Study On The Control Strategy Of Cascade STATCOM Based On Grid Security

With the rapid development of power electronics technology,the conversion and application of electric energy had been more convenient.However,many serious problems had also been brought to the public power grid,such as harmonic pollution,reactive power problem,grid voltage fluctuations,which lead to the decline of power quality,the stability,economy and security of grid operation.Cascaded Active Reactive Power Generator(STATCOM)is an advanced power electronics device that compensates for reactive power in the high-voltage grid and has unique advantages over other reactive power compensation devices.whereas there are also many problems in cascaded STATCOM like compensation current control tracking,H bridge unit DC side capacitor voltage balance control problems.The aim of this paper was to improve the grid security and the grid power quality.Based on the most advanced reactive power compensation device,the cascaded STATCOM circuit topology and working principle was introduced.Meanwhile,the differential equation model of STATCOM in d-q synchronous rotating coordinate system was established and thus the d-q axis decoupling control strategy and the voltage outer loop control strategy of current inner loop were successfully designed.Firstly,the reason of DC voltage unbalance was analyzed emphatically.Then,the three-layer voltage sharing control strategy of DC capacitor was designed and a simulation system model was set up in MATLAB/Simulink software platform for simulation.Finally,based on the experimental prototype platform of STATCOM with cascaded five-level inverter we built,the effectiveness and feasibility of the proposed control strategies proposed in this paper were verified.The experiments results show that STATCOM effectively maintains the grid voltage and improves the power quality of the grid,thus the grid security is effectively ensured.