Research On Source-Side Coordinated Control Strategy Of Power System With Heterogeneous Power Sources

In the context of vigorously developing renewable energy,there are three types of heterogeneous power sources in the power system at this stage: conventional power generation based on synchronous generator(SG),distributed generation(DG)based on renewable energy,and energy storage(ES)with bidirectional energy flow.With the increase of the renewable energy proportion,their randomness and volatility exacerbate the low inertia problem and the voltage regulation difficulty.It also brings great challenges to the economic and safe operation of DGs.Fully considering the unique characteristics and advantages of various power sources in the multi-source heterogeneous power system,and through the cooperation between power sources,is an important way to meet the above challenges.This thesis takes the flexibly controlled DGs and ESs as the research object,and carries out the research on the cooperative control strategy of power sources:1.ES Flexible Control Strategy for Cooperating with the SGAiming at the problems of low inertia and deterioration of voltage regulation caused by the increase of renewable energy proportion,a flexible control strategy of energy storage to assist SG is proposed.The energy storage is arranged at the terminal bus of the SG,and the ES and SG are organically formed into a unified power generation unit called a flexible generator(FG)through the flexible control strategy.The ES under flexible control strategy works in the current source mode and its power output is cooperated with the SG by feeding back SG’s information,which can effectively reduce the occurrence of power oscillation while enhancing the system frequency and voltage stability.The FG can be equivalent to an SG with variable inertia,damping,and internal impedance.At the system level,the FG can directly adopt the control and analysis methods of traditional SG,which is convenient for system analysis and configuration.2.Variable coefficient droop control strategy of DGs for cooperating with SGsAiming at the problem of transient power-sharing between droop-controlled DGs and SGs,a variable coefficient droop control strategy of DG is proposed.The DG reserves some power to participate in the system frequency regulation,and improves the system frequency stability by undertaking more transient power disturbances.Firstly,the transient power-sharing between traditional droop-controlled DG and SG is analyzed theoretically.Based on this analysis,a variable coefficient droop control structure of DG is proposed.In the transient process,the DG works in the variable coefficient mode.Through the decrease of droop coefficient,the DG can quickly bear more load disturbances,reduce the frequency fluctuation and improve the frequency stability of the system.The DG works in the traditional droop control mode in the steady-state.The droop coefficient is restored to the set value,which does not affect the steady-state power-sharing between the DG and the SG.3.Coordinated Schedulable Droop Control strategy of DGsAiming at DGs’ economical and safe operation,a schedulable droop control strategy is proposed.While retaining the droop control characteristics,the active and reactive power of the DG is scheduled through the upper layer scheduling control so as to realize the economic operation of multiple DGs.At the same time,the DG’s frequency recovery and voltage regulation control are carried out through the upper layer control to realize the safe operation of multi DGs.The proposed schedulable droop control contains two scheduling modes,which can realize the power scheduling,frequency recovery and voltage regulation simultaneously.In addition,through the cooperation between layers,the system’s operation can be maintained even when the scheduling orders do not meet the load demand.