High　quality　online　uninterruptible　power　supplies　(UPS)　are　widely　used　in　applications,　e.g.,　precision　medical　equipment　with　critical　loads.　This　article　proposes　a　low-cost　and　high-performance　online　UPS　system.　First,　the　performance　improvement　of　a　bidirectional　switch-based　bridgeless　power　factor　converter,　which　is　regulated　by　a　hybrid　control　strategy　with　load　current　feedforward,　is　studied.　Second,　the　proposed　closed-loop　controller　integrates　improved　predictive　current　control　with　predictive　voltage　control　and　applies　to　the　second-stage　neutral-point-clamped　three-level　inverter　for　low　output　voltage　harmonics.　Moreover,　a　push-pull　DC-DC　converter　interfaces　and　boosts　voltage　of　a　24　V　battery　bank　as　the　backup　energy　source.　Considering　complexity　of　the　UPS　system　as　well　as　cost　reduction,　we　implement　a　multitask　decomposition　method　for　control　on　a　monolithic　low-cost　digital　signal　processor　embedded　with　control　law　accelerator.　Finally,　the　experimental　results　from　a　1　kVA　prototype　can　effectively　verify　validity　of　the　theoretical　analysis　and　design.　©　1972-2012　IEEE.