42v power system.pdf

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42V power system architecture development

M.A. Shrud, A.Bousbaine, A.S.Ashur†,R. Thorn*, A. Kharaz

University of Derby, UK,†University of Al-Fateh, Tripoli, Libya, *Victoria University, Australia.

Keywords: Dual-voltage electrical power system,automotive, power generation, dc-to-dc power modules, 42V power system architecture, and Matlab\Simulink.

Abstract

With the increasing demand for more fuel efficiency and

environmentally friendly car coupled with the consumers’drive for more comfort, safety and luxury car has led to theintroduction of more electrical and electronic systems to the passenger car. This is further impacted by the current trend inautomotive industry to replace mechanical and hydraulicsystem with their electrical counterparts. The handling

capability of the current 14V DC system is getting very closeto reaching the limits. To meet the new growing electrical power demands with minimum fuel consumption andminimum environmental effects, the automobile industry islooking into increasing the present voltage threefold, from14V to 42V for future cars. A shift towards a 42V system will

cut the current of the vehicle by a factor of three. With the

lower current, the size and cost of power semiconductors can be reduced, allowing for their use in applications that couldnot use semiconductors before. In this paper, a detailedmathematical model for a 3-phase, 4kW and 42V Lundellalternator average electrical equivalent circuit will be presented along with the DC/DC converter basedarchitectures for dual-voltage systems. The performance of

the 42V Lundell alternator with the interleaved six-phase buck dc-to-dc converter system is modelled using Simulinksoftware to assess the effectiveness of the model and itstransient behaviour.

1 Introduction

Today, one of the major trends in the automotive industry isthe increasing amount of installed electrical and electronicsystem on the passenger car which results in a growingconsumption of electrical energy. There are several reasons

for the electrification of many automotive functions and theintroduction of new features. Today's consumer wants more

and more features in their cars to increase comfort, safety andluxury. The rain sensor or the electronic seat position controlis an example of an electronic control system that improvesthe comfort, while navigation and entertainment accessoriesare examples of luxury. Another strong trend in theautomotive industry is to replace mechanical and hydraulic

powered components by introducing new electrically powered

solution. In this way, they consume energy only when theyare in use, resulting in lower fuel consumption and better

overall system efficiency. Examples of these, includes electric power steering, pump-motors for engine cooling fans andwater pumps. Additional pressures are due to the increasingdemand for environmentally friendly car with less pollution.

However, looking back through the years, the increasingloads are not recent phenomena. In the near future, higher

growth in the average power for vehicle loads is expected torise to 3.5kW by 2015 as shown in Figure 1[27]. This furthercorroborated by the automobile industry which estimate that

power demand will be in the range of 4 to 5kW by 2010. Thistendency will push the electrical power demand beyond thehandling capability of the today's standard 14V DC systemwhich is around 1kW with peaks above 2kW [20].

In order to meet the growing electrical power demands withminimum fuel consumption and minimum environmentaleffects, the automobile industries have agreed to increase the

present voltage to 42V, given the name “42V Power Net”,which represents a three-fold increase in the system voltage.

The chosen 42V is a compromise between the technicaldemand for increased voltage and personal safety, 60V [37].The work on the new 42V supply systems for passenger carsis mainly carried out by two centres, namely the Consortium

on Advanced Automotive Electrical/Electronic Componentsand Systems, established in Massachusetts Institute of

Technology in America (MIT) and the Forum Bordnetz (orSICAN forum), which represents the European group ofautomobile manufacturers and suppliers. The two groups haveoutlined the existing and future voltage requirements ofvarious vehicle components (Table 1). These specificationsare now widely accepted in the automotive industry [12,35].

0

50

100

150

200

250

1 9 0 0

1 9 0 5

1 9 1 0

1 9 1 5

1 9 2 0

1 9 2 5

1 9 3 0

1 9 3 5

1 9 4 0

1 9 4 5

1 9 5 0

1 9 5 5

1 9 6 0

1 9 6 5

1 9 7 0

1 9 7 5

1 9 8 0

1 9 8 5

1 9 9 0

1 9 9 5

2 0 0 0

2 0 0 5

2 0 1 0

2 0 1 5

Year

C u r r e n t ,

A

0

500

1000

1500

2000

2500

3000

3500

W a t t a g e , w

Current Wattage

Figure 1: Typical vehicle average load current draw versustime.



Table 1: 14V, 28Vand 42V system specification

A shift towards a 42V system involves the reduction ofcurrent for the same amount of power resulting in a decreasein wiring harnesses copper content, which consequently lessweight and lower consumption, as well as the ability tooperate high power loads more efficiently. Unfortunately,economic and technical considerations do not allow an easytransition to single 42V PowerNet and the abandonment ofthe 14V system to history.

Therefore, in the medium to long term most car manufactureswill provide cars with dual voltage systems (42V-14V),

where the 42V power distribution systems will co-exist with

the traditional 14V electrical system in the same road vehicle.In this way, the dual-voltage system provides a smoothtransition period for loads to migrate to the single 42V systemarchitecture. Various architectures for the dual-voltageelectrical systems implementation have been proposed tomeet 42V PowerNet system specification. The mains

architectures under consideration in the automobile industryare a) dual-wound alternator architecture, b) dual-rectifiedalternator architecture and the dc-to-dc converter basedarchitecture [26, 17, 31, 16] as shown in Figure 2.

In the dual-wound alternator architecture (Figure 2a), a 42Valternator has two separate sets of stator windings, each

supplying an output voltage via dedicated rectifiers. The 42V bus is supplied by one winding via a full-diode bridge

rectifier, while the low voltage stator output is connected to phase-controlled rectifier to supply the 14V bus. The two

outputs are controlled by a combination of field control and phase control. However, due to the fact that field control iscommon to both outputs, this poses serious difficulties infully regulating both outputs, and in achieving good use of thealternator machine power capability under all operatingconditions [16].

