Active Snubber Matlab

501

A High Efficiency DC-DC Boost Converter with Passive

Radika P†

Abstract – This paper describes the improvement in converter efficiency by reducing the switching loss and by recovering the snubber stored energy. A capacitive based passive regenerative snubber circuit is modeled for a dc-dc boost converter. The proposed snubber is mainly used to reduce the turn- off loss of the main switch. The energy recovery process and the turn-off loss depends on the size of the snubber capacitance; therefore, the conventional and the proposed converters are designed for high and low input voltage conditions with different sizes of the snubber capacitance. Based on the results obtained, the snubber capacitors are classified as small, normal and large snubbers. The Matlab simulation results obtained are presented.

Keywords: Boost converter, Passive snubber, Regenerative snubber, Turn-off loss, Snubber capacitor,

1. Introduction

In general, soft-switching techniques have been used to reduce the switching losses and stress of a power switching devices. To reduce the stress and the switching conditions for the power switches can be improved by using snubber circuit also. During turn-on condition a series inductor called snubber inductor is used to limit the rate of rise of current (di/dt) through the device. A shunt capacitor called snubber capacitor is used to limit the rate of rise of voltage (dv/dt) across the device at turn-off instant.

During snubbing action energy is stored in the magnetic/ electric field of these components. The stored energy must be removed after each switching transition to assure repetitive snubbing action. The simple way is to discharge the stored energy into a resistor which results in dissipative snubbers [1, 2]. Therefore, dissipative passive snubbers are usually added to the power circuits so that dv/dt and di/dt of the switching devices can be reduced, and the switching losses and stress can be diverted to the snubber circuits.

The size of the snubber inductor/capacitor may be small, normal, or large according to the definition of McMurray [3, 4] as shown in Fig. 1. It shows that the switching loss in the switching device decreases with an increase in snubber. For good snubbing action at high power levels and switching frequencies, a relatively large snubber is, therefore, needed. This result in a large quantity of stored energy in the snubber element and at the same time causes more snubber energy loss. However, the power electronics products are in demand for their high efficiency in saving energy. To cope with the demand, the snubber energy losses of the converters are not negligible and should be improved . In order to improve the efficiency of the system, the use of the regenerative or energy recovery or non-dissipative snubber is necessitated. This snubber is able to recover some of the stored energy, by feeding it back to the supply or load. This may be passive or active one .

In Some Of The Passive Snubber Based Converters

incorporated a snubber circuit with energy recovery transformer . This introduced additional losses. Whereas, the proposed snubber does not use recovery transformer. Also it was observed that generally the studies of dc-dc converter [6, 11-13] had been carried out for a particular value of snubber capacitance and the effect of the size of the snubber capacitance had not been discussed much. Therefore, for a proposed converter, the selection of

†

Corresponding Author: Dept. of Electrical and Electronics Engin- eering, Adhiparasakthi Engineering College, Melmaruvathur, India. Received: December 28, 2012; Accepted: October 22, 2013 Fig. 1. Voltage and current waveforms of a transistor with different sizes of snubber: (a) No snubber; (b) Small

Snubber; (C) Normal Snubber; (D) Large Snubber

A High Efficiency DC-DC Boost Converter with Passive Regenerative Snubber

502

the size of the snubber capacitance which is an important factor to obtain the better performance is analysed. The change in turn-off loss, output voltage and efficiency for different sizes of the snubber capacitance are discussed in the present work. Based on the results obtained, the snubber capacitors are classified as three groups: Group I as small snubber, Group II as normal snubber and Group III as large snubber.

2. Principle Of Operation

The principle of operation of the proposed snubber without energy recovery circuit (Fig. 2) is explained as follows : When switch S turns-off, as in Fig. 2(a), the two capacitors are charged equally by the energy stored in the circuit, here Vc denotes the voltage of each capacitor.

When the switch turns-on, as in Fig. 2(b), these two voltages are superimposed and 2Vc appears across the terminals A and B. If these two terminals are connected with the source or the load through an inductor, the capacitor voltages will discharge resonantly to zero, thus recovering the stored energy of the snubber capacitors. The switch turns-off softly at zero voltage by virtue of being in parallel with the capacitors.

2.1 Circuit Configuration And Modes Of Operation

Fig. 3 shows the proposed boost converter. It differs from a conventional PWM boost converter by adding a passive regenerative snubber network, which consists of snubber capacitors (Cs1, Cs2), snubber diodes (Ds1, Ds2) and the energy recovery circuit components of resonant inductors (Lr1, Lr2) and diodes (Dr1, Dr2). The proposed one has two modes of operation (Fig. 4) based on switch on and off conditions as explained below.

