Project

# Title Team Members TA Documents Sponsor
4 SiCverter (Silicon Carbide Inverter)
Chaitanya Sindagi
Conner Bone
Joshua Powell
Dean Biskup design_document1.pdf
final_paper1.pdf
other1.pdf
proposal1.pdf
## Problem:
The Illini Formula Electric RSO participates in the Electric category of the competition and over the past few years has been gradually getting more competitive. In the competition year of 2021, the team aims to progress their design to a 4 wheel drive design with independently controlled PM motors in each wheel. This requires motor drive units to convert DC power from the battery to 3-phase AC power for the motors. All commercially available drive inverters capable of driving 35kW motors at 600V are too expensive and/or too heavy to be useful in our race car.
## Solution Overview:
The design will use high efficiency silicon carbide MOSFETs, high energy density film capacitors and a high performance microcontroller from TI designed to function well in motor drive applications. It will be designed as a standard voltage source inverter with 3 phase legs and current sensing for all 3 legs for redundancy and noise reduction. A Field-Oriented Control Algorithm will be used to modulate the phase currents and maximize motor efficiency and performance. A motor resolver using a BiSS interface along with a dual CAN communication network will be used for noise immunity on the vehicle. Four of these inverters will be placed on a single large heatsink instead of the industry standard method of using a complex liquid-cooled cold plate. This however, will require ~99% efficiency from the inverter which we believe to be possible. Once achieved, we will have created a lightweight solution with very high efficiency that will cost much less and have more than double the power density of the best commercially available motor drives.

## Solution Components:
### Subsystem 1: Powerstage
The powerstage board will contain the MOSFET module connections, DC link capacitors, gate drive, isolated power supplies and phase current sensing components. These will work together to generate the necessary voltage and current waveforms for the motor to be driven.
The MOSFETs will be Silicon Carbide modules from Infineon in a compact, low-inductive package (FF11MR12W1M1_B11). They will be paired with an array of film capacitors that meet or exceed the performance of the capacitors used in the Infineon evaluation board for the module.

The Gate drivers and current sensors are isolated from the HV section of the board with a 4mm clearance gap to meet/exceed industry standards. They will include fast-acting desaturation and overcurrent protection in order to prevent permanent damage in case of an unintended short. Using split output gate drivers we’ll be able to carefully control the dv/dt of the switch nodes based on measurements taken during double-pulse tests. The isolated supplies chosen will be designed for high dv/dt inverter designs, for SiC voltage levels and with a low isolation capacitance.


### Subsystem 2: Control Board
This board will house all other components including the TI Control Card, motor resolver signal conditioning, CAN transceivers, low voltage power supplies and analog filters.
The purpose of this board is to simply connect the powerstage through the appropriate conditioning to the TI Control Card that houses the microcontroller.
CAN and motor resolver signal conditioning will also be present to allow the inverter to communicate with the rest of the vehicle.

### Subsystem 3: Control Software
This is the software aspect of the design that will be based on the TI MOTORCONTROL SDK and associated resolver libraries.
The primary function of this subsystem is to command the powerstage to deliver the necessary waveforms by using an Field Oriented Control(FOC) algorithm. This algorithm is run on the primary core of the microcontroller.
This is done by first, reading the motor position through the resolver and phase currents from the powerstage and using a park-clarke transform to compute id and iq values, then it will compute the required id and iq current values from the torque request and power limit delivered via the CAN bus and use a tuned PID loop on the difference to compute the necessary changes. Afterwards, an inverse park-clarke transform is used to compute the phase currents followed by a simple six step calculation to compute the PWM values for each phase leg. All of these will be executed on the Control Law Accelerator cores of the microcontroller using TI’s libraries to minimize computation time.

Simultaneously on the secondary core, another program will be logging all important variables at a low speed to CAN as well as at a high speed to a rolling buffer which will be flushed to the SD card in the event of a fault or user triggered event.

## Criterion for a successful solution:
This project aims to build an inverter that has the following attributes-
- Maximum input Voltage = 600V
- Peak Phase Current = 67A
- Average Phase Current(thermal limit) = 45A
- Max Fundamental Frequency = 1.7kHz
- Total weight for all 4 inverters incl. cooling < 6kg
- Power Loss per inverter at peak output <350W

Since the project is extremely complex and board revisions with heavy copper that can operate at maximum current will cost a lot to manufacture, especially in the timeframe necessary, complete functionality before the semester’s end is not expected. Instead, the following goals will be used to determine success of the project -
- Switching performance meets expectations when measured at rated current and power in double pulse testing
- Testing with an RL load at maximum continuous power that the cheaper board can handle, at a wide range of fundamental frequencies
- Theoretical capability to operate at the above-listed performance with no design changes beyond ordering a heavier copper PCB
- Smooth operation of an RC motor at low power

Active Cell Balancing for Solar Vehicle Battery Pack

Tara D'Souza, John Han, Rohan Kamatar

Featured Project

# Problem

Illini Solar Car (ISC) utilizes lithium ion battery packs with 28 series modules of 15 parallel cells each. In order to ensure safe operation, each battery cell must remain in its safe voltage operating range (2.5 - 4.2 V). Currently, all modules charge and discharge simultaneously. If any single module reaches 4.2V while charging, or 2.5V while discharging, the car must stop charging or discharging, respectively. During normal use, it is natural for the modules to become unbalanced. As the pack grows more unbalanced, the capacity of the entire battery pack decreases as it can only charge and discharge to the range of the lowest capacity module. An actively balanced battery box would ensure that we utilize all possible charge during the race, up to 5% more charge based on previous calculations.

# Solution Overview

We will implement active balancing which will redistribute charge in order to fully utilize the capacity of every module. This system will be verified within a test battery box so that it can be incorporated into future solar vehicles.

Solution Components:

- Test Battery Box (Hardware): The test battery box provides an interface to test new battery management circuitry and active balancing.

- Battery Sensors (Hardware): The current battery sensors for ISC do not include hardware necessary for active balancing. The revised PCB will include the active balancing components proposed below while also including voltage and temperature sensing for each cell.

- Active Balancing Circuit (Hardware): The active balancing circuit includes a switching regulator IC, transformers, and the cell voltage monitors.

- BMS Test firmware (Software): The Battery Management System requires new firmware to control and test active balancing.

# Criterion for Success

- Charge can be redistributed from one module to another during discharge and charge, to be demonstrated by collected data of cell voltages over time.

- BMS can control balancing.

- The battery pack should always be kept within safe operating conditions.

- Test battery box provides a safe and usable platform for future tests.