Drawbacks of impedance networks

This paper presents the influence of voltage-fed impedance networks, known as Z-source and quasi–Z-source, as well as some more sophisticated networks on the static and dynamic properties of voltage source inverters. The impedance networks increase output voltage distortions with the second harmonic of the fundamental harmonic and decrease the power efficiency. The distortions of the output voltage increase for the discontinuous current mode of the impedance network. The DC voltage boost factor depends on the impedance network power losses. The impedance networks add 2 resonant frequencies that are very close each other to the control transfer function of the inverter in the frequency range that is close to the fundamental frequency. The influence of the impedance network on the control transfer function depends on the effective damping resistance in the impedance network. The impedance network operation during the “shoot-through” time increases the damping of the inverter output filter. The effective damping resistances and the inductance of the coils depend on the power losses in the magnetic materials. Theoretical models along with experimental verification can help to estimate the real influence of impedance networks on the inverter properties.