Control, Alarm and Indicator Systems in Modern Electric Vehicles

V. K. Sharma, R.D. Kamble, Rakhi Sharma'MAE, Alandi, Pune

1: SOET, IGNOU, New Delhi

Abstract This paper presents the different controls and theirassociated indicator and alarm systems used in modern dayElectric Vehicles (EVs). These electric vehicles are of hybridtype incorporating diesel, petrol or hydrogen as alternate fuelsource. The purpose of different controls is to give smoothstart, passenger comfort, amenities, safety and smooth stop.This is achieved through vehicle management unit and batterymanagement system. Hybrid electric vehicles reduce the airpollution through emission control systems through electronicspark ignition system. The paper gives the details of variouscontrol systems provided in a typical modern hybrid electricvehicle.

I. INTRODUCTION

An Electric Vehicle (EV), is a vehicle with one or moreelectric motors for propulsion. The motion may be providedeither by wheels or propellers driven by rotary motors, or inthe case of tracked vehicles, by linear motors. The energyused to propel the vehicle may be obtained from severalsources such as

* from chemical energy stored on the vehicle in on-board batteries: Battery electric vehicle (BEV)

* from both an on-board rechargeable energy storagesystem (RESS) and a fueled propulsion power source:hybrid vehicle

* generated on-board using a combustion engine, as in adiesel-electric locomotive

* generated on-board using a fuel cell: fuel cell vehicle* generated on-board using nuclear energy, on nuclear

submarines and aircraft carriers* from more esoteric sources such as flywheels, wind

and solar* from a direct connection to land-based generation

plants, as is common in electric trains and trolleybuses.

Hybrid Electric Vehicles (HEVs) typically combine theinternal combustion engine of a conventional vehicle withthe battery and electric motor of an electric vehicle. Thecombination offers low emissions, with the power, range,and convenient fueling of conventional (gasoline and diesel)vehicles, and they never need to be plugged in. The inherentflexibility of HEVs makes them well suited for fleet andpersonal transportation.

Hybrid electric vehicles (HEVs) are powered by twoenergy sources an energy conversion unit (such as acombustion engine or fuel cell) and an energy storage device(such as batteries or ultracapacitors). The energy conversionunit may be powered by gasoline, methanol, compressednatural gas, hydrogen, or other alternative fuels. Hybrid

electric vehicles have the potential to be two to three timesmore fuel-efficient than conventional vehicles.

This paper describes the control systems involved in atypical elecctric vehicle which may be used in hybridconfiguration. The main control systems, alarms andindicators used in EVs include System Ready Indicator,Vacuum Control, Vacuum Alarm, Star-Up Circuit, ChargingDoor Open Circuit, Off Throttle Detection Switch, ClutchDepressed Switch, Neutral Safety Switch, Service BrakeDepressed, Backup Circuit, Shutdown Circuit with lights on,Other alarms.

It is possible to build an EV conversion without thecontrol and safety features described in this paper. However,these safety features are intended to assist and protect acasual driver, who may not be knowing the limitations ofconversion or a driver with long experience and ingrainedhabits. The goal is to reduce the chance of improperoperation by a driver and is always recommended to beincluded in any EV conversion.

II. GENERAL EV CONTROL

The general electric vehicle control diagram is shown inFig. 1. The main feature of the control schematic are theEngine Monitoring System (EMS), Vehicle ManagementUnit (VMU), Motor Management System (MMS), Batterymanagement System (BMS). These control panel undertakethe monitoring and control of acceleration, deceleration,braking, clutch control, motor control, battery monitoringand engine state. The BMS takes care of the state of charge,state of health and state of function of the battery pack. TheMMS and EMS functions control the power and energyrequirement of the electric motor and the internalcombustion engine.

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Fig. 1 General vehicle control schematic

Fig. 2 Control System Architecture for hybrid electric vehicle

The control system architecture for a typical hybridvehicle is shown in Fig. 2. The function of the centralcontroller is to control the operation of the hybrid systemthrough input and output signals manage communicationwith the sub-system controllers, and monitor other systemstatus. According to the driver's command and current statusof the sub-systems, the central controlleer sends propoersignals either to the controllers or the individual componentsto perform certain operations. After the sub-system receivesa command, it sends signal to the corresponding device.

III. ENGINE CONTROL

Control strategies for a hydrogen engine are similar to agasoline/petroleum spark ignition (SI) engine system.However, due to tre chemical and combustion properties ofhydrogen, a hydrogen engine needs more accurate control toassure that the engine reaches maximum horse power andruns at its most efficient operating points.

