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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.

This paper presents the power losses analysis of a three-phase quasi-Z-source inverter. The analysis is based on experimental measurements. For that purpose, the laboratory setup of the considered inverter operating in a stand-alone mode was built. The total inverter power losses have been obtained as a difference between the measured input and output powers of the inverter. The power losses of the inductors in the impedance network were determined based on the measured respective currents and parasitic resistances, switching frequency, and available inductor core data. On the other hand, the power losses of the capacitors in the impedance network were neglected due to low equivalent series resistance of the utilized polypropylene capacitors. The remaining losses were ascribed to semiconductor losses. Following these assumptions, the power losses distribution and the efficiency of the considered inverter were determined over wide ranges of switching frequency, input voltage, shoot-through duty cycle, and phase current RMS value.

U radu su ispitana statička i dinamička radna svojstva sustava trofaznog izmjenjivača kvazi Z-tipa bez priključka na mrežu s reguliranim izlaznim naponom. Regulacijski sustav je realiziran s razvojnim računalnim sustavom MicroLabBox opisanim u radu. Opisan je osnovni princip rada izmjenjivača kvazi Z-tipa i regulacijski sustav kojim se postiže željena efektivna vrijednost osnovnog harmonika izmjeničnog napona. Za potrebe eksperimentalnog ispitivanja sustava realizirana je pripadajuća laboratorijska maketa. Ispitivanja su provedena za različite postavke ulaznog napona, trajanja prostrijelnog stanja i otpora trošila. Određen je optimalni raspon ulaznog istosmjernog napona s obzirom na korisnost i stabilnost rada izmjenjivača te točnost regulacije izlaznog napona.

This paper presents two simple control strategies for a battery-assisted photovoltaic (PV) system with the threephase quasi-Z-source inverter (qZSI). The specific control objectives depend on the operating mode of the PV-qZSI system. In the stand-alone mode, the objective is to keep the fundamental RMS value of the ac-side phase voltage at a desired value, whereas in the grid-tied mode, the objectives are to synchronize the qZSI with the grid and achieve unity power factor. The additional common objective is to operate the PV system close to the maximum power point (MPP). This can be achieved in an open-loop manner by assigning a fixed shoot-through duty ratio, thus avoiding any additional sensors, but the inherent drawback of this method is sensitivity to irradiance and temperature variations leading to suboptimal performance. The proposed control strategies were experimentally tested over a reasonably wide range of irradiance levels in order to assess the overall performance of the PV-qZSI system.