This application relates to a cell (1200) or sub-module for a voltage source converter (1201). The cell includes an energy storage apparatus (101; 101a, 101b) and a plurality of dual-switch semiconductor packages (201), each having first and second semiconductor switches (202, 203) connected in series. The cell is operable in an active state in which an energy storage apparatus (101; 101a, 101b) is electrically connected in series between cell terminals (102a, 102b) and a bypass state in the cell terminals (102a, 102b) are electrically connected via a path that bypasses the first energy storage apparatus. The plurality of dual-switch semiconductor switch packages are configured to provide a first set of semiconductor switches (301; 401) connected between nodes of the cell that are electrically connected in the first active state and electrically disconnected in the first bypass state; and a second set of semiconductor switches (302a, 302b; 402a, 402b) is connected between nodes of the cell that are electrically disconnected in the first active state and electrically connected in the bypass state. The second set of switches comprises a greater number of switches in parallel than the first set of switches.