A Series Of Problems Of DCDC In Electric Vehicle Electrical System

DC/DC Converter, As A Very Important Part Of Electric Vehicle Power System, One Of Its Important Functions Is To Provide The Required Power For Power Steering System, Air Conditioner And Other Auxiliary Equipment. The Other Type Is In The Composite Power System, Which Is Connected In Series With The Super Capacitor To Adjust The Power Output And Stabilize The Bus Voltage. To Supply Power To The Vehicle Electrical, The Location Of The DCDC In The Electrical System Of The Electric Vehicle Is Shown In The Figure Below. Its Electric Energy Comes From The Power Battery Pack, And The Place Is To Supply Power To The On-Board Electrical Appliances.The Position Of The DCDC Used In Conjunction With The Supercapacitor In The Vehicle Power Supply Is Shown In The Figure Below. It May Appear In The Positions Shown In Figures (B), (C), And (D), And (B) Is More Widely Used. A Form Of. DC DC Classification And Working Principle1.1 Isolated And Non-IsolatedWhat Is Electrical Isolation?A Paragraph From Baidu: Electrical Isolation Is The Electrical Isolation Of The Power Supply And The Electrical Circuit, That Is, The Electrical Branch Circuit Is Isolated From The Entire Electrical System, Making It An Electrically Isolated, Independent Ungrounded Safety System To Prevent The Risk Of Indirect Electrocution In The Event Of An Exposed Conductor Faulty Live. After Electrical Isolation Is Achieved, There Is No Direct Electrical Connection Between The Two Circuits. That Is, The Two Circuits Are Insulated From Each Other. At The Same Time, It Is Necessary To Ensure That The Two Circuits Maintain The Relationship Of Energy Transmission. The Main Function Of Electrical Isolation Is To Reduce Mutual Interference Between Two Different Circuits And Reduce Noise.The Non-Isolated Two-Way DCDC Has A Relatively Simple Structure, Each Component Is Directly Connected, There Is No Additional Energy Loss, And The Work Efficiency Is Relatively High. The Requirements For The Capacitor On The Boost Side Are Relatively High. The Main Non-Isolated DCDC Circuit Structures Include A Bidirectional Half-Bridge Boost-Buck Circuit, A Bidirectional Buck-Boost Circuit, A Bidirectional Buck Circuit, And A Bidirectional Zate-Sepic Circuit, As Shown In The Figure Below. Isolated Two-Way DCDC, Adding A High-Frequency Transformer To The Non-Isolated Two-Way DCDC Converter Constitutes An Isolated Two-Way DCDC Converter. The Circuit Topology On Both Sides Of The High-Frequency Transformer Can Be Full-Bridge, Half-Bridge, Push-Pull, Etc. These Isolated Bidirectional DCDC Converters Use More Power Switches, Have A Large Voltage Transformation Ratio, And Have The Advantages Of Electrical Isolation. However, This Type Of DCDC Converter Has A Complex Structure And Relatively High Cost. The Loss Of The Converter Is High. At Low Frequencies, The Iron Core Of The Isolation Transformer Will Be Saturated, And The Loss Will Further Increase. Therefore, Non-Isolated Bidirectional DCDC Converters Have More Advantages Than Isolated Ones In Electric Vehicles. When The Energy Flows From The High Side To The Low Side, The Bidirectional DCDC Converter Works In The BUCK Mode; When The Energy Flows From The Low Voltage Side To The High Voltage Side, The Bidirectional DCDC Converter Works In The BOOST Mode.1.2 The Three Components Of The DCDC SystemThe Main CircuitAlso Known As The Power Module, It Is The Main Body Of The Entire DCDC. A Typical Full-Bridge DCDC Converter Main Circuit Topology Is Shown In The Figure Below. In The Above Figure, Vin Is The Input Voltage, Which Needs To Pass Through The DCDC Loop To Obtain A Required Output Voltage At The Output End. The Primary Side Switch Circuit Modulates The Input Current Into A Rectangular Wave. This Process Mainly Relies On The Controller To Modulate A PWM Wave With A Specific Duty Cycle To Drive The Four Switches To Open And Close In A Predetermined Order And Time, Thereby Realizing The Current Inversion Process. . The Input Voltage Of The Primary Side Can Be Adjusted By The Duty Cycle. The Output Voltage Also Increases When The Duty Cycle Increases, And The Output Voltage Decreases When The Duty Cycle Decreases. The Frequency Can Be Adjusted By Adjusting The Switching Frequency. T1 Bit Transformer, The Transformation Ratio Is N. Transformers Can Not Only Achieve Electrical Isolation, But Also Play The Role Of Voltage Regulation. A Fixed Number Of Turns Of The Primary Coil And Changing The Number Of