INTRODUCTION
Overview of Topic
1.1.1 The reason to choose this topic
Today, due to the strong growth in the number of road vehicles, the air pollution caused by the emissions of these vehicles has become more and more serious, especially in urban areas To save the environment and improve air quality in big cities, governments have introduced strict regulations on fuel consumption and vehicle emissions This is the main driving force for automakers to invest in developing new, environmentally friendly technologies for their product lines, including electric vehicles However, the use of electric motors as a power source still has some problems, such as limited battery capacity, short battery life, large volume of electric motor and battery, long-time charging, high cost Therefore, the current use of electric motors as an alternative source of motivation for motors is still limited, only used in a few specific and necessary cases.
In order to promote the advantages as well as limit the remaining problems of electric motors when used in vehicles, scientists have come up with a solution to combine electric motors with internal combustion engines, or commonly referred to as hybrid vehicles. The powertrains system of hybrid is known for 3 types: series, parallel and series – parallel Regardless of the type of powertrain, a hybrid system must include components such as an internal combustion engine, an electric motor, a generator and a high-voltage battery To find out how hybrid vehicles can reduce fuel consumption, our team decided to choose the topic: “Application of MATLAB in fuel consumption simulation of series-parallel hybrid vehicles”.
- Understanding the theoretical basis and operating principle of hybrid vehicles.
- Research, simulate the model of series-parallel hybrid vehicles for fuel consumption.
- Comparing the simulation result with parameters of manufactures.
1.1.3 Object and scope of the study
- The purpose of this research is the MATLAB simulation model of series-parallel hybrid vehicles.
- Scope of the study: Research a series-parallel hybrid vehicles model and simulation the fuel consumption of model on MATLAB.
- Using the theoretical basis of reference sources to research models.
- Apply or refer to the available vehicle parameters in reality to conduct simulations.
- Using MATLAB to simulate fuel consumption with different driving cycles.
Currently, more and more hybrid vehicles are used, there is a lot of research with the goal of modernizing and minimizing fuel consumption.
F.Schluter, P.Waltermann have studied “Hierarchical control structures for hybrid vehicles – modelling, simulation, and optimization” Based on parallel and serial hybrid vehicle control sequence models through the DSL dynamics system language and Camel software environment, an arithmetic analysis, e.g., nonlinear system dynamics simulation, was made For different levels of the hierarchical control structure, different optimization strategies have been applied to reduce fuel consumption and emissions, and the processes are optimized based on Nonlinear simulation was used.
Mohamed Awadallah, Peter Tawadros, Paul Walker, Nong Zhang studied the “Dynamic modelling and simulation of a manual transmission based mild hybrid vehicle” By combining a powertrain with a manual transmission and a secondary power source in the form of an electric motor driving the output shaft of the gearbox, the authors have researched the creation of a mild hybrid powertrain The dynamic performance of conventional and lightweight hybrid powertrains is compared using mathematical models of the two systems During the system development process, this mathematical model is used to run a variety of simulations for the gearshift control algorithm design, enabling researchers to assess the performance that can be expected and how much is dependent on the system's characteristics.
Pham Quoc Thai and Huynh Duc Tri have studied "Modeling and simulating electric vehicle powertrain." This study describes the implementation of modeling and simulation of an electric powertrain on a 5-seater electric car The models of inverters, asynchronous motors, dynamic models, and load characteristics are built on Matlab/Simulink software. The response parameters of the asynchronous motor, such as speed, torque, and amperage on the stator and rotor corresponding to the moving terrain, are analyzed, and evaluated. Simulation results show that the transmission system operates accurately, stably, and efficiently, with good dynamics.
Master Huynh Quoc Viet has researched "Ứng dụng logic mờ trong điều khiển năng lượng phanh tái sinh trên xe lai động cơ – điện" The author has applied fuzzy logic in regenerative brake control to create the optimal combination of mechanical and electric brakes The brake torque controller has been designed and simulated by Simulink/Matlab on the popular European new combined test cycle NEDC The results of the project
2 obtained are that the actual desired speed of the vehicle and the calculated simulation speed is asymptotically close to each other, the ratio of regenerative braking torque to the required braking torque is very high The brakes recover energy during braking very well, the battery charge status when the vehicle is running on the NEDC cycle always operates at the optimal range through these driving cycles In addition, the operating points of the torque motor are negative That is, the engine acts as a generator The engine also operates in high-efficiency areas The results demonstrate that the hybrid electric-motor hybrid vehicle achieves high regenerative energy results The regenerative brake controller recovered the most energy and ensured safety during braking.
Nguyen Ngoc Dam has a article: Principles of energy recovery in hybrid cars and electric vehicles This project designing a brake energy recovery 5 system is a relatively complex problem when designing the braking system of electric vehicles, hybrid vehicles and fuel cell vehicles There are two problems that need to be solved: firstly, how to distribute the total braking force into regenerative braking force (the part that will be recovered) and the frictional braking force (the part that is not recovered) to be able to regenerate energy as much as possible; the second is how to distribute the total braking force on the front and rear axles to ensure stability and braking efficiency Normally, regenerative braking is only effective on the active axle The electric motor will have to be controlled to produce an appropriate amount of braking force so that the energy recovered is as large as possible, and the total braking force to slow the vehicle must also match the driver's command To meet the above requirements, the hybrid brake system has two main types:parallel hybrid braking system and fully controlled hybrid braking system
Overview of HEV
Established in the 18th century, Automobile has quickly become integral to human development Using automobiles as a mode of transportation has solved many economic problems as well as the transshipment of goods Because of that, the auto industry is developing very quickly, and many ideas and scientific inventions are applied to cars. Initially, there were studies for the development of engine power, gearbox optimization, vehicle safety, and environmental protection issues However, with the increasing use of cars in countries around the world, there is a big issue that also needs to be taken care of, which is the issue of fuel consumption as well as not causing adverse effects on the environment.
