The static var generator (SVG) based on three-level NPC converter is studied. The dual-dq PLL is proposed in unbalanced gird conditions to obtain accurate phase, positive and negative vector. The negative voltage feedforward control strategy is adopted to achieve SVG stable operation in unbalanced gird conditions. Space vector modulation (SVPWM) algorithm based on 60° coordinate system is proposed, which is simple in calculation and easy digital realization. The proposed algorithms are realized in digital control system of three-level SVG based on the structure of DSP and FPGA. The experimental results validate that the system has good dynamic response performance and stability.