Research On Adaptive Control Strategy Of Grid-connected Pv Inverter Under Weak Grid

In recent years, with the promotion and application of photovoltaic technology, research for photovoltaic power generation in remote area has become a hot research area. Due to the long transmission lines and increased transformer links of the grid in remote areas and micro-grid constructed by the distributed power generations, the equivalent grid impedance will increase, in addition, the short-circuit capacit y of grid will be smaller, so the grid has the characteristics of weak grid. In general, the large grid impedance will reduce the gain and bandwidth of the system and slow down the dynamic response, or even lead to resonance and instability of the whole control system. What ’s more, the voltage and frequency fluctuations caused by the low short-circuit capacity will seriously affect the stability of the inverters. Aiming at the above problems, research for the control strategy of PV grid-connected inverter under weak grid has been done in this article to improve the adaptabilit y and stabilit y of the entire power grid system.A single-phase grid-connected PV inverter is made as the research object. Firstly, a mathemat ical model of the control system was built, after analysis, the grid large impedance will seriously affect the performance of the control system. Then, the double harmonic disturbance current injection method was used to achieve the online accurate identification of grid impedance. Further, the adaptive quasi-PRD control method o f PV grid-connected inverter under weak grid was proposed. This control method not only improves the static and dynamic performance of the control system, but also improves the adaptability to the changing grid impedance and improves the power quality. Next, to solve the problem of voltage fluctuations, according to the relevant requirements, the LVRT control strategy was researched to enhance the stability of system under weak grid and improves fault ride-through capability.Finally, the experimental verifications were done in the power of 1k W weak grid single-phase grid-connected PV inverter experiment platform. The experimental results showed the validity and effectiveness of the grid impedance online detection method, the adaptive quasi-PRD control method based on impedance online detection and the LVRT control method that were proposed in this paper.