resonant converter based automobile ignition system · respond primarily to this component and...

Resonant Converter based AutomobileIgnition system

M.Santhosh Rani1, S.S.Dash2,Gangadevi.R3

1,3Department of Mechatronics Engineering,SRM IST, Chennai, India

2Department of Electrical and Electronics Engineering,SRM IST, Chennai, India

April 12, 2018

Abstract

A hybrid full bridge resonant converter used for sparkgeneration in an automobile ignition system is presented inthis paper. Efficiency and capability to produce a spark ofmaximum possible voltage even at high RPM is the signif-icant contribution of this design. Usually, in ignition sys-tems, switching elements (such as inductors in inductivecharge based ignition or capacitors in capacitive dischargebased ignition) must be charged quite often to obtain sig-nificant DC voltages (greater than 10 kV) at the spark plugend. Resonant converter topologies can be used for thispurpose. The proposed system is driven by a hybrid res-onant converter circuit that uses an inductor in series anda capacitor in parallel; Pulses are generated with the helpof an internal microcontroller in the proposed system. Theperformance of this converter is compared with an existingsystem (capacitive discharge type), and the advantages andlimitations are reviewed. Simulation of the ignition systemswas carried out in MATLAB Simulink, and the results arepresented. A prototype of resonant converter based igni-tion system is designed and tested which confirms that itsefficiency is better than that of capacitive discharge basedsystem.

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

Key Words:: Resonant Converter, Ignition System,Capacitive Discharge Ignition, Spark generation.

1 INTRODUCTION

The modern IC engines that run on petrol must not only have theexact mixture of air and fuel, they require a method of igniting thismixture. This is done by the ignition system. The gap between apair of electrodes of the spark plug experiences a high voltage pulse.This process of causing the air fuel mixture to ignite is known asignition. Spark ignition is made possible using highly efficient pulsetransformer circuits which can provide a very high voltage pulse tothe spark plug from a very low average current pulse at its input[1].

1.1 IGNITION SYSTEM COMPONENTS

The ignition system consists of the spark plug, one or more pulsetransformers (typically called coils), timing control circuitry, anddistribution apparatus that supply the high-voltage pulse to thecorrect cylinder[1].

For creating the spark, a high voltage pulse of about 10kV to20kV is provided between the center electrode and the ground. Thishigh voltage pulse varies with each spark plug as the spark gapswill differ. Compression ratios and air fuel ratio. As the residualgas mixture in and around the spark plug is ionized, the voltagerequired to sustain the arc is considerably lower. This arc must bemaintained for long to ignite the air-fuel mixture [1]-[2]. A typicalspark plug configuration is shown in the Fig. 1. The spark plugcomprises a pair of electrodes, separated by a gap. The gap size isvital and is specified for each type of engine. The center electrode isinsulated from rest of the spark plug. One terminal of the batterythat supplies the current to generate the high-voltage pulse for theignition system is connected to the engine block, and frame, andthe ground electrode is at electrical ground potential. [1]-[2].

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International Journal of Pure and Applied Mathematics Special Issue

Fig.1 Spark Plug

The voltage required to generate is supplied by the ignition sys-tem. Fig. 2 shows the traditional ignition system circuit design.This system was widely used until electronic modules were broughtin. The ignition coil houses the primary and secondary coil thatgenerates the high voltage pulse for spark generation. A distribu-tion circuit delivers a high-voltage pulse to the appropriate sparkplug at the right time for ignition[1]-[2].

In a modern engine, the breaker points have been replaced withan electronic control module in which a power transistor controlsthe coil current. Before the advent of modern electronic controls,a rotary switch called the distributor distributed the high voltagepulses.

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Fig.2 Traditional ignition system

1.2 SPARK PULSE GENERATION

As shown in Fig.2, the high voltage pulse required to produce thespark is achieved by switching the current through the primarycircuit of the ignition coil. Traditionally, ignition system had a sys-tem of circuit breakers opening and closing at required intervals. Inbetween pulses, the switches of these breaker points remain closed.The current from the battery is supplied to the primary coil which inturn links itself to the secondary coil by electromagnetic induction.When the spark is to be generated, current flow in the primary coilis interrupted by opening the circuit breakers. A very high voltagepulse is induced in the secondary coil due to the rapid collapse ofthe magnetic field of the primary coil which is caused by the open-ing of the circuit breaker. This pulse is routed to the spark plug viathe distributor. Fig. 3 illustrates the current flow in the primarycoil. At the point a, primary current increases as all circuit break-ers are closed. When these breaker points open, this current beginsto fall at a faster rate.. During this rapid drop in primary current,the secondary high-voltage pulse occurs (Point b). As a resonantcircuit is formed between the coil and capacitor,the primary currentoscillates (the ”wavy” portion; point c) [2]-[3]. Solid-state switcheslike transistors have replaced the breaker points . A transistor in

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saturation is equivalent to a closed switch, and a cutoff transistor isequivalent to an open switch. The transistor state (i.e., saturationor cutoff ) is controlled electronically to set dwell and spark timing.

