Abstract: A topology of Z-source three-level nine-switch converter is studied, and is applied in PV inverter system, which enhances the adaptability of single-polar inverter to voltage fluctuation of PV unit and improves the power quality. Based on the modeling of the three-level nine-switch converter and the Z-source boost network, the topology of the main circuit is designed. On the basis of traditional SVPWM modulation, a method to proportionally compress pulse effect time of original SVPWM is presented, and the spare time is used to direct pulse modulation to realize joint regulation of both driving signals. Taking the power control and voltage control as objective, the control scheme of the proposed converter is designed. The simulation result shows that Z-source network maintains the normal operation of inverter when PV output voltage fluctuates with the varying of irradiation, and the three-level structure makes the output current total harmonic distortion (THD) low.