The acronyms in this article refer to
SSTS: Sub System Technical Specification, subsystem function specification
CTS: Component Technical Specification, component function specification
DCDC: Direct Current Direct Current Converter, DC to DC converter
BMS: Battery Management System, battery management system
VCU: Vehicle Control Unit, vehicle controller
OBC: On Board Charger, on-board charger
PTC: Positive Temperature Coefficient, positive temperature coefficient components
ESC: Electronic Stability Control system, electronic stability system
CAN: Controller Area Network, controller area network
MCU: Motor Control Unit, motor controller
In recent years, as the core technology different from traditional fuel vehicles, the three-electric technology of new energy vehicles has achieved rapid and continuous development.
If you want to have a deep understanding of electric vehicles, you must not bypass the three-electric system. The three-electric system refers to the electric drive system, battery system and electronic control system of electric vehicles. These three systems are also the core technologies of electric vehicles and directly affect the final performance of the product. Today we will take a look at the three-electric system of electric vehicles and its electronic and electrical architecture design.
Table of contents
What is a three-electric system
Introduction to the vehicle development phase
Introduction to the design of electronic and electrical architecture of the three-electric system
1. Determination of the function list
2. Subsystem Functional Specification (SSTS)
3. Component Functional Specification (CTS)
What is a three-electric system
The figure below shows the content of the three-electric system. The three-electric system accounts for more than half of the cost of electric vehicles, and the battery system accounts for the highest proportion of the entire three-electric system.
1. Electric drive system
The electric drive system is the key system of electric vehicles. The operating performance of electric vehicles mainly depends on the type and performance of the electric drive system. The electric drive system mainly includes the drive motor, the transmission mechanism (reducer) and the converter (inverter and DCDC conversion device).
motor:
The drive motor is a device that converts electrical energy into mechanical energy. It is a device that relies on the principle of electromagnetic induction to provide driving force for the vehicle. Motors can be divided into three types: DC drive, permanent magnet synchronous, and AC induction. Different types of motors have different characteristics.
Transmission mechanism (reducer):
Electric vehicles need to meet the needs of climbing and other situations that require low speed and high torque, and meet the characteristics of low speed and high torque. From the perspective of economy, reducing vehicle quality, and development difficulty, most electric vehicles are currently equipped with reducers. The reducer is interposed between the drive motor and the drive half shaft, and the power output shaft of the drive motor is directly connected with the reducer input shaft gear through splines. On the one hand, the reducer transmits the power of the driving motor to the driving half shaft, and starts to reduce the speed and increase the torque. On the other hand, when the car is turning or driving on an uneven road, the left and right wheels rotate at different speeds to ensure the vehicle's stability. run smoothly.
Inverter:
The function of the inverter is reflected in the following aspects: convert the DC power of the battery into AC output to drive the motor; convert the AC power into DC power and store it in the battery during braking energy recovery; convert the DC power of the power battery into AC power to drive the motor. Air conditioning; when charging, convert AC power to DC power to charge the power battery. In some cases, the inverter, reducer, and drive motor can be integrated into one controller, which becomes a three-in-one controller after integration.
DCDC converter:
Convert the high-voltage power of the power battery to low-voltage power (12V) to supply power for the battery and on-board electronic equipment.
2. Battery system
There are three levels of concepts in the battery system: batteries, modules and battery packs. In the power battery pack, in order to safely and effectively manage hundreds of single batteries, the batteries are not randomly placed in the power supply. Inside the shell of the battery, it is placed in an orderly manner according to the modules and packages. The smallest unit is the cell, a group of cells can form a module, and several modules can form a package.
Batteries:
The battery cell is the smallest unit of a power battery, and it is also an electric energy storage unit. It must have a high energy density to store as much electric energy as possible, so that the electric vehicle has a longer cruising range. In addition, the life of the battery cell is also the most critical factor. The damage of any battery cell will lead to the damage of the entire battery pack.
Mods:
When multiple batteries are packaged together by the same shell frame and communicate with the outside through a unified boundary, this forms a module.
battery pack:
When several modules are jointly controlled or managed by the BMS and the thermal management system, this unified whole is called a battery pack.
Type of battery:
At present, the mainstream types of electric vehicle batteries on the market are roughly classified into lead-acid batteries, nickel-metal hydride batteries, lithium cobalt oxide batteries, lithium manganese oxide batteries, lithium iron phosphate batteries and ternary lithium-ion batteries (lithium nickel cobalt manganate batteries), etc., and there are differences in key raw materials, electrolytes, diaphragms, etc. of different types of batteries. The batteries commonly used in electric vehicles are ternary (nickel-cobalt-manganese) lithium batteries and lithium iron phosphate batteries.
