The power quality of the middle and low voltage distribution network will deteriorate due to the extension of power supply radius in the sparse areas. To deal with this problem, a direct voltage control strategy based on power electronic voltage regulator is proposed in this paper. The phase-locked loop of delayed signal cancellation and proportional-integral-resonant regulator are employed in this control strategy. And this control strategy quickly improves the power quality for the low and imbalanced voltage at the end of the line, which can dynamically and continuously compensate the line voltage. On this basis, this paper further deduces and verifies the mathematical relationship between the capacity of power electronic voltage regulator and the power supply radius, which provides a theoretical basis for the configuration of device in engineering. Finally, combined with the actual operation condition in the sparse area, a 10-kV power electronic voltage regulator model is developed in Matlab/Simulink. The results demonstrate the effectiveness of the proposed direct voltage control strategy and the accuracy of the mathematical relationship between the device capacity and the power supply radius.