After many upgrades, in 1899 - 1900, the first hybrid car was born by engineer Ferdinand Porsche and was named System Lohner-Porsche Mixte.
Figure 1.1 System Lohner-Porsche Mixte
A hybrid vehicle is defined as a vehicle that uses two sources of energy: an internal combustion engine and an electric motor.
Although hybrid cars have solved the problem of energy use and environmental protection, scientists are still constantly trying to quickly find an alternative energy source to supply power to the engine instead of using an ICE Many solutions have been proposed, such as engines using hydrogen, natural gas, and bio – diesel but due to the complexity and poor feasibility, many car manufacturers still trust hybrid cars.
Figure 1.2 Toyota Camry Hybrid 1.2.1 Working Principle of Hybrid Vehicle
The vehicle is started and driven at low speeds by an electric motor The internal combustion engine starts up as the vehicle accelerates, and the energy it generates powers the electric motor, which drives the wheels When decelerating and braking, the electric motor uses the vehicle's kinetic energy as a generator to rotate, which will be used to recharge the battery With the combination of an internal combustion engine and an electric motor, hybrid engines are able to operate at higher operating temperatures, consume less fuel, produce more torque with small revolutions, and have reduced pollution in the environment.
Figure 1.3 Working principle of Hybrid Vehicle
Through the drivetrain, the wheels send kinetic energy to the generator At the same time, the generator resistance caused by the generated electricity slows down the car Friction brakes give additional braking torque, when necessary, but the generator cannot.
In this type of architecture, the mechanical connection with the wheels is entirely made with the driving EM The MG2, which functions as a generator and transforms the mechanical energy into electrical energy, is connected to the ICE This power either powers the MG1 to move the vehicle forward or aids in charging the battery
This design enables the management of the internal combustion engine's operating mode, the determination of the engine's best efficiency zone, and the constant maintenance of the engine's operation within that zone.
However, adding two additional electric motors pushes up the weight and price of the vehicle, and the effectiveness of employing the hybrid series is compromised when there are several energy conversions between the internal combustion engine and wheel.
In the parallel architecture, the electric motor and ICE are mechanically connected to the wheels and can both propel the vehicle either together or separately as shown in Figure 1.5
The parallel architecture is more complex than for the series architecture Parallel hybrid has two types of mechanical coupling systems, the speed coupling and the torque coupling:
- Speed coupling can be made possible through a planetary gear set.
- Torque coupling is the most common coupling system used in this architecture. Pre-transmission coupling, post-transmission coupling, and coupling through the road are the three main coupling methods.
The parallel architecture's benefits result from the fact that it is quite similar to a traditional vehicle architecture Volume, weight, and price all increased significantly To target its ideal operating area, the combustion engine is more difficult to operate because it is directly coupled to the wheels.
Series-Parallel architecture which has two power coupling is a combination of parallel architectures and series architectures, so the use of serial-parallel architecture will have more efficiency It provides better control of the internal combustion engine, battery, and power
But not without its downsides This system is large and hefty due to the two electric machines and two connecting systems Although it provides superior engine control, it is also more difficult to control than the prior systems
Figure 1.6 Series - Parallel Hybrid Structure 1.2.3 Comparing Hybrid Vehicle with ICE Vehicle
Modern hybrid vehicles have the following essential characteristics:
Compared with vehicles using ICE, hybrid vehicles have the following advantages and disadvantages: a Hybrid cars are more fuel efficient and emit less
Hybrid cars were developed mainly because of the pressure of the economy to fuel and reduce emissions The following characteristics achieve this goal:
- The diesel engine of the hybrid car is small, so the energy loss is less than ICE engines.
- In S-HEV and SP-HEV, the rotation speed of the TDC can be completely independent entirely of the speed of the car, so the excavator is allowed to work in the modes optimized in terms of fuel economy or emissions.
- Reusing the car's kinetic energy during braking and downhill.
Allow the EDC to not operate in special modes such as: waiting in front of the red light, idling, downhill b Most of the current hybrid vehicles models have a higher selling price than ICE vehicles:
In order to ensure the necessary technical features, compact size, and useful life, the electrical equipment equipped with hybrid cars is usually a high-end type with higher cost Some other issues related to hybrid cars have also been mentioned as follows:
The industry of manufacturing high-grade electrical equipment for hybrid vehicles consumes a large number of unique materials made from rare earth To date, over 90% of the rare earths used worldwide are supplied by China.
- The problem of the life of the propulsion system:
Most hybrid vehicles today are designed so that the ITR does not operate in some special modes, such as waiting at a red light, braking, going downhill, or running at low speed. Thus, during operation, the ICE engine in hybrid vehicles will be turned off and restarted more times than in ICE vehicles This feature can reduce the life of the actuator because the quality of lubrication is often deficient, and the temperature regime is often not optimal in the period immediately after starting up.
- Environmental pollution problems caused by battery:
Most hybrid vehicles today are equipped with Nickel - Metal battery type.
THEORITICAL BASIC OF SERIES-PARALLEL HYBRID SYSTEM
The components of Series-Parallel Hybrid vehicle system
- Gear Box includes MG1, MG2 and Planetary gear unit.
