A converter includes building blocks, each building block being a switching unit. Each building block must be able to receive high power at an elevated switching frequency with low power dissipation in semiconductor switches. The building block includes semiconductor switches and a reactor connected in series, and a series connection of a voltage clamp and a diode. The series connection is connected in parallel to each of the semiconductor switches. The clamps are arranged in such a way that all clamping and voltage control is realised by a clamp connected in parallel with the corresponding semiconductor switch.