AN1948_D Freescale Semiconductor / Motorola, AN1948_D Datasheet - Page 6

• Manufacturer Part Number: AN1948_D
• Description: Real Time Development of MC Applications using the PC Master Software Visualization Tool
• Manufacturer: Freescale Semiconductor / Motorola

6
Development of Motor Control Applications Using PC Master Software
4.
4.1 Visualization of Measured Variables
The Help Page enables the display of additional information the user might be interested in. For
example, there can be a block diagram of the application, description of the control algorithm or
application, description of the user interface of the application, etc. The help page is created in HTML.
A detailed description of PC master software, including the PC master software settings, detailed
descriptions of the of the individual PC master software features, a description of the communication
protocol, creation of PC master software control pages and remote control through the Internet, can be
found in the Motorola Application Notes, listed in
Let’s illustrate the advantages of PC master software for real-world motor control applications. They
are described in examples of common issues the developer is facing during the design of the
applications. The presented examples are based on the application “3-Phase SR Sensorless Motor
Control Using DSP56F80x“[1]. First, the visualization of the variables, measured by an
Analog-to-Digital Converter (ADC), is shown. Then, the visualization of courses of calculated
variables is illustrated. The setting of the controllers and tuning of the application with help of PC
master software is presented. Finally, the on-line setting of the application parameters and variables is
demonstrated.
Precise analog measurement is a key factor for the implementation of almost any motor control
algorithms. Mainly, the phase and/or DC-Bus voltages and currents are measured and utilized for the
control algorithms. Any inaccuracy in the measurement leads to control error and thus to the
deterioration of drive performance.
PC master software enables the visualization of measured variables, as they are converted by the
Analog-to-Digital Converter. The developer can evaluate the actual values and courses obtained from
the analog-to-digital converter and can eliminate possible sources of inaccuracies. Both the Scope or
the Recorder can be used for the evaluation.
A typical example of the visualization of the measured variables is the measurement of motor phase
currents.
Phase currents are measured by current sensors.
phase of a switched reluctance (SR) motor power stage. It includes two power switches and two diodes
per motor phase. The shunt resistor is inserted into the current path of the motor phase. The phase
current is sensed as a voltage drop across the sense resistor. The control signals of the individual
transistors, together with the actual current and the sensed voltage drop on the current sense resistor,
are shown as well. As can be seen, the phase current is not visible at the current sense resistor
continuously, and must be reconstructed by software.
For a reliable reconstruction of the shape of the phase current, the measurement needs to be sampled in
the center of the PWM pulse. The zero current may be set to half of the ADC range, so both the
positive and the negative voltage drops on the phase current shunt resistors can be measured.
Proceeding like this, the current can be reconstructed with required accuracy and credibility.
It is apparent that usage of the oscilloscope for the visualization of the measured current at the ADC
input is quite limited. We can see just PWM pulses on the oscilloscope screen. Also, it is important to
evaluate what the actual value converted by the ADC is, what the influence of the noise is and how
successfully the phase current is reconstructed. For a such purpose, the Recorder can be used to great
advantage.
Development of Motor Control Applications Using PC
Master Software
Real Time Development using the PC Master Software
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
Figure 4-1
Section 6.
illustrates a typical configuration of one
MOTOROLA