The invention relates to a converter (K) for controlling power flows between at least three power networks (QAC, QHV, QNV) having different operating voltages (UA, UB, UC). The converter comprises at least three terminals (A, B, C), each of which is configured for electrically contacting one of the three power networks (QNV, QHV, QAC), and at least two converter cells (Z1, Z2), each having a transformer (T) having at least three transformer coils (W1,A, W1,B, W1,C, W2,A, W2,B, W2,C). At least one of the terminals (A, B, C) is connected to a series connection of converter cells (Z1, Z2), whereas at least one of the other terminals (A, B, C) is connected to parallel connection of converter cells (Z1, Z2) via a bidirectional serial line.