IV. FUEL INJECTION DURATION / TIMING CONTROL

Normally sequential Port Fuel Injection (PFI) is appliedwhich means fuel is injected one cylinder at a timeonlywhen the intake valve is opened. The reason for usingsequential injection rather than group injection is thathydrogen is much lighter than air. It would not wait for theintake valve to open and would rise and disperse in theintake manifold. During the period the intake valve is open,the vaccuum pulls the hydrogen directly into the combustionchamber.

Fuel injection timimg and duration are primarily basedon engine load and speed. Engine dynamometer and chasisdynamomoter tests are performed to develop a fuel injectionduration map. The most desirable time of injection is set to240° - 280° before top dead centre (BTDC) in thecompression stroke.

Furthermore, due to fast flame speed of hydrogen,which is three times the speed of gasoline, ignition timingneeds exact control to prevent knock. The fast flame speedof hydrogen results in reduced engine ignition timing. Thetimimh usually occurs near top dead centre (TDC). If theignition takes place too early, very high pressure is producedin the combustion chamber and brings in knock. Retardedspark can reduce the temprature in the chamber and betteruse in the engine inertia. Low tempratures avoid pre-ignition. Using the engine inertia to push the piston pastTDC and then sparking makes the engine more efficient andpowerful. As engine speed increases, small amount ofadvance timings are also needed to compensate for the flamespeed and combustion process. Based on dynamometer test amap is developed for hydrogen engine timing operation asshown in Fig. 3. The degree of timimg is indexed by engineload and speed.

Fig. 3 Ignition timimg map

V. ENGINE CONTROL SCHEME

The injection and ignition timimg is performed relativeto the angular position of the engine. For a typical 2.34L 4stroke engine, 12 teeth on crank with the teeth spaced 15°apart and one tooth on the cam provide the engine speed andposition. Timimng for injection and spark are referencedfrom top and dead centre (TDC) on the compression stroke.The four engine cycles are shown in Fig. 4 along with theinjection timing window and spark timing window.

Fig. 4 Four engine cycles with reference

Here - EVC refers to Exhaust Valve Closing, EVO is Exhaust ValveOpening, IVC is Intake Valve Closing and IVO is Intake Valve Opening.

The input outputs of the engine control unit (ECU) are

show in Fig. 5. There are seven major inputs into the ECU.The crank shaft and cam shaft sensors determine the currentspeed and current cycle of the engine respectively. Thethrottle position sensor (TPS) is used to determine thethrottle position to reflect the driver's intention. Manifoldabsolute pressure (MAP) and barometric absolute pressure

(BAP) are used to calculate the load the engine is under. Theair temprature sensor determines the temprature of the airentring the engine. The engine temprature sensor is used todetermine the operating temprature of the engine. Theaccurate calculation of the engine load is done by MAP andBAP because engine load is determined by the amount ofvacuum being pulled within the intake manifold. Accordingto the inputs, four fuel injector signals and four ignitionsignals are produced to control each cylinder separately andsequentially. The pressure sensor, temprature sensor andoxygen sensor reading are treated as feedback to adjust themain injection and ignition tables. According to the inputsignals, the ECU generates appropriate injection and ignitionsignals. The relationship of the inputs and outputs is non-

mathematical, and hence a look-up table is used to determinethe pulse width and timing. Interpolation is used forintermediate values of input.

Crane Position -

Cam Position

Throttle Position

Manifold Pressure

Barometric Pressure N

Engine Temperature

Inlet Air Temperature

Optional Sensors

Fuel Air MixtureSpeed Signal -Exhaust GasTemperature *

REF INJ 1

SYNC INJ 2

TPS INJ 3

MAP INJ 4

BAPET

IAT

IGN 1

IGN 2

IGN 3

LAMBDA IGN 4

DIG IN

AUX TEMP AUX OUT

FUELINJECTORS

IGNITIONCOILS

lo.

Waste GateValve

Ideal SpeedValve

Fuel pump relay

Fig. 5 Engine control unit input and output

VI. VACUUM CONTROL

For vehicles with vacuum operated power brakes it isnecessary to include a vacuum pump and vacuum reservoir,check valve, pump, pump control, and pump power.Vacuum pumps are powered from the twelve volt vehicleservice, usually provided by an auxiliary battery. The circuitillustrated is complex but of low cost. A single vacuumsense unit is obtained from specialty suppliers which hasseparate on and off adjustable setpoints, eliminating the needfor several relays. The vacuum switch circuit system withalarm is shown in Fig. 6.