- The adapter assembly includes: a DC-DC converter, an AC-DC inverter.
- THS ECU: Information from each sensor as well as from the ECU (battery smart unit, skid control ECU, and MG ECU) is received, and based on this the required torque and output power is calculated.
- Acceleration pedal position sensor, convert the throttle angle to electrical signals.
- Skid Control ECU, control regenerative brake force
- MG ECU: The hybrid vehicle control ECU receives signals from various sources and utilizes them to control the inverter and boost converter.
12 mechanism allows for the operation of MG1 and MG2 as either generators or motors, based on the specific requirements of the system.
- Battery Smart Unit: The hybrid vehicle control ECU monitors the status of the HV battery, including parameters such as voltage, current, and temperature This information is then transmitted to the hybrid vehicle control ECU for further analysis and decision-making.
- SMR (System Main Relay): The THS ECU utilizes a signal to control the connection and disconnection of the high-voltage power circuit between the HV battery and inverter assembly.
- Auxiliary Battery: The DC/DC converter charges the HV battery module power and provides power to various components such as the audio system, air conditioning system (excluding the electric inverter compressor), and ECUs.
[12] The 2AZ-FXE engine is a 2.4-liter inline 4-cylinder engine The Toyota 2AZ-FXE features a lightweight aluminum block with thin cast-iron cylinder liners and 16-valve DOHC aluminum head with four valves per cylinder (two intakes and two exhaust) It is equipped with an EFI electronic fuel injection system, a water-cooled system, and an oil- lubricated engine system This engine also has a thermostat to help the engine quickly reach operating temperature and a Euro 4 standard emission control system.
A unique form of the 2AZ-FXE engine is variant of the 2AZ-FE, which allows the engine to reduce emissions by changing the relationship between compression and expansion It has the same bore and stroke, but the intake cam and pistons are unique It has a physical compression ratio of 12.5:1.
The large valve overlap leads to a reduction in cylinder charge and reduced torque and power output, but efficiency is increased This combination makes the 2AZ-FXE suitable for use only in hybrid vehicles, where peak torque and power demands can be met by the electric motor and battery.
Fuel consumption, L/100 km (for Lexus - city – 6.9
Table 2.1 2AZ-FXE Engine Specification 2.1.2 Gear Box
- The hybrid transaxle in this vehicle is composed of several key components These include MG1 (Motor Generator 1) and MG2 (Motor Generator 2), a compound gear unit which consists of a motor speed reduction planetary gear unit and a power split planetary gear unit, a counter gear unit, and a differential gear unit.
- The transaxle in this vehicle is designed with a three-shaft configuration On the main shaft, you will find the compound gear unit, which includes the motor speed reduction planetary unit and the power split planetary gear unit, as well as MG1 and MG2 The second shaft houses the counter driven gear and the final drive gear Lastly, the third shaft is equipped with the differential ring gear and the differential gear unit.
- The engine, MG1, and MG2 are interconnected mechanically through the compound gear unit.
- The compound gear system comprises of a planetary gear unit for motor speed reduction and a power distribution planetary gear unit The motor speed reduction planetary gear unit serves the purpose of decreasing the motor speed, allowing the high-speed, high-output MG2 to seamlessly integrate with the power distribution planetary gear unit The power distribution planetary gear unit divides the engine's driving force into two directions: one to propel the wheels and the other to drive the MG1, enabling its operation as a generator.
- The output shaft of MG2 is connected to the sun gear in the motor speed reduction planetary gear unit, while the carrier remains stationary.
Figure 2.3 The gear box of hybrid vehicles
Power Split Planetary The No of Ring Gear Teeth 78
The No of Pinion Gear Teeth 23
The No of Sun Gear Teeth 30
Motor Speed Reduction The No of Ring Gear Teeth 57
The No of Pinion Gear Teeth 18
The No of Sun Gear Teeth 23
Counter Gear The No of Drive Gear Teeth 54
The No of Driven Gear 55
Final Gear The No of Drive Gear Teeth 23
The No of Driven Gear 80
Oil Capacity - Liters (US qts, Imp qts) 3.8 (4.0, 3.3)
Oil Type Toyota Genuine ATF WS
Table 2.2 Gear Box specifications 2.1.3 MG1 and MG2
- Both MG1 and MG2 are characterized by their compact size, lightweight construction, and exceptional efficiency as 3-phase AC permanent magnet synchronous electric motors.
- The functions of the MG1 and MG2 combine highly efficiently both the AC synchronous generator and the electric motor The MG1 and MG2 act as a source of traction assistance to the gasoline engine when needed.
- MG1 is responsible for recharging the high voltage battery (HV Battery), and during the time supplying power to drive the MG2 (Motor Generator 2) MG1 operates as a motor to initiate the car's main engine while controlling the gear ratio of the planetary gear train almost like a CVT.
- MG2 is responsible for driving the wheels to actively move forward or reverse the vehicle During deceleration and braking, the MG2 (Motor Generator 2) acts as a generator and absorbs kinetic energy (also known as regenerative braking) converting it into electricity to recharge the battery HV.
- Both MG1 and MG2 employ a rotor design featuring a V-shaped, high-magnetic force permanent magnet This design maximizes the generation of reduction torque Additionally, they utilize a stator composed of a low core-loss electromagnetic steel sheet and high voltage resistant winding wire These design
17 elements enable MG1 and MG2 to achieve high output and torque within a compact structure.
