An Electrical Overview
LiU Formula Student is a student organisation at Linköping University, Sweden. Every year the organisation heads out to design and build an electric formula style race car, which races against similar organisations from other universities across the world. Even though the organisation is over a decade old, with many combustion style vehicles, the goal of building an electric vehicle has only been active since the fall of 2020.
Starting off for the 2023/2024 season, many electrical systems from the previous year have been tested and working. However since the base design of many systems are very old, many have had to be refreshed and even have a complete overhaul. Every PCB used on the car has been made this season and no old PCBs from previous cars are used. This was made possible by our partnership with Eurocircuits that provided us with high quality PCBs and a fast production. Overall, this means that the current systems used on the car will hopefully last as a baseline for the following years, making the focus on trying to improve the systems and packaging rather than building them anew.
Since the car systems that use PCBs are varied, here is a brief overview of some of them.
Battery Temperature Measurement Unit – BTMU
The Battery Temperature Measurement Unit is used as a custom multiplexer that actively measures the temperature of the lithium cells which build up the car’s battery. This is done with a plethora of contacts and a microcontroller used to pick the highest temperatures and send them to the Battery Management System. The car uses six of these boards to monitor 100% of the cells used, which is half of the total amount of boards compared to the previous year.
Breakout Board – BR
The Breakout Board acts as a I/O-board for low voltage signals used inside the cars accumulator. It is a non-programmable board and carries critical signals like the cars Shutdown Circuit and BMS CAN-communications. This is a board that handles many different signals and is one of the more complex systems due to its size. Therefore a lot of focus went into simplifying the design layout and removing unnecessary components for functions from previous versions of the board.
Tractive System Active Light – TSAL
The Tractive System Active Light is used to signify that high voltage is present outside the car’s battery, i.e the high voltage conductors on the car connected to the battery is above 60 Vdc. It consists of two different variants, one is called HV-TSAL and the other LV-TSAL. The former is used to detect the voltage present outside the battery and the latter is used to control visible LEDs on the top of the car. Green LED means no high voltage is present and red means that high voltage is active.
Tractive System Control Unit – TSCU
The Tractive System Control Unit is a state machine using a STM Nucleo microcontroller along with a PCB-shield with extra logic attached. One of the most important systems on the car, it handles all control signals of the accumulator’s high voltage and low voltage relays and also monitors their mechanical states. It also receives and handles critical signals from many of the other high voltage monitoring systems.
Tractive System Precharge Unit – TSPU
The Tractive System Precharge Unit is as the name suggests a precharge unit meant for safe charging of the car’s inverter before driving. The system uses a comparator and voltage samples from the accumulator and inverter respectively to determine if the inverter has been charged to 95% of the accumulator’s voltage. Since this board is used as the last in series between HV and LV systems, the board is divided into a LV and HV side, using optocouplers as isolation between them.
For more information please visit the Liu Formula Student website.
Bron: https://www.eurocircuits.com/blog/liu-formula-student-redesigning-the-future-of-electric-racing/
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