Research On Stability Control For Dc-linkVoltages Of STATCOM

The STATCOM which is based on the cascaded multilevel inverter can output reactive power with large capacity and less harmonics, which has become a main direction of the STATCOM. But there are unavoidable problems existing in this kind of topology that the dc-side capacitors’ voltages can be unbanlanced and unstable. A strategy that the rectifiers control the balance and the stability is presented.The working principle of the rectifier and the STATCOM is analyzed. The system’s model is established in three-phase coordinate and the two-phase rotated coordinate respectively.According the model,the control system is researched.The rectifier side adopt the voltage-current double-loops decoupling control.The cascaded inverter side is equipped with two different control system:the direct-current control and the indirect-current control.The design method of the controller is also provided.The system model is established in the simulation software SIMPLORER.The simulation result shows that the indirect-current control gives a better transient performance and the direct-current control gives a better management of the active current.With either of two controls,the STATCOM can compensate the inductive and the capacitive component in the power grid.During the operation,the dc-side capacitors’ voltages can have a benign balance and stability.After the hardware and software design of the system prototype,the simulant operating environment is established.The rectifier experiment shows that the rectifier can output a certain amount power with a benign power factor at the input side.The reactive power compensating experiment operates in two different inductive conditions.The result shows that.the prototype can compensate the reactive power in the power grid.And the dc-side capacitors’ voltages are in balanced and stable state all along.