Unidirectional dc voltage conversion device and system and method for controlling same

A unidirectional DC voltage conversion device, comprising two input ports and two output ports and comprising a preceding-stage switch circuit, a front end circuit, a main power circuit, a subsequent-stage switch circuit, a preceding-stage auxiliary isolation switch and a subsequent-stage auxiliary isolation switch, wherein

• each of the preceding-stage switch circuit, the front end circuit, the main power circuit and the subsequent-stage switch circuit is a two-port circuit, and preceding-stage and subsequent-stage ports of the circuits form a cascade connection in sequence;
• a preceding-stage port of the preceding-stage switch circuit is a second input port of the unidirectional DC voltage conversion device, and comprises an input positive terminal and an input negative terminal;
• a subsequent-stage port of the subsequent-stage switch circuit is a second output port of the unidirectional DC voltage conversion device, and comprises an output positive terminal and an output negative terminal;
• when a subsequent stage of the preceding-stage switch circuit and a preceding stage of the front end circuit form a cascade connection, a negative terminal of the port is connected to the preceding-stage auxiliary isolation switch and forms, together with a positive terminal, a first input port of the unidirectional DC voltage conversion device;
• and when a subsequent stage of the main power circuit and a preceding stage of the subsequent-stage switch circuit form a cascade connection, a negative terminal of the port is connected to the subsequent-stage auxiliary isolation switch and forms, together with a positive terminal, a first output port of the unidirectional DC voltage conversion device.