1) Mode 1 Operation: Assuming that, initially, the

S

C is zero. In Fig. 4(a), the main switch S turns-off at zero voltage

Li Is Transferred To The

snubber capacitors charging them equally up to the output

V ). The Diode D Conducts Exactly

in the same manner as diode D of conventional boost converter. During this mode, the voltage across the each

(B)

Fig. 2. Proposed passive snubber (without energy recovery circuit) (a) Two snubber capacitors are charged in

Series When Switch Turns-On

Fig. 3. Proposed boost converter with passive regenerative

(B)

Fig. 4. Modes of operation of a proposed converter: (a)

(1)

Based on the design of turn-off snubber, if the snubber

C .

2) Mode 2 Operation: At the turn-on of the switch as shown in Fig. 4(b), the superimposed capacitor voltage

2

discharges resonantly into the output side. The switch

Ci . At The End Of This Mode Of

operation, the voltage across the capacitors becomes zero. Therefore, at ZVS condition the switch is turned-off again. If the voltage across each snubber capacitor, at the end of

Respectively

during the discharging period.

In Simulation The Performance Of The Converter Is

analyzed at both high (200 V) and low input (15 V) voltage conditions. The boost inductor of the converter is designed

(7)

It shows that the design of inductance depends on its inductor current ripple. Based on some design examples two values of current ripple is assumed for analysis rather than the optimal design values [20, 21]. This leads to four cases. The circuit parameters for each case are shown in Table 1 and Table 2.

3.1 Case I. Input voltage, Vin: 200 V and input boost

Inductance, L: 100 Mh

The obtained result of the conventional boost converter is shown in Table 3.

80.68

The selection of the size of the snubber capacitor is an important factor to obtain the better performance of the proposed converter. Since, the main switch turn-off loss can only be reduced by snubber capacitor, it is necessary to select a snubber capacitor so that further increments of capacitor value will not significantly reduce the turn-off loss. Therefore, using the same reference parameters (Table 1), the proposed converter is simulated for different

). The Obtained

output voltage and efficiency are plotted in Fig. 5. Based on the results obtained, the snubber capacitors can be

Y Group Ii (0.07 - 0.14 Μf) As Normal Snubber

y Group III (0.15 - 0.3 and > 0.3 – 5 μF) as large snubber. In small snubber the capacitor voltage reaches quickly to the input voltage level during its charging condition.

Therefore, it is not sufficient for turn-off protection. The normal snubber provides sufficient turn-off protection. With large snubber the voltage rises slowly to reach the

Protection With Minimum Turn-Off Energy Loss. The

obtained turn-off energy loss of the main switch for three

Deployment In Out-Of-Position Situations

D. Bendjaballah1, A. Bouchoucha1, M. L. Sahli1,2* and J-C. Gelin2

Abstract

Side-impact collisions represent the second greatest cause of fatality in motor vehicle accidents. Side-impact airbags have been installed in recent model year vehicle due to its effectiveness in reducing passengers’ injuries and fatality rates. In meeting these requirements, simulations of folding and deploying airbags are very useful and are widely used. The paper presents a simulation method for the deploying airbags using three materials in different working conditions. Finite element analysis is primarily used to evaluate this concept. In these simulations, the gas flow is described by the conservation laws of mass, momentum, and energy. The numerical results indicate that the FE method in this paper is capable of capturing airbag deploying process accurately.

Keywords: Airbag simulations, Out-of-position, Crash, Modeling, Out-of-position

Background

The passive safety of cars has become a very high prior- ity issue for the automotive industry. Today, there are not only one or two airbags in a car; certain models have ten times more than that. With the increasing usage of airbags, the number of accidents where the airbag itself can cause an injury to the occupant also increases

(Augenstein Et Al. 2003; Gabauer And Gabler 2010;

Audrey et al. 2011). As is well known, safety belts are also now devices designed to provide protection to the users of vehicles during crash events, minimizing the loads necessary to adapt their movement to the move- ment of the car (Freesmeier and Butler 1999; Schmitt et al. 1997). In general, the seat belt is designed to restrain the occupant in the vehicle and prevent the

Occupant From Having Harsh Contacts With Interior

surfaces of the vehicles. The airbag acts to cushion any impact with vehicle structure and has positive internal pressure, which can exert distributed restraining forces over the head and face. As a safety component of auto- mobile, an airbag decreases occupants’ injury likelihood effectively in case of an accident (Ruff et al. 2007). These safety elements can reduce the death rates on the roads, and its protection effects have been widely approved (Crandall et al. 2001; Teru and Ishikawa 2003). With computational tools such as finite element methods designed for dynamic contact problems, crashworthiness simulations can now be used with reliable accuracy to evaluate occupant protection in various collision condi- tions with safety metric/parameters such as acceleration, head injury criteria, intrusion distance, intrusion vel- ocity, and neck forces (neck injury risk or whiplash).

