Control the safety of lithium batteries in electric vehicles at source

In the process of lithium battery production, the evaluation of battery capacity and performance is a very important link. From low capacity mainly used in mobile phones, cameras, hybrid cars(<10A) To the medium capacity(10A-30A) for computers, electric motorcycles, electric vehicles, and then to the high-capacity lithium-ion battery for electric vehicles(30A-120A), all tests are required. Can be used from the factory.

According to the introduction of Li Qiang, systems application engineer of the Asia Pacific Precision Instrument Division of ADI, the most common practice in the industry is to use linear test equipment for small-capacity batteries. Although it is inefficient and inaccurate, it is still acceptable. However, if such test equipment is also used for high-capacity battery testing, it will consume a lot of power during the charging phase, resulting in inefficiency, and it will cause considerable thermal problems in device hardware design.

To this end, ADI abandoned the previous battery energy discharge in the AD 8450/1 precision analog front-end and controller developed for low, medium, and high capacity lithium batteries to be converted into equipment, as well as the ADP1972 pressure-relief/boost PWM controller. The linear architecture of the load, Instead, it uses PWM controllers to provide current and guide it back to the grid or charge other batteries to achieve efficient environmental protection.

How to Control the Safety and Accuracy of lithium battery in Electric Vehicle from the Source

Test data show that in charging mode, when the voltage is 3.5 V, the efficiency value of 20A is 88 %, and the efficiency value of 10A is 90 %; In discharge mode, when the voltage is 3V, the efficiency value of 20A is 89 % and the efficiency value of 10A is 92 %. In addition to efficiency, lithium-ion battery companies are more concerned with cost and reliability. Li Qiang said that the market for lithium battery testing schemes also have discrete device combinations, may use more than ten devices. The ADI solution only uses AD 8450/1 and ADP1972 two chips, highly integrated, and the design size is greatly reduced. And by increasing the switching frequency to 300KHz, sharing the cost between multiple channels with lower precision DAC and ADC, adding phase-shift synchronization between channels can reduce input filtering and reduce the total system cost. At the same time, ADI also provides users with design tools and all reference designs, minimizing development costs and design difficulties, and shortening the development cycle.

How to share DAC and ADC between multiple channels?

The above figure contains two functions: one is to charge the battery, and the other is to discharge the battery, which is determined by the pattern signals of AD 8450/1 and ADP1972. Each function has two modes: constant current(CC) mode and constant pressure(CV) mode. Two DAC channels control CC and CV set points. The CC set point determines how much current there is in the loop under the CC mode with both charging and discharge functions. The CV set point determines the battery potential when the loop enters CV from CC, which is also suitable for both charging and discharging functions.

The precision analog front-end and controller AD 8450/1 uses the internal differential amplifier PGDA to measure the battery voltage and uses the internal instrument amplifier PGIA and the external current resistor(RS) to measure the current on the battery. Then, it compares the current and voltage with the DAC set point through an internal error amplifier and an external compensation network(used to determine whether the loop function is CC or CV). After this module, the output of the error amplifier enters the PWM controller ADP1972 to determine the duty cycle of the MOSFET power stage. Finally, the inductors and capacitors that make up the complete loop. This section describes both charging and discharging functions because ADP1972 is a pressure-relief and pressure-raising PWM controller.

In this scenario, ADC gets a loop voltage and current reading, but it is not part of the control loop. The scanning rate is independent of the performance of the control loop, so an ADC can measure the current and voltage of a large number of channels in a multi-channel system. The same is true for DAC, which allows multiple channels to be set up using low-cost DAC. In addition, a single processor only controls CV and CC settings, working patterns, and management functions, so it can interface with many channels.

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