Figure 2b illustrates the structure of dual-rectified alternator

[7, 32] where a single winding 42V alternator and dual-output

rectifier used to supply both high and low voltage buses. Thetwo outputs are controlled as in the dual-stator alternator

Figure 2: Potential 42V Power-Net Alternator Architectures

architecture, where the field current is used to regulate the42V bus while the phase controlled rectifier is used to controlthe low voltage 14V bus. The drawbacks of dual-rectifiedalternator is the difficulty in independently and dependablyregulate both the 14V and 42V buses under a range of loading

scenarios and large output filters are required due to the verylarge voltage ripple created by switching of the powerelectronic devices, thyristors [7, 9].

An alternative approach is the introduction of dc-to-dcconverter-based architecture [1, 36] (Figure 2c). The 42Valternator generates the required 42V to supply the heavy-load and this is further processed by a dc-to-dc buck converter

to supply power to the conventional automotive loads thatexpected to remain at 14V level. This architecture isconsidered to be, technically, a viable solution for automotivedual-voltage power system for passenger car in the nearfuture. An interleaved dc/dc converter system with six-cells ischosen as it provides a fast dynamic response, a good powermanagement and filtering processes [16, 5, 15, 21]

The ability to model and simulate engineering design of theelectric power system of a vehicle is essential before proceeding to the engineering experimental phase. Hence,

DC-to-DC converter-based architecture, which is composedof a 42V Lundell claw-pole alternator and interleaved six-

phase dc-to-dc buck converter, is modelled using simulinksoftware. Initially, the system is subdivided into three mainsub systems, namely power generation, conversion and load.Each subsystem is analysed separately, then combined

together to form the whole system for real time analysis andevaluation using control-oriented simulators

Matlab\Simulink. The simulation results add significantunderstanding to the behaviour of the system model underdifferent load and transient conditions while at the same timeobeying the automotive specifications.

Electrical system 14V

Car 28V

Truck 42V

PowerNet

Batteryvoltage

12V 24V 36V

Nominalvoltages

14V 28V 42V

Maximumvoltages

24V 34V 50V( ripple )

Maximumdynamic

voltage

- - 58V

Load Dump)(

Power Electronics

rating 60-40V 80-60V

100-75V



2 Power generation

2.1 Analytical model

The system, for a non hybrid electric passenger car with adual-voltage electrical architecture will be discussed with

more emphasis on simulation. The proposed system iscomposed of a 4 kW power generation system buffered by a36V energy storage battery and a 1kW interleaved six-phase buck converter

The heart of any automotive electrical power system used invehicles today is based on the claw pole alternator also knownas the Lundell machine. This is a three-phase synchronousgenerator equipped with a field winding and brushes. It is

modelled as a three-phase set of back emf voltages, with theleakage inductances, Ls, and winding resistance, Rs,

connected in series as shown in figure 3. The output voltageof the alternator is controlled by regulating the field current, if

and rectified using a six diode bridge rectifier. For each cycleof the input voltage there are six intervals of operation of therectifier. During each of the six intervals, only two diodesconduct with the assumption that the amount of the short

period of the “overlap” is zero. The mathematical model foroperational characteristics of the circuit model of thesynchronous generator connected to the full-bridge dioderectifier driving a constant-voltage load [8] is derived inappendix A and its equivalent circuit model is shown inFigure 4. Where V g is the internally generated voltage and Z g the total synchronous impedance and given by equation (1),

shown below.

)1(EV2I3

2

L3

2

R 3

6cosV

33od1s

)(Z

ss

V

s

gg

++π⎥

⎥⎦

⎤

⎢⎢⎣

⎡ ω+=⎟ ⎠ ⎞⎜

⎝ ⎛ π−φ

π

ω

The average current delivered to the constant-voltage loadEo by the averaged equivalent circuit model is given by

equation (2).

)2(Z

Vi

g

)oEdV2(gd

+−=

Where Vs is the peak phase voltage, Is1 is the magnitude of

the fundamental component of the line current, and Vd is thediode voltage drop.

2.2 Alternators Electrical Behaviour

Equations (1 and 2) are used to simulate the alternator

averaged model using Matlab software, with the 14V and 42VLundell alternator machine’s parameters shown in Table 2. In

addition a simulink block diagram was created using the input parameters to produce the desired output simulation results,as shown in Figure 5.

Figure 6 shows the performance curve for the present 14V

automotive alternator which is capable of supplyingapproximately 93A of D.C. current at an alternator speed of

1800 rpm (ideal speed). As the alternator speed increases themaximum output dc current is about 124A at cruising speed(6000 rpm). For comparison the average alternator data forthe Bosch NC 14 V 60-120A model is plotted which shows agood agreement between the developed model and the realcharacteristic of the machine. There are always losses whenconverting mechanical energy to electrical energy. A

normally operated alternator has an average efficiency of 50%and decreases at higher speeds. The losses are related to iron

losses (hysteresis and eddy currents), copper losses, frictionand aerodynamic losses[6, 10,]. The relatively high losses are

L S

P

R s

V d

E o

r p m

I F

k M a c h i n e C o n s t a n t

F i l e d C u r r e n t

A l t e r n a t o r S p e e d

R e f e r e n c e V o l t a g e

D i o d e D r o p

S t a t o r R e s i s t a n c e

S t a t o r I n d u c t a n c e

N u m b e r o f P o l e s

O u t p u t P o w e r

O u t p u t C u r r e n t

P o w e r

C u r r e n t

Figure 5: Simulink functional model of the Alternator

V c

Rs

Rs

Rs

V a

Vb

n

Ls

D1

Ls

Ls

D 2D4

D3

D6

D5

ia

ib

ic

id

Diode Rectifier

Eo

R o t o r f i e l d c o i l

R e g u l a t o r

S l i p

r i n g s

a

b

c

Figure 3: Electrical model of a Lundell alternator system

Figure 4: Synchronous generator model



compensated by the lightweight, compact design and lowinvestments costs.

