Delta Tau GEO PMAC User Manual
Geo PMAC Drive User Manual
System Wiring
27
Shunt Regulation
When the motor is used to slow the moving load, this is called regenerative deceleration. Under this
operation, the motor is acting as a generator consuming energy from the load while passing the energy
into the DC Bus storage capacitors. Left unchecked, the DC Bus voltage can raise high enough to
damage the drive. For this reason there are protection mechanisms built into the Geo Drive product such
as shunt regulation and over-voltage protection.
The shunt regulator monitors the DC Bus voltage. If this voltage rises above a present threshold (Regen
Turn On Voltage), the Geo Drive will turn on a power device intended to place the externally mounted
regen resistor across the bus to dump the excessive energy. The power device keeps the regen resistor
connected across the bus until the bus voltage is sensed to be below the Regen Turn Off voltage at which
time the power device removes the resistor connection.
operation, the motor is acting as a generator consuming energy from the load while passing the energy
into the DC Bus storage capacitors. Left unchecked, the DC Bus voltage can raise high enough to
damage the drive. For this reason there are protection mechanisms built into the Geo Drive product such
as shunt regulation and over-voltage protection.
The shunt regulator monitors the DC Bus voltage. If this voltage rises above a present threshold (Regen
Turn On Voltage), the Geo Drive will turn on a power device intended to place the externally mounted
regen resistor across the bus to dump the excessive energy. The power device keeps the regen resistor
connected across the bus until the bus voltage is sensed to be below the Regen Turn Off voltage at which
time the power device removes the resistor connection.
Minimum Resistance Value
The regen resistor selection requires that the resistance value of the selected resistor will not allow more
current to flow through the Geo Drive’s power device than specified.
current to flow through the Geo Drive’s power device than specified.
Maximum Resistance Value
The maximum resistor value that will be acceptable in an application is one that will not let the bus
voltage reach the drive’s stated over voltage specification during the deceleration ramp time. The
following equations defining energy transfer can be used to determine the maximum resistance value.
voltage reach the drive’s stated over voltage specification during the deceleration ramp time. The
following equations defining energy transfer can be used to determine the maximum resistance value.
Energy Transfer Equations
Regen, or shunt, regulation analysis requires study of the energy transferred during the deceleration
profile. The basic philosophy can be described as follows:
profile. The basic philosophy can be described as follows:
•
The motor and load have stored kinetic energy while in motion.
•
The drive removes this energy during deceleration by transferring to the DC bus.
•
There are losses during this transfer, both mechanical and electrical, which can be significant in some
systems.
systems.
•
The DC bus capacitors can store some energy.
•
The remaining energy, if any, is transferred to the regen resistor.
Kinetic Energy
The first step is to ascertain the amount of kinetic energy in the moving system, both the motor rotor and
the load it is driving. In metric (SI) units, the kinetic energy of a rotating mass is:
the load it is driving. In metric (SI) units, the kinetic energy of a rotating mass is:
2
J
2
1
K
E
ω
=
where:
E
E
K
is the kinetic energy in joules, or watt-seconds (J, W-s)
J is the rotary moment of inertia in kilogram-meter
2
(kg-m
2
)
ω is the angular velocity of the inertia in radians per second (1/s)
If the values are not in these units, convert them. For example, if the speed is in revolutions per minute
(rpm), first multiply this value by 2π/60 to convert to radians per second.
If the values are not in these units, convert them. For example, if the speed is in revolutions per minute
(rpm), first multiply this value by 2π/60 to convert to radians per second.
When English mechanical units are used, there are additional conversion factors that must be included to
get the energy result to come out in joules. For example, if the rotary moment of inertia J is expressed in
lb-ft-sec
get the energy result to come out in joules. For example, if the rotary moment of inertia J is expressed in
lb-ft-sec
2
, the following equation should be used:
2
J
678
.
0
K
E
ω
=
If the rotary moment of inertia J is expressed in lb-in-sec
2
, the following equation should be used:
2
J
0565
.
0
K
E
ω
=