Semiconductor Losses Calculation of a Quasi-Z-Source Inverter with Dead-Time
Keywords:dead-time, loss-calculation algorithm, quasi-Z-source inverter, semiconductor losses, switching energies
A quasi-Z-source inverter (qZSI) belongs to the group of single-stage boost inverters. The input dc voltage is boosted by utilizing an impedance network and so called shoot-through (ST) states. In pulse-width modulations utilized for the qZSI, the dead-time is commonly omitted. However, unintended ST states inevitably occur as a result of this action, due to the non-ideality of the switching devices, causing the unintended voltage boost of the inverter and an increase in the switching losses. Hence, the implementation of the dead-time is desirable with regard to both the controllability and efficiency of the qZSI. This paper deals with the calculation of semiconductor losses of the three- phase qZSI with implemented dead time. An algorithm available in the literature was utilized for that purpose. The algorithm in question was originally proposed and applied for the qZSI with omitted dead-time, where the occurrence of unintended, undetected ST states combined with the errors in the switching energy characteristics of the insulated gate bipolar transistor (IGBT) provided by a manufacturer led to errors in the obtained results. However, these errors were unjustifiably ascribed solely to the errors in the switching energy characteristics of the IGBT. In this paper, a new, corrected multiplication factor is experimentally determined and applied to the manufacturer-provided IGBT switching energies. The newly-determined multiplication factor is expectedly lower than the one obtained in the case of omitted dead time. The loss- calculation algorithm with the new multiplication factor was experimentally evaluated for different values of the qZSI input voltage, the duty cycle, and the switching frequency.