dell g5260, dell g5266, dell latitude cpi battery, dell inspiron 8200 battery,
INTRODUCTION
Distributed battery monitoring system has a wide range of applications, scalability advantages; CAN bus has a high transfer rate, reliability, good merits, will be a combination of both applications, the typical battery monitoring and management system architecture as shown in Figure 1.
Which the remote data acquisition unit that is battery monitoring module.
Monitoring module definition
Functions realize the premise is not to influence or affect the battery performance on small to be negligible based on, to leave the premise for the design of the monitoring module will lose its meaning, because in practical applications are often chained together a number of battery applications, a battery failure will inevitably lead to problems throughout the battery pack.
Monitoring module will realize in the above-mentioned under the premise of the following functions:
To accept the control of the upper controller;
Realize the battery data collection, accurate response to the battery of physical parameters, such as voltage, temperature;
Collected data will be transmitted to the upper controller, the realization of data sharing.
Monitoring module to achieve the physical properties
In the sampling rate> 10khz circumstances,
Voltage sampling
25 ℃ voltage accuracy is better than collecting 0.5%, -40 ℃ ~ 85 ℃ is better than 1%.
Temperature Sampling
Temperature acquisition accuracy ± 2 ℃, -40 ℃ ~ 85 ℃.
Monitoring module system architecture
As shown in Figure 2, the dashed border part of the basic structure for the monitoring module.
The basic structure of a total of three major components: low-voltage circuits, isolation circuits, high voltage circuit. Their respective also consists of three parts:
Low-voltage circuit including: signal processing and conversion circuits, the role of treatment are the control signals from the vehicle, the typical signals such as ignition, you can according to different application requirements design; power circuit and main circuit chip, the role is to give low-voltage power supply circuit, At the same time realize the monitoring module control logic and data processing; communication circuit, the role of controller and the upper and lower parts of the data acquisition communications, a typical upper circuit CAN communications protocol communications, the lower circuit SCI \ SPI, I2C, etc..
Isolation circuit including: the control of the isolation circuit, the role is to achieve low-voltage control circuit for high voltage isolation; power isolation circuit, the role is to achieve low-voltage power supply to high voltage power supply isolation control; communication isolation circuit, the role is to achieve high and low voltage circuit-level communications isolation and to ensure the normal communication.
High-voltage circuit including: signal processing, the role is to package the battery module battery signal, temperature sensors and other signals can be directly converted into electrical signal sampling; power and sampling circuits, the role is to provide high-voltage system power supply, at the same time after treatment sampling signal processing, the analog signal into a voltage signal; communication circuit, the role of treatment for the best digital signal sent out, at the same time to accept low-voltage control loop commands.
Design and Implementation
To only collect voltage and temperature as an example the design of the monitoring modules realize.
Low-voltage circuit: MC9S08DZ60 realize the use of control logic, power supply provided by an external 12V battery; the role of power supply circuit for the battery voltage into a +5 V voltage, the use of chip realize TLE4275G; communications circuit CAN and SPI communication.
Isolation Circuit: The photoelectric isolation relays (PhotoMos Relay) realize the isolation control signal; Power isolation can be used isolated power supply, but also can be used directly from the high-voltage electricity from low voltage control of the isolation method designed to achieve the latter; communications circuit using optocoupler or communication to achieve high voltage isolation core communications loop circuit and low-voltage circuit communications connectivity.
High-voltage circuit: The operational amplifier increases the way RC realize voltage signal conversion and conditioning, the use of NTC thermistor increases pressure circuit temperature signal conversion; the use of high pressure to low-voltage power conversion chip high-voltage power supply control circuit; SPI interface with a 12-bit A / D converter AD7888 realize analog signal to digital signal conversion and transmission of data out. Voltage conditioning circuit, temperature conditioning circuit, AD7888 application circuit in Figure 3, respectively, Figures 4 and 5 below.
The impact on battery performance analysis
The program design, in the monitoring module high-voltage circuit part of the normal work, as a result of the AD7888 consumes only the largest 3mW, OPAMP, isolation device power consumption is only a few mW, so the entire high-voltage power circuit power 50mW or less can be maintained, if the battery monitoring module high side voltage of 48V, then converted to high-voltage side current of only about 2mA. This is the battery at work at every turn dozens of A caused by the current power consumption term is almost negligible, very easy to make up for charging; as a result of high-pressure part of the power monitoring of each module are the same, at the same time high-pressure part of the electricity from the battery modules in series the total voltage, therefore monitoring of each battery module of the electricity load also are the same, high-pressure part of the check from the electric battery will not cause the consistency of bad, and in the circuit does not work, because of the isolation device PhotoMos Relay does not work in the worst-case leakage current through the greatest control and below 1mA for 6AH batteries, in the worst case of 10 years caused by self-discharge monitoring module additional capacity loss of only 1.46% (1e-6 × 24 × 365 × 10 / 6), far below the battery’s own self-discharge standard (usually better in the environment, the performance of the battery self-discharge one year > 25%), therefore long-term use can be assured to meet the motor vehicle / car application required.
System performance
Voltage Detection: In the 20V full-scale such as the cases, the use of 12-bit A / D converter can be realized 4.9mV (20V/4096) resolution, the use of error correction can realize the measurement accuracy of better than 0.01V.
Temperature Detected: performance depends on the temperature sensor.
Advantages and disadvantages of the system structure as well as improved
The system has the following advantages: one, to achieve a higher sampling rate, because the expansion of the external ADC, the main factors affect the speed will only be concentrated in high-voltage signal conditioning circuit allows the signal bandwidth and ADC sampling rate, the current development of electronic technology so that the two can easily do more than 10kHz, which means that short-term test to more than 0.1ms instantaneous voltage changes, so measurable voltage change to the details, and data collection necessary to meet the battery. 2, As a result of the isolation measures voltage, high-pressure side of the impact of low-voltage side can be ignored. High-voltage and low-voltage complete isolation, the performance only depends on the device performance in isolation, such as the use of typical optocoupler such as the realization of DC up to 1000V isolation. 3, due to low pressure side and high side there is no contact, so it eliminates a huge (possibly up to several hundred volts) the impact of common-mode voltage, reducing the design more difficult.
System disadvantage: As each piece of monitoring modules with a microprocessor chip, for each additional vehicle electrical system monitoring module will be an increase in the cost of a microprocessor, thus increasing the monitoring module in the cost of vehicle applications.
Possible improvements: to isolate the logic control circuit features realize the high side, so that the monitoring module by the digital signal directly to the upper controller and lower system cost.
