In-depth Analysis of Electric Vehicles: Complete Working Principles from Core Components to Intelligent Systems
As the core direction of the transformation and upgrading of the automotive industry, electric vehicles are reshaping the transportation landscape with their advantages of environmental friendliness efficiency and intelligence. From a tiny screw gasket to a complex intelligent driving system the collaborative work of every component constitutes the smooth operation experience of an electric vehicle. Starting from the underlying principles this article systematically disassembles the core components working mechanisms and intelligent technologies of electric vehicles leading you to a comprehensive understanding of the "internal logic" of electric vehicles.
I. Power Core: Working Principle of Electric Vehicle Motors
The motor is the "heart" of an electric vehicle and its efficiency in converting electrical energy into mechanical energy directly determines the vehicle's dynamic performance. From the most basic electromagnetic induction phenomenon to industrial-grade three-phase induction motors the development of electric vehicle motors has always centered on the three core goals of "high efficiency high torque and high stability".
(I) Electromagnetic Induction: The Underlying Physical Basis of Motors
The working essence of a motor stems from the interaction between electromagnetic induction and electromagnetic force. We can understand its core logic through a set of simple experiments.
Basic electromagnetic interaction: When a rotatable metal rod is brought close to a magnet the metal rod will rotate toward the magnet. If the metal rod is replaced with an iron disc and moved with a U-shaped magnet the disc will rotate with the magnet and even produce self-rotation. At first glance this phenomenon is caused by the magnet's attractive force but when we replace the iron disc with an aluminum disc (a non-ferromagnetic material) moving the magnet can still drive the disc to rotate which reveals the core role of electromagnetic induction.
Synergy between electromagnetic induction and electromagnetic force: The magnetic field of a U-shaped magnet flows from the N pole to the S pole. When the magnet moves its magnetic field cuts the disc (conductor). According to the principle of electromagnetic induction an induced current is generated on the disc. The direction of the induced current can be determined by the right-hand rule pointing to the center of the disc. The left-hand rule can determine the direction of the force on the disc—point the index finger in the direction of the magnetic field the middle finger in the direction of the current and the thumb points to the electromagnetic force that drives the disc to rotate. The key point is that there must be a difference in rotational speed between the magnet and the disc. If the rotational speeds are the same electromagnetic induction cannot occur and the disc will lose its self-rotational power.
(II) Iteration of Motor Structure: From Simple Devices to Industrial-Grade Design
To achieve continuous and stable power output the motor structure has undergone multiple rounds of optimization and upgrading.
Improvement of basic structure: Replace the aluminum disc with an iron cylinder and the U-shaped magnet with two bar magnets. When the magnet is rotated the cylinder will rotate accordingly. From the force analysis the magnetic field flows from the N pole to the S pole. When the magnet moves downward relative to the cylinder the cylinder is equivalent to moving upward. An induced current is generated according to the right-hand rule and then the force directions on both sides of the cylinder (one downward and one upward) are determined by the left-hand rule ultimately driving the cylinder to rotate.
Application of electromagnets: A coil generates a magnetic field when energized. This type of electromagnet which is "magnetic when energized and non-magnetic when de-energized" has stronger controllability than traditional permanent magnets—increasing the voltage can enhance the magnetic field strength and changing the current direction can reverse the magnetic poles. Based on this characteristic multiple coils are arranged around the cylinder. By continuously changing the current direction a rotating magnetic field can be formed and the cylinder can be driven to rotate continuously without mechanically rotating the magnet which is the core design logic of the motor.
(III) Three-Phase Alternating Current: The Implementation Method of Rotating Magnetic Field
Electric vehicles generally adopt three-phase induction motors and their core lies in generating a stable rotating magnetic field through three-phase alternating current.
Generation of three-phase alternating current: When a magnet rotates around a coil changes in the magnetic field cause the coil to generate alternating current (the waveform of single-phase alternating current is a sine curve). If three coils are arranged at intervals of 120 degrees rotating the magnet will generate three groups of alternating current with a phase difference of 120 degrees namely three-phase alternating current. One end of the three coils is connected to form a neutral line and the other end extends as three phase lines. The voltage between the phase lines is 380 volts and the voltage between the phase line and the neutral line is 220 volts. Different connection methods can meet different power consumption needs.
