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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

ALTERING MOTOR CONTROL PARAMETERS

It is important that you are familiar with the dsPIC assembly language so you can make changes to the motor control software, but expertise is not necessary. The SVM portion of the software is handled as a “black box.” This means that you do not need to know exactly how it works. If you wish to alter the “black box,” further documentation is available from Microchip.^[9] The main motor control scheme is executed at a higher level in “PIC C” language in a file called ACIM.c posted on the Circuit Cellar FTP site.

From ACIM.c, you can manipulate almost every aspect of the motor behavior (see Listing 1). ACIM.c contains a function called DoControl(), which is executed on a time-based interrupt vector. This is where you would make alterations to the code in order to make the motor perform differently. For our project, we needed to get the motor to respond to input the same way that a car would. Some of our colleagues needed to introduce regenerative braking into their software. This was all done within the DoControl() function. However, you cannot allow too many instructions to occur within this function; otherwise, the SVM period may become altered and impede proper operation.

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