Abstract: An inverter type high voltage power supply is required for the acceleration of ITER neutral beam injector (NBI) system. The power supply employs three-phase three-level DC/DC converter as its basic component. This type of power supply can regulate the output voltage rapidly by the duty cycle modulation of the inverter switches. However, when the duty cycle is very small, the output ripple will be large. A new control strategy has been studied for the power supply, the output voltage is regulated by inverter duty cycle combining with adjusting the dc-link voltage. In order to verify the control strategy, a 200 kV/60 A Simulink model and a 400 V/6 A prototype have been established. Simulation and experimental results demonstrate that the topology with this control strategy can limit the voltage ripple while maintain the rapid voltage response.