3. Electric control system
Electronic control system is a general term, including many systems, mainly including: vehicle control system, motor control system, battery management system, as well as thermal management system, drive control system, etc. Will make an introduction.
Introduction to the vehicle development phase
The electronic and electrical architecture design of the three-electric system relies on and is included in the vehicle development process. This part will first briefly introduce the vehicle development stage: the vehicle development stage is roughly divided into 4 stages, the initial stage , concept phase, development phase and optimization phase.
1. Initial stage
Mainly carry out program planning, mainly consider relevant factors such as market segmentation, product positioning, development cost, production cost, etc. After completing the project feasibility analysis, determine the design target framework of the new model.
2. Concept phase
The main work is feasibility and economic analysis and formulation. At this stage, vehicle concept planning, initial design requirements, supplier supply capacity, factory output analysis, market activity concept, after-sales concept, innovative design evaluation, and vehicle performance evaluation will be carried out. And other work, OEMs with strong design capabilities will also introduce virtual vehicle development technology at this stage, carry out early modeling and simulation, and assist in clarifying design indicators.
3. Development phase
Carry out engineering design, complete component design, vehicle integration, prototype manufacturing, test verification, pre-production preparation, etc., to meet design requirements.
4. Optimization phase
It is necessary to confirm whether the actual product meets the functional and physical development requirements, confirm that the output and quality meet the target, and confirm that the cost and profit meet the economic target. For vehicles sold, activities such as maintenance and quality assurance are performed.
Introduction to the design of electronic and electrical architecture of the three-electric system
The electronic and electrical architecture design work of the three-electric system is oriented to the electronic and electrical functions in the three-electric system, that is, it is related to the design of the electronic control system. Its workflow mainly includes the determination of the function list, the preparation and formulation of the subsystem function specification (SSTS) and component function specification (CTS).
1. Determination of the function list
After the completion of the first two stages of the vehicle development stage, that is, the initial stage and the conceptual stage, the specific functions of the three-electric system have been clarified, and the input of functions, that is, the list of functions, has been formed.
The function list often includes domain name, first-level function, second-level function, third-level function, function description, function number, vehicle configuration and other information.
2. Subsystem Functional Specification (SSTS)
The Subsystem Functional Specification (SSTS) achieves the function of connecting the past and the future, meets the requirements of the previous function list, and establishes the requirements of the next layer of Component Functional Specifications (CTS). SSTS structurally disassembles and analyzes complex functions, and defines the combined behavior of multiple components, as well as the interaction information and methods of each subsystem.
SSTS is more specific than the function list, describing signal interaction, function logic, scene analysis, etc. Compared with CTS, SSTS is more abstract, and usually does not involve packaging, implementation schemes, detailed principles, and environmental testing. Also because of abstraction, SSTS has the characteristics of versatility. SSTS can be independent from the implementation plan, but provides a design framework for the implementation plan, so that suppliers can carry out various innovations or reduce cost designs within this framework, but will not deviate from the original design requirements. Therefore, when choosing a supplier solution, car manufacturers can choose the solution with the best quality and cost based on SSTS.
Depending on the function positioning (function list) of the model, the number and functions of the three electronic systems will vary. The following introduces the functions of some basic subsystems.
High voltage power on and off management subsystem
The high-voltage power-on and power-off management system includes high-voltage power-on, high-voltage power-off, and high-voltage power-off in emergencies when the vehicle is started and charged. A typical solution is that the vehicle controller VCU sends a high-voltage power-on and power-off command to the battery management system BMS. The closing and opening of the relay is controlled by the BMS, so as to realize the management and control of the high voltage power on and off of the whole vehicle.
Charge Control Subsystem
The whole vehicle needs to be charged after the charging gun is inserted. In the charging management, the VCU will control whether to allow the BMS to charge according to the status of the whole vehicle. During charging, the BMS will send charging demand parameters in real time according to the working conditions of the battery and monitor the entire charging process. Limit or terminate charging when charging is abnormal to ensure charging safety.
