INTRODUCTION
Overview of Topic
1.1.1 The reason to choose this topic
The rapid increase in road vehicles has significantly worsened air pollution, particularly in urban areas, prompting governments to implement stringent regulations on fuel consumption and emissions to enhance air quality This regulatory pressure has driven automakers to invest in environmentally friendly technologies, including electric vehicles However, challenges such as limited battery capacity, short lifespan, bulky components, lengthy charging times, and high costs have restricted the widespread adoption of electric motors as a primary power source, confining their use to specific applications.
To enhance the benefits and address the challenges of electric motors in vehicles, scientists have developed hybrid vehicles that combine electric motors with internal combustion engines Hybrid powertrains are categorized into three types: series, parallel, and series-parallel Regardless of the configuration, a hybrid system comprises essential components, including an internal combustion engine, an electric motor, a generator, and a high-voltage battery Our research focuses on the topic: “Application of MATLAB in fuel consumption simulation of series-parallel hybrid vehicles,” to explore how hybrid vehicles can effectively reduce fuel consumption.
- 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
Researchers Mohamed Awadallah, Peter Tawadros, Paul Walker, and Nong Zhang explored the dynamic modeling and simulation of a mild hybrid vehicle featuring a manual transmission Their study involved integrating a powertrain with a manual gearbox and an electric motor as a secondary power source to develop a mild hybrid powertrain They compared the dynamic performance of conventional and lightweight hybrid systems using mathematical models, which facilitated various simulations for the gearshift control algorithm design This approach allowed the researchers to evaluate expected performance outcomes and understand the influence of the system's characteristics on overall efficiency.
Pham Quoc Thai and Huynh Duc Tri conducted a study on "Modeling and simulating electric vehicle powertrain," focusing on a 5-seater electric car They developed models for inverters, asynchronous motors, and dynamic load characteristics using Matlab/Simulink software The study analyzes key response parameters of the asynchronous motor, including speed, torque, and amperage on the stator and rotor, in relation to varying terrains The simulation results demonstrate that the transmission system operates with high accuracy, stability, and efficiency, showcasing excellent dynamics.
Master Huynh Quoc Viet has conducted research on the application of fuzzy logic in regenerative brake control for hybrid electric vehicles This innovative approach optimizes the integration of mechanical and electric braking systems The brake torque controller was designed and simulated using Simulink/Matlab, and tested on the widely recognized European New Combined Test Cycle (NEDC) The project yielded promising results, demonstrating the effectiveness of fuzzy logic in enhancing brake performance.
The study reveals that the actual desired speed of the vehicle closely aligns with the calculated simulation speed, indicating a high efficiency in performance The regenerative braking system effectively recovers energy, with a significant ratio of regenerative braking torque to the required braking torque During the NEDC cycle, the battery maintains an optimal charge status, while the torque motor operates in negative regions, functioning efficiently as a generator Overall, the hybrid electric vehicle demonstrates impressive regenerative energy recovery, with the regenerative brake controller maximizing energy recovery while ensuring safe braking.
Nguyen Ngoc Dam's article discusses the principles of energy recovery in hybrid and electric vehicles, focusing on the complexities of designing a brake energy recovery system It highlights two key challenges: effectively distributing total braking force between regenerative and frictional braking to maximize energy recovery, and ensuring balanced braking force across the front and rear axles for stability and efficiency Regenerative braking is primarily effective on the active axle, necessitating precise control of the electric motor to optimize energy recovery while aligning with the driver's braking commands To address these challenges, the hybrid brake system is categorized into two main types: the parallel hybrid braking system and the fully controlled hybrid braking system.
Overview of HEV
Since its establishment in the 18th century, the automobile has become essential to human development, addressing economic challenges and facilitating the transport of goods The rapid growth of the auto industry has led to numerous innovations and scientific advancements in vehicles Initial research focused on enhancing engine power, optimizing gearboxes, improving vehicle safety, and addressing environmental concerns However, as car usage continues to rise globally, the pressing issues of fuel consumption and environmental impact have emerged, necessitating urgent attention and solutions.