1.3 IGNITION TIMING

For maximum power output, ignition should occur just before TopDead Center (TDC) during the compression stroke. Crankshaftrotation acts as a clock, indicating piston position. This timing isusually 8 to 10 degrees in modern vehicles.

Fig.3 Primary Current Waveform

2 CAPACITIVE DISCHARGE BASED

IGNITION SYSTEM

Inductive discharge ignition systems are simple and efficient butthe time required to charge the high inductance coil of the systemis considerable and hence, not suitable for high-speed engines. Toovercome this, Capacitor discharge ignition (CDI) or thyristor ig-nition systems were developed. A CDI module uses a capacitor asthe switching device to switch the current to the primary coil andthereby produce the spark.

The components of a CDI module are as follows: a small trans-former, a charging circuit, a triggering circuit and the main ca-pacitor. First, the voltage into the system is raised up to 250 to300V. This voltage sets up the electric current flow to the capacitorthrough the charging circuit. To prevent discharge of the capacitorbefore ignition, an SCR is placed. This is shown in Fig.4.

When spark generation is required, the trigger receives a signaland fires the SCR allowing discharge of the capacitor to the primarycoil. This coil is of low inductance and does not act as a storage

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medium. It is purely a pulse transformer. Spark production doesnot depend on the coils. It depends completely on the CDI moduledesign.

Fig.4 Capacitive Discharge based ignition system

A CDI system can usually generate the spark of about 50 mJat any given time. Although, this may vary depending on the ca-pacitor used. The standard inductive discharge ignition system orKettering ignition system, produces 25mJ at low speed and dropsoff quickly as speed increases.

3 RESONANT CONVERTER BASED

IGNITION SYSTEM

There are many advantages which have made the resonant convertermore and more popular in isolated dc-dc applications such as highpower density, high efficiency, long hold up time, etc. Power factorcorrection and low THD are also why interest has been increasingtowards resonant converters.

The main advantage is near lossless switching which provideswith high efficiency[4]-[5]. A resonant converter is a switching con-verter with a tank circuit that combines and controls the input-to-output power flow. Resonant converters are based on resonantinverters. As the name suggests, a resonant inverter converts a DCinput into a sinusoidal output with low noise and harmonic con-tent. A square-wave voltage is produced by switch network .Thissquare wave is applied to a resonant tank which is tuned to the

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fundamental component of the square wave. Hence, the tank willrespond primarily to this component and negligibly to the higherorder harmonics.This makes its voltage and/or current, as well asthose of the load, to be essentially sinusoidal or piecewise sinusoidal.Required DC output can be obtained by rectifying and filtering theoutput from the inverter[6]-[9]. This is shown in block diagram inFig.5

Fig. 5 Block diagram of Resonant Converter

Most of the switching losses encountered in PWM converters areeliminated in Resonant converters. The active device is switchedwith either zero current switching (ZCS) or zero voltage switching(ZVS) at its terminals[6]-[10]. ZCS refers to turning on / off ofthe switch when current through the switch is made zero and ZVSrefers to turning on / off of the switch when voltage through theswitch is made zero as shown in Fig.6.

Fig.6 Current and Voltage waveforms of Hard and Soft switching

Thus, a resonant converter can be used in an ignition system.The storage capacitor which should be recharged between cylindersfiring is eliminated in this system. Hence , Resonant convertersystems can theoretically generate a continuous spark. The sparkduration is limited only by practical considerations such as crossfiring within the distributor as shown in Fig.7.

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Fig. 7 Block diagram of Resonant Converter based ignition system

4 SIMULATION & RESULTS

The capacitive discharge based and the resonant converter basedignition system are simulated using MATLAB Simulink (Fig.8 andFig.9). Fig.10 and fig.11 show the output voltage of both systems.Parameters chosen are shown in Table 1 and Table 2.

TABLE 1 COMPONENTS OF CAPACITIVE DISCHARGEBASED IGNITION SYSTEM

Fig. 8 Simulation of capacitive discharge based ignition system

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Fig. 9 Simulation of Resonant converter based ignition system

Fig. 10 Current and Voltage output

TABLE 2 COMPONENTS OF RESONANT CONVERTERBASED IGNITION SYSTEM

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Fig. 11 Output waveforms on primary and secondary side ofignition coil

5 EXPERIMENTAL SETUP

Fig. 12 shows the block diagram of the driver circuit The micro-controller IC DSPic30F4011 receives regulated dc input of 5V froma rectifier and generates the required pulses for the driver circuitof the inverter. Inverter’s output is fed to the filter circuit whichcomprises an inductor and capacitor. The rectifier, inverter, andthe filter circuits constitute the resonant converter.

