Think of the old adage called "Murphy's Law": "Everything that can go wrong will go wrong." Over the past 50 years, electronic component-based systems have been fully developed to provide very advanced monitoring and control functions with exceptionally high reliability. Worried about reliability is generally because of the potential danger to human life, followed by high losses caused by failures and decreased user satisfaction. However, things are never perfect, so there is always a need to constantly improve reliability to produce safe, durable electronic systems.
When system reliability must be guaranteed and there is no choice, the best but most expensive method is to use fully redundant circuits. The exact same circuit performs the same function at the same time, and some form of voting on the execution results always produces the safest effect. In many such systems, if a faulty circuit is detected, the circuit is automatically removed and replaced with an identical backup circuit. This is the ideal topology for long-term reliable operation. On the other hand, the consequences of failures do not always prove that the high cost of full redundancy is reasonable. Such systems rely solely on the inherent reliability of each component used. Failure of a single component can severely damage the system or permanently compromise accuracy. A design with this property assumes a large amount of risk, but can be implemented at the lowest cost.
In the case of highly reliable systems, the intermediate method is fault monitoring, in which the circuit monitors various system components and reports any anomalies. Since anything can happen at any time in the circuit, the more components that are monitored, the better. The response to the detected fault can vary from system downtime (eg, normally closed emergency stop switch on the train) to some simple service alarm (similar to the dashboard on the car). "Fool lamp") Wait.
This article explains how to improve the long-term reliability of a high-voltage lithium-ion battery pack by using the LTC6801 fault monitoring IC. In applications such as electric vehicles, uninterruptible power supplies, medical instruments, and even power tools, the use of batteries as a power source is an ongoing trend, each with varying degrees of reliability expectations.
Long-life battery power challenges
For electric vehicles and a large number of other types of portable devices, batteries have become a major non-traditional energy source. Lithium-ion batteries are very popular because the energy density of lithium-ion batteries allows lithium-ion batteries to be smaller and lighter than batteries of other chemical compositions with the same energy density. For high-power applications, such as electric vehicles, it is necessary to stack hundreds of batteries to form a high-voltage power supply that produces less current and uses thinner and lighter wires. In this type of automotive application, the safety of the driver is the first, followed by the satisfaction of the owner. Therefore, there are obvious reasons for achieving safe and reliable long-term operation. To achieve this, the power of each battery must be continuously monitored to maintain an optimal level for years of use.
In the simplest case, the circuit is required to measure the voltage of each cell in the battery pack. This measurement is typically performed by an AD converter that passes the information to a microcontroller. The controller carefully manages the charging and discharging of all batteries so that the battery does not operate beyond a tight range, and exceeding this range can greatly shorten battery life. In the case of a system with hundreds of individual cells, an integrated measurement circuit can save a significant number of components. The LTC6802 from Linear Technology is such an integrated functional component. With a built-in 12-bit ADC, it can measure and report voltages on up to 12 cells and two temperature sensors. Any number of batteries can be stacked on top of each other, and each set of measured voltages consisting of 12 batteries is serially transferred to a main microcontroller. These measurement devices and controllers form the heart of the battery management system.
Careful control of the state of charge of each cell is extremely important to extend the usable life of the battery, but this may not be enough to satisfy the increasingly demanding automotive customers. In the case of sensitive electronics, the car presents a harsh and dangerous operating environment. To achieve long-term satisfaction without worry, it is necessary to conduct a “what-if†analysis of the system. A few issues to consider are perhaps:
- What happens if one wire that connects the battery is disconnected?
- What happens if the voltage measurement accuracy shifts?
- What happens if the internal register bits remain at a certain value and always indicate a good battery voltage reading?
- What happens if the measurement IC is somehow damaged by a severe system voltage transient?
The most latent problem may cause the controller to erroneously determine that a battery or a battery pack is in perfect condition, and the fact is that the battery or battery pack is not measured in the correct way. Afterwards, these batteries may be completely discharged or dangerously overcharged, but the system is not aware of it at all. Need something to "monitor the monitor" to achieve a higher level of reliable operation.
Battery Management System (BMS) Fault Monitoring with the LTC6801
An alternative to the fully redundant measurement method is to connect the fault monitoring circuit in parallel with the measuring device to function as a basic function of the review system. The circuit in Figure 1 shows a solution for a battery pack consisting of 12 lithium-ion batteries using an LTC6802 measuring device and an accompanying LTC6801 fault monitor.
The LTC6801 is designed with careful consideration of many potential system failures and is also easy to use. An important design requirement is to allow the device to operate automatically without any software. The only external requirement is the power supply (provided by the battery pack itself) and an enable clock signal. Without the clock input enabled, the LTC6801 stays in a static low power state, drawing only a few uA of current from the battery pack. The enable clock can be provided by a system controller or any other source of oscillation such as the LTC6906 silicon oscillator. Upon receipt of the clock signal, the device automatically wakes up and begins monitoring all of the batteries.
Figure 2 is a block diagram of the basic components of the LTC6801. A 12-bit delta-sigma AD converter (ADC) filters and digitizes the voltage of up to 12 cells and two temperature sensors. A 5V regulator and a precisely trimmed 3V ADC voltage reference are built in. All operating characteristics of the device are set by bonding the device pins to a 5V regulator, 3V reference, or V-. No external components are required.
Shenzhen Ruidian Technology CO., Ltd , https://www.wisonens.com