Coil winding and magnetic field formation: The motor consists of a stator and a rotor and the coil is wound in the holes of the stator. The specific winding method is: the coil enters from port A and exits in the opposite direction from the opposite port A; enters from port B at an interval of 120 degrees and exits in the opposite direction from port B; similarly completes the winding of the coil at port C and finally connects the wires returned in the opposite direction together and connects the three phase lines to the three-phase alternating current.
Generation of rotating magnetic field: The waveform of three-phase alternating current changes periodically with time. At different moments the current polarity and magnitude of the three phase lines are different. For example at a certain moment the R phase is positive and the S and T phases are negative; at the next moment the R and S phases are positive and the T phase is negative. This change causes the direction of the magnetic field generated by the stator coil to shift continuously. According to Ampère's rule the direction of the magnetic field generated by each coil (clockwise or counterclockwise) changes with the current. After the superposition of the magnetic fields of multiple coils a continuously rotating magnetic field is formed and the rotational speed of the magnetic field is positively correlated with the frequency of the alternating current.
(IV) Structure and Classification of Real Motors
Industrial-grade electric vehicle motors have been precisely optimized based on basic principles and are mainly divided into two categories: induction motors (asynchronous motors) and permanent magnet synchronous motors.
Induction motors (asynchronous motors):
Core structure: Composed of a stator and a rotor. The stator has grooves inside for installing winding coils. The rotor is a squirrel-cage structure with insulated iron sheets with grooves inside and conductor bars embedded in the grooves.
Working characteristics: When alternating current is passed through the stator coil a rotating magnetic field is generated. The conductor bars of the rotor cut the magnetic field lines to generate induced current and then are driven to rotate by electromagnetic force. Since the rotor speed is always less than the magnetic field speed (there is a slip rate) it is called an asynchronous motor.
Coil optimization: In industrial production a set of winding coils usually has hundreds or thousands of turns. After being wound by a machine they are covered with insulating paint which not only improves insulation performance but also enhances thermal conductivity. To solve the problem of uneven magnetic fields the number of stator grooves will be increased (such as 12 24) and the coils will be connected in series and folded to form different magnetic field structures such as two-pole and four-pole. Two-pole magnetic field motors have high speed four-pole magnetic field motors have large torque and the multi-groove design can further improve magnetic field stability and motor efficiency.
Permanent magnet synchronous motors:
Structural improvement: Arc-shaped permanent magnets are installed outside the rotor (replacing the squirrel-cage rotor). The permanent magnets generate a fixed magnetic field which interacts with the rotating magnetic field generated by the stator coil.
Core advantages: The rotor speed is synchronized with the stator magnetic field speed without energy loss caused by induced current (the energy loss of induction motors is about 3%-4%) and it has large starting torque and excellent low-speed performance.
Existing problems: During high-speed driving the back electromotive force generated by the permanent magnet is opposite to the direction of the motor electromotive force which affects motor efficiency; at the same time the permanent magnet will cause eddy currents resulting in additional energy loss.
Permanent magnet synchronous reluctance motors:
Hybrid design: Combining the advantages of low-speed and high-torque of permanent magnet motors and high-speed stability of synchronous reluctance motors permanent magnets are embedded in the grooves of synchronous reluctance motors to form a composite structure.
Performance optimization: By adjusting the angle between the rotating magnetic field and the permanent magnet magnetic field the back electromotive force can be weakened or even offset enabling the motor to operate efficiently in both low-speed and high-speed scenarios. During startup maintaining the angle of the rotating magnetic field at around 50 degrees can obtain maximum torque.
II. Energy Source: Working Principle of Lithium Batteries and Battery Pack Design
The power of the motor comes from electrical energy and the core energy storage component of electric vehicles is lithium batteries. Lithium batteries have become the preferred energy storage device for electric vehicles due to their advantages of high energy density long cycle life and fast charging capability.
(I) Core Structure and Working Principle of Lithium Batteries
The energy conversion of lithium batteries is based on the intercalation and deintercalation of lithium ions and the core structure includes a positive electrode an electrolyte layer and a negative electrode.
Electrode materials:
Negative electrode: Mainly composed of graphite layers. Graphite has a crystalline layered structure providing space for lithium ion intercalation.
Positive electrode: Lithium-containing metal oxides (such as nickel-cobalt-manganese oxides for ternary lithium batteries and lithium iron phosphate for lithium iron phosphate batteries).
Electrolyte: Organic lithium salt solution coated on the separator allowing lithium ions to pass through but blocking electrons.
