Single input qZ‐source cascaded multilevel inverters : Analysis , design, and implementation

Abstract

The Single Input quasi-Z-Source Cascade Multilevel Inverter (SIqZS-CMI) has the ability to make use of a single DC input source and to share active power among all cascaded qZS modules. This unique feature, do not present in any other quasi-Z-Source (qZS) multilevel inverter in the literature, is accomplished by replacing one of its Z-impedance inductances by a coupled inductor. With this topology, it is possible to make use of a single low voltage PV string, favoring the use of small size residential rooftop systems. In addition, it simplifies the system grounding and the compliance with many Installation, Maintenance, and Safety Codes and Standards. The proposed control strategy enables high quality current injection into the grid, keeping the DC bus voltage regulation, ensuring precise power balancing with symmetric multilevel waveforms. Experimental results from a 5-level SIqZS-CMI prototype demonstrate the system's performance and its advantages.active power sharing, cascaded loop controller, cascaded multilevel inverter (CMI), DC-AC converter, grid-tied, photovoltaic (PV) power system, quasi-Z-source inverter (qZSI) | INTRODUCTIONRecently, Z-source and quasi-Z-source (qZS) multilevel inverters have been presented in literature. 1,2 These converters combine the advantages of cascaded multilevel inverters (CMIs) with the voltage gain provided by impedance-source List of Symbols and Abbreviations: C f , filter capacitor; C in(a,b) , input capacitor of module a and b; C 1(a,b) , capacitor 1 of module; C 2(a,b) , capacitor 2 of module; D 0(a,b) , duty-cycle of the ST; D 1(a,b) , module diode a and b; D 2(b) , module diode b; f grid , grid frequency; f s , switching frequency; i grid , grid current; i in , input current; i P , secondary winding current; I PN(a,b) , current drained from module a and a; L 1(a,b) , inductor 1 of module a and b; L 2(a,b) , inductor 2 of module a and b; L cf , converter-side inductor; L g , grid inductor; L gf , grid-side inductor; m (s), modulation index; N, turns-ratio; V a , module output voltage a; V b , module output voltage b; V grid , grid voltage; V PN(a,b) , module bus peak voltage a and b.;

A transformerless Z‐source photovoltaic grid‐connected inverter with coupled inductor coil

“…Reference [7] proposed a quasi‐Z‐source H‐bridge grid‐connected inverter (QHGCI), which had the advantages of the void of shoot‐through problem and the high DC‐voltage utilization. In Reference [8], two QHGCIs are cascaded to enhance the number of energy storage components and to improve voltage gain.…”