Three-level　dual　active　bridge　converters　based　on　neutral　point　clamped　legs　reduce　the　voltage　stress　of　power　devices　compared　to　two　level.　However,　maintaining　the　capacitor　voltages　balanced　in　a　wide　operating　range　is　the　critical　issue　of　this　converter.　To　mitigate　this　problem,　a　PI　feedback　loop　of　voltage　error　is　known,　but　it　results　in　poor　dynamic　performances.　Complementary　switching　states　(CSS)　is　an　alternative　method　that　provides　better　results　in　terms　of　balancing　time　and　dynamic　performances.　However,　it　provides　only　one　balancing　mode　which　is　not　suitable　for　various　scenarios　of　voltage　errors.　To　improve　the　performance　of　the　CSS　method,　an　extended　CSS　approach　is　proposed　in　this　article.　It　extends　the　balancing　modes　and　quantifies　the　voltage　regulation　for　each　mode.　Then　it　selects　the　modes　appropriately　to　keep　the　same　balancing　ability　for　severe　voltage　imbalance　while　realizing　a　lower　capacitor　voltage　ripple　compared　to　the　CSS　method.　In　addition,　it　significantly　mitigates　the　negative　effects　of　low　sampling　frequency　by　assigning　balancing　modes　adequately.　A　sensor-less　dc　bias　suppression　(DBS)　method　is　also　introduced,　which　uses　the　error　in　the　voltage　regulation　of　four　extended　modes　to　estimate　actual　dc　bias　current.　A　PI　control　loop　is　adopted　to　adjust　the　duty　cycle　of　switches　to　realize　the　DBS.　Therefore,　the　voltage　imbalance　and　dc　bias　can　be　eliminated　simultaneously　by　the　proposed　methods.　Experiment　results　show　the　improvement　of　proposed　methods　in　terms　of　capacitor　voltage　ripple,　dynamic　results,　and　correct　DBS.　©　1986-2012　IEEE.