Charging and discharging process:
Charging: When an external power supply is connected the positive electrode of the power supply attracts the electrons of the lithium atoms in the positive electrode material. The electrons flow along the wire and the lithium atoms lose electrons to become lithium ions which flow to the negative electrode through the electrolyte layer and intercalate into the crystalline layered structure of graphite until all lithium ions are intercalated and the battery is fully charged.
Discharging: When the circuit is connected to a load (such as a motor) the lithium ions return to the positive electrode through the electrolyte layer to restore a stable state. The electrons flow along the wire to the positive electrode and recombine with the lithium ions forming a current to supply power to the load.
Key protection mechanisms:
Safety protection: An insulating layer is provided in the middle of the electrolyte to prevent short circuits between the positive and negative electrodes (short circuits will cause the electrolyte to dry up and cause fires).
Formation of SEI film: During the first charging of a lithium battery lithium ions flow to the negative electrode through the electrolyte layer. Some electrons react with solvent molecules and graphite to form a solid electrolyte interphase film (SEI film). The SEI film can block the contact between electrolyte solvent molecules and the negative electrode avoiding electrolyte degradation. Although it consumes about 5% of active lithium ions the overall benefits outweigh the drawbacks. Scientists continue to improve battery performance by optimizing the thickness and chemical properties of the SEI film.
(II) Types of Lithium Batteries and Battery Pack Design
Common types of lithium batteries:
Ternary lithium batteries: The positive electrode adopts a proportional mixture of nickel cobalt and manganese. They have high energy density and good low-temperature performance and are suitable for models focusing on range and power.
Lithium iron phosphate batteries: The positive electrode material is lithium iron phosphate. They have high safety long cycle life and low cost and are suitable for models focusing on stability and economy.
Composition and cooling system of battery packs:
Modular design: A single lithium battery has limited voltage and capacity. The battery pack of an electric vehicle combines thousands of lithium batteries in series and parallel (for example some models' battery packs contain more than 7 000 lithium batteries) to form a high-voltage battery pack.
Thermal management system: Batteries generate heat during operation. Excessively high or low temperatures will affect performance and safety. The battery pack is equipped with a cooling system. The coolant circulates through metal pipes to reduce the battery temperature; at the same time the thermal management system can monitor the battery temperature and heat the battery at low temperatures. The design of multiple small batteries can achieve uniform temperature distribution reduce hot spots and extend battery life.
Structural layout: The battery pack is usually installed under the chassis adopting a modular integrated design which not only saves interior space but also lowers the vehicle's center of gravity improving driving stability.
III. Energy Conversion: Core Functions and Working Mechanisms of the Electronic Control System
The electronic control system of an electric vehicle is the "brain" responsible for coordinating the work of core components such as batteries and motors. Its core functions include the conversion of direct current and alternating current power output control and thermal management which are key to ensuring the efficient operation of the vehicle.
(I) Composition Architecture of the Electronic Control System
The electronic control system is a complex collection of multiple subsystems mainly including:
Thermal management system: Monitors the temperature of batteries motors electronic controls and other components and maintains each component within the optimal operating temperature range through cooling or heating systems.
Motor control module: The core is an inverter which is responsible for converting the direct current output by the battery into alternating current required by the motor and controlling the frequency of the alternating current to adjust the motor speed realizing vehicle acceleration and deceleration.
High-voltage power distribution module: Distributes electrical energy to high-voltage components such as air-conditioning compressors battery heating units and DC converters.
DC converter: Converts the high-voltage direct current of the battery pack into low-voltage direct current (such as 12 volts) to charge the lead-acid battery which then supplies power to low-voltage components such as vehicle lights wipers and sensors.
(II) Inverter: The Core of DC-AC Conversion
The inverter is the core of the motor control module. Its working principle is to convert direct current into smooth sine wave alternating current by quickly switching circuit switches.
Basic circuit switching: A simple inverter circuit includes four groups of switches. By controlling the on and off of the switches the direction of current flow is changed. For example when S1 and S4 are turned on the current flows in one direction; when S2 and S3 are turned on the current flows in the opposite direction. Continuous switching of the switches can generate square wave alternating current.
High-speed switching and waveform optimization: Transistors are used as switching elements which can switch thousands of times per second meeting the motor's requirements for alternating current frequency (usually 50 hertz requiring 100 switches per second). However the voltage of square wave alternating current changes abruptly and needs to be converted into a smooth sine wave. By taking the average value of square wave pulses a curve close to a sine wave is formed and then a passive filter is added to adjust the signal frequency finally obtaining the sine wave alternating current required by the motor.
