Interleaved or sequential switching - for increasing the switching frequency

Using several IGBTs in parallel it is possible to operate standard IGBTs with higher switching frequencies than usual. Based on this concept the current load and thermal losses are split between the paralleled devices. The free wheeling diodes, however, cannot be controlled actively and therefore do not share in sequential switching. In 3-phase VSI applications there is the danger of overloading one of the paralleled free wheeling diodes. This paper presents a concept of magnetic freewheeling control resulting in the free wheeling current following the same sequential concept as in the IGBTs. Magnetic freewheeling control makes sequential switching applicable to 3-phase voltage source inverters (VSI).