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
While hybrid cars have addressed energy consumption and environmental concerns, researchers are actively seeking alternative energy sources to replace internal combustion engines (ICE) Various solutions, including hydrogen, natural gas, and biodiesel engines, have been suggested However, the complexity and limited feasibility of these options have led many automakers to continue relying on hybrid technology.
Figure 1.2 Toyota Camry Hybrid 1.2.1 Working Principle of Hybrid Vehicle
Hybrid vehicles utilize an electric motor for low-speed driving, while the internal combustion engine activates during acceleration to power the electric motor and drive the wheels During deceleration and braking, the electric motor acts as a generator, converting kinetic energy to recharge the battery This combination of an internal combustion engine and electric motor allows hybrid engines to operate at higher temperatures, improve fuel efficiency, generate more torque at lower revolutions, and minimize environmental pollution.
Figure 1.3 Working principle of Hybrid Vehicle
The wheels transfer kinetic energy to the generator via the drivetrain, while the resistance from the generated electricity slows the vehicle down Although friction brakes provide extra braking torque when needed, the generator alone cannot offer this additional braking force.
In this architectural design, the driving electric motor (EM) exclusively connects to the wheels, while the MG2 acts as a generator, converting mechanical energy into electrical energy This energy is then utilized to either power the MG1 for vehicle propulsion or assist in charging the battery.
This design facilitates the management of an internal combustion engine's operating mode, identifies the optimal efficiency zone for the engine, and ensures that the engine consistently operates within this zone for maximum performance.
Integrating two extra electric motors increases both the weight and cost of the vehicle, while the efficiency of the hybrid series diminishes due to multiple energy conversions occurring between the internal combustion engine and the wheels.
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 advantages of parallel architecture stem from its resemblance to traditional vehicle designs However, this similarity leads to notable increases in volume, weight, and cost Additionally, the direct coupling of the combustion engine to the wheels complicates its operation, making it more challenging to optimize for its intended performance range.
The Series-Parallel architecture, featuring dual power coupling, merges the advantages of both parallel and series architectures, resulting in enhanced efficiency This innovative design offers superior control over the internal combustion engine, battery, and overall power management.
While this system offers enhanced engine control, it comes with drawbacks, including its large and heavy design due to the inclusion of two electric machines and two connecting systems Additionally, it poses greater challenges in terms of control compared to previous 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 systems, the rotation speed of the TDC operates independently of the vehicle's speed, enabling excavators to function in modes that are optimized for fuel efficiency and reduced emissions.
- Reusing the car's kinetic energy during braking and downhill
The EDC should be disabled in specific situations, including waiting at red lights, idling, and driving downhill Additionally, many current hybrid vehicle models are priced higher than traditional internal combustion engine (ICE) vehicles.
Hybrid cars typically utilize high-end electrical equipment to guarantee essential technical features, compact dimensions, and longevity, which often results in increased costs Additional considerations regarding hybrid vehicles have also been discussed.
The manufacturing sector for high-quality electrical equipment in hybrid vehicles relies heavily on unique materials derived from rare earth elements Currently, China supplies more than 90% of the world's rare earth resources, highlighting its dominant role in this critical industry.
- The problem of the life of the propulsion system:
Modern hybrid vehicles often disable the internal combustion engine (ICE) during specific conditions, such as idling at red lights, braking, descending hills, or driving at low speeds Consequently, the ICE in hybrids experiences more frequent shutdowns and restarts compared to traditional ICE vehicles This operational pattern can potentially shorten the lifespan of the actuator due to inadequate lubrication and suboptimal temperature conditions immediately following engine restarts.
- 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
The THS ECU gathers data from various sensors and the ECU, including the battery smart unit, skid control ECU, and MG ECU, to calculate the necessary torque and output power.