Turns On The Secondary Side Can Obtain Different Voltage Levels. The Input Of The Transformer Is A Pulsed Rectangular Wave Obtained By Inversion Of The Left Full-Bridge Circuit, And Is Transmitted To The Secondary Side Of The Transformer, And An AC Sine Wave With Another Voltage Amplitude Is Obtained. After Being Rectified By DR1 And DR2, And Then Filtered By Cf And R1, The Direct Current Is Obtained And Supplied To The Output End.Drive ModuleFor The Four-Way PWM Drive Signal Output By The Control Chip, The Four Power Switch Tubes Cannot Be Directly Driven. Therefore, In General, The Switching Power Supply Needs To Be Equipped With A Driving Circuit To Drive The Power Switch Tube. There Are Many Types Of Drive Circuits, Mainly Including The Following Three:Direct Coupling Type: Each Output PWM Drive Signal Of The Control Chip Drives The Power Switch Tube Through An Amplifier Circuit Composed Of Two Triodes. This Method Cannot Realize The Isolation Of The Control Part From The Main Circuit.Pulse Transformer Coupled Drive Circuit: This Circuit Adds A Pulse Transformer On The Basis Of The Direct Coupling Type, Which Realizes The Isolation Of The Control Circuit And The Main Circuit. However, The Disadvantage Of This Structure Is That It Is Relatively Complicated In Terms Of Design And Manufacture Of The Transformer.Driving Circuit Of Driver Chip: In Order To Drive The Power Switch Tube More Conveniently, Many Companies Have Developed Driver Chips. The Driver Chip Can Output Larger Power And Drive The Switch Tube. Moreover, With The Miniaturization Of The Chip, The Size Of The Current Driver Chip Very Small And Available In Various Packages. Using The Driver Chip To Drive The Power Switch Tube Is Relatively Simple, But The Control Circuit And The Main Circuit Are Still Not Isolated.Control ModuleThe Feedback Of The Main Circuit Mainly Has Three Control Modes: Voltage Control Mode, Peak Current Control Mode, And Average Current Control Mode.Voltage Control Mode: It Belongs To Voltage Feedback And Uses The Output Voltage For Correction. It Is A Single-Loop Feedback Mode. The Output Voltage Is Sampled And Compared With The Input Reference Voltage, And The Obtained Output Signal Is Compared With A Sawtooth Wave Voltage To Output A PWM Wave Signal. The Design And Application Of The Voltage Control Mode Are Relatively Simple, But The Voltage Control Mode Does Not Control The Output Current, So There Is A Certain Error, And The Output Voltage Is Filtered By The Inductor And Capacitor First, Which Makes The Dynamic Response Relatively Poor.Peak Current Control Mode: The Difference Between The Peak Current Control Mode And The Voltage Control Mode Is That In The Peak Current Control Mode, The Sawtooth Waveform Of The Voltage Control Mode Is Converted Into A Superposition Of The Instantaneous Current Of The Inductor And A Small Sawtooth Wave. But The Instantaneous Current Of The Inductor Does Not Represent The Situation Of The Average Current.Average Current Control Mode: It Belongs To The Double-Loop Control Mode, And The Output Signal Of The Voltage Loop Is Compared As The Feedback Signal Of The Reference Current And The Inductor Current. Setting The Error Amplifier Can Average Some High-Frequency Components Of The Input Current, And The Averaged Output Current Can Be Compared With The Sawtooth Wave Generated By The Chip To Output A Suitable PWM Waveform.The Inductor Current And Capacitor Voltage Therefore Require PID Tuning For Both Variables. A Typical Control Flow Is Shown In The Figure Below. The Control Module Is Composed Of Two PID Controllers, Namely The Voltage Control Control Outer Loop And The Current Control Inner Loop. A Reference Voltage Is Given In The Flow Chart, And The Purpose Of The Control System Can Be Quickly Achieved By Designing Reasonable Parameters.Compared With The Three Control Methods, The Average Current Control Method Does Not Limit The Duty Cycle, And Feedbacks Both The Output Voltage And The Inductor Current, Which Has A Better Control Effect. When Using The Average Current Control Method To Design The Feedback Circuit, The Current Loop Is Regarded As A Part Of The Voltage Loop.1.3 Soft And Hard SwitchingWhat Is The Difference Between Hard Switching And Soft Switching In DCDC?Hard Switching And Soft Switching Are For Switching Tubes.Hard Switching Is To Forcibly Turn On Or Turn Off The Switch Regardless Of The Voltage Or Current On The Switch (DS Pole Or CE Pole). When The Voltage And Current On The Switch Tube (DS Pole Or