Non-Regen Versus Regen Operation - PowerTec 2000C Instruction Manual

1.2 NON-REGEN VERSUS REGEN
The POWERTEC Models 2000C and 3000C
are non-regenerative Brushless DC motor controls.
They will not accept energy coming from the motor
due to overhauling loads and high inertias during
deceleration. The models 2000RG and 3000RG from
POWERTEC are regenerative. This section ex-
plains the difference.
When a motor is operating with a load in such a way
that it is drawing current from the power supply, it is said
to be operating in the MOTORING mode. This is the most
common mode of motor operation, used to power indus-
trial processes in almost all applications. The motor is
converting the electrical energy from the plant power
supply into mechanical energy (work) at the motor's output
shaft.
When any electric motor rotates, it produces a poten-
tial at its main terminals. This potential is due to the
movement of the rotor or armature windings through a
magnetic field, as in the case of the brush type D.C. motor
or the induction A.C. motor. This potential is called Counter-
Electro-Motive-Force (CEMF, for short). CEMF is pro-
duced by the motor even when it is drawing power from the
supply, and the CEMF tends to oppose the flow of current
from the supply to the motor. In the case of the brushless
D.C. motor, a field produced by the magnets on the rotor is
Figure 2: Stopping methods for motors compared.
2
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moving around the stationary windings of the stator. If the
voltage produced by the rotation of the motor shaft (due to
the CEMF) exceeds the supply voltage, the motor can not
draw current from the supply as long as this situation exists.
Usually this condition is produced when motor speed is
greater than the speed commanded by the reference, per-
haps due to the amount of inertia of the load being greater
than the amount of inertia which can be slowed by the
motor in the time allotted, or when the load is being moved
by another force faster than the motor wants to turn.
A load in motion will come to a free-wheeling stop
by "coasting" in an amount of time determined by the
speed, inertia, and friction of the load. The faster a load is
moving, the longer it requires to stop. Larger inertias
(generally speaking, more mass) take longer to stop, but a
higher friction load slows it down faster. A moving load
stops in a coasting situation by dissipating the energy of
motion as frictional heat, which acts as a brake. If inertia
is high and friction is low, the load will take a longer time
to stop. Mechanical brakes may be used to increase the
amount of friction.
Non-regenerative motor controls do not have the
ability to slow down a load in a time which is less than the
motor would normally slow down by itself, or come to a
stop, by coasting. It cannot act as a brake, so it shuts off and
waits for speed to fall below that commanded by the
reference at the time (if the control is active). Braking force
may be supplied by the motor by dissipating the energy into
passive resistors connected after the control is shut off
(dynamic braking).
Regenerative motor controls are capable of supply-
ing braking force while the motor control is active. A motor
rotating at a speed which faster than its control is com-
manding becomes a generator. The amount of power
generated is related to the speed, the total inertia, and the
friction of the load and motor combination.
It is also proportional to the dissipative and/or
storage load presented by the controller, which must be
adequate. The regenerative control will accept current
from the motor, and will dissipate the energy received, as
long as the load it presents is sufficient to dissipate the
energy.
When energy is being generated by the motor, and
being accepted by the controller, then the motor is said to
be REGENERATING. A motor in the regenerating mode
develops torque in the opposite direction of its rotation,
and is not drawing power from the supply, as it is in the
motoring mode.
Regenerative power capability gives the motor and
control the ability to change from higher speeds to lower
speeds (including zero speed, and also including the rever-
sal of motor direction) much more quickly than with non-
regenerative types of controls, resulting in more rapid
stops and quick reversals of loads which would otherwise
be a lot more sluggish in these actions.
Model 2000C / 3000C Manual