The demand for electric power in vehicles is increasing asmore electrical loads are added in the cars. The economicfeasibility of the present system continues to decrease. Tomeet the future electrical power demands, 42V automotivegenerators are becoming necessary. As illustrated in Figure 7,the 42V alternator is capable of supplying approximately 71Aof D.C. current at ideal speed. As the alternator speedincreases the maximum output d.c. current is about 15 A

(cruising speed). Though the two alternators provide the sameload current, the power capabilities are quite different. Figure6, shows that the variations power curve for the standardLundell automotive alternator with the speed. It can beobserved that, up to the idle speed the power variesexponentially with the speed, linearly between the betweenthe idle speed and 8000rpm and remains almost constant beyond this speed. The power delivered is about 1.35kW at

idle speed, 1.7kW at cruising speed and a maximum power of1.8 kW at speed beyond 1000rpm indicating a fieldweakening region. The effect of field weakening causes thetorque to decrease as the speed increases while the electric power is kept constant. The power curve for the 42V Lundell

alternator is illustrated in Figure7 which follows the sametrend as for the standard 14V alternator. The power deliveredat idle speed is approximately 3kW and 4kW at cruising

speed.

3 Analysis and simulation of Lundell Alternator System

To assess the behaviour of the output voltage, load currentand load dump characteristic waveforms of the LundellAlternator system a simulink model has been developed,figure 8, taking into account the parameters of the 42Valternator (Table 2). In addition the armature is modelled as aY-connected set of sinusoidal three-phase back emf voltages,

V a , V b , V c, stator windings inductances Ls and stator

windings resistances R s. The phase separation of the

generated three-phase AC voltages are displaced by 3/2π

radians. The generated three-phase AC voltage is rectified by

a full-bridge diode rectifier to produce a DC output power

required for the battery and the rest of electrical load system.Connecting the switch, SW 1 to a battery, permit the response

of the system load dump to be activated.

Figure 8: Simulink model for the internal structure of the 42V

42V 14V Description Parameters

133.65e-333e-3Stator windingresistance

Rs (Ohms)

0.729e-3166e-6Stator leakage

inductanceLs( Henries)11Diode dropsVd (Volts)

3.63.6Field currentIf( Ampers)

1.286e-24.2867e-3Machine constantk

700:1800700:1800Alternator speedrpm

1212 Number of poles p4214Alternator voltageEo (Volts)

Table 2: 14V and 42V Lundell Alternator Parameters

0 2000 4000 6000 8000 10000 12000 14000 16000 1800020

40

60

80

100

O u t p u t C u r r e n t [ A ]

Performance Curve for 4kW/42V Alternator

0 2000 4000 6000 8000 10000 12000 14000 16000 180000

1000

2000

3000

4000

5000

O u t p u t P o w e r [ W

]

Output Power for 42V Alternator

Alternator Speed [ rpm ]

Cruising Mode

Ideal Mode

Ideal Mode

Cruising Mode

Figure 7: Performance curve and output power for a 42Valternator

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

40

60

80

100

120

140

O u t p u t C u r r e n

t [ A ]

Performance Curve for 1.7 kW / 14V Alternator

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

500

1000

1500

2000

2500

O u t p u t P o w e r [ W ]

Output Power for 14V alternator

Alternator Speed [ rpm ]

Cruising ModeCruising Mode

Ideal Mode

Crusing Mode

Ideal Mode

Figure 6: Performance curve and output power for 14V

)a

) b



3.1 Simulation results

3.1.1 Rectified output voltage and load current.

The simulations were performed at cruising speed, 6000rpm

and at constant full field excitation current, Aif 6.3= . Thesimulated output behaviour of the alternator connected to a4kW load and the battery is displayed in Figure 9. The firstsub plot shows the system’s rectified output voltage while thesecond sub plot shows the system’s output load current. It can

be observed that at the beginning of the cycle the outputvoltage rises from around 28V, with an overshoot, to 44V,over a 0.0015ms time span and settles to steady state of 42V behaviour within 0.01ms. The transient voltage deviationsV min , V nom , V max observed in this simulation are within theallowable required range of 42V PowerNet specifications andsatisfy the 42V alternator system, table 1. The load currentramps up from 63A to 100A and then return to its steady state

within 0.003ms.

3.1.2 Response to a step change in the load

Since the electrical load varies for various driving conditionssuch day or night, summer or winter; and city or country sidedriving. The simulation of load change is therefore a veryimportant parameter for circuit behaviour. In order to studythe 42V power generation dynamic performance under loadvariations, step change in loads have been investigated.Figure 10 shows simulation results of alternator rectified

voltage to step changes in the load. The operation of 42Valternator system when load activated from 2kW to full-load,4kW, is satisfactory with very little variation in the outputvoltage observed. These variations have only small influenceon the output voltage and still respect the specifications of the42V automotive standard.

3.1.3 Load dump control

The fault condition which occurs when the battery is suddenly

disconnected while the alternator is charging is called loaddump and is a rather rare event. The standardised

specification requirements impose transient voltage of lessthan 58V. Past research studies have been conducted to

characterise and analyse the 14V automotive transient events[4, 13]. However, for the 42V alternators[22, 23, 25, 29], theyhave mainly concentrated on understanding the effect ofdifferent transient suppression devices on the bus voltageduring a load dump, or have concentrated on active

centralised load dump suppression using various high-currentsemi-conductor devices. The load dump simulation for the42V electrical system has been conducted using thedeveloped Simulink circuit model shown in Figure 8. Withthe battery switch closed, the DC bus voltage rise ismaintained at the required value. When the system is

suddenly interrupted by opening switch SW1 at 0.1s, the DC bus voltage rise reaches 74.84V, figure 11. This is greater

than the standardised

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.0125

30

35

40

45

O u

t p u t V o l t a g e [ V ]

