Optimal Capacity Allocation For Distributed Power Generation System And Control Strategy For Grid-Connected Inverter With Local Load

With the global environmental pollution and energy crisis, renewable energy, such assolar energy and wind energy, will play a more and more important role in energyproduction in the future due to their environment-friendliness and enough reserves. Themost effective way to utilize renewable energy is distributed power generation system(DPGS). This paper focuses on the capacity allocation of DPGS and control strategies ofthe grid-connected inverter.This paper proposes an improved optimal sizing method for wind-solar-battery hybridpower system. The proposed method full utilization of the complementary characteristics ofwind and solar energy and can achieve high power supply reliability. Moreover, theproposed method can ensure small fluctuation of power injected into the grid. And the thebattery’s charge and discharge state are also optimized during the energy conversion.For the LCL-type grid-connected inverter with a local load, this paper analyses thecharacteristic when the local load is connected to the capacitor-side and the grid-side. Andthe system can achieve a better quality of the injected grid current if the ocal load isconnected to the capacitor-side. When the local load is connected in the capacitor-side,decreasing the impedance of inverter-side-inductor-branch or capacitor-branch andincreasing the impedance of grid-side-inductor-branch can effectively suppress theinfluence of the nonlinear local load. The close loop of the injected grid current andutilizing the repetitive controller can significantly increase the impedance ofgrid-side-inductor-branch. The inverter-side current inner loop with the load currentfeed-forward, the capacitor current inner loop and the capacitor voltage loop can reduce theimpedance of inverter-side-inductor-branch and capacitor-branch. And among the threecontrol strategies, the inverter-side current inner loop with the load current feed-forwardcan achieve the best performance. Thus, the grid-side current outer loop and theinverter-side current inner loop with the load current feed-forward is chosen in this paper,which can effectively suppress the influence of the nonlinear local load and the grid voltage.What’s more, the design method of the repetitive controller is proposed, which can adapt the variety of the grid impedance. According to this method, the system can achieve a goodquality of the injected grid current even if the variety of the grid impedance.A6kW prototype of the grid-connected inverter with LCL filter has been built andtested in the lab. The experimental results are presented to verify the effectiveness ofproposed control strategy.