Abstract: Adjustable reactive power compensation device uses the programmable logic controller as the control core, according to several different test condition of the reactive power, designed by multiple small capacity mutual combination parallel capacitor group, through process control with hardware circuit for capacitance of different capacity, complete the required capacity of the parallel combination of capacitor group. The touch screen is used as the man-machine interaction medium to realize the adjustable reactive power compensation by manual selection and increase the frequency protection function at the same time. According to the real motor load test in the laboratory, the adjustable reactive power compensation device operates normally. Under various working conditions, the reactive power compensation device can increase the power factor from 0.2 before compensation to about 0.7. Effectively improving the operating efficiency of the power supply system and reducing the loss on the line. At the same time, on the basis of satisfying the number of working conditions required by the test, the resolution of compensation is increased according to the test data to further ensure that the power factor is greater than 0.6 and the function is more perfect. Now the adjustable reactive power compensation device has been put into use, which ensures the stability of the output voltage of the frequency power supply system and makes the operation of a certain test more stable and reliable.