Power Wiring
ANCA Motion
D-000129 Rev 09
79
5
Regenerative Energy Calculations
5.9.3
Regeneration energy is entirely dependent on the multi-axis drive application where one or more drives can
contribute to the regenerative energy. The applications must consider all the moved masses, velocity,
deceleration, losses from gearbox & motor resistance.
The kinetic energy of the system can be calculated from the Linear and Rotational movement equations:
Linear Movement:
E
M
= ½ m v
2
Where E
M
= Energy in (Joules)
m = motor & load mass (kg)
v = velocity (m/s)
Rotational Movement:
E
J
= ½ J
ω
2
Where E
J
= Energy in (Joules)
J = motor & load moment of inertia (kgm
2)
ω = angular velocity (rad/s)
Mechanical systems should consider the combined effects of linear movement (e.g. gantry) and rotational
movement of the driving motor + gearbox.
System losses such as motor resistance are subtracted from the kinetic energy:
Motor Winding Losses:
E
W
= 3 I
2
M
R
M
t
D
Where E
W
= Motor winding loss energy (Joules)
I
M
= motor current during deceleration (Arms/phase)
R
M
=
motor resistance (Ω Phase-Phase)
t
D
= deceleration time (sec)
Thus kinetic energy regenerated to the DC Bus is simply: E
B
= E
M
+ E
J
- E
W
The electrical energy the DC Bus capacitors can absorb can be calculated from:
DC Bus Capacitor Energy:
E
C
=½ C (V
2
M
- V
2
NOM
)
Where E
C
= Capacitor energy in Joules
V
M
= maximum bus voltage (806V)
V
NOM
= Nominal bus voltage =
U
LL-(3
Φ
)
√2
C = Total Bus Capacitance in Farads
If the kinetic energy (E
B
) is greater than the
DC Bus Capacitor Energy (E
C
) then the brake resistor will be required
to dissipate the excess energy.
Example 1:
A 4 axis gantry system moving in one axis, decelerates from 2m/s to stop in 0.136s. The motor is rotating at
2790rpm when deceleration begins. The full movement cycle takes 0.5s
Gantry mechanical system: mass = 520kg; v = 2(m/s), t
D
= 0.136 (sec)
Electrical motor: R
M
= 0.15Ω, I
M
= 32A
RMS
, J = 0.0088 kg/m
2
,
and
for drive capacitance specifications.
AMD5x PIU(705µF) + 2 x 35A drives(270µF each) + 1 x 20A drive(135µF) + 1 x 12A drive(135µF) , thus total bus
capacitance = 1,515µF
Mains 3 phase line-line voltage: 380V, thus V
NOM
= 537V, thus E
C
= 273J
Thus E
M
= 1040J, E
J
= 376J, E
W
= 63J.
The kinetic energy into DC Bus: (1040 + 376 - 63) = 1353J
Thus dissipated brake resistor is 1353-273 =1080J for each deceleration.
The average resistor power is 1080/0.5 = 2160W. The selected resistor wattage rating should be greater than
this value.
Required resistor power during regeneration is 1080/0.136 = 7.9kW, which is less than the peak power (18kW) of
a
36Ω resistor, so this 36Ω resistor can brake the kinetic energy.
During a PIU shutdown the DC Bus is fully discharged into the brake resistor, which must be able to dissipate this
energy E
C
=½ C V
2
M
= 492J.
For a 36Ω regen resistor and total capacitance of 1,515µF, the discharge has an
Summary of Contents for AMD5x Series
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