AN1965 Freescale Semiconductor / Motorola, AN1965 Datasheet - Page 6

• Manufacturer Part Number: AN1965
• Description: Design of Indirect Power Using the 56F800/E
• Manufacturer: Freescale Semiconductor / Motorola

System Design Concept
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This hardware implementation does not allow direct modification of the pulse duty cycle that feeds to
the switcher (T). The reference voltage of the external PWM comes from a filtered PWM signal from
the hybrid controller, and can be set according to input voltage zero crossing, base frequency, and
output voltage. Therefore, the only analog feedback for device control is output voltage. This
implementation is called indirect PFC and can save the hybrid controller’s resources.
The best shape for the input current is a sinusoid shape. But to reduce complexity and meet standard
requirements, this PFC application utilizes the simplest 3-points approximation, illustrated in
Figure 3-3.
The system was designed in accordance with the following performance specifications:
As shown in
System Design Concept
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Less complexity and avoids overloading the hybrid controller (the majority of resources
arereserved for motor control)
Harmonic content which complies with the standard IEC 1000-3-2
Targeted for 56F800/E EVM platforms
Input power supply voltage 230V 50Hz or 115V 60Hz
Output voltage is set up to 380V DC
Nominal output voltage is set to 385V DC
Nominal output power of up to 180W
Input current harmonic content will comply with standard IEC 1000-3-2
Converts sensed output voltage to a digital value
Software PID regulator for feedback loop
Programs the PWM channel, creating a pattern of the input current
Synchronizes operation to the power line frequency, using mean zero-crossing detector
The desired shape is the result of optimization, and fulfills the following requirements:
Figure
4-1, the PFC control algorithm performs the following tasks:
Freescale Semiconductor, Inc.
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Figure 3-3. Input Current Waveform
Indirect Power Factor Correction
Input voltage waveform
Input current waveform
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