Circuit protection design: To prevent short circuits a NOT gate circuit is set in the circuit to ensure that only one of each group of switches can be opened; at the same time a comparator is used to compare the sine wave with the triangular wave to generate a specific square wave curve further optimizing the waveform smoothness.
IV. Power Transmission: Simplification and Efficient Design of the Transmission System
Compared with the complex multi-speed gearboxes of fuel vehicles the transmission system of electric vehicles is simpler. It mainly adopts a single-speed gear ratio gearbox and achieves efficient power transmission through optimized design.
(I) Core Structure of the Transmission System
Power transmission path: When the accelerator is pressed the battery transmits electrical energy to the motor control module. The inverter converts direct current into alternating current and transmits it to the motor. The rotation of the motor rotor drives the drive shaft. The drive gear on the drive shaft meshes with the power output gear through the reduction gear and finally transmits power to the wheels.
Deceleration and torque increase mechanism: The reduction gear consists of two gears one large and one small. The large gear meshes with the drive gear and the small gear meshes with the output gear. Through the gear ratio design the speed is reduced and the torque is increased to meet the power requirements of the vehicle during driving.
Implementation of reverse gear: No additional reverse gear is required. The controller reverses the rotation direction of the motor according to the reverse gear command to realize vehicle reversing.
(II) Differential: A Key Component for Solving Wheel Speed Differences
When the vehicle turns the outer wheel travels a longer distance than the inner wheel. If the speed is the same the inner wheel will slip. The function of the differential is to adjust the speed of the inner and outer wheels.
Working principle: The differential consists of a ring gear planet gears and wheel axle gears. Power is transmitted from the drive shaft to the ring gear driving the planet gears to revolve. The planet gears mesh with the wheel axle gears on both sides at the same time. When turning the planet gears will rotate on their own axes increasing the speed of the outer wheel axle gear and decreasing the speed of the inner wheel axle gear thus realizing dynamic adjustment of wheel speed.
Structural optimization: Electric vehicles mostly adopt open differentials. Through the precise meshing of gears the continuity and stability of power transmission are ensured and wheel slip during turning is avoided.
(III) Half Shaft and Universal Joint: Connection Guarantee for Power Transmission
The half shaft is responsible for transmitting the torque output by the motor to the wheels and its core component is the constant velocity universal joint.
Structure of the constant velocity universal joint: Composed of balls a ball cage an inner race and an outer race with a dust cover on the outside. The inner race is connected to the drive shaft through splines. The ball cage is placed inside the outer race and the balls are installed between the cage and the inner and outer races.
Core advantages: Regardless of the angle change between the two shafts the rotational speeds of the driving shaft and the driven shaft are always the same (constant velocity transmission). It has the characteristics of high transmission efficiency high precision and strong angle compensation capability and can efficiently transmit motor torque improving vehicle driving efficiency.
V. Driving Stability: Suspension System and Chassis Design
The suspension system and chassis are the foundation for the driving stability and comfort of electric vehicles. The chassis design of electric vehicles is optimized on the basis of traditional vehicles to adapt to the integration needs of batteries and motors.
(I) Suspension System: Absorbing Impact and Stabilizing the Vehicle Body
The core function of the suspension system is to bear the weight of the vehicle body absorb the impact force caused by uneven roads and reduce vehicle body vibration. It is mainly divided into independent suspension non-independent suspension and semi-independent suspension. Electric vehicles mostly adopt double wishbone suspension among independent suspensions.
Structure of double wishbone suspension: Composed of lower wishbone upper wishbone steering knuckle shock absorber and anti-roll bar. The upper and lower wishbones are connected to the steering knuckle of the wheel through steering ball joints. The steering arm is controlled by the steering wheel to push the wheel to rotate; the anti-roll bar is used to control the roll amplitude of the vehicle when turning.
Working principle of the shock absorber: The shock absorber is composed of a spring and a damper. The spring absorbs the impact energy of the road surface and reduces vehicle body shaking; the damper suppresses the oscillation when the spring rebounds and accelerates the attenuation of vibration. The damper has a working cylinder and a reservoir cylinder inside. The movement of the piston is controlled through the flow of hydraulic oil. When the piston moves down the hydraulic oil is squeezed into the reservoir cylinder; when the piston moves up the hydraulic oil returns to the working cylinder keeping the working cylinder filled with hydraulic oil to ensure the shock absorption effect. The expandable liquid nitrogen filled in the reservoir cylinder can reduce resistance gaps and discontinuities.
