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Issue #217 August 2008
Subcategory Winner - Microchip 2007 Design Contest
INTELLIGENT ENERGY SOLUTIONS
Electric Vehicle Inverter Design
Build A System For Powering AC Induction Motors
by Dan Hall, Tristan Kasmer, Doug Krahn, Adam McIntyre, and Dena Ponech
Start | Power Inverter | Gate Drivers | Control Board | Space Vector Modulation | PID Tuning | Altering Motor Control Parameters | HMI | Protocol | Firmware/Software | Sources & PDF
FIRMWARE/SOFTWARE
The daughter board firmware is responsible for assembling CAN bus packets and sending and receiving messages. Currently, the only messages sent by the daughter board are the PID tuning parameters. You can select the PID parameters using sliders in the LabVIEW GUI (see Photo 5a). The GUI software assembles and sends all of the PID parameters in one array, appending each individual parameter with 0xFFFF. This allows the firmware on the PIC18F4620 to parse the array and assemble each parameter into a CAN bus message. When receiving messages, the firmware extracts the data portion of the CAN bus message, puts it into a temporary buffer, and then puts the data onto the UART to be received by the GUI. Because we aimed to minimize the delay of data handling time and make the GUI as “real time” as possible, we processed all of our daughter board’s incoming messages in the LabVIEW application. The HMI handles the incoming string of data using case statements to parse the array and determine the type of data arriving before sending it to the appropriate gauge or graph on the GUI (see Photo 5b).
a) b)  |
| Photo 5a—This is the LabVIEW HMI that enables you to adjust the motor controller’s PID tuning parameters. The sliders adjust the PID of the flux, torque, and speed and save the values in an array that is sent to the motor control board when “Send Parameters” is clicked and there is an indication that the data has been received. b—The real-time HMI enables you to observe feedback from the motor, shaft speed, and graphical representations of the torque and flux. Fault and alarm conditions from the motor and motor controller are also displayed. |
As the electric vehicle becomes a more viable alternative for transportation, this project will be referenced as one way to help with the conversion of a gasoline engine to an electric motor. Currently, the main factors in conversion are safety and battery technology. As these concerns are addressed, an open-source project will be a welcome alternative for those who wish to take on an electric motor modification themselves.
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