Abstract : In digitally controlled AC/AC frequency converters, to ensure that the average output voltage varies sinusoidally, the firing delay angle of each group of thyristors must be modulated. This paper introduces a three-phase AC/AC frequency converter based on DSP chip control, discusses and compares the advantages and disadvantages of several control schemes, and addresses related challenges. Keywords : AC/AC frequency converter; DSP; firing angle; cosine intersection method; triangular wave modulation function method 0 Introduction AC/AC frequency converters directly convert a higher fixed-frequency voltage to a lower frequency voltage with variable output voltage amplitude. To minimize output voltage harmonics, the waveform of the output voltage of the frequency converter used in AC drives must be as close to a sine wave as possible. Therefore, the firing delay angle of the anti-parallel converter must be continuously and alternately phase-modulated. In recent years, the rapid development of microprocessors has led to the increasingly widespread application of digital AC-AC frequency converters in electric drives. This paper uses TI's TMS320F240 DSP chip as the core to study various control schemes for a three-phase AC-AC frequency converter and compares their advantages and disadvantages. The hardware foundation of this system includes the main circuit, thyristor drive circuit, I/O expansion circuit, and data acquisition circuit. The data acquisition circuit generates the zero-current signal for switching and the three-phase synchronization signal. The capture interrupt port CAPINT1 captures the power supply synchronization signal every 60 (10/3ms), enters the synchronization signal interrupt program, and, combined with the states of I/O ports PB1, PB2, and PB3, determines the corresponding synchronization wavefront value for phase identification and thyristor determination. I/O ports PCO, PC1, and PC2 detect the zero-crossing detection signal of the three-phase current. When the zero-crossing signal is valid, the corresponding switching subroutine is entered to perform the switching. At the moment the trigger pulse is generated, the encoded signal is output to the I/O expansion circuit through the data bus to trigger the corresponding thyristor. Based on this hardware circuit, several control methods are introduced, and their advantages and disadvantages are compared. [b][align=center]For details, please click: Research on Control Scheme of Three-Phase AC/AC Frequency Converter Based on DSP Control[/align][/b]