Therefore, HEV batteries need to have high energy density and high power density to achieve efficient energy conversion and high-performance drive.
Ternary lithium-ion batteries, as a high-performance battery, are widely used in the power systems of HEVs. Meanwhile, the battery management system (BMS) has become one of the core technologies for controlling HEV battery packs.
Basic performance and application characteristics of ternary lithium-ion batteries
1. Basic Principles of Ternary Lithium-ion Batteries
A ternary lithium-ion battery is a charge-discharge electrochemical system that uses lithium cobalt acid, lithium nickel acid, and lithium manganese acid as positive electrode materials, and carbon, graphite, and lithium titanate as negative electrode materials. Its charge-discharge process is as follows:
Positive electrode: LiCoO2/LiNiO2/LiMn2O4+Li+ +e- ↔ LiCoO2/LiNiO2/LiMn2O4
Negative electrode: C/LiTi2O4 + Li+ + e- ↔ LiC/LiTi2O4
Overall reaction equation: LiCoO2/LiNiO2/LiMn2O4 + C ↔ LiC + LiCoO2
Ternary lithium-ion batteries have advantages such as high energy density, long life, low self-discharge rate, high charging efficiency and high safety, and are therefore widely used in HEVs.
2. Basic Performance
High energy density: Ternary lithium-ion batteries have a high energy density, typically reaching over 150Wh/kg, which means they can provide devices with a longer operating time.
Long lifespan: Ternary lithium-ion batteries have a long lifespan, typically capable of thousands of charge-discharge cycles, which means they have a longer service life.
High charge and discharge efficiency: Ternary lithium-ion batteries have high charge and discharge efficiency, typically reaching over 90%, which means they can utilize electrical energy more effectively.
Low self-discharge rate: Ternary lithium-ion batteries have a low self-discharge rate, which means that even after long-term storage, the battery's charge will not be significantly lost.
3. Application characteristics of ternary lithium-ion batteries
The main application characteristics of ternary lithium-ion batteries include the following aspects:
High energy density: Ternary lithium-ion batteries have high energy density, which can provide HEVs with efficient energy conversion and high-performance drive.
Long lifespan: Ternary lithium-ion batteries have a long lifespan, which can meet the requirements of long-term use in HEVs.
Low self-discharge rate: Ternary lithium-ion batteries have a very low self-discharge rate, which ensures that HEVs can still start normally after being parked for a long time.
High charging efficiency: Ternary lithium-ion batteries have high charging efficiency, which can shorten the charging time of HEVs.
High safety: Ternary lithium-ion batteries have high safety, which can effectively reduce the safety risks of HEVs.
Design principles and functions of battery management system
1. Design principles of battery management system
The Battery Management System (BMS) is a crucial component of HEV battery packs, primarily responsible for monitoring the battery pack's status, controlling charging and discharging, protecting the battery pack, and predicting its lifespan. The design principles of a BMS mainly include the following aspects:
Battery status monitoring: The BMS monitors the battery pack's status in real time by monitoring parameters such as voltage, current, and temperature to ensure the normal operation of the battery pack.
Battery pack charging and discharging control: The BMS controls and protects the battery pack by controlling the charging and discharging process.
Battery pack protection: The BMS monitors the status of the battery pack, promptly detects abnormalities, and takes corresponding measures to protect the safety of the battery pack.
Battery life prediction: The BMS enables optimized management of the battery pack by predicting its lifespan.
2. Functions of the Battery Management System
The main functions of a battery management system include the following aspects:
Battery status monitoring: The battery management system of hybrid vehicles can monitor multiple parameters of the battery in real time, such as voltage, current, temperature, and charge, to understand the battery's working status.
Charge and discharge control: The battery management system of hybrid vehicles can control the charging and discharging current and voltage of the battery to make the battery work in the optimal charging and discharging state and extend the battery life.
Safety protection: The battery management system of hybrid electric vehicles can provide multiple protections for the battery, such as overcharge protection, over-discharge protection, temperature protection, and short circuit protection, to ensure the safety and stability of the battery.
Balanced Management: The battery management system of hybrid vehicles can manage the balance of each cell in the battery to ensure that the charge of each cell is balanced and to avoid shortening the overall battery life due to differences in the charge of individual cells.
Fault Diagnosis: The battery management system of hybrid vehicles can diagnose battery faults, promptly detect and eliminate battery faults, and ensure the normal operation of the battery system.
Data recording and analysis: The battery management system for hybrid vehicles can record and analyze battery operating data, including battery charge and discharge history, battery state parameters, etc. This data can provide a reference for later optimization and upgrades.
In conclusion, the battery management system for hybrid electric vehicles is a very important system. By monitoring and controlling the battery, it can extend battery life, improve battery safety and stability, and also provide important data references for vehicle optimization and upgrades.