Function Generate, Drive Front Wheels
Figure 2.4 Control system diagram MG1, MG2 2.1.4 Power Split Device
At the core of a Hybrid system lies a compact component known as a Power Split Device The PSD is a planetary gear set that shares the same structure as the planetary gear set found in automatic transmissions However, its operation is fundamentally different from that of a traditional automatic transmission.
The power divider consists of a specific configuration of planetary gears and their meshing arrangement The central gear in this arrangement is referred to as the sun gear, while the surrounding gears are known as the planetary gears The axes of the planetary gears are fixed to a component called the carrier, which rotates around the center of the sun gear All planetary gears are identical in size and equidistant from the center of rotation The outermost gear ring is called the ring gear, and it engages with the planetary gears.
Control Method
2.2.1 Operation mode of serries-parallel hybrid vehicle
The operating mode of the electric motor and internal combustion engine in a powertrain diagram of series-parallel hybrid depends on the charging state of the battery and the power required to move the vehicle When the car is decelerating or braking this power is negative, this part of the power is usually used for regenerative braking Hybrid vehicles are controlled according to the following operating modes:
- Electric Motor Mode: If the charging status of the high-voltage battery is above the minimum level (SOCmin) and the power demand is lower than the power that the battery can provide, the vehicle operates in electric motor mode.
- Hybrid Mode: If the power output of either of the two motors is insufficient to propel the vehicle or if the charging status of the high-voltage battery is below the minimum level, and it is not in the region of highest efficiency for internal combustion engine usage, the ICE and electric motor work together to provide the required power In this mode, the ICE operates in the region near the highest efficiency, while the electric motor supplies the remaining power.
- Internal Combustion Engine Mode: If the charging level of the high-voltage battery is below the minimum threshold (SOCmin), the internal combustion engine provides additional power to charge the battery and propel the vehicle In this mode, the electric motor functions as a generator, supplying regenerative braking energy to recharge the battery The generator's torque is controlled to ensure that the ICE operates in the optimal efficiency region.
- Regenerative Braking: When the vehicle decelerates, the power demand becomes negative, and the charging status of the high-voltage battery is below the maximum level while being lower than the power that can be supplied by the generator, the surplus power is stored in the battery through regenerative braking.
- Hybrid Braking: If the power demand becomes negative during deceleration or braking, the charging status of the high-voltage battery is below the maximum level, and the power required for significant deceleration exceeds the maximum power that can be supplied by the generator, a portion of the power is stored through regenerative braking, while another portion of the power is dissipated through mechanical braking.
- Mechanical Braking: When the power demand is negative, and the charging status of the high-voltage battery has reached its maximum level, only the mechanical braking system is utilized.
By defining the various operating modes, it becomes possible to develop control strategies The control strategies for these configurations are designed based on a reference state, which is typically the hybrid drive mode This reference state serves as a basis for determining the activation conditions of other operating modes It is important to consider the deactivation conditions as well, as they define the transition from the reference state to other modes of operation.
The basis for battery control is that the battery capacity must be greater than the minimum to serve other jobs when not participating in the powertrain For purposes:
- Raising other systems: signal lights, door locks, glass lifting, brake booster, airbag
- The battery needs to be charged when its capacity is less than a certain allowable level.
In this thesis, the threshold values for controlling battery charging are as follows:
- The battery is charged when the capacity is less than 50%
- If the capacity of the battery is >, the generator will not work
- If the capacity is from 50 to 90%, extract 20% of the motor's torque to charge the battery
- Battery capacity > 90% is charged only when going downhill and when braking lightly.
Selection of simulation methods to study the Series – Parallel Hybrid
2.3.1 The simulation method involves establishing a mathematical model to simulate the operation of a hybrid powertrain system with a Series - Parallel configuration.
Figure 2.22 presents a schematic diagram illustrating the powertrain system of a parallel- series hybrid car.
Figure 2.33 Diagram of a series-parallel hybrid powertrain system
The series-parallel hybrid powertrain system diagram is widely used in hybrid vehicles. This diagram typically employs a power split device, such as a planetary gear set, to divide the power flow from the internal combustion engine into two components The first component directly drives the primary drive axle, while the second component drives the generator (St/G).
The engine shaft is connected to the carrier of the power split device The sun gear is connected to the rotor of the generator (St/G) The ring gear is connected to the drive wheels through a gear reduction box with a transmission ratio of u, and it is also connected to the output of the traction motor (G/M) through a reduction gear PR with a transmission ratio of um The planetary gear reduction box (PR) ensures the reduction of rotational speed and the increase of torque of the electric motor to optimize the characteristics of the electric motor with the vehicle's driving speed mode In some hybrid vehicle configurations, the transmission ratio of the PR gear reduction box can be varied according to the driving mode.
When constructing a mathematical model to describe the dynamics of the system in different modes, the elasticity of the powertrain system and the wheel slip are neglected. The influence on the powertrain system, vehicle, and road is accounted for through variations in the resistive force of motion.
Depending on the wheel drive conditions, the power can be delivered to the drive wheels from the electric motor, drawing energy from the battery and the generator (St/G), from the internal combustion engine, or from a combination of the internal combustion engine and the electric motor, in parallel mode and with different power levels The distribution of power from the internal combustion engine in this type of powertrain system is directly controlled by the power split device The relationship between the rotational speeds of these components is described by the Villis formula [15].
