MC3PHAC Motorola, MC3PHAC Datasheet - Page 11

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

Features
MOTOROLA
3-Phase Waveform Generation — The MC3PHAC generates six PWM
signals which have been modulated with variable voltage and variable
frequency information in order to control a 3-phase ac motor. A third harmonic
signal has been superimposed on top of the fundamental motor frequency to
achieve full bus voltage utilization. This results in a 15 percent increase in
maximum output amplitude compared to pure sine wave modulation.
The waveform is updated at a 5.3 kHz rate (except when the PWM frequency
is 15.9 kHz), resulting in near continuous waveform quality. At 15.9 kHz, the
waveform is updated at 4.0 kHz.
DSP Filtering — A 24-bit IIR digital filter is used on the SPEED input signal in
standalone mode, resulting in enhanced speed stability in noisy environments.
The sampling period of the filter is 3 ms (except when the PWM frequency is
15.9 kHz) and it mimics the response of a single pole analog filter having a pole
at 0.4 Hz. At a PWM frequency of 15.9 kHz, the sampling period is 4 ms and
the pole is located at 0.3 Hz.
High Precision Calculations — Up to 32-bit variable resolution is employed
for precision control and smooth performance. For example, the motor speed
can be controlled with a resolution of 4 mHz.
Smooth Voltage Transitions — When the commanded speed of the motor
passes through 1 Hz, the voltage is gently applied or removed depending on
the direction of the speed change. This eliminates any pops or surges that may
occur, especially under conditions of high-voltage boost at low frequencies.
High-Side Bootstrapping — Many motor drive topologies (especially high-
voltage drives) use optocouplers to supply the PWM signal to the high-side
transistors. Often, the high-side transistor drive circuitry contains a charge
pump circuit to create a floating power supply for each high-side transistor that
is dependent on low-side PWMs to develop power. When the motor has been
off for a period of time, the charge on the high-side power supply capacitor is
depleted and must be replenished before proper PWM operation can resume.
To accommodate such topologies, the MC3PHAC will always provide 100 ms
of 50 percent PWM drive to only the low-side transistors each time the motor is
turned on. Since the top transistors remain off during this time, it has the effect
of applying zero volts to the motor, and no motion occurs. After this period,
motor waveform modulation begins, with PWM drive also being applied to the
high-side transistors.
Fast Velocity Updating — During periods when the motor speed is changing,
the rate at which the velocity is updated is critical to smooth operation. If these
updates occur too infrequently, a ratcheting effect will be exhibited on the
motor, which inhibits smooth torque performance. However, velocity profiling is
Freescale Semiconductor, Inc.
For More Information On This Product,
3-Phase AC Motor Controller
Go to: www.freescale.com
MC3PHAC/D
Features
11