CE Pole) Are Relatively Large, The Switch Tube Will Act, Because The Switching Between The Switch Tube States (From On To Off, Or From Off To On) Takes A Certain Time, Which Will Cause The Voltage And Current Will Have A Crossover Area In A Certain Period Of Time When The Tube States Are Switched, And The Switch Loss Caused By This Crossover Is Called The Switching Loss Of The Switch.Soft Switching Refers To Detecting The Current Of The Switch Tube Or Other Technologies, So That The Switch Tube Is Turned On Or Off When The Voltage Across The Switch Tube Or The Current Flowing Through The Switch Tube Is Zero, So That There Will Be No Switching Loss In The Switch Tube.Generally Speaking, The Efficiency Of Soft Switching Is Higher (Because There Is No Switching Loss); The Operating Frequency Is Higher, And The Volume Of The PFC Or Transformer Can Be Reduced, So The Volume Can Be Made Smaller. But The Cost Is Relatively High And The Design Is More Complicated.Further, The Soft Switching Includes Three Control Modes: Bipolar Control, Limited Bipolar Control, And Phase-Shifted Full-Bridge Control. The Obtained Rectangular Waveform Is As Follows:Q1 And Q3 Are Switches On The Leading Bridge Arm And Belong To The Same Bridge Arm, While Q1 And Q4 Are Diagonal Switches And Belong To Two Bridge Arms Respectively. The First Control Method Is Hard Switching, And Both The Second And Third Control Methods Can Realize Soft Switching, But The Third Control Method Is More Flexible And Easier To Implement.Due To The Higher And Higher Requirements For Power Density, Soft-Switching DCDCs That Can Improve Power Performance By Increasing The Frequency Are The Main Directions Of Current Research. Soft Switching Includes 3 Main Control Methods: ZVS Phase-Shift Full-Bridge Conversion, ZCS Phase-Shift Full-Bridge Conversion, And ZVZCS Phase-Shift Full-Bridge Conversion.2 How To Estimate DCDC Power When Supplying Power To Vehicle Electrical AppliancesEach Electrical Equipment Has Its Own Rated Voltage And Rated Current. If The Electrical Equipment In An Electric Vehicle Often Works In A Non-Rated State, The Power Conversion Efficiency Will Be Greatly Reduced, And The Lifespan Will Be Damaged Or Even The Equipment Will Be Damaged. Therefore, The Specifications Of The DCDC Match The Requirements Of The System In Which It Is Located, So That It Can Function Better. The General Selection Idea Is Not To Directly Add All Electrical Power Together, Because They May Not All Work At The Same Time.According To The Different Attributes Of The On-Board Electronic Equipment Of Pure Electric Vehicles, The Electrical Equipment Can Be Divided Into Long-Term Power Consumption, Continuous Power Consumption, Short-Term Intermittent Power Consumption And Additional Power Consumption Equipment Types, And Assigned Different Weights. Among Them, Long-Term Electrical Equipment Includes Combination Meters And Batteries, And The Weight Is 1; Continuous Electrical Equipment Includes Wipers, Motors, Audio Systems, And Instrument Lighting, And The Weight Can Be 0.5; Short-Term Intermittent Electrical Equipment Includes Electric Horns , Various Signal Lights, Controllers And Other Equipment, The Weight Can Be 0.1; The Additional Electrical Equipment Electric Vacuum Pump, Electric Water Pump And Electric Steering, The Weight Is 0.1, 1, 0.3 According To The Actual Situation. Power Consumption Analysis Of Various Equipment3 How To Determine The Electrical Parameters Of The DCDC With The Super Capacitor Application?In The Composite Power System, Supercapacitors Are Generally Defined As The Part That Deals With High Power. In The Discharge Process, The Part Above The Average Value Is Provided For The Peak Value Of The Working Condition; The Braking Energy Recovery Process Is Responsible For The Absorption Of All Or Most Of The Recovery Current. In The Face Of Impact Power, DCDC Has Relatively High Requirements In Two Aspects. One Is The Reaction Speed. In The Power Circuit In Which The Battery Is Connected In Parallel With The Super Capacitor, The Braking Energy Is Generated From The Motor And Transmitted To The Power Source Through The Bus. If The Response Of The DCDC Is Not Sensitive Enough And The Turn-On Time Is Long, The Incoming Energy Will Be Isolated From The Supercapacitor By The DCDC And Cannot Be Absorbed, But Can Only Be Absorbed By The Battery. Excessive Power Will Cause Physical Damage To The Battery. Another Requirement Of The DCDC Is To Be Able To Withstand The Impact Of Instantaneous High Power. The DCDC Connected In Series With The Capacitor Circuit Needs To Often Face The Working State Of The Impact Power. Therefore, When Choosing A DCDC Connected In Series With A Supercapacitor In A Unified Branch, The Important Parameters Are The Power Range, Operating Voltage And Operating Time.