Synergistic effect of the anti-roll bar: Relying solely on the shock absorber to control roll requires the use of too stiff springs and high damping coefficient dampers which will sacrifice the ability to absorb road vibrations. The anti-roll bar works synergistically with the shock absorber which can effectively control the roll amplitude of the vehicle when turning without affecting vibration absorption improving driving stability.
(II) Skateboard Chassis: An Innovative Design for Modular Integration
Electric vehicles generally adopt a skateboard chassis design which integrates core components such as motors batteries electronic controls transmission systems and suspensions onto the chassis to form a structure similar to a skateboard.
Core advantages:
Modular development: The vehicle body is decoupled from the chassis. Mechanical connections are reduced through drive-by-wire systems. The vehicle body can be developed independently in modules. Different vehicle bodies can be docked with the same chassis shortening the model development cycle and reducing production costs.
Space optimization: The battery is laid flat on the chassis saving interior space and improving riding comfort; at the same time it lowers the vehicle's center of gravity reducing shaking during driving and improving stability.
Material selection: The chassis needs to support the weight of the entire vehicle body and usually adopts high-strength steel and aluminum alloy. Steel is strong and durable and aluminum alloy is lightweight which can realize the lightweight design of the chassis and improve the range.
VI. Intelligent Control: Application and Expansion of Drive-by-Wire Technology
Drive-by-wire technology is the foundation of the intelligence of electric vehicles. It realizes power control through wires or electronic signals replacing traditional mechanical hard connections to achieve electronic and precise operation. It is widely used in systems such as accelerators brakes and steering.
(I) Wire Layout and Voltage Classification
The electrical components of electric vehicles are divided into high-voltage components (batteries motors inverters etc. with a voltage of 250-750 volts) and low-voltage components (vehicle lights wipers sensors etc. with a voltage of less than 250 volts). The corresponding wires are also divided into two categories:
High-voltage cables: Orange thick in diameter with anti-electromagnetic interference capabilities connecting high-voltage components such as charging ports on-board chargers battery packs motors and high-voltage power distribution modules.
Low-voltage wires: Yellow connecting low-voltage components and powered by lead-acid batteries.
(II) Drive-by-Wire Implementation of Core Systems
Drive-by-wire accelerator:
Traditional fuel vehicles connect the accelerator pedal to the engine through a steel cable which cannot accurately control the air intake; the drive-by-wire accelerator of electric vehicles replaces the mechanical spring with a sensor. When the pedal is pressed the sensor sends an electrical signal to the motor control unit which adjusts the motor speed according to the signal strength to achieve precise control of the vehicle speed.
Drive-by-wire brake:
Traditional disc brake structure: Composed of hub assembly brake disc brake caliper and hydraulic system. When the brake pedal is pressed the mechanical force is transmitted to the master brake cylinder through the brake push rod pushing the hydraulic oil to the hydraulic piston of the wheel driving the brake caliper to clamp the brake disc to achieve braking.
Drive-by-wire brake improvement: The mechanical connection between the brake pedal and the master cylinder is removed. A sensor is installed on the pedal and the brake caliper is changed to a motor-controlled type. When the brake is pressed the sensor sends an electrical signal to the controller which drives the caliper to actuate realizing electronic braking with faster response speed and more precise control.
Auxiliary braking system:
ABS anti-lock braking system: Sensors are installed on the wheels. When it is detected that the wheels are about to lock the ABS modulator unit intermittently releases the brake pads to make the wheels rotate intermittently avoiding wheel slip and allowing the driver to maintain control of the vehicle especially effective during emergency braking.
Hill-start assist system: It detects the brake pressure through the master cylinder pressure sensor and judges the road inclination through the longitudinal acceleration sensor. When the driver releases the brake pedal the system continues to maintain the brake pressure for a few seconds providing time for switching to the accelerator pedal to prevent the vehicle from rolling back which is suitable for uphill and downhill scenarios.
