Design of modulation signals in a SPWM mode based on TMS320C240

The paper investigates the application of TMS320C240 in generating a series of SPWM waveform signals online for variable frequency loop systems. Using the algorithm of subsection modulation, voltage-frequency ratio as well as numeration of sine function, real time sampling cycle, voltage amplitude, and pulse- width at different frequencies are achieved and the time values are put into the timers of the special event manager EV in TMS320C240. Then through timing interrupt the high-low voltages are sent to the interface circuits to generate real time SPWM waves. A series of SPWM waveform signals where the voltage-frequency ratio and frequency can be changed real time is then achieved. The harmonic of SPWM generated by TMS320C240 is decreased. The output is fast and of good symmetry compared with that of a singlechip. The precision attainable is at the order of 0. 015 Hz in the range 0∼400 Hz.