Rectified output voltage

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

60

80

100

120Load current at full load

L o a d C u r r e n t [ A ]

Simulation time [s]

Overshoot=44V Setting time=0.005

42V

95A

Figure 9: The simulated output voltage and load current.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.520

40

60

80

100


Step changes in load

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.510

20

30

40

50

60

Rectified output voltage response to step changes in load

O u t p u t V o l t a g e [ V ]

Simulation time [s ]

full load-95A50%

75%

45V 43.6V 42V

Figure10: Dynamic response of system to loads variation

0 0.02 0.04 0.06 0.08 0.1 0.12 0.1430

40

50

60

70

80


Rectified output voltage without load dump control

0 0.02 0.04 0.06 0.08 0.1 0.12 0.1450

100

150

200Load current without load dump control


Simulation time [s]

Peak voltage = 74.8 V

Overshoot = 44 V42 V

95 A100 A

170 A

Switch open

Figure 11: Simulated alternator voltage and load currentduring load dump



However, the above procedure could be repeated easily

during the OFF interval, Ts*)D1( − to determine the same

state variable equation of the average value of inductorcurrent. Furthermore, as it can be seen from figure 3(c), thevalue of the inductance needed to ensure that the converter

remains in Discontinuous Conduction Mode (DCM) ofoperation (where the inductor current is zero during part ofthe switching period and both semiconductor devices are off

during some part of each cycle) must be less than criticalL ,

and can be determined as follow;

)7(Vo/)VoVi((*)axIm*fs*2/()D*Vi(criticalL 2 −=

Where criticalLL <

However, the standard dc/dc converter with single structure isnot feasible due to the low voltage, high current, and high

operating temperature characteristics of the converter.Therefore, most power stage of the converter would have to be built in parallel for practical implementation. A common practical approach is to use the interleaved multi-phasetechnique instead of a single larger converter [24, 38, 39, 40].

4.1 Multiphase switching of dc-to-dc converter

The basic building block of the multi-cell interleaved

converter is shown in figure 14. This represents six-cellinterleaved buck converters which are connected in parallel to

a common output capacitor and shares a common load withthe associated control system. The low-voltage side isconnected to the 14V automotive electrical loads while thehigh-voltage side to the on-board power generator (alternator)with nominal input voltage of 42V, and a range between 30Vto 50V during normal operation. In this interleaved six-cell

dc/dc converter architecture, the cells are switched with thesame duty ratio, but with a relative phase shift or time

interleaved of 60° introduced between each cell in order toreduce the magnitude of the output ripple at the output port ofthe converter. The overall output current is achieved bysummation of the output current of the cells. With the phaseof 60° the output of the converter is found to be continuous.Ripple reduction helps to reduce the filtration requirements

needed to contain any EMI the converter produces andthereby decrease the constraints on the electronicscomponents connected to the low-voltage bus. Furthermore,due to the equal sharing of the load current between cells, thestress in the semiconductor switches is reduced and therebyreliability is improved. Another advantage is the ability tooperate the converter when a failure occurs in one cell as well

as the possibility to add new cell to the converter withminimum effort. The ideal design is that the power

management system should be smart enough to manage thekey-off loads from depleting the high voltage battery to the point that the car cannot be started [20, 5, 30, 11].

Using dc/dc power modules two system structures are

possible, distributed and centralized power conversion as

shown in Figure 15. For automotive applications wherevolume, weight, and cost are particularly important. The preferred choice is the 42V/14V DC dual-voltage supplysystem centralised architecture with single battery and is based on the principle that the power processing is achieved

by only one dc/dc power module to supply the existing 14Velectrical loads. Also it lend itself to low cost, low weight,reduced packaging problems created by the second batteryand reduction of the electromagnetic interference (EMI)generated by power switching devices in the system.Furthermore, the removal of the 12V battery does not alter thedynamic operation of the power converter, but the power ofthe converter must cover the power requirement of all the

14V power loads (approximately1000W) under the worst-case scenario. In addition, the non-isolated dc/dc convertertopology is the most appropriate architecture becauseisolation between 42V and 14V buses is not required in theautomotive power net and has the advantage over thetransformer-isolation types in terms of an easy to design, lowvolume, weight, and cost.

In this topology power flows in one direction, but bi-

directional power flow can be achieved by replacing the low-side switch diode with a MOSFET. However, using twoMOSFETs may result in lower losses but will require anothergate driver and additional complexity in the control of the

converter.

Figure 14: Simulink implementation of the interleaved six

cell buck converter circuit with PID controller



Value Description Parameter 30V < 42V<50V Input voltage rangeVi

11V < 14V <16VOutput voltage rangeVo

1kWPower RatingPo-40 °C < T< 90°C Temperature rangeT

300mVOutput ripple voltage ΔVo

1AOutput ripple currentΔ Io

Table 3: Design specifications for a power converter in a

dual-voltage automotive electrical system

To design this six-phase interleaving buck converter system,the following automotive specifications for dual-voltage

automotive electrical systems [9, 14, 18, 28] must be fulfilled

as shown in Table 3. The specifications of the convertershould meet the demand of the 14V electrical loads of 71A atlow output voltage approaching 14V and to meet theoperating temperature range, (105-125C) for thermal designrequirements. For low voltage/high current power converter,

the usage of MOSFETs switching devices with low on-resistance is required for more efficient and practical power

conversion. The inductance value L that guarantees theconverter cells should run in the DCM over the entireoperating range and can be calculated using Equation (7). Since this is a six-phase interleaving converter, the powerstage inductance of each phase is therefore equal to 2.4μH.The output capacitor is another important element, which may

reduce the system cost in multi-phase converter system and isneeded to keep the output voltage ripple ΔV O within allowable

output voltage range to meet the constraints of the designspecifications. The necessary output capacitor has no severeeffect on the value of the inductor current and the switchingfrequency of the converter. Also, the capacitor value does notnecessarily have to be very large to smooth the outputvoltage. Table 4 shows the capacitor variation from 100µF to 400µF along with the value of voltage/current ripple. Figure

16 shows the plot of output ripple voltage versus capacitorvalue from the simulation analysis obtained. To meet theconstraint of the design requirements concerning the voltageripple of the converter system, a capacitor value of 300µF is

chosen.

