With the development of negative ion based neutral beam injection system (NNBI) for China fusion engineering test reactor (CFETR), the output power control system of its supporting the radio frequency (RF) power source is one of the key technologies to realize the improvement of its performance.

The study aims to design an improved output power control system of RF power source to solve the problems of output power stability and insufficient control accuracy in the use of existing RF power sources.

The software and hardware separation control structure designed by ARM+CPLD dual-core were employed to ensure the operation efficiency of the output power control algorithm of the RF power source and the communication stability of the peripheral equipment. Multi-stage progressive power control method and 12-bit digital signal were adopted to control the opening and closing of RF power amplifier, so as to realize high-precision control of output power. The capacitive voltage divider method and current transformer method were combined to accurately sample the actual output power of the RF power source for implementing high-stability control of output power with a closed-loop power control method. Meanwhile, the upper computer software design of man-machine interaction based on serial communication of self-defined protocol was adopted to complete the man-machine interaction function of output power control.

The control system has perfect human-computer interaction software function, and test results of the prototype RF power output power control system with simulation load show that the control accuracy of the output power is higher than 0.1% when the rated output power is 50 kW, and the stability fluctuation is less than 0.5%.

This scheme with impedance matching networks is expected to meet the performance requirements of CFETR NNBI RF power supply for output power control.