- 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 This control
13 mechanism allows for the operation of MG1 and MG2 as either generators or motors, based on the specific requirements of the system
The Battery Smart Unit in hybrid vehicles continuously monitors the high-voltage battery's status, tracking essential parameters like voltage, current, and temperature This critical data is relayed to the hybrid vehicle control ECU, enabling comprehensive analysis and informed decision-making for optimal vehicle performance.
- 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
The DC/DC converter plays a crucial role in charging the high-voltage (HV) battery module and supplying power to essential components, including the audio system, air conditioning system (excluding the electric inverter compressor), and electronic control units (ECUs).
The Toyota 2AZ-FXE engine is a 2.4-liter inline 4-cylinder powertrain known for its lightweight aluminum block and thin cast-iron cylinder liners It features a 16-valve DOHC aluminum head with four valves per cylinder, incorporating two intake and two exhaust valves This engine is equipped with an EFI electronic fuel injection system, a water-cooled system, and an oil-lubricated engine system Additionally, it includes a thermostat for rapid temperature regulation and complies with Euro 4 emission standards.
The 2AZ-FXE engine is a specialized variant of the 2AZ-FE, designed to lower emissions by optimizing the compression and expansion relationship While it maintains the same bore and stroke, it features unique intake cam and piston designs, resulting in a physical compression ratio of 12.5:1.
The large valve overlap in the 2AZ-FXE engine reduces cylinder charge, resulting in decreased torque and power output; however, it enhances efficiency This unique characteristic makes the engine ideally suited for hybrid vehicles, where the electric motor and battery can fulfill peak torque and power requirements.
Fuel consumption, L/100 km (for Lexus
Table 2.1 2AZ-FXE Engine Specification 2.1.2 Gear Box
The vehicle's hybrid transaxle features essential components such as MG1 (Motor Generator 1) and MG2 (Motor Generator 2), a compound gear unit that includes both a motor speed reduction planetary gear unit and a power split planetary gear unit, along with a counter gear unit and a differential gear unit.
The vehicle's transaxle features a three-shaft design, with the main shaft containing a compound gear unit that integrates both the motor speed reduction planetary unit and the power split planetary gear unit, alongside MG1 and MG2 The second shaft is responsible for housing the counter driven gear and the final drive gear, while the third shaft includes 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 features a planetary gear unit designed for motor speed reduction, which effectively lowers the motor speed to facilitate the integration of the high-speed, high-output MG2 with the power distribution planetary gear unit This power distribution unit efficiently splits the engine's driving force into two pathways: one directs power to the wheels for propulsion, while the other powers MG1, allowing it to function 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
The No of Ring Gear Teeth 78
The No of Pinion Gear Teeth 23
The No of Sun Gear Teeth 30
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 Teeth
Final Gear The No of Drive Gear Teeth 23
The No of Driven Gear Teeth
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 MG1 and MG2 systems efficiently integrate the functions of an AC synchronous generator and an electric motor, providing essential traction assistance to the gasoline engine when required.
MG1 plays a crucial role in recharging the high voltage battery (HV Battery) while simultaneously supplying power to drive MG2 (Motor Generator 2) It functions as a motor to start the vehicle's main engine and regulates the gear ratio of the planetary gear train, operating similarly to a continuously variable transmission (CVT).
MG2 plays a crucial role in propelling the vehicle forward or backward During braking and deceleration, MG2 functions as a generator, harnessing kinetic energy through regenerative braking to convert it into electricity, which is then used to recharge the high-voltage battery.
Both MG1 and MG2 feature a V-shaped rotor design with high-magnetic force permanent magnets, optimizing torque generation They also incorporate a stator made from low core-loss electromagnetic steel sheets and high-voltage resistant winding wire, enhancing overall efficiency.
18 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
A Hybrid system features a central component called a Power Split Device (PSD), which is a compact planetary gear set similar to those used in automatic transmissions Unlike traditional automatic transmissions, the PSD operates on a fundamentally different principle, enabling efficient power distribution between the engine and electric motor.
