YASKAWA SGD7W - Page 311

12.8 Regenerative Resistor
12.8.6 Selecting External Regenerative Resistor
12-42
Calculating the Regenerative Energy
This section shows how to calculate the regenerative resistor capacity for the acceleration/
deceleration operation shown in the following figure.
•
Calculation Procedure for Regenerative Resistor Capacity
Note: 1. The 0.2 in the equation for calculating W
K
is the value when the regenerative resistor’s utilized load ratio is
20%.
2. The units for the various symbols are given in the following table.
If the value of W
K
does not exceed the capacity of the built-in regenerative resistor of the SER-
VOPACK, an External Regenerative Resistor is not required. For details on the built-in regener-
ative resisters, refer to the SERVOPACK specifications. If the value of W
K
exceeds the capacity
of the built-in regenerative resistor, install an External Regenerative Resistor with a capacity
equal to the value for W calculated above.
Step Item Symbol Formula
1
Calculate the rotational energy of the
Servomotor.
E
S
E
S
= Jn
M
2
/182
2
Calculate the energy consumed by load
loss during the deceleration period
E
L
E
L
= (π/60) n
M
T
L
t
D
Note: If the load loss is unknown, calculate the
value with E
L
set to 0.
3
Calculate the energy lost from Servomo-
tor winding resistance.
E
M
(Value calculated from the graphs in  Servomo-
tor Winding Resistance Loss on page 12-44) × t
D
4
Calculate the energy that can be
absorbed by the SERVOPACK.
E
C
Calculate from the graphs in  SERVOPACK-
absorbable Energy on page 12-43
5
Calculate the energy consumed by the
regenerative resistor.
E
K
E
K
= E
S
− (E
L
+ E
M
+ E
C
)
6
Calculate the required regenerative
resistor capacity (W).
W
K
W
K
= E
K
/(0.2 × T)
Symbol Description Symbol Description
E
S
to E
K
Energy in joules (J)
T
L
Load torque (N⋅m)
W
K
Required regenerative resistor
capacity (W)
t
D
Deceleration stopping time (s)
J
= J
M
+ J
L
(kgm
2
)
T
Servomotor repeat operation
cycle (s)
n
M
Servomotor motor speed (min
-1
)
T
0
0
t
D
T
L
n
M
: Motor speed
: Load torque
Regenerative
torque
Motor speed
Motor torque