Fig. 12 Block Diagram of driver circuit

TABLE 3 SPECIFICATION OF CIRCUIT COMPONENTS

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5.1 DRIVER & INVERTER CIRCUIT

As shown in Fig. 13, the driver circuit receives the pulses from themicrocontroller. These pulses are sent to 4 different ICs,from wherethe input for the inverter is given.

Fig. 13 Block diagram of driver and inverter circuit

TABLE 4 PARAMETERS FOR CIRCUIT COMPONENTS

5.2 PROTOTYPE

A prototype was made with the stated specifications as shown inFig. 14.

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Fig. 14 Block diagram of driver and inverter circuit

5.3 EXPERIMENTAL RESULTS

Fig. 14 shows the prototype used for spark generation. Fig. 15shows the output of the resonant inverter. This output is passedthrough an inductor and a capacitor (L-C) circuit to reduce noiseand to obtain a pure sinusoidal output which then passes throughthe ignition coil and finally to the spark plug where the spark isproduced. The Specifications and Parameters of the circuit com-ponents used in the experimental setup are given in Table 3 andTable 4 respectively.

Fig. 15 Resonant inverter output

TABLE 5 COMPARISON OF CAPACITIVE AND RESONANTCONVERTER BASED IGNITION SYSTEMS

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6 CONCLUSION

It is observed that a capacitive discharge based ignition system issimple, and the quick charging and discharging of the capacitorenables functioning of the ignition system at high RPM. However,the system can cause driveability problems at lower RPM. Also,the output waveform is a square wave. During the off-time (secondhalf of a cycle) it will enable the inductor to discharge and cause anegative spike voltage. This spike can damage the components overtime. The total harmonic distortion (THD) value of the output ishigh.

The resonant converter based system, on the other hand, has apure sinusoidal wave as the output. This does not give any chancefor inductive discharge, hence increasing the life of the components.The THD of the output wave form is low and most importantly theignition system can work efficiently and both low and high RPM.

It is observed from Table 5 that the resonant converter basedignition system is better than capacitive discharge as it has higheroutput power and efficiency. There are a few limitations as well.The circuit is extremely complicated and the number of componentsis high which result in the ignition system becoming more expensive.

Since switching is carried out at ZVS, the life of the componentsis increased. Since the number of components used is high, thecircuit is complex, but the advantage of high output power andefficiency outweigh the demerits of the system.

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References

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[2] Joel Pacheco-Sotelo, Rosendo Pena-Eguiluz, Leonardo PenaEguiluz,Armando Segovia de los Ros, and German CotaSanchez, Plasma Torch Ignition by a Half Bridge ResonantConverter, IEEE transactions on plasma science, vol. 27, no.4, August 1999

[3] Pfender, Hirsh.N and Oskam.H, Electric arcs and arc gasheaters, in Gaseous Electronics, , Eds. New York: Academic,1978, vol. 1.

[4] Imran. MD, Chandra Mouli.K, Simulation of a Zero Volt-age Switching and Zero Current Switching Interleaved Boostand Buck Converter, International Journal of Engineering andComputer Science ISSN:2319-7242, Vol. 2, Issue 10, October2013, page no. 2966-2974.

[5] Erickson.R.W and Maksimovic.D, fundamentals of Power Elec-tronics,2nd ed. Reading, MA: Kluwer Academic, 2001.

[6] Reza Beiranvand, Mohammad Reza Zolghadri, BizhanRashid-ian, Seyed Mohammad HosseinAlavi, Using LLC ResonantConverter for Designing Wide Range Voltage Source, IEEETransactions on Industrial Electronics, Vol. 58, Issue no. 5,May 2011.

[7] Zhijian Fang, ShanxuDuan, Changsong Chen, Xi Chen, Op-timal Design Method for LLC resonant Converter with WideRange Output Voltage, IEEE Transactions on Industrial Elec-tronics ,978-1-4673-4355-8/13, 2013.

[8] Reza Beiranvand, Mohammad Reza Zolghadri, BuchanRashidian,Seyed Mohammad HosseinAlavi, Optimizing theLLC-LC resonant converter Topology for wide output volt-age and wide output load Applications, IEEE Transactions onpower electronics, vol. 26, no.11, Nov.2011,pp.3192-3204.

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[9] Tsai, M.-C, Analysis and implementation of a full-bridge constant-frequency LCC-type parallel resonant con-verter,Electric Power Applications, IEE Proceedings - Vol.141,Issue: 3 , 1994 , Pages: 121 -128

[10] Bong Chul Kim, Ki Bum Park, Gun Woo Moon, AsymmetricPWM Control Scheme During Hold-up Time for LLC Reso-nant Converter, IEEE Transactions on Industrial Electronics,Vol. 59, Issue no. 7, July 2012.

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