Multi-interaction-based Control And Optimization Of "Source-Grid-Storage" For Power System Stability Enhancement

In order to meet the growing electricity demand and promote the low-carbon development,the modern power system has been shifting toward a system with large-scale grid intercon-nection,long-distance high-capacity high-voltage transmission and high-penetration renewable power generation.In this trend,the stable and safe operation of power system is facing se-vere challenges.In light of this,this thesis aims at the rotor angle and frequency problems of the present power system.Based on the idea of "source-source interaction","source-storage interaction" and "source-grid+inner-source interaction",in this thesis,a series of control and optimization strategies are proposed for effectively improving the power system stability.The main work of this thesis is summarized as follows.1.Coordinated Control of Multiple Synchronous Generators Based on Distributed Control The-oryBased on the distributed control theory,a distributed power system stabilizer(DPSS)that uses the average relative rotor speed error of each SG with respect to its neighboring SGs as the feedback signal,is proposed.In the DPSS,the local SG collects the rotor speed information of its neighboring SGs,and adjusts its excitation voltage for driving its rotor speed to its neighboring SGs' average rotor speed.Through the above way of interaction among SGs(source-source interaction),after system disturbances,the proposed DPSS can quickly attain the SGs' rotor speed consensus.Theoretical analysis shows that under the proposed DPSS,the damping ratio among SGs is increased,thereby the system's rotor angle stability is improved effectively.2.Damping Control of Energy Storage Systems for Increasing the Damping of Synchronous GeneratorsAfter modeling and analyzing the energy interaction between energy storage systems(ESSs)and SGs detailedly,an ESS supplementary damping controller(SDC)is proposed for increasing the damping coefficient of SG.In the proposed SDC,the ESS collects the rotor speed informa-tion of SG and adjusts its current to modify the electrical power of SG.Through the above way of interaction between ESS and SG(source-storage interaction),the proposed SDC is able to in-crease the damping coefficient of SG.Theoretical analysis shows that under the proposed SDC,the system's damping ratio is increased,thereby the system's rotor angle stability is improved effectively.3.Sliding Mode Control of Energy Storage Systems for Reshaping the Accelerating Power of Synchronous GeneratorsBased on the sliding mode control theory,an ESS sliding mode controller(SMC)is pro-posed for reshaping accelerating power of SG.In the proposed SMC,the local ESS collects the local SG's rotor speed and accelerating power information,and adjusts its current to modify the local SG's electrical power,and then makes the local SG's accelerating power to follow the pre-designed reference.Through the above way of interaction between ESS and SG(source-storage interaction),the proposed SMC is able to decouple the interacted SGs and control the dynamic trajectory of the disturbed SGs as desired.Theoretical analysis shows that,after system dis-turbances,the proposed SMC first drives the SG's accelerating power to follow the reference that is pre-designed as proportional to the SG's rated rotor speed error,in finite time? then it decouples the interacted SGs within a multimachine power system,and makes the SGs' rotor speeds converge to the rated value exponentially? finally it attains the re-synchronization of SGs quickly.4.Coordinated Rotor Speed and Pitch Angle Control of Wind Turbines for Participating Grid's Fast Frequency ResponseIn order to enable the wind turbines(WTs)for participating grid's fast frequency response(FFR),a WT-deloading-based FFR strategy is proposed.In the strategy,the WT collects the frequency information of grid,and through the information exchange between the WT's pitch angle control(PAC)and rotor speed control(RSC),the WT coordinately controls the WT's pitch angle,rotor speed,and the active power it transmits to the grid.Through the above way of interaction between WT and grid(source-grid interaction),and interaction between the PAC and RSC within the WT(inner-source interaction),the proposed strategy enables the WT to participate in grid's FFR in a coordinated manner,ultimately improving the frequency stability of power system.Theoretical analysis shows that,compared with existing methods,the strat-egy has lower difficulty in being applied to practice and stronger ability in regulating the grid frequency.5.Coordinated Optimization of Multiple Wind Turbines in a Wind Farm for Participating Grid's Fast Frequency ResponseIn order to coordinate the operation of WTs in a wind farm(WF)in FFR provision,a WF optimal power sharing strategy is proposed.In the strategy,the grid firstly sends the total ac-tive power order(TAPO)that is required for participating FFR,to the WF? then,through the information exchange between the WTs and the WF control center(WFCC)within the WF,the WF coordinately allocates this TAPO(given by the grid)to the WTs within the WF? finally,each WT within the WF transmits active power to the grid according to the active power order received from the WF.Through the above way of interaction between WF and grid(source-grid interaction),and interaction between the WFCC and WTs within the WF(inner-source interac-tion),the strategy enables the WTs within the WF to participate in grid's FFR in a coordinated manner,ultimately improving the frequency stability of power system.Compared with existing methods,the strategy has the advantages of being suitable for a full range of FFR categories,and having less wind energy loss,less WT wear,higher WT safety,and lower communication requirements.