Embedded Systems Design Europe - March 2008 - (Page 20)

cover feature are debounced to eliminate noise or false edges from motor oscillations. The actual motor speed is calculated by counting the edge-triggered signals from the Hall-effect sensors via a software module. Figure 7 shows the hardware block diagram for controlling a three phase BLDC motor. SOFTWARE DESCRIPTION The motor control software is composed of DMC Library modules and the FL motor control routines. Seven of the DMClib modules are used in this application. They are: • • • • • • • Datalog BLDC3PWM Hall3_Drv Mod6_Cnt Rmp2Cntl Ramp_Cntl Speed_PR data from the hall-effect sensors. Other members of the 28xx family may be substituted for the TMS320F2812. For instance, the eZdsp2808 board may be used if the timers driving the PWM and ISRs are changed. Speciﬁcally on the eZdsp2808 board, EPWM1-3 is used for PWM generation, while CPU timer 0 is used for an ISR interrupt source. Similarly, ECAP1-3 capture signals from the halleffect sensors. The motor is driven with PWM signals generated by the DSP and translated to a 3-phase output. The six PWM signals are used to source the 3-phase power inverter. The power inverter 20 converts the six signals to a 3-phase signal that directly powers the motor. The 3-phase power inverter function is handled by an auxiliary motor control board. Spectrum Digital provides two boards that provide this function: the DMC550 and the DMC1500. Either board plugs directly into the eZdsp28xx board. Hall-effect sensors are used for feedback for the fuzzy logic control loop. The commutation instants for the 3-phase power inverter switches are determined by detecting edges from signals received from the hall-effect sensors. The signals are fed into the TMS320F2812’s capture pins and Additionally, the FL motor control is handled by a main FuzzyCtl() routine; this is FuzzyBLDC() for BLDC motors. When conﬁgured, these components demonstrate fuzzy logic control of a variable speed motor. The software works by ﬁrst performing conﬁguration, then application-speciﬁc setup. Speciﬁcally, the GPIO pins are conﬁgured to act as PWMs and CAPture pins. Next the timers and module parameters are initialized, as well as ISR setup. After all peripherals are setup, interrupts are enabled, and the main control loop is entered. The main control loop calls the fuzzy controller once every 8.7 ms. The error values are converted through fuzziﬁcation into fuzzy values and stored in X1[], and X2[]. Once converted, the fuzziﬁed values applied to the fuzzy inference rules. The results from the inference module are stored in Y[]. Output from Y[] is then applied to the defuzziﬁcation module to convert the fuzzy value back to a crisp value. The resulting crisp value is a PWM offset that is added to the current PWM duty cycle; creating a closed loop system. The updated PWM value is checked to see if the new value is within MARCH 2008 | embedded systems design europe | www.embedded.com/europe 014-015-016-018-020-021_EETE.ind20 20 5/03/08 12:49:59 http://www.embedded.com/europe

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Embedded Systems Design Europe - March 2008 Distributors to Increase Embedded Focus Kontron and Quanta to Join Forces Coverity Raises $22m as European Business Booms Help is at Hand for Europe's Industrial Control Developers Milestones in Embedded Systems Microsoft is Recruiting for Embedded Center in Aachen European Designers to Win Cash for Green Designs Duo Work on Smaller Form Factor Europe Invests in Real-Time Java for Multicore Systems Curtiss-Wright Buys Pentland Systems Designing DSP-Based Motor Control Using Fuzzy Logic Lower the Cost of Intelligent Power Control with FPGAs Virtualizing Embedded Linux Back to the Future: Manchester Encoding Is Multicore Hype or Reality New Products Advertising Contacts

Embedded Systems Design Europe - March 2008

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