Delta Tau GEO PMAC User Manual
Geo PMAC Drive User Manual
System Wiring
29
The electrical resistive losses in a 3-phase motor in a constant deceleration to stop can be calculated as:
d
t
pp
R
2
rms
i
2
3
LE
E
=
where:
E
E
LE
is the lost energy in joules (J)
i
rms
is the current required for the deceleration in amperes (A), equal to the required deceleration torque
divided by the motor’s (rms) torque constant K
T
R
pp
is the phase-to-phase resistance of the motor, in ohms (Ω)
t
d
is the deceleration time in seconds (s)
Capacitive Stored Energy in the Drive
The energy not lost during the transformation is initially stored as additional capacitive energy due to the
increased DC bus voltage. The energy storage capability of the drive can be expressed as:
increased DC bus voltage. The energy storage capability of the drive can be expressed as:
(
)
2
nom
V
2
regen
V
C
2
1
C
E
−
=
where:
E
E
C
is the additional energy storage capacity in joules (J)
C is the total bus capacitance in Farads
V
V
regen
is the DC bus voltage at which the regeneration circuit would have to activate, in volts (V)
V
nom
is the normal DC bus voltage, in volts (V)
Evaluating the Need for a Regen Resistor
Any starting kinetic energy that is not lost in the transformation and cannot be stored as bus capacitive
energy must be dumped by the regeneration circuitry in to the regen (shunt) resistor. The following
equation can be used to determine whether this will be required:
energy must be dumped by the regeneration circuitry in to the regen (shunt) resistor. The following
equation can be used to determine whether this will be required:
C
E
LE
E
LM
E
K
E
excess
E
−
−
−
=
If E
excess
in this equation is greater than 0, a regen resistor will be required.
Regen Resistor Power Capacity
A given regen resistor will have both a peak (instantaneous) and a continuous (average) power dissipation
limit. It is therefore necessary to compare the required peak and continuous regen power dissipation
requirements against the limits for the resistor.
The peak power dissipation that will occur in the regen resistor in the application will be:
limit. It is therefore necessary to compare the required peak and continuous regen power dissipation
requirements against the limits for the resistor.
The peak power dissipation that will occur in the regen resistor in the application will be:
R
2
regen
V
peak
P
=
where:
P
P
peak
is peak power dissipation in watts (W)
V
regen
is the DC bus voltage at which the regeneration circuit activates, in volts (V)
R is the resistance value of the regen resistor, in ohms (Ω)
However, this power dissipation will not be occurring all of the time, and in most applications, only for a
small percentage of the time. Usually, the regen will only be active during the final part of a lengthy
deceleration, after the DC bus has charged up to the point where it exceeds the regen activation voltage.
The average power dissipation value can be calculated as:
However, this power dissipation will not be occurring all of the time, and in most applications, only for a
small percentage of the time. Usually, the regen will only be active during the final part of a lengthy
deceleration, after the DC bus has charged up to the point where it exceeds the regen activation voltage.
The average power dissipation value can be calculated as:
100
time
on
%
peak
P
avg
P
−
=
where:
P
P
avg
is average power dissipation in watts (W)
%on-time is the percentage of time the regen circuit is active