When designing an electrical system, engineers must take special care to ensure that the power being supplied to all the electrical components will meet specifications. As such, the design of a safe and reliable power distribution system is critical for ensuring the success of any project that involves electrical systems. In a high-performance automotive application, key design considerations for a power distribution system must also consider minimizing mass, size, and overall complexity.

A basic design alternative for power management in an automotive application is the use of fuses. While fuses do protect electrical components in the event of an overcurrent scenario, they are relatively heavy and occupy lots of space, which hinders the performance of a race car. Previously, SR chose to distribute power using a third-party device. While the third-party product offered many benefits when compared to the basic fuse alternative, the device did not have enough power outputs, lacked customizability, was high cost, and required the use of additional external circuitry to power necessary devices on the car.

Our solution has been designed to meet both the race car’s current and future power distribution requirements. At the same time, it minimizes complexity by consolidating all additional circuits and the design is highly compact which minimizes the overall mass and size. The design features numerous safety features and is highly cost-effect when compared to the third-party power distribution product.

One of the main focuses when designing our project was ensuring that it was well suited to the rapidly evolving nature of racecar design competitions. Year after year, the Schulich Racing car gains additional features and new ambitions are formed. Existing solutions often lack the characteristics and customizability to be suited to such an environment. We’ve improved on such solutions by:

1. Creating a scalable design, allowing other endpoints to be easily integrated and powered by our design in the future
2. Using electronic fuses for endpoint power control eliminates the need to replace or manually interact with traditional fuses
3. Creating a custom PCB design to allow for the integration of our design with future team-built hardware designs
4. Using a holistic approach to power distribution and current monitoring
5. Utilizing onboard power regulation to power lower voltage endpoints
6. Minimizing the cost of our product to be 90% lower than existing power distribution modules for racing applications
7. Incorporating CAN communication to broadcast essential endpoint data to other vehicle modules
8. Protecting each endpoint from fault conditions and implementing safety functionalities such as an emergency shutdown circuit and reverse battery protection

With the advantage of designing a custom solution for the Schulich Racing team, we could make decisions focused specifically on catering to the needs of the race car. This application-specific focus allows our design to be more effective at meeting the needs of the Schulich Racing vehicle than other products on the market while also utilizing modern technologies that outperform traditional fuse boxes which are commonly used by competing FSAE teams. Our solution sought to outperform existing solutions and the FSAE competition through the following features:

1. All power distribution and voltage regulation circuitry are integrated into a single PCB
2. Providing multiple voltage levels, spare outputs, current limits, and trip time delays means that our PDM will be able to power almost any automotive device that Schulich Racing may add in the future
3. Application-specific diagnostic information improves the team’s ability to debug future electrical issues on the vehicle
4. Enhanced safety as a result of the diagnostic information provided by electronic fuses, allowing for constant monitoring and rapid response to fault conditions

Our approach to design validation relied heavily on segmenting our planned overall design into its major components and assembling a PCB for each. We designed PCBs for our microcontroller, power regulation, power shutdown, and electronic fuse modules. Individually, we used these PCBs to conduct targeted test cases, as well as connect them together to verify that our designs could be successfully integrated.

Our final integrated PCB was validated by conducting thorough test cases prepared prior to its arrival. The designed test cases verified every aspect of our design, from basic fuse control to the complex monitoring and fault detection routines, and finally, connecting our design to a test wiring harness which emulates the operation of the real car.

Since our design is anticipated to be used in future generations of the Schulich Racing racecar, delivering an operational minimum viable product was of utmost importance. To ensure our design would be successfully integrated and used in the years to come, we made the following considerations:

• The cost of our solution is 90% lower than the existing solution
• Utilizing a microcontroller family with mature design tools, abstraction libraries, and an easily integrable operating system to minimize the firmware development burden
• Researching commercial and hobbyist designs aimed at solving similar problems to find commonalities, pitfalls, and areas of improvement
• Completing frequent and iterative testing of core circuit designs on test PCBs
• Defining the project scope with tiers of complexity to ensure a minimum viable product is attainable, with the option of adding more complex features
• Leveraging previous experience with specific PCB design tools and firmware development suites
• Reaching out to previous internship mentors for design feedback

The eFuses handle power switching from the 12V protected rail and the power regulation module to all electrical devices in the vehicle. The MCU directly controls power switching while also receiving diagnostic and fault information from each eFuse. Our eFuse modules also contain the hardware to allow for firmware selectable current limits and delays to match the electrical characteristics of any device that needs to be powered.