Drive-by-wire steering:
The traditional steering system connects the steering wheel and the rack through a mechanical shaft relying on an electronic power steering system to reduce steering resistance; drive-by-wire steering removes the mechanical connection. When the steering wheel rotates the sensor sends an electrical signal to the controller which drives the electric motor on the rack to control the wheel steering. It is more suitable for the modular design of decoupled chassis and vehicle body with higher steering precision.
(III) Working Principles of Other Drive-by-Wire Components
Windshield wipers:
Early mechanical windshield wipers were driven by DC motors to rotate worms and gears and could not adjust the speed according to the rainfall; drive-by-wire windshield wipers adopt transistor control circuits combined with capacitors and resistors to achieve intermittent work. They sense the rainfall through the roof rain sensor and automatically adjust the wiping frequency to ensure clear vision.
Airbags:
Traditional airbags rely on inertial ball sensors. During a collision the ball moves to connect the circuit igniting sodium azide to generate nitrogen for inflation but there are risks of toxic gases and false triggering; modern drive-by-wire airbags use sodium nitrate as the gas-generating material combined with Mams sensors distributed around the vehicle body to accurately detect the collision intensity and position and complete inflation within 30 milliseconds to protect the safety of drivers and passengers.
VII. Comfort Guarantee: Heating and Cooling Principles of the Air Conditioning System
Electric vehicles do not have engines and cannot use engine waste heat for heating like fuel vehicles. Their air conditioning systems ensure comfortable interior temperature through specially designed heating and cooling devices.
(I) Cooling System: Working Mechanism of Automotive Air Conditioning
The core of cooling is to transfer heat through the phase change of the refrigerant. The main components include a compressor condenser dryer expansion valve and evaporator.
Working process:
After the compressor starts it compresses the low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant which is transported to the condenser through pipelines;
The condenser dissipates heat through pipelines and fins and the fan accelerates heat dissipation turning the high-temperature and high-pressure gaseous refrigerant into high-pressure liquid refrigerant;
The liquid refrigerant separates gas and liquid through the dryer and enters the expansion valve where the pressure drops sharply becoming low-temperature refrigerant;
The low-temperature refrigerant flows into the evaporator behind the instrument panel. The evaporator absorbs the heat of the hot air in the vehicle to cool the air and the blower blows the cold air into the vehicle;
After absorbing heat the refrigerant turns back into a gaseous state and returns to the compressor to complete the cycle.
Temperature switching: The air flow direction is controlled by the mixing damper. When the evaporator pipeline is closed the air only passes through the heat exchanger (heating device) to generate hot air; when the heat exchanger pipeline is closed the air only passes through the evaporator to generate cold air.
(II) Heating System: PTC Heater and Heat Pump System
PTC heater:
Working principle: Using PTC materials (positive temperature coefficient thermistors) such as nickel-chromium alloy when current flows through electrical energy is converted into heat energy due to resistance. The resistance of PTC materials increases with temperature rise and the surface temperature remains stable after reaching a certain value realizing constant heat supply.
Installation position: Inside the warm air pipeline. After the air blows through the heater it is heated and then sent into the vehicle through the ventilation pipeline.
Advantages and disadvantages: Simple structure and fast heating speed but it consumes battery power and shortens the vehicle's range.
Heat pump system:
Working principle: Similar to a "reverse air conditioner" it uses heat in the air to heat the vehicle interior. The outdoor condenser acts as an evaporator in heating mode absorbing heat from the outside air and turning the internal refrigerant from liquid to gaseous; the refrigerant flows to the compressor and is compressed into high-temperature and high-pressure gas which is sent to the condenser inside the instrument panel. The blower blows air through the condenser to absorb heat and then sends it into the vehicle to achieve heating.
Core advantages: It does not directly consume electrical energy to generate heat but transfers heat from the air. It has a higher energy efficiency ratio can reduce range loss and is suitable for use in low-temperature environments.
VIII. Energy Supply: Charging System and Battery Management
The charging efficiency and battery safety of electric vehicles depend on the collaborative work of the charging system and the battery management system (BMS) to ensure efficient charging and discharging of the battery within a safe range.
(I) Charging Methods: AC Slow Charging and DC Fast Charging
AC slow charging:
Working process: The charging pile outputs alternating current which is connected to the on-board charger through the vehicle's charging port. The on-board charger converts the alternating current into direct current to charge the battery pack.
Characteristics: Slow charging speed (usually takes several hours to fully charge) but low equipment cost and small battery loss suitable for home use scenarios.
