| Nowadays,the world energy situation becomes tense, and meanwhile the grim, wind,solar and other renewable energy sources is attracting more and more attentions.Distributed generation (DG) system is the effective way to use renewable energy. The gridconnected inverter plays a key role in the energy conversion. Intellectualization is thedevelopment direction of power grid and grid-connected inverter also plays an importantrole in the smart power grids. This thesis focus on the control strategies for single-phasegrid-connected inverter with LCL filter.LCL filter has a better harmonic attenuation ability than the single-inductor filter,so itneeds less inductance. This thesis will discuss the performance influence of inductanceratio thesis and branch resistance. LCL filter has resonance characteristics so its stability isa hot research point currently. This paper chooses discrete state feedback control stratege,because it meets all the freedoms in control to improve the control properties, includingresonance damping.This thesis establishes the mathematical model of the single-phase LCL inverter whichlays the foundation of state feedback design based on pole placement. Some importantissues like the appropriateness of continuous design and the zero position of system are alsodiscussed.Two methods of state feedback parameter design including virtual resistanceand PI statespace are introduced and simplified. This paper also does some analysis andcomparison work about them.The relationship between grid voltage and grid current becomes complicated whenusing state feedback. Discrete control system model is turned continuous and the full gridvoltage feedforward decoupling strategy is discovered. The strategy includes a constantportion and some differential portions.This thesis discusses the influence of sampling lagand grid voltage feedforward on weak grid robustness, and verifies that the differentialportion in grid voltage feedforward will harm the weak grid robustness. |
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