Vehicle Goals

Complete the race
Cover the greatest possible distance in a given amount of time

Hardware Goals

Fulfill regulatory requirements for competition
Enable foundational systems required for the efficient operation of a solar vehicle
Maintain high availability to fulfill the above functions

Design Philosophy

The hardware system is highly mission-focused and strives for simplicity while fulfilling the intended goals. The general design philosophy follow’s Elon Musk’s steps for good design:

Establish and challenge requirements: A top-down design approach is taken, starting with system goals and distilling those down to functional and engineering requirements. Requirements are constantly challenged to ensure they accurately reflect the goals of the system. Bias is taken towards having the lowest possible number of requirements to ensure a lean system. If a requirement is missed it can be added at a later stage. Conversely, it is very unlikely that an unnecessary requirement will be identified at a later stage and removed. It’s your job to challenge requirements! Speak up and question everything.
Delete parts: All parts of the system are analyzed and their existence justified. Components not required to fulfill the predetermined requirements should be removed from the system. Before attempting to solve a problem, it should be determined whether the problem needs to be solved in the first place.
Simplify and optimize: The remaining parts are simplified and optimized for the requirement they are intended to fulfill. Simplicity improves efficiency, reduces the chances of failure, and shortens the development cycle which ensures a higher chance of success. However, optimization should not be performed on parts that shouldn't exist, hence it is the last stage in the design process.

High Voltage

Main Power Switch

The main power switch consists of 3 EV200 series relays. One relay is located at each terminal of the main battery and at the positive terminal of the solar input. This allows the battery, motor, and solar array can be disconnected from each other and all HV conductors exiting the battery box to be disconnected from the battery as required by ASC 8.6.A.4. The main power switch is located inside the battery enclosure and controlled by BMS system from the carrier board.

Main Fuse

The [model name and rating] main fuse is present to break a pack short should one occur. It is a [High Speed or Fast Acting Semiconductor Type Fuse] placed before the positive battery relay and be rated for less than 200% of the rated pack current and 75% of the rated conductor current as per ASC 8.5.A.

Battery

The main pack of 288 LG M50 21700 cells is built from 9 4s8p modules in series to deliver a nominal capacity of 5.2kWh. With 36 cells in parallel, the battery voltage ranges from 90V to 153V depending on the state of charge, with a nominal voltage of 130.68V. The size of this battery is limited by ASC 8.2.A.1. Details of the custom battery management system, including the current shunt, can be found under the appropriate low voltage section.

Pre-Charge

Each of the two motor controllers contains 270uF of low ESR capacitance which requires pre-charging to avoid damage from large inrush currents that would result from directly connecting to the HV battery. A pre-charge resistor is bypassed by a switch controlled by the motor controller interface once the HV bus is charged to > 90%. The higher Rdson of using power fets compared to a relay is offset by the lack of hold current, resulting in overall lower power loss.

DCDC

The DCDC takes energy from the main back and provides an isolated source of 12V power for all of the low voltage systems in the car. It is centered around a Vicor DCM3623 240W power module, which is capable of delivering up to 16A.

Solar

The solar array consists of 260 Maxon Gen III UHP cells arranged in 12 panels. The arrangement of the panels is constrained by the fact that MSXV is using the panels originally designed for MSXIV.

Key Parameters

Area

3.98658m2 = 153.33cm2 x 260 cells

As per ASC 8.1.B, SOVs have a maximum solar cell area of 4m2, which is 260.875 of our cells.

Theoretical Power

920.4W = 3.54W x 260 cells

From datasheet given at 1000W/m2

Configuration

MPPT Arrangement Sheet

Panels are connected in two parallel strings each consisting of 5 Nomura MPPTs. Ideal diodes are used to prevent the strings from back feeding each other. The output voltage limit of each MPPT is set such that the maximum voltage of each strings is equal to the max charge voltage of the HV battery, allowing a direct connection to the pack.

Low Voltage

Battery Protection and Management

BMS Carrier

The BMS system consists of 3 board variants:

BMS Current Sense - Monitors pack current and calculates SoC with a fuel gauge IC.

BMS AFE - Measures

Drive Interfaces

Pedal

Steering

Rear Visibility

Since the canopy provides no rear visibility, to comply with ASC 9.5.E Rear Vision a rear view camera system is present. A Mobius USB action camera (Rev B, 116 FOV) connects to a Raspberry Pi Zero which outputs to an HDMI display on the driver dashboard.

Project	Summary

Project	Summary
Controller Board	The “brain” of the boards; all boards that require ‘decision making’ or firmware-controlled inputs or outputs will have a controller board
Power Distribution	This board controls the power flow of all other devices in the car. It chooses who gets power, where the source of the power is, and monitors the power drawn Power Select: selects the power source that the car draws power from. It selects between the AUX (usually used only for fans, horn, telemetry, main contactor relays), and DCDC (LV power from main pack) Power Distribution: contains many firmware-controlled load switches that deliver power to all other boards/devices on the vehicles (boards, fans, horn, lights, etc). Also monitors the current draw for each load. Contains many connectors for other boards to plug into
	Disconnects the battery if the voltage falls below a certain threshold. Provides additional protection features, including fuse to limit short-circuit current inrush-current limiting reverse polarity protection.
Centre Console	Serves as the hub of communication between the driver and the car. Displays useful information (speed, battery state, left/right turn signals, Battery Protection System warnings) to the driver in the form of LEDs and 7-segment displays. It also receives input from 6 buttons, allowing the driver to Power On the vehicle, switch drive states (Drive, Neutral, Reverse), and enable/disable regen braking and hazard lights.
Motor Controller Interface (MCI)	Talks to motor controllers, we control the motors/get motor information through this board.
BMS Carrier	This board is responsible for protecting the battery. Its responsibilities are: Logging Voltage, Current, Temperature Calculating the state of charge Detecting battery faults and acting upon them
BMS AFE	Used to measure cell voltage and temperatures from each individual battery module, and also keep the cells balanced
BMS Current Sense	Measures the total current flowing from the battery pack.
DCDC	Converts the high voltage (110-150V) to the necessary low voltage of 12V nominal (ends up being 13-14V)
Pedal	Measures the angle of both pedals in the car (accelerator and brakes). This information is used to know how much each pedal is pressed, and then use this information to execute some functions (e.g if the accelerator is not pressed then regen braking will occur; if brakes are pressed, then brake lights should turn on)
Steering	Used for measuring steering angle as well as controls present on the stalk (lights, signals, horn).
Solar Sense/MPPTs	Solar sense: Measures the array module and array voltage, temperature, current MPPT: Converting high current low voltage output from the solar panels into low current high voltage power compatible with our batteries and motors
Steering Stalk	The physical steering stalk that the driver uses, taken off an old vehicle, currently in the bay. It contains its own circuitry that must be understood such that we can interface with it and understand how to read its inputs.
Motor Testing	To test the motor and motor controller work correctly
Electrical Systems PVDR/VDR	Comprehensive design report including technical documents mechanical systems, electrical systems, batteries, and solar cells.

Theory of Operation - MSXV Hardware