With: : The teeth of ring gear
: The teeth of sun gear
: The angular velocity of the sun gear
: The velocity of the crankshaft
: The angular velocity of the ring gear
The rotational speed of the traction motor rotor, , is related to the rotational speed of the carrier ring of the planetary gear set, PD, as follows:
When there is no PR (planetary gear reduction) in the hybrid powertrain system diagram:
The torque on the planetary gear stages is related as follows:
: The component of torque from the internal combustion engine transmitted to the sun gear of the planetary gear mechanism PD.
= ( , ) - The torque resistance of the generator (acting on the sun gear)
: The current intensity of the generator
: The number of gears connects with carrier
The G/M (Generator/Motor) unit is an electric machine that can operate in two modes: generator mode and motor mode In generator mode, it can generate the necessary braking torque during the vehicle's braking process while also regenerating braking energy An important characteristic of the considered diagram is the absence of a clutch. The motion when the clutch is disengaged corresponds to the generator's no-load mode, where there is no power transmission from the engine to the drivetrain or to the generator.
According to the kinematic diagram, the speed of the electric generator's rotor is related to the rotational speed of the driven wheel by the following relationship:
When there is no wheel slip, the vehicle's velocity is determined as follows:
The hybrid powertrain system with a planetary power split device, in the case of straight-line motion with non-zero differential input torque, forms a two-degree-of-freedom system By using the D'Alembert's principle, we can write the force equilibrium equation for the system When Mg is not equal to zero, this equation takes the following form:
: The total moment of inertia of the rotating masses in the system leads to the crankshaft.
: The total moment of inertia of the rotating masses in the system is transferred to the rotor shaft of the traction motor.
Are the coefficients characterizing the properties of the power split device PD:
The total moment of inertia can be determined from the energy balance condition of the rotating masses and the kinetic energy of the moving masses, as follows:
Where: : The inertia moment of generator ‘motor
When = 0, there is no power transmission from the engine to the driving wheels or to the generator In this case, the dynamic equilibrium equation takes the following form:
2.3.1 The simulation method involves establishing a mathematical model to
Simulation with specialized software
To simulate the operation of hybrid cars can use many different software such as AVL- cruise, GT power, Advisor, MATLAB The simulation with the help of the software allows us to select the parameters There are a number of hybrid car designs that fit the requirements without the need for a real model Each software has different strengths and limitations.
Because MATLAB provides sample models for simulation and has a rich library for describing objects using Simscape, it allows users to build additional custom blocks using Simulink based on the system's differential equations describing motion Utilizing pre- existing models and functional blocks, along with user-defined functional blocks, makes the simulation of simple systems more straightforward, intuitive, and reduces the time required to build a complete set of differential equations describing the entire system. Therefore, in this thesis, the author chose MATLAB software with Stateflow, Simulink, and Simscape modules as simulation tools.
Modeling and Simulation HEV with MATLAB/Simulink software
Modeling Series – Parallel HEV
To build a block model of a hybrid vehicle, usually, people will divide the model into many separate small blocks With Simscape, the HEV model include the following block:
- Electrical block (including electric motor, generator, converter and battery).
Figure 3.1 Hybrid vehicle model in Simulink using Simscape.
In series – parallel HEV, ICE and generator are the two main components of hybrid transmission.
The engine block uses the controller block's (T) signal from the accelerator pedal as an input to calculate the engine's required torque, and the result is the engine's power (P) and fuel consumption (FC).
Many different kinds of models have been created for many different reasons due to the complexity of the ICE work process The model described in this part is only applicable to the performance study of the hybrid vehicle system, and it only covers the input-output static mechanical characteristics of an ICE Below is a discussion of the models that correlate to these states.
When starting, the starter must overcome the engine torque in order to operate the engine together with the drive shaft clutch.
Based on Newton's rule of motion, the engine model in this state can be created as follows [2]:
+ τ crank - is the required torque to start the engine
+ J eng - is the engine’s inertia (kg.m2)
+ ω eng - is the shaft angular velocity of the engine (rad/s)
+ τ access - is the lumped torque from the mechanical accessories requiring constant torque (N ã m)
+ τ cct - is the closed-throttle torque of the engine (N.m).
When the engine is off, there is negative torque that acts as a brake If the car is running at this time, the drive shaft clutch is engaged, and the engine is described by the equations.
P acc - is the lumped power from the mechanical accessories requiring constant power (W). ω shaft - is the speed of the engine shaft transmitted from the vehicle.
When the engine is on and the drive shaft clutch is engaged, the engine provides propulsion torque and can be described by the equations [2]:
+ J eng - is the engine inertia
+ τ demand - is the vehicle demand torque
+ ω - is the engine angular velocity (rad/s)
+ max(trq eng ) = f (ω) is the engine physical maximum torque
Electrical block includes electrical motor, generator, converter, and battery.
Figure 3.4 Structure of Electrical block
The task of the electrical block is based on the input torque signals distributed by the controller block, to calculate the power consumed by the motor and the charging power for the high-voltage battery. a Battery model
A battery pack is made up of numerous cells that are connected in series, parallel, or both depending on the output voltage, power, and energy capabilities needed by the specified hybrid vehicle system.
Usually, the relationship between the current and voltage seen at the battery terminals is modelled using an electrical circuit Based on the battery's ampere-hour capacity, self- discharge, and charge/discharge efficiency, the battery system's state of charge can be estimated.
