Abstract: In order to comprehensively improve the power quality of medium-voltage（10 kV） power supply system and meet the requirements of centralized sensitive load on power supply reliability, this paper proposes a transformerless medium-voltage power supply quality comprehensive improvement device and its load voltage control strategy. Firstly, the topology and working principle of the device are introduced. The device realizes impedance isolation between the power grid and load by isolation reactor, and weakens the influences of power quality events on loads. The cascaded H-bridge battery energy storage system is used to support and control the load voltage, so as to realize continuous high-quality power supply on the load side. Secondly, the influences of isolation reactor and grid-connected reactor on the operation characteristics of the device are analyzed. Then, the load voltage control strategy integrating grid-connected operation and off-grid operation of the device is proposed, so as to realize the rapid control of the grid power injection, frequency and amplitude of the load voltage. Finally, the feasibility and effectiveness of the device and its load voltage control strategy are verified by simulation analysis and experimental prototype test, and the technical performance of various power supply quality improvement devices is compared.