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CHAPTER 5

FORMULATION OF CONTROL STRATEGY AND

PROTOTYPE DEVELOPMENT

5.1 INTRODUCTION

Plug-in hybrid implementation in a two-wheeler is a good tradeoff

between an electric and IC engine power which ensure sufficient all-electric

range and minimum emissions as well. For heterogeneous India’s traffic

pattern, a single operating mode of the vehicle cannot satisfy the driving

pattern. In order to formulate the control strategy, all types of driving modes

need to be considered. The development of prototype vehicle involves the

design of control system with control strategy suitable for Indian city driving

conditions. This chapter discusses the formulation of control strategy and

development of control system followed by the conversion of selected base

two-wheeler into of plug-in hybrid electric two-wheeler.

5.2 FORMULATION OF CONTROL STRATEGY

The integration of conventional vehicle components with electric

propulsion components results in a vast number of potential hybrid electric

configurations. The series hybrid electric configuration is an interesting

solution for driving in urban areas with passenger cars, light duty vehicles as

well as with heavy-duty vehicles like city buses. On the other hand, parallel

hybrid electric powertrain configuration is more suitable for the family

or higher class vehicle segment, while driving on highway and long

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distances. In addition, a series-parallel hybrid powertrain system has a

complex transmission and increase in the number of components also makes

the integration more complicated (Montazeri-Gh et al 2006). As the

complexity of the vehicle configuration is increases, so do the demands for

control. As people may expect, there is no universal architecture that can be

considered superior in all practical aspects such as energy efficiency, vehicle

performance and range, driver comfort, manufacturing complexity, and

production cost. Therefore, in practice, automakers may choose different

architectures to achieve different goals and meet distinct transport segment

requirements.

Besides the powertrain configuration, a suitable power and energy

distribution system is also important. The control strategy plays a basic role.

A control strategy is an algorithm that manages the power split between the

IC engine and the electrical machine in order to reduce fuel consumption and

pollutant emissions. In a plug-in hybrid electric vehicle, the strategy will

attempt to use most of the energy from the battery pack. However, majority of

global two-wheelers population utilizes small displacement engines, generally

in the order of 50-150 cc. Hence, for two-wheelers of simple architecture with

low cost operation, there is a need to develop a simple powertrain design with

a simple control strategy which is less complex and easy for retro-fitment.

Electrification of kilometres through charge depleting operation in a

PHETW is expected to be a cost-effective way to continue to reducing fuel

consumption beyond HEV technology capabilities. The designed control

strategy does not necessarily provide maximum fuel savings over all driving

demand. This is because the national average daily travelled distance by

two-wheelers in India is close to 24 km/day. As per the survey, it is also

observed that about 61% of two-wheelers drive less than 25 kilometres per

day. Only 7% of two-wheelers travel more than 50 km per day and about 32%

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of two-wheelers travel in between 25 to 50 km per day. Therefore, choosing

the right electric range to handle the daily driving needs is essential. The

control system should utilize a strategy modified in real time depending on

the input from various sensors in the system.

Two control strategies can be applied to PHEV: the all-electric

strategy and the blended strategy (Markel 2007). In all-electric strategy, the

electric motor supplies all the power needed for the vehicle until the battery

reaches the predetermined minimum SOC level. In blended strategy, both

motor and engine work together to provide the power requirements. In this

work, both all-electric and blended strategies have been adopted to suit

two-wheelers in Indian cities to realize better driving performance and good

energy management. In all-electric strategy, it has been planned to cover

average daily travel distance with zero emissions. However, by selecting the

blended strategy at the beginning of the journey itself, the vehicle can travel

more than double the all-electric range with improved fuel economy and

minimum emissions. In both the strategies, the energy from the battery pack

has charge depleting mode. Therefore, three distinct modes were derived and

the switching logic was drafted for each mode of driving. The three modes of

operation are namely electric mode, hybrid mode and engine mode. The

electric mode uses all-electric strategy and hybrid mode uses blended

strategy, whereas engine mode is similar to conventional vehicle operation.

Figure 5.1 shows the simple flow chart of plug-in hybrid electric two-wheeler.

The rider can select the modes based on the driving range and battery pack

state-of-charge.

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Figure 5.1 Plug-in hybrid electric two-wheeler flow chart

5.2.1 Electric Mode

The electric mode of the prototype vehicle aims at providing an

eco-friendly transportation solution in urban driving. In this mode, the

converted plug-in hybrid electric two-wheeler utilizes power from the battery

alone with zero tail-pipe emissions. The charge-depleting all-electric strategy

emphasizes all electric vehicle operation over a desired distance in which

battery discharges to a minimum threshold. So, this mode has all the

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advantages of electric vehicle. The developed prototype vehicle has been

designed to provide an all electric range of about 25 km with further scope for

improvement, as range is a function of both battery size and amperage.

