Rockwell Automation SA500 Drive Configuration and Programming - Manual (Page 107)

SA500 Control Algorithms C-1
A
PPENDIX
C
SA500 Control Algorithms
Depending upon the type of AC motor being controlled, one of four control algorithms
can be configured for each SA500 drive:
• Vector (torque loop)
• Vector (torque loop with speed and position loops and constant power capability)
• Brushless DC (torque loop)
• Brushless DC (torque loop with speed and position loops)
Drives controlling induction motors require a vector algorithm. Drives controlling
brushless DC motors require a brushless DC algorithm. See the block diagrams at the
end of this appendix.
The SA500 vector and brushless DC torque loop algorithms regulate current to the
motor via a sinusoidal PWM (pulse-width-modulation) waveform. The SA500 vector
and brushless DC torque, speed, and position loop algorithms also provide motor
speed and position control, if needed. The following sections describe the torque,
speed, and position loop algorithms.
Torque Loop
The vector and brushless DC torque algorithms are similar with the following
exception. Unlike the vector torque algorithm, the brushless DC torque algorithm does
not need to compensate for slip, which is not a factor in brushless motors. The
brushless motor’s flux is supplied by a permanent magnet in the rotor; thus, no flux
regulation is required. The brushless DC torque algorithm does require the user to
perform an alignment procedure to accurately identify the relationship between the
position of the motor and the resolver.
The torque algorithms use the value in PMI_REF% (102/1102) as the torque
reference (Iq) to the PMI, where a value of +/- 4095 corresponds to the maximum
current supported for the motor. In the vector torque algorithm, the motor currents are
separated into two components, Iq and Id.The Iq component produces the torque in
the motor while the Id component is the magnetizing current which produces the flux
in the motor. The Id component is calculated by the PMI based on the no-load stator
current configuration parameter entered by the programmer. The vector regulator
sums the Iq and Id components to produce a vector that is equal to the total current
required by the motor to produce the desired torque. The vector algorithm supports
constant power operation at speed ratios up to 4:1 using tunable values to weaken the
magnetizing current as function of speed. The brushless DC torque algorithm only
uses the Iq component.
The torque algorithms need to calculate the electrical phase position of the current
reference. In the vector torque algorithm, this is determined from the Id and Iq
reference vector, the motor speed feedback, and the slip calculation. In the brushless