Research On Fault Ride Through Control Of Three-phase Photovoltaic Grid-connected Inverter

Energy crisis and environmental problems prompted the world to step up its own strategic plan in the new energy sector, to develop solar energy as a representative of distributed generation technologies. As a large-scale photovoltaic(PV) power generation system connected into the grid, the influence between inverter and grid has became increasingly significant. Grid interconnection standards require that three-phase PV grid-connected inverter should have fault ride through(FRT) ability when grid encounter fault. However, the traditional FRT control strategies exist the problems of over-currents and active and reactive power coordinated control. So new control strategies are proposed to solve the above problems.With the three-phase PV grid-connected inverter as the object, the inverter output characteristics and working principle of traditional FRT strategies under unbalanced grid voltage condition was first introduced in this paper. Control target design process was analyzed and the mechanism of grid current overflow phenomenon has been revealed emphasisly. A current-limited strategy is proposed to restrain the current overflow, and shows the quantitative analysis results of different schemes. Simulation results verify the effectiveness of the proposed strategy.In order to realize three-phase grid-connected inverter output power and current quality coordinated control under unbalanced grid voltage, the generation mechanism of the current harmonic and power oscillation was discussed with a quantitative analysis in this paper. A new control strategy is proposed to achieve the coordinate control of power and current quality without the need of phase-locked loop(PLL) for positive or negative sequence extraction calculation. Then, to overcome traditional strategy cannot be achieved of controlling for constant power and grid current sinusoidal at the same time, the control strategy based improved instantaneous power is proposed and finally has carried on the simulation.In order to verify the above solution, an experimental platform of three phase grid connected inverter based on TMS320F2812 chip controlled has been built, and Chroma6590 programmable ac source was used to simulate the grid fault. On the platform, the proposed control strategy has carried on the experimental research, the experimental results proved the effectiveness of the proposed schemes.