Quasi-Z-Source Cascaded Multilevel Inverter With Master-Division Control for Photovoltaic Grid Connection

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) can achieve the boost function through the shoot-through state without the requirement of an additional DC boost circuit. Thus, the efficiency of the system is improved, and each power module can be controlled independently, which makes it more suitable for distributed photovoltaic power generation systems. This paper proposes a multi-carrier phase-shifted PWM (MPSPWM) that inserts a shoot-through signal at the switching moment, in order to address the high switching frequency problem caused by simple boost modulation in qZS-CMI. In order to improve the dynamic response of the system and reduce the grid-connected current distortion of qZS-CMI, this paper proposes a master-division grid-connected control strategy. The DC-link voltage division controllers use the sliding mode control to achieve DC-link voltage stabilization, and the grid-connected current master controller adopts an improved deadbeat control to achieve fast tracking of grid-connected current. When the output power of PV arrays is inconsistent, the differential power allocation between modules is realized by setting the module power allocation factor. Finally, the effectiveness and feasibility of the above theory are verified by three-module cascaded qZS-CMI simulation and experiment.