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This application note proposes a time optimized algorithm for three-phase inductiondrive control by the Siemens microcontroller C504.Three sinewave phase currents can easily be generated and controlled by the on-chipCapture Compare Unit (CCU), requiring very few CPU computing time (about 30% at20 kHz PWM frequency in open-loop mode).1 Introduction .....32 Fundamentals of Operating42.1 Controlling Three-Phase Induction Motors 42.2 Generating Variable Motor Currents by Using Pulse Width Modulation (PWM).52.3 Power Amplification of Controller Output Signals by Semiconductor Bridges 62.4 Sinusoidal Weighted PWM ...72.5 Half Bridge Driving with Dead Time Control .82.6 Principle of Generating Sinusoidal Weighted PWM Signals with the C504....93 Hardware Description .113.1 Three-Phase Motor ...113.2 Motor Interface 123.3 Open Loop Motor Control....134 C504 Controller Software Description..144.1 Calculation of Period- and Offset-Values for Compare Timer 1144.2 Considerations concerning the Resolution for the Sine Table Pointers144.3 Changing the Amplitude without using any Multiplication-Instruction .174.4 Generating the Memory Sine Tables .204.5 Compare Timer 1 Interrupt Service Routine Tasks.224.6 Main Program Task...234.7 Flow-Charts.....244.8 Conclusion 29
