Rockwell Automation SA500 Drive Configuration and Programming - Manual (Page 108)

C-2 SA500 Drive Configuration and Programming
algorithm, this is determined from Iq and the rotor position feedback signal. The torque
algorithms produce three current reference output signals, one for each phase of the
motor.
The current reference signals are compared with the current feedback signals,
producing error signals which feed proportional + integral function blocks. The output
of these blocks is a voltage reference. The voltage reference is then compared against
a triangle wave. The output of comparator block is a PWM waveform, which drives the
power devices in the inverter bridge. The PWM waveform closely approximates a
sinusoidal AC voltage.
Speed Loop
Operation of the speed loop is controlled by SPD_ON@ (bit 3 of register 100/1100).
This bit is reset whenever the drive is not in run. The speed loop has a fixed timebase
of 1 msec.
The speed loop uses three input values. Two input speed reference values are
received from UDC tasks: SPD_STPT% (register 105/1105) and SPD_REF%
(register 107/1107). The third input is the velocity output (POS_REG_OUT%, register
209/1209) from the position loop. These values are added together for use in
calculating the speed error.
Speed error is the difference between the sum of the inputs and the speed feedback
value from the resolver. The resolver feedback signal is routed through a notch filter to
reduce any resonant frequencies that may be present. The notch filter is controlled
through NTCH_W% (bit 10 of register 100/1100). Two notch filter parameters can be
modified. The filter’s center frequency can be set through NTCH_W% (register 154/
1154). The filter’s bandwidth can be set through NTCH_Q% (register 155/1155).
The speed error is then fed into a PI block where its output value is added to a
feedforward value to provide a torque output (TRQ_FB%, register 206/1206) for the
torque loop. PI block gain values can be adjusted through the crossover frequency
(WCOS%, register 150/1150) and the damping factor (ZETAS%, register 151/1151).
Speed loop output values are limited by the calculated torque limits. If the positive
limit is reached, TRQ_SP@ (bit 2 of register 200/1200) is set. If the negative limit is
reached, TRQ_SM@ (bit 3 of register 200/1200) is set. The integral value in the PI
block is clamped whenever the positive or negative torque limits are reached.
The speed loop provides two types of velocity feedback: velocity output (SPD_FB%,
register 206/1206) and velocity error output (SPD_ERR%, register 213/1213). These
feedback signals can be used by the UDC module to provide a tachometer loss
velocity error signal. The speed loop itself will generate a fault (FLT_SPD@, bit 5 of
register 202/1202), if the velocity error exceeds the threshold value specified in
SPD_ERR_THR% (register 156/1156).
Position Loop
Operation of the position loop is controlled by POS_ON@ (bit 4 of register 100/1100).
Position loop gain values (i.e., proportional-integral and feedforward values) default to
zero and, unless a non-zero value is entered, will prevent the position loop from
affecting control algorithm operation. The position loop has a fixed timebase of
1 msec.
Note that the speed loop must be turned on (SPD_ON@, bit 3 of register 100/1100)
before the position loop is enabled.