A power divider features a unique configuration of planetary gears, including a central sun gear and surrounding planetary gears The planetary gears are mounted on a carrier that rotates around the sun gear's center All planetary gears are identical in size and evenly spaced from the center of rotation Additionally, the outermost ring gear interacts with the planetary gears, completing the system's design.
Control Method
2.2.1 Operation mode of serries-parallel hybrid vehicle
The operation of the electric motor and internal combustion engine in a series-parallel hybrid powertrain is influenced by the battery's charge level and the vehicle's power demands During deceleration or braking, the power becomes negative, enabling regenerative braking to harness energy Hybrid vehicles function based on specific operating modes tailored to optimize performance and efficiency.
When the high-voltage battery's charge exceeds the minimum level (SOCmin) and the power demand is below the battery's capacity, the vehicle functions in electric motor mode.
In Hybrid Mode, both the internal combustion engine (ICE) and the electric motor collaborate to deliver necessary power when either motor's output is inadequate or the high-voltage battery's charge is low This synergy ensures that the ICE operates near its optimal efficiency, while the electric motor compensates for any additional power requirements, enhancing overall vehicle performance.
In Internal Combustion Engine Mode, when the high-voltage battery's charge falls below the minimum threshold (SOCmin), the internal combustion engine (ICE) assists by providing power to both charge the battery and drive the vehicle During this process, the electric motor acts as a generator, harnessing regenerative braking energy to replenish the battery The torque of the generator is carefully regulated to maintain the ICE's operation within its optimal efficiency range.
Regenerative braking captures excess energy when a vehicle slows down, converting the negative power demand into stored energy for the high-voltage battery This process occurs when the battery's charge is below its maximum capacity and the generator can supply more power than needed, allowing the surplus to be efficiently stored.
Hybrid braking systems utilize regenerative braking to store energy when deceleration power demand is negative, provided the high-voltage battery is not fully charged When the required deceleration power surpasses the generator's maximum output, excess energy is managed through mechanical braking, ensuring efficient energy use during 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
Defining various operating modes enables the development of effective control strategies, primarily based on a reference state, usually the hybrid drive mode This reference state is crucial for establishing the activation conditions for other operating modes Additionally, understanding the deactivation conditions is essential, as they dictate the transitions from the reference state to alternative 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 essential in hybrid vehicles, utilizing a power split device like a planetary gear set to manage power flow from the internal combustion engine This system divides the power into two key components: one directly powering the primary drive axle and the other driving the generator (St/G).
The engine shaft connects to the power split device's carrier, while the sun gear links to the generator's rotor (St/G) The ring gear interfaces with the drive wheels through a gear reduction box featuring a transmission ratio of u, and also connects to the traction motor's output (G/M) via a reduction gear (PR) with a transmission ratio of um The planetary gear reduction box (PR) effectively reduces the electric motor's rotational speed and enhances torque, optimizing the motor's performance based on the vehicle's driving speed In certain hybrid vehicle configurations, the PR gear reduction box's transmission ratio can be adjusted according to the selected driving mode.
In developing a mathematical model to analyze system dynamics across various modes, the elasticity of the powertrain and wheel slip are overlooked Instead, the model incorporates the effects on the powertrain, vehicle, and road by considering changes in the resistive force of motion.
The power delivery to the drive wheels in a hybrid powertrain system can originate from the electric motor, internal combustion engine, or a combination of both, depending on the wheel drive conditions This system operates in parallel mode with varying power levels, and the power distribution from the internal combustion engine is managed by a power split device The interaction between the rotational speeds of these components is defined by the Villis formula.