Increasing the energy capacity of the battery pack provides the ability to

extend the driving distance using electricity, but it would increase the

incremental cost of the battery.

5.2.2 Hybrid Mode

The effectiveness of fuel consumption in hybrid mode depends not

only on vehicle design, but also on the control strategy used. It defines how

and when power and energy will be provided or consumed by various

components of the vehicle (Markel and Wipke 2001). The charge-depleting

blended strategy of hybrid mode in plug-in hybrid electric two-wheeler aims at

providing the maximum utilization of the available energy - battery and IC

engine to run the vehicle. This mode is primarily meant for striking a balance

between emissions and the range of the vehicle.

In the hybrid mode, the control strategy is formulated in such a way

that the IC engine idling and low power modes could be eliminated to a great

extent. For the starting of the vehicle and at low speed-high torque region, the

battery pack supplies the power to the hub motor. The engine is OFF during

idling and low-load driving conditions where the engine efficiency would be

low. However, an electric motor provides high efficiency at low load when

compared to an engine. By adopting this control strategy, IC engine idling and

inefficient engine operation at low power modes are eliminated, which in turn

improves the overall efficiency and reduces the fuel consumption, thus reducing

emissions.

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SPEED >

SET SPEED

Figure 5.2 Hybrid mode flow chart

Figure 5.2 shows the logic flow chart of hybrid mode. The IC engine

takes over only when the speed of the vehicle exceeds the set-speed after a

delay of 5 seconds. The engine will be switched off when the speed of the

vehicle reaches below the set speed and remains in that state for about 5

seconds. However, the set-speed can be varied using the key pad built in the

control system. In the hybrid mode, the IC engine delivers power for high

speed driving and for hill climbing, while the electric wheel hub motor in the

front wheel is engaged for low speed driving. A unique feature of the control

strategy helps in eliminating the idling and low power operations of engine

for better fuel economy.

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5.2.3 Engine Mode

If the total distance to be travelled on a given particular day is more

than the daily average travel distance or if the battery packs SOC level drops

below the minimum threshold limit, the system will permit neither the electric

nor the hybrid mode. The conventional engine mode can be switched ON.

Hence, unlike the electric two-wheeler the range is not limited. This mode is

primarily meant for high speed driving and cruising wherein speed variations

are minimum. Better utilization of the IC engine is done at higher speeds and

the driver has the option of choosing the engine mode during off-peak traffic

hours etc. Since the electric and hybrid modes of a developed Plug-in hybrid

electric two-wheeler are designed for single rider with an average weight of

70 kg, whenever the pillion weight is added to the total vehicle weight the

engine mode will render support without losing the original performance of

the base vehicle.

5.3 DEVELOPMENT OF CONTROL SYSTEM

The control system is an important element in the development of

plug-in hybrid electric two-wheeler. It provides the path for flow of energy

between the various components when the vehicle is in motion. The main task

of the control system is to shift the power required by the vehicle between IC

engine and wheel hub motor. Figure 5.3 illustrates the block diagram of

control system with electronic accessories used respectively. The control

system utilizes a real time strategy depending on vehicle speed. Switching

from electric to hybrid mode and vice versa is facilitated by a microcontroller

which is provided with the above input. The control strategy is fed to the

controller in the form of a coded logic. So, based on the input signals, the

microcontroller decides the energizing of the corresponding relays so as to

actuate the respective relay. This microcontroller is programmed to work in

all the three modes of the control strategy.

Figure 5.3 Block diagram of control system

5.3.1 Microcontroller

The microcontroller is the heart of the control system that decides

the vehicle’s strategy and operation.

device, which integrates a number of the components of a microprocessor

system on a single chip. It has an inbuilt CPU (Central Processing Unit),

memory and peripherals to make it appear as a mini computer. The

microcontroller that has been used for this project is from the PIC (

Interface Controller) series. PIC microcontroller is the first RISC (Reduced

Input Set Computation)

(complementary metal oxide semiconductor).

separate bus for instruction and data, allowing simultaneous access of

program and data memory. EEPROM (Electrically Erasable Programmable

Read-only Memory), EPROM (Erasable Programmable Read

FLASH, etc., are some o

recently developed technology which is used in PIC 16F877. The data is

retained even when the power is switched off. Easy programming and erasing

are some of other features of PIC 16F877. Figure 5.4 shows the pin

of PIC 16F877.

