A New Photovoltaic System Architecture of Module-Integrated Converter with a Single-sourced Asymmetric Multilevel Inverter Using a Cost-effective Single-ended Pre-regulator

Abstract

In this paper, a new architecture for a cost-effective power conditioning systems (PCS) using a single-sourced asymmetric cascaded H-bridge multilevel inverter (MLI) for photovoltaic (PV) applications is proposed. The asymmetric MLI topology has a reduced number of parts compared to the symmetrical type for the same number of voltage level. However, the modulation index threshold related to the drop in the number of levels of the inverter output is higher than that of the symmetrical MLI. This problem results in a modulation index limitation which is relatively higher than that of the symmetrical MLI. Hence, an extra voltage pre-regulator becomes a necessary component in the PCS under a wide operating bias variation. In addition to pre-stage voltage regulation for the constant MLI dc-links, another auxiliary pre-regulator should provide isolation and voltage balance among the multiple H-bridge cells in the asymmetrical MLI as well as the symmetrical ones. The proposed PCS uses a singleended DC-DC converter topology with a coupled inductor and charge-pump circuit to satisfy all of the aforementioned requirements. Since the proposed integrated-type voltage pre-regulator circuit uses only a single MOSFET switch and a single magnetic component, the size and cost of the PCS is an optimal trade-off. In addition, the voltage balance between the separate H-bridge cells is automatically maintained by the number of turns in the coupled inductor transformer regardless of the duty cycle, which eliminates the need for an extra voltage regulator for the auxiliary H-bridge in MLIs. The voltage balance is also maintained under the discontinuous conduction mode (DCM). Thus, the PCS is also operational during light load conditions. The proposed architecture can apply the module-integrated converter (MIC) concept to perform distributed MPPT. The proposed architecture is analyzed and verified for a 7-level asymmetric MLI, using simulation results and a hardware implementation.

Design and development of symmetrical super‐lift DC–AC converter using firefly algorithm for solar‐photovoltaic applications

“…The asymmetric MLI has been investigated a maximum number of levels obtained with a high number of switches and gate driver circuits for generating all levels [14]. Here, symmetric MLI minimum number of levels is applied to achieve maximum output voltage.…”

A new structure of single‐phase two‐stage hybrid transformerless multilevel PV inverter

“…However, the overall performance of the proposed two-stage system is better than the existing topologies in the previous studies. [16][17][18] In Table 4, a comparison of conventional seven-level inverters with the proposed hybrid inverter is given in the previous studies. 12,13 The total number of active and passive components and DC sources required for the realization of seven-level output is fewer in comparison with conventional MLIs.…”

“…It boosts the lower PV voltage to higher DC-link voltage and then converts it to AC to meet the grid peak voltages. 18 All these inverters are good at balancing the DC-link voltage and generating seven levels in the output voltage. In general, two-stage inverters are built with either a line frequency transformer (LFT) or a high frequency transformer (HFT) to boost the voltage and also to provide galvanic isolation for leakage current flow from the grid to PV source.…”

“…16,17 A PV module integrated with new asymmetrical cascaded H-bridge seven-level inverter with reduced device count is also presented in the previous study. 18 All these inverters are good at balancing the DC-link voltage and generating seven levels in the output voltage. But the topologies require a HFT only to boost the PV voltage to grid peak voltage, and there is no isolation between PV and grid.…”

Multistring seven-level quasi Z-source based asymmetrical inverter

“…Among the conventional MLIs, CHB is more suitable for PV based grid-connected system due to its modularity feature. However, Asymmetrical CHB-MLI reported in [4] requires less number of isolated dc sources and switches when compared to symmetrical MLI configurations. Recently, several inverter topologies have been introduced based on reduced switch count for increased output voltage levels.…”