02-10-2023

A Quick Look at Motors

What is a motor? Answer: The motor is a component that converts battery electrical energy into mechanical energy and drives the wheels of the electric vehicle to rotate. What is winding? Answer: The armature winding is the core part of the DC motor, and it is a coil wound by copper enameled wire. When the armature winding rotates in the magnetic field of the motor, an electromotive force is generated. What is a magnetic field? Answer: The force field that occurs around the permanent magnet or the current and the space that the magnetic force can reach or the scope of the magnetic force. What is magnetic field strength? Answer: Define the magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 1/2 meter from the wire to be 1A/m (ampere/meter, SI in the international system of units); in the CGS unit system (cm-gram-second) In , to commemorate Oersted's contribution to electromagnetism, define the magnetic field strength of an infinitely long wire carrying a current of 1 ampere at a distance of 0.2 cm from the wire to be 10e (Oersted), 10e=1/4.103/m, the magnetic field Intensity is usually indicated by H. What is Ampere's Law? Answer: Hold the wire with your right hand, and make the direction of the straight thumb coincide with the direction of the current, then the direction pointed by the bent four fingers is the direction of the magnetic induction line. What is magnetic flux? Answer: Magnetic flux is also called magnetic flux: Suppose there is a plane perpendicular to the direction of the magnetic field in a uniform magnetic field, the magnetic induction of the magnetic field is B, and the area of the plane is S. We define the product of the magnetic induction B and the area S, which is called passing through Magnetic flux on this surface. What is a stator? Answer: The part that does not rotate when the brush or brushless motor is working. The motor shaft of a hub-type brushed or brushless gearless motor is called a stator, and this type of motor can be called an inner stator motor. What is a rotor? Answer: The part that rotates when the brush or brushless motor works. The shell of the hub-type brushed or brushless gearless motor is called the rotor, and this type of motor can be called an outer rotor motor. What is a carbon brush? Answer: The inside of the brushed motor is on the surface of the commutator. When the motor rotates, the electric energy is transmitted to the coil through the phase commutator. Because its main component is carbon, it is called a carbon brush, which is easy to wear. It should be regularly maintained and replaced, and carbon deposits should be cleaned. What is a brush grip? Answer: The mechanical guide groove that contains and maintains the position of the carbon brush in the brushed motor. What is a phase commutator? Answer: Inside the brushed motor, there are strip-shaped metal surfaces that are insulated from each other. When the motor rotor rotates, the strip-shaped metal alternately contacts the positive and negative poles of the brush to realize the alternating positive and negative changes in the direction of the motor coil current and complete the brushed motor coil. commutation. What is phase sequence? Answer: The arrangement order of brushless motor coils. What is a magnet? Answer: It is generally used to refer to magnetic materials with high magnetic field strength. Electric vehicle motors use NdFeR rare earth magnets. What is electromotive force? Answer: It is generated by the rotor of the motor cutting the magnetic force line, and its direction is opposite to that of the external power supply, so it is called counter electromotive force. What is a brushed motor? Answer: When the motor is working, the coil and commutator rotate, but the magnetic steel and carbon brushes do not rotate. The alternating change of the coil current direction is accomplished by the commutator and brushes that rotate with the motor. In the electric vehicle industry, brushed motors are divided into high-speed brushed motors and low-speed brushed motors. There are many differences between brushed motors and brushless motors. It can be seen from the words that brushed motors have carbon brushes, and