SOC Calculation: SOC is the ratio of current charge to rated battery capacity, and battery SOC can be described by the equation
+ Q 0 is total power that can be discharged from the battery when fully load b Electric motor
- Proplusion mode: When a motor is in this mode, it provides propulsion torque, and its operation can be calculated by the equations [2]. o Output torque
= ( , ) o Motor voltage = o Motor required current
+ J mot - is the motor’s inertia,
+ τ mot - is the propulsion torque provided by the motor (Nm),
+ τ spin_loss - is the lost torque due to friction (Nm),
+ τ demand - is the demand torque from the vehicle (Nm),
+ ω - is the motor’s angular velocity (rad/s),
+ max(τmot) = f (ω) is the motor’s physical maximum torque, α1, α2, and α3 are the static friction coefficient, viscous friction coefficient, and Coulomb friction coefficient, respectively, which can be estimated based on test data,
+ η mo t - is the lumped efficiency of the motor, inverter, and controller which may be a look-up table set up based on the test data,
+ V bus - is the high-voltage bus voltage.
- Regenerative mode: motor like a generator, provide torque for the vehicle when brake This operation follows the equations [2]. o Brake torque
+ J mot - is the motor’s inertia,
+ τ regen - is the motor’s negative brake torque (Nm),
+ τ demand - is the demand torque from the vehicle (Nm),
+ ω - is the motor’s angular velocity (rad/s), max(τregen) is the motor’s maximum regenerative torque,
+ η mot - is the regenerative lumped efficiency of the motor, inverter, and controller.
The required traction power is provided by an internal combustion engine and an electric motor for parallel hybrid and series-parallel hybrid drivetrains.
PSD adds the power from ICE and EM together The two main types of mechanical coupling are torque coupling and speed coupling. a Torque coupling
In this instance, the coupler delivers the whole torque to the driven wheels by combining the ICE and EM torques It is possible to individually control the ICE and EM torque.
Due to the power conservation limitation, the ICE, EM, and vehicle's speeds are linked in a set connection and cannot be separately altered The torque coupling is a two-degree- of-freedom mechanical device Ports 2 and 3 are bidirectional input or output ports, although they cannot both be input simultaneously Port 1 is a unidirectional input port.
Here, input and output refer to the flow of energy into and out of the device, respectively.
In the case of a HEV, port 1 is directly or mechanically linked to the ICE shaft, port 2 is directly or mechanically linked to the electric motor shaft, and port 3 is mechanically linked to the driven wheels.
The power balance is defined by the Equation (3.27):
+ T 1 - propelling torque produced by ICE
+ T 2 - propelling torque produced by electric motor
The torque coupler can be expressed as:
Because all torques are connected and cannot be changed individually, the electric motor and generator can be combined.
The electric motor's outputs can be formed together by speeding it up And the speed coupler is formed by 3 ports with 2 degrees of freedom
[11] Port 1 is a unidirectional input and port 2 and 3 are bi-directional input or output, but both are not input at the same time In this context, input and output refer to the energy flowing into and out of the respective devices, respectively.
For a losses speed coupler in steady state, the power input is always equal to the power output from it [11].
[11] The speed and torque in speed coupling relation are:
+ k 1 , k 2 are the structural parameters of the speed coupling device
Figure 3.7 Simulink model for planetary gear set speed coupling device
Regarding the PSD model: The planetary gear consists of three main components:
- The electric motor is coupled to the sun gear.
- An internal combustion engine fitted with a planet gear
- Ring gear that resembles the output to the rear axle
The planetary gear train can produce a range of speed reduction ratios depending on which shaft is driving, driven, or fixed These ratios rely on the sun and ring radii as well as the tooth counts.
The vehicle motion results from the net effect of all the forces and torques acting on it. Longitudinal tire forces drive the car either forward or backward The vehicle's center of gravity works as a conduit for the weight The weight pulls the vehicle to the ground and pushes it in one of two directions, depending on the slope of the incline The vehicle slows down due to aerodynamic drag, whether it is moving forward or backward For simplicity, it is believed that the drag operates via the CG.
The vehicle dynamics are described by the following equations [11]. ̇ = − − (3.31)
2 o Normal load forces on each wheel at the front
= ( + ) (3.34) o Normal load forces on each wheel at the right
+ h: height of vehicle center of gravity (CG) above the ground.
+ a, b: distance of front and rear axles, respectively, from the normal projection point of vehicle CG onto the common axle plane.
+ Vx: velocity of the vehicle.
+ N: number of wheels on each axle.
+ Fxf, Fxr: longitudinal forces on each wheel at the front and rear ground contact points, respectively.
+ A: effective frontal vehicle crosssectional area.
+ Cd: aerodynamic drag coefficient; ρ: mass density of air.
Figure 3.8 Free body diagram of vehicle
[11] In order to model vehicle dynamics and motion, a Simulink model was built, in which there are six ports.
Two input ports: W -Headwind speed, beta - Road incline angle.
Three output ports: V - longitudinal velocity, NF - Front axle normal force, NR - Rear axle Normal force and a conserving port H associated with the horizontal motion of the vehicle body.
Connect tire traction motion to H port.
Figure 3.9 Vehicle Block 3.2.1.5 Control Logic
For the series – parallel HEV, there are six driving mode [11]:
- Startup or light load: The ICE is off, and the battery provides power to the motor
- Normal driving or full thorttle acceleration: the ICE and motor will work.
- During braking or deceleration: The energy generated by ICE is divided into 2 parts, one part is to keep the vehicle drive, the other part is supplied to the generator to recharge the battery even when stopping
The core of this control method is the Model Logic subsystem, a state machine or a Stateflow (a MATLAB tool) logic controller that switches between modes according to driving circumstances The output of this state machine is sent to three distinct subsystems that regulate the engine, generator, and motor.