Thus, new types of airbag products are being developed to handle different collision scenarios.

Become Standard Equipment On Most New Passenger

vehicles (Braver and Kyrychenko 2004; Teng et al. 2007; Yoganandan et al. 2007). The airbag cushion is com- posed of a woven fabric which is rapidly inflated during a car crash. The airbag dissipates the passenger’s kinetic energy thereby reducing injury through biaxial stretching of the fabric bag and escaping gas through vents. There- fore, the performance of the airbag is greatly influenced by the mechanical properties of the fabric. Generally, air bags are designed to deploy in a crash that is equivalent to a vehicle crashing into a solid wall at 8 to 14 mph.

Air bags most often deploy when a vehicle collides with another vehicle or with a solid object like a tree. There are various types of airbags: frontal, side-impact, and curtain airbags. In general, the passenger side airbags are usually larger than the driver airbags (see Fig. 1).

Besançon, France

© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Bendjaballah et al. International Journal of Mechanical

Doi 10.1186/S40712-016-0070-2

Extensive studies have shown that the airbag deploy- ment in load cases consists of two occupant loading phases: a punch-out effect where the airbag bursts out of its container with the airbag and airbag module cover accelerating towards the occupant and a second loading phase during which the airbag is taking on its deployed shape and volume (membrane-loading effect). Bankdak et al. (2002) developed an experimental airbag test system to study airbag-occupant interactions during close proximity deployment. The results provided insight for simulating the effect of inflation energy and mass flow on target response. Bedard et al. (2002) found that while left-side (driver-side) impacts accounted for only 13.5% of all crashes, the fatality rate among these

Crashes Was 68.3% In Comparison To Front Impact

(48.3%), right-side impact (31.3%), and rear impact (38.4%). These studies underscore the importance of oc- cupant safety during side-impact collisions. In the last years, the current market requested to reduce the time and cost airbag development. In order to achieve this result, virtual simulations play an important role since they allow to minimize the number of experimental tests (Pei et al. 2013; Cao et al. 2014). Several simulation models of airbag were established (Wang et al. 2007). It is feasible to optimize the parameters of airbag deploy- ment using simulation technology. Experimental and numerical studies have quantified injury risks to close- proximity occupants from deploying side airbags. These studies have focused on the prevention of the most ad- verse effects of airbag deployment (Duma et al. 2003).

Other studies have proposed airbag characteristics to minimize particular biomechanical responses (Haland and Pipkorn 1996). In a more recent study, Marklund and Nilsson (2003) compared deformation patterns with experimental data as well as the computational costs associated with three different airbag deployment simu- lation methods; they concluded that the SPH method is relatively inexpensive and produces incremental deform- ation patterns that compare most closely to the experi- mental results. The process of inflation of an airbag is one of the determining factors in saving lives. The duration from the initial impact of the crash to the full inflation of an airbag is about 40 ms, and during this time, the airbag goes from being in a folded state to a fully inflated state, with a high internal pressure. After achieving this state, the airbag begins to deflate, thus providing a nice cushion for the body impacting it.

Ideally, the person in the crash should come into contact with the airbag at this time. In the present study, a large volume passenger side airbag model is developed to handle different collision scenarios. The main aim is evaluate the performance of deploying of passenger side airbag using finite element methods (FEM).

Materials

The tensile specimens were made in different airbags (P: Peugeot, R: Renault, and VW: Volkswagen) with a length of 200 mm long and a width of 40 mm. Table 1 shows the mechanical properties of the airbag.

Tensile Tests

To determine the mechanical properties of the material of airbag used in the test pieces, tensile tests were performed on Lloyd EZ20 universal testing machine in Constantine. These tests were conducted using rect- angular samples. The axial force and axial displacement acquired during a test are converted into stress and the strain in order to be used for the fabric material model.

The continuous recording of the stress-strain data was performed during both the load and unload phases. A minimum of five samples were made in order to check the repeatability of the measurements. All the data was collected by using a PC-based data acquisition system and analyzed by commercial software. The picture frame test device that is made for this study is shown in Fig. 2.