DC fast charging:
Working process: The charging pile completes the conversion from alternating current to direct current internally and directly charges the battery pack without the participation of the on-board charger.
Characteristics: Fast charging speed (can be charged to 80% power in half an hour) but high equipment cost and certain battery loss suitable for public fast charging station scenarios.
(II) Core Functions of the Battery Management System (BMS)
Battery balancing:
The battery pack is composed of thousands of small batteries connected in series and parallel. There are differences in the charging status and power of each battery. The BMS adjusts through two methods: active balancing and passive balancing.
Active balancing: Using components such as capacitors and transformers the excess charge of batteries with sufficient power is transferred to batteries with insufficient power to achieve power balance.
Passive balancing: Using dummy loads such as resistors the excess power is consumed in the form of heat to make the power of each battery tend to be consistent.
Temperature management:
It monitors the temperature of the battery pack. When the temperature is too high or too low it activates the thermal management system and heats or cools the battery through coolant to ensure that the battery works within the optimal temperature range (usually 20-40℃) avoiding overheating fires or performance degradation due to excessive cold.
Safety protection:
It real-time monitors the voltage current and power status of the battery to prevent abnormal situations such as overcharging over-discharging and short circuits. During charging if an overcharging risk is detected it automatically cuts off the power supply of the charging pile; during discharging if the current is too large it adjusts the output in a timely manner to protect battery life and use safety.
IX. Energy Recovery: Working Principle of the Regenerative Braking System
The regenerative braking system is a characteristic function of electric vehicles that can convert the kinetic energy during braking into electrical energy for recovery and storage extending the range.
(I) Core Principle: Bidirectional Conversion between Motor and Generator
Forward work (driving mode): The rotating magnetic field generated by the stator coil cuts the rotor generating induced current and electromagnetic force driving the rotor to rotate. The motor converts electrical energy into mechanical energy.
Reverse work (power generation mode): During braking the vehicle's inertia drives the wheels to rotate which in turn drives the motor rotor to rotate. At this time the inverter is controlled to adjust the frequency of the alternating current so that the rotor speed is greater than the rotating magnetic field speed. The rotor cuts the magnetic field to generate reverse induced current and the torque reverses to achieve deceleration. The motor becomes a generator converting kinetic energy into alternating current.
(II) Energy Recovery Process
The inverter rectifies the alternating current generated by the generator into direct current;
The DC converter converts the direct current into a voltage matching the battery voltage;
The converted electrical energy is stored in the battery pack. This process can increase the range by more than 10%.
X. Multiple Power: Hybrid and Extended-Range Electric Vehicles
In addition to pure electric vehicles hybrid and extended-range electric vehicles are important models in the transitional stage combining the advantages of fuel and electricity.
(I) Hybrid Electric Vehicles (Hybrid Electric Vehicles)
Core structure: Equipped with an engine two motor-generator sets (MG1 and MG2) an inverter and a lithium battery pack with a planetary gear mechanism as the core.
Working modes:
Low-speed driving: The engine is not started and MG2 drives the wheels to achieve pure electric driving reducing fuel consumption.
Accelerated driving: The battery supplies power to MG1 and MG2. MG1 drives the engine to start and the engine and MG2 jointly drive the wheels to provide strong power.
High-speed driving: The engine is the main driver and MG1 acts as a generator to charge the battery and MG2 maintaining battery power.
Braking/deceleration: MG2 switches to generator mode converting the kinetic energy of the wheels into electrical energy to charge the battery.
Advantages: No range anxiety environmentally friendly with pure electricity at low speeds high efficiency of the engine at high speeds suitable for complex road conditions.
(II) Extended-Range Electric Vehicles
Core structure: Equipped with an engine generator battery pack and motor. The engine does not directly drive the wheels but only drives the generator to generate electricity.
Working principle:
When the battery power is sufficient the motor drives the wheels to achieve pure electric driving;
When the battery power is insufficient the engine starts to drive the generator to generate electricity. The electrical energy supplies power to the motor or charges the battery and the motor is always responsible for driving the wheels.
Essence: It belongs to the category of pure electric drive. The engine only serves as a "power bank" solving the range anxiety of pure electric vehicles and the driving experience is close to that of pure electric vehicles.
XI. Intelligent Upgrade: Technical Analysis of the Intelligent Driving System
Intelligent driving is one of the core competencies of electric vehicles. Through the collaboration of three major systems: perception decision-making and execution it realizes assisted driving or even autonomous driving functions improving driving safety and convenience.