With: 𝑍 𝑅 : The teeth of ring gear
𝑍 𝑆 : The teeth of sun gear
𝜔 𝑔 : The angular velocity of the sun gear
𝜔: The velocity of the crankshaft
𝜔 𝑅 : The angular velocity of the ring gear
The rotational speed of the traction motor rotor, 𝜔 𝑀 , 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:
𝑀 𝑅 : The component of torque from the internal combustion engine transmitted to the sun gear of the planetary gear mechanism PD
𝑀 𝑔 = 𝑀 𝑔 (𝜔 𝑔 , 𝐼 𝑔 ) - The torque resistance of the generator (acting on the sun gear)
𝐼 𝑔 : The current intensity of the generator
𝑍 𝑐 : The number of gears connects with carrier
The G/M (Generator/Motor) unit is a versatile electric machine that functions in both generator and motor modes In generator mode, it effectively provides essential braking torque during vehicle braking while simultaneously regenerating energy Notably, this system operates without a clutch, allowing for a no-load mode where there is no power transmission from the engine to the drivetrain or the generator.
According to the kinematic diagram, the speed of the electric generator's rotor 𝜔 𝑀 is related to the rotational speed of the driven wheel 𝜔 𝐾 by the following relationship:
When there is no wheel slip, the vehicle's velocity is determined as follows:
The hybrid powertrain system, featuring a planetary power split device, operates as a two-degree-of-freedom system during straight-line motion with a non-zero differential input torque Applying D'Alembert's principle allows us to establish the force equilibrium equation for this system, which is modified when Mg is not equal to zero.
𝑗 𝑃𝑒 : The total moment of inertia of the rotating masses in the system leads to the crankshaft
𝑗 𝑃𝑚 : 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:
𝑢 𝑀 𝑢) 2 (2.18) Where: 𝑗 𝑔𝑛 : The inertia moment of generator ‘motor
When 𝑀 𝑔 = 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
Various software tools, including AVL-Cruise, GT Power, Advisor, and MATLAB, can be utilized to simulate the operation of hybrid cars These simulations enable the selection of specific parameters, allowing for the exploration of multiple hybrid car designs that meet requirements without the necessity of a physical model Each software option offers unique advantages and limitations, making it essential to choose the right tool for effective simulation.
MATLAB's rich library and sample models for simulation, along with Simscape's capabilities, enable users to create custom blocks in Simulink based on differential equations of motion By leveraging existing models and user-defined functional blocks, the simulation of simple systems becomes more intuitive and efficient, significantly reducing the time needed to formulate a comprehensive set of differential equations Consequently, this thesis utilizes MATLAB software, incorporating Stateflow, Simulink, and Simscape modules as the primary simulation tools.
Modeling and Simulation HEV with MATLAB/Simulink software
MATLAB/Simulink software
MATLAB, short for Matrix Laboratory, is a high-level programming language software designed for numerical computation and graphical design It enables users to perform data analysis and calculations through the use of matrices by entering commands via the "Command line."
"mfiles" containing the available commands
MATLAB can do the following things
- Automated Driving Systems: Design, simulate, and test automated driving systems
- Computational Biology: Analyze, visualize, and model biological data and systems
- Control Systems: Design, test, and implement control systems
- Data Science: Explore data; build machine learning models; do predictive analytics
- Deep Learning: Data preparation, design, simulation, and deployment for deep neural networks
- Electrification: Develop electrical technology from components to system
- Embedded Systems: Design, code, and verify embedded systems
- Enterprise and IT Systems: Use MATLAB with your IT
- FPGA, ASIC, and SoC Development: Automate your workflow — from algorithm development to hardware design and verification
- Image Processing and Computer Vision: Acquire, process, and analyze images and video for algorithm development and system
- Internet of Things: Connect embedded devices to the internet and gain insight from your data
- Machine Learning: Train models, tune parameters, and deploy to production or the edge
- Mechatronics: Design, optimize, and verify mechatronic systems
- Mixed-Signal Systems: Analyze, design, and verify analog and mixed-signal systems
- Predictive Maintenance: Develop and deploy condition monitoring and predictive maintenance software
- Robotics: Design, simulate, and verify robotics and autonomous systems
- Signal Processing: Analyze signals and time-series data Model, design, and simulate signal processing systems
- Test and Measurement: Acquire, analyze, and explore data and automate tests
- Wireless Communications: Create, design, test, and verify wireless communications systems
- Biological Sciences: Model, simulate, and analyze biological systems
- Earth, Ocean, and Atmospheric Sciences: Analyze and understand complex geological trends
- Neuroscience: Process and analyze data, drive experiments, and simulate models of brain circuits
- Physics: Control experiments, acquire and analyze data, and compare with simulations
- Container, Web, and Desktop Deployment
- Real-Time Simulation and Testing
Simscape is a powerful software tool that allows users to build physical system models within Simulink By leveraging the MATLAB language, Simscape users can develop physical models that seamlessly integrate with both standard and custom block diagrams This capability facilitates the text-based creation of comprehensive physics modeling libraries, domains, and components, enhancing the modeling experience.
