Speed Controller - PowerTec 2000C Instruction Manual

6.6

SPEED CONTROLLER

The Speed Controller Board (part # 4001-
141107-XXX) handles the speed control of the drive.
It also takes care of the start, stop, jog, emergency
stop, and reverse control logic functions of the Models
2000C and 3000C Brushless DC motor controls.
CONTROL LOGIC - - The Speed Controller
supplies +24VDC (terminal 8 on TB2) to the operator
devices and accepts signals for Emergency Stop (im-
mediate coast stop) on terminal 7 on TB2, ramp stop
(decelerate to zero speed before shutting off - E.Stop
must remain energized during the ramp stop period)
on TB2 terminal 5, and RUN (momentary with hold-
ing contact, or two-wire) on TB2 terminal 4. A jog
function is entered on TB2 terminal 13, but be aware
that the Jog function will override the RUN function if
it is activated while the RUN is active.
The direction of rotation of the motor when
operating in either digital or analog input mode is
determined by the presence of +24VDC at the revers-
ing terminal. If +24VDC is not applied to TB2 termi-
nal 14, the motor will operate in the "forward" direc-
tion. Applying +24VDC at TB2 terminal 14 will cause
the motor to decelerate to zero speed (if it is not
already there), electronically reverse the motor at zero
speed, and then accelerate the motor at the ACCEL
rate to the speed set at the speed pot.
If the control is operating in the digital mode, the
frequency input must be reduced to zero when the
reverse command is applied, then the frequency can be
reapplied once the motor comes to a stop.
SPEED REGULATOR - - All customer
adjusments are located on the Speed Controller Board.
There are also jumpers to range the ACCEL and
DECEL times and to set up the RAMP STOP function.
The speed command is ramped to and from
changing setpoints by the ACC/DEC circuit (remov-
ing the JP2 jumper shortens the time to about 50
milliseconds full scale). The output of the ACC/DEC
circuit is fed to a voltage-controlled oscillator (VCO)
which is linear within 0.5% over the speed range. The
VCO frequency is routed through the Current Control-
ler in case an external frequency is desired.
The reference frequency is routed to the up/
down counter as "count up" pulses. The pulses from
the speed encoder (Current Controller Board) is routed
to the up/down counter as "count down" pulses. A
register holds the accumulated number of error pulses,
which is converted into an error voltage to be used as
a current reference by the Current Controller. The
number of pulses accumulated is directly proportional
to the output current of the control.
Under all normal operating conditions (which
excludes current limit), the number of pulses received
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from the speed reference must be balanced by the feedback
pulses from the motor. In the standard control, the pulse
rate from the motor will be 120 pulses per revolution
(PPR). If the motor is not started, or at zero speed, those
numbers are zero and zero. If the motor is running with a
steady speed reference, the reference and feedback pulse
rates must be the same or the counter would saturate and the
drive would be in current limit.
When a change is made from a steady state condi-
tion, such as an increase in speed command (starting from
zero is an example), pulses are accumulated in the counter
until the motor is drawing enough current to accelerate the
shaft and return more pulses from the encoder than are
coming from the reference. Each extra reference pulse
increases the output current from the control. When the
current is sufficient to accelerate the motor to a speed
higher than that required by the reference pulses, the extra
feedback pulses caused by the higher speed will reduce the
current level until the reference pulses and the feedback
pulses are again in balance.
Notice that this has nothing to do with the frequency
of the pulse trains. The important thing is the number of
pulses in the reference versus the number of pulses in the
feedback. The counter stores the difference in the number
of total pulses. As long as the counter does not saturate (an
adjustable GAIN function), the motor will turn according
to the number of pulses received.
LED indicators are provided for RUN, CURRENT
LIMIT, and ZERO SPEED.
Figure 33: Major parts of the Speed Controller Board
4001-141107-XXX
Model 2000C / 3000C Manual