MC3PHAC Motorola, MC3PHAC Datasheet - Page 18

• Manufacturer Part Number: MC3PHAC
• Description: 3-Phase AC Motor Controller
• Manufacturer: Motorola

MC3PHAC/D
18
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Freescale Semiconductor, Inc.
For More Information On This Product,
Regeneration Control — Regeneration is a process by which stored
mechanical energy in the motor and load is transferred back into the
drive electronics, usually as a result of an aggressive deceleration
operation. In special cases where this process occurs frequently (for
example, elevator motor control systems), it is economical to incorporate
special features in the motor drive to allow this energy to be supplied
back to the ac mains. However, for most low cost ac drives, this energy
is stored in the dc bus capacitor by increasing its voltage. If this process
is left unchecked, the dc bus voltage can rise to dangerous levels, which
can destroy the bus capacitor or the transistors in the power inverter.
The MC3PHAC incorporates two techniques to deal with regeneration
before it becomes a problem:
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Resistive Braking — The DC_BUS pin is monitored at a
5.3 kHz frequency (4.0 kHz when the PWM frequency is set to
15.9 kHz), and when the voltage reaches a certain threshold, the
RBRAKE pin is driven high. This signal can be used to control a
resistive brake placed across the dc bus capacitor, such that
mechanical energy from the motor will be dissipated as heat in the
resistor versus being stored as voltage on the capacitor. In
standalone mode, the DC_BUS threshold required to assert the
RBRAKE signal is fixed at 3.85 volts (110 percent of nominal) where
nominal is defined to be 3.5 volts. In PC master software mode, this
threshold can be set to any value between 0 volts (0 percent of
nominal) and greater than 5 volts (143 percent of nominal) and can
be changed at any time.
Automatic Deceleration Control — When decelerating the motor, the
MC3PHAC attempts to use the specified acceleration value for
deceleration as well. If the voltage on the DC_BUS pin reaches a
certain threshold, the MC3PHAC begins to moderate the
deceleration as a function of this voltage, as shown in
voltage range on the DC_BUS pin from when the deceleration
begins to decrease, to when it reaches 0, is 0.62 volts. In standalone
mode, the DC_BUS voltage where deceleration begins to decrease
is fixed at 3.85 volts (110 percent of nominal) where nominal is
defined to be 3.5 volts. In PC master software mode, this threshold
can be set to any value between 0 volts (0 percent of nominal) and
greater than 5 volts (143 percent of nominal) and can be changed at
any time.
3-Phase AC Motor Controller
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Figure
MOTOROLA
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