brushless motors do not have carbon brushes. What is a low-speed brushed motor? What are its characteristics? Answer: In the electric vehicle industry, a low-speed brushed motor refers to a hub-type low-speed, high-torque gearless brushed DC motor, and the relative speed of the stator and rotor of the motor is the speed of the wheel. There are 5-7 pairs of magnetic steel on the stator, and the number of slots in the rotor armature is 39-57. Since the armature winding is fixed in the wheel housing, the heat is easily dissipated with the help of the rotating housing. The rotating shell is woven with 36 spokes, which is more conducive to heat conduction. The micro-signal of Jicheng training is worthy of your attention! What are the characteristics of brushed and toothed motors? Answer: Because there are brushes in the brushed motor, the main hidden danger is "brush wear". Users should notice that there are two types of brushed motors: toothed and non-toothed. At present, many manufacturers choose brushed and toothed motors, which are high-speed motors. The so-called "toothed" means to reduce the motor speed through the gear reduction mechanism (because the national standard stipulates that the speed of electric vehicles should not exceed 20 kilometers per hour, the motor speed should be at 170 rpm/about). Since the high-speed motor is decelerated by gears, it is characterized in that the rider feels strong power when starting, and has strong climbing ability. However, the electric hub is closed, and it is only filled with lubricant before leaving the factory. It is difficult for users to perform daily maintenance, and the gear itself is also mechanically worn. Insufficient lubrication will lead to increased gear wear, increased noise, and low current during use. Increase, affecting motor and battery life. What is a brushless motor? Since the controller provides direct current with different current directions to achieve the alternating change of the coil current direction in the motor. There are no brushes and commutators between the rotor and stator of brushless motors. How does the motor commutate? Answer: When the brushless or brushed motor is rotating, the energizing direction of the coil inside the motor needs to be alternately changed, so that the motor can rotate continuously. The commutation of the brush motor is completed by the commutator and the brush, and the brushless motor is completed by the controller. What is lack of phase? Answer: In the three-phase circuit of the brushless motor or brushless controller, one phase cannot work. Phase loss is divided into main phase loss and Hall phase loss. The performance is that the motor shakes and cannot work, or the rotation is weak and the noise is loud. It is easy to burn out if the controller works in the state of lack of phase. What are the common types of motors? Answer: Common motors include: hub motor with brush and gear, hub motor with brush and no gear, brushless hub motor with gear, brushless hub motor without gear, side-mounted motor, etc. How to distinguish high and low speed motors from the type of motor? Answer: A brushed and geared hub motors, brushless geared hub motors are high-speed motors; B brushed and gearless hub motors, brushless and gearless hub motors are low-speed motors. How is the power of the motor defined? Answer: The power of the motor refers to the ratio of the mechanical energy output by the motor to the electrical energy provided by the power supply. Why choose the power of the motor? What is the significance of choosing the power of the motor? Answer: The selection of the rated power of the motor is a very important and complicated issue. When the load is on, if the rated power of the motor is too large, the motor is often in light-load operation, the capacity of the motor itself cannot be fully utilized, and it becomes a "big horse-drawn cart". At the same time, the motor has low operating efficiency and poor performance, which will increase running costs. Conversely, if the rated power of the motor is required to be small, it is a "small horse-drawn cart". If the motor current exceeds the rated current, the internal loss of the motor will increase. When the efficiency is low, it is a small matter, and the most important thing is to affect the life of the motor, even if the overload is not much. , The life of the motor will also be reduced more; more overload will damage the insulation performance of the motor insulation material or even burn it. Of