Abstract
A hybrid resonant three-level converter comprised of dual transformers is proposed in this paper, which is suitable for the application of distributed photovoltaic power accessing the medium voltage dc distribution network. The proposed converter can be obtained by adding a control circuit into the traditional neutral point clamped (NPC) three-level (TL) circuit, achieving the basic TL circuit operating with a fixed duty cycle. Pulse width modulation (PWM) is adopted for the control circuit to realize zero current switchings for the basic TL circuit, which delivers most of the power, under full load range. As a result, the switching loss of the converter can be significantly reduced. The influences of the turn ratio of the second transformer and resonant capacitance on the switch current, the peak value of resonant voltage, and the value of the resonant inductance value are discussed in detail, and the parameters design principles are put forward. Finally, a prototype is built to verify the performance of the proposed converter.
1. Introduction
With the advancement of science and technology, the level of solar cell technology has been greatly improved in the past few years. The cost of photovoltaic power generation has been dropped rapidly, and the capacity for power generation has been greatly increased. In the next few years, the focus of the development of photovoltaic power generation in China will shift from a centralized power station to a distributed power generation system. In 2017 China’s distributed photovoltaic power generation will add 19GW (Hu and Liu, 2017; Cheema and Mehmood, 2019; Cheema, 2020). The distributed photovoltaic power generates a DC output which is basically directly connected to the AC distribution network. Therefore, distributed PV access to DC power distribution networks can save many commutation links. It has a low operating cost, high reliability and low transmission losses (Jiang and Zheng, 2012; Song et al., 2013).
