Abstract : The cosine intersection method is widely used in the trigger control of CNC AC-AC frequency converters, which can significantly reduce the harmonic content in the output voltage. However, the cosine intersection method uses an ideal voltage curve as the reference quantity during the control process, so it inevitably has significant drawbacks when used to control sinusoidal current output. The slope approximation method directly uses the ideal output current as the reference quantity, and performs real-time acquisition and calculation of the load current to control the switching of thyristors. This method is simple to calculate, requires less hardware, and can effectively improve the performance of AC-AC frequency converters, improve the sinusoidality of the output current waveform, and reduce the content of low-order harmonics. Keywords : Power electronics; AC-AC frequency converter; Control method; Harmonics 1 Introduction With the development of power electronic devices, the application range of AC-AC frequency converters is becoming increasingly wide. They not only have broad application prospects in steel rolling, cement, and traction, but also, due to their large capacity and high efficiency, can be used as AC excitation devices for variable-speed constant-frequency generators in power systems. Currently, the triggering control methods for CNC AC-AC inverters mainly include the cosine intersection method, the average sampling method, and the improved sampling method. Compared with the latter two methods, the cosine intersection method has significant advantages, reducing the total distortion of the output voltage waveform to a lower level. However, when using the cosine intersection method to control sinusoidal current output AC-AC inverters, since the cosine intersection method uses the ideal output voltage as the reference quantity in the calculation, and generates the output current by calculating and controlling the output voltage, it inevitably leads to problems such as excessively high harmonic content of the output current and significant waveform distortion for inductive loads. This paper addresses the shortcomings of the cosine intersection method in controlling sinusoidal current output and proposes a slope approximation method for sinusoidal current output control. Simulation analysis and experimental verification were conducted, and the slope approximation method and the cosine intersection method were compared. [b][align=center]For details, please click: AC-AC Inverter Slope Approximation Control Method[/align][/b]