The Stateflow logic demonstrates how modes are switched, including the start mode, normal mode, accelerate mode, and cruise mode inside normal mode.
The battery charge is monitored and managed by a different subsystem The engine control subsystem is fundamentally a PI controller, and its output regulates the engine's throttle position.
The torque requirement from the engine is produced by the generator subsystem, which also functions as a PI controller.
The motor control subsystem is similar to a PI controller that determines the motor torque demand.
Chapter 4: MATLAB SIMULATION RESULTS 4.1 Vehicle simulation parameters
Engine (2AZ-FXE) Max output 110 kW @ 6000 rpm
Motor (MG2) Maximum System DC 650 V
Generator (MG1) Maximum System DC 650 V
Battery (Nikel-metal hybride) Nominal Voltage 244.8 V
Table 4.1 Vehicle simulation parameters 4.2 Driving cycle test
4.2.1 The UN/ECE Extra-Urban Driving Cycle (Low Powered Vehicles) is an alternative for Low-Powered Vehicles
MATLAB SIMULATION RESULTS
Driving cycle test
4.2.1 The UN/ECE Extra-Urban Driving Cycle (Low Powered Vehicles) is an alternative for Low-Powered Vehicles
The UN/ECE Extra-Urban (Low Powered Vehicles) Cycle (ECE-EULP) serves as an alternative test cycle for Part 2 of the ECE Type 1 Test specifically designed for low- powered vehicles (https://dieselnet.com).
4.2.2 The Highway Fuel Economy Driving Schedule (HWFET)
The US EPA (Environmental Protection Agency) established the Highway Fuel Economy Test (HWFET or HFET) cycle, a driving schedule used on a chassis dynamometer to assess the fuel efficiency of light-duty cars The HWFET was created primarily to evaluate a vehicle's fuel efficiency while travelling on a highway It is one of the tests used to determine a vehicle's rating for highway fuel efficiency The FTP-75 (Federal Test Procedure-75) test, which simulates urban driving circumstances, is used to get the city fuel economy rating (https://dieselnet.com).
To better reflect actual results, the figures were adjusted downward by 10% (city) and 22% (highway)
4.2.3 The Japanese 10.15 Mode Driving Schedule for Exhaust Measurement and Fuel Economy Test Procedure
For evaluating light duty vehicle pollutants and fuel economy, the 10-15 mode cycle had been utilized in Japan.
A 15 minute warm-up at 60 km/h, an idle test, a 5 minute warm-up at 60 km/h, one 15- mode segment, three repetitions of 10-mode segments, and one 15-mode segment make up the whole cycle The final four parts are used to measure emissions (3×10-mode + 1×15-mode) (https://dieselnet.com).
Results of simulation
4.3.1 Results of the UN/ECE Extra-Urban Driving Cycle (Low Powered Vehicles)
Figure 4.1 Simulated velocity in UN/ECE Extra-Urban Driving Cycle
Based on the standard cycle of ECE, a test cycle was constructed in the thesis for vehicle simulation By simulating the operation of a hybrid vehicle according to the UN/ECE Extra-Urban test cycle, various parameters describing the vehicle's operation can be obtained These parameters include the car's acceleration, power requirements of the electric motors and internal combustion engine at each stage of the cycle, variations in the state of charge of the battery, working parameters of the electric motors/generators, internal combustion engine, power distribution, and more.
The calculated results of the vehicle's acceleration variation when operating according to the UN/ECE Extra-Urban test cycle are described in the figure below The simulation results show that the required acceleration of the vehicle at each stage of the test cycle varies according to the velocity change pattern.
Figure 4.2 Simulated acceleration in UN/ECE Extra-Urban Driving Cycle
Figure 4.3 Evaluated the modes of hybrid vehicle in UN/ECE Extra-Urban Driving Cycle
+ Electric motor mode: Corresponding to stages 2-3 and 12-13, during these stages, the required power to maintain motion is low, corresponding to the vehicle speed
< 50 km/h In these stages, the battery supplies energy for the electric motor, and the battery capacity decreases.
+ Internal combustion engine mode: Corresponding to stages 4-5, 6-7, 8-9, 10-11.
During these stages, the internal combustion engine maintains a steady speed of the vehicle, and a portion of the power is used to drive the MG2 generator to operate in generator mode and charge the battery The battery charging level increases during these stages of stable motion.
+ Hybrid mode: Corresponding to stages 3-4, 7-8, 9-10; this mode occurs when the vehicle accelerates from a speed of 50 km/h or higher At this time, the battery supplies energy to the electric motor, resulting in a decrease in the battery charge level.
+ Regenerative braking mode: Corresponding to stages 5-6, 11-12, 13-14; this mode occurs when the vehicle decelerates from a speed of 15 km/h or higher At this time, the battery supplies energy to the electric motor, resulting in a decrease in the battery charge level.
Figure 4.4 Fuel consumption in UN/ECE Extra-Urban Driving Cycle
The post-cycle simulation displays various scopes and parameters, including total fuel usage, by utilizing the fuel consumption table and a subsystem that calculates the fuel
76 economy over the complete cycle This allows for an analysis of the overall fuel efficiency and consumption of the vehicle during the simulated cycle.
4.3.2 Results of the Highway Fuel Economy Driving Schedule
Figure 4.5 Evaluated the modes of hybrid vehicle in Highway Fuel Economy Driving Schedule
− The Highway Fuel Economy Driving Schedule is a simulation of the operation of
78 the vehicle on a highway, where most of the time the vehicle operates at high speeds (>40 km/h) To meet the conditions on the highway, the vehicle primarily operates in hybrid mode.