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 calculates the required torque by using the (T) signal from the accelerator pedal provided by the controller block, resulting in the engine's power (P) and fuel consumption (FC).
Various models have been developed to address the complexities of the Internal Combustion Engine (ICE) work process This section focuses specifically on a model designed for the performance analysis of hybrid vehicle systems, emphasizing the static mechanical characteristics of ICE input-output relationships The following discussion will explore models relevant to these specific 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]:
+ τcrank - is the required torque to start the engine
+ Jeng - is the engine’s inertia (kg.m2)
+ ωeng - is the shaft angular velocity of the engine (rad/s)
+ τaccess - is the lumped torque from the mechanical accessories requiring constant torque (N ã m)
+ τcct - is the closed-throttle torque of the engine (N.m)
When the engine is turned off, negative torque functions as a braking mechanism If the car is in motion during this time, the drive shaft clutch remains engaged, and the engine can be analyzed using specific equations.
Pacc - is the lumped power from the mechanical accessories requiring constant power (W) ωshaft - 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]:
+ Jeng - is the engine inertia
+ τdemand - is the vehicle demand torque
+ ω - is the engine angular velocity (rad/s)
+ max(trqeng) = 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 electrical block's function involves processing input torque signals from the controller block to determine the power usage of the motor and the charging power for the high-voltage battery, utilizing a battery model.
A battery pack consists of multiple cells arranged in series, parallel, or a combination of both to meet the required output voltage, power, and energy specifications of a hybrid vehicle system.
The relationship between current and voltage at battery terminals is typically modeled using an electrical circuit By considering factors such as the battery's ampere-hour capacity, self-discharge rates, and charge/discharge efficiency, one can estimate the state of charge of the battery system.
SOC Calculation: SOC is the ratio of current charge to rated battery capacity, and battery SOC can be described by the equation
+ Q0 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
+ Jmot - is the motor’s inertia,
+ τmot - is the propulsion torque provided by the motor (Nm),
+ τspin_loss - is the lost torque due to friction (Nm),
+ τdemand - is the demand torque from the vehicle (Nm),
+ ω - is the motor’s angular velocity (rad/s),
The maximum torque of a motor, denoted as max(τmot) = f(ω), is influenced by various friction coefficients: static (α1), viscous (α2), and Coulomb (α3) These coefficients can be accurately estimated using test data.
+ ηmot - is the lumped efficiency of the motor, inverter, and controller which may be a look-up table set up based on the test data,
+ Vbus - 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
+ Jmot - is the motor’s inertia,
+ τregen - is the motor’s negative brake torque (Nm),
+ τdemand - 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,
+ ηmot - 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
The coupler effectively transmits the total torque to the driven wheels by integrating the torques from both the internal combustion engine (ICE) and the electric motor (EM) This system allows for independent control of the torque produced by the ICE and EM.
The power conservation limitation connects the internal combustion engine (ICE), electric motor (EM), and vehicle speeds in a fixed relationship, preventing independent adjustments The torque coupling functions as a two-degree-of-freedom mechanical device, featuring bidirectional input or output ports at positions 2 and 3, although they cannot be used as inputs simultaneously Additionally, port 1 serves as a unidirectional input port.
Here, input and output refer to the flow of energy into and out of the device, respectively
In a hybrid electric vehicle (HEV), port 1 is connected to the internal combustion engine (ICE) shaft, port 2 is linked to the electric motor shaft, and port 3 is associated with the driven wheels.
