Research On Stability And Predictive Control Of Permanent Magnet Direct Drive Wind-Storage And Power Generation System In Island Micogrids

In the recent years,the wind power technology has developed a lot.Numerous regions have begun to build wind turbines and establish wind power microgrids.When this kind of microgrid performs in island mode,the voltage is mainly sustained by diesel generators.As the rate of wind power increases,the frequency regulation capability of microgrids will deteriorate.The energy storage system is adopted in microgrid to improve the capability.Thereby the stability of microgrids can also be improved.For the stability problem of wind-storage system,the model of island wind-storage system is obtained and the stability is analyzed in this paper.Through the analysis of permanent magnet synchronous generator,the state equations of the wind turbine can be obtained.At the same time,the state equations of energy storage can be obtained by deriving the VSG(virtual synchronous generator)method.Then the state equations of wind-storage system can be obtained by combining two models together.The stability of wind-storage system can be analyzed through the joint state matrix.Meanwhile,the effect of inertia and damping coefficients to the system is discussed.For the frequency fluctuation problem in island microgrid,an MPC(model predictive controller)is adopted to the energy storage system.In the face of frequency fluctuation,the traditional VSG method can only provide frequency support according to the designed swing equation.In this paper,the MPC is adopted into the traditional VSG method.Firstly,the prediction model is derived to forecast the change of power under frequency fluctuation.After calculating the optimal power variation,the MPC will change the reference power of VSG.Then the energy storage device can absorb or emit more power under the condition of frequency change,which can reduce the frequency fluctuation.The effectiveness in island wind-storage system is verified in a simulation case.Besides,the effectiveness of load change is verified in a case with simulation and hardware-in-loop experiments.For the problem of insufficient regulation capacity due to constant inertia and damping coefficients in the model predictive controller,a novel control method is proposed by combining fuzzy controller with an MPC.In conventional VSG methods,the inertia and damping coefficients are fixed and the frequency regulation capability cannot be fully utilized in the face of frequency fluctuations in different situations.A fuzzy controller is used to adjust the inertia and damping coefficients of energy storage system in real time by detecting the change of frequency.By adjusting coefficients in real time,the regulation capability of the swing equation can be substantially utilized.The optimal rated power of VSG was modified using the MPC method,which further strengthens the EES support for power needs.The effectiveness in island wind-storage system is verified in a simulation case.Besides,the effectiveness of load change is verified in a case with simulation and hardware-in-loop experiments.