Embedded Systems Design - March 2008 - (Page 24)

0308esd.p16to25 2/14/08 3:51 PM Page 24 cover feature Figure 6 shows the graphical representation of the centroid point calculation for the output vector Y[]. 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 3phase power inverter. The power inverter converts the six signals to a 3phase signal that directly powers the motor. The 3-phase power inverter function is handled by an auxiliary termined by detecting edges from signals received from the hall-effect sensors. The signals are fed into the TMS320F2812’s capture pins and 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. HARDWARE DESCRIPTION The eZdsp2812 board is used in this motor control application. At the heart of the eZdsp board is the TMS320F2812 DSP. The TMS320F2812 is a 150-MHz device that uses timer T1 running at 20 kHz for generating PWM1-6 signals, and timer T2 running The fuzzy controller calculates at 40 kHz for executing inthe absolute and differential based on the SOFTWARE terrupt service routines (ISRs). Additionally, the inDESCRIPTION target set speed, current speed, and put capture pins CAP1-3 are The motor control previous absolute error. used to collect speed data software is composed from the hall-effect sensors. of DMC Library modOther members of the 28xx family motor control board. Spectrum Digital ules and the FL motor control routines. may be substituted for the provides two boards that provide this Seven of the DMClib modules are used TMS320F2812. For instance, the eZdfunction: the DMC550 and the in this application. They are: sp2808 board may be used if the timers DMC1500. Either board plugs directly Datalog driving the PWM and ISRs are into the eZdsp28xx board. BLDC3PWM changed. Speciﬁcally on the eZdsp2808 Hall-effect sensors are used for Hall3_Drv board, EPWM1-3 is used for PWM feedback for the fuzzy logic control Mod6_Cnt generation, while CPU timer 0 is used loop. The commutation instants for the Rmp2Cntl for an ISR interrupt source. Similarly, 3-phase power inverter switches are deRamp_Cntl Speed_PR The output membership function. NM NS ZE • • • • • • • y PS PM -0x10 Figure 5 -0x8 0x0 0x8 0x10 The output membership function multiplied by vector Y[]. y NM NS ZE 0x196A PS PM -0x10 Figure 6 -0x8 0x0 0x13F 0x8 0x10 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 24 MARCH 2008 | embedded systems design | www.embedded.com http://www.embedded.com

Table of Contents Feed for the Digital Edition of Embedded Systems Design - March 2008

Embedded Systems Design - March 2008 Contents #Include Programming Pointers Designing DSP-based Motor Control Using Fuzzy Logic Hardware/Software Verification Enters the Atomic Age Efficient CRC Calculation with Minimal Memory Footprint Programming Your Own Microcontroller Advertising Index Break Points Marketplace

Embedded Systems Design - March 2008

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