The power balance is defined by the Equation (3.27):
+ T1 - propelling torque produced by ICE
+ T2 - 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
Port 1 functions as a unidirectional input, while ports 2 and 3 serve as bi-directional input or output, with the stipulation that both cannot operate as inputs simultaneously Here, input and output pertain to the energy transfer occurring into and out of the respective devices.
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:
+ k1, k2 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
A planetary gear train offers various speed reduction ratios based on the configuration of the driving, driven, and fixed shafts These ratios are influenced by the radii of the sun and ring gears, as well as the number of teeth on each gear.
Vehicle motion is influenced by the combined effects of forces and torques acting on it Longitudinal tire forces propel the car forward or backward, while the center of gravity serves as a weight conduit, exerting downward force and determining motion based on incline Aerodynamic drag, affecting the vehicle regardless of its direction, contributes to deceleration, and for simplicity, it is assumed to act through the center of gravity.
The vehicle dynamics are described by the following equations [11]
2𝐶 𝑑 𝜌𝐴(𝑉 𝑥 + 𝑉 𝑤 ) 2 𝑠𝑔𝑛(𝑉 𝑥 + 𝑉 𝑤 ) (3.33) o Normal load forces on each wheel at the front
𝑛(𝑎+𝑏) (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
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 produced by the internal combustion engine (ICE) is split into two components: one portion maintains vehicle propulsion, while the other is directed to the generator to recharge the battery, even when the vehicle is at a standstill.
The Model Logic subsystem serves as the foundation of this control method, functioning as a state machine or Stateflow logic controller that adapts to varying driving conditions Its output directs three separate subsystems responsible for managing 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
MATLAB SIMULATION RESULTS
Vehicle simulation parameters
Engine (2AZ-FXE) Max output 110 kW @ 6000 rpm
Battery (Nikel-metal hybride) Nominal Voltage 244.8 V
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) is an alternative testing protocol for Part 2 of the ECE Type 1 Test, tailored specifically for low-powered vehicles.
4.2.2 The Highway Fuel Economy Driving Schedule (HWFET)
The US EPA established the Highway Fuel Economy Test (HWFET) cycle to evaluate the fuel efficiency of light-duty cars using a chassis dynamometer Designed primarily for highway driving conditions, the HWFET is crucial in determining a vehicle's highway fuel efficiency rating In contrast, the FTP-75 test simulates urban driving scenarios to assess city fuel economy.
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
The complete cycle consists of a 15-minute warm-up at 60 km/h, followed by an idle test, another 5-minute warm-up at the same speed, one 15-mode segment, and three repetitions of 10-mode segments, concluding with an additional 15-mode segment The last four segments are specifically utilized for emissions measurement, comprising three 10-mode segments and one 15-mode segment (source: DieselNet).
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
In this thesis, a test cycle was developed for vehicle simulation based on the standard ECE cycle, specifically the UN/ECE Extra-Urban test cycle This simulation allows for the analysis of a hybrid vehicle's operation, providing critical parameters such as acceleration, power requirements for both electric motors and the internal combustion engine, battery state of charge variations, and the operational metrics of electric motors/generators Additionally, it examines power distribution and other relevant factors affecting vehicle performance.
The simulation results illustrate the variation in vehicle acceleration during the UN/ECE Extra-Urban test cycle, highlighting that the required acceleration changes at each stage in accordance with the velocity 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 stable motion, the internal combustion engine ensures a consistent vehicle speed while utilizing some of its power to operate the MG2 generator in generator mode, which charges the battery Consequently, the battery's charge level rises during these phases of steady driving.
In hybrid mode, applicable during stages 3-4, 7-8, and 9-10, the vehicle accelerates from a speed of 50 km/h or higher, utilizing energy from the battery to power the electric motor, which leads to a reduction in the battery charge level.
