Limitations of control parameters of the three-phase voltage source inverter containing the soft switching system circuits with safe connections of capacitors and inductors

Transistors of voltage source inverters are switched without losses when their currents or voltages are close to zero when the transistors are switched. This condition can be fulfilled by means of certain resonant processes, whose durations are comparable to the switching times of the inverter transistors. In order to minimize switching losses, the resonant processes cannot be interrupted before they are ended; otherwise such interruption may lead to a hard switching of these transistors. It causes some limitations of the inverter control parameters such as the amplitude modulation ratio and the switching frequency. Durations of the resonant processes are strictly related to values of inductances and capacitances of the applied soft switching system. The paper discusses influence of these values on the amplitude modulation ratio at the constant switching frequency; also limitation of the switching frequency for an assumed maximum value of the mentioned ratio is considered. Additionally, the inverter operation when the resonant processes have been interrupted due to a fault is discussed.