This　paper　describes　a　three-phase　trasformerless　active　filter　system　based　on　hybrid　cascaded　H-bridge　converters　with　delta　configuration.　It　is　intended　for　dynamically　compensating　harmonic　current　of　three-phase　nonlinear　load.　This　active　filter　is　characterized　by　per-phase　series　connection　of　a　high-voltage　converter　operating　at　50　Hz　and　a　low-voltage　converter　operating　at　7.5　kHz.　DC-link　voltages　of　all　converters　are　regulated　purely　by　control　algorithm　without　any　auxiliary　circuit.　The　dc　voltage　ratio　of　2:　1　is　realized　for　the　series-connected　converters　by　injecting　zero-sequence　current　with　fundamental,　third-harmonic,　and　fifth-harmonic　components　to　the　three　clusters.　An　experimental　prototype　rated　at　100　V　and　1　kVA　is　built　up　in　authors＇　lab.　Experiment　results　confirm　the　validity　of　this　dc　voltage　control　method　and　harmonic　current　compensation　capability.