Regenerative braking mode activates during stages 5-6, 11-12, and 13-14 when the vehicle slows down from speeds of 15 km/h or higher In this mode, the battery provides energy to the electric motor, leading to a reduction 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
77 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
The vehicle primarily operates in hybrid mode on the highway, where it typically travels at high speeds exceeding 40 km/h.
The simulation results indicate that both the internal combustion engine and the electric motor consistently provide positive power during acceleration and high-speed maintenance However, during deceleration or braking, the vehicle exclusively utilizes the electric motor's power 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
When simulating the operation of a hybrid vehicle using the Japanese 10.15 Mode Driving Schedule, various results are obtained, similar to those from the UN/ECE Extra-Urban Driving Cycle, and these results are illustrated in 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
The simulated graph of engine torque demonstrates that as a vehicle accelerates to higher speeds, the internal combustion engine generates increasing torque to meet the speed requirements Once the desired speed is achieved, the engine torque stabilizes, remaining constant at a specific level.
- 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 motor's torque (MG2) can be either positive or negative; positive torque signifies the motor's role in generating pulling force, while negative torque reflects the motor's function in using energy to recharge the battery.
The vehicle speed is directly proportional to the motor speed, as evidenced by the similarity in their simulated graphs This relationship exists because the motor is connected to the steering wheel via a motor speed reduction planetary gear unit.
Figure 4.10 Simulated generator in the Japanese 10.15 Mode Driving Schedule
The graph illustrates that the generator's operation is somewhat restricted, primarily due to the efficient functioning of regenerative braking The generator maintains a speed under 12,000 rpm, with positive torque indicating that MG1 is supplying power, while negative torque signifies 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 Schedule
The 2007 Toyota Camry Hybrid boasts fuel consumption ratings of 40 MPG (about 5.8 l/100km) in city driving and 38 MPG (around 6.2 l/100km) on the highway, according to the manufacturer However, simulation results reveal a discrepancy of approximately 1.7 l/100km for city driving and 1.6 l/100km for highway driving This variation may stem from the more rigorous operating conditions during the manufacturer's testing compared to the Matlab simulations, with factors such as friction losses between mechanical components playing a significant role in the differences observed.
CONCLUSION
Comment
This study provides an overview of the structure and power division principles of series-parallel hybrid vehicles, focusing on the internal combustion engine and electric motor It emphasizes the calculation and simulation of fuel consumption efficiency using MATLAB, revealing valuable insights into hybrid powertrain fuel efficiency The simulation results effectively evaluate and analyze the fuel consumption characteristics of hybrid vehicles across different driving conditions and operational modes.
The MATLAB simulation evaluated the fuel consumption of a hybrid vehicle across various driving scenarios, including urban, highway, and mixed conditions It examined the influence of key factors on fuel efficiency, such as battery state of charge, regenerative braking efficiency, and the power distribution between the internal combustion engine and electric motor However, it is essential to recognize that the simulation results are relative and may not accurately represent real-world driving conditions or vehicle performance.
In summary, the MATLAB simulation research on hybrid vehicle fuel consumption has yielded significant insights into the fuel efficiency of hybrid powertrains The study's findings enhance our understanding of the factors affecting fuel consumption and can be applied to optimize hybrid powertrain designs and control strategies, ultimately improving fuel economy in practical driving scenarios.
Research and Development Directions
The research topic can be further developed in several directions to expand its scope and contribute to the field:
Hybrid vehicles exhibit varying emission levels depending on their operating modes—electric, hybrid, and conventional Analyzing the influence of driving conditions, powertrain configurations, and control strategies is crucial for understanding their impact on greenhouse gas emissions and pollutants Strategies to minimize emissions and enhance the environmental performance of hybrid vehicles are essential for promoting sustainable transportation solutions.
- 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
The integration of new hybrid architectures, including hybrid electric turbos, range extenders, and fuel cell hybrids, presents significant benefits and challenges for hybrid vehicles These technologies enhance performance and efficiency while promoting sustainability However, their incorporation requires careful consideration of engineering complexities and cost implications, impacting overall vehicle design and market acceptance.
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