Figure 5.3 Block diagram of control system

Microcontroller

The microcontroller is the heart of the control system that decides

the vehicle’s strategy and operation. Microcontroller is a general purpose

device, which integrates a number of the components of a microprocessor

system on a single chip. It has an inbuilt CPU (Central Processing Unit),

memory and peripherals to make it appear as a mini computer. The

troller that has been used for this project is from the PIC (Peripheral

erface Controller) series. PIC microcontroller is the first RISC (Reduced

Set Computation) based microcontroller fabricated in CMOS

(complementary metal oxide semiconductor). This microcontroller uses

separate bus for instruction and data, allowing simultaneous access of

m and data memory. EEPROM (Electrically Erasable Programmable

y Memory), EPROM (Erasable Programmable Read-only Memory),

FLASH, etc., are some of the memories. Of these, FLASH is the most

recently developed technology which is used in PIC 16F877. The data is

retained even when the power is switched off. Easy programming and erasing

are some of other features of PIC 16F877. Figure 5.4 shows the pin diagram

of PIC 16F877.

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Figure 5.3 Block diagram of control system

The microcontroller is the heart of the control system that decides

Microcontroller is a general purpose

device, which integrates a number of the components of a microprocessor

system on a single chip. It has an inbuilt CPU (Central Processing Unit),

memory and peripherals to make it appear as a mini computer. The

troller that has been used for this project is from the PIC (Peripheral

series. PIC microcontroller is the first RISC (Reduced

fabricated in CMOS

This microcontroller uses

separate bus for instruction and data, allowing simultaneous access of

m and data memory. EEPROM (Electrically Erasable Programmable

y Memory), EPROM (Erasable Programmable Read-only Memory),

f the memories. Of these, FLASH is the most

recently developed technology which is used in PIC 16F877. The data is

retained even when the power is switched off. Easy programming and erasing

are some of other features of PIC 16F877. Figure 5.4 shows the pin diagram

5.3.2 Signal Conditioning Unit

Microcontrollers are widely used for control in power electronics.

They provide real time control by processing analog signals obtained from the

system. A suitable isolation interface needs to be designed for interaction

between the control circuit and hig

unit (SCU) provides the necessary interface between a high power grid

inverter and a low voltage controller unit. The signal conditioning unit accepts

input signals from the analog sensors and gives a conditioned o

DC corresponding to the entire range of each parameter.

accepts the digital sensor inputs and gives outputs in 10 bit binary with a

positive logic level of +5V.

Figure 5.4 Pin diagram of PIC 16F877

5.3.3 Relay

A relay is an electrically operated switch

the coil of the relay creates a magnetic field which attracts a lever and

Signal Conditioning Unit

Microcontrollers are widely used for control in power electronics.

They provide real time control by processing analog signals obtained from the

system. A suitable isolation interface needs to be designed for interaction

between the control circuit and high voltage hardware. A signal conditioning

t (SCU) provides the necessary interface between a high power grid

inverter and a low voltage controller unit. The signal conditioning unit accepts

input signals from the analog sensors and gives a conditioned output of 0

DC corresponding to the entire range of each parameter. This unit also

accepts the digital sensor inputs and gives outputs in 10 bit binary with a

itive logic level of +5V.

Figure 5.4 Pin diagram of PIC 16F877

Relay

A relay is an electrically operated switch. Current flowing through

the coil of the relay creates a magnetic field which attracts a lever and

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Microcontrollers are widely used for control in power electronics.

They provide real time control by processing analog signals obtained from the

system. A suitable isolation interface needs to be designed for interaction

h voltage hardware. A signal conditioning

t (SCU) provides the necessary interface between a high power grid

inverter and a low voltage controller unit. The signal conditioning unit accepts

input signals from the analog sensors and gives a conditioned output of 0-5V

DC corresponding to the entire range of each parameter. This unit also

accepts the digital sensor inputs and gives outputs in 10 bit binary with a

. Current flowing through

the coil of the relay creates a magnetic field which attracts a lever and

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changes the switch contacts. The coil current can be on or off so relays have

two switch positions and they are double throw (changeover) switches. Relays

allow one circuit to switch a second circuit which can be completely different

from the first. For example a low voltage battery circuit can use a relay to

switch a 230V AC mains circuit. There is no electrical connection inside the

relay between the two circuits-the link is magnetic and mechanical.

