High performance of three-level T-type grid-connected photovoltaic inverter system with three-level boost maximum power point tracking converter

A three-phase three-level transformerless T-type grid-connected inverter system with three-level boost maximum power point tracking converter is introduced in this article for high-voltage high-power applications. First, the mathematical model of grid-connected photovoltaic inverter system is built. Second, a multiloop interleaved control scheme is proposed for three-level boost maximum power point tracking converter to reduce the ripple of the inductor current and balance the capacitor voltage of DC bus. A predictive current control method and a power feedforward strategy are also proposed for the T-type three-level inverter part to reduce the harmonic content of grid-connected current and to improve the dynamic response of the system, respectively. In order to solve complex algebraic computation of traditional space vector pulse width modulation or multi-carrier pulse width modulation method, a single-carrier pulse width modulation method is presented for T-type three-level inverter. Finally, all control strategies and modulation method are implemented on a single-chip digital signal processor. A high conversion efficiency, low cost, and low harmonic current could be obtained on a 23-kW experimental prototype.