ElmoMC SimplIQ Software Manual - Manual (Page 118)

SimplIQ Software Manual Commutation
MAN-SIMSW (Ver. 1.4)
8-8
8.4 Auto-phasing and Commutation Search
When starting the motor, the rotor can be located anywhere. The torque of a brushless DC
motor is given by the equation:
) sin( I K T
T
θ ⋅ ⋅ =
(1)
r s
θ − θ = θ
(2)
where:
T is the motor torque.
K
T
is the motor constant.
I is the motor current.
θ is the electrical angle between the rotor and the field at the stator.
θs is the electrical angle of the stator field.
θr is the electrical angle of the rotor.
The angle θs is known because the drive controls it directly. The angle θr is unknown.
If θs is rotated — that is, θs –2πf * t, where f is a frequency and t is the time — the result is
the following sinusoidal torque:
T = K
T
* I * sin(2πf * t - θr) (3)
For that torque, the motor shaft will move according to:
P(t) = A(f) * K
T
* I * sin (2πf * t - θr – φ(f)),
where:
P(t) is the motor shaft position.
A(f)e
jφ(f) is the transfer function of the motor and its load at the frequency f.
By applying a torque of (3) and measuring the position, both A(f) and
r
θ can be identified.
8.4.1 Selecting Parameters
The parameters I and f can be selected from the following range:
Parameter Description
I
The torque is selected by the parameter CA[26], which defines I as a
percentage of the continuous current rating CL[1]. For example, if
CA[26] = 50, then I = 0.5 CL[1].
f CA[15] controls the frequency of the sinusoidal motor torque. The basic
frequency (with CA[15] = 0) is such that a cycle is completed in 128 * TS
microseconds. For a
SimplIQ drive with TS=80, this will be a cycle of 10,240
microseconds, which is about 100 Hz.
The frequency is 2
CA[15] * basic frequency of CA[15] in the range [-4…4].
For example, with CA[15] = 2, the frequency is about 40 Hz, whereas with
CA[15] = -2, the frequency is about 640 Hz.