Figure 5.5 Relay circuit

Figure 5.5 shows the typical relay circuit. The relay circuit is

designed to control the load. The load may either be a motor or any other

load. The load is turned ON and OFF through relay. The relay ON and OFF

is controlled by the pair of switching transistors (BC 547) and is connected in

the Q2 transistor collector terminal. The relay common pin is connected to a

supply voltage. The normally open (NO) pin is connected to load. When high

pulse signal is given to base of the Q1 transistors, the transistor conducts and

shorts the collector and emitter terminal, thus giving zero signals to the base

of the Q2 transistor. So the relay is in the OFF state. When low pulse is given

to base of transistor Q1 transistor, the transistor is turned OFF. At this point,

12 V is given to base of the Q2 transistor so that the transistor acts as the

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conductor and relay is turned ON. Hence the common terminal and NO

terminal of relay are shorted. At this point, load gets the supply voltage

through relay. Table 5.1 gives the switching operation of the relays.

In order to meet the switching functions, the control system has two

relays namely the start relay and stop relay. The control current and voltage of

relay is around 100 mA and 12 V respectively.

Table 5.1 Switching operation of relays

SpeedStart Relay

Position

Stop Relay

PositionOperation

Above 30 km/h NO NOPower flow from battery

to starter motor

Below 30 km/h NC

NC for certain

period and then

NO

Ignition switch is

switched OFF for a

certain period and then

switched ON

5.3.4 Inductive Proximity Sensor

Inductive proximity sensors generate an electromagnetic field and

detect the eddy current losses induced when the metal target enters the field.

The field is generated by a coil wrapped round a ferrite core, which is used by

a transistorized circuit to produce oscillations. The target, while entering the

electromagnetic field produced by the coil, will decrease the oscillations due

to eddy currents developed in the target. If the target approaches the sensor

within the so-called sensing range, the oscillations cannot be produced. Then,

the detector circuit generates an output signal, controlling a relay or a

switch. Figure 5.6 shows the lay-out of inductive proximity sensor. The

proximity sensor use reed switch-based technology, which offers reliability of

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up to 5 million cycles. The standard operating temperature range is

from 40°C to 125°C.

Figure 5.6 Lay-out of inductive proximity sensor

In this work, the sensor is mounted in the front wheel pointing it

towards a metal piece in the wheel and three hexagonal bolts on the wheel

disc are used as metal targets to sense the vehicle speed. Microcontroller

programmed to count as one revolution as three times bolt is sensed. This

speed is given as an input to the microcontroller in order to facilitate the

switching process. An LCD display is also connected to the circuitry that

displays the count value proportional to the wheel speed. Figure 5.7 shows the

inductive proximity sensor fitted with metal targets on the front wheel.

The energy management strategy is fed to the controller in the form

of a coded logic. Based on the input signals, the microcontroller decides the

energizing of the corresponding relays so as to actuate the respective relay.

This microcontroller is programmed to work in all the three modes of the

energy management strategy. Figures 5.8 and 5.9 show the logical circuit and

circuit board with accessories of control system.

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Figure 5.7 Front wheel fitted with proximity sensor

Figure 5.8 Circuit board and accessories of control system

Figure 5.9 Logical circuit of the control systemFigure 5.9 Logical circuit of the control systemFigure 5.9 Logical circuit of the control system

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5.4 PROTOTYPE DEVELOPMENT

Base vehicle platform used for the prototype development was a

commercially available 98cc, 2-stroke petrol vehicle. Figure 5.10 shows the

simple lay-out of a plug-in hybrid electric two-wheeler.

Figure 5.10 Lay-out and energy flow in a converted plug-in hybrid

electric two-wheeler

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The selected base two-wheeler for this work is modified into a

plug-in hybrid electric two-wheeler by retrofitting with wheel hub motor in

the front wheel and the battery pack placed at the foot rest area. The reason

for mounting the hub motor in the front wheel is due to the constraints in

modifying the existing two wheeler design with transmission set-up. The hub

motor drives the front wheel, whereas the IC engine drives the rear wheel

through continuously variable transmission (CVT), as in the existing vehicle.

A 48 Vt battery pack is a set of 4 batteries. The four batteries in the pack are

connected in series so that the output voltage is 48V and capacity is 20Ah.

The battery pack is placed at the foot rest. However, it can be placed below

the seat by adopting some modifications during design and manufacturing of

the vehicle. The inductive proximity sensor fitted with metal targets on the

front wheel gives speed of the vehicle to the microcontroller in order to

facilitate the switching process. A plug is provided for charging the battery

pack using a standard home power outlet through converters when the vehicle

is at rest. Figure 5.11 shows the converted plug-in hybrid electric

two-wheeler. Table 5.2 gives the specifications of the converted plug-in

hybrid electric two-wheeler.

