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A dual-mode input voltage modulation (IVM) control scheme for a three-phase ZCS series resonant (SR) inverter fed three-phase voltage multiplier based DC-DC converter for X-ray power generator is proposed. The three-phase ZCS SR inverter is formed by connecting three single-phase ZCS SR inverters in parallel and delaying the gating signals by 120deg with respect to each other. It operates at constant frequency & duty ratio. The lower arms of all the three single-phase inverters (i.e. which make three-phase ZCS-SR inverter) are connected to a common holding capacitor CH and the voltage VH across it, is controlled by a control circuit. At the turn ON of the converter, the control circuit clamp voltage VH to 0V, causing inverter to see full input voltage and output voltage to rise with maximum speed. As the output voltage reaches 80% of target voltage value, the voltage VH is raised from 0V to (VH)ref, thereby reducing the effective input voltage to inverter. As a result the rise rate of output voltage slow downs and the over shoot is prevented. Experimental results based on the laboratory scale-down prototype are presented to verify the effectiveness of proposed dual-mode IVM control scheme.