Watson-Marlow MM440 - Manual (Page 243)

Issue 10/06 3 Functions
MICROMASTER 440 Operating Instructions
6SE6400-5AW00-0BP0 243
3.23.2 Vector control
Field-orientated Vector control (briefly: Vector control) significantly improves torque
control when compared to V/f control. The Vector control principle is based on the
fact that for a specific load situation or required torque, the required motor current
is impressed with respect to the motor flux so that the appropriate torque is
obtained. If the stator current is emulated in a circulating coordinate system, linked
with the rotor flux
Φ, then it can be broken-down into flux-generating current
component i
d
in-line with the rotor flux and in a torque-generating current
component i
q
, vertical to the rotor flux. These components are corrected to track
their setpoints in the current controller using their own dedicated PI controllers and
are equal quantities in steady-state operation.
Stator axis
Flux axis
Rotor axis
ω
Measured steady state trajectories
ω
1
ω
mR
i
mR
i
S
(t)
i
b
i
a
i
d
i
q
Fig. 3-101 Current Vector diagram in a steady-state condition
In the steady-state condition, the field-generating current component i
d
is
proportional to the flux Φ and the torque is proportional to the product of i
d
and i
q
.
M ~ Φ ∗ i
q
Φ ~ i
d,stat
M ~ i
d
∗ i
q
When compared to V/f control, Vector control has the following advantages:
¾
Stable during load and setpoint changes
¾ Short rise times for setpoint changes ( → better control performance)
¾ Short rise times for load changes ( → better noise/disturbance characteristics)
¾ Accelerating and braking are possible with a max. adjustable torque
¾ The motor and driven machine are protected using the adjustable torque limit,
both when motoring and regenerating (refer to Section 3.23.2.4)
¾ The drive and braking torque are controlled independently of the speed
¾ Full holding torque is possible at 0 speed
These advantages are, under certain circumstances, already achieved without
using speed feedback.
The Vector control can be used both with and without speed encoder.