Figure15: Dc/Dc converter implementations: a) distributedand b) centralized

Table 4: capacitor value versus voltage /current ripple

100 150 200 250 300 350 400-0.01

0

0.01

0.02

Capacitor [ µF]

V

o l t a g e

r i p p l e

[ m

V

]

Ripple voltage versus capacitor variation

Figure 16: Ripple voltage versus capacitor value

.

Current rippleVoltage rippleCapacitor value

30mA6mV100µF

20mA 4mV150µF

16mA3mV200µF

12mA2.5mV250µF

10mA2mV300µF

9mA1.5mV350µF

7mA1mV400µF



4.2 Control design strategies

The control strategy of the proposed converter is based onvoltage-mode-controlled Pulse Width Modulation (PWM)with a proportional-integral-derivative (PID) which takes its

control signal from the output voltage of the switchingconverter instead of current-mode (or current-injected) PWM,

which utilises both the output voltage information and thecurrent information from the inductor to determine the desiredduty cycle. Simulink model for the internal structure of thePID used to control the converter is shown in Figure 17. The

aim is to regulate the output voltage of the converter Vo

across the load resistance R L to mach a precise stablereference voltage V ref . This is achieved by subtracting thedesired reference voltage V ref from the sensed output voltageV O of the converter. The voltage-error thus obtained is passedthrough PID to obtain the desired signal. The individualeffects of P, I, and D tuning on the closed-loop response are

summarized in Table 5[3]. The desired output generatedsignal of the PID enters the PWM unit, where it is comparedwith the constant frequency saw tooth voltage V pwm. The

frequency of saw tooth voltage is the switching frequency fs

of the converter which is100 kHz. The output of the PWM isthe switching control signal, a sequence of square pulses that

drives the semiconductor switch, as seen in Figure 18. The proposed converter necessitates a phase-shift of 60° betweenthe cells to generate the six-switching control signal whichare used to drive the six active MOSFET switching devices ofthe converter system. Figures 19 and 20 show theimplementation of the six-phase interleaving circuit inSimulink and the six phase control signal waveforms

respectively. Another approach is given in [2].

Steady-State

Error

SettlingTime

Over shoot

RiseTime

Closed - Loop

Response

DecreaseSmall

Increase

Increase Decrease Increasing

Kp

Large Decrease

Increase Increase Small Decrease

Increasing KI

Minor

Decrease

Decrease Decrease Small

Decrease

Increasing

KD

Table 5: Effect of independent P, I, and D tuning

2.62 2.64 2.66 2.68 2.7 2.72 2.74 2.76 2.78 2.8

x 10-3

0

0.5

1

1.5

P I D s i g n a l , P W M v o l t a g e

Comparsion of PID singal and Vpwm

2.62 2.64 2.66 2.68 2.7 2.72 2.74 2.76 2.78 2.8

x 10-3

0

0.5

1

1.5Control singal features a constant duty cycle

S w i t c h c o n t r o l s i g n a l

Simulation time [s]

VpwmPID signal

duty cycle

Figure18: Implementation of Pulse Width ModulationSimulink model.

Figure19: Six phases of interleaving in Simulink Figure17: Implementation of PID controller in Simulink



6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2Six-phase control signals

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7

x 10-4

0

1

2

Simulation time [s]

Figure20: Six-phase control signal waveforms

2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.1

x 10-3

71.4

71.42

71.44

C

u r r e n t r i p p l e

[ A

]

Total output current ripple

2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.1

x 10-3

13.995

14

14.005

V

o l t a g e

r i p p l e

[ V

]

Simulation time [s]

Output voltage ripple

Figure 21: Current and voltage output ripples

5 MatLab/Simulink simulations and results

The complete model implementation of the internal structureof the interleaved six-phase buck converter system shown inFigure 14 is implemented in Simulink software to obtain thenecessary waveforms that describe the converter systemoperation for steady-state and transient conditions, using the parameters tabulated in Table 6.

1.3 1.35 1.4 1.45 1.5

x 10-4

0

20

40

C e l l c u r r e n t [ A ]

Current in each cell

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

20

40

60

807 1 [ A ] - Total output current


0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.025

10

15

2014 [ V ] - Outpu t Voltage


Simulation time [s]

Figure 22: Top trace is the individual cell currents then total

output current and bottom trace is the output voltage of theconverter system

Units Value Symbol Parameter Name

volts42Vin Input voltage

volts14VoOutput voltage

-6 N Number of phases

µH2.4L Inductor value

µF300CCapacitor value

.196RL Load resistance

kHz100fsSwitching Frequency

Table 6: Parameters of the simulated converter

Table 7: Output voltage and current ripples versus the numberof cells.

5.1 Ripple cancellation

The first step in the analysis of the multi-phase interleavedconverter system is to investigate the effectiveness of ripple-cancellation related to the variation of current and voltage as a

function of the number of cells using the same settings for thecontrol system. The results obtained are summarised in Table

7. From the results it can be observed that the converterachieves a very good current and voltage ripples cancellationfor four-cells and above. However, though, eight or ten-cellscancellations are better than the four-cell, the implementationcost outweigh the gains in accuracy.