The charging system of the electric vehicle battery pack has two charging paths: DC charging and AC charging . The DC charging port is externally connected to a DC charging pile, and the input DC power is distributed to the battery pack for charging through a high-voltage electrical box. The DC charging method has a larger current and a faster charging speed, which is usually called fast charging. The AC charging port is externally connected to the household AC power supply or AC charging pile. The AC power is converted into DC power through the on-board charger OBC, and then distributed to the battery pack for charging through the high-voltage electrical box. The charging current of the AC charging method is relatively small and the charging speed is slow. Also called slow charging.
thermal management subsystem
The function of the thermal management system is to cool down the motor, cool down the battery when the temperature is too high or heat the battery pack before low-temperature charging, mainly including three waterway control systems: motor waterway control system, battery pack heating and cooling waterway control system, warm core and PTC Heating water system control.
battery management subsystem
Determine the state of the entire battery system by detecting the state of each single battery in the power battery pack, and carry out corresponding control adjustments and strategy implementation for the power battery system according to their state, to realize the charging and discharging of the power battery system and each single cell management to ensure the safe and stable operation of the power battery system.
Energy Management Subsystem
Electric vehicle energy management can be divided into two parts: power distribution management and braking energy recovery control according to the driving and braking forms of the vehicle. The power distribution management is based on the battery, motor and accessories to complete the power distribution of the high-voltage power consumption of the vehicle. The braking energy recovery control combines the vehicle speed, different braking intensity, motor output power and battery charging power to complete the braking energy recovery control of different levels of the vehicle.
Brake Energy Recovery Subsystem
When the vehicle is coasting or braking, the kinetic energy recovered by the motor is converted into electrical energy and stored in the power battery. The VCU completes the braking torque control of the driving motor by judging the braking state of the vehicle, combined with the vehicle running speed, motor limit value, battery limit value, ESC working status and different braking recovery intensity input by the driver, etc. , so as to realize the control of the braking energy recovery of the whole vehicle.
driving subsystem
The vehicle controller calculates the driver's demand torque according to the accelerator pedal opening, gear position, vehicle speed, brake pedal, etc. as part of the vehicle driving and braking capacity calculation. When the VCU calculates the output torque of the vehicle system, it is mainly limited by the output capacity of the motor, the charge and discharge capacity of the battery, the transmission capacity of the transmission system and the energy distribution of the vehicle.
High Voltage Accessory Subsystem
The accessory system control is mainly for the control of the water pump relay, low-speed fan relay, high-speed fan relay, PTC relay, electric vacuum pump relay and PWM output of the water pump managed by the VCU.
3. Component Functional Specification (CTS)
After the subsystem function specification (SSTS) is determined, a specific controller is required to undertake the functions in the subsystem, that is, to assign the function points of the SSTS to different components to realize the design requirements, and a function A point may be related to multiple parts, so that there is a part functional specification.
CTS describes in detail the design principles of the controller provided by the supplier, including control chip requirements, electrical schematic diagrams, control function logic, interactive signals, sleep wake-up, electrical characteristics, performance testing, etc. Several typical component function specifications are introduced below.
VCU (vehicle controller)
The electronic control system takes the vehicle controller as the control core of the power domain, which has sleep/wake-up, low-voltage power management, high-voltage power on and off, vehicle mode management, gear management, torque control, creep control, energy feedback, condensing fan control, Battery thermal management, vacuum pump control, DCDC control, vehicle diagnosis, instrument display, mileage estimation, vehicle anti-theft, power distribution control, high-voltage safety monitoring and other functions. As the core main control unit of the vehicle, the VCU interacts with other control units through hard wires or CAN. By processing the received information, it judges the status of each sub-control unit and the vehicle system, and makes reasonable, Safe instructions, so as to realize the coordinated and safe work of each sub-control unit.
MCU (Motor Controller)
By receiving the vehicle driving control command from the VCU, controlling the motor to output the specified torque and speed, driving the vehicle, realizing the conversion of the DC power of the power battery into the required high-voltage AC power, and driving the motor body to output mechanical energy, the MCU has the fault diagnosis of the motor system protection and storage functions.
BMS (Battery Management System)
Mainly through the collection and calculation of parameters such as voltage, current, temperature, and SOC, and then control the charging and discharging process of the battery, realize the safety and life protection of the power battery, and improve the comprehensive performance of the battery. It mainly includes charge control, discharge control, SOC strategy, energy balance management function, thermal management function, battery safety management function, etc.
DCDC (DC to DC Converter)
The high-voltage direct current of the power battery is converted into low-voltage direct current for powering the low-voltage electrical devices on the vehicle.
OBC (On-Board Charger)
Dedicated to the slow charging process, the grid voltage is connected to the OBC through the ground AC charging pile and AC charging port to charge the power battery.
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