This paper presents an effective maximum power point tracking (MPPT) method for photovoltaic (PV) panels without any voltage sensor in a PV differential power processing (DPP) system. If a fault occurs in the voltage sensor, errors will occur in all control methods, including MPPT, thereby reducing power production efficiency. Therefore, this paper presents an effective duty MPPT method that enables normal MPPT, even without the voltage sensor of the DPP converter used in the PV power generation DPP systems. The proposed method performs MPPT by analyzing the power-loss elements of the DPP converter to recalculate the effective duty cycle used for actual power transmission and reduce the voltage calculation error. The effectiveness of the proposed method is verified in simulations and experiments, and the average accuracy compared with the general P&O MPPT is found to be 98.65[%] on average even without the use of a voltage sensor.