AN1911 Freescale Semiconductor / Motorola, AN1911 Datasheet - Page 12

• Manufacturer Part Number: AN1911
• Description: 3-Phase AC Motor Control with V/Hz Speed Open Loop Using DSP56F80X
• Manufacturer: Freescale Semiconductor / Motorola

Software Design
6.1.1 Acceleration/Deceleration Ramp
6.1.2 Speed Measurement
6.1.3 V/Hz Ramp
12
The process calculates the new actual speed command based on the required speed according to the
acceleration / deceleration ramp. The desired speed is determined either by the push buttons or by PC
Master
During deceleration the motor can work as a generator. In the generator state the DC-Bus capacitor is
charged and its voltage can easily exceed its maximal voltage. Therefore the voltage level in DC-Bus
link is controlled by a resistive brake which is operating in case of overvoltage.
The process input parameter is Omega_Desired (desired speed).
The process output parameter is Omega_Required which is used as input parameter of PWM
generation process.
The speed measurement process uses the on-chip Quadrature Decoder. The process output is
MeasuredSpeed which is only used as information value in PC Master.
The drive is designed as a “Volt per Hertz“ drive. It means that the control algorithm keeps the
constant motor’s magnetizing current (flux) by varying the stator voltage in proportion to frequency.
The common used Volt per Hertz ramp of a 3-phase AC induction motor is illustrated in
The Volt per Hertz ramp is defined by following parameters:
•
•
•
Base Point - defined by f
Boost Point- defined by V
Start Point - defined by V
V
V
V
V (%)
boost
base
start
Indirect Power Factor Correction Using DSP56F80X
Freescale Semiconductor, Inc.
Point
Start
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Figure 6-2. Volt per Hertz Ramp
f
boost
base
start
boost
Boost
Point
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(usually 50Hz or 60Hz)
at zero Frequency
and f
boost
Base
Point
f
base
f (Hz)
Figure 6-2.