Hi all
i have a question for quadrature encode pulse (QEP), for
rotating speed detection.
My encoder has 500 lines, and 3 signal A, B, and index. My DSP is ezdsp f28335.
With sampling frequency of 10kHz and a maximum speed is 50 rev / s, then my PI-speed controller works, but if speed is smaller (for example speed = 10 rev / s) , my controller instable. I have ACI motor, I think it is up to speed detection. But I'm not sure.
With 500 lines encoder, wmax = 50hz, fsampling = 10kHz, then on a sampling period is the max Impuls_counts_differenz: From w [1 / s] = [delta_counts / (4 * 500 lines)] * fsampling.
wmax = 50 = delta_counts_max/(4*500 lines)]* 10 000
===> delta_counts_max = 10 counts / Period
The code looks like that :
EQep1Regs.QDECCTL.bit.QSRC=00; // QEP quadrature count mode
EQep1Regs.QEPCTL.bit.FREE_SOFT=2; //unaffected by emulation suspend
EQep1Regs.QEPCTL.bit.PCRM=00; // PCRM=00 mode - QPOSCNT reset on
///index event
EQep1Regs.QEPCTL.bit.UTE=1; // Unit Timeout Enable
EQep1Regs.QEPCTL.bit.QCLM=1; // Latch on unit time out
EQep1Regs.QEPCTL.bit.IEL = 1; // IEL_RISING
EQep1Regs.QEPCTL.bit.IEI = 2; // IEL_RISING
EQep1Regs.QPOSMAX=4*500 - 1;
EQep1Regs.QEPCTL.bit.QPEN=1; // QEP enable
EALLOW; // Enable EALLOW
GpioCtrlRegs.GPAMUX2.bit.GPIO20 = 1; // GPIO20 is EQEP1A
GpioCtrlRegs.GPAMUX2.bit.GPIO21 = 1; // GPIO21 is EQEP1B
GpioCtrlRegs.GPAMUX2.bit.GPIO23 = 1; // GPIO23 is EQEP1I
EDIS;
In interrupt routine with 10khz = fsampling
interrupt void main_isr(void)
{
float Tmp1;
……………
…………….
………………
if (SpeedMessungcount == SpeedMessungscaler)
// so I can reduce speed_samplingfrequency
/ /speed_samplingfrequency =
fsampling/ SpeedMessungscaler
{
// Check the position counter for EQEP1
RawTheta = (Uint16)EQep1Regs.QPOSCNT ;// QPOSCNT 32 bit
// Compute the mechanical angle
MechTheta = RawTheta/(4*500);// floating point
if ((MechTheta < 0.95)&&(MechTheta > 0.05))
Tmp1 = fsampling* SpeedMessungscaler *(MechTheta - OldMechTheta)*60;//rpm
else Tmp1 = Speed;//rpm
/*
if (DirectionQep == 0) // POSCNT is counting down
{
if (MechTheta > OldMechTheta)
Tmp1 = -(1.0 - MechTheta + OldMechTheta)* fsampling*SpeedMessungscaler;
//
x2-x1 should be negativ
esle
Tmp1 = (MechTheta - OldMechTheta)* fsampling* SpeedMessungscaler;
}
else if (DirectionQep ==1 ) // POSCNT is counting up
{
if (MechTheta < OldMechTheta)
Tmp1 = (1.0 + MechTheta - OldMechTheta)* fsampling* SpeedMessungscaler;
else
Tmp1 = (MechTheta - OldMechTheta)* fsampling* SpeedMessungscaler;
}
Tmp1 *= 60; //rpm
*/
// Low-pass filter
Tmp1 = K2*Speed + K3*Tmp1; // e.g. fc = 50hz , 1. Order
if (Tmp1 > BaseRpm) // BaseRpm = 3000 rpm
Speed = BaseRpm;
else if (Tmp1 < - BaseRpm)
Speed = - BaseRpm;
else
Speed = Tmp1;
// Update the angle
OldMechTheta = MechTheta;
SpeedMessungcount = 1;
}
else SpeedMessungcount++;
}
Can you advise me how i change the speed measurement ?
Many thanks in advance!
Tequila
