Single-Phase Seven-Level Grid-Connected Inverter for Photovoltaic System

ABSTRACT:

This paper proposes a single-phase seven-level inverter for grid-connected photovoltaic systems, with a novel pulse width-modulated (PWM) control scheme. Three reference signals that are identical to each other with an offset that is equivalent to the amplitude of the triangular carrier signal were used to generate the PWM signals. The inverter is capable of producing seven levels of output-voltage levels (V_dc, 2V_dc/3, V_dc/3, 0,−V_dc,−2V_dc/3,−V_dc/3) from the dc supply voltage. A digital proportional–integral current-control algorithm was implemented in a TMS320F2812 DSP to keep the current injected into the grid sinusoidal. The proposed system was verified through simulation and implemented in a prototype.

KEYWORDS:

1.      Grid connected

2.      Modulation index

3.       Multilevel inverter

4.       Photovoltaic (PV) system

5.       Pulse width-modulated (PWM)

6.      Total harmonic distortion (THD)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed single-phase seven-level grid-connected inverter for photovoltaic

systems.

EXPECTED SIMULATION RESULTS:

            Fig. 2. PWM signals for S₁ and S₃.

        

Fig. 3. PWM signals for S₂ and S₄.

Fig. 4. PWM signals for S₅ and S₆.

Fig. 5. Inverter output voltage (V_inv).

Fig. 6. Grid voltage (V_grid) and grid current (I_grid).

CONCLUSION:

Multilevel inverters offer improved output waveforms and lower THD. This paper has presented a novel PWM switching scheme for the proposed multilevel inverter. It utilizes three reference signals and a triangular carrier signal to generate PWM switching signals. The behavior of the proposed multilevel inverter was analyzed in detail. By controlling the modulation index, the desired number of levels of the inverter’s output voltage can be achieved. A TMS320F2812 DSP optimized the performance of the inverter. The less THD in the seven-level inverter compared with that in the five- and three-level inverters is an attractive solution for grid-connected PV inverters.

REFERENCES:

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