Research On Control Strategy Of STATCOM For Suppressing Susynchronous Oscillation In Power System Based On PSCAD

Static synchronous compensator(STATCOM),as a new flexible device,has the advantages of flexible,fast and smooth regulation.The research shows that STATCOM can be used to suppress the subsynchronous oscillation of power system.Therefore,how to control STATCOM reasonably and effectively to quell the torsional vibration process of generator shafting quickly becomes a work of theoretical research value and practical engineering significance.In this paper,the basic theory of nonlinear control and STATCOM are introduced.And the control strategy of STATCOM is studied.The error signal is formed by the difference between the current flowing into STATCOM from the power system and the given current reference value.After the error signal is processed,the trigger pulse signal controlling the on and off of thyristor in STATCOM is formed.It is common to use PI control to process error signals.However,PI control has some disadvantages,such as difficult to adjust the coefficient,poor controllability,slow response speed,etc.,so STATCOM device in PI control mode often can not give full play to its effect.In order to make STATCOM adjust reactive power,stable voltage and tracking current more smoothly and quickly,a nonlinear control strategy ofSTATCOM is proposed.Based on the non-linear principle,a group of multi-objective function groups including the concerned state quantity is found.The dynamic and static performance of the control target is dynamically tracked by the secondary performance index,thus forming a closed-loop control system which can quickly reflect the changes of the active and reactive power of the system,and has the effect of obviously suppressing the subsynchronous oscillation.When the nonlinear control strategy is used alone,there will still be some subsynchronous torsional vibration components with larger amplitude between the fault generator shafting.In order to solve this problem,a nonlinear control strategy of STATCOM combined with terminal angular velocity mode separation control strategy is proposed.The subsynchronous torsional vibration component can be restrained at the fixed modal frequency by introducing the angular velocity modal separation of generator.In order to further speed up the cooling process of the torsional vibration of the shaft system,a multi index nonlinear combined terminal angular velocity mode separation control strategy of STATCOM is proposed.In the design of nonlinear control,the output functions of linear combination of state variables are selected to make the nonlinear closed-loop feedback more timely reflect the change of state variables.Finally,based on PSCAD / EMTDC electromagnetic transient simulation platform,through the analysis of simulation results,it is confirmed that the proposed STATCOM nonlinear control strategy can significantly inhibit the power system subsynchronous oscillation,which has certain advantages andfeasibility.