on power electronics,vol.11,no.3, 1995,pp.439-447.

[3] Fossas and Olivar, “Study of chaos in buck converter,” IEEE Trans. on circuits and systems I, vol.43,no.1,1996, pp.13-25.

[4] S.Banerjee and G.C.Verghese,Eds., “Nonlinear phenomena in power electronics: attractors, bifurcations,chaos and nonlinear control, IEEE press,2001.

[5] M.H.Nagrial and A.Hellany, “EMI/EMC issues in switch mode power supplies,EMC york conference publn,no.464,1999,pp.180-185.

[6] L.Haachitaba Mweene, How to ease EMI to compliance in power converters,EE times-India,2007,pp.1-2.

[7] Olivier Trescases,Guowen Wei,Aleksandar Prodic and Wai Tung Ng, “ An EMI reduction technique for digitally controlled SMPS,” IEEE Trans.power electronics,vol.22,no.4,2007,pp.1560-1565.

[8] R.Giral,A.El Aroudi,L.Martinez-Salamero,R.Levya and J.Maixe, “Current control technique for improving EMC in power converters,”Electronics letters,vol.37,no.5,2001,pp.274-275.

[9] S.Banerjee, A.L.Baranovski, J.L.R.Marrero and O.Woywode, “Minimizing electromagnetic interference problems with chaos,” IEICE Trans. on fundamendals,vol.E87-A,no.8,pp.2100,2004. J.H.B.Deane and

[10] Rupam Mukherjee,S.Nandi and Soumitro Banerjee, “Reduction in spectral peaks of DC-DC converters using chaos-modulated clock,” ,Proc.IEEE Int symp.Circuits Syst,vo..4,2005,,pp.3367-3370.

[11] D.C.Hamill , “Improvement of power supply EMC using chaos,” Electronics letters, vol. 32, no.12, 1996, pp. 1045.

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