Number of phases

4 6 8 10

Voltage ripple 8.7mV 2 mV 1.1mV 0.5mV

Current ripple 45mA 9mA 6mA 3.2mA



The result also point out that the EMI filter is not needed toreduce the peak to peak voltage ripple on the 14V terminals.This may lead to the elimination or redesign of the protectioncircuitry connected to the 14V bus. It can be seen from figure

21 that the ripple of the output voltage and the total inductor

current of the power converter system are better than thedesired specified limits indicated in Table 3. Figure 22 showsthe steady-state waveforms of the individual cell currents, thetotal output inductor current and the output voltage. Thesimulated results show that the curves of the individual cellcurrents are balanced and the time interleaved of the cells isapparent from the relative time delay of each cell's inductor

current. The inductor current in each cell rises to 30A duringeach switching period and goes through an interval in the

discontinuous conduction mode. The sum of the individualcell currents result in a total current of 71A with a ripplecurrent of around 9mA which is less than the individual cellripple current. The simulated results indicate that, the

operation of the power converter system is stable andaccurate. The converter is able to respond and produce the

desired stable output voltage and deliver the required totaloutput current to the load with very low ripple. As a result, nonegative effect on the connected loads, such as small motors,lights and accessories.

5.2 Transient simulation for load variation

The converter is used to supply power to various loads suchas;

• Small motors (2 to 8A @12V). • Very small motors ( less than 2A @12V ) • Lighting system: internal and external lights.

• ECU and Key-off loads

The electrical loads demand varies and depend upon theweather and the driving conditions. A full load condition israrely present for a prolonged period of time and most of thedevices run at light loads (stand-by-mode) for most of the

time. To study the effect of the load variation on the dynamic behaviour of the converter system, the load at the output ofthe converter system is suddenly changed from 50% to 75%and to 100% and than back from 100% to 75% and 50% ofthe full load at time t=0.002, 0.004 and 0.006s respectively.

The simulated results are shown in Figure 23. It can be seenthat the output voltage undershoot varies from 13.12V to

13.28V while the overshoot from 14.735V to 14.89V. Whenthe load at the output of the converter system was suddenlychanged from 50% to 75% and to full-load (1kW). The resultsshow that the performance of the system is stable and well behaved under load variations (disturbances) and the outputvoltage remains within the desired specified limits presentedin Table3.

5.3 Input voltage variation

In real conditions, the alternator output voltage ranges from

30V to 50V during normal operation, with nominal voltage at42V. To study this line of variation, a step change in the input

voltage from 33V to 50V is applied to the model. Figure 24shows a transient response of output voltage behaviourwaveform due to the sudden changes in the input voltage ofthe power converter system. At the beginning of the cycle, at

time t=0.004s, the input voltage suddenly rises from nominal

system voltage of 42V, to 50V. The maximum output voltage(bottom trace) transient is 15.09V, but after a short period thiserror is leveled out in approximately 200ms with a maximumovershot of 1.09V. At time instants t=0.01s, when the inputvoltage suddenly changed from 50V down to 33V, the outputmaximum transient is11.704V. The settling time to return to14V is approximately 0.4ms with maximum overshot of

2.296V. Finally, at time t=0.016s, when the input voltagesuddenly jumps from, 33V to the nominal system voltage, the

maximum output transient is 15.85V. The settling time isapproximately 0.4ms with maximum overshot of 1.85V. Thesimulation results illustrate that the converter system has astrong immunity against line voltage disturbances even with

the 12V energy storage battery being abscent.

5.4 Load variations and supply-voltage variations

The combinations of both the supply-voltage and load

variations that occur in the converter system have beensimulated and the outputs are presented in Figure 25. It can be

observed that the designed system has a low-sensitivity to theload and supply-voltage variations. These variations haveonly small influence on the output voltage and load current,they still respect the specifications of the automotivestandard. It can be concluded that from the results obtainedthe proposed converter can maintain designed output voltage

independently of load and supply-voltage variations.

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

20

40

60

80

L o a d c u r r e n t [ A ]

Step load change from 50% to 75% to 100% and from 100% to 75% to 50%

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

5

10

15

20

O u t p u t v o l t a g e [ V ]

Simulation time [s]

Output voltage due to load change

50%

75%full load

Figure 23: Transient response of the output voltage due tostep changes in load.

6 Complete system model

Figure 26 shows the complete model of the Simulink

implementation of the internal structure of the of 42/14V DCdual-voltage supply centralized architecture system with a

single battery. The proposed complete system is composed ofthe Simulink model of the 42V voltage alternator (Figure 8),

and the Simulink implementation of the interleaved six-phase buck conveter (Figure 14), load dump circuit and the PID



controller. Using the parameters tabulated in Tables 2 and 6,the Simulink model above is used to determine the steady-state and load dump transient characteristics.

6.1 Simulation Results

Figure 27 shows the simulated results of the two buses atdifferent level of voltages and powers. The high voltage

deliver 3kW at an average output current of 71A, while thevoltage, 14V bus, delivers a current of 71A at 1kW. Thesimulation results illustrate that, the operation of the completesystem is stable and accurate. The system is able to respondand produce the desired output voltages and required level ofcurrents.

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.0230

35

40

45

50

55

I n p u t V

o l t a g e [ V ]

Input voltage variation

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.020

5

10

15

20


Simulation time [s]

Output response of input voltage variation

Figure 24: Output voltage due to step line voltage disturbance

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

50

100

L o a d c u r r e n t [ A ]

Output current due to line and load variation

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

5

10

15

20Output voltage due to line and load variation

O u t p u t v o l t a g e [ V ]

Simulation time [s]

Figure 25: Load current and output voltage due to under line

voltage and load change disturbance

The transient response of the 42V bus at 6000 rpm is shownin Figure 28. The transient is induced by disconnecting the42V battery at time t=0.01s. The peak transient voltage on the42V bus is approximately 54.46V which is less than the74.8V peak voltage observed with a single voltage system(Figure 11). The reason for the relative stability is theremaining loads. The 14V bus voltage undershoot is 13.69V

and the overshoot is 14.28V. The results show that the performance of the system is stable and well behaved underload dump and the output voltage remains within the desiredspecified limits presented in Table 3.

Figure 26: Simulink model of the complete dc/dc converter- based system architecture with single battery.

