Installation manual

Danaher Motion Kollmorgen 08/04 System Operation
SERVOSTAR S Installation M-SS-001-01 Rev. T 67
7.3.2.1. Current Loop
Since current and torque are proportional in a permanent magnet
(PM) motor, the current loop is often referred to as the torque loop.
The function of the current loop is to regulate motor current as
directed by a current command signal. The current command signal
from the microprocessor can either come from a direct user input
(OPMODE 2 & 3) or from the output of the velocity loop. There are
actually three current loops, one for each motor phase. Each
current loop receives its own command input from the commutation
loop.
The SERVO
STAR uses a fully digital, pole placement current loop
with high bandwidth and a current loop sampling rate of 16 kHz
(62.5 µs.). All coefficients of the current loop are digitally calculated
inside the drive for a given set of motor and drive characteristics.
The current loop also includes adaptive gain terms to compensate
for some non-linear effects.
The current loop incorporates electrical isolation for protection from
the high-voltage bus. These current loops also convert the output
voltage to a Pulse Width Modulated (PWM) signal providing the
highest efficiency possible. The PWM center frequency can be 8 or
16 kHz according to the drive size.
7.3.2.2. Commutation Loop
This loop converts a single-phase current command signal into a
three-phase, position-modulated sine wave input to the current
loops. The SERVO
STAR has a patented sinusoidal waveform
generator, which uses a technique called Torque Angle Advance to
get top performance out of its motors. The waveform generator is
part of the microprocessor and is updated at a 16 kHz rate. This
provides hi-fidelity sine wave commutation at both low and high
velocities. The sine wave output must be aligned to the back EMF
(MOTORBEMF) characteristics of the motor. This is why resolver or
encoder alignment to the motor is critical.
7.3.2.3. Velocity Loop
The purpose of the velocity loop is to regulate motor speed. Like
the current and the commutation loops, the velocity loop is digital
and uses the resolver or the encoder feedback signals to calculate
actual motor velocity. The command for the velocity loop can come
from a direct user input (OPMODE’S 0&1) or can be the output of
the position loop. The velocity loop is a digital sampling system
operating at 4 kHz.