(I) Perception System: The "Eyes and Ears" of Electric Vehicles
The perception system is composed of various sensors collecting surrounding environmental data to provide a basis for decision-making:
Cameras: Identify visual information such as lane lines traffic signs pedestrians and vehicles relying on algorithms to analyze potential risks but are greatly affected by light.
Millimeter-wave radar: Detect the distance speed and direction of objects through radio waves with a long detection distance (more than tens of meters) not affected by light and weather making up for the defects of cameras.
Ultrasonic radar: Use high-frequency sound waves to measure the distance of close-range objects mainly used for parking assistance and low-speed collision avoidance.
Lidar: Emit laser beams to scan the surrounding environment generating 3D maps with high object detection accuracy and can accurately identify complex road conditions but the cost is high.
(II) Decision-Making and Control System: The "Brain" of Electric Vehicles
Data processing: Fusion and analysis of multi-source data collected by the perception system removing redundant information and extracting key features (such as obstacle positions lane information traffic signals).
Strategy formulation: Formulate driving strategies according to preset rules and algorithms (such as deep learning models) including operation instructions such as acceleration deceleration steering lane changing and parking.
Human-machine interaction: When the system cannot handle emergency situations it reminds the driver to take over the vehicle through sound and light to ensure driving safety.
(III) Execution System: Converting Instructions into Actions
The execution system receives decision-making instructions and controls the vehicle's acceleration braking steering and other actions through drive-by-wire technology. It mainly relies on the drive-by-wire accelerator drive-by-wire brake and drive-by-wire steering systems mentioned earlier to ensure the accuracy and timeliness of instruction execution.
(IV) Classification Standards for Intelligent Driving
According to the classification of the Society of Automotive Engineers (SAE) intelligent driving is divided into 0-5 levels:
Level 0: No automation fully manually operated by the driver without any auxiliary functions.
Level 1: Assisted driving the system provides limited automation (such as adaptive cruise lane departure warning) and the driver needs to control the vehicle at all times.
Level 2: Partial autonomous driving the system can simultaneously control acceleration and steering (such as lane keeping assist traffic jam assist) the driver needs to maintain attention and be ready to take over at any time.
Level 3: Conditional autonomous driving the system completes most driving operations in specific environments (such as highways) the driver does not need to observe at all times but needs to take over when reminded by the system.
Level 4: High-level autonomous driving the system undertakes all driving tasks in areas covered by high-precision maps without driver intervention (such as urban navigation automatic parking).
Level 5: Full autonomous driving realizing autonomous driving in all weather and all terrains the driver does not need any operation and can focus on other affairs.
At present the intelligent driving of mainstream electric vehicles is mostly in the stage of level 2 advanced assisted driving. Level 3 and above autonomous driving are still in the testing and promotion stage. Full autonomous driving (level 5) still needs to break through multiple bottlenecks such as technology and regulations.
XII. Summary: Technical Core and Development Trends of Electric Vehicles
The operation of electric vehicles is the result of the collaborative work of core components: the motor provides power as the "heart" the lithium battery stores electrical energy as the "energy source" the electronic control system coordinates and controls as the "brain" the transmission suspension and chassis ensure driving stability the drive-by-wire and intelligent driving systems improve the control experience and the charging and regenerative braking systems solve the problem of energy supply.
From the perspective of technological development electric vehicles are evolving towards the direction of "more efficient safer more intelligent and more environmentally friendly": motors will further improve energy efficiency and power density lithium batteries will develop towards higher energy density faster charging speed and longer life intelligent driving will gradually break through from assisted driving to high-level autonomous driving and modular chassis and drive-by-wire technology will promote the standardization and diversification of model research and development.
It is worth noting that although electric vehicle technology is becoming increasingly mature safety issues still need to be taken seriously—whether it is battery thermal management the reliability of intelligent driving or the stability of drive-by-wire systems continuous optimization is required. For consumers while enjoying the convenience brought by electric vehicles they should also maintain safety awareness especially in intelligent driving mode and be ready to take over the vehicle at any time to ensure travel safety.
The emergence of electric vehicles has not only changed the way of transportation but also promoted the transformation of energy structure and industrial upgrading. With the continuous breakthrough of technology future electric vehicles will be closer to user needs becoming the core choice for sustainable travel and laying the foundation for building a green and intelligent transportation ecosystem.