The main switching circuit was located near the battery. This circuit

was made to operate on a separate 12V power source to ensure isolation of the

electrical supply of the control system from the main drive electrical system.

This is more advantageous as the control system is more fail-safe and can be

programmed to perform various other actions in case of a failure in the

electrical system of the main drive or an accident. Individual components of

the system operate at different currents and hence suitable wires need to be

used. The wiring has to be fool-proof to ensure that no short-circuiting occurs

under any circumstances. Similarly, it is important to note that there are no

open ends and the vehicle must be electrically safe for a person to handle.

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Figure 5.11 Plug-in hybrid electric two-wheeler prototype

Table 5.2 Specifications of a converted plug-in hybrid electric

two-wheeler

Specifications Converted Plug-in Hybrid Electric Two-Wheeler

Engine 2-stroke (SI)

Engine displacement 98cc

Ignition Electronic

Engine max. power 7.7 bhp @ 5500 rpm

Engine max. torque 1 kgm @4500 rpm

Transmission Automatic (CVT)

Kerb weight 132kg

Maximum speed 95 km/h

Electric motor800 Watt, 48 V hub drive BLDC traction motor,

rated torque 33 Nm @ 150 rpm

Battery 20 Ah, 12 V VRLA traction battery – 4 Nos.

Battery charging

time8 hrs

Wheel base 1,215 mm

Fuel tank capacity 6 litres

Tyre size 3.50x10 4 PR

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5.4.1 Operation of PHETW

There are two keys in the vehicle - one for the electric powertrain

system and another for IC engine powertrain system. In electric mode, only

electric powertrain key is turned ON, whereas in hybrid mode, both the keys

are turned ON. The speed of vehicle is detected by the speed sensor

(proximity sensor) and the signals are sent to the signal conditioning unit. The

signal conditioning unit converts the pulses from the sensor into an equivalent

(0 to 5V) range.

In the electric mode, the electric powertrain key is turned ON and

the IC engine powertrain key is turned OFF. Even as the vehicle accelerates

beyond the set speed, there is no trigger to crank the engine. Hence, the

vehicle continues to drive in the electric mode.

In the hybrid mode, both the electric powertrain key and the IC

engine powertrain key are turned ON. The vehicle starts initially using the

electric motor power and then accelerates up to the set-speed. As soon as the

vehicle crosses the set speed the IC engine is cranked using a starter motor

and drives the vehicle. The IC engine takes over only when the speed of the

vehicle exceeds the set-speed after a delay of 5 seconds. As the engine spools

up, the EMF from the alternator is greater than 12 V, which is fed to the stop

pin of the motor controller. This ensures cut-off of power supply to the motor.

The engine will be switched off when the speed of the vehicle reaches below

the set speed and remains consistent in that state for 5 seconds. However, the

set-speed can be varied by using key pad built in the control system.

In the hybrid mode, the microcontroller keeps the ignition relay

switched ON throughout the mode. The relay operating the starter motor is

switched OFF. When the speed of the vehicle crosses 30 km/h, after a delay

of 5 seconds, the relay operating the starter motor is switched ON for

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5 seconds only to avoid excess cranking. The engine spins and gains speed to

generate sufficient EMF (12-14 V). This is fed to the stop pin of motor

controller, and then power supply to the hub motor is cut-off. As the speed of

the vehicle goes below 30 km/h, the microcontroller keeps the ignition relay

switched OFF for 5 seconds (this is to turn OFF the engine) and is again

turned ON. The relay operating the starter motor is switched OFF and the

generated EMF from alternator comes below 12 V which makes the motor

controller to resume back its power supply to the motor.

In engine mode, electric powertrain key is turned OFF and the

IC engine powertrain key is turned ON. The vehicle is mobilised from the

beginning using IC engine. It can be cranked either by using the starter motor

or by kick start pedal. Alternator gives generated current signal to stop pin of

hub motor controller, hence there is no power supply to it.

5.5 CONCLUDING REMARKS

Based on the driving conditions in Indian cities, the following control

strategies were derived.

Two control strategies namely all-electric strategy and

blended strategy were used.

The control system developed can use three modes: electric

mode, hybrid mode and engine mode. The user can select a

particular mode based on the driving condition and battery

charge condition.

The next chapter presents the testing and performance of powertrain

elements and converted plug-in hybrid electric two-wheeler in detail. This

chapter also discusses the comparison of simulation results with road test

results for simulation validation.