《《Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller》.pdf

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 56, NO. 1, JANUARY 2009 149 Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller Jeyraj Selvaraj and Nasrudin A. Rahim, Senior Member, IEEE Abstract—This paper presents a single-phase five-level photo- voltaic (PV) inverter topology for grid-connected PV systems with a novel pulsewidth-modulated (PWM) control scheme. Two refer- ence signals identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate PWM signals for the switches. A digital proportional–integral current control algorithm is implemented in DSP TMS320F2812 to keep the current injected into the grid sinusoidal and to have high dynamic performance with rapidly changing atmospheric conditions. The inverter offers much less total harmonic distortion Fig. 1. Carrier and reference signals. and can operate at near-unity power factor. The proposed system is verified through simulation and is implemented in a prototype, and the experimental results are compared with that with the con- conventional three-level pulsewidth-modulated (PWM) invert- ventional single-phase three-level grid-connected PWM inverter. ers. They offer improved output waveforms, smaller filter size, Index Terms—DSP TMS320F2812, grid connected, photovoltaic lower EMI, lower total harmonic distortion (THD), and others (PV), proportional–integral (PI) current control, pulsewidth- [3]–[8]. modulated (PWM) inverter. The three common topologies for multilevel inverters are as follows: 1) diode clamped (neutral cl