A separate vacuum sensing switch is used to alert thedriver of low vacuum. This activates just below the low limitof the vacuum pump control turn-on setting. It is connectedto an existing unused warning light such as the low oilwarning light (not needed in an EV) or may be directed to anewly installed indicator. The addition of a low vacuumacoustic alarm enabled after the initial start pump-up is alsoappropriate. A vacuum gauge is essential for setting thevacuum switch control points and may be included as adashboard or underhood instrument.

Electric vehicles can operate at very high startingtorque. Most transmissions (especially truck transmissions)use a very low gear ratio in reverse, lower than low gear. Toobtain this low ratio a very small diameter driving gear isused, subject to breakage if over torqued. A throttle restrictoris used when reverse is engaged. This is done byelectronically limiting the effective throttle dashpot rangewith relays and resistors or mechanically by using a doorunlock motor, or a solenoid to limit the throttle motion whenreverse gear is engaged.

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Fig. 6 Vacuum switch circuit and alarm

VII. ELECTRONIC CONTROL UNIT

The hybrid electric vehicle brings new power trainsystem and its control strategy. The electrical systems thatare enabled by hybrid power train vehicles bring new systempartitioning options. The HEV drive train interacts with thebraking systems, battery charge and discharge systems,combustion engine controls, transmission, and cabincontrols. This interaction drives the need for a central hybridcontrol module that has ultimate responsibility forinterfacing between the various control functions. Figure 7shows the integration of hybrid functions into the othermajor electrical control systems.

The hybrid power train system brings new electroniccontrol units (ECUs) to the vehicle to control the electricmotor, power inverter, battery, and driver informationsystems. Also, the hybrid changes existing systems like theengine control module and transmission control.Additionally, the increased interdependence between theECUs affects control systems that are outside of the hybridpower train system. For example, the antilock brakingsystem (ABS) has to directly interface with the hybrid powertrain.

The traction motor in an HEV is typically a three-phasebrushless DC motor or permanent magnet synchronousmotor. The embedded processor that controls the inverterwill drive the power drivers with a square or trapezoidalwaveform. The control of a three-phase electric motor

requires software that calculates the torque angle for the twoactive phase angles. The system uses dual analog-to-digitalconverters to simultaneously measure the voltage of two ofthe power phases. Using information from the two measuredphases, the third phase can be calculated. The three-phasemotor is controlled by a 32-bit RISC processor with floating-point or Single Instruction Stream, Multiple Data stream(SIMD) to calculate the next phase angle.

The Motor Management System (MMS) block shown inFig. 8 describes the electronic control of electric motor usedto drive the electric vehicle. The power inverter module hasmultiple functions and modes of operation. The primaryfunction of the power inverter is to convert the DC currentfrom the battery pack to a three-phase AC power source todirectly drive the electric motor. The power inverter is oftenused in reverse to charge the battery during regenerativebraking sequences and to pull excess power from the internalcombustion engine to recharge the battery. In many HEVsystems, the battery pack can use a simple 16-bit embeddedprocessor for data collection and measurements across thebattery pack. This data can then be transferred to the 32-bitembedded processor controlling the power inverter module.The higher-performance embedded processor is better suitedto run higher-level strategy algorithms that are moreinteractive between the battery charge/discharge and thecurrent request for torque from the driver. Many of thealgorithms use complex mathematical calculations based onthe battery state of charge, battery temperature, and ambienttemperature. A floating-point or SIMD unit can be used todramatically reduce the computational overhead ofcalculating the multiple filters and computing the phaseangle of the electric motor.

VIII. CONCLUSIONHybrid electric vehicles are enabling a new generation

of efficient and cleaner vehicles. Semiconductors will playan increasing role in controlling the engine, transmission,electric motors, batteries, and module-to-modulecommunications of future EVs. Embedded processors arebecoming more sophisticated and computationally intensivewith every generation through improved timers,communications, caches, and DMA modules. The currentgeneration of embedded processors will have to incorporatefeatures to help control systems with new architecturalenhancements like SIMD, a floating-point unit, a memorymanagement unit, and real-time multiprocessor debugging.The advent of a real-time standard interface for debug, rapidprototyping, and calibration will help to reduce engineeringdevelopment time.

A comprehensive review of the control structureillustrates the relevance and importance of modernelectronics and signal processing in hybrid electric vehicles.The mechanical vehicle using chemical fuel powered byelectric motor is electronically controlled for passengercomfort and transportation.

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Fig. 7 Integration of Electronic Control Unit (ECU) in an Electric VehicleMS-s 4 4 -. - Q 4 ; > g v I P _ . I . . I #a;,;X 4 a 4

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Fig. 8 Motor Management System for electronic control of electric motor in EV

Hybrid power train control system

Battery ManagementPower control

Power inverter &electric motor Engine ECUI I~~~

Existing vehicle control

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