This application note proposes a time optimized algorithm for three-phase induction
drive control by the Siemens microcontroller C504.
Three sinewave phase currents can easily be generated and controlled by the on-chip
Capture Compare Unit (CCU), requiring very few CPU computing time (about 30% at
20 kHz PWM frequency in open-loop mode).
1 Introduction .....3
2 Fundamentals of Operating4
2.1 Controlling Three-Phase Induction Motors 4
2.2 Generating Variable Motor Currents by Using Pulse Width Modulation (PWM).5
2.3 Power Amplification of Controller Output Signals by Semiconductor Bridges 6
2.4 Sinusoidal Weighted PWM ...7
2.5 Half Bridge Driving with Dead Time Control .8
2.6 Principle of Generating Sinusoidal Weighted PWM Signals with the C504....9
3 Hardware Description .11
3.1 Three-Phase Motor ...11
3.2 Motor Interface 12
3.3 Open Loop Motor Control....13
4 C504 Controller Software Description..14
4.1 Calculation of Period- and Offset-Values for Compare Timer 114
4.2 Considerations concerning the Resolution for the Sine Table Pointers14
4.3 Changing the Amplitude without using any Multiplication-Instruction .17
4.4 Generating the Memory Sine Tables .20
4.5 Compare Timer 1 Interrupt Service Routine Tasks.22
4.6 Main Program Task...23
4.7 Flow-Charts.....24
4.8 Conclusion 29