Simulaton Of STATCOM Based On Cascaded Asymmetric Multilevel Topology

The power quality of the distribution system is affected by the user’s load and affects the adjacent loads.The use of static synchronous compensator(STATCOM)to compensate system reactive power and to govern harmonics is an effective method,especially the use of multi-level inverters in high voltage systems to increase power factor and improve power quality is effective means.In recent years,based on the classical topology,asymmetric topologies such as hybrid multi-level inverters are derived,which result in faster response,better dynamic performance and higher compensation accuracyIn this thesis,cascaded asymmetric multilevel inverters are used in static synchronous compensators.The topology of the cascaded asymmetric multilevel inverter,the modulation method,the control strategy and its application in reactive power compensation is studied as the main line.First of all,the current status of cascaded asymmetric multi-level STATCOM at home and abroad is elaborated on,the working principle and control method of STATCOM is analyzed,and current detection methods and modulation strategies is conducted in-depth research on based on instantaneous reactive power theory.Secondly,the topology of the main circuit of the static synchronous compensator is discussed in detail,the circuit working process is analyzed,and the main parameters of the novel topology circuit:the selection of the DC side capacitor and the flying capacitor is discussed.At the same time,taking the particularity of the cascaded asymmetric multilevel topology into account,a mixed modulation strategy is adopted.In the high voltage stage,the pulse modulation with the same frequency as the system is used,and the low voltage stage adopts the carrier phase shift pulse width modulation(CPS-PWM)strategy,which can produce a good inverter input drive signal.Then,the control strategy of the inverter is studied.The direct current control method is used.The dq coordinate transformation method based on the instantaneous reactive power theory is used to obtain the reference command current.The control system model is set up,and the STATCOM can be effectively implemented control.Finally,according to the above research and design of the cascaded asymmetric multilevel static synchronous compensator,the simulation model of the static synchronous compensator is established in the Matlab/Simulink environment.Through the simulation analysis,it is verified that the cascade asymmetric topology STATCOM is effective and feasible under the mixed modulation strategy when load demand changes and the system voltage mutates.