Single-Phase Seven-Level Grid-Connected Inverter for Photovoltaic System
ABSTRACT
A single-phase seven-level inverterfor grid-connected photovoltaic systems, with a novelpulsewidth-modulated (PWM) control scheme is presented. Three referencesignals that are identical to each other with an offset thatis equivalent to the amplitude of the triangular carrier signalwere used to generate the PWM signals. The inverteris capable of producing seven levels of output-voltage levelsfrom thedc supply voltage. A digital proportional–integral current-controlalgorithm was implemented to keep thecurrent injected into the grid sinusoidal.
In this paper single-phase seven-level inverter was developedfrom the five-level inverter. It comprises asingle-phase conventional H-bridge inverter, two bidirectionalswitches, and a capacitor voltage divider formed by and. The modified H-bridge topologyis significantly advantageous over other topologies, i.e., lesspower switch, power diodes, and less capacitor for invertersof the same number of levels.
Photovoltaic (PV) arrays were connected to the inverter via adc–dc boost converter. The power generated by the inverter isto be delivered to the power network, so the utility grid, ratherthan a load, was used. The dc–dc boost converter was requiredbecause the PV arrays had a voltage that was lower than the gridvoltage. High dc bus voltages are necessary to ensure that powerflows from the PV arrays to the grid. A filtering inductanceLf was used to filter the current injected into the grid. Properswitching of the inverter can produce seven output-voltage levels() from thedc supply voltage.
This paper has presented a novel PWM switchingscheme for the proposed multilevel inverter. It utilizes three referencesignals and a triangular carrier signal to generate PWMswitching signals. The behavior of the proposed multilevelinverter was analyzed in detail. By controlling the modulationindex, the desired number of levels of the inverters outputvoltage can be achieved.The less THD in the seven-levelinverter compared with that in the five- and three-level invertersis an attractive solution for grid-connected PV inverters.
The proposed system wasverified through MATLABsimulation.
Block diagram for proposed system
DESIGNG SOFTWARE AND TOOLS:
MATLAB /SIMULATION Software and simpower systems tools are used. Mainly control system tools, power electronics and electrical elements tools are used.
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