Research Of Applying Three-Level Control Strategy On Digital Control Of PV Grid Connected Inverter

With the development of world economy, the environment pollution and energy shortage problem are more and more serious. Solar energy has drawn much attention because of its economic and clean advantage.Photovoltaic grid-connected inverter is the core component of solar energy grid generation system, the research to PV grid inverter has important theoretical and realistic significance.When the demand for capacity and voltage rise in the practical application of photovoltaic system, traditional two-level inverter have been unable to satisfy the requirement of the Power grid on its voltage and quality. NPC three-level inverter has higher equivalent switching frequency, lower voltage on single pipe and voltage waveform of higher quality.it has become the research focus in the power electronics and power transmission technology. This paper first analyzes the basic working principle and working condition of NPC three-level PV grid inverter, compares several common ways of the three-level inverter PWM. attempts to put forward a new hysteresis control strategy with approximate constant frequency, this strategy has the advantages of good tracking response and simple implementation; Second this paper gives a detailed theory analysis and simulation about the problem of the three level inverter Neutral-point potential imbalance problem, chooses a software control strategy to control the neutral voltage. At the same time study unbalanced three phase voltageAccording to the analysis and research of the theory, for a given index, this paper completed the design of the experimental prototype’s hardware and software. In the hardware, the design of control circuit based on TMS320F2812, the design of drive circuit and sampling and protection circuit are expounded; In the software, discuss the main program and interrupt service program design the digital PI adjuster and digital phase locked loop in detail.Based on the above analysis and research, a17kw non-isolated three-level grid-connected inverter DC-AC transform prototype is developed, completed the experimental debugging, and got the experimental results. By analyzing the test waveforms, verify that the work performance of inverter DC-AC transform prototype is reliable, control strategy is practical and feasible.