With the increasing demand and production of electric and hybrid vehicles, both types of vehicles require high-current-capacity batteries to power motors of 50kW or higher, and these all utilize high-voltage systems. Current measurement and detection in automotive battery management systems require isolated measurement methods, and Hall current sensors offer isolated measurement capabilities, making them the preferred choice for this application.
Keywords: Electric vehicle; Hybrid vehicle; Battery management system; Hall current sensor
1: Overview of the functions of the automotive battery management system
The vehicle battery management system (BMS) enables dynamic monitoring. During battery charging and discharging, it collects real-time data on the terminal voltage and temperature of each battery cell in the electric vehicle battery pack, as well as the charging and discharging current and the total voltage of the battery pack. It accurately estimates the state of charge (SOC) of the battery pack, ensuring the remaining battery capacity remains within a reasonable range to prevent damage from overcharging or over-discharging. Furthermore, it continuously displays the remaining energy of the hybrid vehicle's energy storage battery, i.e., the SOC of the energy storage battery.
2: Application of Hall current sensors in automotive battery management systems
During battery charging and discharging, the vehicle's battery management system (BMS) can use Hall effect current sensors to collect the charging and discharging current of each battery in the electric vehicle's power battery pack in real time, preventing overcharging or over-discharging. Furthermore, relying on Hall effect current sensors, the BMS can also detect battery power consumption and promptly report battery status, effectively preventing battery leakage, insulation damage, and partial short circuits. This allows for the identification of problematic batteries, maintaining the reliability and efficiency of the entire battery pack.
In electric and hybrid vehicles, Hall effect current sensors are used in the battery system, motor system, and charging system of the three core electric systems. Compared to gasoline vehicles, Hall effect current sensors are a completely new requirement for electric and hybrid vehicles, and all electric and hybrid vehicles will use them.
The working principle of a hybrid electric vehicle: When the vehicle starts, the battery is fully charged, and its energy output can meet the vehicle's needs, so the auxiliary power system does not need to work. When the battery charge is below 60%, the auxiliary power system starts: when the vehicle's energy demand is high, the auxiliary power system and the battery pack simultaneously provide energy to the drive system;
When the vehicle's energy demand is low, the auxiliary powertrain provides energy to the drive system and charges the battery pack. Because of the battery pack, the engine operates under relatively stable conditions to improve its emissions.
Hybrid electric vehicles operate in two modes: series and parallel.
Series power
The series powertrain consists of an engine, a generator, and an electric motor. These components form the SHEV power unit system. The engine drives the generator to produce electricity, which is then transmitted to the battery or electric motor via a controller. The electric motor then drives the vehicle through the transmission. Light loads are driven by the battery, while heavy loads are driven by the engine.
Parallel power
A parallel-connected engine and electric motor jointly drive a car. The engine and motor are two separate systems that can independently supply torque to the car's drivetrain and can work together to drive the car on different roads.
Hybrid power
Hybrid systems include both series and parallel configurations. Power systems include engines, generators, and motors. Based on different power units, they are categorized as engines and motors.
The dual-engine system is called a dual-engine system because it has two power outputs: one is a traditional internal combustion engine, which uses a 1.8L Atkinson cycle naturally aspirated gasoline engine, and the other is an electric system that relies on an electric motor, battery pack, and electrical control system.
Both of these power sources rely on the E-CVT transmission to deliver power to the wheels. The hybrid system is actually designed to improve the optimal operating conditions of a traditional internal combustion engine.
For example, when the engine is idling at a red light, or when the battery is fully charged, the hybrid vehicle completely shuts off, consuming no fuel. This is also the most fuel-intensive operating condition for an internal combustion engine when starting. It will rely on its rapid torque response, with a large electric motor replacing the car's starter.
So if you drive this dual-engine car, you'll find it very quiet when starting, almost like an electric car. That's why many people say this car is more fuel-efficient in big cities, especially in congested traffic.
The power system of a hybrid electric vehicle mainly consists of a control system, a drive system, an auxiliary power system, and a battery pack.
Hybrid vehicles use a small engine to meet the vehicle's cruising needs, while relying on an electric motor or other auxiliary equipment to provide the additional power needed for acceleration and hill climbing. The result is improved overall efficiency without sacrificing performance.
Hybrid electric vehicles are designed to recover braking energy. In conventional cars, this energy, which could have been used to accelerate the car, is wasted when the driver applies the brakes. Hybrid electric vehicles can recover most of this energy and temporarily store it during acceleration.
When the driver desires maximum acceleration, the gasoline engine and electric motor work in parallel, providing the same starting performance as a powerful gasoline engine. Under less demanding acceleration conditions, hybrid vehicles can rely solely on the electric motor or the gasoline engine, or a combination of both, for maximum efficiency.
For example, a gasoline engine is used when cruising on a highway. At low speeds, no gasoline engine is needed; the vehicle can be driven solely by the electric motor. Even when the engine is off, the electric power steering system remains operational, providing greater efficiency than traditional hydraulic systems.