course, the rated power of the motor is small, and it may not be able to drag the load at all, which will cause the motor to be in the starting state for a long time and be overheated and damaged. Therefore, the rated power of the motor should be selected strictly according to the operation of the electric vehicle. Why do general DC brushless motors have three Halls? Answer: Briefly speaking, in order for the brushless DC motor to rotate, there must always be a certain angle between the magnetic field of the stator coil and the magnetic field of the permanent magnet of the rotor. The process of rotor rotation is also the process of changing the direction of the rotor magnetic field. In order to make the two magnetic fields have an angle, the magnetic field direction of the stator coil must change to a certain extent. So how do you know to change the direction of the stator magnetic field? That depends on the three Halls. Think of those three Halls as having the task of telling the controller when to change the direction of the current. What is the approximate range of power consumption of the brushless motor Hall? Answer: The power consumption of brushless motor Hall is roughly in the range of 6mA-20mA. Generally, at what temperature can the motor work normally? What is the maximum temperature the motor can withstand? Answer: If the measured temperature of the motor cover exceeds the ambient temperature by more than 25 degrees, it indicates that the temperature rise of the motor has exceeded the normal range. Generally, the temperature rise of the motor should be below 20 degrees. Generally, the motor coil is made of enameled wire, and when the temperature of the enameled wire is higher than about 150 degrees, the paint film will fall off due to the high temperature, causing the coil to short circuit. When the coil temperature is above 150 degrees, the temperature of the motor shell is about 100 degrees, so if the shell temperature is used as the basis, the maximum temperature the motor can withstand is 100 degrees. The temperature of the motor should be below 20 degrees Celsius, that is, the temperature of the motor end cover should be less than 20 degrees Celsius higher than the ambient temperature, but what is the reason for the motor to heat more than 20 degrees Celsius? Answer: The direct cause of the motor heating is due to the large current. Generally, it may be caused by short circuit or open circuit of the coil, demagnetization of the magnetic steel, or low efficiency of the motor. The normal situation is that the motor runs at high current for a long time. What causes the motor to heat up? What kind of process is this? Answer: When the motor is running under load, there is power loss in the motor, which will eventually turn into heat energy, which will increase the temperature of the motor and exceed the ambient temperature. The value by which the motor temperature rises above the ambient temperature is called warm-up. Once the temperature rises, the motor will dissipate heat to the surroundings; the higher the temperature, the faster the heat dissipation. When the heat emitted by the motor per unit time is equal to the heat dissipated, the temperature of the motor does not increase, but maintains a stable temperature, that is, it is in a state of balance between heat generation and heat dissipation. Generally, what is the allowable temperature rise? Which part of the motor is the most affected by the temperature rise of the motor? How is it defined? Answer: When the motor is running under load, it is better to give full play to its role, that is, the higher the output power of the load, the better (if mechanical strength is not considered). But the greater the output power, the greater the power loss, the higher the temperature. We know that the weakest temperature-resistant thing in the motor is the insulating material, such as enameled wire. There is a limit to the temperature resistance of insulating materials. Within this limit, the physical, chemical, mechanical, electrical and other aspects of insulating materials are very stable, and their working life is generally about 20 years. Beyond this limit, the life of the insulating material will be shortened sharply, or even burnt. This temperature limit is called the allowable temperature of the insulating material. The allowable temperature of the insulating material is the allowable temperature of the motor; the life of the insulating material is generally the life of the motor.

