How to prolong the service life of automobile battery

How to prolong the service life of electric vehicle battery? Every five car failures are caused by batteries. In the next few years, with the increasing popularity of automotive technologies such as fly-by-wire control, engine management and hybrid power (electricity/gas), this problem will become more and more serious. In order to reduce faults, it is necessary to accurately detect the voltage, current and temperature of the battery, preprocess the results, calculate the charging state and running state, and send the results to the engine control unit (ECU) to control the charging function. Modern cars were born in the early 20th century. The first car was started manually, which required great effort and great risks. The "crank" of the car has caused many fatal accidents. 1902, the first battery-started motor was successfully developed. At 1920, all the cars are started by electricity. Dry battery was used at first, and it must be replaced when the power is used up. Soon, liquid batteries (that is, ancient lead-acid batteries) replaced dry batteries. The advantage of lead-acid battery is that it can be charged from the engine when working. Lead-acid batteries didn't change much in the last century, and the last big improvement was sealing. What really changes is the demand for it. At first, batteries were only used to start cars, honk horns and power lights. Now, before ignition, all the electrical systems of the car depend on it for power supply. The proliferation of new electronic devices is not limited to consumer electronic devices such as GPS and DVD players. At present, electronic devices such as engine control unit (ECU), power windows and power seats have become the standard configuration of many basic models. The exponential growth of load has had a serious impact, as evidenced by the increase in the number of faults caused by electrical systems. According to statistics of ADAC and RAC, almost 36% of automobile failures can be attributed to electrical failures. If we analyze this figure, we can find that more than 50% of the failures are caused by lead-acid batteries. The following two key characteristics can reflect the health status of lead-acid batteries: (1) State of charge (SoC): SoC indicates how much power the battery can provide, expressed as a percentage of the battery's rated capacity (that is, the SOC of a new battery). (2) Operating state (SOH): SOH indicates how much power the battery can store. The indication of charging state is like the "electricity meter" of the battery. There are many methods to calculate SoC, of which two are the most commonly used: open circuit voltage measurement and coulometry (also known as coulometry). (1) measurement method of open-circuit voltage (VOC): The open-circuit voltage of the battery at no load has a linear relationship with its charging state. This calculation method has two basic limitations: first, in order to calculate SoC, the battery must be open and not connected to the load; Second, this measurement is accurate only after long-term stability. These limitations make VOC method unsuitable for online SoC calculation. This method is usually used in auto repair shops. When the battery is removed, the voltage between the positive and negative poles of the battery can be measured with a voltmeter. (2) Coulomb method: This method uses Coulomb counting to calculate the integration of current with time, so as to determine the SoC. Using this method, the SoC can be calculated in real time even if the battery is under load. But the error of Coulomb method will increase with time. Generally, the open circuit voltage and Coulomb counting method are comprehensively used to calculate the state of charge of the battery. Compared with the new battery, the running state reflects the general state of the battery and its ability to store charge. Due to the nature of the battery itself, SoH calculation is very complicated and depends on the understanding of the chemical composition and environment of the battery. SoH of battery is affected by many factors, including charging acceptance, internal resistance, voltage, self-discharge and temperature. It is generally considered that it is difficult to measure these factors in real time in an environment like an automobile. At the start-up stage (engine start-up), the battery is under the maximum load, which can best reflect the SoH of the battery. The SoC and SoH calculation methods actually used by leading automobile battery sensor developers such as Bosch and Hella are highly confidential and usually protected by patents. As owners of intellectual property rights, they usually work closely with battery manufacturers such as Varta and Moll to develop these algorithms. Figure 1. Discrete battery detection solution The circuit can be divided into three parts: (1) battery detection The battery voltage is detected by a resistance attenuator directly tapped from the positive electrode of the battery. In order to detect the current, a detection resistor (12V is commonly used in applications 100 mω) is placed between the negative electrode of the battery and the ground. In this configuration, the metal chassis of the automobile is generally grounded, and the detection resistor is installed in the current loop of the battery. In other configurations, the negative electrode of the battery is grounded. For SoH calculation, battery temperature must also be detected. (2) Microcontroller Microcontroller or MCU mainly completes two tasks. The first task is to process the result of analog-to-digital converter (ADC). This work may be simple, such as performing only basic filtering; It can also be complicated, such as calculating SoC and SoH. The actual function depends on the processing capacity of MCU and the needs of automobile manufacturers. The second task is to send the processed data to ECU through communication interface. (3) Communication Interface At present, LIN interface is the most commonly used communication interface between battery sensor and ECU. LIN is a low-cost alternative to the well-known CAN protocol. This is the simplest configuration for battery testing. However, most precision battery detection algorithms need to sample battery voltage and current at the same time, or battery voltage, current and temperature. For synchronous sampling, at most two analog-to-digital converters need to be added. In addition, ADC and MCU need to adjust the power supply to work normally, which leads to increased circuit complexity. LIN transceiver manufacturers have solved this problem by integrating a regulated power supply. The next development direction of automotive precision battery testing is to integrate ADC, MCU and LIN transceiver, such as ADuC703x series precision analog microcontrollers from analog devices. ADuC703x provides two or three 8 ksps, 16-bit σ -δ adcs, a 20.48MHz ARM7TDMI MCU and an integrated LIN v2.0 compatible transceiver. The ADuC703x series has an on-chip low dropout regulator, which can be directly powered by lead-acid batteries. In order to meet the requirements of automobile battery detection, the front end includes the following devices: a voltage attenuator for monitoring the battery voltage; When the programmable gain amplifier is used with 100 mω resistor, it can support the measurement of full-scale current from below 1A to 1500A. Accumulator, supporting coulomb counting, without software monitoring; And an on-chip temperature sensor. Figure 2. A few years ago, only high-end cars were equipped with battery sensors. Nowadays, there are more and more middle and low-end cars with small electronic devices, which were only available in high-end models ten years ago. Therefore, there are more and more failures caused by lead-acid batteries. In a few years, every car will be equipped with battery sensors, thus reducing the risk of failure caused by the increasing number of electronic devices.