High Performance Control of AC Drives with Matlab / Simulink Models

3.7 Impedance Source or Z-source Inverter

The impedance source or Z-source inverters are special types of inverters that provide the voltage boost capability in conventional inverters. The conventional inverters work as a buck converter only, because the output voltage is always lower than the DC input voltage. Moreover, the upper and lower power switch cannot conduct simultaneously, otherwise the DC source will short circuit. Hence, a dead band is provided intentionally between the switching on and switching off of the complimentary power switches of the same leg. This dead band causes distortion in the output current. These shortcomings are overcome in the Z-source inverter. Two inductors of equal value and two capacitors of equal value, arranged in the form of a letter X with series inductors and diagonal capacitors, are inserted between the DC source and inverter six power switches. This intermediate stage offers the advantage of boosting the DC source voltage, which is a highly attractive solution for renewable energy interface such as Photovoltaic system, Fuel Cells, etc., where the generated voltage is low and the load demand voltage is high. Detailed discussions on the Z-source inverters are given in [49–58]. The concept of impedance source is equally applicable to AC-DC, DC-DC, AC-AC, and DC-AC power converter topology. This section introduces this new class of inverters (DC-AC converter) and will elaborate the basic principle of operation and control power circuit topology ...