− This is reflected in the simulation results, where we can observe that the power from the internal combustion engine and the electric motor is always positive when accelerating or maintaining high speeds In cases where the vehicle needs to decelerate or brake, it relies solely on the power from the electric motor to recharge the battery.
Figure 4.6 Fuel consumption in the Highway Fuel Economy Driving Schedule
4.3.3 Results of the Japanese 10.15 Mode Driving Schedule
Similarly, to the UN/ECE Extra-Urban Driving Cycle, when simulating the operation of a hybrid vehicle using the Japanese 10.15 Mode Driving Schedule, several results are obtained and represented through the following graphs:
- The data of motor and generator
Figure 4.7 Simulated velocity in the Japanese 10.15 Mode Driving Schedule
Figure 4.8 Simulated ICE in the Japanese 10.15 Mode Driving Schedule
- From the simulated graph of the engine speed, we can observe that the engine speed varies, either increasing or decreasing, in response to the vehicle's speed demand.
- Similarly, the simulated graph of the engine torque also reflects this behavior When the vehicle needs to accelerate to achieve higher speeds, the internal combustion engine provides increasing torque to attain the desired velocity Once the desired speed is reached and no additional torque is required, the graph of the engine torque remains constant at a specific value.
- The graph of the throttle position exhibits a similar trend to the speed graph, indicating that when the throttle position is large, the vehicle's speed also increases, and vice versa.
Figure 4.9 Simulated motor in the Japanese 10.15 Mode Driving Schedule
- The torque of the motor (MG2) can have both positive and negative values The positive values represent the process of providing pulling torque by the motor, while the negative values indicate the motor using torque to charge the battery.
- The motor speed is proportional to the vehicle speed (the simulated graph of vehicle speed and motor speed are similar) because the motor is directly connected to the steering wheel through a motor speed reduction planetary gear unit.
Figure 4.10 Simulated generator in the Japanese 10.15 Mode Driving Schedule
- From the graph, we can observe that the operation of the generator is relatively limited, which is attributed to the effective performance of regenerative braking The generator speed is maintained below 12,000 rpm The positive torque represents MG1 supplying power, while the negative torque represents MG1 recharging the battery.
Figure 4.11 Fuel consumption in the Japanese 10.15 Mode Driving Schedule
Manufacturer's specifications 40 MPG (5.8 l/100km) UN/ECE Extra-Urban Driving Cycle 4.127 l/100km
Highway Fuel Economy Driving 4.6 l/100km Schedule
According to the manufacturer's data, the fuel consumption figures for the 2007 ToyotaCamry Hybrid under city and highway driving conditions are 40 MPG (approximately5.8 l/100km) and 38 MPG (approximately 6.2 l/100km), respectively When comparing these figures to the simulation results obtained for the type 1 (city driving) and type 2(highway driving) cycles, there is an approximate difference of 1.7 l/100km for city conditions and 1.6 l/100km for highway conditions This difference could be attributed to the operating conditions of the vehicle during the manufacturer's testing being more stringent compared to the simulation conducted on Matlab Factors such as friction losses between mechanical components could contribute to this variation…
CONCLUSION
Comment
The main purpose of this study is to present a brief overview of the basic knowledge of structure of series-parallel hybrid vehicles Understanding the principle of power division between internal combustion engine and electric motor Calculating and simulating fuel consumption efficiency on series-parallel hybrid vehicles Based on the research conducted in this study, it can be concluded that the simulation of fuel consumption for hybrid vehicles using MATLAB has provided valuable insights into the fuel efficiency of hybrid powertrains The simulation results have demonstrated the ability to evaluate and analyze the fuel consumption characteristics of hybrid vehicles under various driving conditions and operational modes.
Through the MATLAB simulation, the fuel consumption of the hybrid vehicle was assessed in different scenarios, including urban driving cycles, highway driving, and mixed driving conditions Furthermore, the simulation has enabled the investigation of the impact of various factors on fuel consumption, such as battery state of charge, regenerative braking efficiency, and power distribution between the internal combustion engine and electric motor It is important to note that the simulation results are relative and may not perfectly reflect real-world driving conditions and vehicle performance.
In conclusion, the research study utilizing MATLAB simulation for fuel consumption analysis of hybrid vehicles has provided valuable information and insights into the fuel efficiency of hybrid powertrains The findings contribute to the understanding of the factors influencing fuel consumption and can be utilized to optimize hybrid powertrain designs and control strategies for enhanced fuel economy in real-world driving conditions.
Research and Development Directions
The research topic can be further developed in several directions to expand its scope and contribute to the field:
- Emission Analysis of Hybrid Vehicles: Investigate the emission levels of hybrid vehicles under different operating modes, such as electric mode, hybrid mode, and conventional mode Analyze the impact of driving conditions, powertrain configurations, and control strategies on emissions, including greenhouse gases and pollutants Explore ways to minimize emissions and improve the environmental performance of hybrid vehicles.
- Future Hybrid Technologies: Explore emerging technologies and advancements in hybrid systems, such as advanced energy storage systems, power electronics, and regenerative braking systems Investigate the potential
84 of new hybrid architectures, such as hybrid electric turbos, range extenders,and fuel cell hybrids Evaluate the benefits and challenges of integrating these technologies into hybrid vehicles and their impact on performance, efficiency,and sustainability.
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