With　the　development　of　science　and　technology,　the　demand　for　power　quality　is　getting　higher　and　higher.　Voltage　sag　is　one　of　the　most　common　power　quality　events.　It　is　of　great　practical　significance　to　develop　voltage　sag　generator　to　accurately　evaluate　the　impact　of　voltage　sag　on　industrial　sensitive　equipment　and　take　effective　technical　measures　to　reduce　economic　losses.　In　order　to　use　the　voltage　sag　generator　in　different　fields,　its　volume　and　weight　should　be　as　small　as　possible.　At　present,　the　voltage　sag　generator　has　a　large　volume　and　heavy　weight,　which　can＇t　meet　the　volume　requirements　of　industrial　and　laboratory　elevators　and　is　not　convenient　for　mobile　use.　This　paper　designs　a　main　circuit　structure　of　voltage　sag　generator,　which　consists　of　three-level　PWM　rectifier,　DC-DC　converter,　and　three-phase　half-bridge　inverter.　Using　dual　active　bridge　bidirectional　DC/DC　converter(DAB)　instead　of　power　frequency　transformer　can　greatly　reduce　the　volume　and　weight　of　the　circuit.　And　the　three-level　PWM　rectifier,　dual　active　bridge　bidirectional　DC-DC(DAB)　converter　and　three-phase　half-bridge　inverter　are　all　designed　by　modularization,　which　is　convenient　for　disassembly　and　assembly.　PWM　rectifier　and　dual　active　bridge　bidirectional　DC/DC　converter　are　used　to　make　the　power　supply　have　the　function　of　bidirectional　energy　flow.　three-level　half-bridge　inverter　is　used　to　simulate　the　power　supply　characteristics　under　various　fault　conditions.　The　working　principle　of　each　part　of　the　voltage　sag　generator　is　introduced　in　this　paper.　The　simulation　results　prove　the　effectiveness　of　the　design.　©　2019　IEEE.