This study presents the performance analysis of a new asymmetrical multi-level inverter using reduced number of switches for a single-phase grid-tied photovoltaic (PV) system. The solar PV panels of unequal power rating are connected in an appropriate manner to obtain the DC link voltages of suitable ratio for an asymmetrical cascaded multi-level inverter. The PV power, voltages as well as the current injected into the grid have been controlled using the separate maximum power point tracking, voltage controllers and a current controlled technique to achieve the maximum power with sinusoidal current with a unity power factor. The variations of DC link voltages, inverter voltage and injected grid current are simulated and are experimentally verified under the variable irradiation as well as grid voltage fluctuation. The simulation and the corresponding hardware results of the proposed reduced switch asymmetrical seven-level inverter for a low-power residential grid-tied PV system is also presented.

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This article presents a generalised asymmetrical cascaded multilevel inverter (MLI) for a single-phase grid-connected photovoltaic (PV) system and their control strategy. The control strategy, including maximum power tracking along with a suitable interface, is implemented for maximum power transfer from the PV source to the single-phase low-power grid. The balancing of DC-link voltages for an asymmetrical MLI under variable solar parameters as well as grid parameter variation is implemented using the proposed control strategy. The voltage controllers maintain the constant DC-link voltage ratio, whereas the current controller injects the sinusoidal current into the grid at unity power factor and track the grid voltage under variation of grid voltage using grid tracker. Stability analysis of the proposed grid-connected asymmetrical inverter system is also incorporated. The whole grid-tied PV system is simulated in the MATLAB/SIMULINK environment and the exhaustive simulation results of the system under different transient conditions are presented. In addition, a laboratory prototype for a low-power gridtied PV system has been developed and implemented using DS1103. The performance of the system is also tested at varying irradiance conditions and the corresponding experimental results are also presented.

The major concern with renewable sources of energy, feeding the distributed power generation system, is the power quality, reliability and efficiency of the system. This study proposes a novel topology comprising single-phase, seven-level, gridconnected photovoltaic-fed (PV) inverters in parallel. An important expediency of connecting multilevel inverters (MLIs) in parallel is that the failure of any source or the MLI module itself will never stop the overall generation, leading to improved efficiency and reliability of the system. This study also incorporates a novel controller comprising of two DC and an AC controller that independently controls the DC-link voltage of PV system and AC-side voltage so as to inject a pure sinusoidal current at unity power factor into the grid. Also, the AC controller discussed here is self-synchronising, i.e. aloof of phase-locked loop. The power mismatch problem that basically arises due to partial shading conditions in PV system has also been discussed. The MATLAB/Simulink-based proposed two seven-level grid-connected inverters in parallel are modelled and simulation results are presented. An experimental prototype of the PV-fed grid-connected system comprising two seven-level inverters in parallel is developed and tested to validate the simulation results.

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