Fig. 1 a Frontal and side airbags. b Oblique view of facet occupant model in sitting posture following airbag deployment (Lim et al. 2014)

0.150

Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

Page 2 Of 9

Figure 3 shows the stress-strain relationship of the airbag sample under axial tensile loads. The results are showing a linear increase in extension with the increas- ing stresses. This is an expected output and it confirms with the theoretical behavior of a sample subjected to tensile stress. The rupture strain values for different airbags (R/P/VW) were 0.322, 0.441, and 0.472, respect- ively. The measured elastic parameters (i.e., Young’s modulus E and initial yield strength) and Poisson’s ratio are summarized in Table 2. The tensile tests of the woven fabrics can show differences on mechanical prop- erties because woven fabrics can resist in-plane shear loads once the yarn lock-up angle has been reached. The differences of material property on material direction can affect the shape of fully deployed bag (see Fig. 3b).

Theoretical Background

Numerical simulations of airbags use very complex and techniques such as an orthotropic model to identify the mechanical behaviors during the airbag inflation and the fluid mechanics (gas flow) to describe the inflator gas flow (pressure gradient) and improve the representation of the pressures within the airbag. To model the airbag as an orthotropic model, three material constants have to be provided. Assuming a plane stress condition, the

Ð1Þ

where σ is the normal stress and τ is the shear stress, the subscript refers to the principal material directions, i.e., the fill and warp directions. Also, ε and γ are the strain components. The material elastic constants Qij are

Ð2Þ

where E1 and E2 are the Young’s modulus in the fill and wrap directions and G12 is the shear modulus of the fabric material. νij is the Poisson ratio of the material.

The gas exerts a pressure load on the airbag causing it to expand. This expansion puts the airbag under tensile stress lowering the expansion rate. In this study, heat conduction and heat transfer is not taken into account.

Fig. 2 A photograph of Lloyd EZ20 universal testing Fig. 3 Stress versus strain using Lloyd EZ20 machine for a three different airbags at 0° and 90° and b VW airbag test specimens at

Different Angles

Table 2 Physical and mechanical properties of the airbag

Page 3 Of 9

In the deployment of an airbag, an inflator supplies high velocity gas into an airbag causing it to expand rapidly. The gas inside the airbag is assumed to be ideal, to be of constant entropy, and to satisfy the equation of state:

Ð3Þ

Here p, ρ, and e are respectively the pressure, density, and specific internal energy, and γ is the ratio of the heat capacities of the gas. The gas flow is described by the conservation laws for mass, momentum, and energy that

Ð4Þ

here, V is a volume, A is the boundary of this volume,

N Is The Normal Vector Along The Surface A, And U

denotes the velocity vector in the volume. Applying Bernoulli’s equation in the case of an ideal gas with

Ð5Þ

Here, the subscript ex denotes quantities at the throat of the tube. Furthermore u, p, and ρ denote the quan- tities inside that part of the tube that is supplying mass.

Materials And Boundary Conditions

The airbag system mainly consists of three parts: the airbag itself, the inflator unit, and the crash sensor or diagnostic unit. Thus, to study the behavior of the airbag using FE simulations, we need to have an FE model of the airbag in the folded position. A FE model of the airbag was used to simulate the test condition as shown in Fig. 5. LS-DYNA® material model FABRIC (MAT_34) is used to simulate the airbag material. It is a variation of the layered orthotropic material model. Additionally, in the LS-DYNA® material model, fabric leakage can be accounted for. However, for this CAB material, the leak- age is almost negligible and therefore no leakage is specified. The mechanical properties can be determined from the physical test. Typical material properties for airbag fabrics are taken as given in Chawla et al. (2004a) (Table 3). These properties are used to simulate inflation process of airbag (see Table 1). The car dashboard is modeled as the rectangular thin plate using a MAT_RI-

Gid Material, And The Degrees Of Freedom Are Con-

strained in all the directions. The similar properties of thermoplastic polymer are assigned for contact purposes. The porosity of the fabric is assumed zero. The nitro- gen gas is taken for inflating the airbag. Properties of nitrogen gas and initial bag conditions are shown in Table 4. The example on which we perform the study is a typical passenger side airbag. The geometric de- tails have been measured from a commercially avail- able airbag. The initial state of the airbag is a closed rectangular whose sides are to be finished to 482 × 635 mm2 and is shown in Fig. 4.

Table 3 Material properties of airbag and rigid plate used in FE

–

Table 4 Initial values used for FE simulation of the swelling of

3.33 × 10−4

Fig. 4 The initial airbag geometry in the form of a rectangular Bendjaballah et al. International Journal of Mechanical and Materials Engineering (2017) 12:12

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