02-10-2023

Development status and trend analysis of electric vehicle power battery

The development of electric vehicles can be described as twists and turns. In 1834, the first electric car was born. At that time, dry batteries were used and the cruising range was very short. After Karl Benz invented the internal combustion engine in 1886, electric cars all but disappeared. In 1973, the oil crisis broke out in the Middle East, which caused the world's auto giants to set off a wave of research and development of electric vehicles. However, due to the characteristics of batteries and technical limitations, the development of electric vehicles still failed this time. But we saw 1971 when Toyota introduced its first hybrid car, the Prius. It uses a Ni-MH battery with high current charge and discharge capability, which is safe, but has a low specific capacity and a large volume. Development status and trend analysis of electric vehicle power battery The fourth generation Toyota Prius With the birth of the fourth-generation Prius, in addition to the nickel-metal hydride battery for the HEV version, the PHEV version of the car is also equipped with a lithium battery. The specific capacity has been improved, but the safety has been reduced. At this point, we can't help but ask, which type of battery is the best? What is the standard of a good battery? In this regard, Kuang Dezhi pointed out that any type of battery has its advantages and disadvantages, and their suitable applications are also different. Analysis of advantages and disadvantages of mainstream power batteries The current mainstream batteries include supercapacitors, metal hydride nickel batteries, lithium-ion batteries, and fuel cells. Supercapacitors are characterized by being able to withstand instantaneous high-current charge and discharge, but the storage capacity is low, and they cannot be used to drive vehicles for a long time; metal hydride batteries have high-current charge and discharge capabilities, good safety, but low specific capacity and large volume; Lithium-ion batteries have the highest voltage and high specific capacity among these types of batteries, but their safety and low-temperature performance are poor; fuel cells have attracted the attention of more and more people since last year, and have sufficient energy reserves to quickly replenish fuel. But the cost is high, the instantaneous output capability is poor, and the fatal flaw is that energy feedback cannot be performed, so that the driven vehicle cannot only use fuel cells to realize energy recovery during braking. The current mainstream new energy vehicles in the market include Nissan Leaf, Toyota Prius, Chevrolet Volt, etc., and of course the red-hot Tesla Model S. These four vehicles all use lithium batteries or nickel metal hydride batteries without exception, so it can also be seen that among the above four power batteries, lithium batteries and nickel metal hydride batteries are the two types of batteries with the most intense competition. Many people in the industry have their own opinions on parameters such as power density, energy density, and maximum capacity. In fact, not all parameters are high is the best (certainly impossible to achieve). Kuang Dezhi pointed out that the power density is directly related to the application field of the battery. If it is used in a field where hybrid vehicles require high power, it must also require a large power density; if it is used in a pure electric vehicle, the power requirement is not high but energy storage requirements In higher fields, the power density requirements can be lowered, but the energy density must be large enough. Kuang Dezhi emphasized that whether it is a nickel-hydrogen battery or a lithium battery, its power density and energy density can be adjusted by the battery designer according to the application. Development status and trend analysis of electric vehicle power battery Tesla Model S For example, the Tesla Model S has a battery life of 480 kilometers, and its 18650 lithium battery has an energy density of 200 Wh/kg; while the Chevrolet Volt also uses lithium batteries, because its requirements for pure electric battery life are not high. Only 60 km, so its energy density is only 88 Wh/kg (16 kWh ÷ 181 kg). The relationship between the performance of the battery In addition, the performance of the power battery is mutually balanced, or "contained", and the performance of the battery does not depend on a certain characteristic of a single battery, but on the overall performance. From the figure above, we can see that capacity and durability, high temperature performance and low temperature performance, heat dissipation and insulation, tolerance and cost are four sets of "contradictory" parameters. Therefore, Kuang Dezhi emphasized that