Engineering Research Paper Summary Project - Section B 2012

       NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING PGDIE-42

INDUSTRIAL ENGINEERING CONCEPTS ASSIGNMENT

                                                                                                      

                                                                       

 Title: A new deterioration model for electrolytic capacitors in direct

                     current to direct current (DC-DC) converters     

Authors: Yinyu Du, Yong Guan*, Lifeng Wu, Wei Pan, Guohui Wang and Shihong Zhou

(Beijing Engineering Research Center of High Reliable Embedded System, Capital Normal University, Beijing, China 100048. 

                             

                                    Submitted to                                                                    Submitted by

                                 Narayana Rao K.V.S.S.                                  Pratik Dhariwal, 67 

                      Professor, NITIE, Mumbai

                                                

INTRODUCTION

The output filter aluminum electrolytic capacitor is one of the key components that determine the life of direct current to direct current (DC-DC) converters, and so, establishing a deterioration model for the electrolytic capacitor is the basis for analyzing the impact on the converters’ performances. Generally, the main parasitic parameters that indicate the electrolytic capacitor deterioration such as capacitance

(C) and equivalent series resistance (ESR) are separately considered when building the model. However, taking the Buck-Boost converter as the research object, this paper discussed the impact of the two kinds of parasitic parameters simultaneous degradation on the DC-DC converters. Firstly, according to the electrolytic capacitor failure mechanisms, a joint degradation model for the C and ESR-a new deterioration model for the electrolytic capacitor was established. On the basis, this paper discussed the impact on the system pole-zero of the parasitic parameters degradation, analyzed the electrolytic capacitor deterioration on how to affect the performances of the DC-DC converter, and verified the theoretical analysis results through the software simulation experiments. The new model provides the theoretical basis for monitoring the health state of DC-DC converters.

MATERIALS AND METHODS

The theoretical basis

With the average model method of switching element to build the model for the Buck-Boost converter (Weiping, 2006), its equivalent circuit is shown in Figure 1. The output filter aluminum electrolytic capacitor is considered non-ideal component and it is equivalent to an ESR in series with an ideal capacitor.

 H (s) is the transfer function of the sampling network, G_m (s) is the transfer function of the PWM regulator, G_vc (s) is the transfer function of the compensation network and G_vd  (s) is   the  transfer  function   of  the  control  object.  The  main work of this paper is to build the relationship between the key component failure and the converter failure by analyzing the ESR and C simultaneous degradation  on how to lead the  G_vd  (s) pole- zero to change.

The transfer function of the control object is

	(1 +	s			)(1 +	s		)
		w				w
Gvd   (s)  = K1				z 1			z 2
	(1 +	s			)(1 +	s		)
		w	p 1			w	p 2

(1 +

s

)(1 +

s

)

Gvc  (s)  = K 2

w

z 3

w

z 4

s(1 +

s

)(1 +

s

)

w

w

P 3

P 4

Therefore, the system open-loop transfer function is:

T (s) = G_vc (s) ´G_m (s) ´G_vd (s) ´ H (s)

Dwz 2	= f1 (DESR2 , DC)
Dwp 0	= f2  (DESR2 , DC)
DV0  (s) =  f3 (DESR2 , DC)

	Uo(1- M )Ts Re q + 2Uo(1- D)TsLeq		Uo(1- M )Ts2
uo =		+
	2L		8LC

So, the system open-loop transfer function is:

T (s) = G_vc  (s) ´ G_m  (s) ´ G_vd  (s) ´ H (s)

=	5136(s + 4.167 *104  )(s - 8188)(s + 914.9) 2
	s(s + 8188)(s + 4.167 *104 )

Using MATLAB as the simulation software, simulate the aluminum electrolytic capacitor deterioration on how to affect the converter performances through the Bode diagram and the Pole-Zero map of the system open-loop transfer function. According to the joint degradation model, set the values of the ESR and C.

RESULTS

The simulation experiments

Set the values of the parameters in the converter for Vin=24V, D=0.6, R=10Ω, L=320uH, C=160uF, ESR=150mΩ, RL=140mΩ, Vo=35V. Set up the power frequency for fs = 100 KHZ, the crossover frequency for fc = 10 KHZ, the reference voltage of the compensator for Vref = 2.5 V, the output peak value of the PWM for VM =3 V.

Conclusions

The main deterioration mode of the electrolytic capacitor is the degradation of the parasitic parameters such as ESR and C. This paper established a joint degradation model for the ESR and C by analyzing the relation of the parasitic parameters and the electrolyte. Then, analyzed the electrolytic capacitor deterioration on how to affect the system performances (ripple voltage, stability marginand high-frequency anti-jamming capability) from the perspective of the system pole-zero. The simulation results show that the main consequences caused by the aluminum electrolytic capacitor deterioration are the crossover frequency increase, the stability margin decrease and the high-frequency anti-jamming capability decline and these lead the ripple voltage to increase and lead the life of the converter to drop. Comparing  with the simulation results and the theoretical  analysis results, their conclusions are consistent, and the theoretical  analysis has been verified.