FX Series Programmable Controllers Points Of Technique 10
10-15
10.13 Using The PWM Instruction For Motor Control
The PWM instruction ma
be used directl
with an inverter to drive a motor. If this confi
uration
is used the followin
ripple circuit will be required between the PLC’s PWM output and the
inverters input terminals.
Ke
to component values:
R1 - 510
Ω
(1/2 W) R2 - 3.3k
Ω
(1/2 W)
R3 to R8 - 1k
Ω
(1/4 W) R9 - 22
Ω
(1/4 W)
R10 - variable dependent on confi
uration. In this example 1k
Ω
(1 W)
C1 - 470
µ
F
Note: the values of R10 and C1 are dependent on the s
stem confi
uration.
Establishing system parameters and values
It is assumed that the input impedance of the inverter is of a hi
h order. Havin
established
this, the values of C1 and R10 are calculated to
ive
τ
a time result (in msec) approximatel
10
times bi
er than the value used for T
0
in the PWM instruction:
τ
= R10 (k
Ω
)
L C1 (
µ
F)
Durin
this calculation the value of R10 must be vastl
reater than the value of R9. In the
example, R9 is equal to 22
Ω
, where as R10 is equal to 1k
Ω
. This proportion is approximatel
1:50 in favor of R10.
Y0+V0
24V 0V
+
E
e
R1
R2
R3 R7
R10
R
4
R
5
R
6
R
9
R
8
Inverter
C1
5V
12V
Programmable
controller
Motor
Circuit confi
uration for a PLC with source outputs
e
e
m
Y000
t
T
0
PWM D10 K50 Y000
X10
tT0
