Research On Optimal Control For Non Grid Connected Wind Generation Storage System

Wind power as the renewable energy resources which are inexhaustible and definitelyclean is being paid more and more attention by lots of countries. Because the wind is ofinstability and discontinuity, there are difficulties in the grid. The non-grid-connected windpower system is properly considered to solve the problem of the large-scale wind energy. It isnecessary to combine the wind power technology with energy storage technology, which caneffectively inhibit wind power fluctuations, smooth the output voltage and improve powerquality. The main storage device for wind energy systems is battery with high energy density,but it has low power density. The super-capacitor has high power density, so the combinationof a battery with a super-capacitor may make good use of their respective merits, and theperformance of energy storage system is enhanced.In this paper, the non-grid-connected wind power generation with energy storage is set asthe study object. Basing on the analysis of the characteristics of the system, a reasonableequivalent model is established, which includes wind speed, wind turbine, permanent magnetsynchronous generators, diode rectifier bridge, bidirectional DC/DC converter, battery andsuper-capacitor. The whole system has been established in Matlab/Simulink. To capture themaximum wind energy, a maximum power point tracking (MPPT) control strategy is designedto combine sliding mode (SM) control with extreme search control (ESC). Control strategiesinvolve a battery charge/discharge control, a super-capacitor charge/discharge control.Whenwind energy is sufficient and the output power from the wind power system exceeds the loadpower demand, the battery charges first, and if the battery charging current is too high, thesuper-capacitor starts to charge. On the other hand, the battery discharges first, and if thebattery discharging current is too high, the super-capacitor starts to discharge to supply powerfor load.The comparison of simulation on waveform and data shows the advantages of the MPPTcontrol method that is proposed in this chapter. The simulation analyses in both cases,changing in wind velocity or load power demand, can prove the feasibility of the proposedscheme. Bidirectional DC/DC converters keep the battery operating within its safety limitsand maintain the stability of the DC voltage.