Research On The Differential Three-Level Inverter With Stand-alone And Grid-connected Operation Modes

In recent years, the environment problems become more and more serious and prominent, especially the lack of energy which restricts the economy of fast sustainable development. In order to solve the problems, the renewable resources become growing attractive for most countries. The solar energy is one of the most potential green ones, because it’s clean, pollution-free and renewable. As China is rich in solar resource, making a rational use of it means a vital strategy. The photovoltaic (PV) inverter is the core part of the PV regeneration system, as its performance has a direct effect on the PV system. With regards to the PV inverter, it’s meaningful to carry out related research on its topology and control method.Focusing on the research status and development trend of the PV inverter, the single-stage PV ones are further emphasized by introducing the differential structure and three-level (TL) technology. As a result, a family of non-isolated TL DC-DC converter type differential inverters is proposed.The thesis chooses the Buck type TL differential inverter as an example to analyse. When it’s working at the stand-alone mode, two control methods called full-cycle operation and half-cycle operation are presented respectively. The different working stages are discussed in detail too, which are all proved by simulation.The thesis explores the control ways of Buck type TL differential inverter when working at the grid-connected mode. A novel constant-frequency current hysteretic control strategy is put forward. By comparing the simulation waveforms of the new constant-frequency current hysteretic control with the traditional one, its feasibility and superiority are verified.Finally the paper designs the hardware of the Buck type TL differential inverter, including the main circuit, driving circuit, sensing circuit and so on. The DSP chip TMS320F2808, combined with its CCS4.3simulation platform and V2simulator are utilized to produce the switch control software codes and debug the prototype. The final experimental waveforms of the prototype further prove the correctness of the theory analysis.