Harmonics in opposed current converters

Practical switching devices have finite turn-on and turn-off times. Normally a blanking time is added between the turn-off and turn-on of switches to avoid a short circuit during switching. This blanking time results in a current dependent voltage error of the pulse width modulated output of a converter. Topologies based on only one active device in series with a freewheeling diode, like the opposed current converter, do not need blanking time, and the output voltage distortion is greatly improved but not absent. This paper focuses on the harmonic distortion due to nonideal components in the opposed current converter switching leg and compares different modulation strategies. It is shown that the opposed current converter switching leg can be linearized by proper selection of its components. Furthermore, by applying the right modulation strategy it is possible to achieve a double effective switching frequency, as with unipolar switching, while maintaining constant common mode voltage at the output, as for bipolar switching.