Hydrogen fuel cell electric vehicles are still driven by motors. Hydrogen is only used to react with energy for power generation, and finally reacts with oxygen to generate electricity to drive the vehicle. The voltage of a single fuel cell is less than 1V. In order to increase the output voltage, it is generally necessary to stack multiple fuel cell cells in series to form a fuel cell stack. In order to ensure the normal operation of the fuel cell, it is also necessary to match the accessory system for the stack to continuously supply the fuel cell with reactants of appropriate temperature, pressure, flow rate, and humidity, and to discharge the generated water and heat.
The fuel cell system is composed of the electric stack and the accessory system. The health status of the fuel cell is mainly reflected in its monomer voltage. Factors such as over-dryness, over-humidity, lack of gas and other adverse operating conditions and mechanical damage will cause the fuel cell The voltage changes. Therefore, if you want to diagnose the state of the fuel cell or rely on the cell voltage to control the fuel cell system, you need to know the cell voltage of the fuel cell, and use the fuel cell (stack) and inspection together.
The voltage inspection is connected to the single battery on the fuel cell stack through the inspection signal collection line to realize the voltage collection. During the voltage inspection, it is transmitted to the communication tool through the inspection communication (such as CAN bus communication) harness, and then Connect with the host computer through the communication tool to directly monitor or record the collected cell voltage.
As we all know, lithium battery packs need a battery management system (BMS) when charging and discharging, mainly to detect the voltage, current and temperature parameters of the lithium battery; functional safety. Because the fuel cell is different from the discharge principle of the lithium battery, its detection mainly detects the battery voltage, temperature and other parameters, which is the fuel cell stack inspection (CVM).
Because the polarity of the proton exchange membrane occasionally reverses when the fuel cell performs proton exchange power generation, the traditional lithium battery BMS solution is no longer suitable for testing fuel cells. In order to solve the inspection problem of fuel cell stacks, some domestic companies use simulated separation solutions to solve this problem.
Features of Analog Separation Scheme
Use multiple high common-mode voltage operational amplifiers and 12Bit ADC to collect battery voltage, use high-voltage optocoupler for isolation between battery and collection board, and use decoder for battery channel switching. The acquisition board is isolated from the main control MCU, and the acquisition board and the car host use isolated CAN communication.
The signal chain of the scheme is as follows:
The program features:
● 8 high-common-mode operational amplifiers and multiple high-voltage optocouplers can measure 120 fuel cells in series
● Channel measurement range: ±4V
● Isolated 5V single power supply
● 2-way CAN
● The total measurement error is 15mV
● Communication cycle 100ms
● Working temperature: -40-85℃
ADI AFE Integrated Solutions
For the fuel cell market, ADI has introduced the industry’s only AFE integrated solution – LTC6806.
The LTC6806 is a fuel cell monitor that can measure up to 144 fuel cells connected in series with a total measurement error of less than 15mV. The LTC6806 includes 36 input channels, each with a ±5V measurement range, allowing each channel to measure 1 to 4 fuel cells connected in series.
Features of the program:
● 36 measurement channels to monitor up to 144 fuel cells in series
● Channel measurement range: ±5V
● Battery pack voltage range: –80V to 150V
● 5V single power supply
● Stackable architecture supports large fuel cell stacks
● Built-in isoSPI™ interface
● The total measurement error is 15mV
● Measure all units in the system in just 6.75ms
● Delta-Sigma converter with built-in noise filter
● Six general-purpose digital I/O or analog inputs
● Temperature or other sensor input (can drive discharge, fault indicator light)
● Working temperature: -40-125℃
Advantages of this program:
● High integration greatly reduces the use of high-voltage optocouplers, decoders, and isolated power modules, which can reduce the difficulty of PCB layout and PCB size while reducing costs
● LTC6806 built-in filter can effectively reduce the noise interference when the car starts
● LT6806 has a built-in ISO SPI interface, which can be used for daisy chain communication; it is convenient for multi-chip or multi-module cascading
● The whole system is convenient for miniaturization and modular design; it is easier to match the hydrogen fuel cell pack of the car factory
In order to make it easier for users to evaluate the performance of LTC6806 and shorten the project development cycle, ADI provides demo DEMO, which is convenient for customers to test and verify, and shorten the development cycle.
Compared with the traditional separation scheme, LTC6806 can provide superior performance and more protection; it also improves the voltage measurement accuracy and reduces the cost of the whole system. The highly integrated AFE technology facilitates modular and miniaturized design, supports multi-module horizontal cascading and vertical cascading installation methods, and is convenient for users to expand the number of chips arbitrarily, with flexible installation and free application.
The Links: FM400TU-07A G084SN03 V1