Elmo HARSFEN0602, HARmonica 109, Commutation search General, Selecting the parameters

HARSFEN0602ElmoHARmonicaSoftwareManual PRELIMINARYDRAFT

full electrical cycles possible for that motor. Enter the "encoder counts in revolution" CA[18] parameter as the number of encoder counts for CA[19] electrical cycles.

The encoder parameters are listed in the following table.

CA[18] Encoder bits per revolution, after resolution multiplication by 4, in the range [24..10,000,000]. For an incremental encoder with 1000 lines, CA[18] will be 4000

CA[19] Number of motor pole pairs [1..50].

CA[23] Counts per meter (any positive integer)

0:Rotary motor

1:Counts per meter in a linear motor.

This parameter is not used directly by the amplifier – it is just stored there for the convenience of a host

9.4 Commutation search

9.4.1 General

When starting the motor, the rotor can be anywhere.

The torque of a brushless DC motor is given by the equation

T= KT ⋅ I ⋅ sin(θ)

(1)

θ = θs

− θr

(2)

where

T

Motor torque

K T

Motor constant

I

Motor current

The electrical angle between the rotor and the field at the stator

θ

T

r

s

The electrical angle of the stator field

r

The electrical angle of the rotor

The angle θs is known, since the amplifier controls it directly.

The angle θr is unknown.

If we rotate θs , i.e. θs

− 2πf ⋅ t where f is some frequency and t is the time, we get the sinusoidal torque

=

K

⋅

I

⋅

sin(2

π

f

⋅

t

− θ

)

(3)

T

For that torque, the motor shaft will move according to

P(t)= A(f ) ⋅ KT ⋅ I ⋅sin(2πf ⋅ t − θr

− φ(f )) , where

P(t)

Motor shaft position

A(f )e jφ(f )

Transfer function of the motor and its load at the frequency f.

By applying the torque of (3) and measuring the position, we can identify both A(f) and θr .

9.4.2 Selecting the parameters

The parameters I and f can be selected from the range specified below:

IThe torque is selected by the parameter CA[26].

CA[26] defines I as a percentage of the continuous current rating CL[1]. For example, if CA[26]=50, then I=0.5 CL[1].

fCA[15] controls the frequency of the sinusoidal motor torque .

The basic frequency (with CA[15]=0) is so that a cycle is completed in 128 * TS microseconds. For a Harmonica with TS=50, this will be a cycle of 6400

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