User's Manual

PMAC User Manual
Setting Up PMAC Commutation 97
sec)/updates(RateUpdatePhase
)Hz(FreqSlip
)update/cycles(FreqSlip =
The phase update rate for PMAC is determined by the master clock frequency and by jumpers E29-E33
and E98. The default rate is 9.04 kHz, or 9040 updates/sec.
The second piece of information will allow conversion of the rated applied torque to units of DAC bits —
the torque units PMAC uses:
bits) (DAC bits) (DAC
)A(nterRMSCurreMaxAmplifi
)A(RMSCurrentRatedMotor
eMotorTorqueRatedTorqu ⋅=
The third piece of information allows division of the slip frequency by the torque to get slip gain in the
proper units. The equation for slip gain is:
)bitsDAC(Torque
)update/cycles(freqSlip*
38
2
)bitDAC(
)update/cycles
38
2(
gainSlip =
This value then is put into Ix78.
Example:
The technique is best illustrated by an example. Take a system with the following parameters:
Motor: Rated RMS current: 20A
Rated full-load speed: 1755 RPM
Rated line speed: 60 Hz
Number of poles: 4
Amplifier: Maximum RMS current: 40A
PMAC: Peak output for max amplifier current: 32,767 DAC bits (10V)
Phase update rate: 9.04 kHz (9040 updates/sec)
Constant of proportionality: 2
38
From this data, compute the above equations:
Hz50.1
2*60
4*1755
60)Hz(freqSlip =−=
4
10659.1
sec)/updates(9040
)Hz(50.1
)update/cycles(freqSlip
−
×==
Rated Torque = 32768 DAC bits * (20A / 40A) = 16384 DAC bits [2
14
])
2784
16384
10659.1*2
)(
)/2(
438
38
=
×
=
−
bitDAC
updatecycles
gainSlip
Ix78 would be set to 2784.
Setting the Magnetization Current
Warning:
The technique described in this section can involve the measurement of high and
potentially deadly voltages unless measuring voltages well isolated from the power
voltages. Make sure proper techniques for measuring power-level AC voltages are
understood thoroughly before attempting this technique.