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

20

40

O u t p u t V o l t a g e

[ V ]

42[ V ] -42V bus voltage

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

20

40

60

80 71 [ A ] - 42V bus current

L o a d

C u r r e n t [ A ]

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.025

10

15

2014 [ V ] - 14V bus Voltage

O u t p u t V o l t a g e

[ V ]

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

20

4060

80

L o a d

C u r r e n t [ A ]

71[ A ] -14V bus current

Figure 27: Voltage and current of the two buses

The voltage can be further suppressed by the use of thevoltage limiting circuit (Figure 8) and these shown are inFigure 29. It can be seen that the voltage rises only to 45V onthe 42V bus and less overshot/undershoot on the 14V bus.



0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

10

20

30

40

50

60

O u

t p u t V o l t a g e [ V ]

Load dump-dual voltage system

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.0185

10

15

20

Simulation time [s]


Load dump-dual voltage system

54.46V42V

14.28V

13.69V

14V

Figure 28: Dual architecture load dump of 42V battery

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018

10

20

30

40

50

60


42V bus load dump using load dump limiting circuit

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.0185

10

15

20

Simulation time [s]


14V bus voltage

45V

14.2V

13.8V

42V

14V

Figure 29: Dual architecture load dump of 42V battery with

voltage limit circuit

Figure 30 shows the simulation of the dynamic response ofthe system to a step change in load on the 42V bus at 6000rpm (cruising speed). The transient is induced by sudden

change of the 42V bus load from 50% to 75% and 100% andthen back from 100% to 75% and 50% .The loading in the14V bus remains at its nominal value of 71A. The voltage onthe 42V bus deviates from its nominal by approximately 3V.This load step change has little effects on the 14V bus, this isdue to efficient output regulation. The transient voltagedeviations observed in on the 42V bus in this simulation arewithin the preliminary voltage limits specifications that were

given in Table 3. As depicted in Figure 31, step change inload on the 14V bus again from 50% to 75% and 100% andthan back from 100% to 75% and 50% the undershot is 13.3Vwhile the overshoot is approximately14.7V. The voltage onthe 42V bus with 3kW load also deviates from its nominal by

approximately 1V. This transient output voltage remainwithin the allowable specification reported in Table 3.

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

40

60

80

L o a

d

C

u r r e n t

[ A

]Step load changes from 50% to 75% to 100% and from 100% to 75% to 50%

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

30

40

5042V bus voltage due to load variation

O

u t p u t

V

o l t a g e

[ V

]

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.15

10

15

2014V bus voltage due to load change

O

u t p u t

V

o l t a g e

[ V

]

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

40

60

80Output current at 14V bus

L

o a d

C

u r r e n t

[ A

]

Simulation time [s]

Figure 30: Dynamic response of the system to step change inload on the 42V voltage bus

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

40

60

80


Step load changes from 50% to 75% to 100% and fr om 100% to 75% to 50%

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

5

10

15

20

14V bus voltage due to load variation


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

30

40

5042V bus due to load change


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.120

40

60

80

Output current at 42V bus


Simulation time [s]

Figure 31: Dynamic response of the system to step change inload on the 14V voltage bus

7 Conclusion

It can be concluded from the results obtained that the dc-dc based architecture system is a potential solution for a moreefficient and stable automotive electrical power system. Thesystem complies with the demanding requirements of theautomotive industry in terms of current and voltage surges. Itis anticipated that the system proposed here will be of value

in future dual-voltage automotive electrical systems.



[27] M. Miller. “Multiple voltage electrical powerdistribution system for automotive applications”, 31stIntersociety Energy Conversion Engineering Conference(IECEC), volume 3, pp. 1930–1937, (1996).

[28] T.C.Neugebauer and D.J.Perreault. “Computer-aided

optimization of dc/dc converters for automotiveapplications”, IEEE Transactions on Power Electronics,volume18, No.3, pp.775-783, May,( 2003).

[29] C.S.Namuduri, B.V.Murty,and M. G.Reynolds. “LoadDump Transient Control of a 42V AutomotiveGenerator”, 35th Annual IEEE Power ElectronicsSpecialists Conference, Aachen, Germany, pp.389-394,

(2004).[30] P. Nicastri and H. Huang. “42V PowerNet: providing the

vehicle electrical power for the 21st century”, SAEFuture Transportation Technology Conf. Expo., CostaMesa, CA, (2000).

[31] D.J.Perreault and V.Caliskan. “Automotive Power

Generation and Control”, IEEE Transaction on PowerElectrons., volume 19, No. 3, pp. 618–630, May (2004).

[32] C. Patterson, J. O.Dwyer ,and T. Reibe. “Dual voltagealternator", IEE Colloquium on Machines forAutomotive Applications, London, England, November, pp. 4/1–4/5 (1996).

[33] A. V. Peterchev. “Digital Pulse–Width ModulationControl in Power Electronic Circuits: Theory andApplications”, Doctor of Philosophy in Engineering-

Electrical Engineering and Computer Sciences,University of California, Berkeley, spring, (2005).

[34] C.H. Rivetta, A.Emadi, G. A. Williamson, R. Jayabalan,and B. Fahimi. “Analysis and Control of a buck DC-DC

Converter Operating With Constant Power Load in Seaand Undersea Vehicles”, IEEE Transactions On IndustryApplications,volume.42.,No.2,March/April, (2006).

[35] Z.J.Shen , F.Y. Robb, S.P.Robb, and D.Briggs.

“Reducing Voltage Ratting and Cost of Vehicle PowerSystems With a New Transient Voltage Suppression

Technology”, IEEE Transaction on VehicularTechnology, volume 52, NO.6,pp. 1652-1661,November, (2003).

[36] J.G.W. West. “Powering up - a higher system voltage forcars”, IEE Review, pp. 29-32, January (1989).

[37] International Electro technical Commission. “Impact of

current passing through the human body: Part I”, Tech.

