Reduction of switching losses in three-phase three-level voltage source inverters

Insulated Gate Bipolar Transistors are ones of basic switching elements in voltage source inverters with medium and high power rating. The switching losses in these transistors can be significantly reduced using different methods which allow to switch transistors at their voltage or current that are close to zero. In many soft switching systems auxiliary circuits consist of capacitors connected in parallel to the main transistors and resonant inductors which are connected in series to auxiliary transistors. These connections are not recommended because the main or auxiliary transistor may be damaged during disturbances in control systems. Due to these drawbacks, the patented solution, wherein the above disadvantages do not occur, is presented in this paper. Special attention was paid to total losses in the presented soft switching system; these losses were compared with the switching losses in an inverter operating without any soft switching system. This comparison was made for an inverter with a rated power of about 1.2 MW.