AN1965 Freescale Semiconductor / Motorola, AN1965 Datasheet - Page 10

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

Software Design
6.
6.1 Calculating Reference Voltage
10
Warning: Reference voltage calculation coefficients and algorithm depend directly on PFC hardware
This section describes the design of the drive’s software blocks. The software will be described in
terms of:
PFC software periodically updates reference voltage according to the present value of output voltage.
The reference value is calculated as the sum of its average value with the difference between measured
output voltage and its nominal value, shown in
tasked with performing the transformation u_dif = K * u_dif. It rescales the output voltage value,
measured by the ADC module, to the eight bits range of the PWM. The application uses the PWM
output as a Digital-to-Analog Converter.
The reference voltage calculation algorithm uses the DCBus voltage value, measured by the ADC
module in the Motor Control portion of the software. The DCBus value has the following scale:
The function f() is a filter algorithm like a simple Resistance-Capacitance (RC) circuit. The filter time
constant depends on the PFC hardware implementation and defines the output characteristic of the
PFC output voltage. The smaller time constant value provides a quicker output voltage response, but
with less stable behavior.
u_out
Software Design
•
•
•
PFC_OUTPUT_VOLTAGE
implementation.
Calculating reference voltage
Processing milestones
State diagram
DCBus Voltage
u_dif
Figure 6-1. Reference Voltage Calculation
Freescale Semiconductor, Inc.
407V
0V
For More Information On This Product,
Table 6-1. DCBus Voltage Scale
Indirect Power Factor Correction
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k
Frac16 u_out
K*u_dif
Figure
F(ref_voltage)
0.0
1.0
6-1. The structure contains the amplifier model,
Comments
zero level
full scale
f()
ref_voltage