Rep., International Electro technical Commission,Report IEC479-1, (1984).

[38] “High Efficiency High Density Polyphase Converters forHigh Current Applications”, Application note 77, LinearTechnology Inc., Sep. (1999).

[39] “Poly phase, high efficiency, synchronous step-down

switching regulators”, Tech. Rep. LTC1629, LinearTechnology Datasheet, (1999).

[40] “High-frequency multiphase controller,” Tech. Rep.TPS40090, Texas Instrument Datasheet, (2003).



Appendix A

Figure 1 shows the automotive electrical power system whichincludes the alternator, rectifier, battery and loads. The

combination of the energy storage, battery, and the associated

electrical loads is referred to as a constant voltage loadvoltage.

Figure 1: automotive electrical power system: the alternator, battery and load.

Figure 2 show the six conduction intervals within eachoperating period for the circuit shown in Figure 1. Duringeach of the six intervals, two of the six diodes conduct. It is

sufficient to consider one of these intervals for the averaging process.

tω

π2

3

π

3

π

3

2π

di1sI

Figure 2: A sketch of output current waveform for three-

phase diode circuit

D1

D2

Eo

Ls Rs

RsLs

Va

Vc

id

Figure 3 shows the circuit diagram during the interval when

diodes D1 and D2 are conducting.

• Using KVL equation around a closed loop with phases

canda, diodes D1 and D2 and the voltage source oE

gives;

Figure3: Three phase diode bridge rectifier equivalent circuit

diagram during the interval when diode D1 and D2conducting

)1(2

)()(

o E d V

ci s Rdt

cdi s L

ai s Rdt

adi s L

cV aV ll V

++

−−

+=

−= φ φ

Substituting expressions ofcaca iivv and,,,

yield thefollowing expression:

( )

( )

o E d V

t s

I s

R

dt

t s I d s L

t s I s R

dt

t s I d s L

t sV t sV ll V

++

+−−

+−−

−+

−=

+−=

2

))3/2(sin1

(

)3/2(sin1

))(sin1(

)(sin1

)3/2(sin)(sin

π φ ω

π φ ω

φ ω

φ ω

π ω ω

02)]3/2sin(

)3/2cos([1

)]sin()cos([1

)6/sin(3

E d V t s R

t s L s I

t s Rt s L s I

t sV ll V

+++−+

+−−

−+−=

−=

π φ ω

π φ ω ω

φ ω φ ω ω

π ω

Where: ss R b,La =ω=

)2(2

)]3/2sin(

)3/2cos([1

)]sin()cos([1)6/sin(3

o E d V

t b

t a s I

t bt a s I t sV

++

+−+

+−−−+−=−

π φ ω

π φ ω

φ ω φ ω π ω

• Applying the Trigonometric Identity :

)3()cos(sincos α φ φ φ −=+ Aba

Where: )a/ b(tan, baA122 −=α+=

on the right hand side of equation (2)



[ ][ ]

o E

d V

t A s I

t A s I

t sV ll V

++

−+−−

−−=

−=

2

)32(cos1

)cos(1

)6/(sin3

α π φ ω

α φ ω

π ω

)4(2

)32(cos1

)(cos1

o E d V

t s I A

t s I All V

++

−+−−

−−=

α π φ ω

α φ

• First, averaging the left hand side of the equation (4) over

a conduction angle of3

π.

[ ]

)5()3()6

cos(33

sin2

1cos

2

333

)2

(cos)6

(cos33

3/23/

)6/(cos33

)(

3/2

3/ )6/(sin

33

from sV

sV

sV

t sV

t d t sV

π φ π

φ φ π

π φ

π φ

π

π φ π φ

π ω π

ω

π φ

π φ π ω π

−=

⎥⎦

⎤⎢⎣

⎡+=

⎥⎦

⎤⎢⎣

⎡ +−+=

++−−=

+

+ −∫

Now, averaging the right hand side of equation (4).

[[

]]

o E d V

t d t s I A

t d t s I A

t d o E d V

t

t s I A

++

++

−+−−

−−++

=++

−+−−

−−++

∫

∫

∫

2

3/2

3/)()

3

2cos(1

3

)()(3/2

3/cos1

3)(2

)3

2cos(

)cos(13/2

3/

3

π φ

π φ ω α

π φ ω

π

ω α φ ω π φ

π φ π

ω

α π

φ ω

α φ ω π φ

π φ π

( )[ ]

( )

)6(2

sin)3

4(sin1

3

)3

(sin)3

2(sin1

3

2

3/2

3/

)3

2(sin1

3

3/23/

sin13

o E d V

s I A

s I A

o E d V

t s I A

t s I A

++

⎥⎦

⎤⎢⎣

⎡ −−−−

⎥⎦

⎤⎢⎣

⎡ −−−=

++

+

+

⎥⎦

⎤⎢⎣

⎡ −+−−

++−−=

α π α π

π

α π

α π

π

π φ

π φ

α π

φ ω π

π φ π φ

α φ ω π

)7(2

cos2

3sin

2

31

3

2

)sincos3(2

1sin1

3

o E d V

s I A

o E d V

s I A

++

⎥⎦

⎤⎢⎣

⎡+=

++

⎥⎦

⎤⎢⎣

⎡ ++=

α α π

α α α π

2

3

2

3

,)6

(cos33

s L s R g Z

sV g V

ω

π φ

π

+=

−=

Refer to (figure 2), dI can be calculated as follows

133

2cos3

cos13

323

cos13

32

3sin1

3

32

3)(

1

s I s I

s I

d s I

d f T

d I

π π π

π

π π

θ π

π

π θ θ

π

π

π θ θ

=⎥⎦⎤⎢⎣⎡ −=

−=

=

=

∫

∫

The average current delivered to the load by the averagedcircuit model is:

)8()02(

g Z

E d V g V d I

+−=

42v power system.pdf

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