An eFuse, or electronic fuse, is an integrated circuit that acts as a power switch while also providing fuse-like overcurrent protection and other electrical protections including over-voltage protection, under-voltage lockout, and thermal shutdown in case the device’s internal temperature becomes too high. An eFuse has the advantage over a traditional fuse in that it has significantly faster short circuit shut-off protection, typically in the hundreds of microseconds to hundreds of milliseconds range. This makes the eFuse a more precise, and therefore safer, device in automotive applications.

Altium Schematics

Discrete current sensing circuitry has been designed into our module to allow for live current monitoring of individual outputs as well as cumulative board current. Output current is sensed through a carefully selected shunt resistor that is then read by a current sensing IC. The current sensing IC outputs the reading as a voltage that can be sampled by the MCU and used for onboard diagnostics as well as external telemetry. When combined with our onboard voltage sensing, the current reading can be combined to estimate power consumption for individual devices and of the entire power distribution module.

Altium Schematics

The power regulation module is a critical component of our power distribution system and properly regulates the battery voltage to provide the correct power for each of the various endpoints such as the radio and display as well as for the onboard components. Currently on the car, the existing PDM solution does not perform any voltage regulation for any of the outputs, so an external breakout board was required to regulate the battery down to 5 volts for most of the sensors on the car. Our power distribution system removed the need for the external breakout board reducing weight, space, and cost for power regulation on the car.

The main considerations for our power regulation design centered around these characteristics for the voltage regulators:

• Efficiency (Power Dissipation)
• Dropout Voltage
• Current Rating
• Operating Temperature Range
• Voltage Output’s Accuracy
• Input Voltage Range

Based on these design considerations the power regulation module was designed to consist of two switching regulator circuits to regulate the battery (12 volts) down to 8 volts and 5 volts and one linear regulator circuit to regulate 5 volts down to 3.3 volts for the MCU, efuses and CAN transceiver.

Altium Schematics

To protect the driver and vehicle in an emergency scenario, Formula SAE Rules require a shutdown circuit to cut power to the Fuel Pump and Ignition Coils. The shutdown is engaged when either the brake over travel switch or the main cockpit switch opens a circuit going back into the PDM. As a safety-critical function, this shutdown feature is implemented on our PDM solely with MOSFETs rather than relying on firmware executed in the MCU – maintaining reliability and speed of action. In the past, SR used bulky mechanical relays to meet the emergency shutdown requirements, however this new design greatly reduces mass, size, and cost.

Altium Schematic

As SR is an interdisciplinary student team, team members of varying backgrounds and knowledge levels may work with and troubleshoot the electrical systems. The reverse battery protection circuit was included to ensure our design is as safe and user-friendly as possible. In the event our board is connected to a power supply that is in reverse polarity, the reverse battery protection circuit will engage ensuring our board and other downstream components are protected.

Altium Schematic

The MCU module functions as the central control system for our power distribution system. At its core is a specially chosen 144-pin ARM microprocessor that features peripherals to enable the sampling of 23 analog signals, monitoring of 23 digital signals, generation of 5 PWM signals, bi-directional communication over CAN, and control of 21 electronic fuse channels using over 60 digital pins. Of the total 144 pins, our solution utilizes 133. Surrounding the MCU itself are several multiplexing and input conditioning circuits to expand the MCU’s analog signal sampling capacity and convert specific signals to be MCU compatible respectively.

Altium Schematic

CAN (controller area network) is a message-based protocol designed to allow devices to communicate with each other without the need for a host computer. SR uses CAN as the standard protocol for communication between all the on-board equipment. As such, our design solution requires the ability to both read and send messages over a CAN network. The CAN module is designed to act as an interface between a microcontroller with CAN communication support and the CAN physical layer. The microcontroller utilizes the hardware in the CAN module to reliably send and receive messages. Examples of CAN messages broadcast by our device include battery voltage levels, the current draw of specific fuses, and fault events. We also monitor CAN messages from other vehicle components to make decisions about how to control certain vehicle endpoints.

Altium Schematic