only when the relationship between battery performance parameters and the environment is comprehensively considered can it truly have application value. "Safety, life, cost" is the biggest bottleneck my country is a big country of automobiles. In 2014, the production and sales both exceeded 20 million vehicles. However, it is not a big country of automobiles. This is true in the field of traditional automobile technology, and it is also true in the field of new energy vehicle technology. The technical strength of the three core elements of new energy vehicles, batteries, motors, and electronic control systems in my country, is not strong, especially in terms of batteries, which mainly rely on outsourcing. Therefore, the so-called "curve overtaking" can't help but make people feel that it is not worthy of the reputation. Let's look at a set of data first, so that we can have an intuitive understanding of the gap in the development of power batteries at home and abroad. Recently, the official website of PEVE, a well-known Japanese power battery company, released data saying that it has sold 8 million sets of power batteries, and Japanese hybrid vehicles account for 40% of all car sales. In contrast, in 2014, the total sales volume of new energy vehicles in my country was less than 80,000. How many of these batteries come from local Chinese companies? The huge level difference is horrifying. So, where is the gap between my country's power battery technology and the international advanced level? And in what technical bottlenecks? Kuang Dezhi pointed out that the bottleneck of domestic power battery technology lies in life, safety and cost. These three points are not completely independent, but interrelated. Battery life refers to cycle life and shelf life, and the reduction of cycle life mainly comes from the consistency problem in the process of battery grouping. Low cycle life will increase the need for battery replacement, which will greatly increase the cost of electric vehicles. The shelf life refers to the attenuation of the life of the battery in a static state. In automotive applications, the battery is left on hold most of the time. From the perspective of practical application, the attenuation of the battery is very obvious when the vehicle is exposed to high temperature in summer. It introduced that when using Ni-MH batteries, especially power-type Ni-MH batteries, it is more guaranteed that the battery can be used in a smaller mileage range, which can prolong its life. In addition, the operating temperature of the battery also has an impact on the lifespan, the higher the temperature, the shorter the lifespan. The Ni-MH battery is limited to 35°C, and the life will be cut in half for every 10°C increase in temperature. Therefore, when designing, install a thermal management system to manage the battery temperature and keep it used at a constant temperature, which can also prolong the battery life. The most important system related to battery life and safety is the BMS (Battery Management System). Kuang Dezhi emphasized that BMS is the core component to ensure battery application. After the battery has been produced consistently, the main factor that can determine the battery life is the BMS. At present, domestic BMS can basically eliminate potential safety hazards such as overvoltage, short circuit, and extrusion under the conditions of single cells and modules, but the safety of the whole package level has not been completely resolved, which is also one of the bottlenecks of battery technology. Kuang Dezhi added that both domestic and foreign BMSs can be developed by professional companies. However, battery companies must put forward their own requirements for battery internal control and identification of battery characteristics. Because enterprises have the deepest understanding of their own batteries, only independent development can achieve optimal control of products. This is Mr. Kuang's suggestion to domestic battery companies, and Keba itself does the same. Summarize: Like the internal combustion engine technology of traditional automobiles, my country also needs to go through the process from outsourcing to cooperative research and development to independent development in the field of new energy vehicle power batteries. Whether it is for new energy vehicle companies or power battery companies, the pursuit of goals should not be limited to production and sales, but start with small components, concentrate on research and development, and achieve breakthroughs in bottlenecks. As Kuang Dezhi said, although my country lags behind the international level in terms of power battery technology, we are backed by a vast automobile market, which provides us with an opportunity to catch up with and surpass foreign advanced levels.

02-10-2023